# F4U vs F6F & Top-Speed: Let's Settle This



## Zipper730 (Mar 6, 2020)

There's been all sorts of discussions about the performance of the two aircraft which often revolve around position and compressibility error corrections. The claims that seem to pop up are, as follows

The F6F & F4U in top speed and level flights by test pilots in WWII seemed to show much less of a speed discrepancy than listed on the charts: Supposedly this had to do with the fact that Grumman went to rigorous lengths to ensure that the speeds were calculated as accurately as possible, whereas Chance-Vought did a shoddier job. A counterpoint is that all these claims came from Grumman which raises questions as to bias and competition.
Claims from Grumman stated that the F6F-3 & F6F-5, despite reading a difference in 10-15 miles an hour, were actually much closer in top speed due to a repositioning of the pitot-static system so it would be closer to the F4U-1. It seems an odd thing to lying about admitting to (as it seems to be confessing to fraud).
Pilots who raced the F4U's and F6F's after the war said they were fairly close in top-speed as well: This one seems to have a legitimate claim as they might not have had the same biases as Grumman and Chance-Vought (though pilots can be partial to aircraft). That said, I'm not sure what manifold pressures were used in the post-war period, and race-planes are often souped up beyond all recognition.
I'm basically interested in facts and figures, and I'm curious if there were any speed discrepancies in the F4U-4 as well.



 drgondog

S
 Shortround6

W
 wuzak

X
 XBe02Drvr


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## XBe02Drvr (Mar 9, 2020)

Zipper730 said:


> Claims from Grumman stated that the F6F-3 & F6F-5, despite reading a difference in 10-15 miles an hour, were actually much closer in top speed due to a repositioning of the pitot-static system so it would be closer to the F4U-1. It seems an odd thing to lying about admitting to (as it seems to be confessing to fraud).


The devil is in the details, my friend. There is nothing cut and dried about pitot-static system design, as it can get damn close to FM (F_ _king Magic). At best they're dart game compromises between accuracy, durability, and complexity. The biggest issue is coming up with a static air reference value that is unaffected by airspeed, angle of attack, sideslip angle, propwash, disturbed air flow, etc, etc. The surfaces of an airframe are a patchwork of constantly varying "static" air pressures as all of these variables change, and without an accurate static pressure your pitot system has no meaningful reference to compare its sampled dynamic pressure to. The charted calibration factors are approximations at best. Even changing the position or location of the pitot tube (for durability's sake, maybe - ever hear the term "hangar rash"?), will cause a different airspeed indication, even if all other conditions remain equal. Matching Chance Vought's pitot mounting installation might have been Grumman's attempt at an apples to apples comparison, not necessarily with fraudulent intent.
Cheers,
Wes

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## tomo pauk (Mar 9, 2020)

People can invest a hour or two looking at speed graphs produced by independent entities (is this case - US Navy, testers in the UK) and see that F4U was faster on same horsepower and altitude.

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## Zipper730 (Mar 10, 2020)

XBe02Drvr said:


> The devil is in the details, my friend.


I kind of figured that to an extent: That's kind of why I posted it under technical.


> There is nothing cut and dried about pitot-static system design . . . . The biggest issue is coming up with a static air reference value that is unaffected by airspeed, angle of attack, sideslip angle, propwash, disturbed air flow, etc, etc.


It's kind of amazing that they can make the device read accurately with AoA factored in.

As for slipstream, I figured that's why most propeller aircraft have the tubes mounted on the wings.


> ever hear the term "hangar rash"?


Actually, I'm not sure I have. I have heard of road-rash though, but they're almost certainly different things. Regardless, I don't think either can be fixed with latex...



tomo pauk said:


> People can invest a hour or two looking at speed graphs produced by independent entities (is this case - US Navy, testers in the UK) and see that F4U was faster on same horsepower and altitude.


Did they use the same pitot-static systems on both?


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## tomo pauk (Mar 10, 2020)

Zipper730 said:


> ...
> Did they use the same pitot-static systems on both?



The true air speed table/chart was a product of reading the IAS recording, temperature and altitude, transforming that into non-corrected TAS table, that table was then corrected for compressibility and 'position error'. The 'position error' was different on each aircraft type, and it was dependant on the location of pitot tube.

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## XBe02Drvr (Mar 10, 2020)

Zipper730 said:


> As for slipstream, I figured that's why most propeller aircraft have the tubes mounted on the wings.


That's true, but the real issue is the static port(s). They have a way greater effect on accuracy than pitot tubes do, and are so much harder to get right. Getting a reliable and accurate static pressure in the midst of a virtual hurricane of moving air is a real challenge.


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## DarrenW (Mar 10, 2020)

Have to agree with Tomo on this one. I have exhaustively examined test data from many sources and it's glaringly obvious that the F4U had a distinct speed advantage over the F6F at all altitudes and power settings. The US Navy was quite thorough with it's testing procedures and I personally wouldn't question their accuracy. And although there_ may_ have been some errors induced by pilot inability to accurately read US instruments (concerning the British tests) this probably occurred with both airplane types equally. Grumman relocated the pitot static port from the wing tip and placed it on the starboard side mid-fuselage of the F6F-5 which obviously changed the position error and charts reflect this in pilot manuals.

Given the larger wing area and fatter fuselage of the Hellcat it would be logical to assume that it would be slower than the Corsair. Speed differences were more pronounced in neutral blower due to the slightly greater horsepower afforded the Corsair via the ram air affect. Auxiliary blower critical altitudes of the two types were close but not identical and when similarly configured/loaded contemporary models are compared (F6F-3 vs F4U-1A & F6F-5 vs F4U-1D) you could see an average speed differential from around 10 to 30 mph, depending on power settings and altitudes involved:

Performance with wing pylons and centerline racks:

http://www.wwiiaircraftperformance.org/f6f/f6f-5.pdf

http://www.wwiiaircraftperformance.org/f4u/f4u-1d-acp.pdf

Export version of F4U-1D and F6F-5 (probably in 'clean' condition):

http://www.wwiiaircraftperformance.org/f4u/corsair-IV-ads.jpg

http://www.wwiiaircraftperformance.org/f6f/hellcat-II-ads-a.jpg

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## Zipper730 (Mar 10, 2020)

XBe02Drvr said:


> That's true, but the real issue is the static port(s).


Where are they located on the F6F-3 and F4U-1?



DarrenW said:


> Have to agree with Tomo on this one. I have exhaustively examined test data from many sources and it's glaringly obvious that the F4U had a distinct speed advantage over the F6F at all altitudes and power settings.


What I was basically curious about had to do with the fact that...

They calculated based on the plane's IAS
Then corrected for altitude and temperature
Then they corrected for position and compressibility errors
How did they generally determine the latter item? I assume they either had another plane with properly calibrated instruments, or towed some kind of probe behind them.


> And although there_ may_ have been some errors induced by pilot inability to accurately read US instruments (concerning the British tests) this probably occurred with both airplane types equally.


Why would the British have any trouble -- the US and UK both used miles per hour or knots at that point in time.


> Grumman relocated the pitot static port from the wing tip and placed it on the starboard side mid-fuselage of the F6F-5 which obviously changed the position error and charts reflect this in pilot manuals.


Do you have information on the F6F-3 & F6F-5 regarding position/compressibility/both errors? Also, do you have anything on the F4U-1?


> Given the larger wing area and fatter fuselage of the Hellcat it would be logical to assume that it would be slower than the Corsair.


The F6F's propeller might have been more efficient: I remember reading that they started swapping the F4U's normal 13'4" propeller with the 13'1" or 13'2" propeller used on the F6F. They showed a difference in top speed and climb-rates.


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## DarrenW (Mar 10, 2020)

Zipper730 said:


> Why would the British have any trouble -- the US and UK both used miles per hour or knots at that point in time.


 This had been discused in British tests concerning the P-47C (see item 14):

P-47 Tactical Trials


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## DarrenW (Mar 10, 2020)

Zipper730 said:


> Where are they located on the F6F-3 and F4U-1?



The static port is located near the wing tip on the F6F-3. I believe that the F4U series had them located on the fuselage but someone here may know for sure.


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## DarrenW (Mar 10, 2020)

Zipper730 said:


> Do you have information on the F6F-3 & F6F-5 regarding position/compressibility/both errors? Also, do you have anything on the F4U-1?



Check with pilot manuals for the type in question.


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## DarrenW (Mar 10, 2020)

Zipper730 said:


> The F6F's propeller might have been more efficient:



This was true.


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## DarrenW (Mar 10, 2020)

Zipper730 said:


> How did they generally determine the latter item? I assume they either had another plane with properly calibrated instruments, or towed some kind of probe behind them.



This is way above my knowledge level.


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## Zipper730 (Mar 10, 2020)

DarrenW said:


> This had been discused in British tests concerning the P-47C (see item 14):
> 
> P-47 Tactical Trials


This doesn't seem to have to do with units of measurement, so much as the technique of reducing the data. This actually came up on another post, regarding discrepancies in climb performance. I have no idea how they were reducing the data, and I got some discrepancies in the rate of climb.


> The static port is located near the wing tip on the F6F-3.


Right around the same spot where the static port is...


> I believe that the F4U series had them located on the fuselage but someone here may know for sure.


That's an odd spot to put them, you'd be in the slipstream. At least the pitot tube was located on the wing-tip.


DarrenW said:


> Check with pilot manuals for the type in question.


I'll see if there's any on this site...


DarrenW said:


> This is way above my knowledge level.


Yeah, I don't have a clue on that either...


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## DarrenW (Mar 10, 2020)

Zipper730 said:


> That's an odd spot to put them, you'd be in the slipstream. At least the pitot tube was located on the wing-tip.



I think they were concerned with reading air flow in a relatively undisturbed area. Depending on speed and other factors there could be a lot of wake turbulence generated at the wing tips ( aka vortices) that distort the readings.


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## Joe Broady (Mar 12, 2020)

Zipper730 said:


> What I was basically curious about had to do with the fact that...
> 
> They calculated based on the plane's IAS
> Then corrected for altitude and temperature
> Then they corrected for position and compressibility errors





Your steps 1 - 3 are out of sequence, which is understandable since misinformation has been put out elsewhere in this discussion. First off, the chart in the airplane manual gives the correction to convert IAS (what the gauge in the cockpit reads) to CAS (what it would read, if it responded to pressure exactly as designed, and received perfect samples of pitot and static pressure). The F6F pilot handbook gives this:

IAS F6F-3 F6F-5
100 +12 -5
120 +12 -6.5
140 +13 -7
160 +13 -10
180 +14 -11
200 +14 -13
220 +15 -15

For example, if you're flying at -3 Hellcat at 140 KIAS, that equals 140 + 13 = 153 KCAS. That's the correction for position error. (Back in the day it was commonly called "installation error".) To convert to true airspeed, adjust the calibrated airspeed for temperature and altitude. For example, at 10,000 feet and air temperature 10 C, 153 KCAS = 183 KTAS according to my E-6B computer.

The only part specific to the airplane is the IAS to CAS conversion. I've listed the Hellcat figures in the clean configuration. The numbers are different for flaps down. Even the weight can have significant effect due to the greater angle of attack necessary to maintain flight at a given airspeed. The B-36 and C-124 charts show correction curves for different weights.

I know little about how the corrections are determined. As someone else has said, most of the position error comes from inaccuracies in static pressure. Grumman took advantage of that when they relocated the Hellcat static port to address complaints about the Hellcat speed. At least, that's what long time test pilot Corky Meyer said in the book he co-wrote with Steve Ginter. I wonder, were Navy pilots so ignorant of installation error, they were fooled by this change? Of course when you correct IAS to CAS the plane is going no faster than before. And the correction chart is right there in the pilot manual.

Getting back to where those numbers come from, often in flight test operations the plane is modified with a boom on the nose to get air data from a point of undisturbed airflow. The F-100 is one plane which retained the boom on production aircraft. I think it was so long it could be folded on the ground.

Another method is to lower a small bomb-shaped device on a cable. Fins keep the "bomb" pointed straight, and a pitot-static probe samples the air. Famously, the XB-36 lost one of these over Fort Worth. It plunged through the skylight of an elementary school restroom. Several boys were slightly injured by flying concrete fragments from the shattered floor and a toilet was knocked out of commission.

A trailing cone is sometimes employed to get an accurate static pressure when testing large aircraft. A long plastic tube is unreeled from the rear in flight. At the end is a short perforated metal tube to take the pressure sample, which is conducted forward through the plastic tube and sensed by a transducer in the aircraft. At the rear of the assembly is a cone which generates enough drag to keep the long tube taut and stable.

Still another method is to employ a pacer aircraft flying in formation. Often it's equipped with the previously mentioned boom, and its instruments have been calibrated with special care.

References:

Corwin Meyer and Steve Ginter, "Grumman F6F Hellcat," 2012.
(In the book Meyer admits he laid a tremendous egg in the relocation of the static port from its co-location on a boom with the pitot port to the fuselage. Grumman engineers had no previous experience with such an installation, so they put a port on the left side only. But Navy test pilots discovered indicated airspeed would drop to zero in a left sideslip in landing configuration. As senior engineering test pilot, Meyer should have caught that. The fix was to use a static port on both sides of the fuselage.)

Meyers K. Jacobsen, "Convair B-36: A Comprehensive History of America's Big Stick," 1997. (Photo of smashed toilet on p. 34.)

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## XBe02Drvr (Mar 12, 2020)

Joe Broady said:


> Grumman engineers had no previous experience with such an installation, so they put a port on the left side only. But Navy test pilots discovered indicated airspeed would drop to zero in a left sideslip in landing configuration.


Back in the day, Cessna 150s had a single static port, located on the starboard side just forward of the doorpost. One of the things you had to make sure students understood before getting in to slips and crosswind landings was how much that affected IAS. In level cruise flight you could yaw the plane with rudder enough to indicate any speed between Vstall and Vne. Better be sure your student is past the "white knuckle" stage before you try this.
Another neat feature of this static port was that you could easily cover it with a near-invisible piece of shear scotch tape to test their vigilance in preflight inspections. If they didn't detect it and actually got airborne, it was a good opportunity to hammer home the value of noting and remembering power settings, attitudes, and aircraft performance, sound, and feel so they could detect and cope with instrument malfunctions. They got used to the idea of something going "wrong" on most flights.
Cheers,
Wes


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## DarrenW (Mar 14, 2020)

Joe Broady said:


> (In the book Meyer admits he laid a tremendous egg in the relocation of the static port from its co-location on a boom with the pitot port to the fuselage. Grumman engineers had no previous experience with such an installation, so they put a port on the left side only. But Navy test pilots discovered indicated airspeed would drop to zero in a left sideslip in landing configuration. As senior engineering test pilot, Meyer should have caught that. *The fix was to use a static port on both sides of the fuselage*.)




Corky's explanation of the Hellcat's pitot-static system has always troubled me. From everything I've read the F6F-3 had the static orifice located on the pitot head. For the F6F-5 the _one_ static line was moved to the starboard (right) side of the fuselage, along station #97. Whatever he was experimenting with apparently didn't make it to any production aircraft. 

Here is an excerpt from the report concerning flight testing performed by the US Navy on the 310th production F6F-5. It describes the change in placement of the orifice:








http://www.wwiiaircraftperformance.org/f6f/f6f-5-58310.pdf



Joe Broady said:


> IAS F6F-3 F6F-5
> 100 +12 -5
> 120 +12 -6.5
> 140 +13 -7
> ...



The correction data above is from the flight manual dated 1 June 1944 but by publication of the manual dated 1 May 1946 there were major changes to these figures (as before flaps are retracted):
IAS F6F-3 F6F-5
100 +4.5 N/A
120 +4.5 -2.5
140 +6.0 -2.5
160 +7.0 -4.5
180 +7.0 -4.5
200 +8.0 -4.5
220 +9.0 -4.5
240 +9.0 -4.5
260 +10.5 -3.5
280 +11.5 -3.0
300 +11.5 -2.5

As you probably notice, further tweaking of the pitot-static system resulted in much more accurate instrument readings, with the F6F-5 showing the greatest improvement. This was most likely due to the better placement of the static port (starboard side of fuselage and not on wing tip).

Now if one compares performance data of the F6F and F4U found in documents created _after _these modifications the Corsair still maintains roughly the same speed advantage over the Hellcat. This to me proves that during the original flight tests the correct instrument error was taken into account and the test data is indeed accurate and comparable.

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## tomo pauk (Mar 14, 2020)

Enjoy some bacon, Darren.

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## Zipper730 (Mar 14, 2020)

XBe02Drvr said:


> Back in the day, Cessna 150s had a single static port, located on the starboard side just forward of the doorpost.


This would have been in the 1970's to 1980's right?


> One of the things you had to make sure students understood before getting in to slips and crosswind landings was how much that affected IAS. In level cruise flight you could yaw the plane with rudder enough to indicate any speed between Vstall and Vne.


Then how did you know how fast you were going at? I was reading a NATOPS manual on the F-8J and they mentioned that there was a discrepancy in airspeed reading (I think it was 3.5 knots) at high AoA, though in that case, the way one would carry out an approach almost certainly revolved around simply focusing on alpha and glide-path to determine this.


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## wuzak (Mar 14, 2020)

i always thought that the static ports were on the pitot tube:






Pitot tube - Wikipedia 

Even that a pitot tube required static ports in it.

But this discussion and checking in Wiki shows that I was very much mistaken.


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## Zipper730 (Mar 14, 2020)

wuzak said:


> i always thought that the static ports were on the pitot tube


Not always: If you have the static ports on the pitot tube, it's called a pitot-static tube. If you have the static ports elsewhere, it's called a pitot-static system. Technically it's a pitot static system regardless.

I guess you could say that all pitot-static tubes are pitot-static systems, but not all pitot-static systems are pitot-static tubes.

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## XBe02Drvr (Mar 14, 2020)

Zipper730 said:


> Then how did you know how fast you were going at?


Have you ever heard the word "interpolate"? This is one of the many things in flying where you have to depend on experience and a "feel for what's happening" rather than going blindly "by the numbers". Even a Boeing, despite its far more sophisticated static system, will experience an IAS error in a sideslip condition. (Something they don't do much!) In a Cessna 150 (or, I suppose an F6F-5), you note the airspeed before starting your slip, then note again after the slip is established, to give you a correction factor + or - . Hold your airspeed at the corrected value.
In practice, following this exactly has your eyes inside the cockpit too much, so you must quickly learn how pitch attitudes and slip angles can control your airspeed in a slip by visual reference "eyes out". This is where the "truck drivers", "bulldozer operators" and "armchair aces" weed themselves out of the program and the motorcyclists, equestrians, sailors, and gymnasts excel.


Zipper730 said:


> the way one would carry out an approach almost certainly revolved around simply focusing on alpha and glide-path to determine this.


The very essence of all phases of flight. This is why the Squids and the Jarheads have been ahead of the rest of aviation for decades! IT'S ALL ABOUT AOA!! Airspeed/weight/configuration tables are all crutches to hobble you down the path to the holy grail, which is Angle Of Attack, the ultimate determinant of airframe performance and behavior. Terrestrial aviation seems to have a problem absorbing this fact, as so many planes have the sensors, which feed various systems, but don't display AOA to the crew.
Cheers,
Wes


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## DarrenW (Mar 15, 2020)

tomo pauk said:


> Enjoy some bacon, Darren.



Thanks Tomo, it's quite tasty!


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## Zipper730 (Mar 15, 2020)

XBe02Drvr said:


> Have you ever heard the word "interpolate"? This is one of the many things in flying where you have to depend on experience and a "feel for what's happening" rather than going blindly "by the numbers". Even a Boeing, despite its far more sophisticated static system, will experience an IAS error in a sideslip condition. (Something they don't do much!) In a Cessna 150 (or, I suppose an F6F-5), you note the airspeed before starting your slip, then note again after the slip is established, to give you a correction factor + or - . Hold your airspeed at the corrected value.


So, I guess you just have to develop a feel for it in practice. The hardest part to grasp that I would see, is gauging changes in speed (if the speed is reading nothing) either eyes in or outside the cockpit.


> This is where the "truck drivers", "bulldozer operators" and "armchair aces" weed themselves out of the program and the motorcyclists, equestrians, sailors, and gymnasts excel.


Actually, that's the funny thing about the DMV. It teaches you to drive eyes on the gauge. One MPH over during the road test, and you lose. Now, in real life -- you don't constantly monitor the gauge: You just focus on the other cars. If you're passing everybody really fast, then you're going too fast; if everybody is passing you, and you're getting honked at: You're probably going too slow.


> This is why the Squids and the Jarheads have been ahead of the rest of aviation for decades! IT'S ALL ABOUT AOA!!


And for descent, you also use the ball to determine glide-path.


> Airspeed/weight/configuration tables are all crutches to hobble you down the path to the holy grail, which is Angle Of Attack, the ultimate determinant of airframe performance and behavior.


The problem is at high speed, you have to remember what AoA limits correlate to the limiting/ultimate g-load. I figure muscle memory helps out for that.


> Terrestrial aviation seems to have a problem absorbing this fact, as so many planes have the sensors, which feed various systems, but don't display AOA to the crew.


I remember Chuck Yeager didn't have that particular problem. In fact, he criticized the F-15's AoA gauge, saying if you don't know what that that is, you shouldn't be flying.



DarrenW said:


> Thanks Tomo, it's quite tasty!


I think the most common agreement on this forum is bacon tastes good. Honestly, there are wildly varying views on so many things, but we all agree on bacon. Sad for the pigs, but ironically, pigs like the taste of bacon too...


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## XBe02Drvr (Mar 15, 2020)

Zipper730 said:


> The hardest part to grasp that I would see, is gauging changes in speed (if the speed is reading nothing) either eyes in or outside the cockpit.


First of all, you will never see "nothing" on the ASI unless you're fully stalled and tumbling ass over teakettle, and then not for very long. Second, you have many clues to airspeed besides the gauge, such as sound, attitude, vibration, stall horn, and experience. If you're the "white knuckle" type, anxiety will probably prevent experience from coming into play.



Zipper730 said:


> The problem is at high speed, you have to remember what AoA limits correlate to the limiting/ultimate g-load.


Listen, if you're in a machine built for turn 'n burn and you're anywhere near ultimate G load, you're going to be struggling to maintain consciousness and too greyed out to read the G meter precisely, much less calculate AOA equivalents. And if in a plane NOT designed for such antics, what are you doing there in the first place??



Zipper730 said:


> I remember Chuck Yeager didn't have that particular problem.


He was the real deal. The ultimate class act. On a par with John Glenn.
Cheers,
Wes


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## Zipper730 (Mar 15, 2020)

XBe02Drvr said:


> First of all, you will never see "nothing" on the ASI unless you're fully stalled and tumbling ass over teakettle, and then not for very long.


You said the speed gauge would go to zero in large slips...


> Second, you have many clues to airspeed besides the gauge, such as sound, attitude, vibration, stall horn, and experience.


So there are additional cues to use? While not related to flying, it relates to driving: While the blind spot will not allow you to see a car in the mirrors, you actually can often tell they are present. The whoosh sound of the car displacing is audible and right about the time it slips into the blind spot, you can hear it (my vision sucks, but my hearing is pretty good for a guy in his mid 30's).


> If you're the "white knuckle" type, anxiety will probably prevent experience from coming into play.


Generally I've been heavily knowledge driven, and some are able to desensitize one's self.


> Listen, if you're in a machine built for turn 'n burn and you're anywhere near ultimate G load, you're going to be struggling to maintain consciousness and too greyed out to read the G meter precisely, much less calculate AOA equivalents.


So as long as the controls aren't too light, you should be okay if you have good muscle memory, in that particular case?


> He was the real deal. The ultimate class act. On a par with John Glenn.


Both were awesome in their own right.


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## XBe02Drvr (Mar 15, 2020)

Zipper730 said:


> if everybody is passing you, and you're getting honked at: You're probably going too slow.


If you're in BOS, NYC, Philly, DC, etc, and you're less than 15 over the limit, you're an obstacle to traffic and a road hazard. You can have it. I'll settle for Podunk, USA.

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## Zipper730 (Mar 15, 2020)

XBe02Drvr said:


> If you're in BOS, NYC, Philly, DC, etc, and you're less than 15 over the limit, you're an obstacle to traffic and a road hazard. You can have it. I'll settle for Podunk, USA.


Oh, in that case, just drive at the same speed as everybody else. If they're going faster, you're not doing it right, and if they're going slower, you might want to consider your driving habits


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## XBe02Drvr (Mar 15, 2020)

Zipper730 said:


> You can desensitize people with anxiety.


Tell me about it. As a flight instructor, that's what I did for a living. It works for most folks eventually, but the hard core white knucklers never seem to come around, and if they have any sense, self-select out of flying.



Zipper730 said:


> ould be okay if you have good muscle memory, in that particular case?


That's what stick force gradient is all about. If it takes a lot of effort to maintain a high G load, then a pilot blacking out will relax back stick pressure, relieving the G load. FBW planes, with their lack of control feel, don't have this protection, unless artificially built in.


Zipper730 said:


> Oh, in that case, just drive at the same speed as everybody else. If they're going faster, you're not doing it right, and if they're going slower, you might want to consider your driving habits


75 MPH bumper to bumper on the beltway or 50 MPH on city streets doesn't leave enough reflex time.
No thank you!
Cheers,
Wes


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## XBe02Drvr (Mar 15, 2020)

Zipper730 said:


> You said the speed gauge would go to zero in large slip


I suggest you RE-READ this entire thread and pay attention to who said what. The ASI at zero in a slip was a reference to the F6F-5 after the pitot static system had been modified. I personally suspect the accuracy of that statement is questionable. Otherwise, it points to an egregiously bad design.
What I said was that a C150 in level cruise flight could drive its ASI anywhere from Vstall to Vne just by stomping on the rudder and generating a sideslip.
Maybe you should take notes as you read, as you seem to have a penchant for misquoting folks and getting your facts back-to-front in your posts.
'Nuf said,
Wes


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## fubar57 (Mar 15, 2020)

He's all your Wes


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## Conslaw (Mar 15, 2020)

Corky Meyer's statement that the Hellcat's speed was systematically high (10 knots? I can't remember) must be taken with a grain of salt. Let's look at the Hellcat's role as a long-distance carrier fighter. Pilots had to be able to fly on instruments over water for about 400 miles each way then find a carrier that was moving the whole time. If the the F6F's airspeed indicator was 10 knots off, that would have been discovered the first time a fighter wasn't where he expected to be.

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## Zipper730 (Mar 15, 2020)

XBe02Drvr said:


> I suggest you RE-READ . . . . What I said was that a C150 in level cruise flight could drive its ASI anywhere from Vstall to Vne just by stomping on the rudder and generating a sideslip.


Yeah, I did misread that. I stand corrected.


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## XBe02Drvr (Mar 15, 2020)

Zipper730 said:


> Yeah, I did misread that. I stand corrected.


Apology accepted.

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## XBe02Drvr (Mar 15, 2020)

Conslaw said:


> If the the F6F's airspeed indicator was 10 knots off, that would have been discovered the first time a fighter wasn't where he expected to be.


I think you're crediting long range overwater dead reckoning navigation with a bit more precision than existed at the time. Winds aloft data was nowhere near as detailed and complete as it is today, with every airliner's GPS and ACARS updating constantly in real time. 400 miles each way provides plenty of opportunity for variations in wind aloft to obscure a 10 knot error in airspeed.
Cheers,
Wes


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## Conslaw (Mar 15, 2020)

XBe02Drvr said:


> I think you're crediting long range overwater dead reckoning navigation with a bit more precision than existed at the time. Winds aloft data was nowhere near as detailed and complete as it is today, with every airliner's GPS and ACARS updating constantly in real time. 400 miles each way provides plenty of opportunity for variations in wind aloft to obscure a 10 knot error in airspeed.
> Cheers,
> Wes



Ok, but given that, flying many flights of different types of aircraft, if the F6F was always off more than the others, it would begin to show.


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## XBe02Drvr (Mar 15, 2020)

Conslaw said:


> Ok, but given that, flying many flights of different types of aircraft, if the F6F was always off more than the others, it would begin to show.


Well, maybe. Your faith in the precision of these things is greater than mine.


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## Joe Broady (Mar 16, 2020)

DarrenW said:


> Corky's explanation of the Hellcat's pitot-static system has always troubled me. From everything I've read the F6F-3 had the static orifice located on the pitot head. For the F6F-5 the _one_ static line was moved to the starboard (right) side of the fuselage, along station #97. Whatever he was experimenting with apparently didn't make it to any production aircraft.
> 
> Here is an excerpt from the report concerning flight testing performed by the US Navy on the 310th production F6F-5. It describes the change in placement of the orifice:
> 
> ...



In his book Meyer says, "A dual orfice system located way behind the lowered flaps, similar to the Corsairs, finally provided a satisfactory means to give the Hellcat a cockpit indicated airspeed reading comparable to the vaunted Corsair. That was the last we heard of the Hellcat's performance gap with the Corsair."

Again I wonder if the Navy fliers were so ignorant they didn't know to apply the installation error corrections when comparing Hellcat to Corsair.

That performance report says the Hellcat engine was down on power, perhaps due to the carburetor not metering correctly. Heavy carbon deposits on the side of the plane are mentioned. It's not the first time I've see a complaint of substandard engine performance in those reports. Maybe that was the reason Grumman's tests showed Hellcat and Corsair evenly matched in speed. If the engine of their one Corsair exemplar was a little below par, that could account for the result.

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## XBe02Drvr (Mar 16, 2020)

Joe Broady said:


> Again I wonder if the Navy fliers were so ignorant they didn't know to apply the installation error corrections when comparing Hellcat to Corsair.


That depends on the accuracy of the error corrections. There's nothing cut and dried about these things. They're arrived at by theoretical calculatiions modified by measurements and testing and more measurements and more testing, and then the discovery that repeated identical tests are creating inconsistent results, and it's back to the drawing board. And test pilots are well aware of all the details and how to do the calculations, many of them being engineers by training, and practically all graduates of test pilot schools.
Pitot tubes are relatively cut and dried; as long as they're in undisturbed air, their errors are going to be more or less proportional to their misalignment with the relative wind, and that will be determined by AOA and slip angle, if any. Static ports, OTOH, are a much more challenging proposition. An airplane is a complex curvy shape awash in a tornado of its own making, and finding locations where an accurate sample of static atmospheric pressure can be sensed at all possible AOAs and slip angles is nigh impossible. So we settle for what we can get, and live with the resulting errors, bearing in mind that the correction factors are themselves far from perfect. Not a comfortable place for those addicted to cast iron certainties anchored in concrete.
Cheers,
Wes

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## Zipper730 (Mar 16, 2020)

Joe Broady said:


> That performance report says the Hellcat engine was down on power, perhaps due to the carburetor not metering correctly. Heavy carbon deposits on the side of the plane are mentioned. It's not the first time I've see a complaint of substandard engine performance in those reports. Maybe that was the reason Grumman's tests showed Hellcat and Corsair evenly matched in speed. If the engine of their one Corsair exemplar was a little below par, that could account for the result.


Was that common with the F4U? 

Another question would be claims by race pilots that claimed they were similar in speed: That said, I could see a few reasons why that could occur.

These designs were highly souped up with fine-tuned engines: They might not have been as equally fine tuned, which would mean the F6F could have been tuned to squeeze more power out and the F4U wasn't.
The F6F could turn tighter than the F4U: That would have allowed it to complete a circuit more easily. That said, I don't know how these planes compare in sustained agility, and the F4U could out-roll the F6F, which might even things up.

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## DarrenW (Mar 17, 2020)

Joe Broady said:


> If the engine of their one Corsair exemplar was a little below par, that could account for the result.



This could definitely be the case, especially since it seems that there wasn't any critical monitoring of actual engine output, as was the norm during navy testing. From what I gather the F4U-1 under test was an early raised cabin variant and not the later -1D as described in the narrative. Given the less efficient propeller and somewhat troublesome supercharger found on earlier Corsairs, what you suggest becomes even more plausible to me.

Plus it must be remembered that Grumman and Vought were competing for the same navy contracts, and while I do not suggest that there was outright deception going on, it wouldn't be unusual for any manufacturer to capitalize on anomalies found with their competitor's products, especially if it could put them at a distinct advantage during competitive trials. That's why the US Navy test results are more reliable, at least to me anyway.

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## Conslaw (Mar 17, 2020)

I believe in most of what Meyer said, but his assertion that the Hellcat's top speed discrepency with the Corsair was based on a calibration error, I don't see as being credible. If you look at all the tests on ww2aircraftperformance.org, the F4U is consistently tested faster than the F6F, right until the end of the war. When I say this, I'm not knocking the F6F. It was fast "enough", and that's what matters.

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## XBe02Drvr (Mar 17, 2020)

Conslaw said:


> It was fast "enough", and that's what matters.


It would be interesting to imagine what would have happened if the F4U and F6F had entered service just in time to find themselves faced with a sky full of Shidenkais, Raidens, and Reppus.
Cheers,
Wes


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## eagledad (Mar 17, 2020)

Gentlemen

When the Navy tested the F6F-5 and the F4U-1D against an A6M5 and a Ki-61, the speed advantages over the 2 Japanese fighters that the F4U had was always greater than the speed advantages held by the F6F. So for me, it appears that the Corsair was faster than the Hellcat.

FWIW

Eagledad

See

http://www.wwiiaircraftperformance.org/japan/Tony-I.pdf

and

http://www.wwiiaircraftperformance.org/japan/ptr-1111.pdf

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## Zipper730 (Mar 17, 2020)

DarrenW said:


> This could definitely be the case, especially since it seems that there wasn't any critical monitoring of actual engine output, as was the norm during navy testing.


I'm not sure if I read that right. The USN did critically monitor or didn't critically monitor engines during their testing?


> From what I gather the F4U-1 under test was an early raised cabin variant and not the later -1D as described in the narrative.


I thought the F4U-1A had a higher canopy than the F4U-1 (birdcage).


> Given the less efficient propeller and somewhat troublesome supercharger found on earlier Corsairs, what you suggest becomes even more plausible to me.


I never knew the F4U-1 had any supercharger troubles...


> That's why the US Navy test results are more reliable, at least to me anyway.


Less of a vested interest to fudge numbers...



XBe02Drvr said:


> It would be interesting to imagine what would have happened if the F4U and F6F had entered service just in time to find themselves faced with a sky full of Shidenkais, Raidens, and Reppus.


Wouldn't have enjoyed the kill ratio they ended up with, now would they?


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## wuzak (Mar 18, 2020)

DarrenW said:


> Given the less efficient propeller and somewhat troublesome supercharger found on earlier Corsairs, what you suggest becomes even more plausible to me.





Zipper730 said:


> I never knew the F4U-1 had any supercharger troubles...



Given that the main difference between the engines powering the early production versions of the F6F and F4U was the way the carburetor pointed, any problems the F4U had with the supercharger would no doubt have manifested themselves in the F6F as well.

"Less efficient propeller"? Less efficient that what? The 4 blade propeller that came on the F4U-4, or the 3 blade propeller that the F6F stuck with?


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## DarrenW (Mar 18, 2020)

wuzak said:


> "Less efficient propeller"? Less efficient that what? The 4 blade propeller that came on the F4U-4, or the 3 blade propeller that the F6F stuck with?



The three-blade variety, as this was the propeller type mounted to both the Corsair and Hellcat under comparative testing by Grumman in 1943. The four-bladed propeller didn't arrive on scene until later with the F4U-4 and the XF6F-6 prototype. From what I know Meyer never performed comparative flying tests with these two aircraft.

As far as efficiency is concerned, I was referencing a US Navy test document on F4U-1 #17930 which was fitted with a standard 13' 1" F6F-3 propeller instead of the usual 13' 4" propeller. The report clearly states that it was a "better efficiency" propeller and may have attributed to the increased level speed and climb. The various test reports that I've seen seems to support this notion (perhaps a 10 mph or more speed increase can be realized???).The slightly smaller and wider blade propeller became standard on later F4U-1Ds :












http://www.wwiiaircraftperformance.org/f4u/f4u-1-17930.pdf

...and there were other times when the F4U was "stuck" with the F6F's superior propeller:











http://www.wwiiaircraftperformance.org/f4u/f4u-1-50030-final.pdf


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## DarrenW (Mar 18, 2020)

Zipper730 said:


> I'm not sure if I read that right. The USN did critically monitor or didn't critically monitor engines during their testing?



I was referring to the testing performed by Grumman on their F4U "specimen". They apparently flew them in formation at varying throttle settings in order
to gauge speed differences between the two types. The US Navy always thoroughly monitored engine performance during testing. 



Zipper730 said:


> I thought the F4U-1A had a higher canopy than the F4U-1 (birdcage).



I should have been more clear here. All F4U-1 sub-variants (-1A thru -1D) were known collectively as F4U-1s, as this was the major variant. When the raised canopy and other modifications were introduced the "sub-variant" became known as the F4U-1A. I will start using the correct terminology henceforth. 



Zipper730 said:


> I never knew the F4U-1 had any supercharger troubles...



I read this somewhere but for the life of me can't find the reference for it. I was just suggesting another possibility to why this particular F4U may have been under-performing during the tests.



Zipper730 said:


> Wouldn't have enjoyed the kill ratio they ended up with, now would they?



Hard to say. The Japanese were already hard pressed to find competent pilots to man the J2Ms, N1Ks, Ki-100s, and Ki-84s already produced. Who would be flying these "marvels of the air" if they were made in even greater numbers? IMHO that's just as important as the planes themselves.


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## DarrenW (Mar 18, 2020)

wuzak said:


> Given that the main difference between the engines powering the early production versions of the F6F and F4U was the way the carburetor pointed, any problems the F4U had with the supercharger would no doubt have manifested themselves in the F6F as well.



It's not that simple. The carburetor is only part of the equation, as there are many components to an aircraft induction system. In regards to the aircraft in discussion these included intercoolers, main & auxiliary stage blowers, gears & clutches, duct work and it's placement for ram air, supercharger regulator equipment, and various cockpit controls. The make-up of the induction systems found on the F6F and F4U were not identical and each had their own unique peculiarities.


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## wuzak (Mar 18, 2020)

DarrenW said:


> It's not that simple. The carburetor is only part of the equation, as there are many components to an aircraft induction system. In regards to the aircraft in discussion these included intercoolers, main & auxiliary stage blowers, gears & clutches, duct work and it's placement for ram air, supercharger regulator equipment, and various cockpit controls. The make-up of the induction systems found on the F6F and F4U were not identical and each had their own unique peculiarities.



The induction systems were different, including the disposition of intercoolers, but the main & auxiliary stage blowers, gears & clutches, and supercharger regulator equipment was, I'm sure, the same. Certainly the core engine was the same.

If there were problems that the F4U experienced that the F6F did not then it would likely be an installation issue, rather than an issue with the supercharger itself.


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## Zipper730 (Mar 18, 2020)

wuzak said:


> Given that the main difference between the engines powering the early production versions of the F6F and F4U was the way the carburetor pointed, any problems the F4U had with the supercharger would no doubt have manifested themselves in the F6F as well.


Do you mean pointed forwards/rearwards, up/down, or some mix of both? Do you have a picture or a diagram?


DarrenW said:


> I was referring to the testing performed by Grumman on their F4U "specimen". They apparently flew them in formation at varying throttle settings in order to gauge speed differences between the two types. The US Navy always thoroughly monitored engine performance during testing.


Oh, okay.


> I should have been more clear here. All F4U-1 sub-variants (-1A thru -1D) were known collectively as F4U-1s, as this was the major variant. When the raised canopy and other modifications were introduced the "sub-variant" became known as the F4U-1A. I will start using the correct terminology henceforth.


Ironically, I don't think the term F4U-1A was used during WWII. The British called those versions (F4U-1A/1D) the Mk.II, however.


> I read this somewhere but for the life of me can't find the reference for it. I was just suggesting another possibility to why this particular F4U may have been under-performing during the tests.


Oh, okay. That makes more sense. I want to be clear, I have nothing against the F4U or the F6F. I just wanted to make sure all the information is accurate, this could affect important things, like beer-bets (i.e. "I'll bet you a round of beer that..."), and people interesting in making/modding flight-sim games. I would imagine historians would also find this to be interesting.


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## wuzak (Mar 18, 2020)

Zipper730 said:


> Do you mean pointed forwards/rearwards, up/down, or some mix of both? Do you have a picture or a diagram?



One was an updraught and the other a downdraught carburettor. 

I can never remember which had which.

There are plenty of pictures online of the F4U induction system, which was more complicated than the F6F's.

The F4U-4 used a different model R-2800 to the F4U-1, and I believe the carburettor was flipped.

Note that the carburettor on these 2 stage R-2800s was mounted on the engine stage supercharger, the first/auxiliary stage supercharger feeding the air through the intercooler system then to teh carburettor.


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## DarrenW (Mar 18, 2020)

Zipper730 said:


> Ironically, I don't think the term F4U-1A was used during WWII.



The F4U-1A designation was recognized during the war, but it wasn't utilized very often in official documentation. Here's a British performance sheet for the Corsair Mk.II from November 1943 which includes the US version that it was based on:





http://www.wwiiaircraftperformance.org/f4u/f4u-1a-ads.jpg

It should be noted that during British tests the F4U and F6F often did not achieve the same level of performance as their American counterparts but the speed variances between the two types was still very similar to what was experienced during testing in the US, just at slightly lower values. There are a number of theories as to why this often seems to be the case, such as "possibly owing to the difficulty of reading the Standard American airspeed indicator and to the different methods of reduction " (as stated in one British test document), and that the Brits tended to monitor boost pressures (as opposed to US testing which monitored horsepower).

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## Zipper730 (Mar 19, 2020)

wuzak said:


> One was an updraught and the other a downdraught carburettor.


On just the F4U-1 variants? Or the F4U-1 & F4U-4?


> The F4U-4 used a different model R-2800 to the F4U-1, and I believe the carburettor was flipped.


The F4U-4 had a carburetor under the chin, if I recall. If I was to make a guess, I figure it'd be an updraft simply because it's below the engine and the air would probably go up to make the engine, though it wouldn't be the first time I was wrong.


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## wuzak (Mar 19, 2020)

Zipper730 said:


> On just the F4U-1 variants? Or the F4U-1 & F4U-4?
> The F4U-4 had a carburetor under the chin, if I recall. If I was to make a guess, I figure it'd be an updraft simply because it's below the engine and the air would probably go up to make the engine, though it wouldn't be the first time I was wrong.



No, the F4U-4 had an inlet under the nose, but these fed ducts to the auxiliary supercharger, not the carburettor.

F4U-1 had an updraught craburettor (R-2800-8)
F6F-3 had a downdraught carburettor (R-2800-10/10W)
F4U-4 had an updraught carburettor (R-2800-18W)*

* description came from wiki


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## Zipper730 (Mar 19, 2020)

wuzak said:


> No, the F4U-4 had an inlet under the nose, but these fed ducts to the auxiliary supercharger, not the carburettor.


I was under the impression that, once you're in low blower, with both main and aux stages running, you would effectively be in a situation that would see the air go from the carburetor, to the auxiliary stage blower, and from there, to the main-stage blower, and into the cylinders?

From what I recall when in neutral blower the air came from a difference source to the main-stage blower, to the engine? I'd almost swear it came from the intercooler and, instead of going to the intercooler, it went to the engine (pretty strange, because I remember reading/hearing you'd need 2-3 times the amount of airflow through the intercooler as that used for the carburetor)


> F4U-1 had an updraught craburettor (R-2800-8)


Okay, so all the F4U-1's used updraft carburetors, the F6F's used a downdraft system?


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## wuzak (Mar 19, 2020)

Zipper730 said:


> I was under the impression that, once you're in low blower, with both main and aux stages running, you would effectively be in a situation that would see the air go from the carburetor, to the auxiliary stage blower, and from there, to the main-stage blower, and into the cylinders?
> 
> From what I recall when in neutral blower the air came from a difference source to the main-stage blower, to the engine? I'd almost swear it came from the intercooler and, instead of going to the intercooler, it went to the engine



No. There is a bypass to feed the carburetor when in neutral blower, otherwise the air enters the auxiliary blower, is compressed and sent through the intercoolers and then up to the carburetor.

This shows a cross section of the two stage supercharger, the engine being to the left and the auxiliary to the right.




Pratt & Whitney. Две ступени для "Осы" - Альтернативная История 

Note the large port at the lower right. This is one of the discharge ports on the auxiliary supercharger (the other is rotate 180° around the supercharger's axis). This feeds into the intercooler on that side.

You can see the intake port to the auxiliary blower at the middle bottom. Note that there is a butterfly valve in the duct, presumably to close the duct when neutral blower is engaged. The air intake for the main supercharger, above which the carburetor sits, is at the top centre.

(There is also a picture of the R-2800-32W "sidewinder" engine from the F4U-5, which did have an updraught carburetor.
This attachment from another thread shows the layout of the -32W.
https://ww2aircraft.net/forum/attachments/p-w-sidewinder-jpg.97312/ 
)


This is a single stage R-2800 cutaway, which shows the carburetor feeding into the guide vanes and supercharger.





File:Pratt & Whitney R-2800-71 engine cutaway model at Archive room of JASDF Miho Air Base May 28, 2017 01.jpg - Wikimedia Commons 




Zipper730 said:


> (pretty strange, because I remember reading/hearing you'd need 2-3 times the amount of airflow through the intercooler as that used for the carburetor)



I don't know what the excess flow capacity of the intercooler was, but it would have to be enough so that the pressure loss over the intercooler is as small as possible. It woudl be a balancing act between that, the size and weight of the intercooler and the amount of cooling air required.




Zipper730 said:


> Okay, so all the F4U-1's used updraft carburetors, the F6F's used a downdraft system?


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## Conslaw (Mar 19, 2020)

XBe02Drvr said:


> It would be interesting to imagine what would have happened if the F4U and F6F had entered service just in time to find themselves faced with a sky full of Shidenkais, Raidens, and Reppus.
> Cheers,
> Wes



I think the American planes would have done almost as well as they did historically because American pilots were better trained,and they had a huge quantity advantage. The FM2 Wildcat did very well statistically despite a slight performance disadvantage to the Zero 52.

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## Zipper730 (Mar 21, 2020)

So, provided the engines were in proper shape, as was the plane: The speed figures for the F4U & F6F were indeed accurate? When it came to race planes, the fact that they were so modified made it difficult to determine the exact performance they were capable of when used in typical 1940's era combat-trim?


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## DarrenW (Mar 22, 2020)

Zipper730 said:


> So, provided the engines were in proper shape, as was the plane: The speed figures for the F4U & F6F were indeed accurate? When it came to race planes, the fact that they were so modified made it difficult to determine the exact performance they were capable of when used in typical 1940's era combat-trim?



I happen to trust the wartime test results and they can be compared without reservation, as long as the aircraft were flown in similar power settings and were equally configured (i.e. clean or with wing racks/ fuselage bomb shackles/rocket launchers, ect.). The instrument correction tables found in ordinary pilot manuals of the day were generally ignored by the USN and USAAF flight testing facilities, as it was customary to first perform several runs over a predetermined speed course for accurate pressure and temperature readings and then use this data to correct for instrumentation error before actual flight tests were commenced. After this is accomplished the aircraft is ran at various power settings along the marked course and timed. Pacer aircraft with highly accurate recording equipment was yet another means to find these discrepancies and correct inaccurate readings accordingly.

One must also be careful to only compare models that were in service during the same period of the war. Here is an example of testing performed on an early F4U-1 'birdcage' and two early production F6F-3s. All aircraft developed the same horsepower during the tests and were without wing or fuselage racks:

F4U-1 'birdcage' in 'normal' condition, gross weight = 11,194 lbs:





http://www.wwiiaircraftperformance.org/f4u/f4u-1-02155.pdf


F6F-3 in 'normal' condition, weights as shown:




http://www.wwiiaircraftperformance.org/f6f/f6f-3-02982.pdf

A similar speed differential existed in Combat power settings as well (F4U-1A and mid-production F6F-3 are without racks, horsepower ratings unknown):





http://www.wwiiaircraftperformance.org/fw190/ptr-1107.pdf

Now if we compare the later F6F-5 to an earlier Goodyear FG-1A (same as Vought F4U-1A) we start to see this speed gap at high blower critical altitude close to almost a dead heat:

F6F-5 with one wing mounted pylon @ 1655 hp:




http://www.wwiiaircraftperformance.org/f6f/f6f-5-58310.pdf

FG-1A @ 12,057 lbs 'clean' and WITHOUT external pylons):




http://www.wwiiaircraftperformance.org/f4u/FG-1A_14575.pdf

In the previous example we can see the danger in comparing aircraft from different periods of the war. The F4U-1D was the contemporary of the F6F-5 so it would be logical to look at these two aircraft when making performance comparisons. Due to modifications the F6F-5 was on average 10-15 mph faster than the F6F-3 under similar circumstances so this helped erase some of the speed advantage held by earlier F4U variants. I'm positive that Vought worked tirelessly and made incremental improvements along the way just like Grumman, which resulted in increased speeds for the later F4U-1D variant (such as the aforementioned revised propeller).

Here is a comparison that I used earlier in this thread to show the maximum speed difference between the F6F-5 and F4U-1D:

F6F-5 @ 1940 hp with two wing pylons and fuselage bomb shackles (330 knots = 380 mph):




http://www.wwiiaircraftperformance.org/f6f/f6f-5.pdf

F4U-1D @ 1975 hp with two capped wing pylons and fuselage drop tank rack in place (subtract a further 8 mph when pylons are uncapped) :




http://www.wwiiaircraftperformance.org/f4u/f4u-1d-acp.pdf

I believe the altitude given for the F6F-5 in combat power was a typo and should actually read 18,000 ft. This is unimportant however as a maximum of 380 mph was reached at both auxiliary blower critical altitudes. It's very easy to see that later F4U-1Ds were faster than earlier variant F4U-1s and thus maintained a similar margin of speed over the F6F-5 as earlier variants had over the F6F-3.

Finally, (as eagledad already pointed out) comparative testing of the F6F-5 and F4U-1D against captured Japanese aircraft always gave the Corsair an edge in speed over the Hellcat (between 5 - 17 mph depending on altitude):

http://www.wwiiaircraftperformance.org/japan/ptr-1111.pdf

http://www.wwiiaircraftperformance.org/japan/Tony-I.pdf

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## Joe Broady (Mar 23, 2020)

DarrenW said:


> From what I gather the F4U-1 under test was an early raised cabin variant and not the later -1D as described in the narrative. Given the less efficient propeller and somewhat troublesome supercharger found on earlier Corsairs, what you suggest becomes even more plausible to me.
> 
> Plus it must be remembered that Grumman and Vought were competing for the same navy contracts, and while I do not suggest that there was outright deception going on, it wouldn't be unusual for any manufacturer to capitalize on anomalies found with their competitor's products, especially if it could put them at a distinct advantage during competitive trials.



In this case the point of the exercise was for Grumman and Vought to steal some ideas from the other manufacturer's airplane. The Navy loaned Grumman an F4U-1D and said they wanted the Hellcat to be more like a Corsair in the matter of speed and roll rate. Vought was given an F6F-3 and instructed to improve Corsair visibility, stall behavior, landing gear oleos, and cockpit layout. It was the summer of 1943.

According to Corky Meyer, the Corsair was an F4U-1D, Bu No 17781. There are two good photos of the loaner Corsair in the book, but I'm neither knowledgeable nor interested enough to verify the number and photos are consistent with the purported Corsair model.

Grumman was not really able to get the requested improvements. As already mentioned, they "increased" the Hellcat speed by relocating the static port. In the matter of roll response, Grumman even built test ailerons which copied the Corsair profile but that didn't help. The inferior Hellcat roll rate was due to its much higher lateral stability. Meyer says it was inherent in the wing design, and a re-design was out of the question at the height of WW2. Later, the -5 Hellcat got spring tabs on its ailerons (many -3s were retrofitted too), and that did make up much of the disparity.

Vought may have gotten more from this project than Grumman. Meyer implies improved oleo action and stall behavior, raised seat, and extended tail wheel were byproducts of their Hellcat evaluation and could be incorporated in production. But he says a cockpit revision required a total redesign and had to wait until the -4.

Regarding the static pressure sensing, Meyer says it was through a "dual orifice system located way behind the lowered flaps." However, the book reproduces a diagram of external markings on the -5, one of which says PITOT STATIC LINE - DO NOT PLUG OR DEFORM HOLE. It's on the right side only, above the forward bar of the US insignia.

Reference: Corwin Meyer & Steve Ginter, "Grumman F6F Hellcat," 2012.


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## DarrenW (Mar 24, 2020)

Joe Broady said:


> In this case the point of the exercise was for Grumman and Vought to steal some ideas from the other manufacturer's airplane. The Navy loaned Grumman an F4U-1D and said they wanted the Hellcat to be more like a Corsair in the matter of speed and roll rate. Vought was given an F6F-3 and instructed to improve Corsair visibility, stall behavior, landing gear oleos, and cockpit layout. It was the summer of 1943.
> 
> According to Corky Meyer, the Corsair was an F4U-1D, Bu No 17781. There are two good photos of the loaner Corsair in the book, but I'm neither knowledgeable nor interested enough to verify the number and photos are consistent with the purported Corsair model.



I have read Corky's book and was especially interested in what he had to say about the comparative testing performed on the "loaner" Corsair. Being that it was the summer of 1943 it would be impossible for the subject aircraft to be an F4U-1D, as they didn't arrive at units until almost a year later (during April 1944). To further add to this, Mr. Joe Baugher has an excellent website dedicated to aircraft serial numbers and has Bu No 17456 through 18121 as F4U-1As and the test aircraft falls into this block of numbers.

Navy Serial Number Search Results 

It's a minor detail and this could easily have been a typo. As long as everyone understands that the F4U-1 under test didn't have the performance of the later F4U-1D everything is good....



Joe Broady said:


> Meyer implies improved oleo action and stall behavior, raised seat, and extended tail wheel were byproducts of their Hellcat evaluation and could be incorporated in production. But he says a cockpit revision required a total redesign and had to wait until the -4.



Again, production F4U-1Ds had all of these modifications so why would the test airplane be in need of them?



Joe Broady said:


> Regarding the static pressure sensing, Meyer says it was through a "dual orifice system located way behind the lowered flaps." However, the book reproduces a diagram of external markings on the -5, one of which says PITOT STATIC LINE - DO NOT PLUG OR DEFORM HOLE. It's on the right side only, above the forward bar of the US insignia.



Yes along station #97.....


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## Zipper730 (Mar 25, 2020)

DarrenW said:


> One must also be careful to only compare models that were in service during the same period of the war.


Yeah, as there were various changes that allowed higher boost (water injection, higher octane, and the F4U-1's started using the F6F's propeller).


> Here is an example of testing performed on an early F4U-1 'birdcage' and two early production F6F-3s. All aircraft developed the same horsepower during the tests and were without wing or fuselage racks


Looking at the top-speed figures, 395 mph seems a pretty common listing for earlier designs. Later figures would show around 416 or 417 mph with water injection, higher manifold pressures, the F6F-3's propeller, reconfigured cowl-flaps (I'm not sure if this had a propulsive benefit -- it's predominant goal was to keep oil from spraying over the windscreen, but tighter cowls usually do favor speed), and the gun-ports taped-over, using the same basic engine (R-2800-8). They'd apparently eventually eke out speeds of around 425 mph in operational aircraft (F4U-1D), though there was an F4U-1A that saw 431 mph in level flight (that said, the tail-hook was removed and faired over, which would be useless for carrier ops, but beneficial for land-based).

From what I recall, the normal-rated power-settings produce 2550 RPM, 2700 for military and normal-rated power-settings. The gear-ratio seems to be 0.5 regardless of propeller.


> A similar speed differential existed in Combat power settings as well (F4U-1A and mid-production F6F-3 are without racks, horsepower ratings unknown)


The graph which compares the Fw-190, the F4U-1, and the F6F-3 leaves me with more questions than answers.

For starters: I'm not sure what variant of the Fw.190 is depicted. I know little information about the critical altitude figures for the Fw.190's.

As for the F4U-1A: While the aircraft could probably keep its speed slightly over 400 mph on WEP at 25000', it is not the aircraft's critical altitude in normal-rated, military-power, or WEP figures. WEP would see a critical altitude around 20300'. The curves in speed here indicate a drop off from 200'-5000', an increase from 5000'-25000'.

As for the F6F-3: The F6F's top speed usually isn't listed as being 391 mph, the F6F-5 is, but neither have critical altitudes around 25000'.


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## DarrenW (Mar 25, 2020)

Zipper730 said:


> hey'd apparently eventually eke out speeds of around 425 mph in operational aircraft (F4U-1D


Though I have read this from time to time I haven't seen any official documentation that supports it, at least for your standard everyday carrier based F4U-1D fighter-bomber (in any condition). If you do have a credible source please let me know. 

Even Chance-Vought never made this claim:

http://www.wwiiaircraftperformance.org/f4u/f4u-1d-detail-specification.pdf


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## DarrenW (Mar 25, 2020)

Zipper730 said:


> As for the F6F-3: The F6F's top speed usually isn't listed as being 391 mph, the F6F-5 is, but neither have critical altitudes around 25000'



This is interesting to me too. Grumman also estimated the top speed of the F6F-3 to be 391 mph in a 'normal' fighter condition at 25,000 ft: 

http://www.wwiiaircraftperformance.org/f6f/f6f-3-detail-specification.pdf

The specification gives two different critical altitudes while in high blower. Of course these are way above the critical altitude when using Combat power so the test aircraft in the US Navy report obviously wasn't benefiting from the added boost at 25,000 ft.


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## DarrenW (Mar 25, 2020)

Zipper730 said:


> For starters: I'm not sure what variant of the Fw.190 is depicted. I know little information about the critical altitude figures for the Fw.190's.



I believe the consensus is that it was probably an FW 190A-5 variant. Others here could explain the supercharger/engine performance curves much better than I can.

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## DarrenW (Mar 25, 2020)

Zipper730 said:


> Looking at the top-speed figures, 395 mph seems a pretty common listing for earlier designs. Later figures would show around 416 or 417 mph with water injection, higher manifold pressures, the F6F-3's propeller, reconfigured cowl-flaps (I'm not sure if this had a propulsive benefit -- it's predominant goal was to keep oil from spraying over the windscreen, but tighter cowls usually do favor speed).....



I fully agree. The F4U-1A was often retrofitted with the F6F's propeller because it was the better choice. Even the pilot's manual claimed it should be used whenever available:






http://www.jasonblair.net/wp-conten...Manual-for-F4U-Corsair-Aviation-Pubs-1977.pdf


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## DarrenW (Mar 25, 2020)

Zipper730 said:


> Yeah, as there were various changes that allowed higher boost (water injection, *higher octane*, and the F4U-1's started using the F6F's propeller).



The rating of US aviation fuel in the Pacific theater was 130 octane for most of the war, mainly because the performance of Japanese planes (or lack there of) never warranted a push for the higher 150 octane fuel.


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## Zipper730 (Mar 26, 2020)

DarrenW said:


> Though I have read this from time to time I haven't seen any official documentation that supports it


Oh, I didn't know that...


> This is interesting to me too. Grumman also estimated the top speed of the F6F-3 to be 391 mph in a 'normal' fighter condition at 25,000 ft


It almost looks like they just listed the contractor data...


> The rating of US aviation fuel in the Pacific theater was 130 octane for most of the war, mainly because the performance of Japanese planes (or lack there of) never warranted a push for the higher 150 octane fuel.


I thought they eventually did switch to 150? Regardless, it would appear they were able to bump up the manifold pressure, even if it shortened service life.


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## DarrenW (Mar 27, 2020)

Zipper730 said:


> Oh, I didn't know that...



It seems rather commonplace these days to accept without question higher and higher maximum speeds for the various Corsair variants, but if someone even mildly suggests a 400 mph F6F-5 they are called a fool and dismissed accordingly..... but not here of course. 

Some of this has to do with the misinterpretation of source data. Unlike the Hellcat, there are many Corsair test reports on the Williams/Stirling website in which the subject aircraft is a highly modified 'one-off', and not representative of aircraft in actual service. For example, the only F4U-1 which attained 400 mph speeds _without_ water injection was modified with the following: a non-standard higher efficiency F6F propeller, removal of tail hook with faired cut-out, modified cowl flaps, enhanced streamlined tail wheel, removal of catapult hooks, and the shell ejector openings were taped over. Without a tail hook this aircraft could no longer be truly classified as a carrier aircraft. Lastly, many of the Corsairs on the site were tested using Combat power settings, which was not the case concerning the Hellcat. The use of ADI enhanced performance considerably and made an apples-to-apples comparison to planes without it impossible.

In addition to this, there seems to be no F4U-1 variants tested with bomb racks installed, which will make a decent amount of difference in the testing outcome. Marine Corsairs were involved in close air support very early on so they often carried bombs in the performance of their duties. It wasn't until the Hellcat began to displace dedicated shipboard dive-bombers (like the Dauntless) that it began to do 'ground-pounder' work, so up to that point it normally flew in a 'clean' condition. FWIW there are several test reports on the site that give performance figures for the Hellcat with racks installed.

There's also the fact that the F4U is one helluva sexy airplane so it's totally reasonable to accept that it was faster than the portly ole' Hellcat, and it generally was. Problem is that this approach can lead to biased comparisons between the two, which is what we seem to have today. So when people line these two airplanes up side by side, they tend to pull out their 'favorite' performance charts and have at it, but by doing so they sometimes fail to compare them under the same set of real-world parameters. I find the biggest mistakes to be the comparison of variants from different periods of the war and their particular configuration (i.e. racks, water injection, special modifications, etc.).

So what I'm trying to say here is that yes, the Corsair WAS faster than the Hellcat, but by how much depends of a lot of considerations. Unsubstantiated information such as F4U-1Ds flying at 425 mph only leads to distorted calculations however and is something to be weary of when performing any form of genuine comparison between the two airplanes.


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## DarrenW (Mar 27, 2020)

Zipper730 said:


> I thought they eventually did switch to 150? Regardless, it would appear they were able to bump up the manifold pressure, even if it shortened service life.



I think the trend was leading in that direction but the war ended before it became a necessity of any kind. IMHO the power ratings of both the R-2800-8W and -10W were somewhat conservative, and for the most part was implemented to keep engines healthy and happy. Nobody wanted an inadvertent engine failure due to unnecessary over-boosting, especially if it occurred over the vast expanse of the Pacific ocean. By keeping the margins wide pilots who felt compelled to exceed the nominal (and relatively safe) 52" Hg boost rating would do so only if a dire situation warranted it.

Testing was performed on both engines using different sized water jets and carburetor impact pressure settings with very good results being obtained (up to 65" Hg was deemed safe while using 130 octane fuel). Granted the turbocharged P-47 would tend to benefit more from increases in both boost and octane rating but it definitely was on the table for both the F6F and F4U, especially if their performance ever started to lag behind the enemy aircraft that they normally encountered in combat.


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## Dawncaster (Apr 4, 2020)

DarrenW said:


> It seems rather commonplace these days to accept without question higher and higher maximum speeds for the various Corsair variants, but if someone even mildly suggests a 400 mph F6F-5 they are called a fool and dismissed accordingly..... but not here of course.
> 
> Some of this has to do with the misinterpretation of source data. Unlike the Hellcat, there are many Corsair test reports on the Williams/Stirling website in which the subject aircraft is a highly modified 'one-off', and not representative of aircraft in actual service. For example, the only F4U-1 which attained 400 mph speeds _without_ water injection was modified with the following: a non-standard higher efficiency F6F propeller, removal of tail hook with faired cut-out, modified cowl flaps, enhanced streamlined tail wheel, removal of catapult hooks, and the shell ejector openings were taped over. Without a tail hook this aircraft could no longer be truly classified as a carrier aircraft. Lastly, many of the Corsairs on the site were tested using Combat power settings, which was not the case concerning the Hellcat. The use of ADI enhanced performance considerably and made an apples-to-apples comparison to planes without it impossible.
> 
> ...



There was an ongoing party.



DarrenW said:


> Unlike the Hellcat, there are many Corsair test reports on the Williams/Stirling website in which the subject aircraft is a highly modified 'one-off', and not representative of aircraft in actual service.


Hmm, Exaggerated.

There were no special modified planes used in production inspection trials for F4U-1, FG-1, F3A-1, F4U-4 and flight tests for british Corsairs. It is nonsensical to flight test with special modification configuration in a measurement to performance. I don't think the U.S. Navy wasted time and resources on such meaningless things. only few reports for special purposes used special modified planes, of course standard service conditions should not used for special purposes. and added external test devices with taped weapon holes, configuration used by most Corsairs in test, should not be treated as special modification or highly modified 'one-off' as you said, It's common for other models test reports including the Hellcat. and it had only slight effect on relative performance seems due to navy's correction. just see the below sections for details.

But before that, here is a list of all reports on the F4U page of Williams/Stirling website. only a few reports have been used special modified configuration, not many.

- ACP, SAC and British aircraft cards = official performances
- Detail Specifications = estimated performances except F4U-5's
- Maximum Speed of F4U-1 Airplane #02234 ("Cleaned-Up" Version) on War Emergency Power Ratings = clean-up test, of course standard configuration should not be used.
- Performance Characteristics of F4U-1 No. 02155 = no special modification
- Final Flight Report of Production Inspection Trials (TED No. BIS 2125) on Model F4U-1 Airplane = no special modification
- Final Flight Report of Production Inspection Trials (TED No. BIS 2121) on Model F3A-1 Airplane No. 04691 = no special modification
- Final Flight Report of Production Inspection Trials (TED NO. BIS 2122) on Model FG-1A Airplane No. 14575 = no special modification
- Final Report on Project TED No. BIS 2157 Production Inspection Trials of the Model F4U-4 Airplane =no special modification
- Flight Test of Two Model FG-1 Airplanes No. 14796 (British Corsair Mk IV KD 365) and British Corsair Mk IV KD 502 = no special modification
- Final Flight Report of Evaluation of Maximum Practicable Combat Power Rating for the Model F4U-1 Airplane Model F4U-1 Airplanes No's 55937, 50030 = overboost test, of course standard configuration should not be used, and Hellcat had similar modified planes in similar test report.
- Evaluation of Maximum Practicable Combat Rating Performance at Carburetor Impact Pressure of 32.8"- TED No. PTR 0415 F4U-1 No. 50030 = same as above report.
- Memorandum Report on F4U-1, No. 02296: Flight Tests = no special modification
- Memo. Report on F4U-1, No. 02296: Flying Characteristics and Design and Maintenance Qualities of F4U-1 = no special modification
- Corsair I JT.118 Handling trials A. & A.E.E. 30 December 1943 = no special modification
- Corsair Mk.II JT.259 Handling trials A. & A.E.E. 1 February 1944 = no special modification
- Corsair F.Mk.II JT.259 Performance trials and position error measurment = no special modification
- Corsair F. Mk.IV KD.227 (Double wasp R2800-8W) Level speed trials with and without water injection = no special modification
- Report on Comparitive Combat Evaluation of Focke-Wulf 190-A/4 Airplane NAS Patuxent River = no special modification
- Evaluation and Comparison Trials of P-51B and F4U-1 Airplanes. NAS Patuxent River = BuNo.17930 as standard but another one was overboosted.
- Flight Test of Water Injection Equipment - TED No. PTR 2105 F4U-1 No. 17930 = It seems main target, but it's corrected for standard plane by navy, see below sections.

and I've used reports of F6F-5 BuNo.58310 and F6F-5 BuNo.72731 for below drag reduction section, on the F6F page, there were only this two reports on the F6F-5.



DarrenW said:


> For example, the only F4U-1 which attained 400 mph speeds without water injection was modified with the following:


Over 400 mph maximum speed without water injection was common for Corsair except early bardcage type.




*Officially*, F4U-1 showed *407 mph without water injection* and also without F6F type propeller(6501A-0). it's propeller blade design was older 6443A-21(3rd ACP pic) and 417 mph with water injection, It's standard performance for raised cabin F4U-1 without land-based configuration, many later F4U-1s were able to use this performance or even better with land-based configuration.

Birdcage Corsair's 395 mph seems from early troublesome supercharger with faulty pressurization.



DarrenW said:


> a non-standard higher efficiency F6F propeller


Blade design 6501A-0 was not factory installed type for F4U-1, but start service with VF-17 in solomon campaign and many F4U-1s have replaced propellers with this new type.



DarrenW said:


> modified cowl flaps


It's not flap*S*, only top section of cowl flaps was replaced by a fixed plate completely covering the opening and It's *standard *improvement between early birdcage F4U-1 and raised cabin F4U-1. the Corsair that was put into battle without this was even small within the birdcage type.










It is a picture of VMF-215 on Hawaii, so it is at least before May 12. other units have different periods, but also installed within 1943, and standard for raised cabin F4U-1s.



DarrenW said:


> removal of tail hook with faired cut-out
> removal of catapult hooks
> enhanced streamlined tail wheel
> shell ejector openings were taped over


The effect of drag reduction for land-based configuration is not significant. according to Dana Bell, It was about +4 mph with hooks and folding devices removed. case for the F4U-1 BuNo.17930, folding devices remained so just +3 mph(2.4 + 0.6, see below chart) for hooks removed and faired cut-out.

High tail wheel was standard for late F4U-1s, but streamlined wooden block type was not standard. However, after take-off, it seems no way to clear effect than standard high tail wheel to performance, because after tail wheel door closed, only half of the wheel was just exposed.

both Hellcat(F6F-5 BuNo.58310/72731) and Corsair(F4U-1 BuNo.17930) taped over weapons in test, the Corsair's gun blast and shell ejector openings were taped over and the Hellcat's gun barrel openings were sealed/taped and blast tube fairing not installed. in this condition, even the Hellcat's shell ejection chutes opened, It does not seems to be special disadvantageous in terms of drag and performance compared to standard condition for both model. for example, Corsair's drag cofficient for install all six guns was just equivalent to catapult hook, so even at the worst, the effect is only slight as below chart.

Here, drag documents for F4U-1s.




*



*
These drag reductions seem to offset the drag of additional external equipment for test. however, since the drag to be reduced is different according to the added drag, the configuration would also differ to corrected for standard condition.

F4U-1 BuNo.17930's report stated several special instrument leads were carried exterrally from the firewall back to the cockpit. these were faired together to the fuselage by means of doped tape, making a half round projection of approximately 3/4" diameter. and F6F-5 BuNo.58310/72731's report also stated an outside air temperature gage of the electrical resistance type was installed for test purposes on the topside of the right wing pannel. there seems to be a slight difference in their additional drag coefficient each.





It's F4U-1 BuNo.17930, the white line is special instrument leads mentioned avobe.

As a result, F4U-1 BuNo.17930 seems appears to have achieved a drag similar to the service condition, as shown in the comparison to be described later, which is also the evaluation of the USN.

*



*
And this Navy's evaluation was evident by contrasting the F4U-1's ACP and comparison report with F4U-1, F6F-3 and Fw 190, If F4U-1 BuNo.17930 was specially modified for drag reduction, It should be clearly fast in all situations.





But compared to ACP the offical performance for service condition, the speed of BuNo.17930 was the almost identical except for the high speed high altitude range, and the comparative report explains why.









Because the F4U-1's early propeller blades showed a loss of efficiency at high speed high altitude range.

In conclusion, there was nothing so special for F4U-1 BuNo.17930's drag condition compared to standard due to navy's correction, It just seems equivalent late type land-based configuration raised cabin F4U-1. What I can say for sure is that the lots of the water injected clean wing F4U-1s with new propeller blades and land-based configuration was used in battle, and It's performance was unlikely to differ significantly from the F4U-1 BuNo.17930, basically.

However, the question arises then because the F4U-1D's top speed, which replaced the propeller blade design to 6501A-0, was still 417 mph.

From here on out, it's my guess, BuNo.17930 F4U-1's maximum speed 431 mph was for late type land-based configuration with lean mixture but F4U-1D's was not.

*



*
Look at this F6F-5 BuNo.58310 graph, the auto-lean curve showed faster than the auto rich at altitude, the vmax was about 8 mph faster, and the critical altitude increased about 400 ft. The report noted a loss in output from auto-rich due to caburation problems. Due to the similarity of the engine, the Corsair may also consider the possibility of experiencing the similar problem.





Compare the power curves of the F4U-1 BuNo.17930 and F4U-1 BuNo.50030, can see that a similar result is happening, despite the slightly higher manifold pressure caused by the 25 drill water jet, it shows lower altitude performance. on the other hand, it seems that the F4U-1s in early 1944 basically used lean mixture, It was a time when F4U-1's water injection had just begun to be used for battle. In the comparison report with the Fw 190 mentioned above, the F4U-1 also used a lean mixture, but experienced overheating. I guess that more detailed and practical operation restrictions have been applied over combat time increasing, for official performance, it must run for 5 minutes and the cylinder temperature should not exceed 260, as a result, it seems showed the lowered official performance. The F4U-1 BuNo.50030's report contained effort for meet the operation restrictions, However, that is not found in the report of F4U-1 BuNo.17930, perhaps this made the difference.

Back to the F4U-1D, clean wing F4U-1D with new 6501A-0 propeller blades had a top speed of 417 mph at 19,900 ft in official ACP and F4U-1 BuNo.17930 showed 431 mph at 20,300 ft with land based configuration. It shows the difference between critical altitude 400 ft and vmax 14 mph. but F4U-1D was carrier-based configuration, so need to add the drag of carrier-based configuration, references have stated that it was about 4 mph. then vmax difference is reduced to 10 mph and It can be assumed that the F4U-1D is capable of speeding 427 mph at 20,300 feet. hmm, It's similar to the number I saw somewhere. Yes, I also saw the F4U-1D's top speed of 425 mph you mentioned, in several references, It's 8 mph faster than F4U-1D ACP's 417 mph that shows a similar difference with above rich/lean graph. As explained above, if that was the F4U-1D's top speed with lean mixture, it might not be so unusual because It's also 6 mph slower than F4U-1A BuNo.17930 with same propeller, engine and clean wing, 6 mph is a convincing figure for the difference between the carrier-based configuration and the land-based configuration as above documents for drag and reference books. I really want to meet the author of the reference that first used 425 mph.

And it should be remembered that the F6F-5 *also *had these type of speed record - can be achieved, but unofficial. In the November 1944 TAIC test, the F6F-5 showed 409 mph. compared to F6F-5's SAC, It seems to have been a lean mixture as smiliar to above situation. I used to express the opinion that the F6F-5 was clearly a 400 mph over group aircraft, but it seemed to have little or no impact, like when I cope against biases about the Corsair.

If going to do a comparison, it would be better to distinguish between the official and unofficial performances and make comparison in the same classifications with same configuration. for example, the F6F-5 SAC's depressing official performance, Vmax 330 knots (380 mph), should not be compared to the land-based F4U-1's unofficial performance of 431 mph or the F4U-1D's ambiguous 425 mph. Since the F6F-5's that official performance was for a combat condition with three external pylon/racks installed, it should be compared to the 409 mph of the official performance for F4U-1D's combat condition with three external pylons/rack in ACP, even 417 mph cannot be compared. It's a pure fighter configuration without pylons. One interesting data is the July 1944 ACP of the F6F-5N. smiliar performance reduction I mentioned above for F4U-1s also appear in this document with F6F-5 SAC. despite the radar pod's extra drag, this F6F-5N could accelerated to 340 mph at sea level and had a Vmax of 391 mph at 18,800 feet. I felt slight more familiar with my hypothesis, and I also recalled the possibility that the 1944 ACP for the F6F-5 included a Vmax over 400 mph. have to find it. There was F6F-5N's ACP, so there would be F6F-5's.

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

In addition, It should not be forgotten that maximum speed of the FG-1s and F3A-1s were lower than Vought F4U-1s.

The US service Vought F4U-1's maximum speed was almost identical at the sea level for neutral blower stage with least influence of the supercharger, is follows.

for military power

348 mph for Birdcage F4U-1 BuNo.2155
350 mph for F4U-1 ACP
350 mph for F4U-1 BuNo.17930

for combat power

363 mph for F4U-1 BuNo.49832 (2 minutes accelration time limit)
365 mph for F4U-1 BuNo.17930
364 mph for F4U-1 BuNo.50030
366 mph for F4U-1D ACP (clean wing as F4U-1 configuration)

on the other hand, for FG-1 and F3A-1, for military power

339 mph for F3A-1 BuNo.04691
332 mph for FG-1A BuNo.14575
335 mph for FG-1 BuNo.14769

Although the altitude performance varies depending on the condition of the atmosphere and the supercharger, I think that the performance at sea level can be objectively compared. As a result, Goodyear and Brewster Corsairs were slower more than 10 mph with same power setting. As far as I remember, Brewster had a problem with F3A-1's quality control and occurred accidents and through repackaging some internal components, the FG-1 was only a few inches longer than the F4U-1 and there was also Nash's R-2800 installed for some of these Corsairs. These changes may have affected but I have no specific information for it.

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## tomo pauk (Apr 4, 2020)

Just dropping to say that this is one very informative thread.

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## Laurelix (Apr 4, 2020)

F4U-1 - 683km/h at 7000m (WEP)
F6F-5 - 644km/h at 5700m (WEP)

At Sea Level the F4U-1 is like 50km/h faster


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## tomo pauk (Apr 4, 2020)

Is that supposed to be a contribution?


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## Zipper730 (Apr 4, 2020)

DarrenW said:


> It seems rather commonplace these days to accept without question higher and higher maximum speeds for the various Corsair variants, but if someone even mildly suggests a 400 mph F6F-5 they are called a fool and dismissed accordingly.....


After awhile, old sources become accepted without question: Sometimes, the sources weren't in context, or were based on misinterpretations of the source data.


> Unlike the Hellcat, there are many Corsair test reports on the Williams/Stirling website in which the subject aircraft is a highly modified 'one-off', and not representative of aircraft in actual service.


Yeah, when I see those on WWII Aircraft Performance, I generally ignore the report. That said, the one of the F4U-1 doing 417 mph I actually dismissed because of the gun-ports being taped over, an F6F-3's propeller installed, and the top cowl-flap faired over (I mis-read as the flaps faired over -- like those on the wings). Turns out that one was actually a normal modification that was extensively employed in carrier-service.


> For example, the only F4U-1 which attained 400 mph speeds _without_ water injection was modified with the following: a non-standard higher efficiency F6F propeller, removal of tail hook with faired cut-out, modified cowl flaps, enhanced streamlined tail wheel, removal of catapult hooks, and the shell ejector openings were taped over. Without a tail hook this aircraft could no longer be truly classified as a carrier aircraft. Lastly, many of the Corsairs on the site were tested using Combat power settings, which was not the case concerning the Hellcat. The use of ADI enhanced performance considerably and made an apples-to-apples comparison to planes without it impossible.


Some questions

Why would you cover over the shell-ejector openings? I thought the spent casing would be fairly hot after the propellant lit off...
I never knew the Hellcat wasn't being run at combat power settings. How did it perform when water injection was employed



> In addition to this, there seems to be no F4U-1 variants tested with bomb racks installed, which will make a decent amount of difference in the testing outcome.


Yeah, it'd slow it down, though it'd make sense for the USMC.


> IMHO the power ratings of both the R-2800-8W and -10W were somewhat conservative, and for the most part was implemented to keep engines healthy and happy.


I figured that, to some extent, the settings might have been conservative (I didn't consider the overwater nature). That said, I had considered that there might have been various sub-variant level changes to the engine design to allow for higher MAP.


> Testing was performed on both engines using different sized water jets and carburetor impact pressure settings with very good results being obtained (up to 65" Hg was deemed safe while using 130 octane fuel).


How do you vary carburetor impact pressure? As for water-jet, I assume that sets the amount of water you can spray in at once?


> Granted the turbocharged P-47 would tend to benefit more from increases in both boost and octane rating


Was this because of overland use or because of the turbocharger?



Dawncaster said:


> Over 400 mph maximum speed without water injection was common for Corsair except early bardcage type.


The 403 mph figure at 24800' does seem to conform with the comparison with the chart in reply #61 (Page 4), on the Fw.190 and F6F-3. I'm curious why there was such a discrepancy in listed speed (F6F: 391 mph vs. 373.5-377.5 mph; F4U-1: 395 mph versus 403 mph) and critical altitude for both.


> Birdcage Corsair's 395 mph seems from early troublesome supercharger with faulty pressurization.


Faulty pressurization? You mean they weren't producing an adequate boost?

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## DarrenW (Apr 4, 2020)

Hi Dawncaster,

Oh boy, lots to unpack here. I'm very glad you chimed in because I consider you one of the more knowledgeable members on this site concerning the Corsair and wanted to hear what your research on this subject had to say. This wouldn't be a definitive discussion without you. 

There's only a few things I need to clarify though, as I'm in agreement with the majority of the points you've made and I definitely *do not* agree that the Hellcat was faster than published figures due to erroneous airspeed calibration data (which was the original premise of the thread). I also have only been concerned with the performance of F4U-1s and not the F4U-4 or -5 because they are not contemporaries of the F6F-3 and -5 Hellcat.



Dawncaster said:


> Hmm, Exaggerated.



Sorry I misspoke here but my intent was genuine. It depends on what the word "modified" really means to an individual, so I should have worded it more clearly. There were actually two aircraft (No. 02234 & BuNo. 17930) which to me seemed to be _highly_ modified, even if some of these modifications eventually became standard on production aircraft. Another modified aircraft that I was referring to was BuNo. 14575, which had the tail hook removed and had the bottom of the tail cone smoothly faired over. Both BuNos. 50030 and 55937 had the 13' 1" propeller and show testing at non-standard carburetor impact pressure settings so their performance would obviously be better than aircraft with the standard 13' 4" propeller and utilizing authorized impact pressure levels, but you are right that there is also a report where the Hellcat was tested at these non-standard levels too so it's partially a moot point.

And just to make clear the photo you posted of BuNo. 17930 was obviously taken at a different stage in testing than what is found in TED No. PTR 2105, as the special tail wheel faring wasn't installed at that time:

















The report does state that the 'important modifications" were not standard on previous production F4U-1's, but I do agree that similar in-field modifications were being performed, if only at a localized level. From my research it looks like it wasn't until the F4U-1C/D variants that the more efficient 13'1" propeller was fitted to production aircraft so this in itself should be considered a modification for aircraft that came before it.

So the question remains, if BuNo. 17930 was indeed basically a standard land-based F4U-1 in service at the time, why would they bother mentioning those details as modifications, and why were they so interested in knowing how they effected performance? My feeling is that if those modifications were already being included in production aircraft there would be no need to mention them in the report.



Dawncaster said:


> The effect of drag reduction for land-based configuration is not significant. according to Dana Bell, It was about +4 mph with hooks and folding devices removed.



This is interesting as the report you referred to earlier estimated a speed gain of up to 8 mph with these modifications in place and NACA report L5A30 seems to support this conclusion as well. If we subtract 2 mph from this figure for non-smoothed surfaces and non-faired fuselage access doors (not necessary in order to make it a land-based only aircraft - reference the drag document from your previous post for this amount) we get a net gain of 6 mph with the removal of tail hook and fairing over the wing fold joints. I'm also assuming that the catapult hooks were removed to arrive at the 8 mph figure so there's no need to add that drag component back into the equation:





http://www.wwiiaircraftperformance.org/f4u/p-51b-f4u-1-navycomp.pdf






F4U-1





F6F-3




F6F-3

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092668.pdf




Dawncaster said:


> Over 400 mph maximum speed without water injection was common for Corsair except early bardcage type.
> 
> 
> 
> ...



Ok, you got me here, I never consider ACP documents as actual "test reports" so I should have been more careful with my assertion.  Certainly if I was including these handy performance references I wouldn't have mentioned such things as removed tail and catapult hooks, or taped over shell ejector openings as these conditions would render an aircraft useless as a carrier combat aircraft. Be that as it may, there's no other performance figures presented on the website which have aircraft similarly configured that match what is found in this particular ACP so I'm curious which "flight tests" they are referring to.



Dawncaster said:


> However, the question arises then because the F4U-1D's top speed, which replaced the propeller blade design to 6501A-0, was still 417 mph.



While I don't outright question the validity of the ACP concerning the propeller blade design, could the test data presented possibly be for an F4U-1 with the 13' 1" propeller? As you said earlier it was common for this to be the case, especially by the date the ACP was published. Do you happen to have any other official performance data that show the F4U-1 with a 13' 4" propeller making that kind of speed?



Dawncaster said:


> Look at this F6F-5 BuNo.58310 graph, the auto-lean curve showed faster than the auto rich at altitude, the vmax was about 8 mph faster, and the critical altitude increased about 400 ft. The report noted a loss in output from auto-rich due to caburation problems. Due to the similarity of the engine, the Corsair may also consider the possibility of experiencing the similar problem.





Dawncaster said:


> Yes, I also saw the F4U-1D's top speed of 425 mph you mentioned, in several references, It's 8 mph faster than F4U-1D ACP's 417 mph that shows a similar difference with above rich/lean graph. As explained above, if that was the F4U-1D's top speed with lean mixture, it might not be so unusual because It's also 6 mph slower than F4U-1A BuNo.17930 with same propeller, engine and clean wing, 6 mph is a convincing figure for the difference between the carrier-based configuration and the land-based configuration as above documents for drag and reference books. I really want to meet the author of the reference that first used 425 mph.



Not quite sure what to make of your theory but I do find it interesting that engine charts differ for the two F4U-1 pilot's manuals that I have. The manual dated 1 June 1944 has an auto-rich mixture selected for everything but max cruise and minimum fuel consumption settings, while the other dated 15 March 1945 recommends it during take-off only. So it seems that auto-lean was the preferred setting for the R-2800-8W, and because of this I find it difficult to believe that the F4U-1D would be tested in auto-rich only, especially if performance suffered as a result. But I guess anything is possible.

By contrast, the three F6F manuals I have only recommend an auto-rich mixture during take-off and landing.

*1 June 1944*






*15 March 1945*







Dawncaster said:


> both Hellcat(F6F-5 BuNo.58310/72731) and Corsair(F4U-1 BuNo.17930) taped over weapons in test, the Corsair's gun blast and shell ejector openings were taped over and the Hellcat's gun barrel openings were sealed/taped and blast tube fairing not installed. in this condition, even the Hellcat's shell ejection chutes opened, It does not seems to be special disadvantageous in terms of drag and performance compared to standard condition for both model.



As far as shell ejector chutes go, taping them over would make the guns non-functional so besides modifying an aircraft to perform reconnaissance work I don't see a reason for the practice, which was common during the Corsair tests but not the Hellcat. Gun blast tube fairings were only fitted on the first 909 F6F-3s delivered, so I am baffled as to why they are mentioned in the case of F6F-5 BuNo.58310. Just a guess but maybe further testing was performed with this aircraft to see if they would improve performance in some measurable way???

FWIW there has been testing performed at NACA and presented in report L5A30 which found that taping over the shell and linkage ejector chutes of the P-51 under test could yield a 3 mph increase in speed. I can only assume that there would have been even a greater benefit afforded the F4U, seeing that it had more slots to be taped over:






https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092668.pdf



Dawncaster said:


> As a result, Goodyear and Brewster Corsairs were slower more than 10 mph with same power setting. As far as I remember, Brewster had a problem with F3A-1's quality control and occurred accidents and through repackaging some internal components, the FG-1 was only a few inches longer than the F4U-1 and there was also Nash's R-2800 installed for some of these Corsairs. These changes may have affected but I have no specific information for it.



Hmm, it seems that the US Navy judged the two to be generally similar to those produced by the parent company:





http://www.wwiiaircraftperformance.org/f4u/F3A-1_04691.pdf






http://www.wwiiaircraftperformance.org/f4u/kd365.pdf



Dawncaster said:


> I used to express the opinion that the F6F-5 was clearly a 400 mph over group aircraft, but it seemed to have little or no impact, like when I cope against biases about the Corsair.



I agree with you. Even F6F-5 BuNo.58310 reached 395 mph @ 18,750 feet while utilizing Combat power, and this was with a starboard wing pylon installed (known to reduce speed by roughly 5 mph at this height). So we have an honest 400 mph F6F-5 here in a 'clean' condition....



Dawncaster said:


> Back to the F4U-1D, clean wing F4U-1D with new 6501A-0 propeller blades had a top speed of 417 mph at 19,900 ft in official ACP and F4U-1 BuNo.17930 showed 431 mph at 20,300 ft with land based configuration. It shows the difference between critical altitude 400 ft and vmax 14 mph. but F4U-1D was carrier-based configuration, so need to add the drag of carrier-based configuration, references have stated that it was about 4 mph. then vmax difference is reduced to 10 mph and It can be assumed that the F4U-1D is capable of speeding 427 mph at 20,300 feet. hmm, It's similar to the number I saw somewhere.



You seem to have studied the Corsair's airframe drag extensively. Have you considered how much the glossy blue paint scheme and revised wing walkways found on the F4U-1D may have contributed to drag reduction? From what I can tell it may add about 3 mph, but this is only an estimation after looking at all the F6F test data that's available to me.



Dawncaster said:


> Birdcage Corsair's 395 mph seems from early troublesome supercharger with faulty pressurization.



Could you tell me more about this? I mentioned this earlier in the thread but was told that due to engine similarities, whatever problems the F4U was experiencing in this regard would have manifested itself in the F6F as well.

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## DarrenW (Apr 4, 2020)

Zipper730 said:


> I never knew the Hellcat wasn't being run at combat power settings. How did it perform when water injection was employed



Almost all F6F test data on the website shows maximum performance while in Military power. There are a few reports that show testing while utilizing Combat power but when compared to the F4U they are far fewer in number. The data I have seen varied due to height and seems to suggest an increase of about 5-20 mph from S/L to around 22k feet.


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## DarrenW (Apr 4, 2020)

Zipper730 said:


> How do you vary carburetor impact pressure? As for water-jet, I assume that sets the amount of water you can spray in at once?



They used larger water jets and made adjustments to the supercharger fuel and water regulators which allowed for a higher flow rate to occur (hence more impact pressure), and this allowed for higher manifold pressures to be developed safely without detonation which in turn produced more power.


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## DarrenW (Apr 4, 2020)

Zipper730 said:


> Was this because of overland use or because of the turbocharger?



The P-47's turbo system was far more efficient because unlike the supercharged F4U and F6F it continuously maintained the higher boost pressures from sea level up to critical altitude.


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## Zipper730 (Apr 4, 2020)

Dawncaster said:


> The effect of drag reduction for land-based configuration is not significant. according to Dana Bell, It was about +4 mph with hooks and folding devices removed. case for the F4U-1 BuNo.17930, folding devices remained so just +3 mph(2.4 + 0.6, see below chart) for hooks removed and faired cut-out.
> 
> High tail wheel was standard for late F4U-1s, but streamlined wooden block type was not standard. However, after take-off, it seems no way to clear effect than standard high tail wheel to performance, because after tail wheel door closed, only half of the wheel was just exposed.


According to this report, there was a cover over the redesigned tail-wheel. As for the effects on performance, it does seem that there is a substantial performance effect by removing the tail-hook and fairing it over, removing the catapult hooks, and things of that sort. The airplane's paint finish was about normal for a combat aircraft, and the radio, if I recall correctly, remained installed. The report that you have for the drag improvement for A/C #02334 seemed to indicate the removal of the radio antenna, though the shell-ejector openings were not faired over.

That said, looking at your numbers, I see an increase of speed of 13-15.7 mph. I'm not sure how many of these mods were actually implemented on combat aircraft for land-based ops. That said, you'd get around 408-411 mph top speed. That seems to jibe with your figures of 407 mph @ 24800'.

BTW: What is a "free air therm. and additional channel"?


> the F4U-1's early propeller blades showed a loss of efficiency at high speed high altitude range.


Yeah, I'd imagine! If my calculations are right...






... the blades are supersonic at the tips at peak altitude. I could imagine a diameter reduction would be of benefit as you're basically beating the air into bloody submission.


> BuNo.17930 F4U-1's maximum speed 431 mph was for late type land-based configuration with lean mixture


Wait, I thought lean mixture meant a low fuel/air ratio? Is that air/fuel?



DarrenW said:


> The P-47's turbo system was far more efficient because unlike the supercharged F4U and F6F it continuously maintained the higher boost pressures from sea level up to critical altitude.


I think you're mixing up horsepower with boost pressure. Manifold pressure stays the same, but a throttling loss is incurred at lower altitudes with superchargers.


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## XBe02Drvr (Apr 4, 2020)

Zipper730 said:


> Wait, I thought lean mixture meant a low fuel/air ratio? Is that air/fuel?


You thought right. Your understanding appears a little confused. Theoretical peak power occurs at the ideal, or stoichiometric fuel/air ratio, which is at or near lean mixture peak cylinder temperature. So best power occurs at lean mixture settings. The problem is that most engines can't sustain those temperatures for long without overheating and detonating.
Rich mixtures don't GIVE you more power, they help you SUSTAIN more power by cooling the cylinder temps and holding off detonation. Now in a speed test run, you're getting the optimum engine cooling airflow so you've got a little "thermal cushion" in case you want to venture a little on the lean side for a little more power. It's a risky business, however, only to be engaged in with thorough knowledge and good instrumentation.
Some highly efficient modern GA aircraft routinely operate on the lean side of peak cylinder temp when in max range cruise, but they have much lower "power density" and more efficient cooling than a WWII R2800.
Cheers,
Wes

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## Zipper730 (Apr 4, 2020)

XBe02Drvr said:


> You thought right. Your understanding appears a little confused. Theoretical peak power occurs at the ideal, or stoichiometric fuel/air ratio, which is at or near lean mixture peak cylinder temperature.


I thought the rich mix was basically right up on the ideal mix for peak power.


> Rich mixtures don't GIVE you more power, they help you SUSTAIN more power by cooling the cylinder temps and holding off detonation.


I'd have figured excess fuel would just smother things if you didn't have enough air...


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## FLYBOYJ (Apr 4, 2020)

Zipper730 said:


> I thought the rich mix was basically right up on the ideal mix for peak power.



* stoichiometric fuel/air ratio *

Read up about this!

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## DarrenW (Apr 4, 2020)

Zipper730 said:


> I think you're mixing up horsepower with boost pressure. Manifold pressure stays the same, but a throttling loss is incurred at lower altitudes with superchargers.



Yeah I could have worded that better. I should have said that the turbocharger allowed for a constant _realization_ of boost pressures which resulted in constant horsepower, as there were no shift points along the way to detract from maximum horsepower being attained from S/L to critical altitude.

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## pbehn (Apr 4, 2020)

FLYBOYJ said:


> * stoichiometric fuel/air ratio *
> 
> Read up about this!


Oh no, he just might do that.


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## FLYBOYJ (Apr 4, 2020)

pbehn said:


> Oh no, he just might do that.

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## Zipper730 (Apr 4, 2020)

FLYBOYJ said:


> * stoichiometric fuel/air ratio *
> 
> Read up about this!


It was a misunderstanding. Early on, I thought rich meant too much, lean meant too little for optimal and stoichiometric was right on the middle; then I remember seeing a number cited for rich a long time ago (and that's probably the problem), and I think it was 1/6 (fuel/air) which seems very little (might sound stupid but I figured the numbers would be like 1/3 based on the fact that 65% of the air in the combustion chamber was unused), so I guessed the rich mixture was the ideal for power, and lean was best for fuel economy: I'm not sure where I got these ideas from.

Regardless, I stand corrected. 

BTW: The ratio for gasoline is 1/14.7 fuel/air. No idea what jet-fuel would be, but if I were to make a guess, I would figure diesel would be closest.

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## pbehn (Apr 4, 2020)

Zipper730 said:


> It was a misunderstanding. Early on, I thought rich meant too much, lean meant too little for optimal and stoichiometric was right on the middle; then I remember seeing a number cited for rich a long time ago (and that's probably the problem), and I think it was 1/6 (fuel/air) which seems very little (might sound stupid but I figured the numbers would be like 1/3 based on the fact that 65% of the air in the combustion chamber was unused), so I guessed the rich mixture was the ideal for power, and lean was best for fuel economy: I'm not sure where I got these ideas from.
> 
> Regardless, I stand corrected.
> 
> BTW: The ratio for gasoline is 1/14.7 fuel/air. No idea what jet-fuel would be, but if I were to make a guess, I would figure diesel would be closest.


When will you stop guessing? If you think it is important read up on it and remember it?


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## Zipper730 (Apr 5, 2020)

pbehn said:


> When will you stop guessing?


According to this site, the ratio is about 15.06%


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## XBe02Drvr (Apr 5, 2020)

Zipper730 said:


> I'd have figured excess fuel would just smother things if you didn't have enough air...


THINK about this for a second. Would it make sense to have a cockpit mixture control that in its normal range of operation was capable of flooding the engine or leaning it to failure in flight? Would you want to fly that beast? So does it make sense to worry that selecting rich mixture might "smother" the engine?
Now in modern simple airplanes at high altitude, full rich mixture can make an engine run rough and mighty thirsty, but that's because the mixture isn't altitude compensated, and most simple GA airplanes don't cover such a wide range of altitudes. When you see a mixture control with "AUTO" settings for "RICH" and "LEAN", that implies it's altitude compensated, and will adjust the RICH -> LEAN range for the ambient pressure altitude.
Cheers,
Wes


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## Zipper730 (Apr 5, 2020)

In old teacher voice: _And we now get to the subject of improper wording_ j/k



DarrenW said:


> Yeah I could have worded that better. I should have said that the turbocharger allowed for a constant _realization_ of boost pressures which resulted in constant horsepower, as there were no shift points along the way to detract from maximum horsepower being attained from S/L to critical altitude.


I kind of get what you're saying, the ability to get the most horsepower for MAP across the entirety of the performance envelope.



XBe02Drvr said:


> Would it make sense to have a cockpit mixture control that in its normal range of operation was capable of flooding the engine or leaning it to failure in flight?


I should have used a different word than smother, that does sound similar to flooding the carburetor. I meant something more like it'd reduces combustion to a degree.


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## XBe02Drvr (Apr 5, 2020)

Zipper730 said:


> I should have used a different word than smother, that does sound similar to flooding the carburetor. I meant something more like it'd reduces combustion to a degree.


It's not so much an issue of flooding the carburetor as it is of making the mixture to the cylinders too rich to support combustion. ("Yes, Virginia, it is actually possible to do that"). Clearly you've never adjusted the mixture screw on a lawn mower engine.
And yes, it does reduce combustion efficiency to a degree from optimum stoichiometric mixture. That's the "insurance premium" you pay to keep detonation from destroying your engine. The extra fuel cools things down a bit and some of it gets exhausted unburned, contributing to the light show at the exhaust stacks.
Cheers,
Wes


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## Shortround6 (Apr 5, 2020)

Corsair engine flight chart.




copied from Zeno's Warbird Videos - World War II Pilot Training videos & air combat documentaries playing for free over the Internet 

A lot of these military engines don't seem to act like regular car, motorcycle or lawn mower engines. 
Please note the fuel flow figures (3rd column from the right) and the war emergency row.
They had a de-enrichment circuit in the carb that cut the fuel flow when the water injection was operating. It would quickly restore full fuel flow automatically when the water ran ran out. when running in auto rich these engines were far into the richer than stoichiometric ratio would call for area. The extra fuel was being used as a coolant to some extent and not only can you find videos/pictures of some of these planes trailing black smoke on take-off (or the famous puff of black smoke when opening the throttle that sometimes fooled opponents into thinking they had scored hits?) but there are stories of unburned fuel coming out the exhaust pipes. 

But then regular car, motorcycle or lawn mower engines are NOT taking in air/fuel mixture than is several hundred degrees F. and under pressure. 
Look again, the Corsair was using about 1/2 gallon a minute of gas as a coolant at military power.

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## Dawncaster (Apr 7, 2020)

I'm Sorry, Please understand that there are many omissions to meet the 20k character limit and the lower the content, the worse the condition is. It was especially painful when the cited post was changed and the content had to be rewritten. In fact, it's dropped. Mayday! 



DarrenW said:


> Sorry I misspoke (ellipsis) even if some of these modifications eventually became standard on production aircraft.





DarrenW said:


> And just to make clear the photo you posted of BuNo. 17930 was obviously (ellipsis) special tail wheel faring wasn't installed at that time:


I think there seems no 'special tail wheel faring' for F4U-1 BuNo.17930, In my view, It was steamlined wooden block and of course included in photo I uploaded. to be exact, I don't know what 'fairing' you mentioned.





re-upload with red circle for wooden block, and new another shot.





This is early F4U-1's tail wheel section, the tail wheel of the dash-1 Corsair was exposed even after tail wheel door closed. early F4U-1's low tail wheel was not exposed much, but high tail wheel was exposed more.










The report pointed out that the position was farther with switching from low tail wheel to high tail wheel, because it was taller.

As a result, because the previous low tail wheel had been removed and the position of the new high tail wheel was farther, so the slot in that place became gap. of course, it creates drag or other problems. However, the report continues. Wrote '*But*' and describe how solved it - with the wooden block, gap was closed and faired. so there is no need to worry about additional drag from gap.

In conclusion, the report describes its role, It seems to prevent the loss of the performance caused by installing a new tail wheel, instead of special extra performance. this is what I understand.





In fact, few early Birdcage F4U-1s had a fully retractable tail wheel unit. look at the slotless tailwheel door and the tiny size tail wheel.





and among the changes that have been made since F4U-1 BuNo.17930, there was a format that complements the rear of the exposed tail wheel to turn into a streamlined teardrop(I don't have the exact expression for it) shape



DarrenW said:


> So the question remains, if BuNo. 17930 was indeed basically a standard land-based F4U-1 in service at the time, why would they bother mentioning those details as modifications, and why were they so interested in knowing how they effected performance? My feeling is that if those modifications were already being included in production aircraft there would be no need to mention them in the report.


Same as above. see what the report says exactly.




'The airplane was a late model production type incorporating all the latest changes, including the *raised cabin* installation.'

This is the first mentioned in changes list. If you read normally, you can see that the F4U-1 BuNo.17930 was being compared to Birdcage(low cabin) F4U-1.

Conversely, I want to ask a question. Why did you judge that it was comparing to the production model for that time? don't forget, the raised cabin F4U-1(F4U-1A) was already put into combat even in 1943.



DarrenW said:


> Another "modified" aircraft (ellipsis) faired over.


According to Dana Bell, 965 FG-1s were delivered with land-based configuration, It's one of the factory built version.




Removing the folding mechanism and tail hook, after halves of the doors were bolted closed and the cove for the tail hook was skinned over. the aircraft was to average an increased top speed of 4 mph, saved weight was 80 lbs.



DarrenW said:


> This is interesting as the report you referred to earlier estimated a speed gain of up to 8 mph with (ellipsis) we get a net gain of 6 mph (ellipsis) back into the equation:



As above, Land-based configuration gives additional 4 mph *actually *for Corsair, there was no additional 6(or 8) mph.

And seems need some explanation for others also.






F4U-1 BuNo.17930's drag condition was corrected for standard but F4U-1 BuNo.02390 was not.

F4U-1 BuNo.02390 was one of the first batch(2153~2736) birdcage Corsair, It showed problem I mentioned in the previos post.

Let's see what that resulted.

Despite F4U-1 BuNo.02390's higher manifold pressure caused by the 25 drill waterjet, there was a loss of altitude performance, so it produces less horsepower than the F4U-1 BuNo.17930 at many altitudes. However, F4U-1 BuNo.02390 was faster than F4U-1 BuNo.17930 at all tested altitude, This seems shows that the drag condition of the F4U-1 BuNo.02390 was superior than navy standard F4U-1 BuNo.17930, The report noted that the F4U-1 BuNo.17930's drag condition was corrected to standard, but no similar content was found for F4U-1 BuNo.02390 in the report. It was expected to be similar to the land-based F4U-4's drag condition.

So, the report distinguished between F4U-1 BuNo.17930 and F4U-1 BuNo.02390 for speed comparison, but not for climb or other comparisons, It's presumed that the performance difference between the two F4U-1s was not meaningful except Vmax.

And there seems a difference between F4U-1 BuNo.02390's +8 mph drag reduction content and your uploaded photos and content.





These were not actually done with F4U-1 BuNo.02390, only taped wing fold joint was actually done in the flight test for it.





This is actually done in flight test for F4U-1 BuNo.02390's wing section.





This was also not actually done with F4U-1s, unlike the F6F-3/5, the tail wheel of the F4U-1s were exposed when flying except for the few F4U-1s I mentioned above, and the F4U-1s had to be actually tested for flight, making it impossible to achieve such drag reduction. since the F4U-1 BuNo.02390 was of the first batch Corsair, may be able to achieve a complete seal for wind tunnel test, If it had tiny tail wheel unit and slotless tail wheel door. However, flight testing requires taxiing and takeoff, so also impossible for F4U-1 BuNo.02390





Perfect sealing was seems possible because it was a Hellcat and also because it was a wind tunnel test. Well, at least, the Corsair model used in the wind tunnel test was seems the one of the first batch Birdcage F4U-1, considering the cabin's shape, it can be seen that it was early model even within Birdcage F4U-1s. so the tailwheel could be retracted completely in wind tunnel test. of course, as mentioned above, applying to the current topic is unpractical.

And It has already been revealed in the drag-speed chart in the last post that the removal of the tail hook and fair cut-out was only provides an additional performance of 0.6 mph. It's more clear from the drag coefficient and the additional performance obtained.






for example, remove catapult hook, it gives 2.4 mph with reduce 0.0030 drag cofficient. the drag coefficient of the arresting hook is 0.0005, which is one-sixth, so if remove it, can assume that can get an extra performance of 0.4 mph. However, the F4U-1 BuNo.02334 obtained 0.6 mph by just fair arresting hook cut-out. that may be the difference in drag, but the 0.0005 drag coefficient might not included creating a cutout on the smooth fuselage, In that case, 0.4 for hook removed and 0.2 mph for cut-out filled.






In my view, for estimated +8 mph, smooth and faired cowling would have had a substantial impact. because impact of the other drag reduction seems not so great.



DarrenW said:


> FWIW (ellipsis) 3 mph increase in speed. (ellipsis) seeing that it had more slots to be taped over:


Firstly, remember the end of my paragraph you quoted. I wrote 'for example, Corsair's drag cofficient for install all six guns was just equivalent to catapult hook, so even at the worst, the effect is only slight as below chart.'





To install the six guns, need to dig the leading edge of the smooth wing, drill six holes for muzzles, and make six slots for the shell ejector on the under surface. and It's drag cofficient was equivalent to catapult hook - 0.0030. so, can expect to lose 2.4 mph due to the additional drag gained by installing six guns(0.4 mph per gun). then, let's calculate the drag corresponding to 6 of the 12 slots for the shell ejector.





Thankfully, the report you linked to contains information about the extra drag caused by installing x 4 cannon barrels on leading edge. It showed that the F4U-1 with four cannons had a 1 mph speed loss compared to a smooth wing. and the based lift cofficient is unknown, but it also showed 1 mph per 0.0002 for F4U-1.





Referring to other report, it appears to be the drag coefficient obtained at close about 0.2 lift coefficient(just close, difference of 0.0001 occurred on the P-51). and the drag coefficients in the above report were averaged. then now let's look at the drag coefficient that the six gunports impose on the F4U-1. surprisingly, it's zero on average and increase the maximum lift cofficient. It's probably because of the guns that are installed completely inside the wing and gunports design with less gap unlike such as P-51B's. the difference in drag coefficient between 6 gunports and 4 cannon barrels was only about average 1 mph imposed for F4U-1 as above.

http://www.wwiiaircraftperformance.org/f4u/f4u-1d-acp.pdf
and it seems proved with actual performances at F4U-1C/D's ACP. because the Vmax of the F4U-1D and F4U-1C, which have the same drag coefficient except for the armament, differed by only 1 mph at Vmax.

Then now, 2.4 mph penalty entirely could be given to the F4U-1's shell ejector tapping.





Lastly, the Mustang was aerodynamically a much cleaner aircraft than the F4U-1 and It's wings were especially. but laminar flow airfoils are very susceptible to aerodynamic contamination, It seems possible to produce more sensitive results for equivalent drag sources that interfere with the flow of air, and the number of taped under surface slots was equal on both model - three per wing so there were no more taped slots for F4U-1.

Then let's compare it with the actually obtained values. comparing the performance reduction when installing the x4 cannon barrels uploaded above, can see that the Mustang was about 20% more affected than the F4U-1. and for six taped under surface slots, 3 mph for Mustang and up to about 2.4 mph for F4U-1, so the Mustang was 25% more affected. It seems reasonable.

As a result, 4 mph for F4U-1's land-based configuration and up to about 2.4 mph for shell ejector taping, If the shell ejector tapings were Navy standard for the F4U-1, can expect a loss of 2.4 mph for combat service for F4U-1 BuNo.17930 and ACP's official performances, which considered as standard drag condition by the Navy. Also, even though it was considered standard by the Navy, if you think its performance benefits Land-based configuration, can subtract an additional 4 mph. So with the adverse assumption for Navy's standard drag condition, can expect a performance loss is total 4(land-based configuration) + 2.4(shell ejector tapings) = 6.4 mph. this is at least the result obtained by combining the results actually obtained in flight test or calculated in report.









In my view, Navy standard not include land-based configuration of course. otherwise, the speed curves contained in F4U-1 Buno.17930's report and F4U-1's ACP cannot match up to about 16.5k ft(until the old propeller blades begin to lose efficiency), as actually obtained. however, assuming the worst is the least guaranteed performance, I considered both.





(I think Zipper 730's calculation is a good indication of why the early F4U-1's old 13'4" prop was losing efficiency at high altitude high speed range)

In conclusion, the F4U-1 BuNo.17930's 431 mph seems the best performance actually achievable with standard drag condition for standard production F4U-1 with 13'1" prop as Navy stated, even assuming the worst, can subtract up to 6.4 mph.



DarrenW said:


> Ok, you got me here, I never consider ACP documents as actual "test reports" (ellipsis) I'm curious which "flight tests" they are referring to.



It was official performance cleard with operation restrictions for standard configuration, from *actual *flight test. If it was not the actual performance, it was specified in the ACP and It also specifies whether it was a production model or prototype.





Military documents used the ACP to cite the performance of the F4U-1 during the period of validity of the ACP. If the ACP is revised, the old version becomes invalid and the new ACP indicates what the old version was.

ACP, SAC or british aircraft cards, the advantage of 'official' performance is that seems more reliable than individual reports. their performances were corrected to military standards for service use and also cleared for operation restrictions. for example, the water injected F4U-1s in early 1944 use a neutral blower stage to use combat power at sea level in the multiple reports. however, lack of test data with raised cabin F4U-1 or does not meet required performance for operation restrictions, whichever, It seems insufficient to be cleared so could't included in ACP. In fact, unlike the F4U-1s mentioned above, the critical altitude of the cleared water injected neutal blower stage was sea level. I think it's because of the difference in operation restrictions. and estimated that more accurate and practical operation restrictions were applied over time as operating hours increased and more data obtained.





Also, in some cases, it's corrected to the condition that the fuel tank is permanently full. If the performance increase due to the consumption of fuel was included in the official performance, an aircraft that would rise with full tank and jettison it in the operating area would not have been able to achieve it. I am not sure if this applies to how many official performances. However, these examples make the official performance appear to be slight more certain.

Lastly, I don't understand about denying official performance just because didn't find a refered flight test report on the website, even more so if it's not certain that the website contains ALL the Corsair's flight test reports during World War II.



DarrenW said:


> While I don't outright (ellipsis) 13' 4" propeller making that kind of speed?


Page 51 of the ACP specifies that it's a 6443A-21 propeller with a diameter of 13'4". as described above, multiple ACPs for the same a/c do not exist until a new revision is issued.



DarrenW said:


> Not quite (ellipsis) anything is possible.


Remember what I wrote in the previous post. what I just expected based on the data actually obtained.





'Look at this F6F-5 BuNo.58310 graph, the auto-lean curve showed faster than the auto rich at altitude, the vmax was about 8 mph faster, and the critical altitude increased about 400 ft. The report noted a loss in output from auto-rich due to caburation problems. Due to the similarity of the engine, the Corsair may also consider the possibility of experiencing the similar problem.'




'Compare the power curves of the F4U-1 BuNo.17930 and F4U-1 BuNo.50030, can see that a similar result is happening, despite the slightly higher manifold pressure caused by the 25 drill water jet, it shows lower altitude performance. on the other hand, it seems that the F4U-1s in early 1944 basically used lean mixture, It was a time when F4U-1's water injection had just begun to be used for battle. In the comparison report with the Fw 190 mentioned above, the F4U-1 also used a lean mixture, but experienced overheating. I guess that more detailed and practical operation restrictions have been applied over combat time increasing, for official performance, it must run for 5 minutes and the cylinder temperature should not exceed 260, as a result, it seems showed the lowered official performance. *The F4U-1 BuNo.50030's report contained effort for meet the operation restrictions, However, that is not found in the report of F4U-1 BuNo.17930, perhaps this made the difference.*'

I was also not convinced that it was AUTO LEAN or AUTO RICH. But I assumed so. even if a higher manifold pressure was achieved, it was because the data were actually obtained that the use of AUTO RICH mixture for cooling lowered the altitude performance. another example is the F4U-1 BuNo.02390 I mentioned at the above of this post. and I think my explanation of the bold part in above paragraph was lacking in the previous post.





This is part of the report for F4U-1 BuNo.50030, the report states that performance has been reduced to standard conditions in accordance with standard flight test methods. In the report of F4U-1 BuNo.17930, no similar content can be found and I speculated that it was the main factor that made a difference in performance. also, since the F4U-1s in the report included over-boosting to the extent that they did not meet the requirements, I expected that the AUTO RICH mixture was likely used for cooling.



DarrenW said:


> Could you (ellipsis) F6F as well.



It's not just faulty pressurization, It would lead to a fatal malfunction, spark to jump the gab and burn out the distributor points, there were complete engine failure on some flights above 29,000 feet.

for Hellcat, If the F4U-1's improvements were properly feed back and applied to the F6F-3, the F6F-3 would be free in this problem, because the first air combat was in the fall of the 1943 for Hellcat.



Zipper730 said:


> According to (ellipsis) jibe with your figures of 407 mph @ 24800'.



Seems to be misunderstood or misread, if not, I don't know why are you trying to treat official performance for cleared with operation restrionction at standard configuration as a special modified configuration... Read above, I think your calculation missed the starting point. there was no substantial performance effect.

http://www.wwiiaircraftperformance.org/f4u/f4u-1-02334.pdf

In the F4U-1 BuNo.02334's report, standard F4U-1 expected 404 mph @ 25300' for military power and ACP showed 407 mph @ 24800' actually obtained for military power. this is a fairly close result and seems resonable for Navy's estimate.





Considering this, it's even more so.

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## DarrenW (Apr 7, 2020)

Hi Dawncaster,

Very nice parade of data, I appreciate all the hard work you went through to provide it. I gave you some more bacon... 



Dawncaster said:


> Lastly, I don't understand about denying official performance just because didn't find a refered flight test report on the website, even more so if it's not certain that the website contains ALL the Corsair's flight test reports during World War II.



I'm sorry that you feel that I'm discounting "official performance" as this couldn't be farther from the truth. Like most investigations, it's always best to have as many different sources of data to draw conclusions from. You definitely seem very well-schooled concerning the F4U so I was just casually asking if you could produce more than what we normally find on the Williams/Stirling website. It was never meant to dismiss what has already been discussed in this rather lively thread.



Dawncaster said:


> It was official performance cleard with operation restrictions for standard configuration, from *actual *flight test. If it was not the actual performance, it was specified in the ACP and It also specifies whether it was a production model or prototype.



I understand this. The only difference is that inspection trial test reports tell us so much more concerning the aircraft under test. The ACP was a handy performance document to be used operationally, so they lack a lot of the detailed testing parameters which one can find in the inspection trials. 

So basically your theory is that the performance figures for the F4U-1D's were taken while utilizing auto-rich settings, as this is a way to explain why the two ACPs in question show the same Vmax for a 'clean' F4U-1 while using the two different propeller types. Sorry, but I don't agree with this line of logic because by the time the latter ACP was printed (1 August 1945) auto-lean was the accepted mixture setting (pilot manuals confirm this) and one would expect testing to be performed in order to show operational considerations.

I was only suggesting that _maybe_ the performance data shown in ACP dated 1 March 1944 was for an airplane which was fitted with the 13' 1" propeller, even though the document listed the production propeller instead. You insisted earlier that it was extremely common for this propeller to be fitted to Corsairs by this time so that's why I put forth my own theory but you roundly dismissed it and that's ok. We'll most likely not solve this question in the immediate future without new data coming to light. Until then, I will accept that the "official" maximum speed of the F4U-1D is 417 mph, because both Chance-Vought and the US Navy say it is so. 

We both can agree however that a dedicated land-based F4U-1D would be faster than the carrier version but by how much is still in debate. Could it be the 8 mph difference seen when comparing official and non-official figures (417 mph vs 425 mph)? I don't know but it could be one possibility for the disparity.

So even with these questions we can still say with a fair degree of certainty that the F4U was faster than the F6F at all altitudes, as long as power settings and configurations were similar. The amount of the speed differential however has yet to be fully determined.

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## Dawncaster (Apr 7, 2020)

DarrenW said:


> Hi Dawncaster,
> 
> Very nice parade of data, I appreciate all the hard work you went through to provide it. I gave you some more bacon...
> 
> ...



Well, the previous post was 'dropped' as I said. I cut the quote to the limit, but couldn't include more contents, you'll find out it if you try to write a new article quoting the whole my post. and I tried to write a new article with the remainder, but canceled due to I have no power for it. A post that only has the word "deleted" is a trace for it. due to the lack of energy, this post has a lot of recycled parts....





Firstly, I really don't seem to be good at explaining, as you said, Mixture was a hypothesis to explain the actual power losses, but the important thing about it is that there has actually been a loss in power. I think it's because of the difference in operation restrictions.





This is part of the report for F4U-1 BuNo.50030, the report states that performance has been reduced to standard conditions in accordance with standard flight test methods. In the report of F4U-1 BuNo.17930, no similar content can be found and I speculated that 'standard' Flight Test Methods was the main factor that made a difference in performance. I think it is the same as operation restriction.

Perhaps the operation restrictions in early 1944, when the F4U-1 ACP and F4U-1 BuNo.17930 were tested, was lax compared to 1945 when F4U-1 BuNo.50030 or F4U-1D were tested. and seems that It's more accurate and practical operation restrictions were founded over time as operating hours increased and more data obtained.

For propeller blade design and suggestion about it, my lack of explanation seems to have caused the problem again. I wrote 'new 6501A-0 propeller blade start service with VF-17 in solomon campaign and many F4U-1s have replaced propellers with this new type', but I didn't mean it was extremely common. for example, If the limited to F4U-1 of VF-17, it could be said to be common. but if expand the target to the entire F4U-1s in operation, there were far more old 13'4" propeller than the new 13'1" propeller. to be exact, many F4U-1s have been replaced with new propellers, but not much compared to the whole. I just wanted to say it started service early and was not unique. well.. I doubt that I expressed it correctly this time. In conclusion, considering the characteristics of the ACP mentioned in the last post, It's highly unlikely to be the performance of the 13'1" propeller for me.









Also, it should not be overlooked that there is actually another 'standard' sample with a 13'1" propeller, F4U-1 BuNo.17930. cross-validation with ACP and F4U-1 BuNo.17930 well shows both the matching and difference of performance that should be between the 13'1" propeller and the 13'4" propeller under the same 'standard' drag condition(showed the characteristic of a 13'4" propeller losing efficiency in a high-altitude, high-speed range above 16.5k ft, while at the same time the two F4U-1s show matching performance at same drag conditions below 16.5k ft.). It seems allows to infer that the performance of the ACP was that of a 13'4 "propeller.


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## DarrenW (Apr 7, 2020)

Don't you just love talking Corsairs and Hellcats? It's probably one of my favorite past times, and I thank Zipper very much for creating this very interesting thread....

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## DarrenW (Apr 7, 2020)

Dawncaster said:


> For propeller blade design and suggestion about it, my lack of explanation seems to have caused the problem again. I wrote 'new 6501A-0 propeller blade start service with VF-17 in solomon campaign and many F4U-1s have replaced propellers with this new type', but I didn't mean it was extremely common. for example, If the limited to F4U-1 of VF-17, it could be said to be common. but if expand the target to the entire F4U-1s in operation, there were far more old 13'4" propeller than the new 13'1" propeller. to be exact, many F4U-1s have been replaced with new propellers, but not much compared to the whole. I just wanted to say it started service early and was not unique. well.. I doubt that I expressed it correctly this time. In conclusion, considering the characteristics of the ACP mentioned in the last post, It's highly unlikely to be the performance of the 13'1" propeller.



That's ok because it's very hard sometime to convey exactly what you mean in such a way that all will understand exactly as it was intended. I have done that a few times here as well.

So maybe the extra performance achieved when using the more efficient propeller wasn't that spectacular after all? If the increase was only a few miles per hour at best it might still be beneficial to some extent but not a true game changer. That could be another explanation for the similar speeds with different propellers.

And I do trust quite a bit about what you had to say here and I learned a lot, because you are a "Corsair guy" while my area of study is the Hellcat.

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## Zipper730 (Apr 7, 2020)

Dawncaster said:


> Please understand that there are many omissions to meet the 20k character limit


Yeah, I've run into that at times.


> I think there seems no 'special tail wheel faring' for F4U-1 BuNo.17930


Basically, I was kind of referring to the modification of the rear that sort of blended the taller tailwheel into a tear-drop when retracted.

This image you posted earlier, but I'll use it for an example...







While this may/may not sound ignorant: I'm curious why they went to the whole trouble of redesigning the whole tailwheel? Was this related to visibility?


> Removing the folding mechanism and tail hook, after halves of the doors were bolted closed and the cove for the tail hook was skinned over. the aircraft was to average an increased top speed of 4 mph . . . . Land-based configuration gives additional 4 mph *actually *for Corsair, there was no additional 6(or 8) mph.


What caused there to be such discrepancies between the drag-coefficient chart and the itemized chart that displayed methods to increase speed?

Looking at this image...






Was it possible to fair over any of these plates for an operational aircraft? As for the fairing over the wing-fold line, was this done on land-based aircraft?


> In my view, for estimated +8 mph, smooth and faired cowling would have had a substantial impact.


Wait, they could have made improvements to the engine cowling?


> I think Zipper 730's calculation is a good indication of why the early F4U-1's old 13'4" prop was losing efficiency at high altitude high speed range


Actually, even with the 13'1" blade -- it's still supersonic at the tips. It's just not quite as extreme 1.0699 vs 1.0791 within 200 feet of each other in altitude. That said, with the F6F's propeller you're going 6 miles an hour faster at the same altitude.











> In conclusion, the F4U-1 BuNo.17930's 431 mph seems the best performance actually achievable with standard drag condition for standard production F4U-1 with 13'1" prop as Navy stated, even assuming the worst, can subtract up to 6.4 mph.


That would put you about 0.6 mph of 425 mph.


> F6F-5 BuNo.58310 graph, the auto-lean curve showed faster than the auto rich at altitude, the vmax was about 8 mph faster, and the critical altitude increased about 400 ft


Critical altitude goes up because you have a lower fuel/air ratio, and it's closer to the stoichiometric ratio for gasoline combustion.


> http://www.wwiiaircraftperformance.org/f4u/f4u-1-02334.pdf
> 
> In the F4U-1 BuNo.02334's report, standard F4U-1 expected 404 mph @ 25300' for military power and ACP showed 407 mph @ 24800' actually obtained for military power. this is a fairly close result and seems resonable for Navy's estimate.


If I read this right, the test involved a 13'0" propeller instead of the F4U-1's 13'4", or the F6F-3's 13'1" design. The gear ratio was also 0.4 instead of 0.5. So the ability to estimate performance to within 500 feet was pretty decent at the time?

To be honest, looking at this image: This seems to fit the F4U-1A/C/D's arrangement pretty good. I would have thought the bubble would have slowed the plane down a bit, not sped it up by 2 mph.


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## Zipper730 (Apr 8, 2020)

DarrenW said:


> Testing was performed on both engines using different sized water jets and carburetor impact pressure settings with very good results being obtained (up to 65" Hg was deemed safe while using 130 octane fuel). . . . They used larger water jets and made adjustments to the supercharger fuel and water regulators which allowed for a higher flow rate to occur (hence more impact pressure), and this allowed for higher manifold pressures to be developed safely without detonation which in turn produced more power.


So this has to do with pressure carburetor set-up the ratio between impact and venturi pressures, or something of that sort?


> Don't you just love talking Corsairs and Hellcats? It's probably one of my favorite past times, and I thank Zipper very much for creating this very interesting thread....


No problem, Darren


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## DarrenW (Apr 8, 2020)

Zipper730 said:


> So this has to do with pressure carburetor set-up the ratio between impact and venturi pressures, or something of that sort?



I'm sorry, I really don't know much more about the water injection system than can be gleaned from pilot's manuals and test reports. I'm sure there is someone here that can help you with your questions better than I can. I actually would like to learn more about how the system works as well.....


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## Dawncaster (Apr 8, 2020)

Zipper730 said:


> Basically, I was kind of referring to the modification of the rear that sort of blended the taller tailwheel into a tear-drop when retracted.
> 
> This image you posted earlier, but I'll use it for an example...
> 
> View attachment 576522


Good point.

In fact, I also considered that possibility, but the It should be visible at the ground, was not found in the included photo for F4U-1 BuNo.17930 report and others.






And I actually found a 'block' in the attached F4U-1 BuNo.17930's photo. I guessed with it the block mentioned in the report because the block was not found on the high tail wheel of the F4U-1s in service.










*



*
But it is possible that you are correct, as I wrote above, I also have made the same guess as you.





Because I have a photograph of it installed on F4U-1 BuNo.17930

In this case, I miscalculated what was called 'block' and the specificity of F4U-1 BuNo.17930 is further reduced.

When I saw the old guess again from you, I began to get confused again and began to feel as if my old guess was right. I mean, I think your guess is right.

I realized again that I knew too little about this beautiful aircraft. 



Zipper730 said:


> While this may/may not sound ignorant: I'm curious why they went to the whole trouble of redesigning the whole tailwheel? Was this related to visibility?



If the performance was most considered, the smooth surface of the first batch F4U-1's tiny tailwheel unit and the slotless tailwheel door, would have been the best. It seems to me that continued improvements to the tailwheel section are related to improved landing capabilities. As noted in the old post, it affected performance but was slight, on the other hand, landing capabilities would have come as a greater issue for the F4U-1, which targets carrier operations.



Zipper730 said:


> What caused there to be such discrepancies between the drag-coefficient chart and the itemized chart that displayed methods to increase speed?



Charts from the Navy and NACA reports appear to be based on lift cofficient for level flight(about 0.2). But the other appears to have been zero lift drag coefficient chart. so instead of applying it as it is when I use it, I only made a relative comparison based on the data actually obtained from flight and calculation. In addition, NACA's drag coefficients were averaged figures, and even with similar commented drag reduction, there may be slight differences in actual work for drag reduction to F4U-1.



Zipper730 said:


> Looking at this image...
> 
> 
> 
> ...



According to Dana Bell, the wing fold seams were taped, puttied, and smoothed. As the attached photo shows, Some Corsairs even carried a "Wings Won't Fold" warning.








Zipper730 said:


> Wait, they could have made improvements to the engine cowling?


They did, with F4U-4 and other post war variants. but that's not what you're trying to say.





Air leakage creates drag, so if faired it and make smooth surface, the drag coefficient will decrease.

The above picture is F6F-3's cowling with a total of 6 cowling flaps, 3 on each side. for drag reduction, faired cowling-flaps and hinge line-gap-leakage gives 3 mph.

Assuming that the F4U-1 BuNo.02390 had 18 cowl flaps because there was no mention in the report that the fixed upper plate was installed, because there was more air leakage, it can be expected that making a smooth surface by fairing it is more likely to achieve more performance.



Zipper730 said:


> Actually, even with the 13'1" blade -- it's still supersonic at the tips. It's just not quite as extreme 1.0699 vs 1.0791 within 200 feet of each other in altitude. That said, with the F6F's propeller you're going 6 miles an hour faster at the same altitude.
> View attachment 576539
> 
> View attachment 576540


Then perhaps a major change in design has affected it than tip speed. The old 13"4' propeller was called the narrow chord prop and the new 13"1' was called the paddle blade prop.

And I have a few points to make. The performance of the first batch birdcage F4U-1 with 395 mph Vmax and 348 mph at S.L, which you labeled 1944/7/28, was actually measured in 1943/1/28 and F4U-1D's detail specification was company estimated figures. too many differences and variables exist between the two samples - between actual first batch birdcage F4U-1 and company estimated F4U-1D. In order to know the performance achieved by the new propeller, except for the propeller, the same power, same airframe and same drag condition will be required.

I think I've already introduced samples that are 'standard' to compare the 13'4" propeller with the 13'1" propeller. F4U-1 ACP and F4U-1 BuNo.17930 with 'standard' drag conditions by the Navy and measured performance in similar period(1944/3/1 for ACP and 1944/3/4~1944/3/8 for F4U-1 BuNo.17930).







Cross-validation with ACP and F4U-1 BuNo.17930 well shows both the matching and difference of performance that should be between the 13'1" propeller and the 13'4" propeller under the same drag condition. It showed the characteristic of a 13'4" propeller losing efficiency in a high-altitude high-speed range above 16.5k ft, while at the same time the two F4U-1s show well matching performance(or showed a convincing similarity) at same drag conditions below 16.5k ft. according to this, If make a comparison at same altitude for military power as you did, the 13'1" propeller was abuot 8 mph faster at 25,000 feet.

In conclusion, the Navy succeeded in correct the F4U-1 BuNo.17930 to 'standard' drag condition for production F4U-1(F4U-1 ACP), and as a result of installing a new propeller, it seemed able to clearly identify the performance that could be achieved compared to the old propeller. I recommend using these for calculation because it's Navy corrected samples to military standard that well showed the performance difference caused by the replacement of the propeller for F4U-1 at same and standard condition.



Zipper730 said:


> If I read this right, the test involved a 13'0" propeller instead of the F4U-1's 13'4", or the F6F-3's 13'1" design. The gear ratio was also 0.4 instead of 0.5. So the ability to estimate performance to within 500 feet was pretty decent at the time?



F4U-1 BuNo.02334's four-bladed propeller would be closer to F4U-4's because it was also four-bladed propeller with 0.45 gear ratio. and the propeller's diameter seems affected not only by the propeller blade design, but also by other units. for example F4U-4's propeller diameter was 13'2" with 6501A-0 blades but F4U-1's propeller diameter was 13'1" with same 6501A-0 blades. And the report described F4U-1 BuNo.02334 that the new propeller(6501A-0) was installed 'instead' of the old propeller(6443A-21), the 'standard' F4U-1 mentioned in the report would have had an old propeller(6443A-21).

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## DarrenW (Apr 8, 2020)

Dawncaster said:


> In conclusion, the Navy succeeded in correct the F4U-1 BuNo.17930 to 'standard' drag condition for production F4U-1(F4U-1 ACP), and as a result of installing a new propeller, it seemed able to clearly identify the performance that could be achieved compared to the old propeller. I recommend using these for calculation because it's Navy corrected samples to military standard that well showed the performance difference caused by the replacement of the propeller for F4U-1 at same and standard condition.



Hi Dawncaster,

I took one last look at what you had to say concerning rich vs. lean mixtures and the subsequent horsepower/speed produced and noticed that there was a 25 hp/9 mph difference between BuNo. 17930 & 50030 at 20,000 feet. They both had the more efficient F6F-3 propeller, taped shell ejector openings, and weighed exactly the same at 12,162 lbs. The only drag component that was different between the two was that BuNo. 50030 had tail and (quite possibly) catapult hooks installed:

*F4U-1 BuNo. 17930*




http://www.wwiiaircraftperformance.org/f4u/f4u-1-17930.pdf

*F4U-1 BuNo. 50030*







http://www.wwiiaircraftperformance.org/f4u/f4u-1-50030-final.pdf 

After realizing that F6F-5 BuNo. 58310 was 8 mph faster while using a lean mixture rather than rich, I was curious what the horsepower difference was between the two settings as well, which turned out to be roughly 70 hp (1660 hp vs. 1590 hp). Being that the horsepower difference between the two F4U-1s was only 25 hp, I'm puzzled as to why a seemingly large 9 mph speed difference exists between them? Of course a portion of it can be attributed to the extra drag of the tail and catapult hooks, but according to your calculations this is at most only 3 mph. Do you believe 25 hp is enough to produce the extra 6 mph? 

I'm not really sure myself, I'm just intrigued by the topic and want to exhaust all avenues before moving on to things less mentally exhausting..... 

P.S. If we subtract the 2.4 mph for open shell ejector openings in the wings of BuNo. 50030 we get a maximum speed of 418.6 or about 419 mph. This seems very close to what is quoted in both the ACP and the Chance-Vought document concerning the F4U-1D.


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## Dawncaster (Apr 8, 2020)

DarrenW said:


> Hi Dawncaster,
> 
> I took one last look at what you had to say concerning rich vs. lean mixtures and the subsequent horsepower/speed produced and noticed that there was a 25 hp/9 mph difference between BuNo. 17930 & 50030 at 20,000 feet. They both had the more efficient F6F-3 propeller, taped shell ejector openings, and weighed exactly the same at 12,162 lbs. The only drag component that was different between the two was that BuNo. 50030 had tail and (quite possibly) catapult hooks installed:
> 
> ...



First of all, the paragraphs you quoted are for F4U-1 ACP and F4U-1 BuNo.17930, remember what I wrote in the paragraphs above it.

_'I think I've already introduced samples that are 'standard' to compare the 13'4" propeller with the 13'1" propeller. F4U-1 ACP and F4U-1 BuNo.17930 with 'standard' drag conditions by the Navy and measured performance in similar period(1944/3/1 for ACP and 1944/3/4~1944/3/8 for F4U-1 BuNo.17930).'_










_'Cross-validation with ACP and F4U-1 BuNo.17930 well shows both the matching and difference of performance that should be between the 13'1" propeller and the 13'4" propeller under the same drag condition. It showed the characteristic of a 13'4" propeller losing efficiency in a high-altitude high-speed range above 16.5k ft, while at the same time the two F4U-1s show well matching performance(or showed a convincing similarity) at same drag conditions below 16.5k ft. according to this, If make a comparison at same altitude for military power as you did, the 13'1" propeller was abuot 8 mph faster at 25,000 feet.'_

_'In conclusion, the Navy succeeded in correct the F4U-1 BuNo.17930 to 'standard' drag condition for production F4U-1(F4U-1 ACP), and as a result of installing a new propeller, it seemed able to clearly identify the performance that could be achieved compared to the old propeller. I recommend using these for calculation because it's Navy corrected samples to military standard that well showed the performance difference caused by the replacement of the propeller for F4U-1 at same and standard condition.'_

There seems to have been a lack of explanation for mentioning the 'similar period' and 'standard'.

F4U-1 ACP : 1944/3/1
F4U-1 BuNo.17930 : 1944/3/4 and 1944/3/8

Look at the date attached to their performances. the 'period' in which their performance was measured is virtually the same, In other words, the 'standard' for this period seems also virtually same for both F4U-1s. however, there was a gap with F4U-1 BuNo.50030 and I had already mentioned it in the my old post.







_'Firstly, I really don't seem to be good at explaining, as you said, Mixture was a hypothesis to explain the actual power losses, but the important thing about it is that there has actually been a loss in power. I think it's because of the difference in operation restrictions.'_







_'This is part of the report for F4U-1 BuNo.50030, the report states that performance has been reduced to standard conditions in accordance with standard flight test methods. In the report of F4U-1 BuNo.17930, no similar content can be found and I speculated that 'standard' Flight Test Methods was the main factor that made a difference in performance. I think it is the same as operation restriction.'_

_'Perhaps the operation restrictions in early 1944, when the F4U-1 ACP and F4U-1 BuNo.17930 were tested, was lax compared to 1945 when F4U-1 BuNo.50030 or F4U-1D were tested. and seems that It's more accurate and practical operation restrictions were founded over time as operating hours increased and more data obtained.'_

Of course, the 'reduced' performance would not have been as good as the first obtained. the mixture setting was just one of the hypotheses for explaining the actual power loss. because of the different period, there seems to be too many variables under different standard. In fact, F4U-1 BuNo.50030's report was referred the F4U-1 BuNo.17930's report PTR 2105. so under the Standard Flight Test Method at that time, the 'reduced' performance of the F4U-1 BuNo.17930 was may have been similar to F4U-1 BuNo.50030's and may not have been so special as to stated it.

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## DarrenW (Apr 8, 2020)

Dawncaster said:


> First of all, the paragraphs you quoted are for F4U-1 ACP and F4U-1 BuNo.17930, remember what I wrote in the paragraphs above it.
> 
> _'I think I've already introduced samples that are 'standard' to compare the 13'4" propeller with the 13'1" propeller. F4U-1 ACP and F4U-1 BuNo.17930 with 'standard' drag conditions by the Navy and measured performance in similar period(1944/3/1 for ACP and 1944/3/4~1944/3/8 for F4U-1 BuNo.17930).'_
> 
> ...



I remember reading all of this before but I believe that I finally understand what you were getting at. If F4U-1 BuNo. 17930 were tested in 1945 it wouldn't have reached a maximum speed of 431 mph, due to different operational guidelines which changed the testing methods employed. It most likely would have had a performance very similar to BuNo. 50030 (maybe a few miles per hour faster because it was configured for land use only). Things such as safety were probably the driving force behind the operational restrictions that were implemented after knowledge was gained over time about the aircraft's performance limitations.

Of course this is the case as well for the performance data found in the ACP dated 1 March 1944. It would also be reduced by roughly the same amount as F4U-1 BuNo. 17930.

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## Dawncaster (Apr 9, 2020)

DarrenW said:


> I remember reading all of this before but I believe that I finally understand what you were getting at. If F4U-1 BuNo. 17930 were tested in 1945 it wouldn't have reached a maximum speed of 431 mph, due to different operational guidelines which changed the testing methods employed. It most likely would have had a performance very similar to BuNo. 50030 (maybe a few miles per hour faster because it was configured for land use only). Things such as safety were probably the driving force behind the operational restrictions that were implemented after knowledge was gained over time about the aircraft's performance limitations.
> 
> Of course this is the case as well for the performance data found in the ACP dated 1 March 1944. It would also be reduced by roughly the same amount as F4U-1 BuNo. 17930.



I'm glad you understood my posts correctly, my hypotheses were to guess how it was done. my lack of explanation seems to have troubled you.

and That's why I've always considered Hellcat's actually achievable maximum speed to be over 400 mph(about 410 mph). for example, according to AHT,

' Jan. 44, A modified F6F-3, including some of the features to be included in the later F6F-5 version, is flown at a speed of 410 mph at 21000 feet altitude. '

In my view, this is similar to the case in F4U-1 BuNo.17930, It was conducted in early 1944, and improvements for late production model were applied to test plane. what's regrettable is that I don't have a detailed report on it.

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## Zipper730 (Apr 9, 2020)

Dawncaster said:


> In fact, I also considered that possibility, but the It should be visible at the ground, was not found in the included photo for F4U-1 BuNo.17930 report and others.


Just look at the image again... move your finger about an inch to the right the front part of the tear-drop blending is right there, it looks like it's under the wing, but it isn't -- it's under the tail, in front of the wheel...


> If the performance was most considered, the smooth surface of the first batch F4U-1's tiny tailwheel unit and the slotless tailwheel door, would have been the best. It seems to me that continued improvements to the tailwheel section are related to improved landing capabilities. As noted in the old post, it affected performance but was slight, on the other hand, landing capabilities would have come as a greater issue for the F4U-1, which targets carrier operations.


Would it affect bounce or approach angle, based on attitude or visibility?


> Charts from the Navy and NACA reports appear to be based on lift cofficient for level flight(about 0.2). But the other appears to have been zero lift drag coefficient chart. so instead of applying it as it is when I use it, I only made a relative comparison based on the data actually obtained from flight and calculation. In addition, NACA's drag coefficients were averaged figures, and even with similar commented drag reduction, there may be slight differences in actual work for drag reduction to F4U-1.


So the reason has to do with the fact that the coefficients are under different conditions? You calculated by the effect on the actual plane in flight.


> According to Dana Bell, the wing fold seams were taped, puttied, and smoothed.


This would have only been on land-based aircraft, correct? Having wings that won't fold seem useless for carrier ops...


> They did, with F4U-4 and other post war variants. but that's not what you're trying to say.


From what I remember, I was under the impression that a redesign to the cowling would have got more performance than the various other proposals for the F4U-1


> Then perhaps a major change in design has affected it than tip speed. The old 13"4' propeller was called the narrow chord prop and the new 13"1' was called the paddle blade prop.


It would have a greater surface area per blade, which would move more air; additionally, you may/may not see a thickness/chord ratio that might be lower, which would favor high speed performance. The cross section of the blades might also differ in the two designs.

As for the dates made for performance, I'm not sure where I got the July 28 date from. Looking at the data I derived everything from, it seemed to be from October 31, 1944. The aircraft number matches up too. As for the performance of the F4U-1D figures being based on company estimates, that could be dubious.


> I think I've already introduced samples that are 'standard' to compare the 13'4" propeller with the 13'1" propeller. F4U-1 ACP and F4U-1 BuNo.17930 with 'standard' drag conditions by the Navy and measured performance in similar period(1944/3/1 for ACP and 1944/3/4~1944/3/8 for F4U-1 BuNo.17930).


Much of the performance is the same at lower altitudes, with more at higher altitudes using the same manifold pressure settings, so it seems the propeller did the bulk of the work. I'm not sure if fairing over the top cowl-flap had any effect on speed.


> F4U-1 BuNo.02334's four-bladed propeller would be closer to F4U-4's because it was also four-bladed propeller with 0.45 gear ratio. and the propeller's diameter seems affected not only by the propeller blade design, but also by other units. for example F4U-4's propeller diameter was 13'2" with 6501A-0 blades but F4U-1's propeller diameter was 13'1" with same 6501A-0 blades. And the report described F4U-1 BuNo.02334 that the new propeller(6501A-0) was installed 'instead' of the old propeller(6443A-21), the 'standard' F4U-1 mentioned in the report would have had an old propeller(6443A-21).


From what I recall, the F4U-1 had a gear-ratio of 0.5 not 0.45. That would improve the tip-speeds of the blades. That said, I was under the impression that the F4U-4 used a different blade design.

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## DarrenW (Apr 9, 2020)

Dawncaster said:


> and That's why I've always considered Hellcat's actually achievable maximum speed to be over 400 mph(about 410 mph). for example, according to AHT,
> 
> ' Jan. 44, A modified F6F-3, including some of the features to be included in the later F6F-5 version, is flown at a speed of 410 mph at 21000 feet altitude. '
> 
> In my view, this is similar to the case in F4U-1 BuNo.17930, It was conducted in early 1944, and improvements for late production model were applied to test plane. what's regrettable is that I don't have a detailed report on it.



I have read that about the F6F-3 too and that's a very good comparison. It would fall in line with the average speed advantage the Corsair held over the Hellcat throughout much of the war. I will have to be more careful in the future concerning test report dates and possible changes to the methods employed during testing. Thanks for bringing all of this to light.....

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## DarrenW (Apr 9, 2020)

Zipper730 said:


> As for the performance of the F4U-1D figures being based on company estimates, that could be dubious.



Yes that can be an issue sometimes, but thankfully Vought acknowledges a maximum speed that is pretty much identical to what we see in the ACP for the F4U-1D.


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## DarrenW (Apr 9, 2020)

Although the 13' 1" propeller became the preferred option, the original 13' 4" variety was still an acceptable substitute. This tells me that it's performance was considered reasonable and enough for the job at hand. This was probably because a large portion of the fighting in the PTO took place at low and medium altitudes, so there wouldn't be a lot to choose from between the two types anyway in a practical sense. 

AN 01-45HA-1 (1 June 1944)






AN 01-45HA-1 (15 March 1945)

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## DarrenW (Apr 9, 2020)

Zipper730 said:


> I'm not sure if fairing over the top cowl-flap had any effect on speed.



Not challenging you on this, but how did you draw this conclusion?


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## Dawncaster (Apr 9, 2020)

Zipper730 said:


> Just look at the image again... move your finger about an inch to the right the front part of the tear-drop blending is right there, it looks like it's under the wing, but it isn't -- it's under the tail, in front of the wheel...
> design.


I'm sorry, but could you explain it with photo?



Zipper730 said:


> Would it affect bounce or approach angle, based on attitude or visibility?


It would have affected at ground runs, not only AOA and visibility but also take-off distance and take-off speed.





And the bounce problems have been solved by improvements in oleo.



Zipper730 said:


> So the reason has to do with the fact that the coefficients are under different conditions? You calculated by the effect on the actual plane in flight.


It remains unchanged because it's figure actually obtained from flight tests. I was talking about the zero lift drag coeiffcient chart used to make relative comparisons in the process because I had to divide it up for explanation. It had different lift condition compared to the drag coefficients of NACA charts based on level-flight.



Zipper730 said:


> This would have only been on land-based aircraft, correct? Having wings that won't fold seem useless for carrier ops...


I'm pretty sure. because it can take off from carriers barly, but cannot land.



Zipper730 said:


> From what I remember, I was under the impression that a redesign to the cowling would have got more performance than the various other proposals for the F4U-1


However, the cowling of the F4U-1 was not redesigned during the service....



Zipper730 said:


> As for the dates made for performance, I'm not sure where I got the July 28 date from. Looking at the data I derived everything from, it seemed to be from October 31, 1944. The aircraft number matches up too.







Performance curve what I mentioned was this.



Zipper730 said:


> I'm not sure if fairing over the top cowl-flap had any effect on speed.


Even if it's only few of the total cowl flaps, I guess it would slight affect to performance because it provides more air leakage. although it's expected to almost flushed at Vmax due to the overload relief system.

But for comparison, I think you don't have to so consider the speed difference caused by it. as the actual obtained results showed, the Navy had correct the drag condition to standard.

In fact, It was a improvement to get rid of oil leakage, not air leakage. after installed it, pilots won't have to learn to look for rain clouds to give their windscreens a quick wash.



Zipper730 said:


> From what I recall, the F4U-1 had a gear-ratio of 0.5 not 0.45. That would improve the tip-speeds of the blades. That said, I was under the impression that the F4U-4 used a different blade design.


F4U-1 BuNo.02334 had 0.4 gear ratio four blade 13'0" dia propeller with blade design 6501A-0, compared to standard 0.5 gear ratio three blade 13'4" dia propller with blade design 6443A-21, I felt it was more similar to F4U-4.

*



*

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## Dawncaster (Apr 9, 2020)

DarrenW said:


> I have read that about the F6F-3 too and that's a very good comparison. It would fall in line with the average speed advantage the Corsair held over the Hellcat throughout much of the war. I will have to be more careful in the future concerning test report dates and possible changes to the methods employed during testing. Thanks for bringing all of this to light.....



You're welcome. I also want to thank you. despite the lack of explanation following the flow of my esoteric consciousness, pointed out what I was trying to say.

We share the experiences of two great fighters suffering from biases. 



DarrenW said:


> Although the 13' 1" propeller became the preferred option, the original 13' 4" variety was still an acceptable substitute. This tells me that it's performance was considered reasonable and enough for the job at hand. This was probably because a large portion of the fighting in the PTO took place at low and medium altitudes, so there wouldn't be a lot to choose from between the two types anyway in a practical sense.
> 
> AN 01-45HA-1 (1 June 1944)
> View attachment 576747
> ...



Good point, Agreed. It is convincing considering the situation that from the end of the Rabaul campaign to the arrival of the F4U-1D, the F4U-1 was mostly used for ground attacks.

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## DarrenW (Apr 9, 2020)

Dawncaster said:


> We share the experiences of two great fighters suffering from biases.



Yes, but luckily we're both here to help set the record straight....

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## Dawncaster (Apr 9, 2020)

DarrenW said:


> Yes, but luckily we're both here to help set the record straight....


OH No, I forgot to put 'can' between 'We' and 'share'.


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## DarrenW (Apr 9, 2020)

Dawncaster said:


> OH No, I forgot to put 'can' between 'We' and 'share'.



I understood exactly what you meant....

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## Zipper730 (Apr 10, 2020)

DarrenW said:


> I'm sorry, I really don't know much more about the water injection system than can be gleaned from pilot's manuals and test reports. I'm sure there is someone here that can help you with your questions better than I can. I actually would like to learn more about how the system works as well.....


Off the bat, I figure 
S
 Shortround6
and 
W
 wuzak
might be able to better explain the matter -- wuzak might be the forum's authority on engines.


> Not challenging you on this, but how did you draw this conclusion?


It had to do with the basics of cowl design (and there might be errors here, so bear with me -- I'm used to being the village idiot when it comes to propeller driven aircraft).

Propeller: Since almost all aircraft were tractor props, the propeller would be in front of the cowling. The propeller accelerates the airflow and increases the pressure of the flow.
Cowl-Lip: The cowl is divergent in shape, which slows down the airflow going through the cowling: This effectively provides more pressure and more air in a given area to absorb the heat from the engine. Provided the velocity is slowed down and builds up pressure, yet remains fast enough to carry away the heat, you have a design that seems workable. While increasing pressure does produce heat, it's not particularly massive (this becomes more significant when supersonic), and the air outside is very cold, and the air temperature isn't that high.
Air-Cooled Engine: Air flows from the cowl-lip to the engine, and is heated up substantially by the engine. This causes the air to absorb the heat, and bringing down the engine temperature. It also causes the air to heat up, and expand. Provided the expansion goes more rearwards than forwards, you have a degree of "thrust" that is produced (unfortunately, it almost never equals the amount of drag, but it will negate some of the drag produced by the assembly).
Aft Cowl / Cowl-Flaps: I'm not sure the exact term but it's basically the shape of the cowl/fuselage behind the engine, which form a convergent shape. Theoretically you want to make the shape quite convergent as it accelerates the airflow the most, but pressure plays a role in imposing limits on this. The pressure gets too low, and you'll see the air dam up, so you'll have cowl-flaps to allow extra area for the air to escape. This arrangement reminds me a bit of the nozzles on jet-fighters, which are fully open at idle to allow the airflow plenty of area to escape; as the engine spools up, the exhaust pressure goes up, and the nozzle can be narrowed down, and produce a faster exhaust velocity. When 100% power is produced, the nozzles are narrowed in as much as possible. This set-up seems the same on cowling flaps.
Some aircraft have tighter cowlings than other aircraft, being barely big enough to encompass the engine they're built around; a more prominent bell-mouthed shape, a fatter spinner, and a narrower aft-cowling, and so on. These are generally aimed at reducing cooling drag, though they have a tendency to reduce cooling. I figure, if the top-cowling flap was faired over by a metal-plate, then the airflow would have to escape out the other flaps, or the cowling would simply be "tighter" in the back.



Dawncaster said:


> I'm sorry, but could you explain it with photo?


Sure...






I encircled the area in a brighter shade of red than the area you encircled, and connected them together. The front area is the front of the tear-drop.


> It would have affected at ground runs, not only AOA and visibility but also take-off distance and take-off speed.


The higher tail-wheel seems to increase takeoff run in either carrier deck operations, and also raises takeoff speed. The only benefit I can see is visibility.


> And the bounce problems have been solved by improvements in oleo.


So, the tail wheel had no effect on this matter?


> I'm pretty sure. because it can take off from carriers barly, but cannot land.


Makes sense


> However, the cowling of the F4U-1 was not redesigned during the service....


The cowling configuration question was a hypothetical...


> Performance curve what I mentioned was this.


I didn't even notice that... that's normally something I would immediately spot.


> Even if it's only few of the total cowl flaps, I guess it would slight affect to performance because it provides more air leakage. although it's expected to almost flushed at Vmax due to the overload relief system.


I would figure the top cowl-flap being covered over would reduce air-leakage, since the flap is closed? Also, what's the overload relief system?


> In fact, It was a improvement to get rid of oil leakage


That, I already know. And I'd agree with it on that.

As for your graph on the F4U-4, I was under the impression that, up to this point, that the propeller was 13'4" instead of 13'2". You learn something new everyday. As for the gear ratio being reduced from 0.5 to 0.45, is definitely smart.






While the tip-speed is still quite high, it only goes supersonic at critical altitude in WEP and Military power settings, despite being considerably faster...

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## Graeme (Apr 10, 2020)

Zipper730 said:


> Sure...
> I encircled the area in a brighter shade of red than the area you encircled, and connected them together. The front area is the front of the tear-drop.



I'm pretty sure your "front of the tear-drop" circle is part of the wing. Imagine the wheel retracted - it's nowhere near the front of the wheel....


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## Dawncaster (Apr 10, 2020)

Zipper730 said:


> I encircled the area in a brighter shade of red than the area you encircled, and connected them together. The front area is the front of the tear-drop.


Ah, I didn't expect it to look that way.










It's flap linkage.



Zipper730 said:


> As for your graph on the F4U-4, I was under the impression that, up to this point, that the propeller was 13'4" instead of 13'2". You learn something new everyday. As for the gear ratio being reduced from 0.5 to 0.45, is definitely smart.
> 
> While the tip-speed is still quite high, it only goes supersonic at critical altitude in WEP and Military power settings, despite being considerably faster...


It's a cool calculation again.





Probably a similar case, for F4U-1 BuNo.50030, the recommended 2700 RPM appears to be rather disadvantageous in terms of Vmax.

Well, calculation seems to have used the detailed specification of F4U-4. Unless otherwise noted(as F4U-5's detail specification), the detail specification typically includes the estimated performance.






I recommend using the last edition of the official performance for Navy standard.

F4U-4's maximum performances


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## Zipper730 (Apr 10, 2020)

Dawncaster said:


> Ah, I didn't expect it to look that way. . . It's flap linkage.


I guess I was wrong then... 

I'd guess there are two important questions to ask

Did they ever put the "tear-drop" arrangement on an operational aircraft?
Do you have any pictures of such an aircraft from the side or aft quarter?



> It's a cool calculation again.


It's not a complicated math calculation (SQRT*((FPS)^2+(RPM/60)^2)))/Speed of Sound at Altitude, but it's nice to illustrate the tip-speed. It seems that the goal in such a large propeller was to drive up climb-rates (which is a low-speed domain on propeller aircraft) at low-speeds. Performance gets sacrificed at high speeds (particularly altitudes where the speed of sound is lower).

Looking at this, I would figure the first three figures were based on wartime-emergency power, with the remaining three on military-power.






I'm reminded of a pilot who found that at certain speeds, lowering the RPM on the governor actually gave him better performance. It's probably for the same reason as on this graph. I'm curious how often pilots in practice would run at 2600 in favor of 2700 at WEP settings at 18360 feet, and at 23480-23500', at 2500 in favor of 2700? It seems like it would have certainly provided more speed...


> Well, calculation seems to have used the detailed specification of F4U-4.


Oh well, I could run some numbers for based on actual flight test data.






BTW: What's the WEP figures for the R-2800-18W in WWII times? I'm seeing 2380 hp & 2450 hp, and I'm not sure if either are accurate.


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## Zipper730 (Apr 10, 2020)

BTW: I'm not sure who said this, but somebody said that there were early problems with the F4U-1 that, in addition to issues with the supercharger, there were flights were complete engine failure occurred about 29000 feet (well below the aircraft's service ceiling) due to malfunctions where sparks would jump the gap and burn out the distributor points.

Why did this happen?


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## Dawncaster (Apr 11, 2020)

Zipper730 said:


> I guess I was wrong then...
> 
> I'd guess there are two important questions to ask
> 
> ...







Yes, it was installed on the late F4U-1s. The picture I uploaded was also service aircraft. and it appears that half of the tail wheel doors have not been opened because it's land-based configuration. therefore, so it was easy to see the streamlined block on at ground.





But in practice it was divided and attached to the tail wheel door, so if the tail wheel door is entirely opened, a slight more care should be taken to find it.





In conclusion, because I couldn't find it in the photo attached to the report of F4U-1 BuNo.17930, so I had assumed that it was a structure like a dark block wrapped around a strut, and bias that it would have been a 'special modification' would have also had slight impact. but it was a 'standard modification' and the F4U-1 BuNo.17930's photo attached to the report appeared to have been shot earlier than the test.



Zipper730 said:


> It's not a complicated math calculation (SQRT*((FPS)^2+(RPM/60)^2)))/Speed of Sound at Altitude, but it's nice to illustrate the tip-speed. It seems that the goal in such a large propeller was to drive up climb-rates (which is a low-speed domain on propeller aircraft) at low-speeds. Performance gets sacrificed at high speeds (particularly altitudes where the speed of sound is lower).
> 
> Looking at this, I would figure the first three figures were based on wartime-emergency power, with the remaining three on military-power.
> 
> ...



Great, perhaps the below content of the manual is also about it.





What's interesting is that can find this in the F4U-1 manual, but not in the F4U-4 manual.



Zipper730 said:


> BTW: What's the WEP figures for the R-2800-18W in WWII times? I'm seeing 2380 hp & 2450 hp, and I'm not sure if either are accurate.



It's not clear. documents during World War II specify 2450 BHP of 60"hg and 2650 BHP of 70"hg. 2380 BHP was the figure specified by 1946 ACP.



Zipper730 said:


> BTW: I'm not sure who said this, but somebody said that there were early problems with the F4U-1 that, in addition to issues with the supercharger, there were flights were complete engine failure occurred about 29000 feet (well below the aircraft's service ceiling) due to malfunctions where sparks would jump the gap and burn out the distributor points.
> 
> Why did this happen?



It looks like the contents of a post I wrote a few pages ago.

According to Barrett Tillman, It was traced to faulty pressurization from the Pratt and Whitney supercharger, which sometimes aloowed the spark to "jump the gap" and burn out the distributor points.

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## Zipper730 (Apr 11, 2020)

Dawncaster said:


> Yes, it was installed on the late F4U-1s.


That's pretty cool.


> Great, perhaps the below content of the manual is also about it.


That seems to cover it, though normal rated power usually involves a lower manifold pressure, which is easier to achieve, even at higher altitudes.

The fact that it's not included in the F4U-4 might just be that it performs well enough to not really require the need for fine-tuning the RPM.


> It's not clear. documents during World War II specify 2450 BHP of 60"hg and 2650 BHP of 70"hg. 2380 BHP was the figure specified by 1946 ACP.


So 2450 @ 60" and 2650 @ 70".


> It looks like the contents of a post I wrote a few pages ago.
> 
> According to Barrett Tillman, It was traced to faulty pressurization from the Pratt and Whitney supercharger, which sometimes aloowed the spark to "jump the gap" and burn out the distributor points.


Does this have to do with the air having an insulating effect against electricity? I remember another member talking about this on high altitude designs because with less air, it makes it easier for electrical currents to jump.


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## DarrenW (Apr 11, 2020)

Zipper730 said:


> It had to do with the basics of cowl design (and there might be errors here, so bear with me -- I'm used to being the village idiot when it comes to propeller driven aircraft).
> 
> Propeller: Since almost all aircraft were tractor props, the propeller would be in front of the cowling. The propeller accelerates the airflow and increases the pressure of the flow.
> Cowl-Lip: The cowl is divergent in shape, which slows down the airflow going through the cowling: This effectively provides more pressure and more air in a given area to absorb the heat from the engine. Provided the velocity is slowed down and builds up pressure, yet remains fast enough to carry away the heat, you have a design that seems workable. While increasing pressure does produce heat, it's not particularly massive (this becomes more significant when supersonic), and the air outside is very cold, and the air temperature is high.
> ...



Thank you Sir for the info......

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## DarrenW (Apr 15, 2020)

OK, now that we've been buried in the endless minutiae of countless test reports for most of this thread, I have a small question which has alluded me for quite some time. From the performance figures listed in the F4U-1D ACP which was discussed earlier, there is a further _decrease_ in Vmax when pylons were uncapped (409 vs. 401 mph): 






By comparison the speed figures for the F6F-5 were taken with pylon sway bracing installed, but no mention of a capped or uncapped condition:






Does anyone have photographs or drawings of a capped pylon? They must have been covers which could be easily placed over the pylon to improve performance (possibly so the pylon didn't require complete removal when not in use):


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## Dana Bell (Apr 15, 2020)

Hi Darren,

Hope these images help!

Cheers,



Dana

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## DarrenW (Apr 16, 2020)

Dana Bell said:


> Hi Darren,
> 
> Hope these images help!
> 
> ...


 
Thanks Dana for the great pictures, they definitely help. Does the last photo show the pylon in the capped condition? I'm also assuming that there was some sort of attachment that included sway bracing, the type dependent on whether bombs or drop tanks were to be carried.


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## XBe02Drvr (Apr 19, 2020)

Dawncaster said:


> According to Barrett Tillman, It was traced to faulty pressurization from the Pratt and Whitney supercharger, which sometimes aloowed the spark to "jump the gap" and burn out the distributor points.





Zipper730 said:


> Does this have to do with the air having an insulating effect against electricity? I remember another member talking about this on high altitude designs because with less air, it makes it easier for electrical currents to jump.


Yes. Air is a pretty decent insulator at sea level, but the thinner it gets, the thinner its insulation value gets. Engines operating above 18-20K generally need to have the Magneto's, and sometimes the entire ignition system, pressurized. All it takes is one leaky seal amongst the many in the system, and arcing and sparking set in. Not only hurts performance, but generates radio interference as well.
Cheers,
Wes


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## Zipper730 (Apr 21, 2020)

XBe02Drvr said:


> Yes. Air is a pretty decent insulator at sea level, but the thinner it gets, the thinner its insulation value gets. Engines operating above 18-20K generally need to have the Magneto's, and sometimes the entire ignition system, pressurized.


When was this starting to become a common feature on aircraft engines?


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## XBe02Drvr (Apr 23, 2020)

Zipper730 said:


> When was this starting to become a common feature on aircraft engines?


When did engines with high tension ignition start operating for extended periods above 20K? That's your history assignment.


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## Zipper730 (Apr 23, 2020)

XBe02Drvr said:


> When did engines with high tension ignition start operating for extended periods above 20K? That's your history assignment.


Searching...

Update 4/24, I haven't been able to find anything. That said, if I had to make a guess, it's probably when altitude records started exceeding 30000' which would be 1919-1920. That said, I'm not sure when mass-produced systems came around...


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## Joe Broady (Apr 24, 2020)

During a test climb to Hellcat service ceiling, Corky Meyer had the engine quit at 32,640 feet "as though someone turned off the ignition switch." Fortunately he got a windmill start after losing about half his altitude. By this time the engine was cold and running poorly so he immediately landed. His next two attempts to reach service ceiling had the same result. Remembering that Grumman's neighbors at Republic were regularly flying the R-2800 at 40,000, Meyer got on the phone. Republic's chief test pilot told him straightaway that they'd never get over 32,000 without a pressurized ignition harness.

"As P-38, P-47, Hellcat and Corsair fighter operating altitudes increased to well above 35,000 feet, the atmospheric pressure 'insulation' of the wires decreased so much from sea level to these altitudes that it allowed the spark electrical energy to easily jump through the normal rubber insulation protection and short out prior to reaching the spark plugs."

"The pressurized harness was developed by sealing each of the wires into flexible tubes from the magnetos to the spark plugs and then pressurizing the wires, magnetos and spark plugs by an air pressure pump driven by the engine."

"We then found out that the Army Air Corps had a very high priority and requisitioned all of the pressurized harnesses that Pratt and Whitney had built for the 40,000 foot ability of the Republic P-47 because it was soon going into high altitude combat in Europe... Needless to say we got the Navy brass in Washington to get us one of the pressurized harnesses for our Hellcat and I made a most anti-climactic climb to 39,455 feet altitude, which was just what we had predicted for the Hellcat's service ceiling."

Incidentally, for flights above 30,000 feet Grumman had their pilots pre-breathe oxygen for 30 minutes while riding a stationary bicycle in order to work the nitrogen out of their blood.

Meyer and Ginter, "Grumman F6F Hellcat," 2012.

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## Laurelix (May 16, 2020)

F6F-5:
Empty Weight: 4780kg
Loaded Weight: 5630kg
Wing Area: 31.0m2
Engine: Pratt Whitney R2800-10W
Take Off: 2135hp (WEP)
2000hp at SL / 1755hp at 1650m / 1800hp at 4800m / 1650hp at 6400m
-
Max Speed: (Military Power)
547km/h at Sea Level
629km/h at 7050m
-
Max Speed: (WEP)
559km/h at Sea Level
644km/h at 5700m
-
Rate of Climb: (Military Power)
Time to 6000m: 8:24
-
Sustained Turn Time: (WEP, Sea Level)
21 seconds
-
Stall Speed: (At Sea Level, No Flaps)
163km/h IAS
-
Armament:
6x 12.7mm M2 (400 rounds per gun)

References:
• http://alternatewars.com/SAC/F6F-5N_Hellcat_ACP_-_1_July_1944.pdf

• http://www.wwiiaircraftperformance.org/f6f/f6f-5-72731.pdf

• http://www.wwiiaircraftperformance.org/f6f/f6f-5-58310.pdf

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## DarrenW (May 16, 2020)

Laurelix said:


> F6F-5:
> Empty Weight: 4780kg
> Loaded Weight: 5630kg
> Wing Area: 31.0m2
> ...



Hi Laurelix,

Your maximum speed is correct for an F6F-5 in a 'clean' condition but in reality most combat missions were flown with an assortment of bombs, rockets, and drop tanks. The wing and fuselage racks required for this normally lowered top speed by 11-16 mph (16-26 km/h), depending on altitude (without munitions and drop tanks of course). Climb rate seems to be with pylons installed.

Your empty weight looks more like an aircraft with a basic loading, which included fuel, oil, and the pilot. According to Grumman actual empty weight was 9079 lbs (4118 kgs).

And while I have seen WEP ratings at S/L as high as 2250 hp, I think your figure of 2135 hp is more accurate. I derive this from WEP testing performed from 58 - 64 inHg, where unauthorized levels were required to achieve the 2250 hp output.

Not to be too critical, but the given stall speed should state a 'power off' condition. With 'power on' and no flaps the stall speed was closer to 97 mph (156 km/h) and 80 mph (129 km/h) with flaps.

Where did you get that turn rate from? Just curious how it was determined.....


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## Laurelix (May 18, 2020)

DarrenW said:


> Hi Laurelix,
> 
> Your maximum speed is correct for an F6F-5 in a 'clean' condition but in reality most combat missions were flown with an assortment of bombs, rockets, and drop tanks. The wing and fuselage racks required for this normally lowered top speed by 11-16 mph (16-26 km/h), depending on altitude (without munitions and drop tanks of course). Climb rate seems to be with pylons installed.
> 
> ...



It’s estimated by me. I have a list of planes with documented turn time. Then I compare F6F-5’s power to weight ratio, stall speed and drag coefficient compared to them to give a rough estimate value for its sustained turn time.


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## Laurelix (May 18, 2020)

DarrenW said:


> Hi Laurelix,
> 
> Your maximum speed is correct for an F6F-5 in a 'clean' condition but in reality most combat missions were flown with an assortment of bombs, rockets, and drop tanks. The wing and fuselage racks required for this normally lowered top speed by 11-16 mph (16-26 km/h), depending on altitude (without munitions and drop tanks of course). Climb rate seems to be with pylons installed.
> 
> ...


With Pylons you’re looking at F6F-5 doing 
523km/h at SL (WEP)
608km/h at 5700m (WEP)


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## DarrenW (May 18, 2020)

Laurelix said:


> It’s estimated by me. I have a list of planes with documented turn time. Then I compare F6F-5’s power to weight ratio, stall speed and drag coefficient compared to them to give a rough estimate value for its sustained turn tim



That's interesting. Do you have the sustained turn time for the F4U-1?



Laurelix said:


> With Pylons you’re looking at F6F-5 doing
> 523km/h at SL (WEP)
> 608km/h at 5700m (WEP)



Those look correct if there are also rocket launchers installed. Speed is normally 4 - 6 mph (7 -10 km/h) faster with just wing pylons and fuselage bomb shackles, giving a WEP top speed of 329 mph (530 km/h) at S/L and 384 mph (618 km/h) at 18,700 ft (5700 m). 

NAVAER performance figures dated January 1949 for the F6F-5 under similar conditions are 318 mph (512 km/h) at S/L and 380 mph (612 km/h) at 18500 ft, but to me the speed at S/L looks closer to performance while in Military power, which I expect to be at least 10 mph faster (there are BuAer wartime test reports that support this conclusion).

It must also be noted that Grumman performance numbers were always greater than those given by the US Navy, but some of this obviously had to do with aircraft configuration and condition. The manufacturer normally tested aircraft without pylons and such, while the opposite was normally true for the military. For instance, Grumman report 2422C dated 15 Mar 1945 states a maximum speed of 350 mph (563 km/h) at S/L and 400 mph (645 km/h) at 20000 ft, which are very close to your figures in post #135.

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## Zipper730 (May 19, 2020)

So you could basically say the following

All other things equal: An F6F & F4U of the same period will see the F4U with a speed advantage over the F6F?
Variables that affected the performance of the F4U would have included
Quality of paint-job
Removal of hook & covering over it for land based units
Smoothing & puttying over the fold-lines for land-based units, and the wing-fold mechanism
Redesign of the later F4U-1's canopy
Replacing the 13'4" propeller with the 13'1" propeller when possible.
Redesign of the tailwheel from short to high
Addition of a streamlined fairing behind the taller tailwheel on some desigins
Replacement the 13'4" propeller with the F6F's smaller 13'1" propeller
Improvement of pylon design

Others would be improvements to the supercharger, a pressurized ignition harness, higher MAP ratings and allowances for higher engine temp (lean mix), water injection, and higher carburetor impact pressure.

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## DarrenW (May 19, 2020)

Zipper730 said:


> So you could basically say the following
> 
> All other things equal: An F6F & F4U of the same period will see the F4U with a speed advantage over the F6F?
> Variables that affected the performance of the F4U would have included
> ...



Yes, that's a great summation of what we have discussed so far....


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## Reluctant Poster (May 19, 2020)

Joe Broady said:


> During a test climb to Hellcat service ceiling, Corky Meyer had the engine quit at 32,640 feet "as though someone turned off the ignition switch." Fortunately he got a windmill start after losing about half his altitude. By this time the engine was cold and running poorly so he immediately landed. His next two attempts to reach service ceiling had the same result. Remembering that Grumman's neighbors at Republic were regularly flying the R-2800 at 40,000, Meyer got on the phone. Republic's chief test pilot told him straightaway that they'd never get over 32,000 without a pressurized ignition harness.
> 
> "As P-38, P-47, Hellcat and Corsair fighter operating altitudes increased to well above 35,000 feet, the atmospheric pressure 'insulation' of the wires decreased so much from sea level to these altitudes that it allowed the spark electrical energy to easily jump through the normal rubber insulation protection and short out prior to reaching the spark plugs."
> 
> ...


The British didn't have the same problems. They had better spark plugs which were less susceptible. From the Fedden Mission Report that I posted recently:








According to the book "The Vital Spark" the British used ceramic in lieu of mica for the insulator and platinum for the electrode. The British manufacturers designed spark plugs to fit the American engines and produced them to allow fitting to American aircraft as they arrived. Roosevelt even mentioned this in a speech to Congress:

" After the United States Eighth Air force began operation from Britain the summer of 1942, the British undertook to double their production so that they could provide all our Eighth Air ice Fortresses with these plugs. Since early in 1943 virtually every United States Flying Fortress has taken off from British bases with these plugs in each of its four engines."

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## DarrenW (May 20, 2020)

Reluctant Poster said:


> The British didn't have the same problems. They had better spark plugs which were less susceptible. From the Fedden Mission Report that I posted recently:
> 
> 
> View attachment 582100
> ...



This is very interesting, thanks for sharing it.

So if I understand this completely, these "inferior" spark plugs actually forced the American engineers to improve the associated electrical components (in order to help make up for this deficiency), and in the end created equipment which was superior to what was being developed in Britain at the time. I suspect that the combination of British spark plugs and American magnetos/harnesses made for a winning combination indeed. Pretty neat stuff.


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## Zipper730 (May 20, 2020)

It seems that the reports from 1942-1943 seem to indicate top speeds of 388-395 mph at critical altitudes of 23800' to 24350': It would appear at this point, the airplane was pretty much in the baseline configuration. I'm not sure why the critical altitude varied by 550', though if I made a guess, it might be a lower manifold pressure (388 mph @ 24350' vs 395 mph @ 23800') seen in the earliest designs.

There was a report dated February 8, 1943 which included a variety of modifications that seem to be based on the NACA report that suggested various ways of cleaning up the F4U (smoothing over wing panels, access doors, skin irregularities, removal of the wing-walkways, arrester and catapult-hooks, as well as fairing over the arrester hook cut-outs). It would appear that the aircraft (BuNo #02334) was an F4U-1 (corrected). The engine was re-geared from the normal 0.5:1 to 0.4:1, and fitted with a 4-bladed 13'0" propeller in lieu of the normal three-bladed 13'4" propeller, and fitted with water-injection aimed at bumping up manifold pressure to 58" (early aircraft seemed to top out around 52-54").

According to estimates they could get the design up to 432 mph if horsepower was increased from 1650 to 1875, and 442 mph, if 2000 horsepower could be achieved with the modifications listed: Testing carried out on on January 31, 1943 showed a top speed of 431 mph @ 23825' and 428 mph @ 22840'.






What's of interesting note (in addition to keeping the propeller tip speed subsonic at maximum speed), is the claim of the F4U-1 reaching 404 mph @ 25300': While I read that this was an estimate -- I'm curious how they came up with such numbers in still air.

While I know there's methods to increase speed at altitude by lowering the RPM, and ways to increase critical altitude by leaning out the fuel/air mixture (something which might be dangerous), the RPM was reading 2700, so short of some inexactitude of terminology (i.e. bullshit), they appeared to have eked out performance that bested the normally listed figures for the F4U-1.


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## Dana Bell (May 20, 2020)

Hi Zipper,

BuNo 02334 was the 182nd Birdcage F4U-1, though that doesn't change the importance of the report.

Cheers,



Dana

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## DarrenW (May 21, 2020)

Zipper730 said:


> What's of interesting note, in addition to that, is a statement of the F4U-1A reaching 404 mph @ 25300....



Part of the issue is that 404 mph was an estimate and not accomplished during actual testing. The earliest F4Us were hard pressed to reach 400 mph under operational conditions, but this was eventually overcome by various modifications and thus the -1A variant was born. 

It must also be recognized that when the report was written (February 1943) a "standard F4U-1" was the birdcage variant and not the modified F4U-1A.


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## DarrenW (May 21, 2020)

During wind tunnel testing NACA determined that the speed of the F6F-3 could be improved by as much as 20 mph with various air frame modifications (to reduce aerodynamic drag), but of those mentioned in the report Grumman only deleted the lower cowl flap. I believe that given the performance edge already held by the Hellcat over the enemy it was more critical to keep production as simple and cost effective as possible in order to provide as many fighters for the US Navy as they could.


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## DarrenW (May 21, 2020)

Zipper730 said:


> I'm not sure why the critical altitude varied by 550', though if I made a guess, it might be a lower manifold pressure (388 mph @ 24350' vs 395 mph @ 23800') seen in the earliest designs.



A variance such as that could be attributed to slight differences found in the natural operation of the auxiliary stage regulators involved and/or piloting technique.


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## Zipper730 (May 22, 2020)

Dana Bell said:


> BuNo 02334 was the 182nd Birdcage F4U-1, though that doesn't change the importance of the report.


The reason I came up with that was because there was a picture of the F4U-1A on the top of the page, and the link and summary were the first on the list. 

Regardless, the aircraft depicted couldn't have been the intended aircraft because it had a three-bladed propeller, and the aircraft for this test had a four-bladed propeller. 

BTW: I'm not sure what modifications were intended for the canopy on this design, though it was listed in the report.



DarrenW said:


> Part of the issue is that 404 mph was an estimate and not accomplished during actual testing.


That's a good point, and for all I know, the might have chosen to risk a degree of terminological inexactitude, as Winston Churchill would say.


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## Dana Bell (May 22, 2020)

When did the F4U-1A first start to appear, and when did it become standard?


My production delivery lists end on 24 July 1943 with the 873rd Vought Birdcage. The 950th Vought Corsair was BuNo 17647 - the first raised cockpit aircraft (or "1A"). Since that's only 75 airframes later, I'd guess that the first 1As began rolling off the assembly line in August or early September 1943.

Cheers,


Dana

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## DarrenW (May 22, 2020)

Zipper730 said:


> Do you have any graphics that depict proposed mods?



They can all be found here in this report: 

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092668.pdf 

I know that you're at least somewhat familiar with this document, as we discussed it earlier on in this very thread. 

If you look at figures 7c, 23, 29a, 30b, 31, and 39b for airplane 10 (F6F-3) you will see drawings of the proposed changes and their effect on speed. Granted one modification suggested by NACA would not be suitable for carrier aircraft (removal of wing fold joints) but it does give a pretty clear indication that there was a lot of room to improve the aerodynamics of the F6F and thus increase it's maximum speed. All told the F6F-3's Cd was reduced by more than 28 percent. By comparison the P-51B, which was aerodynamically a much cleaner airplane, had it's Cd reduced by slightly less than 23 percent with suggested modifications. 

Be aware that a few of the suggestions made by NACA couldn't be accomplished in the "real world" (such as completely enclosed exhaust stacks), and were only there to show where aerodynamic improvements could possibly be made that had the greatest effect on a particular airplane's maximum speed.

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## Zipper730 (May 22, 2020)

DarrenW said:


> If you look at figures 7c, 23, 29a, 30b, 31, and 39b for airplane 10 (F6F-3) you will see drawings of the proposed changes and their effect on speed.


Looking at what I've see, one proposal was to minimize the gaps in the cowl-flaps (+3 mph); another was to seal over the gaps at the wing-fold joint and gun-access & ammunition doors (+4 mph); add a full-length fairing for the main-landing gear doors (+5 mph); internally seal the bulkhead and/or add external fairings from the openings at the tail-wheel and arrester hook (+3 mph), and; remove radio antenna.

The removal of the radio antenna is ridiculous: Radio is needed; fairing over the wing-fold joints would be unsuitable for carrier-ops, and fairing over the gun access/ammo doors would render the plane unusable (unless the doors could be covered when not in use).

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## DarrenW (May 22, 2020)

Zipper730 said:


> The removal of the radio antenna is ridiculous: Radio is needed; fairing over the wing-fold joints would be unsuitable for carrier-ops, and fairing over the gun access/ammo doors would render the plane unusable (unless the doors could be covered when not in use).



I believe they were concerned about the mast and it's drag invoking qualities. If you look at figure 39b there are examples of radio antenna installations that basically have zero effect on speed. Applying these to the Hellcat and other aircraft would improve speed by 1.5 - 2 mph.

NACA found that reducing panel gaps in the wings (possibly with special seals) would allow for smoother air flow without actually removing the panels all together.


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## Zipper730 (May 23, 2020)

DarrenW said:


> I believe they were concerned about the mast and it's drag invoking qualities. If you look at figure 39b there are examples of radio antenna installations that basically have zero effect on speed. Applying these to the Hellcat and other aircraft would improve speed by 1.5 - 2 mph.


That sounds reasonable, as far as I can see. Would that have affected production seriously?


> NACA found that reducing panel gaps in the wings (possibly with special seals) would allow for smoother air flow without actually removing the panels all together.


Would that have been hard to implement, and how would the speed reduction compare to removing the panels altogether?

Also, I'm curious which exacted a greater penalty: The drag produced by the wing-fold, or drag produced by the ammo-bay doors? The ammo bay doors look like they'd be a bigger offender because they were just open gaps.

How many land-based F6F's were used?


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## Reluctant Poster (May 23, 2020)

According to Dietmar Hermann’s “FW190 Long Nose” as a part of the performance enhancing experiments conducted on FW 190 V53 (a D-11 prototype), all gaps on the engine cowling were sealed with rubber. This resulted in a 17 km/h increase in maximum speed. These mods never made it into production. A lot of these types of enhancements never made it into production because it would slow production down. Those that did would often not survive in the field, an example would be the retractable tailwheel of the 109 which tended to be locked in place. In a lifetime of tinkering with cars I have developed an intense dislike of gaskets which tend to fall apart when disassembled or refuse to reseal. Remember that materials back in 40s were not as durable as today


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## Zipper730 (May 23, 2020)

Reluctant Poster said:


> According to Dietmar Hermann’s “FW190 Long Nose” as a part of the performance enhancing experiments conducted on FW 190 V53 (a D-11 prototype), all gaps on the engine cowling were sealed with rubber. This resulted in a 17 km/h increase in maximum speed. these mods never made it into production. A lot of these types of enhancements never made it into production because it would slow production down. Those that did would often not survive in the field. an example would be the retractable tailwheel of the 109 which tended to be locked in place. In a lifetime of tinkering with cars I have developed an intense dislike of gaskets which tend to fall apart when disassemble or refuse to realest. Remember that materials back in 40s were not as durable as today


So, you suspect that attempts to keep the cowl-flaps sealed right would either be impossible to keep in the right condition, and might be difficult to implement on a wartime footing?


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## Reluctant Poster (May 23, 2020)

Zipper730 said:


> So, you suspect that attempts to keep the cowl-flaps sealed right would either be impossible to keep in the right condition, and might be difficult to implement on a wartime footing?


I think once you take it apart its is difficult to re-seat. Years ago I took out the dash board of one of my VW Corrados. Getting it back together was not a trivial task. I had the luxury of time, I can imagine that under wartime conditions a lot of the parts would left out. A Corrado in some ways is a good example as only 97,000 were produced and although it was based on a mass produced car it was largely hand assembled by Karmman. Similarly while working on my friends BMW CSi 3.0 (also assembled by Karmann) I found myself cajoling things into place. The engines in both cars are different story, the parts do fit readily if you can get at them.

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## DarrenW (May 23, 2020)

Zipper730 said:


> That sounds reasonable, as far as I can see. Would that have affected production seriously?



Maybe. Once a concept is finalized and production is underway something even as minor as changes in the color of paint will effect production output enough to be noticeable.



Zipper730 said:


> Would that have been hard to implement, and how would the speed reduction compare to removing the panels altogether?



Not really sure, the increase in speed would probably be somewhat less because the surface wouldn't be as smooth as if they were completely fared over. As I said earlier the performance of the F6F was high enough "as is" and there really wasn't a need to make many of the changes suggested by NACA. If Japanese aircraft performance was greater it would have been more imperative to implement these modifications, but it wasn't. 



Zipper730 said:


> How many land-based F6F's were used?



There were four US Navy squadrons which operated for a time on land, VF-1, 33, 38, and 40. VF-1 was stationed in Tawara, while the other three were in the Solomons. All of these units were rotated out by early 1944. There were also five US Marine night fighter units which were land based. VMF(N)-541 was stationed in the Philippines and VMF(N)-534 in Guam, while VMF(N)-533, 542, and 543 served in Okinawa. There's also VMD-354 which flew recce Hellcats out of Falalop in the later stages of the war. 

Unlike the F4U, the F6F was always considered "suitable" for carrier use so those that were land based maintained the folding wings and tail hook for possible operations at sea. If you figure 20-30 airplanes on average per squadron we would have maybe about 200-300 Hellcats exclusively operating from land, but this is only a guess on my part. I can do further research into this if you are interested, as I have the source material available (USN records) in order to examine this more closely.


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## Hiromachi (Jan 28, 2021)

Apologies for reheating this thread, but I found discussion very interesting and helpful in understanding a few things.

So based on the above discussion and estimates, I was wondering what would be prop efficiency of that 13'11" unit used on F4U / F6F ? 
I've tried searching myself for the data of 23E50 constant speed unit with 6501A-0 blades, especially in form of some blade noise research by NACA or maybe prop efficiency evaluation but NASA archive did not help me here and I found nothing.


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## Zipper730 (May 3, 2021)

Hiromachi said:


> Apologies for reheating this thread, but I found discussion very interesting


No biggie, we do this all the time


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## Zipper730 (May 17, 2022)

Things I should have asked earlier but didn't

*Fuel/Air Ratio*



XBe02Drvr said:


> Rich mixtures don't GIVE you more power, they help you SUSTAIN more power by cooling the cylinder temps and holding off detonation.


At the risk of sounding stupid: Does this apply with carburetor/pressure-carbs only or with direct fuel-injection as well?

*F6F Speeds*



DarrenW said:


> F6F-5 BuNo.58310 reached 395 mph @ 18,750 feet while utilizing Combat power, and this was with a starboard wing pylon installed (known to reduce speed by roughly 5 mph at this height). So we have an honest 400 mph F6F-5 here in a 'clean' condition....


I should have addressed this earlier, but looking at that speed figure, 400 mph seems completely plausible if no wing-pylon was installed (not sure how common this was at the time of the test).



Dawncaster said:


> That's why I've always considered Hellcat's actually achievable maximum speed to be over 400 mph(about 410 mph). for example, according to AHT, ' Jan. 44, A modified F6F-3, including some of the features to be included in the later F6F-5 version, is flown at a speed of 410 mph at 21000 feet altitude. '


Not bad.

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## XBe02Drvr (May 18, 2022)

Zipper730 said:


> At the risk of sounding stupid: Does this apply with carburetor/pressure-carbs only or with direct fuel-injection as well?


"The stupidest question is the unasked question." (I forget whose quote that is.)
It's basic internal combustion facts. Regardless of the induction system, the best theoretical power output comes at a mixture that generates more heat than most engines cooling systems can dissipate and is on the ragged edge of detonation. So high power settings require a richer mixture than the ideal, or "stochiometric" best power mixture, the extra fuel serving to cool the engine and create a safety margin between operation and detonation. That's Fuel Mixture 101 from the perspective of us peons who only fix them and fly them.
To get the real skinny, you should consult Cullum (Snowygrouch, as he's known here on the forum) for the engineer/designer perspective. Wait..he'll probably see this, jump on here, and set the record straight.

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## Zipper730 (May 18, 2022)

Snowygrouch


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## Snowygrouch (May 18, 2022)

This is a bit messy so I`m not 100% sure whats being asked - however I think it would be instructive if I shared whats called a "mixture response curve"

This was developed for aero engines in the late 1930`s, and was at least published first by German engineers (this is not necessarily proof of others ignorance on it).

The mixture response curve was the fuel chemists creation after they started realising how worthless the Octane number was once you get down to very detailed development, because the Octane number (pre about 1942) was done at ONE air/fuel ratio, ONE engine speed, ONE air temperature ONE ignition advance. It didnt take long before engineers realised that if you vary those parameters, the detonation limit (analogous to the Octane number) jumped around all over the place, and in certain circumstances some engines made LESS power on fuels with higher octane fuels (once you get down to looking at differences of jus a few points).

So they decided to measure knock resistance across the full range of air/fuel ratios and make a graph (a more primative version of this is what the Allies essentially did when the 100/130 PN grade fuel specifications were jointly agreed between the UK and USA, which measured octane at TWO air/fuel mixtures not ONE, hence 100 Octane lean/130 PN at rich, its essentially the same fuel as 100 Octane from 1940, just measured with greater diligence).

Germans being Germans decied that a couple of points were no good, they wanted a complete curve, so they measured it at perhaps six or more points.

An example is below, in short you can make a LOT more power at rich mixtures for two reasons, firstly the cylinder may be kept cool by the extra fuel (a lot more than
can actually be burned, potentially) which raises the knock limit so you can increase boost, and secondly you can obviously burn more fuel because there are more
fuel carbon and hydrogen molecules floating about inside the cylinder to combine with oxygen.

Of course, if you have an air cooled engine it may be advantagous to run at a rich mixture a lot of the time to help keep temperatures down, which is a reliabilty factor,
but this doesnt mean that you CANT make a lot more power at rich mixtures if you are able to do so.

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## Zipper730 (May 18, 2022)

Snowygrouch
,

I remember something that 
X
 XBe02Drvr
saying something awhile back about how rich mixtures tend to see flames shoot out the stacks: I'm curious if that contributes to a significant increase in overall exhaust thrust?


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## Snowygrouch (May 18, 2022)

Zipper730 said:


> Snowygrouch
> ,
> 
> I remember something that
> ...


It probably would as the gas will have higher temperatures, which means greater energy.


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## DarrenW (May 18, 2022)

Zipper730 said:


> *F6F Speeds*
> 
> I should have addressed this earlier, but looking at that speed figure, 400 mph seems completely plausible if no wing-pylon was installed (not sure how common this was at the time of the test).


By the fall of 1944 wing pylons and fuselage bomb shackles/"T" bracing were a very familiar sight on fleet Hellcats (both F6F-3 and -5 models). Rocket launching hard points were common as well. Much of this had to do with the aircraft being increasingly tasked with the fighter-bomber role. Maximum level COMBAT speed of the F6F-5 with these additional items has been quoted in NAVAER documents to be 380 mph (one wartime source also has it at 386 mph). From what I can figure, two wing bomb racks gave a 10 mph deficit, while fuselage bomb shackles and rocket launchers reduced maximum level speed a further 6 mph.

So yes, 400 mph was certainly possible with a 'clean' F6F-5 in good working order, but due to operational needs this wasn't a normal configuration for Hellcats by this period of the war.

It's interesting to note that an F4U-1D with two uncapped wing pylons and fuselage drop tank rack had a maximum COMBAT speed roughly equal to the F6F-5 in a 'clean' configuration.


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## XBe02Drvr (May 19, 2022)

Snowygrouch said:


> It probably would as the gas will have higher temperatures, which means greater energy.


Hey, an "afterburner" equipped piston pounder!

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