Corsair and Hellcat in Europe

[BiffF15]

Gents,

I was under the impression that the F8F Bearcat had its engine canted a few degrees down to help with what I do not know. Any validity in that statement from what you have come across?

Also think the F6F, more so in the F8F, and the Hawker Seafury the "hump backed" layout is more prevalent.

Cheers,
Biff

 

[Airframes]

Canted down to achieve the desired thrust axis ?

 

[DarrenW]

Gents,

I was under the impression that the F8F Bearcat had its engine canted a few degrees down to help with what I do not know. Any validity in that statement from what you have come across?

Also think the F6F, more so in the F8F, and the Hawker Seafury the "hump backed" layout is more prevalent.

Cheers,
Biff

Canted down to achieve the desired thrust axis ?

Can't speak for Bearcat but the Hellcat had a negative thrust line so the rather large wing could be mounted at the minimum angle of incidence in order to reduce drag in level flight. That's what gave the aircraft its distinctive tail down flight attitude.

 

[mcoffee]

Down thrust is used to help mitigate the pitch excursions that occur with changes in power settings. Likewise, side thrust is used to help mitigate the effects of asymmetrical thrust inherent in propeller driven aircraft at high angles of attack. Neither are about visibility over the nose.

 

[Zipper730]

Can't speak for Bearcat but the Hellcat had a negative thrust line so the rather large wing could be mounted at the minimum angle of incidence in order to reduce drag in level flight. That's what gave the aircraft its distinctive tail down flight attitude.

I thought the thrust line was pointed up so that it'd hit the wing at an angle of attack that would increase the lift of the wing, and lower the AoA for flight?

 

[GregP]

The down thrust is there only to avoid a hard nose-up pitching moment upon application of a significant amount of power. That's ALL it is there for. The last thing you need on a missed approach in bad is to add power, nose up, and stall.

 

[YF12A]

Speaking of thrust line reminds me of a story told to me by my Father. In the '40's when he was working for American Overseas Airlines, they had one Lockheed Constellation that from day one from Lockheed always required a fixed amount of rudder trim, no matter what. No one could figure it out. My Dad thought about this and figured they needed to "baseline" the entire plane to make sure everything was straight. He convinced his manager they needed an expensive surveyors measuring device, I don't know what it was, and started measuring the plane. First, the fuselage from the nose through the middle rudder. Then the left and right rudders to be sure they were in parallel. Then they started with the No. 1 engine. When they got to No. 3 engine, the problem was found. That engine mount had been made crooked. It was off laterally by enough to cause the problem, but was not noticeable visually. Lockheed got a call, a new mount was sent, problem solved. And yes, my Dad made sure they checked No. 4 as well!

 

[DarrenW]

One thing I believe hasn't been mentioned here so far is that if the F4U or F6F were de-navalized while serving in the ETO they would probably gain a minimum of about 8 mph at critical altitude by fairing over the tail hook and wing irregularities associated with the folding wings, as well as the removal of catapult attachments (the overall reduction in weight due to these modifications would probably have some small effect on level speed but not nearly as much as the added streamlining). And while this may seem like a relative miniscule gain in performance, every bit of an improvement surely helps. Add in the use of 150 octane fuel and there is the possibility for decent performance gains up the their respective critical altitudes.

The last page of this document details the expected improvements in level speed by incorporating these physical changes (which incidentally closely mirrors the findings in NACA document L5A30):

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

According to Bill (drgondog) climb should likewise improve by 300+ fpm and range would improve slightly without the added weight of the hook and wing fold structures:

Could the later model P47 establish complete control of air over Germany without P51

 

[Shortround6]

From Wiki;

"
Since Corsairs were being operated from shore bases, while still awaiting approval for U.S. carrier operations, 965 FG-1As were built as "land planes" without their hydraulic wing folding mechanisms, hoping to improve performance by reducing aircraft weight, with the added benefit of minimizing complexity.[53][54] (These Corsairs' wings could still be manually folded.[55])

A second option was to remove the folding mechanism in the field using a kit, which could be done for Vought and Brewster Corsairs as well. On 6 December 1943, the Bureau of Aeronautics issued guidance on weight-reduction measures for the F4U-1, FG-1, and F3A. Corsair squadrons operating from land bases were authorized to remove catapult hooks, arresting hooks, and associated equipment, which eliminated 48 pounds of unnecessary weight"

Bolding by me. Granted the wings could still fold but redesigning the wing and taking out the hinges was probably lot of work for little benefit.

 

[DarrenW]

Corsair squadrons operating from land bases were authorized to remove catapult hooks, arresting hooks, and associated equipment, which eliminated 48 pounds of unnecessary weight"

Sounds about right. America's Hundred Thousand puts the weight of arresting gear used by the F6F between 35.7 and 37.4lbs (depending on whether it's a -5 or -3 model). But reading posts to similar threads on the subject leads one to believe that de-navalizing an aircraft could yield hundreds of pounds in weight saving measures. Not knowing the reduction that can be realized by removing the wing folding mechanisms and it's associated hardware, I'm under the impression that much of this extra weight inherent in carrier planes can be attributed to the strengthening of the overall airframe to withstand the daily abuse of carrier operations. That's why just adding a hook to a land-based plane and calling it good is normally never enough to make it a viable shipboard machine. And of course it wouldn't be feasible nor prudent to make the airplane less structurally strong in the hopes of improving it's performance.

However, wind tunnel tests have shown that by eliminating gaps and irregularities associated with folding wings and fairing over tail hook assemblies, level speed can improve enough to make it a worthwhile endeavor (especially when added to other drag reducing measures).

 

[GregP]

Not sure why anyone would want de-navalize a Corsair or a Hellcat since they are Navy fighters and would retain the wing fold mechanism, the heavier construction of naval aircraft and other "Navy" items. The USAAF was not "hard up" for fighters and any Corsair of Hellcat presence in the ETO would be from a Navy source.

That's in the real world, not in a "what if."

If it just specualtion, you could look at several civilian Corsairs or Hellcats of taoday. Some have been de-navalized to an extent, and most have had armor remove as well as guns and unnecessary hardware items that drop things from wings or belly. You can't do that today as a civilian.

 

[DarrenW]

Not sure why anyone would want de-navalize a Corsair or a Hellcat...

This is just a fun exercise, and one that we often see on the forum. I for one love carrier planes so you won't get me to agree to any changes.

One the other hand, numerous Marine Corps Corsairs had their tail hook assemblies removed and faired over because the aircraft were land based and did not require the added weight and drag associated with the equipment. SR6 mentioned that almost a 1,000 "land based" FG-1s were built and wing modification kits were offered in the field as well, so it wasn't just a fantasy after all.....

 

[GregP]

The Corsair was originally land-based in US service, and some stayed that way. But they all had Naval construction and folding wings except the original FG-1s from Goodyear that did not have folding wings. The F2G-1 had manual wing fold and the F2G-2 had hydraulic wing fold. Tail hooks could be added or removed on all by maintenance personnel, but major structure remained Naval in construction.

Just for fun things ARE fun. I was just wondering.

 

[Zipper730]

The Chance-Cought (actually Vought-Sikorsky ... all the drawings start with "VS" anyway) F4U Corsair gave the Japanese a nasty surprise. I was a very good fighter and, in its later versions, was simply outstanding by any measure of success of fighter prowess.

Plus some figures that show it's turning circle as being crap (Americas Hundred Thousand) from what I remember seemed to have erroneously listed the turn rate of the F4U-1 as being with it's flaps up and the P-51 with it's flaps down to some degree.

If I recall drgondog had listed the turning rate of the F4U as being consistently better than the P-51. The rate of roll I don't know how they compare, but it's possible that the fact that the F4U-1 with it's very high g-tolerances compared to even the P-51, and the fact that it's flaps could be used to an extent in tightening up turns, it seems like it would be better at turning than most would expect.

Now the F6F also has extreme g-load figures and can utilize its flaps in turns. The turning circle of the aircraft is quite good flaps-up, and with plain flaps (versus the F4F's split-flaps), provide a big difference in rate of turn when extended (and in doing so, provided a greater range of speeds where it could actually out-maneuver an A6M), and would have made it a formidable opponent to tangle with (neither the Me-109 and Fw-190 couldn't turn as good).

It's roll rate wasn't as good as the F4U, and was similar to the F4F, which wasn't all that good. With that said, consider the following

• Captain Eric Brown stated that the F4F's roll-rate was comparable to either the Hurricane or Sea Hurricane (I forgot which), but required more muscle power to make it roll in the desired fashion, but if your arms were strong enough, you were good.
• The Hawker Hurricane's roll-rate varied wildly based on certain variables including the way the aileron was rigged, and the type of lubrication involved. When all worked well, it rolled quite smartly. When rigged badly, it rolled poorly.
• The Hurricane and Sea Hurricane might not have had the same rate of roll. Remember, carrier suitability requires good roll-control down to very low speeds, which could make the ailerons stiffer at higher speeds.
• The way people compute roll-rate figures don't necessarily factor in differences from rolling to the left or right (the figures were sometimes averaged), the amount of time it takes to reach full roll rate (sometimes averaging it).

Grumman's chief test pilot, Corky Meyer, has said in print (Flight Journal) that the Hellcat and Corsair flew side by side when at the same power levels when HE tested it except in the main stage (where it was 5 - 6 mph slower since the Hellcat didn't use ram air to avoid carburetor icing, and the same speed in low or high blower stages), and surmised the difference in airspeed was pitot tube placement on the Corsair since they verified the speed of the Hellcat with rigorous means. He says the Corsair was "optimistic" on airspeed and the Hellcat wasn't.

The F6F-5 might have been the aircraft noted as it was a bit faster than the F6F-3, and if paired with an earlier F4U-1 (top speed 395 mph), and possibly even the first WEP versions (417 mph), it would make quite a bit of sense.

One thing I believe hasn't been mentioned here so far is that if the F4U or F6F were de-navalized while serving in the ETO they would probably gain a minimum of about 8 mph at critical altitude by fairing over the tail hook and wing irregularities associated with the folding wings, as well as the removal of catapult attachments

That would put the F6F-3 to 387 mph and -5 to 399 mph.

Add in the use of 150 octane fuel and there is the possibility for decent performance gains up the their respective critical altitudes.

How much of a benefit do you think would have came out of that?

According to Bill (drgondog) climb should likewise improve by 300+ fpm and range would improve slightly

The climb figures seemed all over the place without the F6F-3 and -5. Some figures were around 2900 others were around 3650. That gives me anything from 3200-3950 fpm.

Since Corsairs were being operated from shore bases, while still awaiting approval for U.S. carrier operations, 965 FG-1As were built as "land planes" without their hydraulic wing folding mechanisms

Interesting...

Granted the wings could still fold but redesigning the wing and taking out the hinges was probably lot of work for little benefit.

How much weight would be trimmed off? Pure curiosity.

 

[BiffF15]

Gents,

A little information on what flaps do for your turn. I'm not Drgondog but will give it a shot.

First there are four ways in which a turn is measured or discussed, those being instantaneous / sustained and rate / radius. When an aircraft starts a max performance turn at high speed the pilot pulls to the aircrafts G limit. Pulling to the G limit results in a turn of a X degrees per second. As the aircraft slows it gets to what today is called corner velocity. That is the speed at which max degrees per second is obtained, also coincidentally enough it's the speed at which an abrupt full aft stick will not result in an over G. Below this speed if airspeed is continued to be bled off (energy depleting) then The degrees per second stay about the same up to a certain point then start to slack off. At the start of this turn his circle is large and shrinks as his speed burns off. Eventually it stops shrinking and starts growing again, think I can no longer turn hard or I will fall out of the sky. So I have to relax back pressure on the stick and roll out some, hence the rate of turn goes down and the radius goes up. Again this is a max performance energy depleting turn, AKA a radius fight.

Next is the hard turn which is energy sustaining. A sustained hard turn is measured both by degrees per second and turn circle size. Degrees are less per second than the max performance turn but over time will turn more degrees sense he never gets so slow he will fall out of the sky. Also radius is larger. This is called a rate fight in today's parlance.

With this in mind the former aircraft, in the max performance turn, goes after a better turning aircraft. As he maneuveres he burns energy but needs a little better turn in order to get or keep his nose out in lead ( in order to gun his opponent). He is bleeding energy and introduces flaps or greater drag in order to keep or maybe increase his turn rate / decrease his turn radius. This last sentence is the key to this entire conversation. Those flaps will tighten his turn, decrease his radius but only for a VERY short time as they are more DRAG. His motor did not get more powerful when he selected his maneuvering flaps.

They are not the end all be all, but are just another tool in the pilots tool box to be used only in certain situations.

Cheers,
Biff

 

[DarrenW]

How much of a benefit do you think would have came out of that?

Basically a 10-15 mph increase in speeds below critical altitude could be realized in each blower stage with the use of 44-1 fuel, however these particular altitudes will be lower than when utilizing the normal 130 octane fuel. Overall maximum speed previously obtained at original critical altitudes would not be very different. Climb performance should improve as well under the same circumstances.

In other words, low to medium altitude performance would improve but there would be negligible differences at altitudes above 18kft.

 

[GregP]

Zipper, the F6F was designed without ram air to the carburetor on purpose, and Grumman would not add ram air under any circumstances. The reason was to preclude carburetor icing at low speeds around the carrier. Many Corsair went in due to carb ice in the circuit, but no Hellcats did. They had non-combat operational losses, to be sure, but not due to carb ice.

The last Hellcat prototypes, two XF6F-6s, were good for 417 mph, but the war ended and F8F Bearcat was on the way, so they weren't proceeded with.

The climb figures are not really all over the place. The 3,650 is at WEP and the 2,900 was a normal rated power. In fact, ALL the highest numbers for maximum performance of any piston aircraft were at WER, if it had one, or max power. In reality, most never got anywhere near the max numbers unless diving or running for their life.

You need to go do some research on the weight saving. Look up a standard incremental weight table for any Corsair and see if you can find it.

 

[Zipper730]

Basically a 10-15 mph increase in speeds below critical altitude could be realized in each blower stage with the use of 44-1 fuel

With or without the modifications described?

Overall maximum speed previously obtained at original critical altitudes would not be very different.

I thought the critical altitude was dictated by the manifold pressure limits? I figure if the manifold pressure limits were raised (high octane), the pressure limit would go up throughout the whole envelope until the blower could not produce enough boost to produce the new manifold pressure?

Climb performance should improve as well under the same circumstances.

By how much would you guess just on 44-1 fuel, and with the other mods?

Zipper, the F6F was designed without ram air to the carburetor on purpose

I understood that

Many Corsair went in due to carb ice in the circuit, but no Hellcats did.

Didn't know that. I'm curious if they had carburetor heat in either design?

The last Hellcat prototypes, two XF6F-6s, were good for 417 mph, but the war ended and F8F Bearcat was on the way, so they weren't proceeded with.

The F8F was a better choice. The -1 had truly breathtaking climb figures and better radius than the F8F-2 when configured for escort; the -2 was faster and longer legged on internal fuel.

The climb figures are not really all over the place. The 3,650 is at WEP and the 2,900 was a normal rated power.

The 3650 figures seems to be a military power setting, though there is another figure listing 3200 at military power.

You need to go do some research on the weight saving. Look up a standard incremental weight table for any Corsair and see if you can find it.

You mean the listing of the weight of all the components?

 

[DarrenW]

With or without the modifications described?

This would be the probable performance boost without any airframe modifications.

I thought the critical altitude was dictated by the manifold pressure limits? I figure if the manifold pressure limits were raised (high octane), the pressure limit would go up throughout the whole envelope until the blower could not produce enough boost to produce the new manifold pressure?

We'll probably need someone with a better understanding of superchargers to explain the science behind this to you. I'm going by aircraft performance charts that show critical altitudes (aka, full throttle height) dropping as maximum manifold pressures increase. For instance, a Hellcat running at 52" Hg ("military power") reaches critical altitude in high blower at around 23,000ft, but with 60" Hg ("war emergency power" or WEP) it drops to around 18,500ft. Using 150 octane fuel could conceivably boost manifold pressures upwards to 70" Hg, so I would expect another drop in critical altitude to occur then as well.

By how much would you guess just on 44-1 fuel, and with the other mods?

From what I've seen after examining countless performance charts I would expect about a 500fpm increase in ROC if boost pressures were increased from 60" to 70" Hg. Not really sure about how much "de-navalizing" an aircraft would improve climb as I don't have any good figures on the total weight that all these modifications would remove. I also haven't seen any real world data on an actual airplane showing test results both with and without the mods. Drgondog said a 300+ fpm increase could occur but that was only his best estimate.

 

[Zipper730]

This would be the probable performance boost without any airframe modifications.

Okay

We'll probably need someone with a better understanding of superchargers to explain the science behind this to you.

I know that critical altitudes are lower for higher power settings. I was thinking about detonation, which occurs as a function of manifold pressure (and resulting heat): I figured if the manifold pressure could get higher without detonation...

From what I've seen after examining countless performance charts I would expect about a 500fpm increase in ROC if boost pressures were increased from 60" to 70" Hg.

That's pretty good, so with a climb rate of 2900 feet per minute, you'd now see 3400, and for 3200, you'd now get to 3700, and for 3650, you would be able to get up to around 4150?

Not really sure about how much "de-navalizing" an aircraft would improve climb as I don't have any good figures on the total weight that all these modifications would remove. I also haven't seen any real world data on an actual airplane showing test results both with and without the mods. Drgondog said a 300+ fpm increase could occur

Are those figures addable to each other? For example 500 fpm from 44-1 fuel; 300 fpm for stripping down so 300+500 = 800? Or is there some other variable?