Curtiss-Wright: Loss of Don Berlin and downfall

[kool kitty89]

How did the F6F deal with this issue?

Longer landing gear. Not very practical to add on the F4F. The bent wing on the F4U allowed shorter landing gear that could double as dive breaks. I think the P-47 may have had less prop clearance than either the F4U or F6F.

 

[Shortround6]

F6F just used big landing gear

Grumman used the retract into-the-fuselage gear on the Wildcat. They used an outward retracting gear (of considerable size) on the Avenger and then used Boeing style rearward retracting gear on the Hellcat. Like big P-40 gear (Curtiss paid royalties to Boeing). P-47 used landing gear that retracted 9" in length as it retracted into the wing to have room for the gun bays and it used a smaller diameter prop than the navy planes. The F6F also had the biggest wing of the 3. According to AHT the F6F used a prop 3 in smaller than the F4U and had about 1.6in less clearance. For all three it was a juggling act to fit the landing gear into the wing and leave room for the gun bays and on the Navy planes the wing fold.

The thing is ALL 3 of the fighters designed to use these big radials were designed to use the engines and propellers from the start. They weren't trying to shoe-horn a 1600-1700hp engine with an 11-11.5 ft prop into an airframe designed for a 11-1200hp engine (and the Curtiss P-36 started with a 900hp engine) and a 9.5-10ft prop. AS four blade props became more common they could be used to fit higher powered engines into existing planes (P-51 for one) but that is just a bit too late for most/all of the R-2600 powered fighters in Dec of 1941 schemes.

 

[Shortround6]

Longer landing gear. Not very practical to add on the F4F. The bent wing on the F4U allowed shorter landing gear that could double as dive breaks. I think the P-47 may have had less prop clearance than either the F4U or F6F.

Correct, From what I could find in AHT the P-47 had a fraction over 4in, The F6F had a bit over 7 in and the F4U had 9in.

 

[kool kitty89]

Correct, From what I could find in AHT the P-47 had a fraction over 4in, The F6F had a bit over 7 in and the F4U had 9in.

Wikipedia throws out a 6 inch clearance figure for the P-47 for what that's worth. (at a guess the 6 vs 4 inches could be differences between the toothpick and paddle props)

The 3-bladed XF6F-1 seems like it has a bit more clearance than the 3 or 4-blade R-2800 powered versions, but it might be an optical illusion.

http://static.thisdayinaviation.com...at-Bu.-No.-02981-left-front-quarter-large.jpg

vs

http://greec.free.fr/word/Monographie_Hellcat/Grumman F6F HELLCAT_fichiers/image002.jpg
http://www.afwing.com/images/f6f/xf6f-3.jpg

vs

http://static.thisdayinaviation.com...d-11-May-1944.jpg.pagespeed.ic.sUdujQVtMo.jpg

vs

https://upload.wikimedia.org/wikipedia/commons/e/e2/XF6F-6_Hellcat_NAN9-88.JPG


I couldn't find any XF6F-1 pictures in a blade-down position to make it more obvious.

 

[kool kitty89]

Not really on topic but given the P&W engine supercharger talks in here and not thinking it's complex enough to merit starting a new thread and I keep forgetting to ask for clarification when it comes up but:

The 'neutral' setting in the auxiliary supercharger stage on P&W engines (or at least R-1830 and R-2800), when set to neutral does the aux stage also get bypassed by some sort of valve in the intake manifold or is it left in series with the freewheeling impeller putting some degree of drag (and possibly throttle lag) on the intake airflow? The latter seems the simpler and more likely case and probably has similar aerodynamic impact as a swirl-type throttle inlet but more like having the guide vanes stuck at some fixed position. (so limiting the critical altitude for the take-off/neutral position but not really decreasing peak power like a throttle plate or kink in the intake manifold would -similar peak power but at a somewhat reduced critical altitude)

If it's really close to the behavior of a swirl throttle, it might actually increase take-off power by reducing the critical altitude for the integral supercharger. (allowing throttle plates in the carb inlet to be closer to full open on take-off)

 

[Shortround6]

I am not sure about the the one on the Wildcat but the F4U used doors in the ducts to bypass the Auxiliary stage and provide "RAM" air to the carb on the engine supercharger. The F6F did NOT and air always went through the auxiliary supercharger and intercooler.

Since the early F4U could only hold take off power of 2000hp to around 15-1600ft (Yes hundreds, not thousands) I would say that the supercharger on the engine was pretty much optimized for sea level take off as it was.

For a power at altitude chart see: http://www.wwiiaircraftperformance.org/f4u/02155-level.jpg

 

[kool kitty89]

Perhaps the Corsair's arrangement saw its greatest gains in terms of cruise performance with somewhat better specific fuel consumption due to ram and lack of suction losses. (in conditions of wide-open throttle in neutral gear)

The Corsair's higher speed might mean a bit more gain from ram airflow as well.

 

[GregP]

Navy fighters HAD to have more clearance since they were landing on carriers. The full stroke of the gear was going to be used most of the time with some oaccasional slight leaning forward of the nose until the arrester wire stopped the nose-over with tsnsion.

Standard Navy requirments for shipborne aircraft of the time with conventional landing gear.

 

[Shortround6]

Quite true. The problem starts to come in when people here in the forum want to take an existing fighter with clearance "X" and "simply" stuff in a much larger engine which needs a bigger prop which will reduce clearance to "0" or negative numbers. To get the clearance back you need longer landing (or bigger wheels or....?).

 

[kool kitty89]

I seem to recall the ferried P-47s that were carrier launched had to use catapults in a 3-point take-off configuration. I think P-40s managed conventional deck take-offs well enough for ferrying, but landing would obviously be another story. (tail-hook issues aside, there's the beating the gear has to take and the tire pressure limits for carrier deck impacts)

 

[GregP]

Or leave the prop diameter the same and go to wider chord blades or more blades.

 

[kool kitty89]

In the case of a switch from the R-1830 to R-2600, using more blades or wider chord blades (or both) would still leave the problem of the larger diameter engine cowling obscuring several inches more of the prop blades. I'm sure good cowling design minimizing thrust losses would be important here, but I'd think there'd still be some losses in any case. Admittedly, you'd be in a similar situation for the R-1820 (albeit less extreme given the shorter engine and lesser cooling airflow requirements) but in either case this may be a bigger concern than raw drag added to the airframe from increased frontal area. (particularly on aircraft with bulky fuselages already considerably wider than the engine/cowling diameter -unlike the Fw 190 or P-36)

 

[Shortround6]

In a perfect world the available props would always match the needs of every engine and airframe combination. The real world wasn't quite so accommodating. The availability of 4 and 5 blade props lagged behind the need at times. The same with wide cord blades. The engine makers got ahead of the prop makers at times. The engine maker often only had to make a few different models of the same engine (at one time). The prop maker had to make enough different prop hub and blade combinations to suit the same engine for fighters to bombers and transports.

The Lockheed Ventura never got a 4 bladed prop. It did get some rather wide cord 3 blade ones to suit it's limited space for propellers.

But it was somewhat later in timing than many/most of the R-2600 fighter proposals. Venturas were also noted for being rather fast at low altitudes. Speed at altitude wasn't as marked.

" Two Pratt Whitney R-2800-31 rated at 2000 hp for takeoff, 1600 hp at 11,900 feet. Performance: Maximum speed 322 mph at 13,800 feet, 296 mph at sea level." for a PV-1.
Due to the engine or perhaps the props had something to do with it? A 12ft prop has around 43% more 'area' than a 10 ft prop. What works well at sea level doesn't work so well as the air thins out.

 

[GregP]

True. but Navy Patrol planes didn't need great altitude performance since they were searching for small targets in the ocean and if they got too high, they coundn't see much detail. So it wasn't much of a factor. I am under the impression that most of the Lockheed twins were not used at high altitudes, but that could just be my impression and unrelated to actual use. I never specifically looked into them much since I was always more interested in fighters and bombers in large-scale use.

Had they needed the altitude performance, however, everything you said would have and does come into play. Natrually, there were obviously some higher altitude uses for them and I was speaking of the most common uses of the Lockheeds, not an absolute rule. Some people out there always assume absolute rules and war makes them seldom true.

 

[kool kitty89]

Due to the engine or perhaps the props had something to do with it? A 12ft prop has around 43% more 'area' than a 10 ft prop. What works well at sea level doesn't work so well as the air thins out.

The same was true for part of the reasoning for adding the broader chord props to the P-38K (better thrust at high altitude, though I suspect better low speed thrust/climb performance at all altitudes would also be relevant).

High speed drag vs thrust on larger area propellers varies a good deal as well as was seen with the variety of paddle props tested on the P-47. P-47 Performance Tests A 20 inch prop diameter (10 inch radius/ground clearance) range in the props tested there too.

 

[Shortround6]

The Lockheed twins went through quite a history of change. They started as the Lockheed 14 Super Electra with 875hp 9 cylinder P&W Hornets or 900hp Cyclones. They crept up to 1100-1200hp twin wasps or Cyclones and got a Fuselage stretch to become the Lockheed 18 Lodestar. A few were built as B-37s with 1700hp R-2600s but the majority of the contract was switched to R-2800 engines. PV-2 got a bigger wing but it was outboard of the engine nacelles. Ultimate performer was the Howard 500 executive transport with post war 2500hp R-2800CB engines, prop hubs from F4U-4s (according to wiki) and prop blades (cut ?) and spinners from DC-6s. The Howard 500 shared only certain parts with the Lockheeds.

Even the slightly older Howard Super Venturas got landing gear from the PV-2 Harpoons to handle the higher weight.

Weight empty had doubled, from 10,750lbs for an Early 14 with Cyclone 9s to 23,000lbs for the Howard 500 ( which had a pressurized fuselage and new, wet wings). The change took almost 20 years. Granted that could be speeded up some but stuffing 1700-2000hp engines into planes originally built for 900-1100hp engines does take a bit of doing.


The Navy got away with the 3 bladed props and they worked pretty well for what the Navy wanted/used the PV-1/PV-2 for. But a small diameter 3 bladed prop with narrow blades in 1941/early 1942 probably wouldn't have given the performance the advocates of an early R-2600 powered fighter are looking for.

 

[kool kitty89]

The P-47 tests are also a good example of showing prop changes having the biggest impact on rate of climb at all altitudes (and would likewise apply to take-off performance), so even aircraft or engines not needed or suited for high altitude propeller performance would still have concerns for large prop areas and good efficiencies at low level in as far as low speed thrust for take-off, climb, and sustained turn performance.

Besides, if you want high altitude performance in the F4F, the 2-stage R-1830 was going to be the better bet in 1940 anyway. (the likes of the F2A's R-1820-40 might fare better too given the power/thrust to weight in play compared to R-2600s available at the time or even the later B series -I haven't seen full details on the R-1820-40, but it seems to have somewhat higher critical altitudes than the R-1820s used on the Martlets, maybe closer to the FM-2's R-1820-56 without water injection; still more frontal area and less power than the 2-stage R-1830 though)

The R-2600 would have better fit a USN fighter somewhat smaller/lighter than the Corsair or F6F-3 optimized for the larger engine and aimed at combat below 16,000 ft. (also early enough to actually make the R-2600 attractive and necessarily considering both the older/lighter/less powerful A series engines as well as potential 1700 hp B series variants -and possibly R-2800 powered developments) Sticking any R-2600 into a direct F4F-derived airframe would probably end up with something worse than the F4F-3, and going back to the drawing board was the only sensible solution. (my remaining point is simply that Grumman could have done so much earlier than the XF6F-1 being built in 1942, potentially as a direct follow-on to the XF4F-2 -developing an outright successor replacement for the F2A rather than developing the F4F into a viable competitor -of course, Grumman was also putting resources into the XF5F in the same late 1930s time period)


Anyway, none of this really applies to Curtiss given they didn't have a major stake in the carrier borne fighter arena.

 

[GregP]

Here's one that got an engine MUCH larger than designed for. I don't have the test flight results, but it looks good on paper ... sort of ...

Looks like it got a very expensive polish job, too! I bet THAT took awhile ... of course, now you can see it from 100 miles away in the sun! The engine-out performance suffered, though.

I wonder which way that center wheel retracts.

 

[Elmas]

Here's one that got an engine MUCH larger than designed for. I don't have the test flight results, but it looks good on paper ... sort of ...

View attachment 296724

Looks like it got a very expensive polish job, too! I bet THAT took awhile ... of course, now you can see it from 100 miles away in the sun! The engine-out performance suffered, though.

I wonder which way that center wheel retracts.

Yes, but this model of B29 was expecially developed for dive-bombing.....

 

[GregP]

That's very good!

I hadn't even considered dive bombing. Maybe it's the fastest bomber with a propeller ever built since it only has the drag of one engine. But the Reynolds number is 911.