# P-40Q vs P-60A/D



## wuzak (Jul 5, 2014)

If Curtiss was given the go-ahead to manufacture a "new" P-40 replacement for the late war period, which would be better, The P-40Q with its two stage Allison, cleaned up aero and bubble canopy, or the P-60A (turbo V-170) or P-60D (2 stage Merlin) with its laminar flow wing and revised cooling systems?

An alternative may also have been a P-60 with 2 stage Allison (don't think one was ever built).

We can ignore the R-2800 P-60s (P-60C and P-60E) because that would require a lot more rework for production lines).

The XP-60 (Merlin 28 ) was about 20mph faster than the P-40F (V-1650-1/Merlin 28 ).

Which has more long term potential?


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## rogerwilko (Jul 5, 2014)

As I'm biased, i would prefer the Bell product just for it's more modern tricycle landing gear and cannon setup.

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## rogerwilko (Jul 5, 2014)

Sorry. I was too fast with my digits. I thought you meant the P400 Airacobra!!


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## Shortround6 (Jul 6, 2014)

wuzak said:


> If Curtiss was given the go-ahead to manufacture a "new" P-40 replacement for the late war period, which would be better, The P-40Q with its two stage Allison, cleaned up aero and bubble canopy, or the P-60A (turbo V-170) or P-60D (2 stage Merlin) with its laminar flow wing and revised cooling systems?
> 
> An alternative may also have been a P-60 with 2 stage Allison (don't think one was ever built).
> 
> The XP-60 (Merlin 28 ) was about 20mph faster than the P-40F (V-1650-1/Merlin 28 ).



The P-60 had more "potential" but seems to have been handicapped by the initial requirement for the eight gun armament, which helped lead to that 275 sq ft wing, great when you hung the R-2800 on the nose but not so good with 1300-1500hp engines. 
Ideal (or at least better) would have been a wing designed from the start for six guns and about 230-240sq ft with the airfoil used on the P-60. Wing might have been 150-200lbs lighter and had less drag than the big wing allowing for higher performance with the lower powered engines. Please remember the IV-1410 that started this was _"supposed"_ to give 1600hp at 25,000ft with a turbo. Maybe they also wanted the big wing for high (over 30,000ft?) work? 

Once you give up on the turbo the P-60 series is stuck with too big a wing for the available power of the engines (unless you use the R-2800) even if the airfoil is better than the P-36/P-40 wing. 

Old airfoil on right sized wing vs new airfoil on too big wing, which has more potential? 

Which has more long term potential?


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## Capt. Vick (Jul 6, 2014)

P-60 all the way.


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## nuuumannn (Jul 6, 2014)

Can't say I know anything other than what I've read here or on the net about the P-60. To remain competitive in a European environment, the inline engined aircraft would have to be two-speed two-stage engine powered, either V-1650-3 and above or Merlin 60 series. Either the P60D or P-40Q with two-speed two-stage engine.


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## RpR (Jul 9, 2014)

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## RpR (Jul 9, 2014)

As P-60s were second thought aircraft from the the death of the P-53 due its engine not being available and as the P-53 and P-60 were simply a modified P-40, the Q, had it not been the least favorite son of Curtiss would have easily been the better.

Better Allison engines existed but were not considered important till too late the in the war but had the Q with the improved Allison been built it was faster than any P-60 with excellent handling.

The was no reason for the P-60 except the mind of Curtiss money crunchers.
Don Berlin left Curtiss in 1941 because of Curtiss cluster-f mentality in wasting money on doa designs rather than simply improving the P-40.

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## wuzak (Jul 9, 2014)

The only performance numbers I have seen for the P-60 was the XP-60 with Merlin 28, which was faster by about 20mph than the P-40F with a similar engine, and the XP-60A with the turbo which may, or may not have, been measured at 420mph (within a couple of the P-40Q).

The P-60D with 2 stage Merlin flew earlier than the P-40Q. I have yet to see any performance figures for that version.

One wonders what a P-60 with the same 2 stage V-1710 could have done in comparison to the P-40Q.

The reason for the P60 was a request from the USAAF for a Packard Merlin airframe with the laminar flow wings.


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## wuzak (Jul 9, 2014)

BobR said:


> As P-60s were second thought aircraft from the the death of the P-53 due its engine not being available and as the P-53 and P-60 were simply a modified P-40, the Q, had it not been the least favorite son of Curtiss would have easily been the better.



The Q was 2 or 3 years later than the XP-53 proposal and the XP-60 program. The XP-60 program was basically cancelled before the P-40Q started. It was never a choice between the two.



BobR said:


> as the P-53 and P-60 were simply a modified P-40





BobR said:


> Don Berlin left Curtiss in 1941 because of Curtiss cluster-f mentality in wasting money on doa designs rather than simply improving the P-40.



If the XP-60 was "simply a modified P-40" then wasn't it an attempt to improve the P-40?


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## Shortround6 (Jul 9, 2014)

Perhaps a bit too much blame on the


> Curtiss money crunchers


.

How much of the blame can be put on Curtiss or how much goes to the USAAC for the eight .50 cal armament I don't know. 

There was quite a craze for laminar flow wings in 1940-43, it is a wonder that the USAAC didn't ask for a modified Stearman with laminar flow wings 

It took a while before people realized that the laminar flow wings didn't work in the real world as well as they worked in wind tunnels. 

Even if you are a money cruncher, if your main customer is putting out requirements for _"NEW"_ aircraft (like the XP-55) you can either go along and give then new designs, try to argue with them that the old design with a few tweaks will do just as as good a job, or just go out of business anyway as your competitors give the customer what the customer says it wants. 

to a 1939/40 request Bell offered;






Speed _est_: 425mph at 19,500ft. 

Vultee got a contract covering engineering data and wind tunnel models on June 22, 1940 that lead to






Curtiss submitted the XP-55 Ascender and later built a full sized low powered test rig _at company expense_ to keep the project alive.

Northrop came up with the 






These were ALL in response to the Circular Proposal R-40C, issued November 27, 1939 which called for "a fighter that would be much more effective than any extant--with a top speed, rate of climb, maneuverability, armament, and pilot visibility, all of which would be far superior to those of any existing fighter. In addition, the fighter was required to have a low initial cost and had to be easy and inexpensive to maintain. The Army specifically mentioned in R-40C that they would consider aircraft with unconventional configurations." *

Submitting a slightly modified P-40, even in 1941 when the original engine some of these planes were designed around was canceled and they were scrambling for substitutes was unlikely to find favor with the purchasing agency. They were looking for a major change in performance/capability and not a small increment. Unfortunately the major change was running into some problems with trans-sonic drag and most if not all of the performance estimates were way off. 

In this field of prototypes the XP-53/60 was actually somewhat low risk. Take P-40 fuselage and stick on a new wing and engine. 

Please note that the _original PAPER_ proposals for all these aircraft were made in 1940 when Curtiss was making long nose P-40s and was just starting work on the P-40D/E.

*From Joe Baughers website.


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## GregP (Jul 9, 2014)

Modifications are usually attempts at improvement. Otherwise, why make the mod? 

The only reason is to test a new configuration.

Nice pics, Shortround.


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## Shortround6 (Jul 9, 2014)

Army was looking for a major change, not an extra 20-30mph. 

Granted it was a question of how much performance could be had when, an extra 20-30mph in 6 months or an extra 75mph in two (or more)years, but even number crunchers are looking for what the company can be producing 2-4 years down the road.


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## GregP (Jul 9, 2014)

I am wondering what sort of "major change" the army was expecting without a major change in engine horsepower. Using basic aerodynamics you can easily calculate the horsepower required for a quantum jump in speed, and about the only thing you can do about it is to lower the coefficient of drag and increase the coefficient of lift. Doing both simultaneously isn't easy.

I haven't ever looked at the specifications (R-40C) that were passed around which generated the planes Shortround shows above, but since they are all pushers and of "interesting" design, I'd bet there was something in there leading them all toward that configuration. The group certainly includes some unusual designs. They all flew, but none were world-beaters. I haven't seen a single good review of the XP-55 or the Northrop, and have yet to see any flight report on the Vultee. I wonder if any of this group was a decent aircraft or could have been turned into one.

Had the same amount of effort been put into a new conventional design, I'd bet the performance might have been slightly better than what was actually produced.

I also wonder if the R-40C spec somehow found it's way to Japan since the Japanese Kyushu J7W1 Shinden looks right at home with the bunch above.






And there is more than one such beast about. Here's an SAI-Ambrosini SS.4.






There was a fascination with the configuration even after the war. This is the Sud-Ouest SO.8000 Narval 6.






All flew, but none made production. There are more such oddities, and it's almost as if everyone thought the other guys were onto something new until they built one for themselves and found out otherwise.


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## gjs238 (Jul 9, 2014)

https://en.wikipedia.org/wiki/Saab_21


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## m37b1 (Jul 9, 2014)

P-60x was really just an evolution of the P-40, so -


If the early fighters, P-39, P-40 and P-38 (to a lesser extent) were given the same sense of urgency for improvement/evolution, that types like the Spit and Bf109 had, you'd have:

P-63: In USAAF service, Maybe with Merlin power. (Any thoughts on it's performance with a two stage Merlin)?

P-40Q: (or something like it) Again, maybe with Merlin power. Laminar wing added at some point. 

P-38x: Merlin power, laminar wing . . . . . Who knows.

All of the above would have been good fighters.

BUT . . . . We had better, more modern designs on the way and fighters were needed NOW. 


I guess my answer is P40Q.


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## wuzak (Jul 9, 2014)

GregP said:


> I am wondering what sort of "major change" the army was expecting without a major change in engine horsepower.



The three winners of R40C were supposed to be powered by the Pratt Whitney X-1800 (XH-2600) sleeve valve H-24 engine. This was cancelled, so alternatives were substituted - the Lycoming XH-2470 for the XP-54 and the R-2800 for the XP-56. The Xp-55 went back to the V-1710.


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## GregP (Jul 9, 2014)

I recall these facts, Wayne, but am seriously wondering why the projects proceeded when the projected powerplants weren't going to be available. If they anticipated some level of performance with X HP, they should have been able to anticipate the performance with X - Y HP, and should have elected not to spend the money for such performance.

None of them were parcicularly fast with the Vultee P-54 Swoose Goose coming in at 382 mph, the Northrop P-56 coming in at 417 mph, and the Curiss XP-55 coming in at 390 mph. The Douglas XB-42 ws a pusher and went 410 mph with two Allisons, mostly by virtue of being very streamlined and having little in the way of armament projections sticking out. The Saab J-21A-2 of 1943 managed 404 mph on a 1,475 HP DB 605. 

So NONE of the pushers of WWII were as fast as a decently-designed conventional aircraft. You'd think someone would have noticed after one or two.

I realize the pushers were destined to be very fast when equipped with overpowered jets, but none of the propeller units was especially much of an advance. I suppose they had to try to find out, but so many of them makes little sense to me. Try a coupe and se what you get. If it pans out, you have your advance. If it doesn't why waste so much money on so many of a configuration that offers so little?


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## wuzak (Jul 10, 2014)

Greg, only the XP-54 was measured at that speed. The XP-56 was flown to a speed about 100mph less than that, NACA estimating top speed at around 360mph. The power of the R-2800 was not dissimilar to that of the X-1800/XH-2600, but it caused a fatter fuselage which caused aerodynamic interference with the props, causing them to become much less efficient.

The problem with the XP-54 was that it was huge - large and very heavy. The reason for this is that was the requirements that the USAAF set for it - using the 37mm cannon and having a tilting nose to help aim it, and a pressurised cabin, etc. The XP-54 did receive an engine of similar performance - the XH-2470. There were also proposals to power it with the V-3420.

The XP-55 was a disaster from the beginning.


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## GregP (Jul 10, 2014)

So we agree the pushers were pretty much duds ...


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## wuzak (Jul 10, 2014)

Certainly the XP-55 and XP-56 were duds.

The XP-54 was better, but still not very good.


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## Koopernic (Jul 10, 2014)

I don't think you can declare the CP 54,55,56 duds aerodynamically or the pusher concept dud, or the canard concept dud except the Curtiss XP-55 Ascender, since it never really solved its span-wise flow issue despite trying all the right moves to cure it: slats, wing fences. The problem seems to have been that they missed out on the high powered engines they were designed for. What is not apparent to me is the nature of the engines used: For instance did the Northrop XP-56's PW R-2800 have a single stage, two stage or turbo charger. Did the Ascender receive the turbo charged Allison.

Most 400+ mph piston fighters of WW2 achieved that kind of speed because of a high altitude supercharger of some kind. The DB605 being and exception because of its unique design.


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## wuzak (Jul 10, 2014)

XP-54 had turbos.
XP-55 did not, it had a single stage V-1710.
XP-56 had two stage R-2800.

The XP-55 was essentially a trial airframe, so only used a simple V-1710.


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## Shortround6 (Jul 10, 2014)

Part of the problem was that they were running into that trans-sonic drag thing. (if I have that right) were the drag rises more steeply at _around_ mach 0.6 or 424mph at 20,000ft. SO a lot of the early estimates were somewhat off. 

Different airframes and airfoils ran into this problem at slightly different speeds (slightly being 20-40mph?) but if the onset of the drag rise was at a bit higher speed it offered a considerable advantage in that critical just over 400mph area. 












The Charts are a simple ones and just addresses the wing drag and not fuselage or fuselage to wing/stabilizer junctions (or radiators/canopys, etc).

A 10% change in the drag co-efficient in an 20-30mph speed range is going to play havoc with the drag calculation since the power required goes up with the cube of the speed and the higher speed needs 10% more power before cubing? 

It may be that getting very fast prop fighters (over 440mph??) required not only a lot of power but some rather large elements of luck. Luck in that the shapes chosen for the fighters was done without _full_ knowledge of the problem? 
Some designers/teams guessed right and some guessed wrong?

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## drgondog (Jul 10, 2014)

Shortround6 said:


> Part of the problem was that they were running into that trans-sonic drag thing. (if I have that right) were the drag rises more steeply at _around_ mach 0.6 or 424mph at 20,000ft. SO a lot of the early estimates were somewhat off.
> 
> *Transonic drag usually starts at the leading edge where the rate of change is highest for conventional airfoils (I.E a fat wing has a steep gradient in t/c). The local 'transonic bubble' moves aft to the max T/C (25% for conventional, 45% for a Mustang) as the local flow from leading edge to the Mac T/C approaches M=1. At or about that local 'velocity point' the full blown shock wave forms.
> 
> ...



The Spitfire windscreen hit critical Mach before the wing as an example of your pint - ditto 109, but both the FW 190D-9 and Mustang wing preceded the windscreen/canopy combination..due to the increased slopes of the windscreens, analogous to wing sweep delay of drag rise over wing.


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## Shortround6 (Jul 10, 2014)

Thank you Dragondog. 
It is good to have confirmation from one who has studied and knows the subject rather than one who has read a _little_ and is somewhat guessing (me 

For those who have "America's Hundred Thousand" there is a graph (No 75) on page 593 that shows the _change_ in drag coefficient with mach number for the P-39N-1 and the P-51D. The data comes from different sources but it does show above mach 0.6 a rather dramatic difference in the curves. Up until about mach 0.6 the changes in drag coefficient were straight lines. It is the start point of the curves and the sharpness of the curves that could cause some real big differences between estimates and actual performance until they got a better handle on things.


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## GregP (Jul 10, 2014)

Wave drag is interesting but many of the more conventional designs seemed to cope with it just fine.

I thought most of the piston pushers were well under 400 mph and was not thinking of wave drag as much as comparing them with conventional designs that were almost universally faster than the pushers whether they were canard or not.The Swoose Goose had a tailplane, the XP-56 wasa flying wing, and the XP-55 had canards, but they were all pretty slow relative to the P-47, P-51, and even the P-38. At least the Douglas bomber broke 400 mph.


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## tomo pauk (Jul 10, 2014)

The F4U was making 480 mph with turbo engine aboard, and the F8F-2 was topping 440 mph, despite the whooping thick wing (18% TtC ratio at root) and not so fancy NACA 230 series airfoil. The same airfoil, but of thinner variety, was allowing for a good turn of speed for the Fw-190 and Ta-152 fighters.


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## davparlr (Jul 10, 2014)

The XP-54, 55, 56, were never developed to their full potential so its not reasonable to call them duds. In addition to the aeronautical issues already mentioned, events changed such that enthusiasm for them waned. First they were designed for heavy armament for the interceptor role, a role that soon disappeared from necessity. Second the AAF had an aircraft that was quickly fulfilling their needs, the P-51, which was already pushing the limits of propeller performance. And finally, jet engine development was being recognized at the way to go after the late model props peak out. There was just no money to be spent on these aircraft to fix any normal development problems. Take for instance, the XP-56 for example. The first one was lost due to tire blowing out but the second one was performing well except the engine was not generating full power and the aircraft was flying nose heavy. Issues which could have been reasonably solved but no effort was made due to the above issues.

I like the looks of the J7W1 and SAI SS-4, they look a lot alike.


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## davparlr (Jul 10, 2014)

wuzak said:


> If Curtiss was given the go-ahead to manufacture a "new" P-40 replacement for the late war period, which would be better, The P-40Q with its two stage Allison, cleaned up aero and bubble canopy, or the P-60A (turbo V-170) or P-60D (2 stage Merlin) with its laminar flow wing and revised cooling systems?



Would any of these planes perform better than the P-51? Why waste the money, build more P-51s.


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## GregP (Jul 10, 2014)

I believe the Fw 190D-9 was right in the area where Shortround pointed to. If I recall correctly, it's top speed was 426 mph at best altitude. I believe the Ta 152's were a bit faster with the H-model being faster up around 40,000 feet with engine boost, but no faster than the Fw 190D-9 down near 20,000 feet.

Most of the radial-powered Fw 190's were right in the area pointed out by Shortround and Drgondog as the area of wave drag rise .. in and around 400 to 420 mph depending on variant, weapon racks, aerials, etc. The most often-quoted speed being about 408 mph or so. It would surprise me if the quoted top speeds were other than with clean airframes.

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## Shortround6 (Jul 10, 2014)

The Fw 190D-9 speeds given in the tests on Mike Williams site usually specify wither or not they have the center line drop tank rack (ETC 504 I believe ?).

I can't claim to prove one or the other _if_ this trans sonic drag rise was responsible for the big difference between a lot of the 1938-42 _estimates_ and the actual tested top speeds or not ( and some companies seemed to consistently over claim/estimate).
but it seems reasonable given the general lack of high speed wind tunnels at the time. While research was going on at the time into things like the comprehensibility burble I don't know how long it took to go from the laboratory to the commercial design teams. First effect was noted on propellers so first research was done on airfoils. Pre war the US had a 24 in high speed tunnel?


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## wuzak (Jul 10, 2014)

davparlr said:


> Take for instance, the XP-56 for example. The first one was lost due to tire blowing out but the second one was performing well except the engine was not generating full power and the aircraft was flying nose heavy. Issues which could have been reasonably solved but no effort was made due to the above issues.



There were more issues with the XP-56's performance than the engine giving less than expected power. 

The size of the R-2800 and the shortness of the fuselage meant that the transition from the biggest cross section around the engine was quite steep causing flow separation and turbulent air ahead of the propeller. Additionally the exhaust was ejected into the turbulent flow and the cooling outlets were just ahead of the prop. The XP-56 may not have cracked 400mph even if it had 5000hp.


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## GregP (Jul 10, 2014)

Meaing it was a dog in comparison to more conventionally-designed aircraft.

Most of the R-2800-powered fighters did break 400 mph, even one version of the F6F did.


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## wuzak (Jul 10, 2014)

GregP said:


> Meaing it was a dog in comparion to more conventionally-designed aircraft.
> 
> Most of the R-2800-powered fighters did breal 400 mph, even one version of the F6F did.



Yes, the XP-56 was a shocker.

Production chances were slim even if it was a success. Northrop had to mill the magnesium sheet used in construction as the thickness, as supplied, varied by an unacceptable amount. Then he had to invent a process for actually welding the parts together.


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## GregP (Jul 10, 2014)

I recall they had to invent and re-invent a lot of things to build the SR-71 Blackbird, too. Many things had never been done before.

The same was true of the B-58 Hustler.

It's probably the same for anything that represents a big jump in performance, materials, or both.

That being the case, the Republic XR-12 Rainbow would probably be in that category since it was so much faster than any previous big 4-engine aircraft. It was some 90 mph faster than a B-29 that was at full rattle and trying to go fast!


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## nuuumannn (Jul 10, 2014)

> All flew, but none made production. There are more such oddities, and it's almost as if everyone thought the other guys were onto something new until they built one for themselves and found out otherwise.



There were many aircraft that were configured like this on the drawing boards around the world that were successful, the Saab previously mentioned and the de Havilland Vampire, but the reasons behind this layout were as much down to a desire to place the powerplant at the back - a distinct advantage on prop driven fighters, to enable armament to go in the nose, as much as drag reduction, which is why de Havilland went with that configuration in the Vampire.



> Would any of these planes perform better than the P-51? Why waste the money, build more P-51s.



And that's precisely what the US military did. That's essentially the basis of the discussion in the P-40 with a two-speed two-stage Merlin thread.


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## Koopernic (Jul 11, 2014)

Fw 190D9 speeds and climb rates are somewhat misleading in terms of indicating the potential of the type or as a direct aerodynamic comparison due to the manufacturing problems the airframe suffered in comparison to allied types. 

The point I am making is that excellent as P40Q was the purchasing decisions made by Air Material Command probably reflect, by this stage of the war, an eye to the future of P-40 development into 1945 since they could not assume that operation overlord would succeed or that the disintegration of German industry would happen; they must assume that the Germans are able to deploy new types of aircraft. It's quite clear that the P-40Q would have coped with German aircraft up to the deployment of the Me 109K4 DM (October 44), Fw 190D-9 (Nov 1944) and Me 109G10 (Nov 1944) and that by late 1944 it would benefit from 150PN fuel and improvements to the engine.


Now, back to the Fw 190D9, The single stage Jumo 213A1 engine was already out of date had been taken over from cancelled bomber production (Ju 188E) and so had to be used up. The proper fighter versions the Jumo 213B and C were never produced. Because the engine lacked WEP in its bomber form no less than 3 types of add on WEP were cobbled on as modifications, in many cases, in the field. In theory it could take a motor mounted canon but because of the original propellers and gearbox etc the Fw 190D9 retained the 13.2mm cowling guns which added drag.

FW 190 D-9 Flight Trials
You can see one test here showing 430mph with a bomb rack using B4 + MW50 at 1.8 ata boost. 

Compounding this was the airframe tolerance issues due to the war situation (Forrest factories). One problem was the "engine seal gap". There were actually two of these aerodynamic bulkheads: one at the front of the engine behind the radiator that stopped high pressure air from the radiator and general flight leaking into the engine compartment. This bypassed the heat thrust recovery effect of the radiator and the cowl flaps. The other was the gap between the back of the engine compartment and the firewall ahead of the cockpit. If this was sealed properly it would also stop much of the air from the first seal finding a path out. The problem could be solved by adhering to manufacturing tolerances or by using a strip of rubber. Neither was easy to achieve in the Reich at this time, rubber was quite hard to obtain both synthetic and of course natural.

Using C3 fuel they could get to 437mph and also nearly as much with B4+MW50 at 2.02 ata. This is only 14psig boost at a time the inter-cooled Griffon 60 was doing 21psig and the Merlin 25psig on 150PN fuel.

A most interesting speed curve is 'curve 3' on this speed chart headed "A-ladder als bodenmotor" which shows a stunning speed of 404mph at sea level.
http://www.wwiiaircraftperformance.org/fw190/fw190d9speed2chart.jpg

By optimizing the LF /1st gear or A gear drive for for sea level.

I'll translate:
"A Lader" means 1st gear supercharger from "A" for first and "Ladder" roughly "Loader" i.e. first stage or LF supercharger.
"Als bodenmotor" means "as a sea level optimized motor' boden means ground as in bottom. German language has a separate word for "high altitude supercharger" (Hohenlader) and low altitude supercharger (bodenlader) as well as an engine optimized for sea level *"bodenmotor"*.

A few Fw 190D13 and D12 were produced and a handful entered service, these had a 2 stage 3 speed supercharger without inter-cooler and could do 455mph at altitude. Due to an undersized radiator this was only possible in bursts as the cowling cooling girls had to be opened and this kept speed down to much less. The engine it was to receive was the Jumo 213EB which had an inter-cooler and was expected to operate at 488mph. Engine production was supposed to start in late 1944. The 3 speed 2 stage Jumo 213E1 fitted to the Ta 152H could supposedly also be fitted.

The Ta 152 series could be thought of as Fw 190D with plugs inserted before and aft of the cabin to increase fuel tankage, space for MW-50 and cryogenic nitrous oxide. Speed was about 472mph at about 41000ft and service ceiling 48500ft. Good enough to get to a B-36C in 1947.

Wing span was increased by adding a larger chord at the wing root though the structure was new. This allowed a large amount of fuel to be carried there as well as bigger guns: the long barrel 30mm Mk 103 could be fitted for synchronized firing. The ta 152H had longer wing tips than the Ta 152C which was optimized for lower altitudes, higher roll rate and speed. Clearly the Ta 152c and Ta 152H were going to be somewhat slower than the Fw 190D13 with the same engines due to higher weights and drag but made up for it be lower wing loading and more efficient aspect ratios. The expected growth of the Jumo 213 engine to 2600hp or more would have made this point moot. The Fw 190D13 was to be retained as a fighter bomber, outer wing guns removed and replaced with fuel tanks, TSA2D toss bombing sight fitted. Some were being used to test the Mk 213 revolver canon (which can be synchronized to fire through the prop).

Building a P-40Q infrastructure hurts your P-51H and P-80A infrastructure which would have been needed by 1945 given Luftwaffe developments.


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## GregP (Jul 11, 2014)

Never saw a flight report that showed that speed. And the Ta 152H was a non-starter as a combat aircraft. They never delivered more than 43 of the Ta-152's of ALL varities and they were fighting 1,000 + plane raids in numbers of less than 25 at a time. 

Never a formula for success, and they didn't have it ond the end.


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## davparlr (Jul 11, 2014)

wuzak said:


> There were more issues with the XP-56's performance than the engine giving less than expected power.
> 
> The size of the R-2800 and the shortness of the fuselage meant that the transition from the biggest cross section around the engine was quite steep causing flow separation and turbulent air ahead of the propeller.


I think that if you look at the main fuselage size, not including the aerodynamic flaring behind the cockpit, you will see that there is only a small taper from the engine area to the propeller, certainly not as much as on the 400 mph B-36 engine nacelles, which appears to be about 50% or more over a short distance. And since the XP-56 was cancelled before any wind tunnel testing, flow separation and turbulence concerns are hypothetical.



> Additionally the exhaust was ejected into the turbulent flow and the cooling outlets were just ahead of the prop.



Again, looking at the B-36, it appears to have implemented a pusher prop in very similar manner as the XP-56 with both the exhaust and cooling air exiting right before the prop and I am sure that extensive wind tunnel testing went into making that an efficient design. Also, the Do 335, another fast pusher (and puller) type also put engine exhaust and cooling air right into the rear prop. I think the comment on the impact of dumping exhaust and cooling air into the prop was overstated.




> The XP-56 may not have cracked 400mph even if it had 5000hp.



An unsupportable comment. Although larger, the XP-56 had a very similar configuration as the Me 163 and the German plane was aerodynamically capable of almost 700 mph. Of course the Me 163 was smaller and had a very small engine and fuel was pretty well centered, so stability would have been less a problem. The XP-56, with its heavy 2800 engine amid ship would have taken some work to get the CG correct, It would have always been sensitive in pitch. The airframe itself was very clean and, given it size, as clean as the Me 163 (I don’t know about the airfoil of either, however).

There could be many reasons the XP-56 did not meet airspeed predictions, one, is of course it was a dog to start with. Some more reason are poor engine performance, improper propeller design, poor airflow ducting, fat wings, unrecognized interference drag, improper CG (maybe likely) and others. Maybe the plane was flown out of trim. Wind tunnel testing would have aided significantly in identifying any design problems. They never occurred because the need for such propeller aircraft was past.

Based on many other aircraft of similar designed engine installation, I suspect engine cooling would have been a problem.
View attachment 267011
View attachment 267012
View attachment 267013


However, another significant feature of the XP-56 was its wing sweep; put in for stability ala Me 262. The sweep was 32 degrees, only 3 degrees less than the F-86/Mig15 and it would have encountered handling issues that were yet to be understood. And interesting thought here is that had the XP-56 actually gone into wind tunnel testing in May, 1944, would the advantages of swept wing high speed drag reductions come to the desks of aerodynamicist across the country? Possibly. 

Another note to all those out there that think the Ho 229 could have saved the Reich in 1946. The Ho 229 would have had all the stability problems and more as the XP-56. It was many years away from being a viable warplane.


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## wuzak (Jul 12, 2014)

davparlr said:


> I think that if you look at the main fuselage size, not including the aerodynamic flaring behind the cockpit, you will see that there is only a small taper from the engine area to the propeller, certainly not as much as on the 400 mph B-36 engine nacelles, which appears to be about 50% or more over a short distance. And since the XP-56 was cancelled before any wind tunnel testing, flow separation and turbulence concerns are hypothetical.



True, I overstated the taper.

Look at the relative size of the B-36 props to its nacelles and the XP-56's to its fuselage. 

IIRC the B-36 did have some issues with prop vibrations. I certainly have read that the XB-35 did with its pusher props.

The taper of the B-36's nacelles were over a longer distance than the XP-56s.


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## wuzak (Jul 12, 2014)

davparlr said:


> I think that if you look at the main fuselage size, not including the aerodynamic flaring behind the cockpit, you will see that there is only a small taper from the engine area to the propeller, certainly not as much as on the 400 mph B-36 engine nacelles, which appears to be about 50% or more over a short distance. And since the XP-56 was cancelled before any wind tunnel testing, flow separation and turbulence concerns are hypothetical.



Yes, it is hypothetical. I found it in _American Secret Pusher Fighters of World War II_ as a suggestion for the XP-56's poor performance.




davparlr said:


> Again, looking at the B-36, it appears to have implemented a pusher prop in very similar manner as the XP-56 with both the exhaust and cooling air exiting right before the prop and I am sure that extensive wind tunnel testing went into making that an efficient design. Also, the Do 335, another fast pusher (and puller) type also put engine exhaust and cooling air right into the rear prop. I think the comment on the impact of dumping exhaust and cooling air into the prop was overstated.



The B-36 has turbos, so its exhaust has less (relatively speaking) energy. It is also confined to one area on the prop arc.

The Do 335 had somewhat more distance between its exhausts and rear prop. and, again, is confined to two areas of the prop arc.

The point, as I understood it, was that the exhaust in the XP-56 energised already unstable air flow.




davparlr said:


> An unsupportable comment. Although larger, the XP-56 had a very similar configuration as the Me 163 and the German plane was aerodynamically capable of almost 700 mph. Of course the Me 163 was smaller and had a very small engine and fuel was pretty well centered, so stability would have been less a problem. The XP-56, with its heavy 2800 engine amid ship would have taken some work to get the CG correct, It would have always been sensitive in pitch. The airframe itself was very clean and, given it size, as clean as the Me 163 (I don’t know about the airfoil of either, however).



Entirely unsupportable.

The big benefit the Me 163 had compared to teh XP-56 is that it was not dependent on a propeller for forward propulsion. Stick a rocket in the XP-56 and problems with airflow off the stubby fuselage may not have been as significant a problem as it was historically. 

The theory is not that the turbulent flow off the fuselage caused excessive drag, but that it severely reduced the propeller efficiency.


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## GregP (Jul 12, 2014)

Big difference in cross section between an Me 163 and the XP-56. We have an Me 163, well ... a 100% full scale replica, as well as a real Japanese rocket interceptor based on the Me 163, and you could never get an R-2800 in either of the rocket planes, even if there was nothing inside the fuselage at all.


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## davparlr (Jul 12, 2014)

wuzak said:


> True, I overstated the taper.
> 
> Look at the relative size of the B-36 props to its nacelles and the XP-56's to its fuselage.



B-36 engines were almost twice the power with twice the cooling and twice the exhaust. 



> IIRC the B-36 did have some issues with prop vibrations. I certainly have read that the XB-35 did with its pusher props.



The XP-56 engine was probably more closely coupled than the B-35 or 36. What I was surprised at was that there was no issues with the counter rotating prop gear box. It seems to have been a problem with almost all other applications. Perhaps both of these issues were undiscovered due to lack of flying time.



> The taper of the B-36's nacelles were over a longer distance than the XP-56s.



No doubt but it looks like the taper was pretty severe.


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## davparlr (Jul 12, 2014)

wuzak said:


> The B-36 has turbos, so its exhaust has less (relatively speaking) energy. It is also confined to one area on the prop arc.



Can't argue here although it has two exhaust ports which would have expanded he impact area.



> The Do 335 had somewhat more distance between its exhausts and rear prop. and, again, is confined to two areas of the prop arc.



Yes, but the expansion due to the forward placement of the exhaust would have impacted a larger area of the prop individually.



> The point, as I understood it, was that the exhaust in the XP-56 energised already unstable air flow.



I have a hard time biting on the turbulent airflow. The fuselage appears too clean. Exhaust disruption is a possibility but could be addressed (route exhaust to the end of the vertical stabilizers?). Also, Consolidated, Dornier, and Northrop did not seem too concerned about locating the exhaust in front of the propeller. I would guess that the cause of the poor performance would be the exhaust disruption of the prop or, more likely, and based upon the flight test performance (the plane was nose heavy), the plane was out of trim due to messed up cg. Or, the wings were draggy.


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## davparlr (Jul 12, 2014)

GregP said:


> Big difference in cross section between an Me 163 and the XP-56. We have an Me 163, well ... a 100% full scale replica, as well as a real Japanese rocket interceptor based on the Me 163, and you could never get an R-2800 in either of the rocket planes, even if there was nothing inside the fuselage at all.



The design would have to be blown up to incorporate such a large engine, as the XP-56 was. However, Cd and aerodynamic performance should not change with the size of the design, otherwise wind tunnel models would always have to be full size. Area drag certainly would and power would have to be added accordingly. But, if a small version works aerodynamically, it is reasonable that the big version would also. Now, it is true the two aircraft are not identical but scope wise they are similar.


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## GregP (Jul 12, 2014)

Similar configurations, yes, but the entire fuselage of the XP-56 was pretty fat while the Me 163 is pretty thin by coparison. To be sure, I'd have to take measurements and try scaling an Me 163. but the XP-56 just looks slow to me and it was. Some analysis might shed some light, but it's not that interesting. I've never seen a Cd0 for either aircraft and am not sure if there are already some analyses already out there to peruse.

So I'll agree the planforms are similar and say it might have been a different beast with a jet or rocket engine in it.


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## davparlr (Jul 12, 2014)

Here's another short, stubby and blunt-nosed aircraft about the same size as the XP-56 and is known to be pretty fast.


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## Milosh (Jul 12, 2014)




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## wuzak (Jul 12, 2014)

davparlr said:


> I have a hard time biting on the turbulent airflow. The fuselage appears too clean. Exhaust disruption is a possibility but could be addressed (route exhaust to the end of the vertical stabilizers?). Also, Consolidated, Dornier, and Northrop did not seem too concerned about locating the exhaust in front of the propeller. I would guess that the cause of the poor performance would be the exhaust disruption of the prop or, more likely, and based upon the flight test performance (the plane was nose heavy), the plane was out of trim due to messed up cg. Or, the wings were draggy.



Quickly reading back through the book _American Secret Pusher Fighters of World War II_ by Gerald H Balzer, I've found that the fusealge alone wasn't thought to be the culprit for flow separation and the poor performance of the aircraft. The wing was thick (18%), which would not help, but it was the wing/fuselage interface which caused the flow disruption, due to the change in cross sectional area. The cooling intakes at the leading edge of teh wing were also thought to cause some flow disruption.

NACA's performance summary of the XP-56 _estimated_ its top speed to be 340mph. Clearly there was more than an underperforming engine at play.


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## wuzak (Jul 12, 2014)

wuzak said:


> Look at the relative size of the B-36 props to its nacelles and the XP-56's to its fuselage.





davparlr said:


> B-36 engines were almost twice the power with twice the cooling and twice the exhaust.



And the same diameter. The point I made about the size of teh B-36's props was that more of teh blade area would be in the free stream, and this the efficiency would be higher.

The F8F's prop was entirely in the free air stream, though the size of the radial and the blockage caused by the fuselage would have reduced the prop's efficiency - NACA did a study that showed that propellers were slightly less efficient ahead of radials than in-line engines due to the flow restriction behind them.


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## wuzak (Jul 12, 2014)

We seem to have wandered off-topic and started talking about unconventional fighters. Which is unusual, since the XP-60 was far from unconventional.

XP-60










XP-60A





XP-40Q-1





XP-40Q-2





XP-60
Specifications
Crew: one
Length: 33.625 ft (10.25 m)
Wingspan: 45.44 ft (13.85 m)*
Wing area: 275 ft² (25.6 m²)
Empty weight: 7,008 lb (3,179 kg)
Loaded weight: 9,700 lb (4,400 kg)
Powerplant: 1 × Rolls-Royce Merlin 28 (eqivalent to Packad V-1650-1), 1,300 hp (969 kW)

Performance
Maximum speed: 387 mph (623 km/h) @ 22,000ft (6,706m)
Service ceiling: 29,000 ft (8,839 m)
Time to climb: 7.3min to 15,000 ft (4,572 m)

*Data is from Curtiss P-60 which differs in wingspan from Curtiss P-60 - Wikipedia, the free encyclopedia in wing span, though the area specified is the same.

XP-60A
Specifications
Crew: one
Length: 33.625 ft (10.25 m)
Wingspan: 41.33 ft (12.60 m)*
Wing area: 275 ft² (25.6 m²)
Empty weight: 7,008 lb (3,179 kg)
Loaded weight: 9,700 lb (4,400 kg)
Powerplant: 1 × Allison V-1710 with B-14 turbo, 1,300 hp (969 kW)


Performance
Maximum speed: 420 mph (623 km/h) @ 29,000 ft (8,839 m) estimated **
Service ceiling: 35,200 ft (8,839 m)
Time to climb: 6.5min to 15,000 ft (4,572 m) estimated
12.4min to 25,000 ft (7620 m) (_Vees for Victory_)

*data from Curtiss P-40Q, which now agrees with wiki on span
**_Vees for Victory_ doesn't mention this performance as an estimation. 


For comparison purposes (and since it used teh same engien as the XP-60)
P-40F
General characteristics	
Crew: One
Length: 31 feet 2 in, from P-40F-5-CU 33 feet 4 in (10.16 m)
Wingspan: 37*ft 4 in (11.38*m)
Wing area: 235.94*ft² (21.92 m²)
Empty weight: 6,590*lb (2,990*kg)
Loaded weight: 8,500*lb (3,855*kg)
Maximum gross takeoff weight: 9,350*lb (4,238*kg)
Powerplant: 1 x*Packard V-1650-1, 1,300*hp

Performance	
Maximum speed: 364*mph at 20,000*ft (585*km/h)
Service ceiling: 34,400*ft (10,500 m)
Climb rate: to 20,000 ft (6,100 m) in 11,6 min

Curtiss P-40 Warhawk variants - Wikipedia, the free encyclopedia


P-40Q
General characteristics	
Crew: One
Length: 35 feet 4 in (10.77 m)
Wingspan: 35 feet 3 in (10.74 m)
Maximum gross takeoff weight: 9,350*lb (4,238*kg)
Powerplant: 1 x*Allison V-1710-121, 1,425*hp

Performance	
Maximum speed: 422*mph at 20,500*ft (679*km/h)
Service ceiling: 39,000*ft (11,887 m)
Climb rate: to 20,000 ft (6,100 m) in 4.8 min

Curtiss P-40Q


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## wuzak (Jul 12, 2014)

Oh, and the XP-60 first flew on September 18, 1941. The XP-60 was converted to XP-60D spec with the V-1650-3 in August 1942.


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## GregP (Jul 12, 2014)

Give me the P-40Q any day. 4.8 minutes to 20,000 feet as opposed to 6.5 minutes to 15,000 feet for the XP-6A.

That 4.8 minutes beats a lot of 1944 - 1945 competition.


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## wuzak (Jul 13, 2014)

GregP said:


> Give me the P-40Q any day. 4.8 minutes to 20,000 feet as opposed to 6.5 minutes to 15,000 feet for the XP-6A.
> 
> That 4.8 minutes beats a lot of 1944 - 1945 competition.



I would imagine that the XP-60A could have climbed better had it the 1700hp the XP-40Q had available.


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## GregP (Jul 13, 2014)

Maybe, but it didn't. I'm looking at the planes you wanted to compare, not something that might have been created from it by modification.

If you start doing that, you can't come up with an answer since everything has a "what if" attached to it.


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## Shortround6 (Jul 13, 2014)

The trouble with comparing the P-60 and the P-40Q is that by the time the P-40Q comes along the P-60 is a done deal. And I mean _well_ past 'stick a fork in it, it's done' 

By the time the XP-40Q is flying with a 1700hp engine the P-60 has gone to the "E" model using the same engine as a Hellcat (tested Elgin Field Jan/Feb 1944). And the P-60 is far from a finished product. The Merlin powered XP-60D had crashed on May 6th 1943.
The XP-60E with the Hellcat engine was supposed to do "Maximum speed was 410 mph at 20,200, 391 mph at 24,200 feet," with an engine giving 1650hp at 22,500ft. Of course the radial engine tends to screw up a drag comparison with a P-40Q. 






As I said back in post #3 the P-60s _as built_ were saddled with a 275sq ft wing, which while showing a bit less drag than the P-40 wing didn't really allow a big performance jump with the available engines. The P-60 was supposed to have been refitted with a two stage Merlin but no performance figures seem to have shown up? 

Armament was cut from the initial eight guns to six and then four in an attempt to get the performance up to what was wanted. Had the designers been given a four gun requirement to begin with the wing, while still laminar flow, might have been a lot closer to the size/area of the P-40 wing with some gain in performance. 

The P-40Q performance is certainly competitive with a number of aircraft _in service_ in the spring/summer/fall of 1944. The trouble is that the P-40Q is NOT using a production engine and production engines with that power rating don't show up until the winter of 1944/45 (if then). 

The "what if" falls back to what engines were _really_ available when and what the differences in the air frame (wing/s) were.

another picture:






BTW, for all those people who want to stick an R-2600 on a P-36.... It is just about the same diameter as an R-2800.


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## BiffF15 (Jul 13, 2014)

wuzak said:


> We seem to have wandered off-topic and started talking about unconventional fighters. Which is unusual, since the XP-60 was far from unconventional.
> 
> XP-60
> 
> ...



Gents,

Here is my question or questions:

The first XP-60 has inward retracting landing gear on what looks like an elongated P-40 type wing with 6 guns, while the XP-60A (fatter fuselage) has no gear doors and I'm unable to determine which way the gear went. On the P-40Q models it looks like the standard retract aft gear. Since drag and armament were both of serious importance, why didn't Curtis give the Q model inward swinging gear for less drag? This would open up room for more guns as it appears the Q used some space for the gear, and some for the coolers? 

Cheers,
Biff


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## Shortround6 (Jul 13, 2014)

A P-40 used a fairly narrow track landing gear (not as narrow as some but narrower than others) of 8ft 2.5 in ?











On most of the P-40s there were two fuel tanks _inside_ the wing between the wheels, one behind the other on the centerline. 

Also on the P-40, it used a 5 spar wing with the the #3 spar not quite being mid cord, it was right in front of of the wheel well with #4 being right behind the wheel well ( and having a slight curved section to clear the wheel). 

On the P-40 the landing gear struts did NOT retract into the wing but laid on the bottom of the wing with fairings over them. 






This left spars #1 2 un-notched. Redoing the P-40 landing gear for either inward or outward retraction and flush fitting basically calls for a new wing structure which rather negates the advantages of using the existing P-40 tooling. 

BTW, thanks for the question as I had not really thought about and looked into before you asked.

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## BiffF15 (Jul 13, 2014)

Shortround6,

Thanks for the explanation! I'm thinking another way of looking at is:

-The P-40Q had the fuselage cutdown for the bubble canopy (eventually) which I'm sure was a significant engineering task
-The Q also had to have more engineering work done to integrate the new "nose" / coolers / radiators into the K/N front section
-The standard P-40 wing had to be "clipped", plus tooled for more cooling ducts and possibly two more guns (total of 6)/ or cannons
-The P-60A wing had inward swinging gear (engineering work already done for the Warhawk fuselage integration)

It seems to me that most of the "lego" parts were at the Curtiss plant but not put together into one cohesive design (although the Q in my opine is the ultimate looking P-40 varient). Notice to all I said OPINE.

Why not combine all the above into the Q to lower drag / increase armament and speed? 

I'm guessing that Curtiss had enough on it's plate that it couldn't focus enough talent into solving this. I've been a fan of the Q since I was a kid and always sort of thought of it as a serious "could have been".

Cheers,
Biff


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## Shortround6 (Jul 13, 2014)

To go one at a time:



> The P-40Q had the fuselage cutdown for the bubble canopy (eventually) which I'm sure was a significant engineering task



I don't know. A number of other aircraft were certainly cut down and fitted with bubbles. While there is a change in tooling and fixtures each plane may be an individual when it comes to how this relates to strength/structure and airflow to the rudder. It may be a simple task or not. 



> The Q also had to have more engineering work done to integrate the new "nose" / coolers / radiators into the K/N front section



I believe (and could be wrong) that this is where the majority of the work was done. It is essentially forward of the "fire wall" although it is possible the fire wall was moved. On 90 something percent of the fighters built in WW I the cowling and exterior of the fuselage/engine covering had _NO_ real structural function aside from holding itself together. 



> The standard P-40 wing had to be "clipped", plus tooled for more cooling ducts and possibly two more guns (total of 6)/ or cannons



Clipping _may_ require very little work as the wing tips outboard of the ailerons were a separate structure bolted/fastened to the last real wing rib at that point. Much like the Spitfire or Zero wing tips. Leave off the original wing tip and build fit new shorter one down to a fairing strip or cover. 

The "story" ( and could be wrong) is that the P-40Q used the inner gun bay (Or space for inner gun) for space for cooler with the new intake and exhaust. In fact this "story" _may_ be in error.







Spacing seems to too far from the other guns unless the air took a detour outwards from the scoop (possible if the area required for the cooler exceeded the height available in the new duct.) but it also _appears_ that the intake was not into the wing itself but a duct scabbed onto the bottom of the wing or a combination. Could be wrong but most photos aren't much better. This may well leave room for the restoration of the 6 gun armament with little trouble. 



> The P-60A wing had inward swinging gear (engineering work already done for the Warhawk fuselage integration)



The only real "integration" is running control/hydraulic and electric lines. P-40 wing and fuselage were such that the fuselage _sat_ on top of the wing. the wing was not attached to each side of the fuselage.






Now where Curtiss put the fuel on the P-60 I don't know and what the arrangement of spars were on the P-60 I don't know. Given the extra 40 sq ft of wing area and the need to move the guns outwards to clear a bigger propeller there may have been more room in the P-60 wing to put things. Or the deeper fuselage may have allowed for the fuel tank to be above the landing gear? 

If all you are planning to keep on the P-53/60 is the basic fuselage from firewall to rudder post and _above_ the wing you have a lot more scope to move things around than trying to keep the existing wing structure like the P-40Q.

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## Shortround6 (Jul 13, 2014)

A few more pictures of the XP-40Q














and a model






The duct on the model doesn't seem to quite match the drawing or the location quite match the photos but since there were two/three different bubble top "Q"s you can't be sure something is wrong unless you have the serial numbers and/or date. 

We KNOW the first "Q" _started_ without the bubble and had a different engine.





It looks like the duct _IF_ it got larger near it's middle as the drawing and at least one photo show, could have intruded on the gun space. Since the gun access panel is on the bottom of the wing (ammo went in the top) getting pictures of the gun bays is going to be hard.

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## BiffF15 (Jul 13, 2014)

Shortround,

The last shot is very tellling, as it looks like the first mod was to cut down the fuselage and add the bubble canopy. The nose of that particular airplane looks to be unmoded and sporting a 3 blade prop.

If the plane did have radiators or ducting occupying space the an inboard gun would normally go in, it would be "lightly armed" to say the least. I thought if they went to a more normal inward retracting gear then it would open space for radiators and weapons (move the rad's more inboard from where they currently are depicted. Of course, looking at things in 2014 is a bit different than the early 40's.

Cheers,
Biff


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## GregP (Jul 13, 2014)

Hi Biff,

I don't know for sure, but if you look at the picture of the model it looks as if the vertical space between the bottom of the exhaust manifolds and the bottom of the cowling appears to be about the same height as the spinner.

If you thn look at the last pic, it looks as if the vertical space between the bottom of the exhaust manifols and the bottom of the cowling has a similar comparative measurement.

It's tough to really tell for sure, but the cowling could be after modification.

Can't argue the 3-bladed prop, though.


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## Shortround6 (Jul 13, 2014)

One book says that the wheels were 8ft 2 1/2in from center of tire to center of tire. The tires were also 30in in diameter. 

The Mustang was 11ft 10in. 

You need landing gear long enough to keep the prop out of the dirt 

I won't say it was impossible, the P-47s landing gear got shorter as it retracted (about 9 in ?) and the F8F used a double hinge;






But it does add another layer of complication.

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## GregP (Jul 13, 2014)

Watching a Bearcat gear retraction on jacks is very interesting. 

Most people have never noticed that the gear is double hinged and are very surprised when they see it in person. They can look right at it and never realise how different it is because they are not paying attention to the details, they are just looking at airplanes. Some of these people are pilots, many are A&P mechanics. Once you point it out, the mechanics usually want 50 pictures of it up close, just because it is so unusual.


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## BiffF15 (Jul 14, 2014)

GregP,

Also note the "carb intake"? on top of the nose (like the standard P-40) which is not present on any other P-40Q shot I remember seeing. It seems that the particular shot we are looking at is just after the canopy change. Leads one to wonder why they didn't do it to the standard P-40 since it looks to be a drastic improvement in visibilty.

Cheers,
Biff


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## GregP (Jul 14, 2014)

Hi Biff,

Methinks you are correct. Since the carb air scoop is there, it's probably as you said earlier. I was trying to figure the cowl height and ignored the scoop in front of my eyes.


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## m37b1 (Jul 14, 2014)

That's an XP-40N. Standard P-40 with experimental bubble canopy. This was also included on the Q.


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## Shortround6 (Jul 14, 2014)

The Curtiss fighter timeline is long and convoluted and some of what is printed doesn't make sense (at least to me) so I will try to set out a chronology. Just of orders/first flights/ first production of major models. NO PERFORANCE.
Each series has it's own color, and I left out the XP-42 

Nov 1934-construction of prototype Hawk 75 begins.
May 1935 first flight of Hawk 75 with Curtiss XR-1670 engine.
June 16, 1936 Curtiss gets an order for 3 Y1P-36 aircraft.
Feb 16 1937 Army orders XP-37
March of 1937 sees delivery of first Y1P-36 and testing is done at Wright Field in June.
April 1937 sees XP-37 fly the first time. 
July 7, 1937, the Army ordered 210 P-36As
July 1937 Don Berlin gets permission to install a V-1710-19 in the 10th P-36 airframe to create the XP-40
December 11, 1937 Army orders 13 YP-37s. 
April of 1938 sees first production P-36 delivered. 
October 14, 1938 sees XP-40 fly the first time.
April 26, 1939 sees contract of 524 P-40s placed. 
June 1939 sees first YP-37 delivered.
September 29, 1939 sees Army order two XP-46 Prototypes.
November 27, 1939 has USAAC issue Circular Proposal R-40C which leads to the XP-55 
April 4, 1940 Sees first production P-40 delivered.
May 1940 sees the British (and French) order the model 87 which would become the P-40D/E
June 10, 1940 Sees the proposed substitution of the modified P-40 (D/E)for the experimental P-46
June 22, 1940 sees the USAAC issue a contract for preliminary engineering data and a powered wind tunnel model for the XP-55. 
October 1, 1940, the USAAC ordered two examples of the Model 88 under the designation XP-53 
Nov 15th (?)1940 sees the start of the P-60 project with one of the P-53 airframes to be powered by a Packard Merlin V-1650-1
February 15, 1941 sees the XP-46A (unarmed) fly
April 29, 1941 sees Curtiss submit proposal for the XP-62 to an Army requirement issued in Jan
June 27, 1941 sees Army place a contract for two XP-62 prototypes, one to finished in 15 months and one in 18 months. .
June 30, 1941 sees the first flight of a P-40F prototype with a Merlin 28 engine
July 1941 1941 sees first deliveries of the Kittyhawk I/P-40D/E
September 18, 1941 sees first flight of Melrin powered XP-60
September 29, 1941 first flight of XP-46 (armed)
October 21, 1941, a contract for 1950 P-60As is placed using turbo-charged Allison engines. 
October 28, 1941, 600 P-40Ks were ordered for Lend-Lease supply to China. It was envisaged that this would be the last P-40 model to be built in quantity, the P-60 replacing the P-40 on the Curtiss production lines thereafter
November 1941 sees the P-53 airframe assigned to the P-60 project.
December 2, 1941 sees the low powered flying test bed for XP-55 program first flight. 
December 20, 1941, work on the P-60A project was ordered halted, but it was decided to continue with 3 prototypes, two with Allison engines, one with a GE turbo and one with a wright turbo. Third airframe was to get the Chysler V-16. 
Jan 1942 sees first production P-40Fs with Packard Merlin engines. 
May 1942 sees first production P-40Ks come off the line. (some sources say Aug ?) 
July 10, 1942, a USAAF contract was issued for three prototypes under the designation XP-55.
August, 1942 sees original XP-60 repowered with two stage Merlin V-1650-3 and renamed XP-60D
November 11, 1942 sees first flight of XP-60A with Allison but without turbo
Nov 1942 also sees Curtiss propose using the P W R-2800 on the P-60 airframe. Army buys it to the tune of a 500 plane order. 
Nov 1942 sees first P-40Ms built with Allison engine using 9.60 supercharger gears. None are for US use, all are for lend-lease. 
December 2, 1942 sees Army cancel the XP-60 with Allison engine and Wright turbo and substitute P W R-2800 with single rotation prop instead of contra props. designated XP-60E 
March 1943 sees first of the Lightweight P-40N-1s
March 1943 also sees at least ground testing of first XP-40Q although it _might_ be with a single stage engine? 
May 26, 1943 sees first flight of XP-60E
July 19, 1943 sees first flight of XP-55
July 21, 1943 sees the XP-62 program pretty much canceled after delays and official flip-flops, limited work to continue for research. 
Dates for XP-40Q are hard to come by, we know it was being tested (2nd airframe ?) in Nov 1943. 
Nov 30 1944 Last P-40N-40 rolls out the door.

I hope this helps. 
Hopefully it shows that Curtiss was NOT sitting back fat, dumb and happy building P-40s

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## Shortround6 (Jul 14, 2014)

m37b1 said:


> That's an XP-40N. Standard P-40 with experimental bubble canopy. This was also included on the Q.



I believe you are correct. Descriptions of the 1st XP-40Q say it kept the turtle back *and* kept the top mounted airscoop, at least to start.


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## m37b1 (Jul 14, 2014)

Nice job! I'll need to draw a family tree for the Curtiss efforts.


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## GregP (Jul 14, 2014)

It'll look more like a weed.

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## drgondog (Jul 15, 2014)

Shortround6 said:


> I believe you are correct. Descriptions of the 1st XP-40Q say it kept the turtle back *and* kept the top mounted airscoop, at least to start.



The first XP-40Q was P-40K-10 42-9987. I once found an obscure pre-flight test reference report citing engine vibration rests in May 1943 for 9987.


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## GregP (Jul 15, 2014)

I've posted it before in here, but here's my drawing of an XP-40Q. Actually I drew the 3-View. The 3-D illustration came off the web and I added it just for decoration ... it's not my work.






I might have to do one of XP-4Q #1, but the problem would be to find good views all taken at the correct point in time ....


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## m37b1 (Jul 15, 2014)

Man! That plane looks good from any angle!


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## GregP (Jul 15, 2014)

Does, doesn't it? Even if it wasn't put into production it sure LOOKS like it should have been.

Ah well, no use crying about what didn't happen and, as I've said before, the alternative planes we DID produce did the job quite well.


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## vikingBerserker (Jul 15, 2014)

Man that is a good looking aircraft!


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## BiffF15 (Jul 15, 2014)

Yeah, the Q is definitely my favorite looking P-40 as well!


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## davparlr (Jul 17, 2014)

back to an off subject topic.


I read your review of the XP-56 on another site and I thought it was very good and generally well thought out. However, there are several areas that still cause me mental confusion (not a difficult thing). I’ll address these as I go along.



> Quickly reading back through the book _American Secret Pusher Fighters of World War II_ by Gerald H Balzer, I've found that the fusealge alone wasn't thought to be the culprit for flow separation and the poor performance of the aircraft.


 I agree, it looks pretty smooth


> The wing was thick (18%), which would not help,


 true, but the F8F also had 18% thickness


> but it was the wing/fuselage interface which caused the flow disruption, due to the change in cross sectional area.


 definitely could be the problem however other aircraft had reducing cross sectional area interfacing with the wing interface, the F8F and F6F are a couple. These reductions were less than the XP-56 but it in turn was much less than that of the B-36.


> The cooling intakes at the leading edge of teh wing were also thought to cause some flow disruption.


 also possible. They look clean and not particularly different from other successful designs. Internal ducting could also have caused a problem which could also affect engine performance. They also do not look as near as disruptive as the Do 335 aft engine cooling intake would be.

A bit more on exhaust location. In the thread “B-36 – Why a Pusher” post #23 clearly shows the exhaust exits are located at about 50% of the length of the props and about 6 ft in front of the props. The XP-56 exhaust at approx 10% of the length of the prop and about 4 ft in front of the prop. However, I do not think either one of these is a big issue. Unless the fuselage is in stall, an intolerable situation, the airflow will follow the outline of the fuselage which would keep any turbulence from the exhaust close to the hub, and the least sensitive part, of the prop. This is apparent by the exhaust stains on the sides of airplanes. 



> NACA's performance summary of the XP-56 _estimated_ its top speed to be 340mph. Clearly there was more than an underperforming engine at play.


I am not sure this was done by NACA but rather by the military. In any case, I think this was just an extrapolation of flight test data and not a technical analysis of the design.

The XP-56 did not meet its performance criteria. It may have been a serious design flaw or a combination of some or all of the above issues, or a faulty engine. A component analysis indicates a solid design. The fuselage appears to be as clean and aerodynamic design as possible. It is bit portly for my liking but portly does not mean aerodynamically inefficient (the Bell X-1 was a bit portly, too). The wings, while a bit thick, was not out of the mainstream of high performance design and was similar to other aircraft in overall size, and it was swept which could have provided a much better limiting mach. Add on to that well know vertical tail designs and that is the overall aerodynamics, nothing stretching technology. The interfaces of all that could indeed be a problem, but again, something not new technology, something wind tunnel testing could identify, and reasonable fixes could be made. My overall feelings, based on pilot reports on heavy nose flying and effort to keep the plane flying, is that the plane was never properly trimmed or Cg properly placed. Both could affect top speed and fuel performance. However even if the fixes were simple and the performance criteria was met, the plane was advanced and would have taken some time to work out the issues of a horizontal tailless flying and also operating a swept wing aircraft. The need for these planes had passed.

Without wind tunnel data, we will never know. And, as with so many old aircraft operations, the endless debate goes on.


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## Clayton Magnet (Jul 20, 2014)

Separated at birth?
anyone?
ah to hell with it


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## Clayton Magnet (Jul 20, 2014)




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## GregP (Jul 20, 2014)

Nice comparison, Calyton!


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## wuzak (Jul 20, 2014)

The P-60E is a nice looking aircraft.

I guess the belly radiator is the oil cooler? Maybe the intercooler?

The P-60E used the same R-2800-10 as the F6F and was faster, though slower than teh similarly powered F4U.


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