P-40Q vs P-60A/D

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

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

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.

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.

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?

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 'drag rise' defined as a 10 increase in Cdo (The compressibility factor of drag added to Cdo) is associated with the build up from the adverse pressure gradient now beginning at the leading edge of the airfoil instead of the incompressible flow separation normally associated around the max T/C..

The point was reached as low as M=.55-.60% for the P-38, closer to .60-.62 for the 109 and .66 for the Mustang

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.

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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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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.

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.

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.

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.

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.

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?

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

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.

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?

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.

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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.

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.

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.

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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.

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!

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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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.

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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.

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.

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.

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.

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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.

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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.

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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 267011View attachment 267012View 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.