Could you have designed a better P-39?

[davebender]

Luftwaffe Resource Center - A Warbirds Resource Group Site - Heinkel He 112
No. I mean the He-112B. Prototype first flight was May 1937. So you've got plenty of time for Bell to license the design and get it into production.

 

[Shortround6]

The YP-39 during testing at Wright-Pat during 1939 reached 390 at 20kft (of course armament was not fitted) It was estimated that with armament and war kit it would have reached 375 at 20kft.

There is some debate about this claimed performance and a some evidence that no such flights with those performance figures were ever flown.

 

[Shortround6]

In other words, scrap the design and start over with something better.

Perhaps Bell could purchase rights to license build the He-112B and DB601 engine. You get an overall better aircraft and can fire the 37mm cannon through the prop hub. 8)

The better aircraft part is debatable.
the DB 601 wasn't really a production engine in 1937 was it?
The German's didn't seem to get much of any gun to work firing through the prop hub until after 1940.
Max inside diameter of the tube through the 601 engine was in the order of 70mm wasn't it?
Might be tad small for the American 37mm gun:

File:M4 cannon drawing.jpg - Wikipedia, the free encyclopedia

even if the barrel fits there is quite a bit of gun to fit behind the engine without intruding into the cockpit or moving the cockpit rearwards.

 

[MikeGazdik]

I think we are getting too radical. Improving the P-39 is the name of the game, not replacing it all together.

In my opinion, 3 thing items detracted from the P-39 : Altitude capable engine, Range, Armament.

If the 1st is addressed, the other two can be dealt with through evolution. The armament would be changed as many fighters were during the war. The range would be handled in a smaller scale by drop tanks and maybe some internal changes.

The plane itself will not be made into something that will negate the need of the P-51, but it may be a large step between the historical P-39 and the P-51.

The P-39 obviously had limitations. But I think because the P-40 was just enough better, and produced in greater numbers early in the war, the P-39 was easy and quick to be put aside by the USAAC. It wasn't a pile of junk, as the Russians disproved, its main detractor was high altitude performance.

 

[Colin1]

The P-39 obviously had limitations. But I think because the P-40 was just enough better, and produced in greater numbers early in the war, the P-39 was easy and quick to be put aside by the USAAC. It wasn't a pile of junk, as the Russians disproved, its main detractor was high altitude performance.

In what way was the P-40 'just enough' better?
It couldn't fly any higher, never carried cannon and no version of the P-40 was as fast as the P-39.

 

[MikeGazdik]

In what way was the P-40 'just enough' better?
It couldn't fly any higher, never carried cannon and no version of the P-40 was as fast as the P-39.

But the P-40 was a traditional layout with the engine in front, so I think it was more readily accepted by pilots and possibly maintenance. And it also had slightly more range, and the armament after the B/C models was standardized.

Thats what I meant by "better", I should have clarified. Speed wise the Airacobra was faster, and in handling they are very close.

 

[davebender]

The P-39 had some bad handling characteristics. Like entering a stall while conducting the low level strafing runs it was designed to do. The P-40 was somewhat underpowered (power to weight ratio) but it had no bad habits. At least that's my impression (which may not be correct).

 

[krieghund]

The company was trying to better the design

Case in point, the XP-39E (Model 23) had the following improvements

A 2 stage 2 speed supercharger on the V1710-47 1325HP at T.O. and 1150 HP at 21,300ft

A larger wing with laminar airfoil, b=35' 10" S=236

Speed 386 Mph at 21,680ft
Ceiling 35200ft

Weight empty = 6936 lbs
Loaded= 8200
Gross= 8918

Fuel normal 100 US gal Max 150 US gal

Contracted=11 Apr 1941 First flown 26 Feb 1942

Also the XP-39 (model 11) was ordered on 7 Oct 1937
First flight 6 Apr 1939 Flight to 390 mph at 20000ft Wednesday 11 Apr 1939

Also you guys don't want the He-112 you want the He100D in this same time period.

 

[krieghund]

The NACA did its best to help industry realize these dramatic increases of speed in production aircraft. This effort can be seen clearly in Langley's cleanup of the Bell XP-39 Airacobra, eleventh in the series of military planes subjected to the NACA operation. Bell's chief engineer Robert J. Woods (a former LMAL employee in Eastman Jacobs's VDT section) had designed the unconventional plane-its power plant amidships, at the center of gravity, and its cannon in the nose-as a 400-MPH fighter. At Wright Field in the spring of 1939, the unarmed XP-39 prototype (with a turbosupercharged Allison engine, rating 1150 horsepower) flew to a [199] maximum speed of 390 MPH at 20,000 feet. The aircraft reached this speed, however, with a gross weight of only 5550 pounds, thought to be about a ton less than a heavily armored production P-39. That meant that the existing aircraft, when normally loaded, would have a hard time exceeding 340 MPH. Still, the test performance impressed the Air Corps enough for it to issue a contract, three weeks later, for 13 production model YP-39s. Gen. Henry H. "Hap" Arnold, desperate for a new fighter, hoped that the speed of the airplane could be increased to over 400 MPH by cleaning up the drag. On 9 June 1939 he formally requested NACA approval for immediate testing of the XP-39 in the Full-Scale Tunnel.(21)
Actually Langley had received the XP-39 from Wright Field three days before Arnold's request, which had been put in writing on 6 June to satisfy NACA headquarters. On 8 June, Robert Woods and other representatives from Bell arrived at Langley to see the NACA's experimental setup and witness the initial round of tests. For the next two months the FST team systematically investigated the airplane's various sources of drag. On 10 August, Lawrence D. Bell, president of the Bell Aircraft Company, visited Langley to discuss the test results obtained to date. Bell was shown preliminary data from the FST indicating that the prototype in a completely faired condition had a drag value of only 0.0150 compared to 0.0316 in the original form. This meant a maximum increase in speed, if all the NACA's suggestions for drag improvement were met, of 26 percent. The NACA realized, of course, that not all of the changes to the configuration studied in the FST were feasible for the production aircraft. Fifteen days later, the head of the FST team reported that by cuffing the propeller at the point where it met the hub, streamlining the internal cooling ducts of the wings, lowering the cabin six inches, decreasing the size of the wheels so that they could be completely housed within the wing, and removing the turbosupercharger and certain air intakes, the speed of the XP-39 airplane for a given altitude and engine power could be increased significantly. Extrapolating from the same weight airframe to a more powerful (1350-horsepower) engine with a geared supercharger, he estimated that the top speed attainable with the aircraft might be as high as 429 MPH at 20,000 feet. The FST head did not know precisely how much additional air would be required to cool the bigger engine, but he did believe that even if this increase was very large, it would not prohibit the plane from obtaining at least 410 MPH.(22)
Bell incorporated enough changes recommended by the NACA to improve the speed of the airplane by about 16 percent. These changes included installation of an engine that could be equipped with a gear-driven supercharger but had only 1090 horsepower - 60 horsepower less than the engine which had driven the unarmed XP-39 to 390 MPH at Wright Field in the spring of 1939 (and 260 horsepower less than that used hypothetically by the FST head in his paper study).
Source: NASA History website ch7

20. See Paul L. Coe, Jr., "Review of Drag Clean-Up Tests in Langley Full-Scale Tunnel (From 1935 to 1945) Applicable to Current General Aviation Airplanes," NASA TN D-8206 (Washington, 1976) and Laurence K. Loftin, Jr., Subsonic Aircraft: Evolution and the Matching of Size to Performance, NASA RP-1060 (Washington, 1980), pp. 265-268.
21. Arnold to NACA, "Full-Scale Wind-Tunnel Tests of XP-39," 9 June 1939, RA file 674.
22. Smith J. DeFrance to Chief, Aerodyn. Div., "Estimated High Speed of the XP-39 Airplane," 25 Aug. 1939; Abe Silverstein and F. R. Nickle, "Tests of the XP-39 in the Full-Scale Tunnel," 27 Sept. 1939. Both in RA file 674.
23. "Comments of Representatives of Bureau of Aeronautics on Report of Drag Reduction on XP-39 Airplane," 2 Nov. 1939, ibid

 

[Shortround6]

The claimed 390mph of the XP-39 before the wind tunnel tests must be viewed with some suspicion.

Unless something has changed in the last few years, no real record of such a flight has been found. No date or name of pilot who achieved this speed.

The original extension shaft had some torsional vibration issues and was redesigned with a larger diameter and thicker walls. The new shaft was not fitted to the plane until it came back from Langley. Some sources claim that because of the shaft problem NO full power flights were made during this time period. RPM being limited to 2600rpm I believe. There were also issues with both radiator and oil cooling.

The NACA also reported that the inter-cooler design allowed way too little airflow at climbing speeds and way too much airflow (adding to drag) at high speed. Perhaps their calculations were in error?

There were also reported problems with directional stability.

How many hours of flight time did the XP-39 achieve before it was sent to Langley?

 

[davebender]

Also you guys don't want the He-112 you want the He100D in this same time period.

That depends on the cut off date for obtaining a license agreement. I think something could be worked out during 1937 when the He-112B was available. But I doubt the American Government would allow a license agreement after September 1939.

Even better idea....
The Fw-190 prototype was flying 1 June 1939, powered by the BMW139 radial engine. Rush the license agreement and get the blueprints out of Germany prior to the invasion of Poland. Now make an American version of the Fw-190 powered by the Wright R-2600 engine. You might beat the German version into mass production as the BMW801 engine wasn't ready for prime time until 1942.

 

[krieghund]

Not trying to deviate too much....

The He100V1 flew 22 Jan 1938 and it pretty much has the shape of the 'D' production series
The He100D-0 production armed batch flew Sept 1939 and pretty much retained the demensions of the 1st prototype.

Just imagine it with a DB601E installed and 3 x MG151/15

The Fw190v1 flew 1 Jun 1939 and had shape differences of the 'A' series
The first of what could be reconized as the FW was the the Fw190V5 in Apr 1940 and the first Fw190A-0 production series on Mar 1941.

The He100 was more developed at this date and would have caused problems during the BoB as it had alot more endurance than the Bf190E and 50 mph faster

 

[davebender]

We have no choice. Making the P-39 into a decent combat aircraft is easier said then done.

 

[gjs238]

Returning to USAAC Circular Proposal X-609 in February 1937 and the planes that were designed as a response...

Turbochargers were perceived as the solution to high altitude performance (P-38, P-39, and later Seversky/Republic designs.)
The P-38 Seversky/Republic designs made the turbo work, why not the P-39?

It seems the basic design was just too small - more room was needed for proper inter/after cooling and fuel capacity (and to accommodate the pilot.)
It also seems that an enlarged P-39 (ala P-63) could accommodate the turbo and necessary cooling without requiring extensive ductwork as with front engine/rear turbo designs.

?

 

[Shortround6]

It also seems that an enlarged P-39 (ala P-63) could accommodate the turbo and necessary cooling without requiring extensive ductwork as with front engine/rear turbo designs.

Considering that the P-63 had no inter-cooler (or room for one) and tried to rely on water/alcohol injection instead I would say that any enlarged P-39 is going to have to be even larger than a P-63.

Please note that two different mock inter-cooler set ups were tried on a later P-39. Both reduced the speed of the P-39 by 30mph or better at lower altitudes because of increased drag. A third or fourth design may have done a bit better but you are going to wind up trading better high altitude performance for less low altitude performance.

Also noting that other modifications were made to the engine to allow it to make the 1325hp or more of the later models besides just putting on a different supercharger means that a 1939-40 version of the plane will have the extra weight and drag of the turbo installation and larger fuselage but no additional power untill the plane exceeds 15,000ft or so of altitude.

 

[Shortround6]

Still haven't seen anything to convince me that either Heinkel would have been any better than the American planes of the time (1940-41).

Would either one carry the fuel the Americans required for range?

Considering that the engine mounted cannon never worked in SERVICE use until until late 1940 or early 1941 and that the MG/FF cannon was feed from from 60 round drum means a rather limited armament.

Are you proposing that the Americans adopt Germans guns JUST for this fighter?

The Americans could probably have built faster, better climbing fighters in 1938-1940 if they adopted both limited fuel and limited armament (and nobodies planes had armor or self sealing tanks at the time) and lighter structure.

 

[davparlr]

The P-39 should have been much better. XP-39 appears to have been better until AAF redesigned it.

Install Merlin (preferred) or Allison w/turbo, hire North American engineers to redo aero, replace wings with larger, cleaner wings, more fuel in new wings and anywhere else, one 20 mm and four .50s

I don't see a problem with putting in the P-38 Allison with turbo and intercooler. Looks like it would fit and high altitude performance would improve significantly.

 

[Shortround6]

The P-39 should have been much better. XP-39 appears to have been better until AAF redesigned it.

It appears that the XP-39 never flew at the often touted speeds and climb figures that are given for it.

Given the NON-OPERATIONAL status of the turbo charger at the time the AAF may have had little choice in the redesign if they wanted planes in squadron service in 1941.

Merlin's track record in 1939 was being installed in Hurricanes and Spitfires with fixed pitch props and going into Fairey Battles with constant speed props. It also offered 100-150 less horsepower for take-off.

 

[Colin1]

The P-39 would have benefitted from a better supercharger, this could have potentially come from the V-1650 so Bell and the USAAC surrendering the notion of a turbocharged fighter was not the death-knell in any sense for the Bell fighter.

The P-39 was a tight ship, it was the smallest possible wrapper around the biggest (for the period) armament and powerplant. It's safe to speculate that the V-1650, with better supercharging, would not have posed much of an intrusion into space that the V-1710 wasn't currently occupying.

The altitude issue was not beyond redemption, the biggest problem for the P-39 in such a tight design was that someone forgot the fuel.

A wet wing needs to be considered out of necessity. An arrangement with the guns bay running ventrally (for servicing access) to the nose and a fuel cell on top of this directly in front of the engine, with the pilot accomm directly forward of this might also be considered. This arrangement gives the pilot an unprecedented view of his battlespace and the fuel cell could well have little adverse effect on c of g in this location.

The downside is the proximity of pilot to the airscrew, if he has to belly in and the blades fold back in the characteristic fashion, are they going to chop in to the cockpit and cause him harm? An engine emergency cut-out might allay fears. The second point would be in the instance of a rough belly-in, if the powerplant is dislodged, it will invariably move forwards and rupture a fuel cell containing an unspecified amount of fuel with the inevitable consequences for the pilot.

Somewhere down the P-39 line I would take the canopy arrangement the same way as the P-47 and P-51; the omission of the doors would facilitate more conventional side-panel instrumentation in the same way that it did with the Typhoon and the now-solid side walls add to the structural rigidity. A sliding hood would give better all-round vision previously cramped by framing and the mast.

 

[gjs238]

While I think that a better supercharger was technically possible at the time of the P-39 debut, one was not developed and not available. The most feasible way to obtain good altitude performance was via turbcharging, as was done with the P-38 and the Seversky/Republic designs.

The turbo improves high altitude performance, but weight and drag penalties degrade low level performance.
The P-38 and Seversky/Republic designs are subject to the same benefits detriments, yet they managed to implement the turbo successfully.

Why the disparity?
Why can't the turbo work for (an enlarged) P-39, yet be successful for the others?

If the turbo is so bad, then why not remove the turbos to lighten up simplify the P-38 or P-47 on the argument that low to medium altitude performance will improve?