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Excellent first hand information, thanks for posting. It was also said that no tumbling was possible during normal flight or landing even with nose ammo expended. The plane needed to stall at a high AOA at near vertical. Did your test verify that? Thanks again.I was one of the participants in the 1970s P-39 tumbling study. And yes it was totally an unofficial and unfunded test. But now everyone involved is either retired or passed on, so no one can get in trouble, but it can be good lesson on how sometimes historic research gets done. At the time I was an aerodynamics engineer at Beech Aircraft involved in new aircraft development and as part of my job I did both flight testing and wind tunnel testing including many spin tunnel tests at Langley. I studied aviation history both as a hobby and to gain knowledge and data for my vocation of engineering. A friend of mine, who was also an aeronautical engineer and history buff, had been doing research on the P-39 stories of tumbling. He had gone thru the old Wright Field reports and noted that they had seen no tendency of the aircraft to tumble, but he also noted that the flight testing was all done with an equivalent full mass of ammunition in the nose and full fuel. He had interviewed several P-39 combat veterans and they had indicated to him that the tumbling occurred on the return from combat missions when the ammunition had been expended and fuel burned off. He asked me if I had at looked at the NACA P-39 spin tunnel test data? I told him yes, but only from the point of view of the effect of the door opening and of the pilot escape path. But I also informed him I had a spin tunnel test to do at NASA Langley in a few weeks and would ask see the P-39 test data while I was there. My NASA friends pulled the P-39 test file for me and the NACA spin tunnel test had been done at a request from the AAF which called out the test requirements. The AAF had only requested testing at full gross weight and that was all that was done. There was no sign of tumbling seen. Now one has to remember that in WWII the Langley tunnels were running 7 days a week, three shifts a day, so there was little time was for exploring outside the formal test request. During a coffee break in the spin tunnel conference room, I brought up the P-39 tumbling. The NASA engineers got interested and also read the file. Now in the 1970's, the offices, hallways, and conference room in the spin tunnel building all had old spin tunnel models hanging from the ceilings. Now it just so happened one of the models hanging in the conference room was the P-39. Also Jim Bowman, head of the spin tunnel at that time was in on the coffee break and mentioned that in WWII he had been an apprentice in the model shop where the P-39 model was constructed. Well as you probably know engineers and wind tunnel technicians are nothing but over aged little boys, thus a plan was formed to refurbish the P-39 model and test it in those other flight conditions. Of course this was all done on lunch hours and coffee breaks! A few check points were made at the gross weight loadings which repeated the original WWII tests. The model was then reballasted to simulate no nose ammunition and low fuel and retested. And with this loading the P-39 model would sometimes tumble.
Disagree with you on the crappy altitude performance.As I read through this the one over riding thought about the XP-39 is that it was not a very good fighter as built. Kelsey wrote the specs but he was very disappointed in the performance and room for growth into a viable high altitude capable Pursuit aircraft. It was "the Small Solution' compared to the XP-38. It was always cursed with marginal stability, short range and crappy altitude performance (Allison issue, however).
Bell just never did develop either experimental or production aircraft considered better than average (except by 1943 VVS standards) - nobody even claims that either the X-1 or X-1A were 'great'. That changed with Bell Helicopter due largely to Bart Kelley post WWII.
Wuzak,
While the normal cruise of a P-51 was about 275 mph, a P-51 didn't have to speed up to cruise with a Mosquito. Mostly the 275 mph cruise speed of the P-51 was to allow it to zig-zag above the bombers to it could stay with them. A P-51D/K had a range of 1100 miles at a speed of 395 mph at 2400 rpm according to the 1944 pilot's manual charts from this forum. Of course, that was not the optimum range for the P-51D/K, but it COULD do it. The 275 mph was the best bomber escort cruise. Heck, it can go 1,500 miles at 370 mph at 2,500 rpm with 269 gallons of fuel on board.
Watton was covered with a thin layer of snow as they took off at 0920 in NS569. Prior arrangements were made to rendezvous at 0925 with four P-51s from 20th FG at 18,000 feet over Cromer. They would provide escort to Stettin and return.
The Mosquito met the fighter escort as planned; but now heavily loaded with l,000 gallons of fuel, flew at a severe speed disadvantage. Geary attempted to maintain economical cruising speed but outpaced the P-51s and was forced to throttle-back to continue flying formation with them. The Mustangs had long-range drop tanks and were also fully loaded. Once involved with enemy action, they would jettison their tanks, and therefore, were attempting to conserve and obtain maximum range from their fuel supply. This exacerbated the problem. It was a very-long flight to the Polish border, and on three occasions Geary throttled-back and did not receive the mileage planned.
The typical Mosquito wasn't going to do that. Normal cruise was about 295 mph and could go to 325 mph and later 360 mph or so. Yes, it could go faster, but not at cruise speed. Anything over 340 mph was getting into shorter ranges unless you had a specific type, like maybe a 1945 NF. Mk 30. It COULD cruise at 364 mph at 27,500 ft, but max speed was 397 mph at best altitude and the range at 360 mph wasn't all that great. There really weren't all that many Mosquitos that could hit much more than low 400 mph.
The F Mk. II could hit 358 mph. The NF Mk. XV could hit 408 mph or so. The B Mk. IX could hit right at 405 mph. The FB Mk. VI could hit 368 mph or so. The IV could hit 367 - 380 mph depending on the exhaust stub. The PR Mk. XVI could hit 401 mph. These are all maximum speeds in FS gear and optimum altitudes. Any MS gear speed was 15 - 20 mph slower. Yes, it was a fast, amazing airplane, particularly when cruising into hostile airspace, but not faster than a P-51 if the P-51 wanted to fly that fast.
Hi Biff,
By "not babying the Allisons," I mean Steve was sometimes pulling 55"+ MAP. Not always, of course, but I'm assuming when they went vertical on the way up from less-than-high airspeed. The P-38 will outclimb the P-51 at lower altitudes, but not likely from low-but-identical airspeeds. I rather doubt the P-51's were babying their Merlins, either when looping from airshow airspeeds. Neither was either type using even full military power in the airshow clip. After all, they weren't exactly flying with 145 performance number fuel. I doubt if anyone in the formation was pulling more than about 1,000 - 1,100 hp.
As for the comment about what it doesn't show (not yours, Biff), what it clearly tells me is the dissimilar aircraft have no problems flying formation. Our fighters cruise to airshows and other public displays together routinely in formation, and they don't have any trouble. We have even had a P-47, P-38, and P-51 information with an F-22, and THEY didn't have any trouble with it, either.
In fact, I have never heard any of our pilots, speakers, or visitors say they had any trouble flying in formation with another aircraft type. Not sure where the notion they would have trouble staying in formation with dissimilar aircraft would even come from.
I'm sure they wouldn't do it for extended periods unless there was a reason to do so, but the capability is certainly there. Liquid-cooled inline fighters would probably have trouble flying for extended periods at 185 mph (plug fouling), but the radials would have little difficulty cruising at 250 - 280 mph except for the extra fuel consumption. They certainly have the ability to cruise with one another for some time, should the need arise, regardless of altitude, unless you happen to be right at the altitude where a supercharger in one of the birds changes gears automatically.
I'd place a bet that Biff flew formation in an F-15 with something other than another F-15 at some point.
Mal H, THANK YOU for posting!
Hi Biff!
WWII engines are surprisingly reliable. I worked the Planes of Fame airshows for more than 10 years and we generally flew three days (Fri, Sat, Sun) with something like 65 - 70 sorties per day. We had a VERY low rate of problems. Did we have issues? Sure.
Figure 50 sorties per day for 3 days to be conservative. That's 150 sorties per airshow for 10 years. 1500 sorties. I recall 1) one Corsair that couldn't get one wing to fold down, 2) a flat tire, 3) A Grumman F3F that backfired during landing and blew the crankcase gaskets out (dropped oil everywhere), and 4) a couple of aborted takeoffs due to a rough engine. That's around 5 aborts in 1500 sorties, or about 0.3% aborts. Pretty good! I might have missed a few more, but not many. So, these engines are NOT fragile.
Typically, they use some decent power for takeoff / Initial climb, and then throttle back for economy. The government isn't paying for fuel. Steve Hinton told me he doesn't shy away from using 2,000 Hp on takeoff in a Bearcat or other R-2800 aircraft, but not for extended periods. A clip below shows him doing some aerobatics in a Tigercat. Listen and tell me he's not running the R-2800s above cruise power!
In our P-38, we are not running the turbos. Thye are installed but non-operational. I know of only one P-38 currently running the turbos at this time, but I suppose there coupld be more than one. In a stock P-38, the little scoop on the side of the boom near the trailing edge is the turbocharger air intake . Since we aren't running the turbos, we have that blocked off and the carburetor intake feeds from the center of the boom-front airscoop intake. The outer two boom-front air intake sections feed the oil coolers.
As for the Allison operation in the P-38, the "normal" military max was about 1100 HP / 2600 rpm at sea level AND at 30,000 feet, 57" MAP. Steve might pull that or close to it briefly during a vertical climb for maybe 5 - 10 seconds or so and then throttle back on the way down because there isn't any reason to rawhide the engines unnecessarily. Then again, he might leave power in it all the way around. I have not flown a fighter through a vertical maneuver and don't know for sure. I have ridden in a P-51 through a loop / roll, but confess I wasn't watching the throttle at the time. Power WAS added for the loop, but we also got some airspeed from a slight dive to start. These aircraft normally cruise at economy settings and only throttle up for takeoff and airshow maneuvers to keep them safe on vertical lines. Mostly, they don't fly aerobatics. I'd say most flights might see a 3 - 4 G break or two, possibly more Gs than that, but very few flights actually see much in the way of aerobatics. Usually, that is for airshows and maybe the occasional dogfight with a friend. If you fly a private fighter as a civilian, I'm sure the temptation to play is occasionally overwhelming. Maybe you can expand on that a bit. Our museum pilots generally fly these aircraft to not stress the engines / airframes too much and not use excessive fuel without a good reason. An airshow aerobatic demo is one good reason, and they DO practice enough to maintain safety and a low-altitude waiver when they do airshow aero.
Below is an example of an airshow crash at Biggin Hill when the P-63 pilot didn't throttle up to do a safe vertical maneuver. He basically pulled up from low-cruise power, stalled or maybe just torqued around at the top with low airspeed. He had plenty of power on tap but didn't use it, and did sort of a lazy semi-spin into the ground.
To be safe, you need the proper speed and power setting for the maneuver you are doing. But you are a fighter pilot and rather obviously KNOW that. I doubt you'd try a vertical maneuver in an F-15 without adding some thrust to keep airspeed. Maybe you can expand a bit on airshow F-15 power settings for vertical maneuvers from level flight.
It has been too many years gone by and I do not remember the exact flight conditions from which we saw tumbling. But in the spin tunnel the aircraft starts out at 90 degrees angle of attack and decreases down until it reaches a spin (or in this case tumble) or if not flys out.Excellent first hand information, thanks for posting. It was also said that no tumbling was possible during normal flight or landing even with nose ammo expended. The plane needed to stall at a high AOA at near vertical. Did your test verify that? Thanks again.
Is there any evidence these a/c used greater than 100PN fuel
Arrival of the newer P-38J to fill in behind the P-38H was supposed to help, but did not help enough. The J model's enlarged radiators were trouble-prone. Improperly blended British fuel exacerbated the problems: Anti-knock lead compounds literally seethed out and became separated in the Allison's induction system at extreme low temperatures. This could cause detonation and rapid engine failure, especially at the high power settings demanded for combat.
Disagree with you on the crappy altitude performance.
The N model (produced Dec '42-April '43) had a service ceiling of 38,500', a combat ceiling (1000fpm) of 31000' and a climb rate of 2650fpm at 20000'. Most other contemporary (late '42-early '43) fighters climbed at only about 2000fpm at 20000' including the P-38F/G, P-47 (not even in combat yet), P-51A, Hellcat (not even in combat yet), Corsair, Typhoon, FW190 and Zero. The Me109G could climb with the P-39N and of course the Spitfire IX outclimbed everything in the sky. None of these planes (except P-51A) was considered a low altitude plane.
Despite going all the way through the Q model designation, there were really only two production P-39 models: D/F/K/L with the earlier Allison models -35 and -63 with the 8.8 supercharger gears and the later M/N/Q with the later (late '42) Allison -83 and -85 with the higher rated 9.6 gears. Airframes were the same, differences included propellers, reduction gears, armament, radios and (different models of the Allison) engines. Of the 9500+ P-39s built, over 7000 had the higher rated 9.6 geared engines from late '42.
The earlier D/F/K/L models with the 8.8 engines were low/medium altitude planes but could match the N model in climb if their weight was reduced from standard 7650# to around 7200# which was easily done by removing the .30 caliber wing guns (200#) and the extreme nose armor plate (100#) and a few other unnecessary items. But, in their standard configurations at 7650# they had a very difficult time reaching high altitude (over 20000') with their ubiquitous 110gal drop tanks. Reduce the weight to 7200# and that restriction goes away.
There is a nice story of detonation with Allisons early in their deployment to Europe. It was eventually traced to the difference in aromatics in gasoline. Basically, the Allisons were jetted at the factory using U.S. fuel (2% aromatics) and were thus improperly jetted for the British fuel (20% aromatics). It took a short while for this to be "discovered." When it was found, the issue was rather quickly corrected, resulting in better-running Allisons in Europe. After that, the issue never resurfaced.
By the time Merlins were being built in the U.S.A., the aromatic thing was past, and they were never mis-jetted from the factories.
There were a number of early "stumbling blocks" to U.S. mission in the ETO. They were eventually all ironed out. All sides had stumbling blocks and we have had many threads about it. The Germans ironed out theirs in the Spanish Civil War. The British started out the war flying in Vic formation, and didn't switch to finger-four until later when the advantages of it became obvious. So, we tried things our way at first and found out for ourselves what worked and what didn't, just as the other air forces had.