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Yes, but you're forgetting the XP-39 had no guns, no armour and virtually no equipment for those first few flights. It weighed less than 4000Lbs empty, which is one reason why it climbed to 20,000ft in five minutes. So if Bell had decided to make a carefully planned publicity speed run, twenty minutes might give time for the extra-lightweight prototype to climb to 20,000ft and make the run, and 47 minutes would be plenty. And the XP-39B without the turbo and weighing over 300Lbs more still managed 375mph in the thicker air at 15,000ft. So, no, you have not conclusively proven the XP-39 didn't fly at 390mph.......So, if the XP-39 did do 390mph or anywhere near to it it had to be done in May, (repeating the above none of the April flights were long enough to get to 20,000ft, do a high speed run and get back down on the ground again.) with a high drag oil cooler duct, a radiator that had problems (like at 350mph the radiator was supposed to have 16,900 cubic ft of air going through but only 10,250 cu ft was needed to cool the engine) and the engine was limited to 90% or less of rated rpm, unless the pilot disobeyed instructions.
And the XP-39B without the turbo and weighing over 300Lbs more still managed 375mph in the thicker air at 15,000ft. So, no, you have not conclusively proven the XP-39 didn't fly at 390mph.
Which other manufacturer was as desperate as Bell to get an order to avoid going bust? Which then extends to how desperate a test pilot might be to keep his job that he'd agree to make such a flight. And then you have bravado and just plain guts. During the second flight of the Hawker Typhoon prototype, chief test pilot Philip Lucas noticed the fuselage had started to suffer a structural failure, with a tear large enough to push his hand through opening in one side. Lucas stubbornly refused to bailout, the accepted procedure in such a situation, and saved the prototype. Whilst he was awarded the George Medal for his bravery, he admitted in later years that one possible cause of the failure was some flight manouveres "not in the official test plan"....What other aircraft in all of WW II established record setting climbs to altitude and did high speed runs in the first two hours of testing?....
The British would have rejected the whole order if Bell hadn't have been able to meet the "within 3% of 400mph" requirement. As I already mentioned, the British Direct Purchase Commission to the US weren't exactly the best and brightest, so I'm not surprised they signed some bad contracts. As it was, they were under pressure to buy just about anything. The P-40 snuck under the barrier because they arrived reasonably early and were judged suitable for the Middle East. By the time the P-400s arrived in the UK, we had loads of Spitfire Vs and the Hawker Typhoon was supposed to soon be sweeping the Luftwaffe from the sky. The Bf109F meant nothing without good altitude performance was going to be used as a fighter in the UK. The Desert requirement was already being met by the mediocre but trusted Tomahawk, and a "much-improved" Kittyhawk was being promised by an equally dishonest Curtis, leaving no role for the troublesome P-400s. Not surprisingly, the RAF jumped at the chance to offload the P-400s to the Russians.....See Bell's lies to the British about performance and the special aircraft needed to even get to 3% under the contract performance to keep the contract going.
The British would have rejected the whole order if Bell hadn't have been able to meet the "within 3% of 400mph" requirement. As I already mentioned, the British Direct Purchase Commission to the US weren't exactly the best and brightest, so I'm not surprised they signed some bad contracts. As it was, they were under pressure to buy just about anything.
The P-40 snuck under the barrier because they arrived reasonably early and were judged suitable for the Middle East.
Because they didn't say "No, none of this will do." They should have brought a pallet of RR Merlin engines with them and said, "Here, build me something round this, we'd rather wait for something better than order just anything." But they ordered the available P-40. If they had of insisted on the Merlin as the powerplant, we might have had a Merlin-engined P-38 in 1941, which would have been invaluable in every theatre and much more useful than the eventual P-40F/Kittyhawk MkII, and the Mustang MkI would have been a world-beater from the start.......Why do you think the BPC were "not the best and brightest"? Because they bought P-39s?....
Agreed, but it doesn't say much for the state if the US industry when you consider the US was technically ahead in stressed-metal construction, wing design and turbocharging, that the best they could provide was the Tomahawk. The Mustang was definitely a better effort, but, IIRC, a lot of the design work on the P-51 was actually done after they spent a lot of time studying a captured ME109..... After all, the American bombers were very good, probably the best available anywhere until the Mosquito arrived.......The P-40 was ordered because the RAF needed fighters and the P-40 was the only US fighter that had any chance of being available in a short period....
The P-40 had two big advantages over the Hurricane (and Spitfire). Firstly, it had much better range, which was vital for overseas operations. Strangely, the RAF didn't use drop-tanks with the Tomahawks. The other advantage was the Allison V-1710 stood up to Desert conditions better than the RR Merlin. Whilst some of this was down to the down-draught carb inlet, the Allison came with superior air filters, probably because the USAAC expected their aircraft to operate throughout the USA's many and varied environments. And in the Desert theatre in mid-1940, the RAF expected to only be fighting the Italians, and their fighters were inferior to the P-40B/C and had equally poor altitude performance. But in the ETO the fighting was getting to higher and higher altitudes, and the RAF was worried about high-altitude bombers like the Ju86 (which actually proved to be a bit of a flop)......What made the P-40 suitable for the Middle East but not for northern Europe?
a lot of the design work on the P-51 was actually done after they spent a lot of time studying a captured ME109.....
Because they didn't say "No, none of this will do." They should have brought a pallet of RR Merlin engines with them and said, "Here, build me something round this, we'd rather wait for something better than order just anything." But they ordered the available P-40. If they had of insisted on the Merlin as the powerplant, we might have had a Merlin-engined P-38 in 1941, which would have been invaluable in every theatre and much more useful than the eventual P-40F/Kittyhawk MkII, and the Mustang MkI would have been a world-beater from the start.
The Mustang was definitely a better effort, but, IIRC, a lot of the design work on the P-51 was actually done after they spent a lot of time studying a captured ME109..... After all, the American bombers were very good, probably the best available anywhere until the Mosquito arrived.
Hi Tomo,
I love the chart but am a bit curious about it. I have some observations.
1) It shows the "original airplane" doing 340 mph;
2) The "modified airplane with supercharged engine" doing just over 390 mph;
3) And the "modified airplane with altitude blower engine doing just over 400 mph.
But ...
The "original airplane" DID have a supercharged engine; the 1,150 HP Allisons V-1710-17 (E2). It had a B-5 two-stage turbosupercharger. They never flew an Allison in an airplane that wasn't at least supercharged. So, exactly what is the first curve referring to? Some other powerplant that wasn't supercharged? I can understand the curve with and without the altitude turbosupercharger, but the third curve (the so-called "original airplane") makes me scratch my head and wonder what they were thinking about.
Did the source for this set of curves explain the three curves enough to answer what the first curve was supposed to depict? Just curious, no other agenda here.
To get the "production" Airacobra I to within 4% of the contract speed (it actually did a somewhat better, about 1% low) Bell resorted to a number of 'tricks' like 20 coats of primer sanded between coats. And the finish camouflage coat was lightly sanded to eliminate the seams left by the camouflage templates.
They also used a wood filler (plastic wood?) around the canopy to smooth the canopy to framework.
Certain panels were made of heavier gauge sheet metal to prevent distortion at high speed.
Improved fasteners/linkage for the landing gear doors to improve fit when closed.
and others, like no radio mast and fairings over the
One of my favorites
the test plane actually had slightly smaller elevators and rudders and slightly larger horizontal stabilizers and vertical fin. Not adopted for any other aircraft.
I don't know if some of these changes did anything or not but some certainly did and the the trick with the paint was totally unusable on a production aircraft.
The difference in speed between S/N AH 579 (standard ) and S/N AH 571 (modified) was 20mph in top speed.
Now take a 371mph aircraft that was only a few days old at the factory ramp and fly it in service (or extended tests at a different location) for several weeks and see how the fit/finish deteriorates.
However, I can think of no other fighter in WW II that was modified to such an extent for an acceptance test, there may have been some?
Hi Tomo,
Just so we're communicating with clarity, the turbo charged version of the XP-39 was a 2-stage system,
with the lower-altitude stage being the engine-driven supercharger and the higher-altitude stage being the turbocharger.
The turbocharger by itself was one-stage but, when combined with the engine-driven supercharger, resulted in a 2-stage system.