I'll just leave this here:
http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2990_PHQ-M-19-1297-A.pdf
http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2990_PHQ-M-19-1297-A.pdf
XP-39 II - The Groundhog Day Thread
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Nice hotrod! In no way relevant to a combat airplane. No cannon, no wing guns; a toothless tiger, but it would make an awesome dragster.
P-39 Expert
Non-Expert
This was a P-39C modified like the P-400 serial AH 571 that made 391mph in the performance acceptance tests for the British. Slightly different tail, glazed finish, etc. but with experimental 9.6 supercharger gears in a standard -35 engine (normally 8.8 gears). Too bad this engine (as the -59 and -61) wouldn't pass the 150 hour tests, would have been a quick and easy way to add 3000ft of critical altitude almost immediately and get P-39N performance a year earlier. The 9.6 gears had to be widened to improve durability and that modification set the engine back a year to fall 1942. I think going to the aluminum intake manifold without the backfire screens may have enabled the -59/-61 engines to pass the 150 hour test without having to widen the gears, but who knows.
Honestly I don't think the aerodynamic modifications (different tail, glazing etc) were really necessary. The standard P-39C test in July 1941 in wwiiaircraftperformance indicated a top speed of 379mph and the 9.6 gears added 20-25mph so that's about 400mph right there. The P-39C weighed only 7075lbs gross without self sealing fuel tanks and armor plate, but a standard P-39D with the tanks and armor only weighed an additional 75-100lbs without the .30cal wing guns and the 100lb nose armor plate. Oh well.
Snautzer01
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windhund116
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Perhaps not "toothless" in that the C model had all the machine guns in the nose: 2 x .30cal and 2 x .50cal. No mention as to them or their openings being taped or not.
Just interesting that the changes could make such a difference. Makes me wonder if the early P-39s were a little 'loose' on their production tolerances; panels not fitting correctly, etc. Perhaps Bell had a 'production learning curve' before they got it right.
That would add to the explanation for the difference between the prototypes and production early planes, and why the N & Q models were able to approach 400mph, 30+ more than the D models.
Just a thought.
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File it next to the P-38K.
F104 "Widowmaker." Was the crash due to The Cat in the Hat's navigation error?
No.
Santa had one too many Hos and didn't have his IFF on...
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Smoothness matters! Bigtime. A high performance sailplane can lose two to five points off its glide ratio just by flying through a swarm of insects and contaminating its leading edges. If you're going to fly a Mooney or an Aerostar or MU2 in winter, you need to polish every last vestige of frost from your airfoils. (Don't forget the props!)
Just for giggles, we went out and "tufted" the Mooney one day with six inch lengths of yarn, then went out and practiced slow flight and stalls, first with "clean" wings, then with mud splattered on the leading edges and first third of the top surfaces, and baked in the sun. "Whoa, Nellie!" Noticeable difference in cruise speed, and airflow started detaching from the wing surface at significantly lower angles of attack. She never attained enough AoA to trigger the stall warning, and the stall was abrupt and never symmetrical. We kept higher than normal speed in the landing pattern, and landed flat and fast. Things to remember if you ever encounter inflight icing in a Mooney, a Comanche, or any other "slippery" airplane.
BTW, everybody has a "production learning curve". It goes with the territory. At GE, every time we had to build a new assembly, the first batch of 50 would have a 10%-25% QA rejection rate. And then a bunch more would fail their initial fire test, sometimes spectacularly. The worst were "brass retrieval" type Vulcan ammo drums and feed mechanisms.
Great info!
Bell's learning curve may have been steeper, since they had only produced the XFM-1 before the P-39.
They learned well, considering the company went from inception in 1935 to the X-1 in 1946.
Just curious; did you work at the GE plant in Schenectady or Syracuse?
P-39 Expert
Non-Expert
That's great performance! But that's just a projection, not an actual test. It's dated 10/28/39 and the P-39C didn't start production until early 1941.
P-39 Expert
Non-Expert
That's great performance! But that's just a projection, not an actual test. It's dated 10/28/39 and the P-39C didn't start production until early 1941.
Good catch! I read it as 1940.
Looking more closely I see that this was the Bell model 12; the P-39C was the model 13. This would put the aircraft as the XP-39 or perhaps the projection of the XP-39B, since the only P-39 flying in October 1939 was the XP-39!
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Bell and his cheif engineers were no strangers to aircraft design and production.
Bell himself was well involved in the industry, last working for Fleet/Consolidated before founding Bell Aircraft.
Bell had industry experience, but they didn't have an experienced factory staff. And understanding a business is not the same as running one; there is a learning curve there in everything from hiring to marketing to quality control to anticipating industry direction.
Bell didn't have to learn everything from scratch, but he had to build the company from scratch, except for the building. Consolidated left that and Bell grabbed it.
An illustration: Curtiss delivered 1,200+ P-36/P-40s in 1940. Bell delivered 926 P-39s in 1941 (plus 13 prototypes in 1940).
As both companies ramped up production, Curtiss went to 2,200+ in '41, 4,400+ in '42, and 4,200+ in '43. Bell increased more slowly at first, 926 in '41, 1,973 in '42, then passed Curtiss with 4,900+ in '43. In addition, Bell was able to develop a significantly better fighter using the same basic configuration, the P-63, while Curtiss never did find an acceptable P-40 follow-on. Lessons well learned and applied.
GregP
Major
The chart above is dated 10/29/39. The XP-39B was first flown 25 Nov 39. So, at the time this chart was made, the only flying P-39 was the XP-39. Perhaps the XP-39 was NOT flying at the time since it well might have been being modified into the XP-39B at the time of this chart. On wwIIaircraftperformance, the P-39 reports START with the YP-39, not the XP-39. The chart was made from Tables VI and VII of the XP-39 test report. Since I don't have that report, I have no idea wheter the data were projected or were as-tested. From discussions we had more than 60 pages back, I'm going to assume the data were projected, not as-tested.
Looks like a hot rod on paper but ... hey ... the Douglas X-3 Stiletto looked pretty fast on paper, too. It wasn't when actually flying in real air. It was much more of a, "Hey, look what we made, and it FLIES!" Turned out to be decidedly subsonic unless it was in a 25°+ dive.
Methinks the P-39 chart above is projected, not tested.
Looks like a hot rod on paper but ... hey ... the Douglas X-3 Stiletto looked pretty fast on paper, too. It wasn't when actually flying in real air. It was much more of a, "Hey, look what we made, and it FLIES!" Turned out to be decidedly subsonic unless it was in a 25°+ dive.
Methinks the P-39 chart above is projected, not tested.
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See post #2,033
GregP
Major
Post 2033 doesn't say the chart is projected performance. That's the point I was trying to make, not the XP-39 part.
I have never found an actual XP-39 test flight report that is from that time, but I have a book that clearly state 390 mph for the XP-39 from 1946. It also says the gross weight was 6,204 lbs.
Who knows, maybe the test flight report will show up at some future date. I'm not expecting it, though. Cheers.
I have never found an actual XP-39 test flight report that is from that time, but I have a book that clearly state 390 mph for the XP-39 from 1946. It also says the gross weight was 6,204 lbs.
Who knows, maybe the test flight report will show up at some future date. I'm not expecting it, though. Cheers.
P-39 Expert
Non-Expert
This chart may not be too far off depending on the weight. The power is listed as 1150hp at 15000' which is just about what Allison projected in fall of '41. Allison thought they could just plug in the 9.6 supercharger gears but turned out they wouldn't take the additional MP and had to be redesigned/widened. This projected C model probably weighed 5800lbs with the cannon and twin .50s. That's about a ton lighter than production P-39s. A 5800lb P-39 with 9.6 supercharger gears would probably perform like that chart says.
Yeah, I've seen the 390mph figure repeated on many sources, but no primary source of origin for it.
What is odd for a projected graph is the line labeled "Actual Time To Climb Curve" and a dashed line that I assume is the projected time to climb. Also, the abrupt 'switch' from "Military Power" to "Normal Power" at around 19,000 feet on the Rate Of Climb curve as indicated by the switch of solid and dashed lines.
This chart is "Figure 8" of some report. Also of interest would be "Tables VI and VII."
I also wonder who "Asey" (Casey?) and "Robinson" were.
If someone could find Bell report "12Y005" we'd know. Maybe.
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