windhund116
Senior Airman
- 360
- Jul 3, 2017
Yeah. That is what I was taught by a mechanic. Convection action.
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The valve stem in a sodium cooled valve was hollow with the sodium not filling the void, the sodium moved up and down the valve stem as the engine ran giving much more rapid heat transfer from the hottest to the coolest part.
Hello Juha3,
The M-82FN engine installed in these aircraft had a critical altitude in high blower of only 4650 Meters.
Do you find it a bit odd that the aircraft would reach its maximum speed that much higher?
The altitude difference seems a bit much for ram effect.
- Ivan.
Gosh, this report stated that lightened P-39Ks could fight up to 27000'. Only reduced by 600lbs. Wonder who came up with that idea?So to strip 1500 pounds from the P-39, what should be removed?
USAF Historical Study No. 101
Report pgno. 90 (PDF pgno. 101)
Gosh, this report stated that lightened P-39Ks could fight up to 27000'. Only reduced by 600lbs. Wonder who came up with that idea?
I don't know, I'm a historian by training without any formal technical training, being only interesting in also the technical side of warfare. One Soviet graph attached.View attachment 600747
The weight would likely be the 30-cal wing guns and installation kits, plus a little extra. I did notice that the weight saved by changing the 37 mm cannon for a 50-cal was negligible and not worth the engineering effort. Removing the wing guns would not have affected the CG much, either.
The P-39C had a service ceiling of 33,300 feet, already comfortably above 27,000 feet. Right, the South Pacific doc probably meant 27000' combat ceiling (climb 1000fpm)
The P-39D had a service ceiling of 31,100 feet, already comfortably above 27,000 feet.
The P-39N had a service ceiling of 35,900 feet, already comfortably above 27,000 feet. 38500', P-39N test attached.
The report cited was about P-39Ks, and I can't find a test report on a P-39K just now. P-39K test chart attached, compared with A6M2 in red. I'm assuming it was as good as a P-39D and not better than a P-39N. I am surmising that the P-39K could, in fact, get to 27,000 feet, but not in time to stop the Japanese raiders with the warning time they had available.
Taking out the wing guns would have made it climb better, but not by all that much. But losing 650 pounds WOULD have made the climb slightly better at the expense of losing firepower. Sounds like what they wanted at the time, but I'm having trouble getting my brain around how a slightly better climb would allow them to get up to the bombers without knowing the warning time they had for the raids. We'd have to know their warning time to see how much climb difference would have resulted in a good outcome. But, it seems that whatever climb improvement they got, it made a difference. See the attached P-39K chart, improving climb to 1000fpm at 27000' would be about a 500fpm increase. Closer to my estimate.
It still would not have made the P-39 dogfight with a Zero at 27,000 feet (or anywhere else, for that matter), but it could give them a firing pass at the bombers. No AAF plane would dogfight with a Zero.
This is an interesting report, but it doesn't have enough meat in it to make an intelligent analysis of what they removed to save 650 pounds or how much change in climb it made. The P-39K had a 1,325 hp Allison instead of a 1,200 hp unit, and removing the wing guns, installation kits, and ammunition was the likely source of most of the weight.
If you look at the P-39N (same engine hp), the rate of climb at 25,000 feet was 1940 fpm. From the data I have ... P-39N HP (-85) was about 100HP more than the P-39K (-63) above critical altitude. P-39K -63 engine had 8.8 supercharger gears, same as the -35 in the P-39D/F/K/l, same HP at 12000' and above. See chart below.
The Allison should have been making about 1,050 hp at 15,000 feet, where it had a climb rate of 3,340 fpm at 7,274 pounds. If we remove 650 pounds, we get 6,624 pounds, where the climb rate SHOULD be about 3,668 fpm, an improvement of 327 fpm or 9.8%. The time to climb to 15,000 feet was 4.15 minutes. Shaving off 9.8% makes it close to 3.75 minutes. If we assume about a 9.8 % gain to 25,000 feet, we go from 8.04 minutes stock to 7.25 minutes when 650 pounds lighter. This is, admittedly, a 1st-order approximation and is likely a bit optimistic. You're comparing the P-39N -85 engine to the P-39K -63 engine which only developed about 100HP less above critical alt. See chart below.
So, logically, a change of somewhere around 45 seconds to 27,000 feet made the difference. That assumes the P-39s were unopposed and could hit the bombers when they got there. Sounds a bit unlikely, but this report would indicate that it was the case. The G4M "Betty" bomber came in at between 18000' and 22000', sometimes slightly higher. 27000' would pose no interception problem.
All I can say is that if a change in climb of 45 seconds made the difference, then maybe removing the wing guns was a good answer. I just have never seen much indication they DID that on a large-scale basis in the USAAC/F in WWII. AAF didn't remove the wing .30s on a large scale basis. All this shows they should have.
Waaaaaiitt...*SNIP*
The Allison should have been making about 1,050 hp at 15,000 feet, where it had a climb rate of 3,340 fpm at 7,274 pounds. If we remove 650 pounds, we get 6,624 pounds, where the climb rate SHOULD be about 3,668 fpm, an improvement of 327 fpm or 9.8%. The time to climb to 15,000 feet was 4.15 minutes. Shaving off 9.8% makes it close to 3.75 minutes. If we assume about a 9.8 % gain to 25,000 feet, we go from 8.04 minutes stock to 7.25 minutes when 650 pounds lighter. This is, admittedly, a 1st-order approximation and is likely a bit optimistic.
*SNIP
Hi Ivan.
I show the P-39D with the V-1710-35. 1,150 hp at 12,000 feet and 3,000 rpm
I show the P-39K with the V-1710-63. 1,100 hp at 13,800 feet and 3,000 rpm. I am assuming it dropped about 50 hp from there at 15,000 feet. The P-39K with the -63 also had a WEP rating of 1,580 hp at 2,500 feet and 60" MAP, but that would not have still been in use at 27,000 feet since it was a 5 minute rating. I based my estimate on Military power, not WEP.
I think you are quoting figures for the -59 (1100HP at 13,800'). The -59 was the original attempt at the 9.6 supercharger gears that didn't prove reliable. Widening the gears in the -83 and -85 made the 9.6 gears reliable. The -63 had the same HP as the -35 at 12000' and above.
I fully realize that the P-39 was not considered a great airplane, but the performance of the P-39N at 15,000 feet from wwiiaircaftperformance shows 3,340 fpm climb. That's about P-51D territory. At 26,000 feet, a test on a P-51D shows 2,780 fpm climb. The P-39N shows 1,940 at 25,000 feet. Clearly, the P-51D is better up high. P-39N climb was really good, better than most all other contemporary 1943 fighters (Thunderbolt, Corsair, Hellcat, FW190, Zero, Typhoon) and was available a year before the Merlin P-51 made combat. P-39N climbed better than the 109G below 20000', about the same above that. Of course nowhere near the Spitfire IX climb rate.
But at 17,400 feet, the P-51D shows 2,965 fpm while the P-39N at 15,000 feet shows 3,340 fpm. Different story. Down near 15,000 feet, the P-39 is right in there with the P-51D. At least, the test airplane was. The dog of the group seems to be the P-39D which, for some unexplained reason, shows poor climb perfomance that was "recovered" in later models. That tells me there is something wrong with the P-39D test. I just don't quite know what it is and the interest level is dropping fast since the P-39 was never considered a great fighter by the U.S.A. ... only the Soviet Union loved it, and they did great with it. The P-39D climb figures were about the same as the P-39K, both had the 8.8 geared engines (-35 vs -63).
Maybe we needed to look at their operations!
Please expand above.So, this P-39K shows a true airspeed of 353 mph at 25,000 feet, and the rate of climb is about 760 fpm or so. But, if you look at the P-39N test, at the same altitude, the rate of climb is 1,940 fpm and the speed is 370 mph.
Keep in mind that in the test the K was climbing at normal power 2600rpm and the N was climbing at combat power 3000rpm. The K was still under the 5 minute limit until mid 1942. After mid year 1942 the K would be able to climb at combat power 3000rpm for 15 minutes. K still wouldn't climb like the N since the N had a more powerful engine, but it would climb better than the test (3000rpm vs 2600rpm). The curved lines between 12500' and 15000' on the climb test attached shows the 5 minute mark when the rpm was reduced from 3000 to 2600. The blue dots estimate the climb rate at 3000rpm. That would show a climb rate of 1000fpm at 27000' with NO weight reduction. (The red dots are for the A6M2).
Interesting, to say the least but, thinking of the attachment above and the statement that the P-39s could not reach 27,000 feet, the actual tests show ANY of the P-39s could have gotten to 27,000 feet, but the particular model of the airplane has a LOT to do with what the climb rate and top speeds are when you get there. I am left with the dictinct impression that my earlier premise was correct, the P-39 could get to 27,000 feet, but not within the time allowed for by the early warning system in the above report. In that case, perhaps removing the wing guns would actually make the mission possible. It would NOT make the P-39 a better mount against the Zero, maneuverability-wise, but could make it possible to actually intercept bombers at 27,000 feet and interrupt their mission. As the attached chart shows, at normal power 2600rpm the K model would only be climbing at 500fpm at 27000', too low for combat. At 3000rpm the K model would still be climbing at at least 1000fpm, commonly know as combat ceiling (not service ceiling 100fpm). Again, before ANY weight reduction.
Most Japanese bombing missions were NOT at 27,000 feet, if you go look at the after action reports that I have seen. Things don't always stay the same, and the Japanese apparently didn't always come in at low altitudes. At least the P-39 had a good cockpit heater! Japan's best bomber, the G4M Betty bombed at between 18000' and 22000'. I don't know of ANY Japanese bomber capable of bombing at 27000'. Turbocharged B-17 and B-24 bombers flew at only 25000'. A 27000' combat ceiling was plenty.
Thank you Mike Williams for saving these performance test data charts and reports!Nice to have test data when you look at specific questions.
Found all these charts mysalef, but thanks for posting. It tells me the P-39 was exactly waht we all thought, basically a low-to medium altitude fighter. Once you get above mid-teens, it stats running out of power. Since single-stage engines do that, where did 66 pages of posts come from?
Cheers everyone.
Any reference to Dr. Seuss gets a Bacon rating...Hello GregP,
Well, there are plenty of single stage but multiple SPEED or variable SPEED superchargers that do a lot better than that.
Most of the German fighters used single stage superchargers.
The single stage but two SPEED V-1650-1 installed in the P-40F and P-40L was a lot more capable at altitude than the single stage single SPEED Allison.
66 Pages of posts???
The Title for this thread should actually be the same as the Dr Seuss book:
"The Places You'll Go".
We seem to cover a lot of ground in this thread and you never know where we will end up next!
- Ivan.