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In this discussion 50ft/minute is considered important, have you ever tried walking at 50ft/min? Slower than any bride or funeral cortege down a cathedral aisle. Without modern laser or other sensors I don't see how any 1940s aeroplane could be measured to such limits of accuracy.Hi ThomasP. It will take me a day, but I will get to it. I like number crunching like this - although all my calcs come with a 30 second / 30 yard warranty.
Not all airplanes are the same. Two consecutive a/c off the assembly line will have different performances. They all must be within a certain performance tolerance, of say +/-5%. P-39 Expert, I will let you do the math.
They were as identical (except weight) as the manufacturer could make them. Same contract, same engine, same HP, same airframe. Different internal equipment.
The two planes were as identical as the manufacturer could make them, except for weight. The difference in climb wasn't from different propellers, atmospheric conditions, symmetrical airfoils, tail fillets, .30cal gun ports etc. It was because one was 836lba heavier than the other.
Expand above.
Naturally it is only as accurate as the inputs. Based on reading numerous Air Corp reports, some of which have calibration info, I have a confidence the results are better than a WAG.In this discussion 50ft/minute is considered important, have you ever tried walking at 50ft/min? Slower than any bride or funeral cortege down a cathedral aisle. Without modern laser or other sensors I don't see how any 1940s aeroplane could be measured to such limits of accuracy.
According to the tests, the P-39N (available from Nov 1942) outclimbed the Griffon Spitfire and was about the same speed. The N would substantially outclimb the P-51A (same engine) and was very close in top speed. The N outclimbed the 1943 Thunderbolt, Corsair and Hellcat substantially at 20000', just like I said. The P-39N was equipped with full armament including the wonderful four .30s for the tests, no weight reduction needed.
DP.845 was the prototype Spitfire XII. It was fitted with a Griffon IIB engine and normal span wings. The report noted a Rotol "experimental" propeller was fitted, however, it was previously reported that this model propeller was "rather inferior" in climb and that maximum level speed did "not show any appreciable difference" to production propellers. AFDU Report No. 61 noted that speeds of a production Spitfire XII (EN.223) with Griffon III and clipped wings "were found to be almost identical" to DP.845. For comparison, Spitfire XII MB.878 with Griffon VI operating at +12 lbs/2750 RPM achieved 394 mph at 18,100 ft. (15th part of Report No. AAEE/692,o). The Spitfire XII Aircraft Data Sheet is in good agreement with these test results.
For the Germans it was performance, like climb and speed.I believe the engines had to be within +/- 5% of the rated power to be considered acceptable.
Not sure how much performance testing the factory acceptance tests went into. Certainly they checked for proper running and operation.
Clearly the aircraft were not "as identical as the manufacturer could make them, except for weight", considering that the propeller was different and there were small changes to the airframe.
How much do these differences make? We will never know unless we test the differences independent of other factors (such as weight).
As I said above, the engine performance can vary from one to the next, and since they did not have torquemeters installed we will never know if the the P-39C and P-39D engines varied from the published performance ratings (ie we don't know if the engine was producing more or less power than the standard rating).
I haven't made anything up, just quoting an AAF report. Why would a General quote a figure for climb at 100fpm?
It translates to 10000'. It will decrease with altitude. Just like all climb rates.
Agree with you and it wouldn't make any difference anyway.
And you are an expert?
.....
Very slightly different performance. The propeller with the biggest difference was a British Rotol propeller. What are the odds of that propeller being used on an American plane? The propellers used on the Allison engine (like in the P-39) had very small differences.
The two planes were as identical as the manufacturer could make them, except for weight.
Indeed . That thread was in the time of tranquility. The age before this Age of Repetition.Hi Snautzer01,
I forgot. That was back before there was mass hand sanitizer, wasn't it?
I just remember the old currency but my experience of "farthings" was we had them all over the place and they were worthless. There is something magnificently comic about it all, and I didn't even venture into "guineas".
But could the P-39 nuke Japan?
Wait...is this the wrong thread?
Don't forget, once you do all that you need to move the radio forward or the CG will be out of whack...Yes it could...but you'd have to strip off excess weight, fit bulged bomb-bay doors, and add a Merlin 86 engine.
Are you sure you mean Vx, best angle of climb speed? My creaky old memory is that Vy, best rate, is the low point on the power required curve, which would put Vx on the backside of the curve and would actually require more power to maintain level flight. If you're holding waiting for a landing clearance, your best endurance speed is at or about Vy, as long as icing is not a factor. If it is, you have to hold at a higher speed to keep from icing your under surfaces. Tail stalls are generally fatal. (AmEagle ATR at Roselawn, IN, Colgan Q400 at BUF).for power required to maintain level flight at Vx, I'd expect the required power to go up as you go higher. The rate of climb test is not a top speed test and is run mostly at whatever best rate of climb airspeed is. I'd say it's somehwere around 1.4 * stall speed and slightly increases as you climb, and the power required to maintain level flight at Vx increases, too, as you climb.
I used a Cox .020 for my P39C, but had to step up to a Wen Mac .024 for my P39D because of the 836 grains of extra weight. The D snapped its "down" control line and went into a series of tight loops until it hit the ground.If it matters I used a Cd of.020for the P-39C and .022 for the P-39D.
[EDIT: My apologies, I used a Cd of .021 for the P-39C]
You forgot the buoyancy effect differences of the methane gas created by various dietary choices!Surely all the weight added by the well-fed pilot will alter the climbing rate of a P-39D more than a P-39C, right?
My apologies, sir. There's only so much stuff I can process at one time, and that slipped by. Mea culpa, mea maxima culpa!You forgot the buoyancy effect differences of the methane gas created by various dietary choices!