P-39 Expert
Non-Expert
Okay, how much would that 20 degrees affect the performance of a P-39K or A6M2 at 24000'?
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Yes - 20 degrees C (36F) and when computing performance calculations, it will make a difference.
Okay, how much would that 20 degrees affect the performance of a P-39K or A6M2 at 24000'?Yes - 20 degrees C (36F) and when computing performance calculations, it will make a difference.
The chart says that even with a drop tank the "service ceiling" was over 27000'. Wish the report had been more specific.
I think most would be inclined to believe that the P-39K could handle itself at 27000' with the weight reduction. General was pleased with the results.
Reducing the weight increased the climb rate and ceiling just like I have been telling you.
Okay, how much would that 20 degrees affect the performance of a P-39K or A6M2 at 24000'?
I was wanting a number, like 3mph or 50fpm.That would be indicated in performance charts based on the flight testing of both aircraft.
So, they throw one really crappy propeller (Rotol) in with the other 4 and it's 330fpm less than the standard prop. Wonder why the HP was so low on that one?As they say, please expand.
Rotol props needed a Spitfire behind them to produce a decent climb performance up to 40,000 feet.So, they throw one really crappy propeller (Rotol) in with the other 4
We're talking about the P-39C and D, and two props by the same manufacturer, same diameter, different blade (if it was really different). Why would the AAF specify a different prop if it hurt climb rate that much?
Whether you buy it or not doesn't change the fact that a wing of that design with that loading is just not going to perform as efficiently in air that thin with so little excess power available as the more lightly loaded, better airfoil, higher L/D Zero wing will.I'm not buying the less efficient wing.
On my office wall behind my desk I have a 3' x 3' picture of an F-86 Sabre. When I have to explain to someone whatever issue is at hand and I get that blank stare, I point to the Sabre, as in the point went over your head like this Sabre.So, they throw one really crappy propeller (Rotol) in with the other 4 and it's 330fpm less than the standard prop. Wonder why the HP was so low on that one?
The differences in the other props were in the 200fpm range, barely measurable.
We're talking about the P-39C and D, and two props by the same manufacturer, same diameter, different blade (if it was really different). Why would the AAF specify a different prop if it hurt climb rate that much?
You are quoting performance under standard conditions. As has been explained to you, there is no evidence these were "standard" conditions and the greatest likelihood is that the conditions were much less than optimal.
As for being "inclined to believe", you are welcome to believe what you want as you tend to anyway, but that does not change the contents of the document which states that 27,000 feet was a service ceiling. As has been explained to you, the "service ceiling" of a standard P-39K was over 30000' BEFORE any weight reduction. They reduced the weight by 650lbs and increased the combat ceiling to 27000.
General Harmon should have been pleased with this experiment; it actually worked! The other experiments did not work out nearly as well.
I don't believe anyone is disputing that reducing weight will usually increase climb rate and ceiling. The question is really how much effect they will have. We just don't believe your "calculations" have any basis in reality and that there were other more important factors that differed between the P-39C and P-39D tests.
Just to humour you for a second, what do your calculations tell you the increase in climb rate would be at 25,000 feet and please show your work. What do your calculations show the increase in service ceiling would be? This has been explained to you before. The difference in climb rate between the two virtually identical (except weight) planes was 1000fpm at 10000'. The difference in weight of the two planes was 836lbs. Divide 1000' by 836lbs and you get 1.2fpm per pound of weight. That means if you reduce the weight of the P-39D by 300lbs the climb rate improves by 360fpm. If you add 200lbs to the P-39C then you decrease the climb rate by 240fpm. That's at 10000'.
No amount of slightly different propellers (of the same diameter by the same manufacturer), an inch in length, fin fillet, symmetrical airfoil, adjustments to standard atmosphere or ANY OTHER FACTOR is going to make a difference of 1000fpm climb except almost a half ton of weight. The planes were virtually identical except for 836lbs weight.
- Ivan.
Expand aboveYou are quoting performance under standard conditions. As has been explained to you, there is no evidence these were "standard" conditions and the greatest likelihood is that the conditions were much less than optimal.
As for being "inclined to believe", you are welcome to believe what you want as you tend to anyway, but that does not change the contents of the document which states that 27,000 feet was a service ceiling.
General Harmon should have been pleased with this experiment; it actually worked! The other experiments did not work out nearly as well.
I don't believe anyone is disputing that reducing weight will usually increase climb rate and ceiling. The question is really how much effect they will have. We just don't believe your "calculations" have any basis in reality and that there were other more important factors that differed between the P-39C and P-39D tests.
Just to humour you for a second, what do your calculations tell you the increase in climb rate would be at 25,000 feet and please show your work. What do your calculations show the increase in service ceiling would be?
- Ivan.
Absolutely nothing wrong with a symmetrical airfoil. The A6M2 will be gasping for air just like the P-39K at 27000'. Sure it has a much lower wing loading, and will be more maneuverable at 27000' just like it is at 10000'. But it won't climb any better and it sure won't dive any better.Whether you buy it or not doesn't change the fact that a wing of that design with that loading is just not going to perform as efficiently in air that thin with so little excess power available as the more lightly loaded, better airfoil, higher L/D Zero wing will.
The only planes that could match or exceed the Zero in combat performance at those altitudes were those of later generations that had significantly more surplus power available at altitude.
Especially in the technical ideas supermarket, if you don't like it for some reason, you don't buy it, and that, is that.Armchair experts have way more knowledge than anyone
I'm not buying the less efficient wing.
Yes the AAF tested different propellers on the P-40F. Obviously some were better than others. The P-39 had an Allison engine. The props tested on the Allison P-40E were all remarkably similar in performance, both in speed and climb. One would think that would be the better comparison in this case.On my office wall behind my desk I have a 3' x 3' picture of an F-86 Sabre. When I have to explain to someone whatever issue is at hand and I get that blank stare, I point to the Sabre, as in the point went over your head like this Sabre.
Perhaps... the Air Corps was oh, I don't know, TESTING different propellers? I mean why else would they use the same plane weighted the same with different props? It does happen.
Also, if Wes talks about wing efficiency I wouldn't really argue with him unless you're a pilot with a sh!t ton of hours or a aerodynamic engineer, just my opinion of course.
I was wanting a number, like 3mph or 50fpm.
... because the atmospherics are different in different parts of the world. That is why you see "adjusted to standard atmosphere" of data sheets.
Case in point: a prop with the same blade count but a higher propulsive surface area (a "paddle blade", if you will). In the denser air at lower altitudes the added rotational drag of the blades will keep trying to slow RPM, driving the governor to "fine" the propeller pitch to keep RPM constant, reducing the efficiency of converting HP to thrust. This is not so much an issue with a behemoth like the R2800, as the P47 so impressively proved. But where the paddle comes into it's own is at altitude, where the thinner air reduces drag, allowing more efficient pitch angles, but also demanding more propulsive surface area to convert the limited available HP into thrust.Very often, two different propellers have characteristics that give them advantages under different conditions.
Okay, how are you going to make up the other 700fpm? Phantom CG problems? A tail fin fillet? The extra inch of fuselage length?
Think it was maybe the 836lbs of extra weight?
If you all are done patting yourselves on the back, can any of you divide 1000 by 836?
I suggest you look at the Me109K which was tested with one prop but used a different prop for serial production. Iirc one was best in climb and the other for speed.So, they throw one really crappy propeller (Rotol) in with the other 4 and it's 330fpm less than the standard prop. Wonder why the HP was so low on that one?
The differences in the other props were in the 200fpm range, barely measurable.
We're talking about the P-39C and D, and two props by the same manufacturer, same diameter, different blade (if it was really different). Why would the AAF specify a different prop if it hurt climb rate that much?