Aircraft performance curves

[Graham Boak]

It is perfectly true that some of the available information is not fully defined, or of doubtful origins, but this does not lead to the conclusion that all should be discarded. A comparison of several such datasets - the more the better, surely? - will soon lead to discovering which are realistic and which are not. However, even the best can be viewed as a measure of the capabilities of the aircraft, if idealised compared with service conditions.

The development of an aircraft cannot be understood and appreciated without understanding the technical changes that did or did not happen, that were or were not possible at the time. Some part of this is most easily expressed in terms of these fairly simple curves, annotated as necessary.

From these charts can be obtained basic drag data, which when coupled with engine power, weight and lift can be used to produce all the intermediate climb, dive and acceleration points you suggest. Perhaps you are not aware that there is a simple conversion between climb rate and acceleration?

Every aircraft ever built would take a little while to accelerate the last few kph/mph to meet a true Thrust=Drag level speed. (Early high subsonic jets possibly excepted, due to the rapidity of the drag rise.) I don't see the value of this comment.

Comparisons are also best made using these charts. The relative performances of the Spitfire Mk.V, LF Mk.V, Fw 190A and Spitfire Mk.9 can be shown very easily on such a figure, especially the differing variations with altitude. To express all this in words would take many sentences, and would lack the clarity of the picture. Comparative areas of combat advantage are clear, with their key points of changeover.

ideally, it would be best to see the full flight envelope in terms of Specific Excess Power contours, but this technique was not available at the time. Some studies have been done to generate this but apart from one on the P-40 vs Zero I can't bring any to mind. Modern sources rather lack the knowledge available in the original aerodynamic offices. Without this we can only do the best we can with the data available, knowing that the air has not changed, and neither have the laws of physics. The more data, the better the job.