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.

[Kutscha]

A picture, err graph, is worth a thousand words of text.

[Christer Bergström]

No, Graham, these graphs shouldn't should be completely discarded. As I said, I don't say that aircraft performance curves is totally superfluous, but it requires technical knowledge to be able to use those curves properly, and I find it surprising that no one of those who have such high thoughts about their own technical knowledge have discussed the weaknesses of these ordinary performance curves.

Also, for what do we need to know a Hs 129 ground attack aircraft's different average level flight top speeds at clinic tests at 17,000 ft, 22,000 ft, 24,000 ft, and 28,000 ft respectively?

I am always out looking for good WW II combat aircraft data, and would love to learn e.g. which is the source to the Bf 109 F-2 performance curves which Franek has access to.

[Christer Bergström]

Sorry for "bumping", but maybe Jukka and Franek missed my questions?

For what do we need to know a Hs 129 ground attack aircraft's different average level flight top speeds at clinic tests at 17,000 ft, 22,000 ft, 24,000 ft, and 28,000 ft respectively?

Which is the source to the Bf 109 F-2 performance curves which Franek has access to?

[Juha]

Hello Christer
I'm not Jukka but where he demanded different average level flight top speeds at clinic tests at 17,000 ft, 22,000 ft, 24,000 ft, and 28,000 ft respectively for Hs 129?
I even checked the locked book thread and Jukka never asked that. He missed performance graphs, so why to misrepresent his oppinion. IMO You are playing a cheap trick, in fact stupid old propaganda trick.
Why????????????????

I cannot say that I'm surprised but
Juha

[Ruy Horta]

Lets keep on track people.

[Dénes Bernád]

Originally Posted by Christer Bergström

For what do we need to know a Hs 129 ground attack aircraft's different average level flight top speeds at clinic tests at 17,000 ft, 22,000 ft, 24,000 ft, and 28,000 ft respectively?

A technical description of the Hs 129, based on field tests, gives the max. ceiling at only 4000 m (13000 ft.)!

[Gizmo]

Originally Posted by Christer Bergström

Which is the source to the Bf 109 F-2 performance curves which Franek has access to?

Probably it's "Kennblatt fur das Flugzeugmufter Bf 109F-1 und F-2 mit DB601N motor", Berlin 1941.
If anybody is interested, I can send these curves via e-mail.

[Christer Bergström]

Juha, maybe I misunderstood Jukka. Okay? I was curious just for what we need performance curves for a ground-attack plane like the Hs 129. If you can't explain that, then please allow Jukka to do that.

Gizmo, I'd be grateful if you could send me a scan of those Bf 109 F-1 & F-2 curves in an e-mail.

Probably it's "Kennblatt fur das Flugzeugmufter Bf 109F-1 und F-2 mit DB601N motor", Berlin 1941.

I still wonder which source Franek has for his Bf 109 F-2 curves. Yes, maybe his source is the one you mentioned, but I doubt that since he specifically said only the Bf 109 F-2. So if he has another source, it would be interesting to learn which one. Do you have another source, Franek?

(BTW, it's "Flugzeugmuster")

[Graham Boak]

I believe that Jukka is looking for more technical data in aircraft books: to restrict this wish to the simpler performance curves is to misrepresent his argument. There is much more to be said about an aircraft's technical side than just the performance terms.

However: given the level speed it would be possible to calculate the drag co-efficient. From this other performance data can be calculated. For example, payload-range, turn radii and accelerations that would be of interest to almost any combat type. It would be possible make much realistic comparisons than can be found in anecdotes, usually from the winners.