Affects of Critical Alpha on Mach number
Joined: Jul 2009
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From: France - mostly
Originally Posted by Jane-DoH
Does the maximum AoA vary with mach-number?
regards,
HN39
P.S. NACA Technical Note No. 1390 shows effects of Mach number on lift coefficient, pressure distribution, AoA, etc. Another illustration is shown in Boeing Aero Magazine no. 12 .
Last edited by HazelNuts39; 24th February 2011 at 10:58. Reason: P.S.
Joined: Jun 2004
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From: UK
Try this link, near the end is a graph of CLmax vs mach number for the DC9.
High Lift Systems: Predicting CLmax
You can see that the maximum coeficient of lift decreases above about M 0.3.
This is one of the reasons why indicated stalling speed (CAS) increases with altitude (the other being compressibility error).
High Lift Systems: Predicting CLmax
You can see that the maximum coeficient of lift decreases above about M 0.3.
This is one of the reasons why indicated stalling speed (CAS) increases with altitude (the other being compressibility error).
Joined: Jul 2009
Posts: 1,682
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From: France - mostly
Rivet gun;
Thanks for the link to an article containing a wealth of interesting data. Could you indicate the source of the article?
In the graph of CLmax vs mach number for the DC9 (no flaps, no flaps), I note that CLmax increases between Mach 0.8 and 0.9 . That seems somewhat odd and I see no reason for it. Can you explain it?
regards,
HN39
Thanks for the link to an article containing a wealth of interesting data. Could you indicate the source of the article?
In the graph of CLmax vs mach number for the DC9 (no flaps, no flaps), I note that CLmax increases between Mach 0.8 and 0.9 . That seems somewhat odd and I see no reason for it. Can you explain it?
regards,
HN39
Joined: Dec 2010
Posts: 291
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From: Europe
Hazelnuts
Maybe because it is labelled tail off from flight test ???? 
Seriously, it might be just the flight test value, which could be buffet limited rather than a genuine stall, and an estimated correction for tail load which might or might not be credible.
Source I think is the course notes for Stanford University AA241
In the graph of CLmax vs mach number for the DC9 (no flaps, no flaps), I note that CLmax increases between Mach 0.8 and 0.9 . That seems somewhat odd and I see no reason for it. Can you explain it?
Seriously, it might be just the flight test value, which could be buffet limited rather than a genuine stall, and an estimated correction for tail load which might or might not be credible.
Source I think is the course notes for Stanford University AA241
Thread Starter
Joined: Dec 2010
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From: New York & California
Does this trend of critical AoA reducing with mach number increasing continue when going supersonic?
I'm just curious because if I recall supersonic airflow can go very rapidly around rough edges (and from what I remember this is why you can use an airfoil with a diamond cross-sectional shape at supersonic speeds), though on the other hand, you have a shockwave on the leading edge that you don't have on a subsonic wing and that does tend to produce some turbulence behind it and that could make airflow separate a bit easier...
I'm just curious because if I recall supersonic airflow can go very rapidly around rough edges (and from what I remember this is why you can use an airfoil with a diamond cross-sectional shape at supersonic speeds), though on the other hand, you have a shockwave on the leading edge that you don't have on a subsonic wing and that does tend to produce some turbulence behind it and that could make airflow separate a bit easier...
