Affects of Critical Alpha on Mach number

[Jane-DoH]

Does the maximum AoA vary with mach-number?

[HazelNuts39]

Does the maximum AoA vary with mach-number?If you mean the AoA for maximum lift - yes, it varies with Mach number.

regards,
HN39

P.S. NACA Technical Note No. 1390 (http://naca.central.cranfield.ac.uk/reports/1947/naca-tn-1390.pdf) shows effects of Mach number on lift coefficient, pressure distribution, AoA, etc. Another illustration is shown in Boeing Aero Magazine no. 12 .
(http://www.boeing.com/commercial/aeromagazine/aero_12/attack_fig4.html)

[Upper Air]

Dont forget flying control reversal tendency at or around Mach 1. Miss Jane.

UA

[Rivet gun]

Try this link, near the end is a graph of CLmax vs mach number for the DC9.

High Lift Systems: Predicting CLmax (http://adg.stanford.edu/aa241/highlift/clmaxest.html)

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).

[HazelNuts39]

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

[CliveL]

Hazelnuts
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?

Maybe because it is labelled tail off from flight test ???? http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

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

[Jane-DoH]

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...