Re: Stalls

From: (Nitin Gupta)
Organization: Massachvsetts Institvte of Technology
Date:         06 May 94 18:02:14 
References:   1
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  or MIME structure (Robert Dorsett) writes:

> But the shockwaves still exist.  You can see them when the airplane is
> flying 90 degrees to the sun; the shockwaves change the refractive
> property of air in the vicinity, and can be seen as little span-wise
> reflections dancing along the middle to rear of the wing.

I looked into this, and i'm not so sure that the faint "reflections" are  
due to changes in refractive index. To be sure, pressure and temperature  
do change n, the refractive index, of air. At 15degC and 1atm pressure at  
500nm wavelength light (dominant visible for humans), n=1.00028.

At worst case (to maximize deviation from "standard condition"), n=1.00059  
at 2atm and 1.0030 at 10atm pressure and 0degC. Unless these shockwaves  
are of very large pressure, I do not see n changing enough to manifest  
enough contrast to actually be visible on a sunny day. I'm not into  
airfoil dynamics, so I have no idea what the nature of schockwaves are in  
terms of their temporal pressure.

Reference: 74th ed. CRC

blue skies
Nitin Gupta                             MIT NanoStructures Laboratory       NeXT Mail Encouraged           617 253 0722