Speed of Heat

In article ,
Don Hammer wrote:

On 14 Mar 2005 21:23:47 -0800, "vlado" wrote:

Is there a rule of thumb for 'speed of heat'?

I don't have a CR-2 with me, but it seems like the ram rise at M.82 is
about 7 deg C.

The Mach heating temperature rise ratio (T_t / T_s) at M0.82 is .13348
referenced to absolute temperature regardless of altitude and other
atmospheric conditions. For example, if the static air temperature
(T_s) is -40F, then the total temperature (T_t) is +16F. The Mach
heating formula is:

TAU = T_t / T_s = 1 + ((gamma-1)/2)M^2

For a typical atmospheric gamma value of 1.4, the equation reduces to:

T_t / T_s = 1 + .2M^2

Converting -40F to absolute:

-40 + 459 = 419R

Insert temperature and Mach into the formula:

T_t / T_s = 1 + .2 * .82^2 = 1.13448

And:

T_t = T_s * 1.13448 = 419 * 1.13448 = 475R = 16F

So, if the outside air temperature is -40F ambient (zero velocity), then
at M0.82 the total temperature would be +16F.


Icing conditions don't occur at flight levels for cruise anyway, so a
jet aircraft will only ice during climb, decent, or holding.

This is not correct. Icing conditions can and do occur at any altitude
in which visible moisture is present.

If the
old gray matter serves me, I think Rockwell proved the aircraft could
fly acceptably with any ice load it was expected to encounter. The
type certificate for the military versions show them as VFR only when
operating in the civil system. I doubt seriously it could pass the
testing now required for certification. I seem to remember some de-ice
mods to later versions, but I'm not sure. They did de-ice the engines
and the windscreens are heated. Most of these aircraft are in the
scrap yard by now I would imagine.

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