Speed of Heat

In article
,
"Kurt R. Todoroff" wrote:

In article R5QZd.71896$Tt.15712@fed1read05,
"BTIZ" wrote:

All of the others talk of temperature rise do to compressibility based on
mach number, but no one really addressed the speed accounting for friction
of air molecules on the sheet metal which warms the aircraft. War story
time, low level over the plains of eastern Montana, near Conrad and Havre
Bomb Plots (Radar Bomb Scoring sites) and the outside air temp was
about -15F, however, we were moving along at about .88mach at 500ft AGL,
and
the skin temperature was about 100F, not a worry about accumulating icing.

Some one else referred to "Speed of heat" as being Mach 1, because most
aircraft need after-burner or "heat" (reheat) as the Brits would say.. to
make Mach1. BTDT


BT

Hi BT,

What were you flying? Most of my time is in the F-111D and the EF-111A.
I've also flown the F-15, C-130, C-141, KC-10, E-3. Did your aircraft
have a skin temperature indicator or a total temperature indicator?
Aircraft component heating is due to Mach compressibility, not skin
friction. I'm confident that your 100F value reflected total
temperature which is based on Mach compressibility.

The "speed of heat" received it's colloquial name because the speed of
sound is based only on the static temperature of the fluid medium, not
on pressure or density as is often mistakenly believed.

Kurt is quite correct in this.

You can determine the temperature by taking the Mach number, finding the
local ambient temperature/total temperature ratio. (all temperatures are
absolute temperatures)
At Mach = 1.0, the ratio is 1.2;
at Mach = 1.5, it is 1.34;
at Mach = 2.0 it is 1.8;
at Mach = 3.0 it is 2.8.

Just add the OAT to 459.7 deg F or 273.2 deg C to get the absolute
temperature.