# Talk:Aerodynamic heating

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## Low velocities

The article says "Aerodynamic heating is not a factor at subsonic speeds", but it is present isn't it? As T_amb*(gamma-1)/2 * M^2 is continous, then heating is taking place at all speeds, and whether it is significant depends on what is being considered. For example, Mach 0.5 in air at 20 deg C gives a temperature rise of close to 15 deg C. JBel 19:44, 12 November 2007 (UTC)

DoneMangogirl2 02:40, 14 November 2007 (UTC)

## History

It is surprising to learn that ancient authors believed that lead sling-bullets, heated by their passage through the air, would melt in flight.

Lucretius, On the Nature of Things[1] --
Just as thou seest how motion will o'erheat
And set ablaze all objects, - verily
A leaden ball, hurtling through length of space,
Even melts.
Virgil, The Aeneid[2], Book 9, Stanza LXXV --
His lance laid by, thrice whirling round his head
The whistling thong, Mezentius took his aim.
Clean through his temples hissed the molten lead,
And prostrate in the dust, the gallant youth lay dead.

Although they were incorrect, it does show that the idea of aerodynamic heating has a long history - and demonstrates quite sophisticated thinking from early times. Gaius Cornelius (talk) 16:58, 30 April 2008 (UTC)

## what formula?

what are the correct formula to use when calculating the the aerodynamic heating on a bullet or on an aircraft wing, such as the edge of a delta-winged surface designed to have an attached shock wave? -- 99.233.186.4 (talk) 19:33, 2 February 2010 (UTC)

does effective temperature of the air increase with the square of the velocity? as, T = mv2/( 3kB ) where m=mass of an air particle? (see thermodynamic temperature#cite_note-Boltzmann-15). This would make mach-20 feel like a 50000 K plasma. is it right? -- 99.233.186.4 (talk) 19:40, 10 February 2010 (UTC)

The related page http://en.wikipedia.org/wiki/Ram_pressure provides a formula. The two pages should either be linked or condensed into a single article.

## Mach numbers when dealing with high altitudes?

It seems strange to use Mach ratings for speed of re-entry, since they decrease with altitude. The article says, "The heating induced by the very high speeds of reentry of greater than Mach 20 is sufficient to destroy the structure of the vehicle." How can this be useful information, when Mach 20 at altitudes where re-entry takes place may be a significantly lower velocity than at sea level? Is this statement instead referring to sea-level Mach ratings?

If it's a literal Mach rating, adjusted for the average altitude for re-entry, it may be misleading to simply refer to it this way, without also giving an actual velocity (in meters per second, for example). —Preceding unsigned comment added by Aerodanar (talkcontribs) 20:10, 21 June 2010 (UTC)

It is primarily the Mach number, not the velocity, that determines how gasses interact with an object. MarcusMaximus (talk) 01:24, 29 July 2011 (UTC)

## Concorde

The sentence relating to Concorde has 3 errors I believe:

1. It's "Concorde", never "The Concorde"
2. Only fairly standard aluminium alloy was used throughout, which is why its top speed was restricted to Mach 2.02. See the Heating Issues section in the Concorde article.
3. I've read several books about Concorde and this is the first I've heard of the use of heat sinks in the leading edges. Given the supersonic flight time, mass required for a heat sink and lack of anywhere to dump the heat, this seems very unlikely indeed. The fuel was used as a heat sink for the cabin air conditioning, possibly the original writer was confused with this? — Preceding unsigned comment added by 86.9.196.114 (talk) 08:30, 1 January 2013 (UTC)