"Gene Kearns" wrote in message
...
On Sun, 22 Feb 2004 02:18:40 GMT, "Jay Honeck"
wrote:

Look at a graph from one of those data-capturing engine monitors some
time. The steepest lines on the graph will always be at takeoff. Even
pulling power and diving can't cool the engine as fast as the takeoff
roll can heat it up.

So would this be proof that damage from "shock cooling" is a myth?

No. The offender is thermal shock... heating or cooling.....


It's not clear to me that the stresses in shock heating should be
the same as for shock cooling. Just because people don't
(apparently) suffer from the effects of shock heating doesn't
by itself preclude the possibility of shock cooling.

On take-off, the equilibrium is disturbed by heat being applied
uniformly around the cylinder bores. Any distortions result in
forces being applied to metals at low temperature. Speed is low,
so cooling (and hence cooling distortions) are minimal.

In cruise and at least the initial part of the descent, metal temperatures
are higher. Whether this makes metals more or less susceptible to
cracking, I've no idea - but if shock cooling is a fact and shock
heating isn't, we should expect metal to be more fragile at higher
temperatures. Also, since the initial airspeed is higher, changes in
cooling (speed-up during descent, closing cowl flaps) will alter
temperatures (and introduce differentials) on the 'cooling' side which
are far less uniform than during the initial climbout.

In summary, take-off -- low metal temps, less cooling, similar
'outer surface' temperatures, faster temperature change, descent --
high metal temps, more cooling, distorted 'outer surface'
temperatures, slower temperature change. Quite different
régimes.