john B. wrote:

A document named "Flight test of P-51H Airplane", dated 14 October
1945, is available on the Web and states in part that:

Elevator trim for take off is 1 degree Nose Heavy, i.e., nose down.

It goes on to state that "at high manifold pressures approaching 90
Hg, where water injection is required, the elevator trim is inadequate
and excessive forward pressure on the control stick is necessary to
maintain level flight."

Maybe that "Flight test... " document was about a particular airplane
that needed some re-rigging. The words "inadequate" and "excessive" say
unsatisfactory.

The stock P-51 was made to be handled by twenty-something-year-old
pilots with little experience. The vertical fin on the stocker is turned
to offset P-Factor, relieving some of the need for the pilot to hold
rudder at high power and low speed.
The Reno racers are rigged differently. They have their fins set
straight, they want to minimize trim drag.

So, it appears that even at low (take off) speed the P-51H required
some nose down trim and at high power settings the elevator trim was
inadequate to maintain level flight and the pilot had to hold forward
pressure on the stick.

And that would be draggy at 400+ mph.

When operating at high power settings it is obvious that full nose
down trim plus additional stick force will be required. If while
flying in this condition the elevator trim tab were to separate from
the aircraft it is logical to assume that extremely violent nose up
forces would occur.

All depends on the horizontal stab incidence. I think the trim tab
should be doing very little at high speed.



Cheers,

John B.