JP wrote:


The P-39/P-63 examples can't probably be compared directly with this matter
in question. These designs both have a large reduction gear casing in front
of the plane. The support structure for this PSRU looks very firm. Perhaps
the safety cage type center fuselage structure has something to do with the
lack of severe resonance problems? Any known resonance problems with these
aircrafts?

JP

I doubt any such information would be of value here since the those
PSRU has a gun barrel through it. Assuming any contact between the gun
and the PSRU any resonance solutions would be different.

Dan, U.S. Air Force, retired