Dudley Henriques wrote:
Most of the actual sound the ear picks up from an airplane is caused by the
prop. In the case of the Mustang, with a Hamilton Standard propeller, you
have a prop with an 11 foot 2 inch diameter. Naturally a prop this size has
a tip speed problem so in a stock Merlin its geared down to a .491:1 through
a reduction gear to the engine RPM. At 3000 RPM , the prop is actually
rotating at 1473RPM. Its mostly the sound the prop makes as it works the air
coupled with the exhaust tuning through the tubes that gives the 51 its
distinctive sound. There's also a contribution through the radiator that
adds just a "touch" to the mix.
My conception has always been that its a moaning sound; sort of like a low
pitched moaning wail.
Dudley

I've only heard a Mustang flyby once and it was memorable. I went to
the Corsairs over Connecticut roundup last year and heard a few low
passes by a 4-ship that gave me goosebumps. Gotta love round engines.
The owner of my company flew P-51s in WW2 based at Martlesham Heath.
They'd transitioned from the P-47s (early D models with the razorback
canopy) to the -51 and their type training consisted of a copy of the
AFM and a few spins around the patch and they were mission qual'd.
Yikes.