Jim wrote:
I had a short round trip that averaged 121 the other night. For pre-flight
planning I use 115 to be on the safe side, it seems to work out about right.

Hi Jim,

Yep, just for grins I guestimated airspeed from some logged flights
where I know the RT distance. ~120 kts seems entirely consistant --
few knots faster if it was just two of us and fuel to the tabs,
few knots slower if it was max gross. One of the planes we flew
had some speed mods (wingtips, wheel pants, gap seals) and it did
seem to make a difference of a knot or two.

BTW Chuck Slusarczyk (the CGS Hawk guy) opined that different planes
of the same make and model commonly have a few knots difference in
TAS even if they're w/in tolerance on the wing installation and properly
rigged, just from the sum of subtle differences here and there.

Cheers,
Sydney