Before you go too far, check your tach, as somebody else already
suggested, and -- what rpm can you really get at full throttle, level
flight, 7500 ft? You might find that the tach is off by 100 and/or the
rpm tops out at 2750 or so at 7500ft. If that is the case I'd say you
have exactly the right prop. Climb props and cruise props are
poorly named. A cruise prop that won't turn redline at 7500 ft is
definitely slower than a climb prop that will turn redline at full
throttle at 7500. Non-boosted of course. Add to that the fact that
the climb prop will get you up to 7500 quicker.

Ross Oliver wrote in message ...

Last week I flew my Grob from San Jose (RHV) to Torrance (TOA)
and back. Total time was nearly 6 hours, but burned
only about 30 gallons of fuel. The book says 9 gallons per
hour at 75% cruise. I've noticed this before, that it never
burns nearly as much fuel as I would expect. Another thing I
noticed during the flight that I had never thought much about
before is that in cruise, the throttle is about 3/4 closed, even
at 2600 RPM at 7500 feet MSL. Redline is 2700, and opening the
throttle further would push past redline. I haven't flown any
other planes in a while, so I can't recall whether this
throttle position is unusual.

All this seems to say that I am cruising around at Best Economy
(which the book says is 45%, 5.3 gal/hr). This would also explain
why I get only 105 kts IAS, rather than 115-120. I would
surely like to go faster, but I can't figure out how without
exceeding redline RPM. Is my tach in error? Do I need a different
prop? (fixed pitch) What else should I be checking? The engine
is a Lycoming O-320, same as a Warrior.


Happy landings,
Ross Oliver