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Certainly wouldn't argue with your hypothesis, Charlie. Whichever it is,
pulling the power back to idle with the new combination does definitely
increase the rate of descent over the old prop/gearbox combination. I
generally carry around 3000-3200 rpm abeam the touchdown point, I may
decrease it to 2800 rpm if it looks like I am going to be long, but I think
I will pick a calm day and see what an "idle" from abeam looks like from a
rate/angle of descent with the new prop/gearbox.
Thanks for the insight
Ed.
My non-prop-guy (but RV-experienced) opinion is that you might have had
a bit more drag but what you really had was a lot *less thrust*.
My 1st RV-4 had a 72" dia cruise prop (would run 195 mph at 2550rpm,
9.3gph in still air on 160hp) so it probably wasn't too far from your
prop. If prop rpm at idle was set higher than around 700rpm (sitting
still on the ground) you almost couldn't make the plane land because of
the extra thrust.
Is there a chance that you got used to a flattened approach slope with
the old gearbox/prop because it was still making a fair amount of
thrust? With the wider ratio gearbox & pulling the engine to idle, I'll
bet you actually got the prop slow enough to stop making thrust.
Charlie
(always trying to fly patterns at idle from abeam the numbers to
touchdown)
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