Originally Posted by sailingfun

Many flying Vans RV's have looked at this question since the aircraft has such a poor glide ratio. Quite a few have actually shut the motor off and ran tests. The aircraft glides far better with the prop stopped then windmilling. Probably on the order of 20 to 25%. This is a fairly small aircraft often with a big prop. If the prop is composite it's fairly easy to get it stopped. If it's metal it can be more difficult since there is no ability to feather. Course verses fine pitch also makes a difference but not nearly the effect stopping the prop has.