Ed, while I was working for an
aircraft manufacturer we did a fair amount of flying with the prop
stopped. Two things pop out one is the the most efficient position is
without the prop being horizontal. I.e. don't align it with the wing it
causes separation drag. More interestingly, in my Lancair 360 I have
tried several configurations, Prop stopped, prop windmilling and prop
windmilling full course (low rpm) and the results were suprising. The
airplane had a better glide distance with the prop windmilling and prop
full coarse. This is initially suprising but when you think about it
, it makes sense. The Lancair is very low drag and the flat plate area
of the stopped prop is very large compared to the total drag of the
airplane. No other airplane that I have tested has this unusual
performance change. The turbine Lancair with it's big prop is also
suprising with the prop in feather, it will glide with an apparent L/d
of about 20.
Scott is quite right that the gliding distance is remarkable with
the prop in full decrease. I have done a fair amount of gliding with
the engine stopped (close to a long airport) and the change is gliding
distance (L/D) is huge. One must keep in mind that the engine may not
restart so care is required.
Jack Webb
L 360, L IV
ATP, CFI Airplanes & Instruments, Multi,
& Sea
Many Type Ratings
Experienced Experimental Test Pilot both multi and single engine
Former Chief Engineering Test Pilot for a Major Manufacturer
AeroSpace Engineer BSAE
Ohio
>One other thought which I hope
will spawn further input, I've been told by many that, given the
altitude, one should consider pulling up and stopping the prop. Again,
I've >been told that the flat plate drag drops dramatically. Anyone
have any hard info on this?
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