idle v windmill....fine pitch v course pitch
Here is a good Refrence:
http://www.auf.asn.au/groundschool/umodule2.html#vspeed
The intent of the following is to get you to think about how you are going to test, configuration, technique and what you are going for. Are you trying to show how great your plane guides in the most ideal config or what the glide will be in a real world emergency. Also weight and even more
winds have a huge affect on how far you will guide or not. You are looking for MIN SINK, independent of wind. Max glide distance involves winds. Keep that in mind for a real world situation and speed.
Consider pulling your prop control out, low rpm, full course. This may extend your guide (a quasi feathering of the prop if you you will). Now will that work if your engine is really shut down (windmilling) verses idle (which is making a little power still)?
If you want more conservative numbers leave the prop to fine pitch.
The question that always comes up is
do you have enough oil pressure to get the constant speed prop off the stop with windmill RPM. This has been debated for a long time. I lost track of the common wisdom, but it comes down to the prop you have and governor. There is one AFM I was told for a single engine plane that suggest you do go to course pitch with an "emergency guide". I suspect if its for real it can't hurt.
Multi engine plane props have counter weights that throws the props to high pitch (feather) and also have gas charges in the hub to help it go into feather. Your prop of course has none of this. However some claim they can get the pitch to change with the engine shut down and windmilling, some say it makes no difference. So if you want to use the KISS principle you can just leave the prop full fwd.
I suspect with idle power you are making a little thrust (or at least less drag) verses a true engine failure with a windmilling prop.
When windmilling a dead engine the air flow has to push the engine around which is energy and drag.
Some say if you have an engine failure you should pull up into a near stall to stop the prop from windmilling? Well that is another debate and I say nice and theory but not practical, at least for a generic glide test. The stop the prop technique may have some validity, but obviously it's not practical at low altitude.
Glide test have always had there issues or controversy when it comes to technique. In the end does it really matter if your best glide is off 10 mph or (9 to 1) or (11 to 1) in the real world? Weight and WIND has a BIG affect on best glide speed and distance. If you are gliding into a wind go faster, with a tail wind slower. For the space shuttle it matters. Bottom line if you want it for emergency glide planing you want conservative.
Consider (at your own risk) getting some altitude over a airport (non-towered, low use, long runway) and
shutting the mixture off, for a one time test. Compare that to flying with idle power (w and w/o prop course). That way you can determine the affect it has if any. If you do shut down the engine, cool the engine off a little level at low power before shutting down.
When I was doing multi engine piston plane CFI stuff, I shut down many engines for single engine flight Demos. The all started up again. Of course if it did not re-light, I had another engine and you have only one.
The Real world: I have heard RV builders claim glide ratios of (7.5 to 1) to (12.5 to 1) and speeds from 87 mph to 120 mph? In RV's my personal engine failure speed is, Vos or Oh S#@^%. I go right to 100-110 mph at first and than fly the plane. Why? it is easy to remember and works pretty well. Than I'll fine tune speed, but first I am trouble shooting and picking and aiming at a landing point.
If you get into a real power off landing and are trying to "milk a glide", you are in trouble. Never go below 80 mph (unless you are flaring). I realize there are variation between RV models, but they all have the same wing. The best thing about doing the glide test is getting a feel for the plane and it will tell you when it is sinking. Try slow speeds and fast speeds, try gross weight and solo min fuel.
(edited: Larry P., thanks for the clarification, I concur. Hevansrv7a, as far as Max L/D x 1.316 = best range at SL, a little fast for min sink. I think Vy is a good starting point for min sink. For best efficiency the Carson speed is Max L/D x 1.316 = or about 120kts or 138 mph. It is faster than best range. Again min sink is not Vbg, best glide. With Vbg, head wind fly faster, tail wind fly slower. Here is a good article.)
www.eaa1000.av.org/technicl/perfspds/perfspds.htm
Here is a good description if Vx nd Vy:
http://selair.selkirk.bc.ca/aerodynamics1/Performance/Page10.html