REFLECTOR: Gliding Distance

Brooke Wolf bwolf1 at tds.net
Tue Jun 19 22:08:56 CDT 2012


Thanks Scott.  This is going to be fun to check out!

Brooke



> 
> From: Scott Baker <scottb33333 at gmail.com>
> Subject: Re: REFLECTOR: Reflector Digest, Vol 87, Issue 110
> Date: June 19, 2012 9:44:42 PM EDT
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Reply-To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> 
> 
> On 6/19/2012 8:48 PM, Brooke Wolf wrote:
>> Scott,
>> 
>> Great idea.  I will try it and let you know.  I do have a couple of questions.
> 1.  In flat pitch at idle power, it seems that the prop would be driving the engine.  If I pull the prop all the way back to a more coarse pitch, the engine may drive the prop.  Am I right in these assumptions?
> 
> SB> At idle power, the engine will drop several hundred RPM by pulling the propeller fully back to coarse pitch. Is the engine developing thrust? I think so, but not much.
> 
> 2. Is there anything I need to be cautious of in pulling the prop all the way back during inflight idle operation? Any undue stress on the engine? How about return to normal operation?
> 
> SB> No issues in pulling the propeller back to full coarse pitch during a power off glide. When returning to normal operation, it is best to slowly bring the propeller control to fine pitch (over a period of several seconds) to avoid a rapid increase in RPM. I understand this is more important with engines with counterweighted crankshafts, causing less stress - and also to avoid possible overspeeding of the engine.
> 
> 3. I would be interested in finding out how to determine the "zero thrust" prop pitch setting. This setting would better define glide performance. Any ideas?
> 
> SB> No ideas on how to obtain 'zero thrust' in a propeller that does not feather. What's important to this discussion is. short of stopping the propeller in flight, bringing the propeller back to low RPM during a power off glide will result in the best possible glide ratio. With an approximate best glide speed of 95 mph or 8,360 feet per minute ... and an approximate 600 feet per minute power off glide rate of descent (gear UP, propeller LOW RPM), this should yield somewhere close to a 14:1 glide ratio.
> 
> Thanks Brooke (neophyte piston pilot)
>>> 
>>> Brooke,
>>> I encourage you to do some more power off glide tests, this time however bringing the propeller control all the way back to low RPM. The difference in glide performance is amazing. It's like an automobile going into overdrive! Do this at an altitude where you can bring the propeller back to normal RPM slooooowly during the transition back to normal flight operations. A lightly loaded XL should give a 14:1 (or better!) power off glide ratio. Looking forward to you next report!
>>> Scott B.
>>> 
>>> 
> 
> 
> 
> 
> 
> 
>>>> > From: bwolf1 at tds.net
>>>> > Date: Tue, 19 Jun 2012 12:26:23 -0400
>>>> > To: reflector at tvbf.org
>>>> > Subject: REFLECTOR: Gliding Distance
>>>> > 
>>>> > I am planning some overwater trips in the near future and the subject of gliding distance naturally comes to mind. I have done some limited test flying with my airplane (XLRG w/Aerocomposite variable pitch prop). The results of my gliding performance are not too good. All tests were done around 6000ft with throttle at idle and wheels up. Here are the results:
>>>> > 
>>>> > 80 KIAS - 900fpm…….. yields a glide performance of 1.38 miles/1000 ft altitude
>>>> > 85 KIAS - 1000fpm……..yeilds a glide performance of 1.41 miles/1000 ft altitude
>>>> > 100 KIAS - 1250fpm …..yields a glide performance of 1.34 miles/1000 ft altitude
>>>> > 
>>>> > As you can see, 85 KIAS appears to be the best glide speed.
>>>> > 
>>>> > I know there may be a big difference in what I tested and what happens in the real world with a windmilling or stopped prop. Have any of you brave test pilots done any testing with a windmilling or stopped prop? What were the results? What kind of glide performance did others get with throttle at idle? Is there anyway to correlate throttle idle glide performance with windmilling or prop stopped performance? What is the best way to stretch a wheels up glide on a Velocity?
>>>> > 
>>>> > I would like to get a discussion going on this and find what others have experienced. Thanks.
>>>> > 
>>>> > Brooke, N108BG, XLRG-5, 145 hours
>>>> > 
>>>> > 
>>>> 

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