REFLECTOR: Gliding Distance

[Brooke Wolf]

Rene

That is some good stuff.  What I am getting from your post is this.  In the event of an engine failure, after all restart attempts have failed and a dead stick landing is planned…….bring the prop control all the way back.  The resulting increased glide performance would multiply your options due to increased time and distance availabilitys.

I would also be very curious to know how to stop a prop.

Brooke


> 
> From: David Rene Dugas <renedugas at gmail.com>
> Subject: Re: REFLECTOR: Reflector Digest, Vol 87, Issue 110
> Date: June 19, 2012 10:09:55 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>
> 
> 
> Does anyone know at what speed the prop stops if the engine is off?  If an engine failure occurred, could one pull up to a stall (68 kts) for a moment and stop the engine spin (and the prop).  If so the subsequent glide ratio should almost double.  I just don't know if that is slow enough to stop the prop.  A spinning prop is like dragging a huge flat disk the diameter of your prop as long as it is spinning.  If it stops the only drag are the three stationary paddles almost as good as a feathered prop.  I have never stopped the prop and I'm not recommending it but IF someone has I'm interested.  9:1 with spinning prop seem about right and is what I use for emergency calculations but I think it is very likely 12 to 15:1 is likely if the prop can be stopped.  
> In an emergency, if one forgets to go to coarse pitch and is descending with flat pitch one can get a huge kick in the butt by going coarse if you see you are going to be a little short changing the potential energy of the spinning engine into thrust with coarse pitch.  Try it on approach sometime with the runway made pull the prop back quickly and feel the boost even at idle.
> Rene'
> 
> 
> On Jun 19, 2012, at 7:48 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?
>> 
>> 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?
>> 
>> 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?
>> 
>> 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.
>>> 
>>> On 6/19/2012 12:26 PM, Brooke Wolf wrote:
>>>> 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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