REFLECTOR: Reflector Digest, Vol 87, Issue 110

[Scott Baker]

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.
>>
>>