Here is a little safety trick for all you guys with
GPS. This is particularly important for all of us
doing non aircraft engine installations.
Climb up to about 5000 feet AGL over your air port
and kill the engine. Note how far you can glide from the GPS
data for a 1000 foot decent at best glide speed in a straight
line.
Then do the same for two 90 degree turns. This will give you a
feel for altitude loss as a function of distance when making
dead stick landings. It would help if you have your landing
field lat longs in a way point in your GPS just in case. this
will give you a glide ratio for your particular airplane
rather than assuming it is the standard for light planes of
around 7:1.
It would be great if Greg Richter allowed specific glide ratio
data to be entered into his moving map program. If your engine
quit your moving map program could then tell you if you could
make it to a particular emergency landing field. Assuming of
course the lat longs are in his moving map program for all
possible landing fields.
Paul Lamar
Good idea. I was surprised at how much the glide ratio
deteriorated with the engine stopped. I had assumed the prop
was generating about the same drag at engine idle as engine
stopped. Had 600 - 700 fpm sink rate at idle and 900 fpm with
engine dead. My Anywhere Map GPS (running on Ipaq) shows cone
of safety around airports when you plug in your glide ratio.
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
Could this be a result of having a fairly high pitch prop
which is still producing some thrust at idle? The CAFE test
guys go to extreme lengths to zero out thrust by measuring
fore/aft position of the crankshaft (centering it within its
possible end-play) while actually adding power above idle
rpm when they do their glide ratio measurements. If the
engine is not running at all, then a stopped prop should
have less drag than a windmilling prop. For an analogy,
consider a gyroplane with rotating vs. stopped rotor.
Windmilling might be a moot point with wood props &
reduction drives, but if you fly a conventional a/c engine,
it's good to remember how to get max glide if it quits.
Charlie England
The problem with high pitch props extending the landing task has been pointed out
by others. This is the reason that a low idle speed is important with a fixed pitch
prop. The high pitch that we are dealing with will still produce measurable amounts
of thrust. Note that the 2.85 ratio redrive is an advantage here because of the
slower prop speed when the engine is at idle. This has caused me some concern
since PP motors are not known for their smooth idling characteristics. However, it
appears that if the throttles are located next to the rotor housing on a PP motor that
the idle will be acceptable. It is completely unknown if the redrive will have any
objections to the low RPM - seems likely that there will be a idle speed limit due to
harmonics with the engine/redrive combination (This probably isn't stated exactly
right from an engineering view, but this seems to describe what most people have
described). I should have answers to these questions before I fly.
Ken Powell
RV-4
(Hope to fly in this lifetime!!!)
Flying in this Life Time (Ihope!!!)
I am not sure but I would not be a bit surprised if the prop just
stops. Kind of hard to rotate the engine 2.17 times as fast as the
prop from air pressure alone. Perhaps in a dive.
The 2.85:1 might be even more difficult.
In any event if it does not stop you could pull up and you may be able
to stop the prop if there is no possibility of restarting the engine.
To reduce drag and extend your glide.
If the engine idles only and does not respond to the throttle I would
say that is a rather rare failure mode. These should be things you
should find out about in early testing with plenty of altitude.
Perhaps Tracy or someone else flying can do these tests for us.
The prop does stop. Going 100 mph it would stop, pointing the nose down a bit the prop will
try to turn, maybe half a revolution now and then.
Finn
Do you know the RV3 glide ratio Finn with the prop stopped?
Paul Lamar
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