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Alan,
Your Coupe has a range of minimum flying speeds varying from max power
to power off. Fred Weick put
significant effort into designing the Coupe so that the difference in these two
extremes of minimum flying speed are as little as possible. Saunders Aviation which bought Coupe
manufacturing rights from ERCO reduced that variance even more with the split
elevator.
With zero power, the up elevator can only push the tail down so much,
giving a minimum flying speed that is almost constant for your plane.
When you have some power, the slipstream will push the raised elevator
down even more. This results in more
nose up and greater angle of attack and therefore an even lower minimum flying
speed.
At high power settings, the tail can be pushed down pretty far. If the tail is pushed down too far, you
would lose the “characteristically incapable of spinning” feature of
Coupes. That is why, Fred Weick
told me, that the D model has the 9° up travel limitation – with 13° up travel,
the 85 hp engine and 1400 lb. gross weight, the tail could be pushed down so
far the flying characteristics were judged by the FAA to be unacceptable.
I’d only get about 5 mph difference between zero power and some
power. I used this to good effect
on long runways. Just as I flared, I’d raise the power from idle by a couple of
hundred rpm (just enough I could hear the difference in rpm) and I’d hold the
nose on the landing light on the far end of the field. With this mild power setting giving a
low sink rate in ground effect and a moderate nose up attitude, I got 100% squeakers
– very good for impressing passengers and other pilots.
When the engine fails, the prop normally windmills. The windmilling prop will give extra
drag – a little bit more drag than you get at idle. This will lower your gliding distance and ratio. If you could stop the prop by raising
the nose, you’d be back to about the drag you get with an idling engine. I made
the personal decision that I wouldn’t (normally) try to stop the prop – it’s
better, I decided, to just pick a good place to land and concentrate on putting
it there.
I’ve rarely seen experienced instructors recommend turning off the
engine for gliding practice in GA aircraft. Besides, there’s no **guarantee** you could start it while
flying the plane. I guess, if I
had a 5,000-12,000’ runway all to myself, I might try a series of
engine-turned-off landings (but I doubt the tower would like me much if I
did). I’m not going to do such
practice in a Coupe at a 2,000-3,000’ airport.
Turning off the master switch won’t affect the engine at all. Turning off the mags will. I don’t know what would be the effect
on the engine of turning the switches back on, with the engine windmilling,
after you’ve loaded the cylinders with some weird fuel-air mix or with globs of
liquid fuel.
I’d just suggest practicing your power off landings at idle with your
target being a line about 1,000’ down the runway. Be firmly aware, that with a zero-power, windmilling prop,
you won’t glide quite as far as your idling-prop practice. Maybe you could simulate the
windmilling prop by having your passenger hold both arms straight up out the
open windows. (Holding arms down toward the wing-root diminishes glide even
more, I’ve heard.)
These are good playing things to give you a challenge and make puttering
around the airport more fun.
Enjoy.
Ed
Burkhead
http://edburkhead.com/
[EMAIL PROTECTED] (remove the XXX)
-----Original Message-----
From: alan1
[mailto:[EMAIL PROTECTED]
Sent: Friday, September 05, 2003
10:16 AM
To: Ed Burkhead
Subject: [SPAM] Re: [COUPERS-TECH]
glide ratio
Ed,
Thank you for relating
your gliding performance testing procedures and calculations. I have one
question, however. How do I determine my Ercoupe's minimum flying speed ? Power off, yoke full back or with enough power to
maintain altitude?
Also, as someone suggested, should I
practice over the field by turning off the mags and/or the master switch and
see what happens? If I do that, can the engine be restarted mid-air
should the need arise? Will the prop stop or will I just drop?
O
*<==N99616==>*
/ \
o o
Alan & Marilyn
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