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Date: Tue, 03 Aug 2010 16:49:59 -0400
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Subject: Re: [LML] flap coupling
From: bob mackey <n103md@yahoo.com>
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Wolfgang says:
> I have looked at that and adding a plate to the bellcrank
> at the end of the flap actuator in the 320/360 can give an
> attachment point for the coupling spring right next to the
> elevator push rod.

Sounds like the right idea to me. However, from my experience,
I don't think 90 deg is the angle you will want. The flap affects the desired
elevator position most strongly when most of the way down.
My spring goes slack when the flaps go into reflex. Effectively that
gives me a two-stage spring rate (X lb/in and 0 lb/in).
I don't know the spring rate off hand, but the spring is about 0.040" wound in
3/8" diameter and about 4-5" long. Yours will be different depending on the
lever arm of your bellcrank, and your elevator pushrod may also have a
different lever arm at the elevator or bob weight.

You can have a smoother force curve by letting the angles of the bellcrank
work for you. I'm guessing you will want the spring pulling 90 deg to
the bellcrank when the flap is all the way down. As the flap comes up, the
rate will decrease. You'll have to tweak the spring rate to get it
right over the
full flap deflection / speed range.

Of course you want to make sure that the new parts can never jam the elevator.
I flew my test flights with the console open and a pair of wire cutters at hand.

-bob