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 lancair.list@olsusa.com; Fri, 11 Jun 1999 19:45:55 EDT
Date: Fri, 11 Jun 1999 19:43:31 -0400
From: John Cooper <snopercod@citcom.net>
Subject: Control Surface Balancing
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Being an engineer by training, I almost went nuts trying to figure the
proper way to balance the elevators. (but we're much better now...)

I figured they should be statically balanced with the carry-thru aluminum
channel in place, after balancing the halves individually. But then I
started to wonder...

What about the weight of the elevator push-rod resting on the actuator arm
ahead of the elevator CG? You have a mass system where, when you pull back
on the stick, you don't want any unbalanced masses to tend to raise the
elevator further when the G-forces start. Then what about the entire
elevator being behind the CG of the aircraft, so that when one initially
pulls back on the stick, the _initial_ G-forces on the empennage are negative?

I decided not to balance with the push rod installed...not sure why...I
just gave up. My small brain blew a fuse at that point.

To do the two elevator halves, I weighed the carry-thru part and attachment
hardware, and guessed where the centroid of the assembly should be, then
found a weight which was equivalent to half of the carry-thru weight and
set it on each elevator half in the appropriate place to simulate the
carry-thru assembly being in place.

Disclaimer: I have not flown yet.

Aside: The paint weighs a LOT more than you think. It's much easier to
overbalance your elevators then drill the excess out, than to have add lead
later like I did. Sheesh!


[The elevator bellcrank on the MKII tail (and the IV and ES tails as
well, AAMOF) is a bit different than the AL channel carrythrough that
was used on the original Lancair 320 tail, and has the weight of the 
pushrod attached at the bottom of the assembly, immediately below the
axis, so the weight distribution is a bit different.  My personal
feeling about balancing the elevators is to overbalance each half
individually with the respective bellcrank half installed, and then to
fine tune the complete assembly (with the complete elevator bolted
together through the belcrank halves) to the recommended slightly aft-high
condition just before finish paint is applied.  

I am not flying yet either... I haven't even done the original balance,
(decided to do that after the stab is installed on the airframe and the
bodywork is underway), but the above seems to be the most reasonable
approach to getting everything done according to the stated requirements.

    <Marv>     ]

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