Re: Aeronca 11AC Chief Project FS

On Jun 23, 5:55 pm, Jay Maynard <jmayn...@[EMAIL PROTECTED]
>
wrote:
> What do you consider a "very disturbing amount"? I want to try it on my
> Zodiac.

Jay, I moved the tip of the stabilizer fore and aft about three
inches, which resulted in the four main stabilizer mounting tabs
moving in a twisting/shearing motion relative to each other. I first
did this on a 601XL which was built by one of our local EAA chapter
members. I thought for sure that the guy had forgotten a piece of
metal someplace. But one of our other EAA chapter members is an
engineer, he read the plans, and determined the tail attach had been
built per plans.

Then I tried to duplicate this fore-aft movement on a CH 701, which
uses a similar mounting, and was able to move it some amount as well.
Then I tried it on another 601XL which was built by the factory (QSP
in Cloverdale, CA) and was able to move the stabilizer fore and aft an
inch or two, again with the twisting/shearing motion on the stabilizer
mounting tabs.

I am definitely NOT an engineer, and cannot run any numbers or make
any authoritative statements about the structure. Chris Heintz IS an
engineer, and supposedly a very good one. But I will say that if/when
I build my 701 I will research and add some more aluminum back there
to stiffen and reinforce the structure so you can't move the stab tips
fore and aft. There are probably little or no assymetrical NORMAL
FLIGHT LOADS on it, but small movements back and forth caused by air
buffeting and vibration over some period of time can easily cause the
metal to become brittle and/or crack. Speaking as an AMATEUR mechanic,
I believe the problem is that the stabilizer mounting tabs are not
sup****ted against bending or movement in one or two directions, and
the tabs stick up too far above the upper longeron for the off-axis
loads to be totally absorbed by the thickness of the metal.

Real engineers are more than welcome to correct me, disagree, or tell
me the problem is valid but far too small to cause a problem. Call me
a dinosaur, but I don't think you should be able to move the
stabilizer on an airplane that far fore and aft while watching the
fuselage structure twist from medium force hand movements.

And in response to what someone else posted, the 601 is not the best
or safest airplane by any stretch. The DC-3 / C-47 has a 70+ year
record of flying without ever one single structural failure.