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Concept comments and questions

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Joe Diederichs

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Jul 20, 1990, 3:37:13 AM7/20/90
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Some notes and questions on the Concept 30 after a couple of gallons:

I'm still in the process of trying to beat down the new-ship problems
with my Concept and get it into reasonable flying shape. As for my flying,
I'm at the hovering and close-in-figure-8's stage (turns always away).

After a few flights the main gear fit got sloppy, so I installed 2 of the
main gear shims which go above the engine mount main bearing. This is a
pain because you have to tear the whole machine down and guess how many
shims are required. I tried 3 and it was too tight. 2 is just right
(for now).

The machine was going niceably lean at about 1/3 to 1/2 tank. A GMP
flybar weight on the klunk line to get the klunk on the bottom of the tank
seems to have helped this a lot. The fuel is still sloshing around a lot
though. I think some vibration is coming from the engine fan/starter cone.
There is some noticeable runout on these and I haven't ripped it apart to
try to line it up better. I'm not sure how I'd improve the runout anyway.

I spun the clutch with my electric starter when I first got the machine.
When I went in to tighten it up, I used a dowel in the carb throat and really
reefed on it. This may have caused the fan to distort and result in the
runout. Anyone worked on this?

The top main mast bearing froze up on me (the inner race on the plastic
pitch rod guide became my new bearing). I think this bearing may have
come without grease/oil. I used teflon grease on the replacement.

Finally, blade tracking is inconsistent. The blades will be in track, then
go out a bit. I'll adjust it (which requires trying different links to get
one which happens to be the right length since the full-turn-at-a-time links
don't allow fine adjustment of tracking). This will fix it for a short time,
and then it will go off in the other direction. I've heard the real answer
is the SX thrust bearings for the blade holders which aren't available yet.
Hostetler said in one of his articles he fixed this problem by pulling out
the blade holder bearings, popping the shields, cleaning in kerosene, and
re-greasing with teflon grease. Anyone tried this? The Concept Hotline
at tower hobbies says they've only heard of this on machines with heavy
blades like Yale's.

So, I'm slowly but surely beating the problems out of it. It seems like
it has the potential to be a good flying machine. We'll see. Comments
or suggestions would be greatly appreciated.

Fly a lot but don't crash,
Joe Diederichs

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