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Old Jul 03, 2015, 08:14 PM
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FYI:

A tail heavy plane needs down trim to lift the heavy tail for level flight. When you roll to knife edge the down trim pushes the plane towards the landing gear.

A nose heavy plane needs up elevator trim to hold the tail down for level flight. When you roll to knife edge this up trim will pull the plane towards the canopy.

Trim 3DHS airframes for as close to hands off knife edge as possible and they fly their best. Don't worry about the elvator lining up with the horizontal stab. The CG is not correct just because the stab lines up with the elevator...but that seems to be what a lot of misinformed people try to do.
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Old Jul 03, 2015, 09:11 PM
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thanks for all the input

i was getting roll coupling in knife edge. i will aim for cg with no pitch coupling to start....

matt
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Old Jul 03, 2015, 10:14 PM
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Quote:
Originally Posted by G.P. View Post
Trim for level flight at about half throttle. Roll to knife edge. If it tucks to the gear it is tail heavy. If it pulls to the canopy it is nose heavy. Adjust CG and retest until it is almost hands off in both directions. You should be able to get it hands off in one direction, but usually not both directions due to the spiralling prop wash. The plane will require a slight push on the elevator when inverted when the CG is correct. It will not be hands off inverted. That is how AJ designed it and it will track better and fly best with the CG in that location.
It tucks to the gear as is so we'll move the pack ahead some.
It does need a bit of down elevator now, more than I think it should.

I have a 6s setup, 500g motor and 20x8 Falcon with nylon spinner and alloy back plate. Currently pack is about 2" ahead of wing tube, sound close?
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Old Jul 03, 2015, 10:28 PM
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Quote:
Originally Posted by G.P. View Post
FYI:
Don't worry about the elvator lining up with the horizontal stab. The CG is not correct just because the stab lines up with the elevator...but that seems to be what a lot of misinformed people try to do.
This might be my issue then. I've been trying to CG without trimming as I assumed Elev and Horz.Stab should align.
Should make some more progress barring this new info.
Thanks
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Old Jul 03, 2015, 10:34 PM
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Quote:
Originally Posted by mattnat View Post
thanks for all the input

i was getting roll coupling in knife edge. i will aim for cg with no pitch coupling to start....

matt
Not sure if CG will help with that. It's a good place to start though. I should clarify that there is coupling in high alpha knife edge. Normal knife edge flight should have minimal coupling.

Quote:
Originally Posted by gimpygolden View Post
It tucks to the gear as is so we'll move the pack ahead some.
It does need a bit of down elevator now, more than I think it should.

I have a 6s setup, 500g motor and 20x8 Falcon with nylon spinner and alloy back plate. Currently pack is about 2" ahead of wing tube, sound close?
My airframe is the old 70" electric only version. Sounds like you should be in the ballpark though.

Moving the CG forward will require even more of a push when inverted. Reducing the amount of elevator expo will make it so you don't have to push the stick as far and may help give you more of the feel you want. You may just have to find a CG that is a compromise.
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Old Jul 03, 2015, 10:39 PM
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Rcg user fmidgett (http://www.rcgroups.com/forums/member.php?u=36746) and Andrew Jesky made a great DVD called "All Things Slick" that went over the proper set up and trimming of the 70" Slick. You may still be able to get a copy by sending Fred a PM.

Andrew Jesky Takes RC to a Higher Plane Volume II, All Things Slick (1 min 58 sec)
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