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Old Oct 10, 2012, 10:45 AM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
4,277 Posts
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How do you eliminate pull to gear in knife edge flight

My CAP 232 (the on in my avatar) pulls to the gear in knife edge flight. Is there anything to be done to eliminate this pull. I know it can be mixed out, but prefer to not mix if I can help it. I've read and done the triangulation trimming, balance and adjusted the incidence on the wing. I know the scale aerobatic planes are a different animal, as far as trimming is concerned, than a pattern plane.

I need to build a new wing, as I broke the current wing in flight if that would make a difference.

Thanks!

Ken
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Last edited by kenh3497; Oct 10, 2012 at 12:08 PM.
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Old Oct 11, 2012, 08:01 PM
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exf3bguy's Avatar
Joined Oct 2011
503 Posts
Trimming.

Ken, trimming is always a compromise. The things that are going to affect this tuck in knife edge are: CG, wing incidence, thrust angle and dihedral.

Moving the CG forward will help but could take away from other areas of performance. The forward CG will require a bit of up trim that will help fix the issue.

When setting up an aerobatic model, I always set the engine and stab to zero and the wing at pos. .5 degrees.

Adding Dihedral on a low wing model like the Cap can help as well but again can cause other things. The first thing that comes to mind is roll coupling when rudder is applied.


My first IMAC airplane was a Ohio Models 33% Cap. I remember having to run the CG a tad forward and mix the rest out. Nothing wrong with a mix as long as it is not excessive.
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Old Oct 11, 2012, 10:09 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
4,277 Posts
This cap started life a s a H9 "sport 40". It was the silver with the sharks mouth. Crashed at about 10 flights and the rebuild turned into a scratch build saving a few key components like the cowl, canopy and turtle deck. It had zero roll coupling and performed flawlessly except for the tuck on knife edge. I might just rebuild the wing as is. I never was a great knife edge flyer any way

I did reduce the dihedral a tad from stock when I rebuilt the plane. Maybe I should go back to the higher amount????

Ken
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Old Oct 17, 2012, 11:31 PM
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neddis's Avatar
United States, OR, Hermiston
Joined Apr 2011
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Quote:
Originally Posted by exf3bguy View Post
Nothing wrong with a mix as long as it is not excessive.
Just out of curiosity, how much mix do you think is too much? I have a Pilot-RC 25% SBach that tucks to the gear quite a bit in KE. I don't want to move the CG - I really like it where it currently is. I have experimented with forward and back and it is just about neutral now and flies best that way. I have to mix about 14% to keep it in a straight line in knife edge.
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Old Oct 18, 2012, 10:17 AM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
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Quote:
Originally Posted by neddis View Post
Just out of curiosity, how much mix do you think is too much? I have a Pilot-RC 25% SBach that tucks to the gear quite a bit in KE. I don't want to move the CG - I really like it where it currently is. I have experimented with forward and back and it is just about neutral now and flies best that way. I have to mix about 14% to keep it in a straight line in knife edge.

I'm in the same boat as you as far as happy how the plane flies. I haven't used any mix so far. I was looking for a setup cure first. I don't compete with this plane. It's just a sport flyer, a very good sport flyer.

Ken
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Old Oct 23, 2012, 09:04 PM
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exf3bguy's Avatar
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Quote:
Originally Posted by neddis View Post
Just out of curiosity, how much mix do you think is too much? I have a Pilot-RC 25% SBach that tucks to the gear quite a bit in KE. I don't want to move the CG - I really like it where it currently is. I have experimented with forward and back and it is just about neutral now and flies best that way. I have to mix about 14% to keep it in a straight line in knife edge.
The percentages don't mean a whole lot. My JR stuff will show % much lower then my Hitec A9 for the same thing. IMO if you need to mix anything that requires more then 1/8" mix travel as measured at surface TE then you need to make airplane adjustments.
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Old Mar 21, 2013, 02:45 AM
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tele1974's Avatar
USA, OH, Olmsted Falls
Joined Feb 2007
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This is a good read. I have my IMAC and Pattern planes setup with Bryans method.
Also, check out the testimonials.

http://www.hebertcompetitiondesigns....ing.aspx?ID=11
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Old May 15, 2013, 12:05 AM
Kevin S. Gribben
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Joined Mar 2011
363 Posts
EXF has it right....a little forward on the CG... as long as it doesnt loose rudder authority. Most of mine.. 5% on mix goes a long way, that is more than enought to keep it straight.
On some of my 45% I switched to 30% wheel and pant configuration that will reduce the drag on the belly. Though a lot comes from the high pressure on the canopy whe established in the knife.
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Old Jun 15, 2013, 10:38 PM
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winston mo
Joined Oct 2006
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I too at 1st was opposed to mixing my rudder to elevator but after trying it a few weeks ago I fell in love with my mix. I've had a complete change of mind. Now it's just like triming a plane. I've even found my stall turns to be better. of course Mine was tucking to the canopy. I heard that tucking towards the canopy was a tail heavy condition.
I mixed 6% elevator to my rudder. At 1st I had my mix on a switch but I found no need to switch the mix off.
I now really enjoy the death slides and flying my planes around in a KE pattern.
My planes that I used the mix on is a 3DHS 41 inch edge and a 26 cc goldwing Yak.
I'm now going to work on mixing my other planes as well.
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Old Jul 05, 2013, 02:18 PM
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Joined Apr 2011
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I think airplane configuration also plays a role in what it can do better than others. CAPs were perhaps hot favorites in mid 90s (real plane). Later Extras took the podium.
CAPs low wing with dihedral, and stab placement almost on top of the aft turtle deck is very peculiar.
One can never have a plane executing every move perfectly.....there is always a trade off. CAPs do tuck towards belly in KE, but I think they perform beautiful snaps....no other plane does is so elegantly.

Coming back to the query of belly tuck... if your CoG is spot on (according to trim chart) then mix in 2-5% up elev with rudd. BTW I always keep those mixes on.

My two cents.
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