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        Discussion How do you eliminate pull to gear in knife edge flight

#1 kenh3497 Oct 10, 2012 09:45 AM

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

#2 exf3bguy Oct 11, 2012 07:01 PM

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.

#3 kenh3497 Oct 11, 2012 09:09 PM

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:o

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

Ken

#4 neddis Oct 17, 2012 10:31 PM

Quote:

Originally Posted by exf3bguy (Post 22976562)
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.

#5 kenh3497 Oct 18, 2012 09:17 AM

Quote:

Originally Posted by neddis (Post 23031743)
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:D.

Ken

#6 exf3bguy Oct 23, 2012 08:04 PM

Quote:

Originally Posted by neddis (Post 23031743)
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.

#7 tele1974 Mar 21, 2013 01:45 AM

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

#8 Kevin2035 May 14, 2013 11:05 PM

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.

#9 kerwin50 Jun 15, 2013 09:38 PM

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.

#10 riz1963 Jul 05, 2013 01:18 PM

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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