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Old Oct 08, 2013, 08:42 PM
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Piper Cub Incidence

Built an Ikon West 1/4 scale Super Cub last winter. Had it out a few times this summer and this thing flies miserable, nothing like Cubs I've had in the past. I noticed during building that the incidence on the plans was 0 wing and 0 stab. I debated changing this but thought what the heck, follow the plans. Seems that I remember a Sig 1/4 scale that I built about 15 years ago had positive incidence in the stab. This new Cub seems very tip stally and the tail doesnt pop up when you give it throttle like other Cubs I've had. CG is at 25% so dont think thats an issue. Whats the consensus? Should this thing have positive stab incidence? Any Ikon West Cub fliers out there have input?
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Old Oct 09, 2013, 07:19 AM
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I have two BUSA 1/4 scale cubs. On both the wing and stab are 0-0. The dihedral on one is 0 and the other (not built by me) is just a few degrees, I'm guessing 3 or so degrees. Firewall is 0 right and down thrust. They both fly fine for me. I prefer the no dihedral wing myself. Both are CG'd on the spar. I test flew a strange cub for a friend that had a symmetrical airfoil wing. It was a nightmare, no amount of trim could make it fly straight. I found out later that the firewall had broken off and had been repaired. Flights before this had been ok. I can only assume the firewall repair was not straight since the rest of the plane had not been touched.
Edwin
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Old Oct 09, 2013, 11:40 AM
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When you measure the incidence, is that at the top of the fuselage,where the wing sits ? If so,the wing has about 2 degrees positive incidence through the effective airfoil...Flat bottom wings are measured for incidence through the center of the leading edge, through the center of the trailing edge from a side view.

Try balancing nearer the spar, as Edwin suggests- more like 30 % back...

Hope you get it worked out.....love them Cubs.
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Old Oct 09, 2013, 02:13 PM
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Very correct. I was referencing off the flat bottom.
Edwin
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Old Oct 13, 2013, 04:32 PM
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Try washing out the wingtips.
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Old Oct 13, 2013, 08:21 PM
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Washing the wingtips makes sense with the stall references made by OP. I would also ask what the throw is on the aileron during the down position ... in regards to the up position of the opposite aileron. sometimes less throw on the down travel compared to the more throw in the geometry of the up-travel of the coresponding aileron can give a smoother flight experience. maybe a rudder mix could help too?
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Old Oct 14, 2013, 03:36 PM
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I can't remember the last time I flew a plane with the CG that far forward. It will affect the elevator trim you carry, and thereby reduce the tendency of the tail to come up on the take off roll. If you check your old Sig plans, the CG is probably like Ed and Earl suggest, above.

The washout comments are good too. Check out a good full scale Cub drawing, like Paul Matt's. You will see that the wing has washout, 2 degrees if I remember correctly. It is a scale detail that can be seen, and it can only help.

The stab is adjustable on the full scale. On the model, that usually means you just use elevator trim.

Jim
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Old Oct 15, 2013, 01:04 PM
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Gotfuel:
I also have a IKON-N-WST 1/4 Super Cub. Mine is only framed up and requires finishing. So I'm very interested in what resolves the issue.
Rick
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Old Oct 15, 2013, 04:22 PM
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Originally Posted by RiBell View Post
Gotfuel:
I also have a IKON-N-WST 1/4 Super Cub. Mine is only framed up and requires finishing. So I'm very interested in what resolves the issue.
Rick
Hi Rick- what is the marked balance point on your plans, just for reference ?
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Old Oct 15, 2013, 04:40 PM
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Originally Posted by epoxyearl View Post
Hi Rick- what is the marked balance point on your plans, just for reference ?
That's going to take some time to find out as I'm in the middle of deconstructing and rebuilding my hobby room.
however it was marked at 4- 4.75 or 102mm to 121mm in the Hangar 9 1/4 scale Super Cub manual. I'm in that range with my Hangar 9 ARF and it flys great with a Zenoah 26. It's for sale as I don't need two Cubs
Rick
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Old Oct 15, 2013, 10:39 PM
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There is no washout in the tips and I am using differential in the aileron throw. Down is about half the throw of the up. CG may be an issue if you are stating 4 to 4.75. I believe mine is a little over 5 inches. Good Lord, a tail heavy Cub, can't think of much worse.
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Old Oct 16, 2013, 09:32 AM
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Quote:
Originally Posted by RiBell View Post
Gotfuel:
I also have a IKON-N-WST 1/4 Super Cub. Mine is only framed up and requires finishing. So I'm very interested in what resolves the issue.
Rick
I wouldn't worry too much. I think the problem is relative to this specific airframe, and not the design, itself

I have several IKON models. All fly beautifully.

Back in the day, I had a few coversations with Emil Neeley, the designer. I know that each design was thoroughly flight tested before they were placed on the market.
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Old Oct 16, 2013, 11:02 AM
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Originally Posted by TomCrump View Post
I wouldn't worry too much. I think the problem is relative to this specific airframe, and not the design, itself

I have several IKON models. All fly beautifully.

Back in the day, I had a few coversations with Emil Neeley, the designer. I know that each design was thoroughly flight tested before they were placed on the market.
Agree'd However it would be a good thing to know just the same. If nothing else just to make sure I don't have a similar problem.
Rick
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Old Nov 13, 2013, 07:41 AM
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What was the outcome? did you narrow down the trouble?
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Old Jan 15, 2014, 02:24 PM
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I have a Sig 1/4 scale cub (in the process of refurbishing)... when it was maidened, it was set up with the CG 4 1/2" back from the leading edge (empty)... 1 1/2 degrees washout at the wingtips... the wing was built with half the dihedral, so about 3/4 degree; the cub looks better with just a tad dihedral, but Sig had too much by default... and the wing incidence was set using a robart incidence meter, with the tail raised to 0 degrees, the wing incidence is about 3 degrees (taken through the "chord line" of the airfoil)... the engines has 0 degrees right thrust, and 2 degrees down thrust... as soon as power was applied the tail came up, and within 120 feet she was airborn on her own with a very low rate of climb out, so I was happy with the initial setup.... no trim was needed at cruise; at full throttle just a couple clicks down and right aileron trim was needed.... this was with a saito TD130, swinging a 16-6 master airscrew classic series propeller.... will be adding an os ft160, swinging a 18-6 Xroar laminated prop, should be interesting to see what the trim setting differences are.
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