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What is wrong with my cub

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Old 03-29-2006, 09:34 PM
  #1  
nimitz
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Default What is wrong with my cub

Hi all..I got a small cub with a 25 magnum motor on it.It was built with plans.name of plans,I don`t know..super cub,I think.When I try to take off ground,it goes to right and won`t go straight. I hand launch it and it flies about two feet and noses over to the right hard.Balance is o.k.
everything seems o.k. I shimmed the wing up a 1/4 inch in back and seems to help but still no go.last time was hand launch..don`t want to tear it up.only tried once to hand launch..[X(]

Any help appreciated.
have fun whatever you do,nimitz
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Old 03-29-2006, 10:48 PM
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Default RE: What is wrong with my cub

sounds like the rudder could be off a little.take a long straight edge and place it against the rudder allowing it to extend to the front of the plane It should come out in the center of the front of the plane,
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Old 03-30-2006, 06:32 PM
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N46203
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Default RE: What is wrong with my cub

Is everything nice and straight? Wings aren't warped or anything?
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Old 03-30-2006, 09:18 PM
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Default RE: What is wrong with my cub

is this your first model?

It could be many things

the lateral balance is off - check by trying to balance the model by the nose and tail/rudder, which wing does it fall to put weight in the opposite wingtip

the CG is off. If it's nosing over and falling off to one side is sound nose heavy and is tip stalling. needs more speed and/or shift the weight back a hair, models that small use 1/8 inch increments. I quick trial would be just use a half tank of fuel see if that make a difference if it does then definitely shift the weight back, plans are not always right when it come to CG. nose heavy models are sluggish take a long time to lift off the ground and tip stall, tail heavy models are jittery and can become uncontrollable very quickly

the ground loop problem sound like a typical sort coupled tail dragger, the engine is just torquing it around. have to use rudder to hold it straight, probably isn't any engine offset to help it either.
it's a small model does it have ailerons. control surfaces on each wing if it does try setting the trim the other way.

look for twist and warps in the wing. with a cub it pretty easy to take a twist out with a heat gun and re shrink the covering. Also with cub is actually helps to have a little wash out in the wing. that when each wing gradually twists forward having less incidence to wards the wing tip. It would be subtle like less than a degree.

now when your taking off are you adding power gradually or gunning it. Try gunning it holding full left rudder and gradually letting off the rudder as it gains speed.
and on HL are you sure your not twisting your wrist. throw it straight out not up. If you throw it up it can stall then tip stall causing it to roll usually with the engine torque to the right. just some thoughts
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Old 03-31-2006, 07:32 AM
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Default RE: What is wrong with my cub

Hay,fellas tnx a bunch.I`ve looked at most all things I could think of and the suggestions you have sent me. It is a small tail dragger. I`ll hang it on the wall and look at it. It is a neat little cub.I wouldn`t want to tear it up.It may be the motor is set square instead of the left a tad.

A friend of mine built this. it is the second plane I got off him.He built a citabrie which flew perfect.It is one of my favorite planes.

have fun,nimitz
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Old 03-31-2006, 12:32 PM
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Default RE: What is wrong with my cub

Hi!
Show us a picture please.
The most important thing is ...is the wing straight and do you know how to check it!?

Regards!
Jan K
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Old 04-01-2006, 12:29 PM
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Default RE: What is wrong with my cub

hi
a cub can be a real bitc.... to get airborne. the most likely problem is a warp in one wing panel as has been noted. also check incidence of horizontal stab and wing. wing should be no more than 1 to 1.5 degrees positive. if you are using struts be sure struts are of proper length so as not to distort wing incidence when installed. a cub is not a good first airplane to start to learn to fly with. you mentioned left thrust in engine...should have right thrust 2 to3 degrees right. and as stated check rudder to be sure you do not have right deflection in it.

good luck and happy flying

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Old 04-01-2006, 08:04 PM
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Default RE: What is wrong with my cub

Hi,All.. right now I have the motor off the cub. Looks like motor is no way to change thrust as cowling is built permanently on plane with blind nuts for motor.wing is straight as far as I can tell.I`ll try to get a photo if possible.My friend been flying for 40 + years and he`s stumped.

I had a sturdy birdie[ a drain pipe with a motor on it].It done the same thing,but not as bad..
I wrecked the bird so many times I lost count. A friend has one and he has flowen the same bird over 550 times.He`s wrecked it also but we repaired them.

I`ve dead sticked a alpha 40 five times the same day trying to get that evolution motor to run right.It took a while to find the trouble on that plane.The plug in the gas tank was loose a little letting air in,loosing my pressure.

Didn`t mean to ramble,just a little of my experences.I can fly but am noway a expert pilot.
been at it for three years now.but,man do we have fun..Oh,yes..I`m 72 yrs young

thanks,nimitz
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Old 04-08-2006, 12:45 PM
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Default RE: What is wrong with my cub

hi
most hobby shops carry shims for this purpose, comes in as pck of 3 and make like wedges. you will get a 1 degree, 2 degree and 3 degree. these can be combined for additional side thrust. they are mounted behind engine mount.

good luck and happy flying
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Old 04-08-2006, 01:18 PM
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Default RE: What is wrong with my cub

The alignment of the main gear is very critical on the Cub. Make sure you have a little toein on the main gear. It is easy to get to active on the rudder also. If you have exponential, dial in about 50% on the rudder and be careful to not overcontrol it. It also helps to have it fairly nose heavy for your first flights, not more than 25% of the chord back from leading edge. Build up plenty ground speed before applying any up elevator. It should take off by itself with no added up elevator. If you have some instructors at your club, have one of them take it off for you the first few times.
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Old 04-08-2006, 01:21 PM
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Default RE: What is wrong with my cub

Tnx for the reply. The crazy motor is mounted on two wood beams [so to speak] that are part of the plane.I could do that if it was a removable mount.

tnx,nimitz
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Old 04-08-2006, 01:26 PM
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Default RE: What is wrong with my cub

Me again. I`ve had a instructer with 40+ yrs flying doing the maiden flight.Right out of the gitgo it starts circling around us 0n the ground. I hand lanched it the second time after shimming the wing a 1/4 inch in the rear. it went about 10 or 15 feet and nosed over to the right..We got a sale coming up this summer. I think I`ll let someone else figger it out.

many thanks,nimitz
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Old 04-26-2006, 06:47 PM
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Default RE: What is wrong with my cub

LOL The exact same this happened to me, kept doing tail spins
with no speed behind it, i took it to a flight instuctor, he said it was the P-Factor
So i sold it.
lol
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Old 04-27-2006, 10:50 AM
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Default RE: What is wrong with my cub

ORIGINAL: nimitz

Hi,All.. right now I have the motor off the cub. Looks like motor is no way to change thrust as cowling is built permanently on plane with blind nuts for motor.wing is straight as far as I can tell.I`ll try to get a photo if possible.My friend been flying for 40 + years and he`s stumped.

>The thrust angle can be easily changed by inserting washers between the
>motor mount and the firewall for left/right thrust and between the mounting
>lugs on the engine and the motor mount for up/down thrust. As for the blind
>nuts, just thread a bolt part way into it and tap them out with a hammer.
>Epoxy some dowels in the holes and redrill the holes (remove the fuel
>tank 1st so you don't inadvertantly drill a hole in it - don't ask how I know )

I had a sturdy birdie[ a drain pipe with a motor on it].It done the same thing,but not as bad..
I wrecked the bird so many times I lost count. A friend has one and he has flowen the same bird over 550 times.He`s wrecked it also but we repaired them.

I`ve dead sticked a alpha 40 five times the same day trying to get that evolution motor to run right.It took a while to find the trouble on that plane.The plug in the gas tank was loose a little letting air in,loosing my pressure.

Didn`t mean to ramble,just a little of my experences.I can fly but am noway a expert pilot.
been at it for three years now.but,man do we have fun..Oh,yes..I`m 72 yrs young

thanks,nimitz
Also check the incidence of the horizontal stab/main wing. If it were my plane, I would have the incidence at 0/0 to a MAX of 1 degree positive on the main wing.

For your landing gear, make sure the wheels are slightly toed in. This will provide very good ground handling.
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