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Piper Cub trainer rolling to right on take off.

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Colin Anderson06/04/2014 14:00:34
278 forum posts
48 photos

Hi Guys,

A couple of days ago I got to fly my Piper Cub via the buddy box system. The plane was taken up by my instructor and trimmed for stable and level flight. However, on take off the plane tries to roll strongly to the right. Why should this be, when it can be flown hands off once airborne? It's a real mystery to me and also to my instructor, who is a pilot of full size aircraft! My instructor manages to take off with my plane in spite of the rolling tendency, but this will obviously be a problem when I get around to doing take offs and landings. I feel I need to find a solution before that time. So, if you guys have any ideas on this I'd appreciate the input.

Cheers.

Andrew Russell 206/04/2014 14:12:55
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100 forum posts
29 photos

Is the thrust line correct on the plane?

when your cruising around the sky you will be flying at half throttle so you will not notice as much if it is off but at full throttle a properly trimed plane will want to pull the way the motor is pointing.

Depron Daz06/04/2014 14:30:58
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760 forum posts
173 photos

Do you have any thrust wedges behind the motor? If so, where? Is this electric or gas?

Is the wing horizontal and square with the rear stabilizer? Are the ailerons set up properly and flat with the wing surface? Have you checked the CoG correctly from nose to tail? What I mean by this is, hold the plane by the motor shaft and hold the tail by letting it rest on a finger (or similar) held flat and perpendicular and see what side is heaviest. You need to have the plane fully laden with battery or fuel as if you were going to fly.

It sounds to me to be build issue, so check that the wing is absolutely square to the fuz and tail on all angles, check CoG as poorly described above, and check motor thrust lines.

Colin Anderson06/04/2014 14:33:48
278 forum posts
48 photos

Hi Andrew,

Yes, that makes sense. However, my thrust line is central; no left or right thrust and no down thrust. There is a very small amount of right trim dialled into the rudder, as it had a tendency to fly to the left. It is a very small amount, but could this be the reason? And, if so, why does it not effect the plane once airborne?

ken anderson.06/04/2014 14:41:33
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8634 forum posts
779 photos

hello Colin(nice surname by the way).....couldn't be something as simple as the undercarriage is slightly off ....try rolling it along the ground-not using any power...see if it tracks straight......

ken Anderson....ne.....1..... Anderson clan dept.

Colin Anderson06/04/2014 14:43:28
278 forum posts
48 photos

Hi Budgie,

There are no thrust wedges. I will check the CG as you suggest. It is correct fore and arft, but I never checked it laterally. I will also check the wing and see if its heavier on one side than the other. Thanks for that.

If these issues turn out to be correct; why would it only effect the take offs and not the rest of the flight? Is it due to more prop wash on take off?

Power is an Irvine 40 glow in a 73" Cub.

Colin Anderson06/04/2014 14:50:09
278 forum posts
48 photos

Hi Ken,

The undercarriage is something that never even crossed my mind! Could it really have that effect? I'll have a look at that. Thanks uncle, cousin, distant relative? :-D

PatMc06/04/2014 14:52:15
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4383 forum posts
524 photos

Prop wash will tend to make it turn left, the rudder right trim to correct this will probably be at least part of the reason it turns right on the ground. Also check out Ken's suggestion.

Lindsay Todd06/04/2014 14:55:57
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1710 forum posts
1709 photos

Generally Cubs have pretty good characteristics so as Ken suggests I would take a look at the undercarriage. It could be caused by a number of things, the U/C not being straight, the axels giving the wheels toe out rather than toe in or straight, one of the wheels having more friction than the other and causing drag, definitely worth checking out to make sure as any of these could cause the problem you describe. Linds

Colin Anderson06/04/2014 15:00:28
278 forum posts
48 photos

Thanks guys,

I will check this out as you both suggest. If it turns out to be so simple I will be very happy!

john stones 106/04/2014 16:16:36
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11449 forum posts
1516 photos

Hi Colin

Have a look at the tailwheel they easily get bent, could be steering it to right on take off.

Stevo06/04/2014 16:46:43
2699 forum posts
419 photos

Erm... Piper cub? Flair - has down and right thrust built in..??

Plenty of calls to check geometry and as I mentioned in my email - Incidence; particularly wing warp. 1 degree is enough for major problems.

If you were closer please feel free to get it round here for a free check over yes

Is it due to more prop wash on take off?

- That will slew it left on the take off run...

Colin Anderson06/04/2014 17:31:02
278 forum posts
48 photos

Interesting you mention the tail wheel, John. The tail wheel is connected to the rudder which, as I stated above, has slight right trim. However, at the point where the model rolls this would not be on the ground.

Hi again Stevo,

Are you coming to my resque again? Are you saying that the Flair Cub has built in down and right thrust? If so, I hadn't realised.

My referral to the prop wash was concerning the right trim on the rudder. I was just wondering if a higher prop was on take off would give the control surfaces more "authority" and thus induce the roll. Regarding wing geometry, incidence or warp; I can understand how they would effect the plane. However, if problems effect the plane on take off why do they not manifest themselves during normal flight?

By the email, do you mean previous ones or have you sent me one recently? I did send you one recently about my first flights, complete with the pilot you kindly sent me. Perhaps you never received it? Regarding your very kind offer: I'm in Langley, Berkshire. How far apart are we?

Stevo06/04/2014 17:35:35
2699 forum posts
419 photos

I replied yesterday afternoon @ 14:41 wink

Afraid we are miles apart... I'm by the Dartford Tunnel in Kent !

Flair Cub has two beech rails that point the engine down and to the right yes

However, if problems effect the plane on take off why do they not manifest themselves during normal flight?

Errrrmmm.. ooohh.... hmmmmm...

Buy an incidence gauge!

Edited By Stevo on 06/04/2014 17:36:31

Colin Anderson06/04/2014 18:10:30
278 forum posts
48 photos

Now that you mention it, Stevo, you're right the rails are set slightly downward, producing down thrust. I'm still sure about the right thrust, though. This is the problem with a kit with no plan; a plan would make things so much easier to see and refer to.

I wouldn't say you're a million miles away, as I sometimes visit my sister in laws in Chislehurst, but I take your point. As for the email, I never got it. I did look in the usual suspect places and its not there either. Any chance you could resend it?

Incidence gauge? Yes, that's a good idea. You can see why I'm confused though. In theory a problem showing up at take off out to affect the plane's flight characteristics to some degree. However, thanks to you guys I've got quite a few suggestions. The answer is in there somewhere. I'm sure I'll find it.

will -006/04/2014 18:19:17
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587 forum posts
19 photos

I take it it;s not as simple as that you were taking off in a crosswind?

Biggles' Elder Brother - Moderator06/04/2014 18:24:03
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Moderator
15748 forum posts
1460 photos

Colin,

just to understand better - you say it "rolls to the right" do you really mean "rolls" - as in the left wing lifts? Or do you mean it veers to the right in the steering sense?

I ask because these are two different problems.

BEB

Colin Anderson06/04/2014 18:36:52
278 forum posts
48 photos

To answer your question first Will. The Cub is taking off directly into wind. My instructor is a qualified pilot (passenger jets and a Pitts special) so I have every faith in his abilities.

Hello once again BEB!

Viewed from behind the model the left wing rises, the Cub rolls to the right and begins to turn. It is definitely a roll, rather than yaw. Stevo has sent me a very informative email with enough information for me to get to the bottom of this. I'm sure between us all we'll solve the anomilly!

Edited By Colin Anderson on 06/04/2014 18:38:10

Edited By Colin Anderson on 06/04/2014 18:39:26

Stevo06/04/2014 18:50:39
2699 forum posts
419 photos

The roll will automatically be compensated for by the pilot as it rises off the ground - then..... it's then trimmed for level flight at height...

Then ...

Does it still roll at take off?

Heres a real grasp at straws... engine running backwards with a pusher prop on.... I'll get my coat!

john stones 106/04/2014 19:13:29
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11449 forum posts
1516 photos
Posted by Stevo on 06/04/2014 18:50:39:

The roll will automatically be compensated for by the pilot as it rises off the ground - then..... it's then trimmed for level flight at height...

Then ...

Does it still roll at take off?

Heres a real grasp at straws... engine running backwards with a pusher prop on.... I'll get my coat!

Get mine Stevo, tailwheels of floor embarrassed

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