Flight trim question

[Jim Oliver]

Hey all you trim experts---

I have been flying my Score with Tom Dixon ST 51---working on trim issues.

When I am trying the Square 8, at the bottom corner on the vertical downline of the inside square, if I really hit the corner hard, the outboard wing flips up.  Very scary!!

I have had to add a tab to get the wings level upright/inverted and have about 2 oz. of tip weight, the leadouts are well forward.  I am using an APC 12x6 on 65 ft. eye to eye .018 braided lines.  The APC prop is to avoid adding nose weight, as is the Tru-turn spinner.

Any help will be appreciated.

Jim

[captcurt]

Does it do the same thing on the inside squares??

How about if you do a hard pull out from a wingover?

Also, does it do the opposite on an outside hard corner?

Curt

[Bruce Perry]

My guess is that it's stalling.  Have you taped the hingeline?  It would be slowed down from the previous part of the trick and would be more prone to stalling as a result of slower airspeed.  If it is fine in the other areas that Curt asked about and only does it at this part of the pattern you could experiment with a faster lap and longer lines.  It seems as though the tip weight is "more" than adequate and you may be masking another problem.   You may have a twist in the wing/flaps and some mistrim in the leadout location and tipweight. 

I just fought a similar issue with my latest, in the end it needed, a flap tweak, tip weight, pushrod adjustment.  In there I also changed engines, prop size, tank type, etc....  However, the good news is it is a weapon now.

I would return to a known bench trim, perhaps one from a friends setup that works, and then work backwards to find the source of your problem. 

A thought just occured to me, if your hingelines are taped make sure they haven't split.  This has also happened to me where an airplane suddenly started haveing a Goofy pullout from an hourglass.  Turns out the OB wing had some damaged hinge tape.  Once repaired all was well again.

Digital Diagnosis of trim is very difficult... Good luck with your efforts.


Bruce

[Jim Oliver]

Thanks guys,

Haven't taped the hinge lines--will do that before next flight. 
I, too, think it may be stalling.  I have reduced the line spacing at handle which helped a little, can do more there also.  I also have reduced the elevator travel but haven't flown it with the reduced travel.

The flaps seem to be un-tweekable; horn wire too springy to hold a tweek, hence, the flap tab.

I'm sure it will get better, if I don't stick it in the ground first.

Jim

[Trostle]

You did not explain which way your tab is set.  Whichever it is, and depending on its size and how much deflection you have, you have still got a lot of tip weight at 2 oz.  Given that tip weight and whatever your trim tab is, you have a warp somewhere that is not doing you any good.  A step in the right direction would be to get rid of the warp, then get rid of the trim tab and use just enough tip weight to keep get your wings level for both inverted and upright flight.  Then come back and tell us if the outboard tip is still throwing itself like it does not yet have enough tip weight.

Keith

[phil c]

Jim, start by taping the flap and elevator hinge lines. That could very well be your problem if the outboard flap gap is closing when the controls are moved.  It is very unlikely the wing is stalling.  If you have too much flap movement, relative to elevator, the inboard flap could be stalling and causing a roll.

Then start trimming with some inside and outside loops.  Gradually tighten them up until you can see if there is any difference in line tension.  If the plane starts to lose tension in one direction, but not the other, you have a warp.  Straighten the wing if possible, or tweak the flaps if you can't bend the wing.

Then make sure the leadouts are close to the calculated best position.  Do some more loops and adjust the tip weight to minimize rolling either inboard or outboard.  Then work the tipweight, leadout position, and rudder offset together, they all interact, to get the best balance between level flight and overhead line tension.  Generally the rudder offset should be minimal, just enought to make sure the plane isn't getting left rudder.

[Gary Anderson]

You did not explain which way your tab is set.  Whichever it is, and depending on its size and how much deflection you have, you have still got a lot of tip weight at 2 oz.  Given that tip weight and whatever your trim tab is, you have a warp somewhere that is not doing you any good.  A step in the right direction would be to get rid of the warp, then get rid of the trim tab and use just enough tip weight to keep get your wings level for both inverted and upright flight.  Then come back and tell us if the outboard tip is still throwing itself like it does not yet have enough tip weight.

Trostle is correct, I have checked three different score and they seem to have the same warp. Maybe their jig is off, check the trailing edge with a level, I found all three has a warp on the outside wing. Might be these where from the same patch. Good luck fixing it, Gary

[Jim Oliver]

Guys,

The tab was installed to correct a roll to the outside (outboard wing low when upright, high when inverted).  I had the very same problem with two Tutor II's.  Have not been able to see a warp in either of the wings.  (I do know what a warp looks like, having built more than a few!!)

I have noted that the Tutor II and Score designs have the wing mounted rather low in the fuse and have wondered if the problem is related to CG being above the tether point.  A little worse on the Tutor II design than the Score. 

The tab achieved wings level both ways. 

I have sealed the hinge lines but have not flown again, yet.

Will report after the next flight.

Thanks,
Jim

[captcurt]

It takes very little "visible" warp to create a roll as you describe--perhaps only apparent with a blocked up model being measured.

I and remember, it is some areodynamic assymetry that is the culprit, not necessarily a twist that is visible.

However, I would attempt to remove the twist at the wing rather than with a tab.  Problem is, the tab changes effect with changing airspeed--and that is exactly what happens in a hard corner.

Remove nearly all of the tip weight and fly the plane upright and inverted w/o the tab.  Ensure that the flaps are not twisted and are aligned.  Adjust the wing twist to remove opposite rolls up/inverted.

When level, THEN start adjusting the tip weight to trim the corner.

This follows the basic Walker trim flow chart--it is available in a variety of places on-line.

FWIW

Curt

[Trostle]

Guys,

The tab was installed to correct a roll to the outside (outboard wing low when upright, high when inverted).  I had the very same problem with two Tutor II's.  Have not been able to see a warp in either of the wings.  (I do know what a warp looks like, having built more than a few!!)

I have noted that the Tutor II and Score designs have the wing mounted rather low in the fuse and have wondered if the problem is related to CG being above the tether point.  A little worse on the Tutor II design than the Score. 

The tab achieved wings level both ways. 

I have sealed the hinge lines but have not flown again, yet.

Will report after the next flight.

Thanks,
Jim

OK, you have a tab trying to force the outboard tip up when flying upright.  You have more than enough tip weight to force the outboard tip down when flying upright.  At different speeds,  like in the dive portion of a square and in the pullout of that dive, the tab will have a different effect on the roll tendencies of the model.  The tip weight wants to make the outboard tip flop around, and depending on the relationship of that tip weight to the leadout position and the CG as well as the vertical CG, coupled with the rolling effect of the tab, all sorts of things can be happening, particularly if exacerbated by a warp in the wing.

In all due respect, I am sure you know what a warp looks like.  A number of us have found that the incidence meter that Robart sells is indispensable.  It can measure variances in wing incidence to within 0.1-degree.  I doubt that your calibrated eyeballs can measure quite that close.  (My last wing was built on a dead flat board, jigged up to maintain as straight of a wing as I thought I could build.  By every way that I could come up with, short of the incidence meter, the wing looked and checked out that it was straight during construction and after it was completed.  Then, I flew it.  Something was wrong.  Put the incidence meter on it and there was 0.5 degree difference from one wing tip to the other.  Straightened out the twist -- the airplane flies pretty good now like to 2nd place at the recent VSC when the airplane was about one week old.)

Indeed you might not have a warp, but there is something wrong to be using a tab like you are using and to have that much tip weight.  It will be interesting to hear the results after you have taped the hinge line.

Keith

[Gary Anderson]

OK, you have a tab trying to force the outboard tip up when flying upright.  You have more than enough tip weight to force the outboard tip down when flying upright.  At different speeds,  like in the dive portion of a square and in the pullout of that dive, the tab will have a different effect on the roll tendencies of the model.  The tip wants to make the outboard tip flop around, and depending on the relationship of that tip weight to the leadout position, coupled with the rolling effect of the tab, all sorts of things can be happening, particularly if exacerbated by a warp in the wing.

In all due respect, I am sure you know what a warp looks like.  A number of us have found that the incidence meter that Robart sells is indispensable.  It can measure variances in wing incidence to within 0.1-degree.  I doubt that your calibrated eyeballs can measure quite that close.  (My last wing was built on a dead flat board, jigged up to maintain as straight of a wing as I thought I could build.  By every way that I could come up with, the wing looked and checked out that it was straight during construction and after it was completed.  Then, I flew it.  Something was wrong.  Put the incidence meter on it and there was 0.5 degree difference from one wing tip to the other.  Straightened out the twist -- the airplane flies pretty good now like to 2nd place at the recent VSC when the airplane was about one week old.)

Indeed you might not have a warp, but there is something wrong to be using a tab like you are using and to have that much tip weight.  It will be interesting to hear the results after you have taped the hinge line.

Keith     You're correct, if you don't have an incidence meter you can use a two foot level, on the trailing edge and most likely you will find a different. Good luck correcting the problem, Gary