trim question

[Brent Rogillio]

i have plenty of line tension flying level laps but on inside loop i loose tension at the top but on outside loop i don't. I flying 86d profile Sabre.

[Dan McEntee]

   Lots of things can work together to cause this, but the firstthing to look for is a warp in the wing/flaps/stab/elevators. Site the airplane from the back end. Put it on it's nose with flaps and elevator in neutral position, and compare the trailing edges to the top and bottom of the wing and horizontal stab. Any warps will be evident. The warp is working against you in inside loops but for you on outside loops, so I'm guessing it's flaps need to be tweaked. Does the airplane fly straight in level flight and inverted? That knowledge will help in finding the fix.
  HAPPY NEW YEAR!
   Dan McEntee

[Dave_Trible]

Dan is right about looking for the warps.  If the airplane seems to fly with the wings level both upright and inverted then you'll just have to trim the gremlins out.  There could be some complex reasons but to start solving it try bumping the leadouts back about 3/32" at a time.  A little more tip weight might help.  Add a little engine offset.  Try not to add rudder offset unless you are flying very slow lap times- or speed her up just a knotch.  You'll learn a lot about trimming and find the sweet spot.  Make only one change at a time so you'll understand what causes what.

Dave

[Brent Rogillio]

It flies level up right and inverted it kind of hard to tell sometimes because it does have diehidrel in the wing. also i notice more power less problem with the line tension on the loop.

[Howard Rush]

also i notice more power less problem with the line tension on the loop.

More RPM in outside loops than inside loops can cause the line tension issue.  I had that happen on the first flight of my first Impact.  I thought it was a warp, but it was a mislocated fuel tank.  The fix is to lower the tank.

Once you get the engine running the same in outsides and insides, make sure the vertical CG is level with the leadout guide at the wing tip.  Then onward to the Walker trim chart: http://flyinglines.org/pw.trimflow1.html .

[Tim Wescott]

More power = less problem, but masking problems with more power should be an absolute last resort.

Dihedral makes it harder to diagnose things.  On a normal straight-winged stunter we'd tell you to sight down the wing in level and inverted, and make sure the wing looks the same both ways.  With dihedral you can either try noting what fuselage trim is level with the top of the wing and sight on that, or you can look at the wheels.

Even better, if you have a friend with calibrated eyeballs, have them look at the thing -- in level flight with level lines the wings should be level both upright and inverted.  If the outer tip is down both upright and inverted then you have too much tip weight; if the outer tip is up for both you have too little (and my, aren't you lucky to still have a plane!); finally, if the outer tip is farther up when you're upright than when you're inverted (or visa-versa) then you have a warp that'll loosen your lines on the insides but tighten them on the outsides (or visa-versa).

Howard is correct about motor run -- if you're flying electric this isn't an issue, but if you're flying slime you need to trim the tank height like anything else.  So note that the next time you fly.  If you have a helpful friend, or if you're comfortable doing it yourself, time your laps both upright and inverted -- you want them to be the same.  Once you get that straightened out, then note whether the engine tends to speed up in insides or outsides.

Once you know whether you're banking or whether your tank height needs adjusting, then you can move on to the appropriate correction.

[Brent Rogillio]

Thanks for all the info

[Brett Buck]

Thanks for all the info

    If it is running the same speed inside and outside, most of the rest of it does not matter, just tweak the flaps to even out the tension. If it is not running the same speed inside and outside, then fix that (which might be a tough challenge, depending on your engine), then see what you have.

     Brett

[EddyR]

If plane is level upright and inverted and speed is the same through turns then outboard flap is to big and is rolling model in on inside loops. Watch model in overhead eight and look for model throwing wing to one side at intersection as controls are changed. That is the easy spot to see it.
EddyR

[Brett Buck]

If plane is level upright and inverted and speed is the same through turns then outboard flap is to big and is rolling model in on inside loops.

   If the outboard flap is too large, it will roll in on both inside and outside loops, not just insides. If it is rolling in one way and out the other (as is suggested by the description) the issue is likely a warp, and in any case, the solution is a tweak (or tab deflection, if there is one).

     Brett

[EddyR]

Brett   If one flap is lifting more than the other the plane  will roll away from the the flap with the extra lift.. Trim 101. All the old classic models with large inboard flaps do this. They roll away on insides and in on outsides. Many carry warts on the outboard flap to get in trim.
EddyR

[Brett Buck]

Brett   If one flap is lifting more than the other the plane  will roll away from the the flap with the extra lift.. Trim 101. All the old classic models with large inboard flaps do this. They roll away on insides and in on outsides. Many carry warts on the outboard flap to get in trim.
EddyR

  I am aware of that. But that is not the symptom. He has more tension on outsides than insides, that suggests a warp that would be cured with a tweak. There are other potential causes, of course, but to first approximation, you tweak it until it has the same tension inside and outside.

    Brett

[Perry Rose]

There's a possibility that the plane is too nose heavy and needs to be brought into balance so the lead outs won't be so far back which will cause excess drag.

[Steve Helmick]

First things first...flap tweek to get it flying level. Because of the dihederal and wing sweep, this could be solved by putting a "gunsight" on the wingtip and fuselage...or adjusting until line tension is equal on insides & outsides. Flying "lazy 8's" is a good way to do this, except for me. I tend to scare myself when I do non-regulation horizontal 8's.  Steve

[Doug Moon]

Hello Brent,

When hunting down problems like this always start with the easy stuff first.  

You have told us it s flying upright and inverted level.  That's good.  We are to assume the model is straight. I am assuming is a proven design as well.

Your statement about more power has me wondering. Do you mean more speed or more power? Speed will always mask a problem until too much creates its own.  There is a happy medium in there for every setup.

Do you have a fixed rudder with offset built in?  This is really key when it comes to proper LO setting from the get go.  I fly with an airfoil sanded into the  rudder and find I use a further forward LO setting than models where I used an almost straight rudder.  These little things are good to know when making an initial setup.

So looking at option 4 on the Walker Trim Flow Chart, you need to adjust leadout, rudder, TW, and engine offset if you can. Where to start is the next question right?

I would move the lead outs forward maybe 1/4" and fly 2 times and note what you get. If the conditions worsen the exact same symptoms then you know you went the wrong way.  If the condition seems a little better but not quite there add some TW and fly two times and see what you get. If it continued to get better as you added TW then move the LOs forward again and fly. If better still then add more TW and fly again. I say fly two times so you can really see what the changes are.  If it is a drastic change right away then there is no need for the second flight. Just change and move on.

It could be that the inside turn is causing too much yaw and you lose tension. By moving the LOs foward you pull the nose in and fight this natural yawing condition that you have on the inside moves. The outside yaws the opposite direction.  It is common to start or trim a plane initially with the LOs to far back. It's the natural instinct to move the LOs back and "point the plane away from you" but in some cases it makes the maneuvering worse.

The WTFC (Walker Trim Flow Chart) is an awesome tool. Thank you Paul for putting it out there for all to us to use. I used to have one in my flight box all the time.  Then I spilled fuel on it and well it was ruined.    It really helps you look for issues in the right order and then find the proper compromise for the model.  Works on ALL adjustable stunt panes.

I like to think of trimming as "Sneaking up on it."  Then all of sudden "BOOM" it all just works.

Keep us posted.

Thanks

[phil c]

Don't overthink this.  If the plane drops the outboard tip or gets light on the lines when making an inside or outside loop it has a warp, improperly cut airfoils, uneven flaps, or something else making it roll when the controls are applied.  Until that is fixed any other trimming is a waste of time.  One short flight will diagnose it.

take off and fly level.  If it looks OK to you and your helper do a couple largish insides slightly to the left of downwind(wind helps if there is a left roll you can't see).  Then do a couple more 45 deg loops.  If they are OK go inverted.  If it still looks level to your and your helper do a couple largish outsides to the right of downwind.  If they are OK try a couple tighter outsides.  Getting light on the lines on insides means it is rolling left(in at you), light on outsides means it's rolling right.  Dropping a tip on insides is rolling right, on outsides it's rolling left.

If it still seems fine try turning tighter loops, making sure the loops are dead downwind.  A perfectly straight plane should eventually be able to do at least one full control loop both inside and outside.

If there are any signs of getting light in one direction and dropping the outboard tip turning the opposite way you've got problems.  See above for tips.  If a flapped plane needs more than an eighth in. or so of tweaking you've got other problems such as ribs cut with the curves cut uneven, or perhaps the stab is grossly misaligned.

Once the plane flys mostly straight as you can get it, then go on to trimming the other things such as tipweight, rudder offset, flap areas, thrustline, etc.  The PW flow chart will help a lot then for fine tuning.

[Tim Wescott]

If there are any signs of getting light in one direction and dropping the outboard tip turning the opposite way you've got problems.  See above for tips.  If a flapped plane needs more than an eighth in. or so of tweaking you've got other problems such as ribs cut with the curves cut uneven, or perhaps the stab is grossly misaligned.

Or the wing is warped.

[Brent Rogillio]

Perry Rose and Gill Causey helped with the sabre on the trim problem. Main problem was it was yawing and we moved the lead out forward and also added weight to the tail. It was little nose heavy. Flys 100% better. Thanks to all.

[Doug Moon]

Perry Rose and Gill Causey helped with the sabre on the trim problem. Main problem was it was yawing and we moved the lead out forward and also added weight to the tail. It was little nose heavy. Flys 100% better. Thanks to all.

Glad you got it worked out.

[Tim Wescott]

It's weird that yaw would have caused an asymmetrical line tension issue -- but with sweep and dihedral both in the mix, I can see how maybe that would be the case.

Keep an eye out for roll -- as you get an airplane into better and better trim, whatever problem is worst will change.  Just because this improvement came about by getting rid of yaw doesn't mean that the next one won't be roll.

All the best, keep us posted.

[Doug Moon]

snip>>>It's weird that yaw would have caused an asymmetrical line tension issue <<<snip

Not really. Of course certain designs and setups will show this tendency more than others. 
Inside turns yaw the model out and outside yaws the model in.  Our lead out guide finds the happy medium.  Go off a little too much in one direction and you get what Brent was experiencing.  Keep going in the wrong direction and both turns will suffer.

I was surprised when there were so many replies about a wing warp.  A wing warp would roll the model both upright or inverted.  His initial question made it sound like it was good on way and not so good the other. It would make sense to be an adjustment and not a major build or design flaw...just my thoughts on it...

I also understand many are answering from their own experiences.  There is a lot of good information on this thread.

[Brent Rogillio]

Doug, you hit the nail on the head on your first  assessment. you mention the leadouts and CG.