Weeble-wobble on outsides

I know this isn't a normal situation but am hoping one of the trim masters can give a few tips that might help. We have described the airborne video system and overweight Dancing Girl in the "Unusual Happenings out at the field" thread. This is a non flapped bipe, 540 square inches that weighs 53 (ouch) ounces. It has a little rudder offset, 2 deg engine offset and the leadouts are fixed about 1/2 inch behind the cg. Hey what can I say, it was built 20 years ago... I have no idea how much tip weight is in it but the camera on the outboard wing adds 1.5 ounces about 1/2 way out on the wing.

This airplane has always had a wobble problem with outsides but with the extra weight of the video system it really wobbles bad. Insides are not too bad, I can soften the corners enough to fly a pretty respectable inside square but outsides are terrible even with soft corners. Except for the outside wobble It actually doesn't fly real bad at 53 ounces.

Anyone have any ideas on a quick fix for the wobbles?

Thanks,
Bob

How far out of normal does the camera and xmtr take the VCG?

AS far as tip weight, if you add 1.5 oz half way out that would be like adding .75oz at the tip--surely enough to upset proper trim.

You might need to take out some of the original tip weight to compensate. Going back through the regular trim cycle is probably wise.

Also, not knowing what the package looks like, assymetrical drag could be changing the yaw situation. Is there no way to mount the package on the centerline?

Just some thoughts--sounds like fun.

>Also, not knowing what the package looks like, assymetrical
>drag could be changing the yaw situation. Is there no way
>to mount the package on the centerline?
>
>Just some thoughts--sounds like fun.
>
>Curt

I wasn't even thinking about the yaw thing (maybe I just wasn't thinking) when I posted, but you are right. That, itself, will further upset trim. Quite a bit, in fact, (and leadout position and yaw, and...) If you bring it back to the center or add some drag to the inside or...

How does it Wobble, Bob? Can you describe it? Obviously the camera is going to add extra "tip weight" and the only way to compensate for this is to remove weight from the offending tip or add (ouch) weight to compensate on the inside. With the leadout position, either the cg needs to be adjusted to the leadout position or the leadouts need to be adjusted to the cg. Since this is a continuing adjustment, dependent also on speed, line size and length, and even conditions (wind) we now know to make these things adjustable.

I am thinking right now, however, that you have a vertical cg problem, especially with the camera mounted. Hang the plane by the leadouts and compare how it hangs compared to a plumb bob. If the plane is leaning, as I suspect, you may be able to move the camera location, or add compensating weight (more ouch) in the opposite direction. It is like dynamically balancing a tire. You often need to add weights inside and outside on the tire (top and bottom on the plane) to dynamically balance it.

Thanks for trying to help guys,

Curt, if you will look at the other thread you can see a picture of where everything is mounted. The reason I chose this plane in the first place was because I thought I could just mount the camera on the top wing at the CG but forgot about the prop being in the way. As it turned out the camera had to be moved outboard in order to get away from the prop taking up to much of the image.

Surprisingly the vertical CG isn't that far off, I did hang it by the leadouts after installing the system and it hung straight with just a little nose down. Also surprisingly it isn't yawing any more with the camera than it did prior to adding all the garbage. It does have some yaw, you can see about half of the outboard wheels tire behind the inboard wheel when it is flying level.. <> 1/8 inch. I could break the rudder and set it straight or maybe a little inboard but that isn't something I would look forward to doing.

I went ahead and pulled the covering at the outboard wing tips and found an ounce and a half of lead between both wings. Add 3/4 ounce for the camera and the poor thing had 2 1/4 ounces of tip weight. I removed it all and am going to put 1/4 ounce only in the bottom wing. This in itself will probably make a big difference.

So what do you think, should I break the rudder?

"break the rudder"? I prefer the term "re-adjust the rudder". Breaking it is what I do when I land inverted. A little humor there, darn little.

>I am thinking right now, however, that you have a vertical
>cg problem, especially with the camera mounted. Hang the
>plane by the leadouts and compare how it hangs compared to a
>plumb bob. If the plane is leaning, as I suspect, you may
>be able to move the camera location, or add compensating
>weight (more ouch) in the opposite direction. It is like
>dynamically balancing a tire. You often need to add weights
>inside and outside on the tire (top and bottom on the plane)
>to dynamically balance it.

Note that what you are describing is not really a vertical CG issue. The static CG could be right down the middle, and the situation you describe could still exist. If you put a bunch of weight in the outboard tip of the upper wing, a similar amount in the inboard lower wing, you might still have the CG be the same in all three directions. But there would still be some "dynamic imbalance", or in techical terms, there would be significant "products of inertia" that would make the airplane not want to rotate cleanly around the "pitch" axis. I use quotes on the "pitch" axis because what you really have is that the inertial pitch axis is not the same as the structural pitch axis, so the definition in this case could be ambiguous.

I still haven't been able to see anything more than a small static angle resulting from the vertical CG being off a bit. But it's clear that excessive products of inertia could easily create (or solve...) assymetrical inside/outside roll and yaw motions.

Bob,
Is it ready to go again?

Depends on what comes out of this thread, everything is fixed from the crash but the covering and patching that won't take long.

Bob,
How hard would it be to make an adjustable rudder? Or is that something that really isn't necessary?

Wish Saturday would hurry up and get here!

I put up two flights today on my lunch hour down at Veterans Park.
It was hot but I had fun

It really wouldn't be that hard, just would mean the thing would be grounded for a couple more days. I wanted to have it ready to go for the Thursday evening club meeting but it looks like I will be in Branson on Thursday.

>It really wouldn't be that hard, just would mean the thing
>would be grounded for a couple more days. I wanted to have
>it ready to go for the Thursday evening club meeting but it
>looks like I will be in Branson on Thursday.

Meeting on Thursday? I thought the club meetings were on the first Thursday of each month not the last. Did we change something when I wasn't looking?

BTW
I vote for not doing anything that will delay the test for Saturday!

Yep you are right, not this Thursday.. Someone at the field last Sunday said "This Thursday".. I didn't even look at a calendar until you said something.

Leonard,

I really can't describe how it wobbles, kinda half stall half just doing what it darn well feels like doing but mostly just wobbling around at the end of the lines. I have a profile that kicks up the outboard wing on outsides and that is fairly easy to see but this thing just seems to wobble in all directions at the same time. I know it isn't but it seems like it is..

Just another thought here after looking at the pix. It seems as though the VCG might not be affected here as the camera package is centered somewhat between the wings.

I understand what Brett said about the Inertia products--it is the difference between static and dynamic balance.

Has the plane slowed down any? If it was portly prior and the drag slowed it up by a couple MPH, it might get generally unruly.

Bob- I have thought about this for a while and have decided that the problem is most likely the stagger in the wings, (if there is any) I think when you go inverted the top wing is doing most of the lifting and if it is staggered forward then that mean the CG is farther back making it easier to stall, or something like that, I know the stagger will cause it to weeble Wobble on outsides because it is the same with real airplanes.. You may want to check up on my facts before you do anything major though. BEN

So a Stagerwing Beech would wobble on the insides

nope, because the cg on those is rigged for level flight, in other words, if a staggerwing went inverted, It would be extremely sluggish.

it also may have something to do with the incidence of the two wings in comparison of each other.. BEN

I need to let you read the construction article Miller wrote when he published the Dancing Girl design. He explains why there is negative incidence in the top wing. I will dig it out and bring it to the field this weekend.