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Old Jan 05, 2014, 12:49 AM
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NE1 ever offset a wing servo to cancel peg mass?

I can't be the first to think of this. But if you have a 3-4 g t blade why not mount that top drive wing servo closer to the root to help with lateral balance?.
And as a followup ? Do any TX's let you use a 3 pt curve to program servo travel?
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Old Jan 05, 2014, 12:54 AM
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I did it with my Neos.
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Old Jan 05, 2014, 12:59 AM
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IIRC...Oleg built one of his Taboos with one of the servos closer to the root of the wing a few years back. It's really hard to come up with something that hasn't been tried before.

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Old Jan 05, 2014, 01:01 AM
Hugh Blackburn
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Bob McGowan did this with an Absalut back around 2005.

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Old Jan 05, 2014, 01:03 AM
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It just seems like it would be standard especially when using the new heavier t blades?
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Old Jan 05, 2014, 01:31 AM
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It certainly has been done and is much better than adding lead to the opposite wing tip. I'm of the philosophy that 4g is way too much weight for a peg install. My blades are probably around 1-1.5g installed. I use straight blades, not T blades or gull wings, for that very reason. To each their own, though.

Many people paint stripes only on the non-peg side of the wing to balance it out. There are other ways of doing it I'm sure. Or you could just use aileron trims to keep it flying straight. GT did an analysis that concluded that the extra drag from the aileron trim had less effect than the extra weight used to balance the wing.
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Old Jan 05, 2014, 04:02 PM
G_T
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A T-blade can be down to about 1.4g. A straight blade can be down to about 0.8g without getting too extreme. Many are two or even three times this weight. That is seriously way too much weight to be putting on the wing tips! All the work we do to increase launch height, and then just throw it away with a blade and even in some cases with balance weight on the opposite wing tip! Not ideal, IMHO.

Dr. Drela, many years ago, showed how to easily make a throwing blade that is under a gram. They are comfortable, efficient, and more than strong enough.

A T-blade is harder to make light but it can be done. 1.4g is the lightest I'd achieved, by cutting down one of Gavin's old blades reducing all the mass that wasn't needed.

Install in both cases should be a couple tenths of a gram. A straight blade needs more reinforcing around it. A T-blade needs more epoxy (filled, lightened, but still structural) to glue it in. I consider that part about break even.

People are routinely doing the equivalent of throwing an extra penny on the throwing blade side of the wing. Is it any wonder they encounter trim issues?

Gerald
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Old Jan 05, 2014, 04:40 PM
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So that begs the question: how light is light enough without compensation?

Even if I had a 1g throwing peg, wouldn't that still lead to trim issues?
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Old Jan 05, 2014, 05:32 PM
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I've never noticed a need to trim for a ~1g blade.
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Old Jan 05, 2014, 05:35 PM
G_T
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Given the state of production of wings, it is more likely you'll have trim issues from slight warpage of the wings or the flaperons. In any event, 1g extra mass at a wing tip of a 270g model only moves the CG a tiny bit laterally. The wings have great leverage - the trim will be almost invisibly small.

Ideal of course is to have no imbalance and light wing tips. Having a light throwing blade, and moving the servos in the wings a little, is one way to achieve this. From when I've investigated it, generally adding weight to the light wing tip is not a good approach. It does more damage to performance overall than trimming would do. The sink rate increases more from the added weight than the increase which would be caused by the extra drag from slight trim.

There can be exceptions when the imbalance is sufficiently severe - though at that point one is pretty much screwed anyway. Then I'd suggest seriously offsetting the servos.

Alternatively, one could design wings specifically for blade vs non-blade side. Nobody is doing this and I don't think the required work is worth the payoff.

When looking at trim issues with DLGs, people look at the weight of the throwing blade. But they neglect to look at the drag of that blade. The drag attempts to yaw the plane towards the blade. A tiny bit of rudder or slight offset of the vertical tail, could compensate. On the last plane I built (almost finished) the vertical tail is offset towards the non-throwing blade wing. So its drag is offset from the centerline of the plane. This should help compensate the drag of the throwing blade.

If one doesn't compensate the drag, then (1) the plane wants to yaw (2) one uses a tiny bit of rudder to compensate, so (3) the plane now flies slightly sideways due to the lateral force generated by the rudder.

It is best to use light, low drag throwing blades. Not thick chunky heavy ones.

FWIW, blisters or calluses on fingers are a function of the trailing edge shape of the blade (look up Drela's design for a good suggested shape) and even more a function of how the blade is held and released. But that would be the subject for a different article.

Gerald
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Old Jan 05, 2014, 11:04 PM
Eggcellent...
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Hey, Bill Watson did a DLG with an asymmetric wing several years ago.

Tom Watson
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Old Jan 06, 2014, 11:14 PM
It's a mere flesh wound!
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Quote:
Originally Posted by tewatson View Post
Hey, Bill Watson did a DLG with an asymmetric wing several years ago.

Tom Watson
No relation
Do you mean this one:

Buddy
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Old Jan 07, 2014, 11:02 AM
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What a waste of time! what a useless attempt at improving anything! that's not an airplane!
That guy could have better spent his time refinishing his wood deck!
My attempt at sarcasm and imitation.

But , really moving the CG away from the arm is a concept worthy of exploration to improve the engergy that can be imparted to a DLG
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Old Jan 07, 2014, 11:57 AM
G_T
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More pilots are power limited than speed limited. Hence the desire for higher aspect ratio lighter DLGs. Therefore moving the mass farther out won't help much if at all.

Gerald
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Old Jan 07, 2014, 02:11 PM
2013 US F3K Team Manager(ret)
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Quote:
Originally Posted by Buddy Roos View Post
Do you mean this one:

Buddy
That was Breck Baldwin's version of an asymmetric DLG.
It is much more extreme than Bill's.

You can check it all out on this thread: Asymmetric DLG design...
Here is Bill's: (Photo by Chris Adams)
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