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Old Nov 24, 2011, 03:53 PM
yyz
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Quote:
Originally Posted by Jimbello View Post
My understanding is similar to yours Dean. Surely, this provides a "geared" up or increased mechanical advantage of the servo and reduced backlash effect (mostly referred to as "slop").
Any increase in the servo arm length for a fixed or given control surface horn length will decrease these advantages and make the set up more prone to flutter.

Can someone confirm or contradict this reasoning?

And flutter at 70 mph.?? How do the DS gliders regularly fly and many times this speed without flutter?

Jim.
The longer control horns at the surface side of the chain will reduce the throw available on the control surface and will make for a stiffer and more flutter-resistant linkage.

If the surface is induced to flutter, say by uneven or turbulent flown on one side, you want the surface to have as little mechanical advantage (leverage) against the other end of the linkage (the servo) as possible.

Imagine the control horn was a foot long. Try to move the control surface against all the leverage the servo now has against the surface. This is the opposite of using a "cheater bar" on a wrench to break a frozen lug nut free.

Now make the control horn as short as possible, say even with the hinge line. The servo now has very little leverage and the surface can easily move (ie, flutter).

If you look at it the other way around, you want the servo to have maximum leverage (sacrificing travel) against the surface trying to move (flutter).

My earlier statement was confusing,

Mike

ps: Something is really wrong if going 70 mph caused that glider to flutter to failure. Even flying through shear (eg, strong thermal) at that speed shouldn't have caused it to break up.
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Old Nov 27, 2011, 01:57 PM
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This really sounds like a design problem. Flutter can be controlled with counterbalances, either aerodynamic or weights. An expensive xc ship should not have this problem.
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Old Dec 01, 2011, 05:29 PM
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Thanks for the scetch Dean, appreciate it.
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Old Dec 01, 2011, 05:41 PM
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on the actual speed of the plane at the time of flutter;

We know the ground speed was 70MPH, if we know how much altitude was lost over a specific time (convert to MPH), then we can use triangle properties and use 70 squared times X the distance traveled down in elavation over time (MPH) and square that , and it will equal the planes actual flight speed squared.

It's hard to explain but simple multiplication and division.

Did the altimeter data include the verticle drop over a time period at the end Dean?
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Old Dec 07, 2011, 07:20 PM
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Scott,
I quickly looked at the GPS recording wanting to know the speed obviously.
As I remember it seemed low 70 or maybe 80. What needs to be factored in is that I put so much down trim in the glider headed for the ground basically trying to do an outside loop. Not much forward progress GPS wise hence the low speed.

How fast, will never know. For sure more than 100 as I have final glided that fast. Rich Spicer has final glided his at 140.

Point of failure in my mind is the control horn to pushrod connection. Sullivan or Dubro clevis with a brass tube or in my case an aluminum rod drilled to clevis pin dimension, I believe 1/16".
This joint seemed tight on the plane but playing with it in your hand not so tight. The glider was three plus years with several hundred miles on it and wear went unnoticed. A drop of CA makes a world of difference.

Regards Dean
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Old Dec 08, 2011, 11:56 AM
yyz
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Quote:
Originally Posted by DEAN GRADWELL View Post
I like to build fixtures in an attempt to make components interchangeable.
Very clever, Dean. I never know whether or not to trust the relative angle of incidence established by the wing fairings/fillets on the fuselage (eg, whether they are correct/the same in relation to one another and the stab).

You seem like a very trusting fellow!

Mike
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Old Dec 08, 2011, 08:24 PM
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Mike,
I'm not sure I follow you.
The fixture I made was to locate incidence pin holes, servo wire holes, and spar joiner holes on the fuselage. The fuselage is built in a mold so every one will be the same but the hole location may vary. The stab location is another story to be described later.



Regards Dean
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Old Dec 08, 2011, 09:59 PM
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Excellent idea, Dean. I was thinking of making bigger wings for an Icare ASW 27 that has pretty small wings and this will help!
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Old Dec 08, 2011, 10:59 PM
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Mike,
I think I know where you are going.
Follow along as I check wing alignment.
Regards Dean
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Old Dec 09, 2011, 12:41 PM
yyz
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Quote:
Originally Posted by DEAN GRADWELL View Post
Mike,
I'm not sure I follow you.
The fixture I made was to locate incidence pin holes, servo wire holes, and spar joiner holes on the fuselage. The fuselage is built in a mold so every one will be the same but the hole location may vary. The stab location is another story to be described later.



Regards Dean
My point was that you need to trust the guy that made the molds that both sides of the wing fillets/fairings are in alignment with each other (ie, have the same incidence angle). I'm sure the MXC doesn't have that issue.
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Old Dec 09, 2011, 05:10 PM
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Mike,
Your right, left and right close but perhaps not perfect.

RnR uses a Robart incidence meter and fine tunes alignment with the registration/incidence pin.

I'm a tool nut so I tried to improve on the Robart unit using all kinds of digital stuff but have gone back to using Robart.

The fixture I showed is for locating the holes in the fuselage. Next I'll back drill into the wing root.

I had someone ask how I do it and that is why I'm posting this. I'm sure boring for most.

Regards Dean
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Old Dec 11, 2011, 10:49 PM
yyz
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Quote:
Originally Posted by DEAN GRADWELL View Post
Sometimes transfering hole locations can be frustrating. Scraps of plastic can save alot of measuring.
Great tip! To ensure that both wing halves have the exact same incidence, I typically rip a long length of 1/2" or 3/4" plywood about 6" wide on the table saw taking extra care to make sure the cut is straight and the wood stays against the rip fence.

Cut that piece of wood in half, lengthwise. Those two pieces are then glued, on edge to your table with thick CA so that they straddle both sides of your fuselage. You know have a cradle with parallel edges that serves as an alignment jig for ensuring both wing halves match.

If the fuselage fairings don't match the wing, that's what electrical tape is for!

Sorry if that was obvious or repeating old news,

M
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