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Jeyoung65(at)aol.com
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 Posted: Wed May 16, 2007 6:31 am Post subject: Recent crashes |
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I have been reading the post on wing failure and flutter of the XL. I am building a HD so do not know how the XL wing is build or attached to the fuselage. On the HD there is a main "I" spar attachment bolts, Rear "Z" spar and leading edge skin attachment screw. Maybe someone can help me out. On the flutter I thought the main reasons were loose hinge points, I would have to include loose cables here, also loose connection between the ailerons. Wing stiffness can effect flutter. Has anyone checked to see what type of hinge was used on the aircraft that reported flutter or wing failure. Jerry-GA
DO NOT ARCHIVE
See what's free at AOL.com.
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ashontz
Joined: 27 Dec 2006
Posts: 723
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| Posted: Wed May 16, 2007 6:42 am Post subject: Re: Recent crashes |
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I think wing stiffness is the main culprit here. Aeroelastic analysis treats every connection point as a spring. The more stiff springs you have the less flex. Any wing will flutter being that one end is connected to something (the fuselage) and the other isn't. The trick is to have the wing rigid enough that the flutter speed is well ABOVE anything the plane is capable of. Even though the HD has the same wing span over all, effectively the wing from a rigidity view point is only 9.5 feet instead of nearly 12' due to the fact that the HD has the center wing and then the two shorter wing panels. Any twisting in the HD is carryied over a 9.5 foot span instead of a 12 ' span before it hits a mounting point. And the mounting point in the HD has additional rigidity built in to handle the landing gear stresses. That being the case, the individual ribs in the HD, even if the spacing is identical to the XL, are carrying less twisting forces each.
One good static test would be to put all those lead shot bags on the wing and then shake the wing to simulate flutter. I suspect the results would be that the wing not only shakes fairly easily, but that the structure fails short of the design limits. That wing with the shot bags on it probably has a pretty good twisting spring like rocking to it that slowly dampens. I'd bet the HD DOES NOT exhibit similar characteristics and would take more weight to produce similar results.
Just my two cents, but an XL wing with more ribs put under the same test would more than likely fair better.
Check this video. http://www.airspacemag.com/multimedia/video/b747.php
You'll see that the wings on this 747 are flapping up and down, but if you look closer you'll notice that they're flapping up and down because the angle of attack is changing at the wingtips. You can reall see the wing twisting distortion if you look at the engines. The lifting force of the wings gets translated to a twisting force the further out on the wing you go, obviously. As the wing twists back the lift in that area increases causing the wing tip to rise, it then it reaches a maximum force of twist resistance in the wing and then it snaps back the other direction and in the process reduces the angle of attack forcing the wing down til the maximum twist reistance is reach in the other direction, result; flap flap flap. Increase the rigidity of the wing and decrease the ability to flex and cause this fluttering condition.
The more rigid the wing, the less chance for the
[quote="Jeyoung65(at)aol.com"]I have been reading the post on wing failure and flutter of the XL. I am building a HD so do not know how the XL wing is build or attached to the fuselage. On the HD there is a main "I" spar attachment bolts, Rear "Z" spar and leading edge skin attachment screw. Maybe someone can help me out. On the flutter I thought the main reasons were loose hinge points, I would have to include loose cables here, also loose connection between the ailerons. Wing stiffness can effect flutter. Has anyone checked to see what type of hinge was used on the aircraft that reported flutter or wing failure. Jerry-GA
DO NOT ARCHIVE
See what's free at AOL.com.
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gboothe5(at)comcast.net
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| Posted: Wed May 16, 2007 7:49 am Post subject: Recent crashes |
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Jerry,
I don’t think wing flutter or aileron flutter or elevator or rudder flutter has ever been verified. There has been much conjecture on what some think they saw in videos. Certainly loose cables could account for many control surface problems. FYI- according to a search by Bill Naumuk, there have been no reported structural failures on the HD model.
Gary Boothe
Cool, CA
601 HDSTD, WW Conversion 90% done,
Tail done, wings done, working on c-section
From: owner-zenith-list-server(at)matronics.com [mailto:owner-zenith-list-server(at)matronics.com] On Behalf Of Jeyoung65(at)aol.com
Sent: Wednesday, May 16, 2007 7:30 AM
To: zenith-list(at)matronics.com
Subject: Recent crashes
I have been reading the post on wing failure and flutter of the XL. I am building a HD so do not know how the XL wing is build or attached to the fuselage. On the HD there is a main "I" spar attachment bolts, Rear "Z" spar and leading edge skin attachment screw. Maybe someone can help me out. On the flutter I thought the main reasons were loose hinge points, I would have to include loose cables here, also loose connection between the ailerons. Wing stiffness can effect flutter. Has anyone checked to see what type of hinge was used on the aircraft that reported flutter or wing failure. Jerry-GA
DO NOT ARCHIVE
See what's free at AOL.com.
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n787xl(at)aol.com
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| Posted: Wed May 16, 2007 9:45 am Post subject: Recent crashes |
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Gary B.
I attached an aileron yesterday and found them to be fairly heavy. They would need about 1.5 lbs at 6" to balance. I am assuming that wing flutter may have happened in Oakdale crash.
I will balance my ailerons as a precaution.
James Schultz
Placerville (Swansboro), CA
601xl, tail, wings, ailerons & flaps done.
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