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  #31  
Old 12-05-2006, 11:24 PM
Stephen Lindberg Stephen Lindberg is offline
 
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Location: Olympia, WA
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Mike S: The tank is part of the wing D section and carries torsion loads. The front spar carries almost all of the bending loads; the tank and outboard leading edge probably none. The tank also strengthens the front spar against buckling. Your conjecture about load paths is wrong. The front spar gets thicker as it nears the wing root because bending forces increase dramatically at the root. You are correct, if the spar is not properly sized or if the increase in thickness of the spar bars is not done smoothly at the correct places, then a stress riser at that location can cause in an unanticipated weakness. Many thousands of us have bet our lives, and continue to be our lives, that Van designed a strong, safe wing. Based on its service history, it is a very safe design. Now, why did the 8 wing break midspan as opposed to some other location? You'd have to ask the man who designed the wing. I will speculate that it has something to do with the outboard front spar being stronger than required for just the flight loads. This is often the case in airplanes because the wing has to be stiff as well as strong, and the requirements for stiffness in the outboard section (and the requirement for ruggedness for ground handling) often results in an outboard spar that is stronger than needed than to just carry the bending forces. I'm not an engineer but I am interested in these types of questions. A good primer is "Design for Flying" by David B. Thurston, McGraw-Hill, 1978.
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Last edited by Stephen Lindberg : 12-05-2006 at 11:28 PM.
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  #32  
Old 12-06-2006, 10:19 AM
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Mike S Mike S is offline
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Steve, thanks for the reply----------you are right, of course, concerning the torsion loads, I was only addressing the bending loads.

As far as the design engineering, I have no doubts there, just wondering if a builder took "short cuts" with the spar reinforcements (I.E. just cut them off at the end of the tank instead of a long taper or whatever the design is) could that then have contributed to the failure at that point.

Mike
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  #33  
Old 12-06-2006, 10:32 AM
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Sam Buchanan Sam Buchanan is offline
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Concerning an RV-8 crash several years ago:

Quote:
As far as the design engineering, I have no doubts there, just wondering if a builder took "short cuts" with the spar reinforcements (I.E. just cut them off at the end of the tank instead of a long taper or whatever the design is) could that then have contributed to the failure at that point.
The RV-8 (and I believe all RV-3, 7, 9, and 10) main spars are delivered from the factory fully assembled. They have machined spar caps instead of the doublers used on the RV-4 and -6. This has removed the possibility of the builder mis-assembling the spars.
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  #34  
Old 12-06-2006, 11:00 AM
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Mike S Mike S is offline
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O.K., got it.

As I said in my first post in this thread I havent yet built a RV wing, I was just speculating what may have led to this particular failure of this one aircraft.

Seems like the culprit lies elsewhere.

Thanks for the info.

Mike
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  #35  
Old 12-06-2006, 03:37 PM
markpsmith markpsmith is offline
 
Join Date: Aug 2005
Location: Houston
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Quote:
Originally Posted by gmcjetpilot
Other jets limit control surface deflection at high speed. On new jets, F16 the computer limits the loads not the pilot.
True. The Viper will let us only pull 9.0g's, however, g overshoots in the realm of 9.2-3 g's are possible. We also have rolling (asymmetric) g limits that are lower than 9g's. But the computer does not factor in the rolling g's. If the rolling g limit is 6g's the jet will let you roll while pulling 9g's which would technically be an over-g.

When we carry bombs we have g-limits as low as 5.5g's (symmetric). The jet will still let you pull 9g's. I doubt the wing would fail, however, it would likely cause quite some damage. I have only seen a 7g over-g in this configuration which caused no structural problems.

Just thought I would add something to this discussion - as it is well above my cranium.

My question to this discussion would be...I thought that the horizontal stab would typically fail before the wing?

Mark

Last edited by markpsmith : 12-06-2006 at 03:40 PM.
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  #36  
Old 12-06-2006, 08:40 PM
Roger Moore Roger Moore is offline
 
Join Date: Oct 2005
Posts: 64
Default RV Strengths and Weakness

You may or may not have heard about my experience with a pre 1984 RV4, an article was published in "Sport Aerobatics". My airplane was built by two very experienced builders but I damnd near pilled the engine off of it. We found all 4 weldments were broken on inspection and had to replace them with the post 1984 redesign. This aircraft was never overstressed on landing or airborne. This is a weakness of the RV design in the RV4 of pre 1984 manufacture. Roger Moore
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  #37  
Old 01-05-2018, 03:02 PM
Pilot Dog Ship Pilot Dog Ship is offline
 
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Location: South Surrey, B.C., Canada
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Default Regarding airliner wing design

“The Boeing 767 has 4 ailerons. The out board ailerons LOCK out at higher speeds to reduce loads”.

I think this statement requires some clarification. It is true that, depending upon the design, the outboard ailerons are prevented from deflecting either when the flaps are up or above a certain speed.
My understanding of this feature is to prevent aileron reversal at higher speeds, wherein the aileron deflects but has so much effect that it twists the outer wing in the opposite direction, the net result being the aircraft rolling in a direction opposite to that commanded. The B-47 comes particularly to mind. In its handling notes it describes-at increasing speeds-the ailerons having less and less effect, no effect at all then having the reverse effect.
One way to prevent this would be to make the wing more resistant to the twisting force realized from the aileron deflection. The downside of this solution is greatly-increased structural weight as well as impacting all the other design compromises in the wing.
Above certain speeds, an inner aileron( with a shorter moment arm to the longitudinal axis than an outer aileron) can generate the desired rolling forces and therefore it’s a better design decision to build a wing with two, smaller ailerons on each wing. With the outer unable to move above certain speeds, the outer wing can be built lighter, making the overall airframe lighter.
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  #38  
Old 01-05-2018, 03:15 PM
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RV8JD RV8JD is offline
 
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Default Inboard Ailerons + Roll Spoilers

Quote:
Originally Posted by Pilot Dog Ship View Post
Above certain speeds, an inner aileron( with a shorter moment arm to the longitudinal axis than an outer aileron) can generate the desired rolling forces ...
In addition to roll spoilers on the wing.

(Wow, resurrecting an 11+ year old thread!)
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