Wing building

[Earl Haury]

If a pilot can't break an airframe - it's too heavy. That being said, I've used  3/4" o.d. 0.027" wall 6061-T6 aluminum tubes in 7-8# 60 size pattern planes without problems. I tested these by supporting on the ends and adding barbell plates in the middle (more severe than in normal installation), and measured about 1/4" deflection @100#. Failure was about 110#. The 7/8" x 0.035" tube normally used deflects about 1/16" with 100#, I've not loaded one to failure.  So - even the small tube would handle 10G's in a 10# airplane. It would be interesting (and maybe exciting) to load a 7/8" CF tube to failure. I'm not surprised that the failure point is the tube mount in the wing foam. It would also be interesting to use a G-force sensor with a data logger to get some real load data.

Earl
  ----- Original Message ----- 
  From: Bob Richards 
  To: discussion at nsrca.org 
  Sent: Saturday, January 08, 2005 7:56 PM
  Subject: Re: Wing building


  IHMO, if wing tubes are being bent (and there are reports to that effect) then the plywood support ribs are a moot point.

  If we go to stronger wing tubes, then the weak point will move somewhere else, probably the ribs or whatever is used to support the wing tubes.

  It appears to me that over the last 10 years, a lot of effort has been put into designing weight out of our planes. It all started, or certainly escalated, when the engine size restriction was lifted. I remember thinking at the time that people would use the biggest engines they could shoehorn into the plane, and the airframe strength was going to be compromised to stay under the weight limit as a result.

  There have not been, to my knowledge, very many in-flight structural failures, so we keep shaving stuff off our airframes. Now we have a schedule with a real stresser of a maneuver. Snap -- literally! Guess we need to put something back in the plane!

  I also think it was interesting that none of the pattern planes were 2m UNTIL there was a 2m limit. Nevermind that we did not have the horsepower to effectively fly a plane that size, or that a 2m airframe was even optimal, all of a sudden everyone had to have a 2m plane.

  The F8F Bearcat from WWII had wingtips that were designed to blow off if the stress limit of the plane was exceeded. Maybe that is what we need now. :-)

  Bob Richards.

   
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