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Testing Different Wings

Old 05-07-2011, 05:20 AM
  #1  
hillbillynamedpossum
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Default Testing Different Wings

I always wondered what the mode of failure would be on a "sheeted" wing. To that end, I built a nice, strong wing and piled concrete blocks on top of it till it broke. Who says West Plains is dull?

I finally broke down and built my self a hot wire foam cutter. I used an "e" string and a battery charger....it works pretty good.

I used regular old white pebbly strofoam for the cores. The profile is a Clark "Y" 12" chord. The cores weighed about 2 ounces each. This test was conducted using fiberglass/plastic screen "wire" from the lumber yard and 2 coats of Durhams Rock Hard Water Putty. As the pictures tell, theres just enough Durhams on the wing to cover the screen wire.

I plan to do simular tests with plain old drywall mud and spackling, just to see that the sample weight and strength will be. More on that later....



On the left side I wrote down my measurements....Let me explain my shorthand. The fractional measurements are the distance from the bottom of the wing to the table...if you subtract each measurement from the "no-load" you will get the deflection. the numbers next to that are short hand for lbs and ounces.....so 13-4.3 is 13 pounds and 4.3 ounces....sorry for all you metric folks out there....IM NOT FRENCH!

As the photos show I used 1 1/2" cap blocks for weights and piled them on until I had a failure.

As I added more blocks I just wrote + (the weight of the added block)

After the failure I stacked up the blocks that the wing DID hold and sat them on the scale and weighed them all at once. That gives me a truer weight.

I was amazed to find that under a 51 lb and 14.2 oz load the wing only had a 15/32 deflection.....very cool!

I expected the failure to happen on the compression side....and it did....no surprizes there.



Stay tuned,

Possum
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Old 05-07-2011, 07:42 AM
  #2  
Larry3215
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Nicely done!

Yup, most fiberglass layups are stronger in tension than compression, but I wouldnt have been too surprised if yours had failed in tension. That rock hard water putty isnt exactly the recommended or normal bonding agent

Its pretty brittle when hard and would have a tendency to delam and crack with relatively small deflections.

I suspect the drywall mud will be even worse as it has very little bonding strength.

Both are pretty darn heavy too. Id be interested in seeing the same test done using minwax or some similar latex polycrylic as a bonding agent. Thats something we would actually use on a plane

How stretchy is that screen material? That will effect the strength a lot. I would think the plastic version would be too stretchy but Ive never tried it.

I have to say, I really like your investigative spirit!
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Old 05-07-2011, 09:39 AM
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mclarkson
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Nice work. 52 pounds is more than enough for any of my planes!

My wife works at the National Institute for Aviation Research where, as a statistician, she takes data from just that kind of test (on composite materials.)
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Old 05-07-2011, 11:52 AM
  #4  
CHELLIE
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Good Work Possum what I do with larger thicker Foam wings from 9mm up is to use a Square Slow Stick Fuselage kit and epoxied it into the wing, that makes them nice and strong and able to wistand 9 + Gs, I buy them a BP hobbies for 8.95 and you have a lot of other hardware with it too that can be used on your planes, Hope that helps, Chellie

http://www.bphobbies.com/view.asp?id...5&pid=NGWSV376

Fuselage Boom x 1 pce., 10x220mm Doubled-sided Tape x 1 pce, Removable fixture x 2 pcs., TS1M1.7* 10 Screw x 4 pcs, Fiber glass Stick (3x218mm)x2pcs., Push rod x 2 pcs,Fiber glass Stick (3x218mm)x2pcs., Push rod x 2 pcs Price: $8.95
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