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Wing loading

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Old 09-09-2017, 10:16 AM
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bdeveci
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Default Wing loading

I'm plannig to carry out a wing loading test to my 1:16 scale A340-200 before maiden. Positive "g" will be 3g and negative "g" will be 1.5g. The weight of the fuselage (including fuel) is 15kg and the wing (including engines) is 9 kg.
So, what shall be the test load on the wings? 15kg times "g" or 24kg times "g" ?

Bülent
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Old 09-09-2017, 04:16 PM
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I guess if you are planning on flying with the wings on I would use 24kg. Post some pictures I'd love to see your bird!
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Old 09-10-2017, 08:29 PM
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Stactic test flight load, 3G 72kg positive and 1.5G 36kg negative.
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Old 09-10-2017, 10:39 PM
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bdeveci
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Originally Posted by JohnBuckner View Post
Stactic test flight load, 3G 72kg positive and 1.5G 36kg negative.
thanks for the answers but, since the wing is a self-equilibrated body, my feeling is not to account for the wings weight.
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Old 09-11-2017, 06:52 AM
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Do the wings not support their own weight, as well as the fuse and cargo/passenger weight and fuel? When a full sized plane wings are stress tested, the wings are subjected to the "G" loads across their full length, using multiple stressing points. They are then held for extended periods in a "stressed" condition to see if they hold up. I've see, driving to work, a jet with the wingtips pulled up to almost twice the height of the fuse, being held there for several days. My thought is they were waiting to see if the wings were going to break under the load. As I see it, if you're looking at 24Kg AUW at 1G, I'd test them at 72Kg for 3Gs.
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Old 09-11-2017, 07:51 AM
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Self-equilibrated body, Hmm no clue as to the meaning of that word and perhaps an interesting concept but in the real world if you are going to static flight load test then the full gross weight of the aircraft is included. I am no engineer but this was the procedure that I used with the one full scale airplane that I built in the experimental category and accepted by our FAA

Actually here in the US depending upon the category a general aviation civil aircraft is to be certificated in (standard, ultility or aerobatic) an additional safety factor is imposed as a percentage over the specific limits for each category

Now in the case (in the US) in the experimental category and in the case of a model airplane you are the engineer and can make the decision on how you are going to do such things as well decide on your own limits.

I would be pleased to hear about such regulations that may or may not apply to especially the giant models in your country. it is fascinating how especially some countries in Europe have very liberal laws concerning the giant scale stuff.

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Old 09-11-2017, 09:16 AM
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e•quil•i•brate

v. -brat•ed, -brat•ing. v.t.
1. to balance equally; keep in equipoise or equilibrium.
2. to be in equilibrium with; counterpoise.
v.i.
3. to be in equilibrium; balance.
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Old 09-11-2017, 06:40 PM
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Really??
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Old 09-11-2017, 07:17 PM
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Originally Posted by bdeveci View Post
thanks for the answers but, since the wing is a self-equilibrated body, my feeling is not to account for the wings weight.
Actually, that term is not accurate. Been thinking about it for a while and I BELIEVE a wing can't be a self-equilibrated body since it wouldn't fly if it was. It's motion through the air MIGHT make it weightless but it wouldn't create lift since, to do so, it would have to go past equilibrium. A wing is either supported by the plane's structure and landing gear or it's supporting the structure. To be in equilibrium would change nothing since the wing is still being supported by the landing gear until it attains enough speed to lift the plane on it's own.
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Old 09-14-2017, 03:40 AM
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Wing weight isn't a part of the load on the wing's spar in flight. The wings in flight actually have a negative weight- they weigh less than zero as far as the spar is concerned. All of the stress on a spar comes from fuselage weight. That's even true on a flying wing design as the center of the wing carrying fuel, engine, batteries, etc. is the only load the wings see.

That said, 3 G is not much of a safety margin for a model. Sure, a gently flown scale plane might not ever see more than that, but aerobatics planes routinely see 10 G or more. I think if it were mine (just as opinion here) I'd start with 5 times the fuselage weight and hold the wings at the middle when testing. That doesn't perfectly replicate flight loads, but it would tell you if the design is sound. Others with more knowledge and experience than me may weigh in with better suggestions.
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Old 09-14-2017, 09:21 AM
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Originally Posted by jester_s1 View Post
Wing weight isn't a part of the load on the wing's spar in flight. The wings in flight actually have a negative weight- they weigh less than zero as far as the spar is concerned. All of the stress on a spar comes from fuselage weight. That's even true on a flying wing design as the center of the wing carrying fuel, engine, batteries, etc. is the only load the wings see.

That said, 3 G is not much of a safety margin for a model. Sure, a gently flown scale plane might not ever see more than that, but aerobatics planes routinely see 10 G or more. I think if it were mine (just as opinion here) I'd start with 5 times the fuselage weight and hold the wings at the middle when testing. That doesn't perfectly replicate flight loads, but it would tell you if the design is sound. Others with more knowledge and experience than me may weigh in with better suggestions.
thanks for your answer. I'll consider your 5g suggestion. Attached is a photo of my bird. Still needs a lot of work....
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Old 09-15-2017, 03:38 AM
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The wing center needs to support only
the weight of the fuselage. Test the wing
center with the weight of the fuselage times
the number of G's.

Support the wing on a saddle where the
fuselage would mount and spread weights
over the wing in the fashion that the air would
push while lifting the plane.

Each side of the wing can be tested for its
ability to support the weight of the engines.

Support the wing by its engine mount and
spread weights over that side in the same manner.
Use weights totaling the engine weight times the
number of G's. This will test the ability of the
wing, nacelle and engine mount to carry the
weight of the engine, though it doesn't factor
in the engine's thrust.

Jenny
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