Wing Load Test?

[Aerodude45]

I remember hearing or reading somewhere that Leonard tested a Legal Eagle wing to 1,000 lbs. Anyone know anything about this? I'm curious, as my plane is in a public workshop and I've had a few non-airplane folks ask about my wings wondering how all of them sticks can support an airplane, and I'd like to be giving them accurate info. Thanks! 

[Steve]

I remember hearing or reading somewhere that Leonard tested a Legal Eagle wing to 1,000 lbs. Anyone know anything about this? I'm curious, as my plane is in a public workshop and I've had a few non-airplane folks ask about my wings wondering how all of them sticks can support an airplane, and I'd like to be giving them accurate info. Thanks!

Look here in the old Yahoo Group files: https://groups.yahoo.com/neo/groups/EaglersNests/files/Loading%20a%20Legal%20Eagle%20Wing/

[Dan_]

About that test...

Leonard tested the hell out of that wing...

Most use a load schedule calculated by an engineer to load the wing according to the actual air loads it will see according to the aerodynamic loss of lift all wings experience.

That load schedule usually goes out evenly to somewhere around the lift strut attach, then dramatically tapers off out to the tip.  (see attached)

Leonard loaded his wing evenly all the way out to the tip, which put way more strain on the outboard part of the span than it would see in flight.

[Aerodude45]

Yep, testing a wing with evenly distributed weight and not accounting for loss of lift due to spanwise flow is a great way to be conservative! I could pull out my NACA book that has load-distribution charts and calculations for various airfoils and aspect ratios to see if I can estimate an "adjusted" G-limit, but I don't think it would be worthwhile or in any way necessary.

That's awesome. I didn't realize there had been an article in Sport Aviation about it.

[Dan_]

a great way to be conservative! 

The wing is for sure up to the task Leonard intended, and with what should be a comfortable margin...

[ParQld]

Steve, is there a better version of this. Higher in Resolution. This images are very pixelated and almost impossible to read?

anyone got another copy ?

Look here in the old Yahoo Group files: https://groups.yahoo.com/neo/groups/EaglersNests/files/Loading%20a%20Legal%20Eagle%20Wing/

[JohnB]

Yep, I know a little about it as I helped load the bricks on the wing.
The chart shown earlier is a bit misleading as it is a tapered wing, not Hershey bar like the XL (that was the wing we tested)  This will give a different span loading.   I consulted with an aero engineer on how to distribute the bricks as far as span wise but forgot to ask him about chord-wise loading.   As a result we had WAAAAAYYYYY more loading on the rear spar than necessary.   
Should have had about 75% on the main spar and 25% on the rear.   As the spars are of similar construction and the front spar is MUCH stronger in bending than the rear we (and the engineer) concluded that even thou we only claimed 4G's the rear spar was tested to 6 or more.
As a side note when Leonard let the jack down supporting the wing I had my ear on the floor next to the wing listening for any snap, crackle or pop,   not a peep.  Leonard bought lunch that day, Happy Camper.

John B.

[scottiniowa]

It can be safely said, that if you talk to 3 different aeronautical engineers about a wing loading test, you will get 3 different ideas or answers on proper way to do it and weight distribution.  This seem to be an area where a uniform formula could be at hand. But this is often not the case.  A fairly simple reason is the fast difference in wings.

Such as struts at 50% of wing length, vs 35%, two spars (legal eagle XL) or one box spar  and then of course, low wing vs high wing, Cantilever wing... sigh

All that being said, it sure looks like Leonard tested his well, and it certainly has been well proven.

[Dan_]

There is a formula and Aeronautiacl engineers have been doing it this way at least since Mr. Schrenk got his paper published by NACA...




There is a shortcut that simply loads the wing evenly out to one chord length in from the tip and tapers from there down to one "weight unit" at the tip.  This is usually a single sandbag or layer of bricks...  This method is accepted I do believe by the European equivalent of our FAA which requires all home-built aircraft in Europe to have a wing stress test.

A wing in flight experiences relative wind from the slipstream.  This is fine until you start to get near the tip of the wing, then the air knows it does not have to split and go over the wing.  It can go around the end...

When it does this it tries to take adjacent air molecules with it.  This sets up a flow which is outbound ^{High pressure area} on the bottom of the wing and inbound ^{Low pressure area = partial vacuum} on the top (remember Bernoulli).  This mechanism is the cause of phenomena known as wingtip vortices.

This flow pattern kills the lift in this area so that part of the wing is mostly just creating drag.  The aerodynamic loses due to this process amount to one half the lift being lost for the area of one chord length in from the tip.

Steve Wittman came up with a way to deal with this problem, with his triangular wing tips he first put on his V-8 Tailwind.   He essentially tried to reduce the part of the wing that was doing nothing but causing drag.

You see many examples of his design on modern aircraft...

File attached: