Structural load test for Mite wing

[Scott Royall]

How many of you wonder each time you fly if your wing is still as strong as it was when it was new?
Many of you already know that I have a wing that was built by an amateur builder that I plan to use on my Mite that I am re-building. I have authorization from the FAA to register it as an experimental amateur built airplane with the home built wing.
I have serious questions about the structure of this new wing. It looks good on the surface. The workmanship is acceptable. It seems to be built to specifications according to the plans. But, the builder was deceased before I bought the wing so I never had a chance to talk to him to find out about the processes he used in building the wing. His family didn't know much about it either.
So, I am in the process of designing a static load test to verify that the wing is strong enough to fly on confidently. When I am finished I will either have a very expensive pile of firewood or a wing that I don't have to worry about.
The problem is that I am not an engineer. When I started this project I don't know anything about structural formulas or loads or stress test. Do any of you know about these things? I am interested in any suggestions at this point. If you know of any articles or have any expertise in the processes that I am facing I would love to hear about what you know.
I will report to you guys from time to time about how things are progressing.

[Glenn]

Hey Scott:

I was a 'sand bag' for a sailplane wing test in '75. The builder was an aeronautical engineer and needed sand bags. He weighed several 'bags' one morning. I'm guessing that there was 30 of us of all sizes. Later that night we were all asked to come back. He had the wing inverted and supported by a forklift at the center section. Our names were written at specific wing sections where we were to sit. I don't know exactly how this was calulated. I know the weight is to be ditributed evenly. I suspect MAC is an issue to where less weight is distributed along the wing as the cord narrows. This should be pretty easy to figure out if you know the aspect ratio of the wing (wingspan/mac). I'm sure it's published someplace. Then you have to determine what you are willing to test the wing to. It's been a long time, but I seem to recall it's 150% max g limit and I seem to remember that Standard Catagory aircraft are certified at 4.4 g's. That comes out to like 5610 lbs. Oh MY! Don't take my word on it. Certification spec's are spelled out in the FAR's.

Anyway, the forklift goes up and up and up 14' before the tips came off the ground. We were hanging on for our lives. That wing made the most sickening breaking noises, bangs, pops and groans but stayed intact. Then they went out and flew it! Unbelievable. I don't recall if they ever tested it for negative loads. The sailplane eventually met it's demise when it was put into an inadvertant spiral dive while positioning for a turn point photo and could not recover. The pilot bailed and several witnesses swear that the tips were touching each other before the wings failed.


Now I don't know what wing you have but I flew Daves Mite with his homemade wing and it flew very nice and was very fast. Dave said he followed the plans exactly and was amazed how Mooney could design a wing so simply that you didn't need a jig. That bothered me, but the fact was, it flew straight and fast. He also used modern glues which was a good thing.

You may want to contact Dan Beltrami. He built a new wing for his Mite. Don't know how or if he tested his wing. I just know that Dan's Mite had a difficult time out running a J-3. Sorry Dan. It was true. Ask Ernie Buenting. He owns it now. Dave may have a contact number for Dan.

Don't know if this helps any. Made a really long story, though. My thoughts are that if Dave built it then it's probably okay. He was a cleaver guy. I have no doubt that his wing on 4177 was as strong or stronger than original. However, if your wing is composite, you're on your own! You are so very fortunate to get the Fed's Experimental blessing. Good luck!

[Salvador A. Sanlley]

How many of you wonder each time you fly if your wing is still as strong as it was when it was new?
Many of you already know that I have a wing that was built by an amateur builder that I plan to use on my Mite that I am re-building. I have authorization from the FAA to register it as an experimental amateur built airplane with the home built wing.
I have serious questions about the structure of this new wing. It looks good on the surface. The workmanship is acceptable. It seems to be built to specifications according to the plans. But, the builder was deceased before I bought the wing so I never had a chance to talk to him to find out about the processes he used in building the wing. His family didn't know much about it either.
So, I am in the process of designing a static load test to verify that the wing is strong enough to fly on confidently. When I am finished I will either have a very expensive pile of firewood or a wing that I don't have to worry about.
The problem is that I am not an engineer. When I started this project I don't know anything about structural formulas or loads or stress test. Do any of you know about these things? I am interested in any suggestions at this point. If you know of any articles or have any expertise in the processes that I am facing I would love to hear about what you know.
I will report to you guys from time to time about how things are progressing.
Scott, I recommend you talk to a structural engineer at Mooney Aircraft and ask the questions. I assume they will be sensible to your problem since its one of the first Mooney on the market. If not, any aircraft manufacturer could be of help.

[Scott Royall]

Hi everybody.
I have tried 3 different times to get this follow up posted and each time I have written a long explanation and then found out that Mite Talk had timed out and I lost all the stuff I had written. I got so discouraged that I just decided to wait a while before I tried again. This time I am writing in Word and I’ll post it as attachments to the site.

I finally found someone with the right credentials and experience to give me some advice on the way to perform the wing test. I had to promise not to use his name for liability reasons. We talked about the purpose for the test and the procedures and loads to use. My advisor finally said that he would be comfortable with the process I have listed in the attachments. This guy has a really good resume and I trust his recommendation.

The test loads are fairly low because this is not intended to be a destructive test. I do want to fly on the wing not break it. The repetitive loading and inspections for deformations should reveal if there are any structural flaws in the workmanship on the wing. The amount of deflection under weight and the distribution of the deflection from wingtip to wingtip should show whether the strength is adequate.

I’ll also attach a spread sheet that I used to calculate the load and the distribution of the load for the test. I would appreciate any comments about the assumptions I made and the numbers I used.

It will be a while still before I get the test done I’m starting a new business and time is scarace these days. Till then I’ll enjoy hearing about your successes and your flying experiences.

[Scott Royall]

Hi Guys,
Is there anybody out there any more? I am feeling like this is my personal blog these days.
I finally got 80, 40 lb bags of concrete out to my hangar and loaded most of them on top of my wing which was mounted upside down in a jig for the stress test. For those of you who had faith in Dave Grubert's building skills, your faith was validated. The load test was designed for a 4g load but I went all the way to 5g's and the wing did great. It deflected evenly and returned to its original shape just like it is supposed to. It did make some unsettling noise form time to time but I had been warned that it would and that the noise was normal. I have attached a short slide show with some of the pictures we took with a time laps camera.
I am so glad to have this test over with. Now I can go back to working on my Mite knowing that I have a good wing for it. It will be so nice not wondering if the wing is any good every time I fly.

PS I should thank Lowe's Home Improvements for supplying the bags of concrete. I went to them and explained fully my need for the weight and asked if I could pay a fee or some kind of rental for short term use of their inventory. They said that I could buy the bags and return all that I didn't break, with no charge. I returned all of them and they graciously helped me unload them back at the store. They have my business.

[Scott Royall]

I’ve reached a major milestone, for me, on my mite. The gear retract, flaps, ailerons and nose wheel steering are all working. Next I’ll put the tail on and get the trim, elevators and rudder working. Then I'll have to disassemble complete the covering and finishes and reassemble for the final time.

[Keith Mackey]

Looks great, Scott, congratulations on your progress. You'll find it flies much better if you replace that piece of plywood on the mount with an engine.:)

[Scott Royall]

All the flight surfaces are assembled. Now it is time to disassemble for final finishes. After that I'll start working on the metal section including the engine.