seemefly_1

After some bad crashes and bad repairs my old trainers wing is not great of shape. Some busted balsa and a crack going along with were the two halves are connected. I was told to epoxy it with some alcohol as thinner so it could get in the crack and then put books for pressure on the wing, I fallowed these directions but was wondering if any of you know how I could test the wing to make sure its alright without putting it in the air as a risk to the plane.

If a picture is needed I'll post on.

jetmech05

without testing to destruction..flight is the only way I know of...just take it easy at first.....
the best way to repair is to glue the cracks then use the same materal, same thickness to glue over one side of the crack...this now becomes a doubler.....just like a full scale repair

seemefly_1

thanks i guess thats the only option

Campgems

Wing repair is actually eaiser that fuselage repair. Where a spar is broken, pull it back into place, and then cut a slot into in and put a CA hinge in and Ca it into place. this will result in a very strong joint. For broken ribs, just put the parts back together and a little thin CA and they are good to go. The spars, LE and TE are the critical parts of a wing when it comes to repair. If you need to replace a LEor TE sheet at the fracture point, cut the patch sheet on an angle to the grain matching the cut in the existing sheet. This joint gives you almost two times the glue joint of a butt joint.

The center cracking is unusual. That is usualy the last point of failure. The thinned epoxy will get in an adhear things together.You may want to consider a strip of lite fiber glass over the center joint, or even something like a dryer fabric softner sheet, after it has been through the dryer, as a patching compound. Once you laminate something on the joint, it will be OK. There was a great article on laminating a while back on one of the magazines, I forget which one. The major point was that two very frail componentes laminated together will result in a much stronger piece that either of the components could give by their self. Put that to use when repairing. Easy on the glue and keep things simple.

I've only seen one wing break in flight and it was on a 4*60 that had a lot of air time, and crashes, by more than one owner. It just wore out. My last 4*60 hit nose first so hard that the wing was crushed in about 1" at the point it contacted the fuselage. Ihad a very hard time stomping on the wing to break it up for the trash bin. You would be susprised on the strenght of the wings and center joint.

Don

HighPlains

My Feedback: (1)

If we knew the speed and radius of a turn or loop we could figure out how many g's it is pulling and get a fair estimate of a static load the wing has to carry.

But that is the rub as they say.

Most trainers fly in a range of around 70 mph give or take 10 mph. So now what kind of radius of turn is the question.

For a worst case, let's say the radius is 30 feet.

This would give a g load of about 11 g's, or 12 at the bottom of a loop.

So if your trainer weighed 5 lbs. with the wing weighing 1 lb, you could estimate that the center section of the trainer better be capable of holding at least 50 lbs. distributed over the bottom surface of the wing with the airplane held upside down. Fortunately, the weight of the wing itself drops out of the equation because it lifts itself.

One thing about the 50 lbs of weight. It is not equally distributed across the bottom of the wing in the test. All that energy that spills off the wingtips to create a rotating vortex means that the tips do less of the lifting than the root of the wing. So perhaps 2/3rds of the weight is lifted by the inner half of each wing panel.

And please note, that all the numbers above are based on estimates of turning radius and speed. Faster and tighter increase the load. The speed increases the load by the square of the speed, while the radius only changes it proportionally. So if the strength is in doubt, fly slower.

john2364

You should be fine, epoxy is much stronger then wood. If you are really worried then 1) cut it in half 2) cut out the ribs and any other cracked pieces up t the extent that they are cracked, 3) get some balsa of the same thickness, 4) make new ribs and other broken pieces 5) glue in place and recover that area. you can always do a good repair on this stuff because the glue will form a stronger joint then it would have had as a solid piece.

Lnewqban

Post a picture, if you can.

HighPlains has described very well the only way to test the wing other than flying it.

seemefly_1

thanks for all the help


just subscribe to this post and i will get one in the morning

seemefly_1

here are pics, it was not as wide but the epoxy seemed to stretch it

Campgems

It looked as if the root rib was seperated from one side of the wing. It also looks lke major jamage to the LE on both wing halfs. I expect that just pouring epoxy into the crack isn't going to work as there is quite possilbly damage that you can't see. John2364's suggestion of skinning the wing and pulling the damaged wood of and get a look at the total damage would be worth considering. Myself, I wouldn't put that wing in the air without a lot more repairs, or build a replacement wing.

Don

Lnewqban

I second Campgems' post.

That wing needs much tender loving care.

Do you have any experineced builder in your club that could take a look to the wing in person?

seemefly_1

sure do

Lnewqban

Better that way. [sm=thumbs_up.gif]

An experienced builder will see and feel with his hands weak points that we cannot see through the pictures.

Any big chunk of glue is weak by itself, since it can crack easily with vibrations and changes in temperature; that it is used in joins that fit well, or with a back up mesh where extended on big surfaces.

Get ready to glass that join of the two half wings, and recover some areas.

Cover can be removed with heat application on the damaged area.

For great construction learning, I recommend you this excellent site:

http://www.airfieldmodels.com/

Best of luck with your model!

CafeenMan

The wing may be fine and it may not. As has been said, there are two ways you can know for certain:

1) Fly the plane. If it breaks then you know it wasn't fine.

2) Pull the covering and maybe some of the center sheeting and whatever you need to pull to see everything you need to see.

A wing like that is about as easy to build as a wing can get. If it's an ARF you may be able to buy a replacement wing.

apwachholz

seemefly_1 -

Ur going about it the right way and getting the help of someone who's familiar with this type of thing. Props 2u for that one (yes, pun intended). Second, a simple way that I stress test my wings when required, is to pick the aircraft up by its wing tips. Then give it a hefty bounce or two. If you are uncomfortable of doing the aforementioned then your wing is probably not solid enough for flight and could fail under the weight of the plane/structure/G's. Here's a link to a YouTube vid from Boeing that shows a real world example of this kind of "stress" test.

[link=http://www.youtube.com/watch?v=pe9PVaFGl3o]Boeing Wing Loading Test[/link]

Hope you find this helpful and keep flyin' - regardless of how frustrating it may seem. You'll only get better with time.

Cheers!

Top_Gunn

My Feedback: (6)

For ordinary flying (no strenuous aerobatics), if you can pick the airplane up by the wing tips without the wing breaking, the wing is strong enough for flight.

Yes, I know, a plane in flight will experience several G's, while a plane held up by the wing tips experiences only one. But the wing of a plane in flight is supported not just at the tips, but along its whole length.

The biggest problem with repairing wings is that fixing a broken spar can easily make that part of the spar stronger than the rest, and so the wing won't flex the way it did when it was new. Then, if you do something strenuous like a loop, the wing may snap just outside of where the spar was repaired. Fixing a crack in the center wouldn't present this problem.