dukman

Hello All!!

I'm sad to be asking for suggestions on how to repair the wing on my Hobbico Superstar 40 RTF (please see the pictures following the post). I was coming in a little low final and a Nevada version of a tree decided to jump up and grab my plane. [>:] If it wasn't for the tree I feel it would have been a great landing. I usually end up landing past my pilot position, but have been getting better at landing closer to center. This time it was further out than I thought. [X(]

A couple guys at the field I fly at said it shouldn't be a problem to repair, but I couldn't fully visualize their method of repairing it. I was wondering if maybe someone would know of a link to some wing kit plans that uses the same type of wing structure. From that I should be able to see how to repair it.

As I don't have much spare time I went ahead and ordered another Superstar ARF version. I plan on just taking the wing from that so I can get back up in the air sooner. However, over time I would like to fix the damaged wing. I feel it would help me learn a bit about building, as well as covering, without having to worry too much about messing up.


Any help would be greatly appreciated!

Thank you

- Donald

FHHuber

For the smashed leading edge:

You will need some 1/16 inch balsa sheet. Probably 1 sheet 3 inch X36 inch will do it all with some spare. You will also need some appx 1/2 inch X 1/4 inch rectangular balsa. (make sure the size is larger than the leading edge material. I'm guessing at the leading edge size)

First... Open the covering and sheeting past the damaged area. Just cut it back to the first good rib on each side and back to the spar.

saw out the shattered wood with a razor saw or a hacksaw blade.

Lay some heavy paper or cardstick such as used to hold a t-shirt square in the package next to a good rib and trace the outside. (include the sheeting)

Now carefully draw another rib section 1/16 inch inside of the one you traced. (that allows for the sheeting thickness) Cut this out and check that it fits properly next to a good rib. Trim as needed. (may have to make 2 or 3 to get one good pattern.) cut out the correct opening to match the leading edge material.

Make replacement rib sections from 1/16 thick balsa (available at Hobby Lobby craft stores if no model aircraft shop is near) Make 2 extras.

Glue one of the extra rib parts made right onto each of the first good ribs to "double" them. You need the width to attach the replacement sheeting. You can CA these... or use yellow glue.

To get things to line up correctly... you will need to do things a bit oddly... Patch 1 to 2 inch wide from the spar forward of the lower sheeting Glue this in place with yellow wood glue and pin it. Let dry overnight. Now you have a platform to aid in gluing the stub ribs in place.

Now glue the other stub rib(s) in. (not absolutely sure you need to cut out the one that is in the second picture... if in doubt ... chop it out.)

Now glue on the replacement rectangular stock to replace the leading edge section that was smashed. this needs to fit snugly with as little gap as possible at both ends. The ends should be epoxied in with 30 min epoxy, allowed to soak in for about 5 min then apply a bit more before putting the pieces together and pinning in place. (use T-pins or you'll never get them out)

when that is dry you can finish patching the sheeting. I recommend using yellow glue as it sands easier than CA and you get a better repair. make sure you apply glue to all the ribs where the sheeting will touch them.. (very hard to do with CA on the upper side...)

Wait 24 hours then sand smooth.

Now you can patch the covering.

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The center section... you can't trust the dihedral joint any more. Strip the covering (peel back from center toward tips DON'T score the sheeting at all more than 1/2 inch from the joint!) for 2 inch width on each side of the joint. You can leave the peeled back covering attached and it will iron back down.

Get some 2 inch wide "2 oz" fiberglass "tape" (or cut from fiberlgass cloth)

Be careful not to get epoxy in the aileron torque rod openings... Better to not reinforce withing 1/2 inch of those openings on the bottom than to glue the torque rods in thier tubes.

use 30 min epoxy to adhere the cloth to the balsa. You want to use the smallest amount of epoxy which will make the cloth turn transparent. I paint the wood with epoxy, then scrape most of it off with a credit card, then lay the cloth on and rub it down (wearing rubber gloves) 1/2 the width of the cloth should be on each side of the joint.

Only add just enough epoxy to finish turning the cloth transparent... more is just excess weight.

Once the epoxy is cured you need to sand the joint (careful not to sand the balsa beside the epoxy...) to rough it up or the covering won't stick.

You can iron the covering back down and then patch the seam and any tears as they had you do before. Or you can patch with new MonoKote. (you need some Monokote to patch the LE covering anyway... )

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The servo mount I can not see the damage well enough to say what you need. The previous repair methods should give you a good idea though. Maybe just making some braces from scraps of the LE stock and epoxying them to the surface of the wing and the broken plywood servo mount will work. (make sure if you do that... the new epoxy is applyed on freshly sanded areas of the fiberglassed joint... then it will be strong. If you don't sand first the epoxy layers will separate. You could even pull the servo and do this repair running the fiberglass joint renforcement up onto the plywood servo mount, doing both repairs at once... then it would be rock solid.)

phread59

FH pretty much has this one put to bed. I would only make 2 suggestions. When you cut the leading edge cut it at an angle. Looking down at the top of the wing angle the leading edge cuts away from you perpendicular to the edge. This will give you more gluing surface. It is called a scarf joint. Just cut the new replacement at an angle. I would reccomend 45 degrees. I would also take a small piece of wood behind the joints as a scab.

The center section, I would junk the straps. Epoxy the wing dihedral brace and the inner ribs and so on together. Then do the fiberglass like FH said.

The servo mount, i would make a patch where it ripped out with your spare balsa. Then epoxie it back in. This is a guess, as FH said the picture is unclear.

Good luck getting your plane back into the air.

Mark Shuman

dukman

FHHuber,

I really appreciate that long explanation on how to repair the wing! The step by step walk through is really helpful. I'll have to print these out.

Would you be able to go over fiberglass tape/cloth? I'm not sure what it is and its purpose.

Thank you!!


phread59,

Thank you for the 2 suggestions! Would you happen to know of any sites w/ this technique diagrammed?



I went ahead and took a few more pictures of the joint as well as where the servo sits. You guys said you really couldn't see the damage there. Hopefully the following pictures will help out a bit.


A question I do have is about the dihedral joint. The joint was never epoxied when I put the wing together. All there is is a metal rod (about 6 inch) through a hole in the ribs near the joint of the two wing halves. There is also a shorter metal rod near the back of the wings (by the torque rods). Because of the accident would I need to now go ahead and epoxy the wings together or would those rods still suffice? Also, I read in a manual somewhere about using CA to reinforce screws such as the ones used for the straps (ie put a little CA in the hole, let dry and then screw in again). On the other hand is it just better to epoxy the wing together instead of using the rods and straps?



Again, thanks for the help guys!


- Donald

dukman

Here are a couple more pictures of the wing damage:

FHHuber

The pictures of the servo mont show that it was never properly glued in... and the glue joints failed. You can just reglue it... but you MUST do a better job of it. I bet you used CA... you need to use epoxy this time.

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The metal rods MIGHT or might not still be adequate for keeping the wing together. The problem is the wing has been stressed and there are signs the metal straps were pulled on in the crash, loosening the screws holding them on. If the wing was put through that much stress... the tubes the metal rods are in may have cracked, or the joints holding the tubes in place may be weakened.

We just had a duplicate aircraft (exact same ARF model) at our club field which had no visible damage to the wing have the joints holding the tubes in place fail in flight. The previous trip to the airfield te model had drug one wingtip and smacked the other down hard on its last landing. 2 flights on the recent trip to the field and suddenly the wing had 3 times as much dihedral and was VERY difficult to control. Luckilly one of the club's best instructors was holding the master box for the training flight, and was able to GENTLY bring it back in.... so the only damage was the cracking dihedral bracing.

Because of this recent experience with the same ARF and the appearance of your metal straps... It is better to go ahead and epoxy the wings together and do the fibreglass reinforcement. This will transfer the majority of the loads off of the metal rod, and onto the wing sheeting. (and the sheeting CAN handle it easilly.)

You want to leave the metal rods inplace when you glue the wing halves together. If they do nothing else... they will aid in getting the joint straight. If the structure is still able to hold up to flight loads... then the fiberglass reinforcement would be un-necessary... (but its just not worth the risk to skip doing it.)

Unfortunately... I don't have any pictures of how to do the fiberglasing job. Its not hard... and the only 2 potential problems if the cloth is laid flat would be excess epoxy,(which is just dead weight and not a very serious problem...) and gluing the torque rods in place so the ailerons would no longer move. (which would be VERY bad...and hard to fix.)

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the last picture shows what appears to be some crushing of the leading edge on what would be the left wing near the center... you need to see if that is just loose covering or if there is hidden damage.

dukman

FHHuber,

I'll just take your suggestion of epoxying the wing together instead of relying on the rods and straps (as well as possible hidden damage). I'll go ahead and remove the straps and pull back the covering around where the rods go in and check for any damage. You are correct about the stress on the straps. When I found the plane in the tree there was at least a half an inch gap between the wing halves from when the wing smacked into the thick branch. The impact must have been pretty good since part of the fuselage right behind the wing was pulled off as well. I'm assuming it'll just be cutting out a triangular piece of sheeting w/ the same thickness as used on the fuselage.

As with the servo mount, the aircraft model was a RTF and the mount was already glued in place when I bought the kit. The manual just mentioned putting the two wing halves together using the rods and screwing in the straps. I'll go ahead and epoxy the servo mount this time.

Thanks for your help!

- Donald

Dukester

My Feedback: (31)

Donald,

I just did a very similar repair to an Avistar (note to self: no more inverted limbo under the old phone lines on a windy day....). FH has covered everything very well, but only thing I will add is that since you will be stripping the one wing for the repair, don't be afraid to cut the sheeting back as much as you feel like to get a good look for how the wing structure is put together. New sheeting is a breeze to do and is actually easier in a big section rather than trying to patch in a small piece.

Good luck,
Duke

dukman

Duke,

Thanks for the suggestion! After reading everyone's posts a few times over the repair is starting to seem less difficult than I originally thought. I'll just have to be careful with the epoxy when putting the wing halves together.

- Donald

phread59

A scarf joint is hard to explain but real simple to see. If you have some spare balsa sticks laying around (or any sticks for that matter as long as they are square) mark one with a 45 degree angle. Stack the sticks on top of each other. Now saw through them. Place the 2 cut pieces together. You now have a scarf joint. To make it easier to saw straight. Put a verticle line on the sticks that goes to one end of your 45 deg. line. You now have a verticle guide to give your saw a good reference. You should be able to get a good joint.

Be sure you pull covering and inspect the fuse. The one picture shows damage. There could be cracks and other damage hidden under the covering.

Good luck with the repair. It is not a real difficult one. Just take your time. And do not be afraid to pull covering and check for more damage.

Mark Shuman