fixing broken wing spars (actually ribs)
 

Hi,

I was flying today with an instructor when he told me that my plane was just blowing around and that control was really bad. It was a little bit windy but a kadet Lt-40 made it out just fine. I got home and i noticed that some of the spars were loose. I tore the covering back and all the spars on the right hand side were shot.

How would i go around fixing it. some are broken, some have gaps etc.

Any help is much appreciated

RE: fixing broken wing spars
 

The broken pieces in the pictures are called wing ribs. The spars are the pieces that go into the grooves in the ribs from center to tip normally about 1/4" square at the thickest part of the wing top and bottom.

There are several ways to make the repairs. If all the pieces are there and can be aligned then thin CA will do the trick. You may need to add some wood and then reform the airfoil if the top curve is missing. The ribs seem to have a large portion removed probably to lighten the structure. Adding some small pieces vertically will help keep the airfoil shape and add a lot of strength.

EXCAP232

RE: fixing broken wing spars
 

Thankx EXCAP232 for the quick reply.

For fixing the wing ribs do you mean this?. Black lines representing the new wood pieces to be added.

And are you saying that these ribs are supposed to be cracked and loose to begin with just to lighten it up a bit? Also can this be a reason for slugish aileron control?

Thankx

RE: fixing broken wing spars
 

How many times have you flown the model? How many sudden arrivals has it had?

Those RIBS look like they have been subjected to some pretty hard treatment...

I have a suspicion that the wing has been fairly severely overloaded at some stage. This kind of rib crushing happens when the wing tries to bend, and the spars want to get all chummy and close together. You been doing aerobatics with it? Pulled out of a loop too quick or too hard? Landed on the roof instead of wheels?

If all the ribs are like that then that wing really needs a rebuild. You might be able to do it if you can extract enough of a rib to make an accurate template. Use that to carefully cut new ribs and slide them into place with a slow setting adhesive (no ca here!!). Have the wing well pinned down before you start, and mark (on the TE and back of the mainspars, where each rib fits. THEN ADD VERTICAL WEBS BETWEEN THE SPARS ON BOTH WINGS.

It is going to be a slow and pains-taking experience, but an interesting one and a good test of your building skill.

RE: fixing broken wing spars
 

Pic

RE: fixing broken wing spars
 

i think you have miss understood "EXCAP232"

what he measn is peice the rib back together like a broken tea pot :)

as for the "are they suposed to be loose?" NOOOO ;) as "probligo" said that wing looks like its seen some pretty heavy stress at some point and this has caused your problem, thats why your ribs are damaged..

i must admit if it was my plane i would think hard because that wing looks a little dodgy to me to say the least[sm=cool.gif] a complete re build may be your only option if the wing is like that all the way through just my opinion :)

RE: fixing broken wing spars
 

Probilgo,

I have been doing aerobatics with it lately and this plane has had tons of dead stiks=crashes. I have rebuilt a lot of parts including the elevator when it snapped in half. I will certanly follow your recomendation and rebuild the wing before flying

RE: fixing broken wing spars
 

A wise choice airmaster..

many pilots would have taken the easy way out and payed for it latter ;)

RE: fixing broken wing spars
 

Hey Scalebuff,

Lets say that the spars were still broken when it goes up again. just for curiosity purposes(because im curious) would the wing just disintegrate?

RE: fixing broken wing spars
 

well lets just say i wouldnt like to put it through its paces :)...

but yes your right the wing is able to flex a lot more in that condition it will only get worse and one day you could have a flying rocket on your hands :D

i wouldnt say it would go in the next flight but i would not like to be at the controls when it does lol

RE: fixing broken wing spars
 

I would be extremely concerned if someone were to fly a model in that kind of condition.

It is pretty much as Rick has said, except that I would leave out the "LOL".

If an out of control model like that were to hit someone or something, the lawyers would be lining up at the flying field gate before you could pick up the pieces.

Anything like this has the potential to do major damage to the public perception of our sport. That, IMO takes it way out of the "LOL" category.

RE: fixing broken wing spars
 

LOL :D sorry i found that quiet funny but very true.

RE: fixing broken wing spars
 

How do you apply the monokote or whatever outter surface material is chosen after the wing is repaired. How do you get it to form tight to the structure? Do you heat it? I am just curious because I am sure I will have to repair a wing in the future.


Thanks,


Wings

RE: fixing broken wing spars
 

By a iron or heat gun or both.
When you get your monokote or what ever you choose.
BE SURE to read the application instructions.

RE: fixing broken wing spars (actually ribs)
 

That's some impressive damage. I've never seen that kind of damage from flight loads alone, that kind of damage looks to me like the wing was crushed at some point, like somethign falling on it in transport or something.

Is the damage localized to the ribs you have shown in the picture, or does it extend farther out on the wing? If it does extend most of the wing, I'd really say it is crush or crash damage, since the flight loads at the tips are actually very light.

While you are in there repairing, you should consider adding some shear webs on the inner 1/3rd of the bays. A shear web is a bit of balsa sheet with the grain running vertically that is glued between or against the spars, along the spar (ie 90 degrees off from the ribs). It prevents the spars from flexing towards each other or shearing past each other side to side. I can't see what's going on in front of the spars, but you need to get a look in there as well, and you really should consider cutting away the sheeting in the wing center setion and checking in there. The flight loads on the center section are much higher than even 6" away from the fuse.

RE: fixing broken wing spars (actually ribs)
 

Your post did not say whether this is a kit airplane or an ARF. Not that it matters much, but I had broken ribs in 2 sets of wing that were on my Ultra Stick 60. I would have put the plane together and flown it if it hadn't been that the clear/yellow film was used on the wings. The manufacturer made it right and sent 2 sets of wings to put on the plane. Only 1 would have been enough if they had packed the first set correctly. By the time they were shipped to me, there were 4 broken ribs in each half. If you haven't had the plane that long and if it is an ARF you might try the manufacturer.

RE: fixing broken wing spars (actually ribs)
 

Montague,

It seems that the damage is localized to the ribs althrough some of the wood backing has been broken in. Ill attach a pic so you understand what im saying. Im going to see if i can remove 1 good rib and make 4 copies. Also is it ok if i use thicker balsa for the ribs its all i have right now?

Thankx

RE: fixing broken wing spars (actually ribs)
 

pics

RE: fixing broken wing spars (actually ribs)
 

Wow, ok, you have shear webs already, though the wood grain is sideways and not vertical as it should be. Still, they should have prevented anything from happening in flight. It really looks to me like crush damage. I accidentally steped on my wing a bit ago (don't ask how I managed it), and the damage was simular to yours, but not as extensive (I felt my foot hitting somehting that shouldn't be there and caught myself). I really doubt you managed to do that kind of damage just by flying.

And you say there is nothing like this on the left wing? Or in the rest of that wing?

Anyway, since the ribs themselves don't actually have a lot of loading on them in flight individually, I'd just put them back together like a puzzle and hit wth thin CA. The results will be just as strong or stronger than it was before.

You could use thicker wood, but I don't think there is any need for it. 3/32 should be as thick as you need for a .40 size plane.

RE: fixing broken wing spars (actually ribs)
 

There is no damage on the other side of the wing. A lot of the ribs cant be put back like a puzzle because all the pieces arnt there. a lot of them have huge gaps in the middle where a piece would fit in. Am i better off to just fabricate new ribs as i will be flying with it next season and the seasons almost over here. until it gets really cold[X(]

RE: fixing broken wing spars (actually ribs)
 

The holes in the spars(RIBS) is buging me. I have built the
LT-40 3 of them was kits and one was a ARF and
niether had them holes in the spars(RIBS).
I wonder if this is newer kits/arf or older kits/arf
then the ones i dealt with.Theres another person
in this form that has some pic of his newly built
wing of his LT-40 and it dont have them holes.

Click on the below link and look at his wings.

[link=http://www.rcuniverse.com/forum/upfiles/13790/Nl29581.jpg]LT-40 wing [/link]

RE: fixing broken wing spars (actually ribs)
 

Randy41,

As far as i know this arf was made a long time ago maybe about 4 years or so. The riles look like they have been there from the start. Yesterday i managed to piece 1 rib back together and im going to make the other 3 over the next couple of days

Thankx

RE: fixing broken wing spars (actually ribs)
 

Most ARFs have holes in the ribs. They are there for the building jigs used to put the planes together quickly. All the ribs are slid on to two parellel metal rods, then spars, LE and TE stock, etc is added. Then the wing is slid off the rods and finished. You can acutally buy or make this kind of jig yourself. Way back when, they were a common way to build a symetrical wing and keep it straight. You can take the ribs from any kit you're working on, and using a drill press and a good bit, you can bore the holes yourself if you want.

Oh, some kits have holes in there to save weight. This is espeically common on 3D or other acrobatic planes that need to be light above all else. And the airfoils on most 3D planes are really thick, so you can save a lot of weight by putting holes in the ribs.

And no, the holes don't weaken the ribs by a noticeable amount when it comes to flight loads. It might make the rib easier to break in handling or crashing, but not in flight.

RE: fixing broken wing spars (actually ribs)
 

Maybe so maybe no. I have had to repair the monokote
on my ARF a few times and i Know it dont have them holes.
Its my trainer plane for the newbees and at times they can be
kinda hard on her. Yes: I built this ARF kit from brand new.
It still seams strange to me.

ALL DONE!!!!!!!
 

well it took a while with school work but i rebuilt the whole left side of the wing. I made Randy41 happy by not drilling holes for the ribs that i fabricated. Check out the pics and tell me of anything more to be dont before i cover her all up again:D:D