Why is rib stitching done?

[shaneyee]

I've been reading about rib stitching on full sized planes and I'm wondering why it was necessary. Isn't the glue they use strong enough to hold the fabric to the ribs?

Also, does the stitching go throught the wing and tie both surfaces together?

Thanks

Shane

[vintage1]

I am no expert - they are to be found in the scale forum - but my impression is the fabric was not glued at all. It was stretched stitched and nailed.

And the doping did not penetrate far enough to be of much use either.

I am not sure if the stitches went right through or not..many WWI wings were ultra thin, so one suspects it probably did.

[Work in Progress]

I wouldn't want to commit my neck to a fabric-covered flyig surface unless it was all stitched! The main virtue is that if something rips a hole in one panel (birdstrike, collision, anti-aircraft fire, or just an aged brittle bit ripping off) it won't spread across the whole surface.

Quite a good description of the process here:
http://www.supercubproject.com/afs.aspx

The materials have improved over the years but the principles are very much those used pre WWI.

[skylark3f]

An interesting question... most of them seem to be here lol.

I am no expert so don't quote as I can really only speak for sailplanes using nylon fabric such as seconite. The way they cover the gliders is cover the whole wing structure with dope, three or four coats, then after it has dried, lay the seconite over the top. The dope is then "reactivated" using a cellulose thins which is pushed through the fabric. Then once the thinners has evaporated and the dope dried again, the whole shooting match is painted with dope to get things nice and tight and water proof. It is my understanding that this system works well enough with the modern materials not to need stitching, even on the massive under-cambered wings of something like a T-21 (with the Göttingen 535 section i believe). Although some people still do stitch on the under cambers for good luck.

Even though I think modern aircraft use the same technique, I seem to recall seeing stitching on a relatively new Robin DR-400 (presumably using seconite fabric) and I'm sure stitching is still used for vintage stuff where irish linen is still used. I think in these cases, the covering is stitched to stop rips from spreading as already said. Maybe the higher speeds are why the stitching is done in power and not in gliders even with the modern dopes and fabrics?

As for the stitching itself, whenever I've seen it done, it has only been around the ply-web of the rib and each side has been done independantly, not with the same length of string.

Jack

[Majortomski]

To answer the original question, NO glue on the uppersurface IS NOT strong enough to hold down the fabric. I lost a friend in a Erocoupe becase the repair shop left the rib stiching out.

Its principle purpose is to hold the fabric to each of the ribs.

It can be done with stiches that go completely through the wing then back up again. or as stated above a stich that just catches the outer chord of a rib, or as done on later series taylorcrafts a metal strip is screwed to the upper and lower chord of the ribs.

[matwiyj]

Remember the way an airfoil generates lift is mostly from a vacuum on top of the wing pulling up on the wing skin. I would prefer to have it attached as securely as possible.

Jarod Matwy
Winnipeg, Canada

[Mister UHU]

"You learn something everyday"

[skylark3f]

I suppose the reason they stitch the fabric on power and not on gliders is due to higher speeds they generally fly at as well as perhaps a higher wing loading? (more weight per unit area == more lift per unit area therefore more 'suction'?)

[Majortomski]

Are you sure there isn't any stitching on a glider?, It just may have enough rib tapes and filler coat over them that you can't see them.

[shaneyee]

This is very educational. I sometimes don't appreciate the precautions and backups that go into manned flight. R/C is a bit more forgiving ;-) and I often patch things up with glue, tape and hope just to be able to fly at short notice.

Shane

[JerryHall]

Rib stitching is quite a process...I have built 2 full size 200 hp Cristen Eagles in the past...Rib stitching was called for every inch within the area of the propeller slipstrean, and 2" apart outboard to the tip..
Stitching is done by looping the waxed linen thread around the rib top and bottom using a very long needle and then tied off with a specific knot... The knot is snugged up and then poked down through the hole into the interior of the wing so it is completely hidden...Then, using the long needle the cord is fed back through the same hole and over to the next set of holes and the process is repeated again and again... All stitching is done with one continious piece of lace, so at first you might start out with a piece of lacing 8 or 10 feet long..
Very repetitive work..

[skylark3f]

Majortomski,

Yeah I'm pretty sure that stitching on glider wings is not all that common. The glider I am in now doesn't really count (SF-27 with the top surface all skinned in plywood and the majority of the bottom surface also) but I have had user shares in things like Skylark 3s (hence the name) and have both removed covering from old Olympia/K13/K7 etc wings as well as 'helping' to recover them again and there has definetly been no stitching there.

I have also been to a few vintage glider rallies here in the UK and have not been aware of any stitching on the gliders there either. The only time I have seen it done was on the underside of a pair of K13 wings to prevent the fabric from pulling away from the under-camber presumably.

Jack

[Thomas B]

I remember rib stitching our club 2-33 bits that were covered in fabric......although at least one of them did use the the washers, screws or pop rivits approach in place of rib stitching.

Interestingly enough, the famous and talented Steve Whittman was killed when his OD experimental plane came apart and crashed on a cross country flight.......the root cause of the failure was an adhesion failure on his covering job. Mostly Steve's fault, as he mixed two systems of covering that were not, in the end, compatible. Plus, his little cross country aircraft was cruising at around 200...which really increases the loads on the fabric on the wing.

I vote for rib stitching AND gluing, if my rear end is in the pilots seat....:)

[41tcraft]

Yup, the top and bottom surfaces are tied together with a drop stich and a scine knot to keep the fabric adhered to the ribs where there is no adhesive used. It adds a lot of strength to the airframe when it is properly done. Before the advent of beuterate dope the seams were stiched together as well. I didnt know that gliders didnt use rib stiching, you would think the airfoil would deform, maby they use the fabric rivets? I would be interested if anyone had any expeeriance with covering gliders. I have only covered old biplanes, cubs and the like.

[Thomas B]

Most fabic covered sailplanes rarely fly above 80 knots.

[Brian Molloy]

FYI . . . Ultra-Lights/Hang Gliders use rib stitching too. The Easy Riser is tail-less bi-plane, and needed a reflexed airfoil to offset the negative pitching moment (original, unmodified design). If the glue failed, the fabric on the upper surface could pull loose and thus "balloon-up" away from the rib(s). . . presto, you have a new airfoil with no reflex . . . ouch.

http://aeroweb.brooklyn.cuny.edu/specs/unknown/easyrisr.htm