Rib stitching alternative

Discussion in 'General Experimental Aviation Questions' started by oldcrow, Feb 6, 2019.

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  1. Feb 6, 2019 #1

    oldcrow

    oldcrow

    oldcrow

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    Please chime in on this all of you Fabric covering gurus. ( or should I say "dope" heads)
    I am thinking about building a "Texas Parasol" and I was looking at the way the wing ribs are made. It seems as if rib stitching would be near to impossible with this type of construction. ( I would fear that the compression rib would cut the rib stitch over time) Any way even though it is not a high speed aircraft I would like the added security of knowing that I would not get any separation from my ribs and fabric. So this is my thought. Instead of stitching through the fabric with wax chord, why not wrap the wing at each rib location with heavy duty upholstery thread. Tie it nice and snug, apply more fabric bonding cement and then the pinking tape. Am I making any sense? The Texas Parasol wing uses two aluminum tubes for the spars with the ribs in between them. You would wrap the chord around the spars AND each rib over top of your fabric then sealing with pinking tape.
    Once again please chime in on this if you are real familiar with aircraft covering techniques.
    thanks
     
  2. Feb 6, 2019 #2

    TFF

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    As thread, upholstery thread will not be tougher than airplane cord. Worse, probably not; although I think regular sewing thread might stretch because it is twisted like a cable. You may have to put anti chafe tape anywhere you might think it would cut in. Are they foam ribs?
     
  3. Feb 6, 2019 #3

    Hot Wings

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    Structurally, that just isn't a good idea. As a way to illustrate: Imagine a tow rope drawn taught between a well stuck car and the tow truck. It's very easy (but kind of dangerous) to walk to the center and pull up on the rope by hand.

    Have there been reports of the compression ribs on the TP cutting the rib stitching being a common problem? The TP plans that I have are also unclear if the "C" channel is aligned with the ribs so that the edge or the base is proud of the rib material. I didn't find any specifications for the foam rib thickness but if the "C" channel material is cut to the full 3" mentioned and bent to fit 2" tube then the compression rib should be fully under the surface of 1/2" thick foam and the rib stitching would not be in contact with the aluminum compression member.

    Also the guy that drew the plans is a member here. He might have some insight and be willing to add his thoughts?
     
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  4. Feb 6, 2019 #4

    Pops

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    Just layout for the rib stitching and if a stitch is to close to something, vary the stitch distance closer or put a stitch on each side. I have built 3 sets of geodetic constructed wings and had to have 3 different wing stitch layouts on each wing to miss everything inside the wing. Rib stitch cord works, why try to re-invent the wheel, especially when your life depends on it.
     
  5. Feb 6, 2019 #5

    FritzW

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    A couple of ideas:

    1) Deburr the flanges real good and put a 1/4" strip (or two) of the good, old school, cloth medical tape over the edges. (time honored way of doing this sort of thing and much cheaper than the AS&S tape)
    2) *Bend a second flange on the compression rib flanges.
    3) *Setup a quick drilling jig and drill lacing holes through the center of the ribs (it would be easier than it sounds).

    * tp stich.jpg

    To second what Hot Wings said, wrapping the rib -chord wise- won't do you any good (the dreaded zero cosine angle problem).

    I'm probably not understanding your comment on the flanges. There are photos on pages 28 and 29 that show the flanges of the compression ribs facing out. ...and two rows of rivet holes drilled right along the two highest stressed areas on the spars :/
     
    Last edited: Feb 6, 2019
  6. Feb 6, 2019 #6

    Hot Wings

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    Apparently different plans versions. I've not built, or even seen, a set of TP wings and my first impression of the drawings I have is this:
    rib33.jpg
    Very different than what you have shown.......
     
  7. Feb 6, 2019 #7

    Dana

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    I'm not clear on what the TP wing construction looks like. Can somebody post a picture, or a picture of the plans?

    If I understand the OP correctly, the proposal is to run reinforcing thread chordwise, around the wing just like, and under, the finishing tape, rather than piercing the fabric and going top to bottom. If so, bad idea, thread running in that direction would contribute no significant strength. And if you're talking about upholstery thread instead of normal lacing cord, that's what the original builder of my Fisher did... more than half of them were broken when I got the plane and I had to re-ribstitch it.

    Some planes use screws or rivets or clips instead of ribstitching. It only works with ribs that are strong enough in tension (i.e. metal ribs), and (I'm told, never did it myself) while it's easy the first time, stripping a wing for recovering is a hassle, the ribs get beat up removing the fasteners.
     
  8. Feb 6, 2019 #8

    Hot Wings

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  9. Feb 6, 2019 #9

    Dana

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    OK, I see now. As far as wrapping the rib stitching around the compression struts, yeah, not a great idea if there's a sharp edge, but with tape protecting it as mentioned above, probably OK. Actually the manual doesn't mention rib stitching at all, and many ultralights don't have any, relying only on the glue to hold the fabric to the ribs. Some people are comfortable with that, others aren't, but you don't hear many reports of ultralights falling out of the sky after shedding their wing fabric.
     
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  10. Feb 6, 2019 #10

    wsimpso1

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  11. Feb 6, 2019 #11

    oldcrow

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    Hey thanks for the quick reply every one. No the plans don't ever mention rib stitching so I guess it is not needed. I just wasn't sure, Ive seen so many plans out there that call for it. Hopefully I will be starting this summer on my project.
     
  12. Feb 7, 2019 #12

    wsimpso1

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    The the loads trying to pull the wing skins away from the ribs is comprised of two parts. First is the air rushing around the outside of the wing with stationary air everywhere inside. The moving air is at lower pressure than the stationary air. Then there is the lift, which is just the difference between how hard the air is being pulled down on the bottom and how hard the air on the top is being pulled up. Well, ultralights have really low wing loadings and thus small differences between top and bottom, and fly really slow, so the air pressure due to that is small tool. In the end, a lot of ultralights need modest strength attachments.

    Double the airspeed, and the inflation effect gets four times bigger. Faster airplanes usually have higher stall speeds from higher wing loading too, and so the covering requires more strength as you go faster...

    Billski
     
  13. Mar 21, 2019 #13

    Turd Ferguson

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    There is another popular series of plane with a deeply undercambered wing that the designer did not rib stitch. Ray Stits said it should be stitched, that the glue was not strong enough to hold. I'm going with with what Ray said.
     
  14. Mar 21, 2019 #14

    Victor Bravo

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    Yes, but correctly applied fabric glue is pretty darn tenacious. The air actting on the bottom of an undercambered wing is pressing the fabric against the ribs (above ambient pressure) for the most part IMHO.
     
  15. Mar 28, 2019 #15

    pittsdriver

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    Just did a Supercub with rivets and it was very easy. They are large head 1/8" rivets and you can get them from Spruce. Called Maule rivets or fabric revets.
     
  16. Mar 28, 2019 #16

    Turd Ferguson

    Turd Ferguson

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    This is true but the shrinking action of the fabric is causing it to pull away. So the question would be how much force is the glue seeing once the fabric is shrunk?
     
  17. Mar 28, 2019 #17

    pittsdriver

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    If you are going to glue the fabric and not rib stitch use Airtech or Superflte. Put two coats of glue everywhere the fabric is going to stick. When you cover just glue the fabric around the perimete like normal and then shrink like normal. Now you can iron down the fabric over the ribs then one thin coat of thinned glue. Now do the rib tapes like normal. The Airtech and Superflite have the strongest glue and are the easiest fabric systems to work with. I like the Superflite because you reduce it with MEK or Acetone. I do a lot of fabric work and find the Superflite is the best system on the market. Stitts is way too much work and has other drawbacks and the Stewart System is OK but harder to work with.
     
  18. Mar 29, 2019 #18

    Deuelly

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    Curtiss had one of the most ingenious ways to attach fabric two ribs I've ever seen. The P-40 and Helldiver used it and probably others. You can have the fabric secured to all the elevator ribs of a P-40 in about five minutes. Granted that's aluminum construction. I'll try to load some pictures tomorrow. Basically it's a circular extruded channel on the top of the ribs. A rod is slid into the channel locking the fabric between the rod and channel. If you ever build a fabric covered metal wing it would be the only way to go
     

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