wing and aileron nails

[Guest]

Re: wing and aileron nails

So a thought provoking question..... (I hope)

Do we really care if the nails back out?
They're on really there to hold things in place during assembly. Once the fabric, leading edges etc. are in place, is even the complete loss of the nails likely to lead to any sort of significant failure?
S

Hi Scott,

Well it worked, you made me think.

The leading edge structure of ribs and curled aluminum sheet in addition to the trailing edge will provide a structure that keeps the front and rear of the ribs spaced consistently from one another in the spanwise direction. Also it will keep the forward part of the ribs oriented "vertically" (ie. orthogonal to the span).

The fabric and it's attachment to the ribs will keep the center portions (between the spars) of the ribs consistently spaced and "vertical" if the butt rib and wing tip are attached to the spar. This will maintain tension on the fabric in the spanwise direction which is needed to keep the center portion of the ribs in place. Taylorcraft butt ribs mount on the butt end of the spar so that is good.

When I imagine this structure I see a leading edge and rib structure holding a number of ribs that are all attached to a trailing edge with a tight fitting fabric bag wrapped around all of it attached to each rib. The fabric bag is being pulled at each end in the spanwise direction thus putting tension on the fabric and keeping each rib separate from it's neighbor.

You don't even need spars in it to imagine this structure. If I apply a vertical load to it this structure it will fail when the leading or trailing edge bends or the fabric tension is not sufficient to keep the center portion of the ribs in place.

Imagine putting spars in it and they now provide the means of pushing the fabric out at the butt and tip thereby putting tension on the fabric.

The ribs slide over the spars and can move up and down on the spar depending on the difference between the height of the spar and the height of the hole in the rib. This amount can be different by up to 3/4" so a rib could in theory be moved up or down quite a bit.

Usually I line up the top of all of the ribs in a straight line so that it ends up that there is a gap between the top and bottom of the spar and the rib hole. Each rib may have different gaps but the tops (and bottoms) of the ribs make a straight line.

That nails hold the rib in the placement I described above.

If I remove the nails after the wing was assembled I imagine that the ribs would eventually slide up enough that the bottom of the rib hole pressed against the bottom of the spar when in level flight. The wing surface may look funky at that point and I suspect that the trailing edge would look wiggly too.

In negative loaded wing conditions the ribs could slide all the way down so that the upper spar surface was was pressing against the top of rib's spar hole. The transition to this state may be awkward and unpredictable in flight as well as the transition back to level flight conditions. We don't like unpredictable

Here is another thought that I almost forgot. Will the top and bottom of the rib (flange) be able to handle the load it must apply to the spar and will the spar be able to handle the rib applying that load. Will the rib hole get deformed? Will the spar get cut into by the rib hole?

The load on each nail for a 1200 lbs plane with 15 ribs per wing and 6 nails per rib at 4g is;

(4 x 1200) lbs / ((15 x 2) ribs x 6 nails per rib) = 4800 lbs / 180 nails = 27 lbs/nail

That works out to about 81 lbs applied to each rib flange at the spar hole and 81 lbs applied to the spar top and bottom by the rib flange which could be merely a sheet metal edge depending on design. That may not be so good depending on the design. Rib nails will keep the ribs in place so I guess I will care.

That's my thought so far, Dave R.

[PA1195]

Re: wing and aileron nails

Short story about aileron fastener and component continuity. Removed ailerons from my former PA-11 for recover. Twenty years since last cover job. Typical Piper all metal construction unlike Taylorcraft.

Both trailing edges fell off the ribs with the fabric, some pieces of them separated as well. Several ribs were floating in the assemblies and the leading edge was not fully attached to the spars. Many loose rivets and PK screws loose or turned to dust. Corrosion.

Most standard drain grommets were open and no saltwater use but obviously there were conditions conducive to the ingress of water, high humidity, and subsequent corrosion. The plane was on floats for most of the summers in relatively dry Fairbanks.

The only aileron component really holding hands was the fabric covering. Repairs to many rivets/screws plus some new ribs and both trailing edges was required. The hinge and pushrod assemblies were ok. The steel aileron end was corroded but salvageable. No flight malfunction occurred nor was there any visible indication of an internal compromise. The rest of the airframe was normal for that age I was told.

Edit: Forgot to add the rib stitching was intact so must include it in the following co-pilot category.

God and glue were my co-pilot.

Gary

[astjp2]

Re: wing and aileron nails

dave, you forgot to include the friction coefficient....

[Scott]

Re: wing and aileron nails

So yes, assuming the loss of all the nails, things are going to get a little weird (depending on the height of the spars), but no significant failure.

I kinda think that by the time nails have backed out to the point where they no longer provide any support, (they're 100% in shear so they need to break or fall out completely), you've got many other problems urging you to think about rebuild.

What I can say (referring back to my earlier post) is that the Factory Tcraft ailerons when new had virtually no structure attaching the ribs aft of the spar to the spar. It's basically the fabric and the tension on the top and bottom surface that hold them together.

[Guest]

Re: wing and aileron nails

dave, you forgot to include the friction coefficient....

LOL! (at myself!)

Yes I did and any interference fits as well.

It's Scott's fault, he made me think about it!

Dave R

[Guest]

Re: wing and aileron nails

So yes, assuming the loss of all the nails, things are going to get a little weird (depending on the height of the spars), but no significant failure.

I kinda think that by the time nails have backed out to the point where they no longer provide any support, (they're 100% in shear so they need to break or fall out completely), you've got many other problems urging you to think about rebuild.

What I can say (referring back to my earlier post) is that the Factory Tcraft ailerons when new had virtually no structure attaching the ribs aft of the spar to the spar. It's basically the fabric and the tension on the top and bottom surface that hold them together.

One other thought about ailerons; they undergo torque to make them move up and down.

So they need to have the leading edge wrapped around the nose rib and fastened to the nose rib as well as the top and bottom of the spar so as to form a torque tube (a.k.a. box beam). That torque tube allows the belcranks, hinges and control brackets to move the aileron. You need that structure in tact.

The aft portions of the ribs need to be able to stand up to the torque applied when the ailerons are up and down also.

Dave R

[Scott]

Re: wing and aileron nails

Exactly why the absence of any significant attach structure on the aft side of the Taylorcraft aileron spar is a little concerning. The rib web (no flange, no nails) ends up crammed into the back of the spar, cutting into the wood. No flange, no nails. That's how the torsion and compression loads are transferred to the spar.

Isn't it a little ironic to be concerned about nail types, when nails (and structure) are missing completely from the ailerons of most of the Taylorcraft fleet?

As it turns out it doesn't appear to be a big deal. The ailerons seem to make it from one rebuild to the next without the nails and structure, without failing in a dramatic way. Although my aileron spars were cut in every rib location, the real concern (from an imminent failure perspective) was the centre hinge push-rod attach points which were rotten and crushed.

Oh, the photo shows typical aileron rib. You can see the upper flange has buckled under the compression load and the rib web crammed into the spar. Torsional loads then result in the rib web literally sawing into the spar.

[Guest]

Re: wing and aileron nails

Exactly why the absence of any significant attach structure on the aft side of the Taylorcraft aileron spar is a little concerning. The rib web (no flange, no nails) ends up crammed into the back of the spar, cutting into the wood. No flange, no nails. That's how the torsion and compression loads are transferred to the spar.

Isn't it a little ironic to be concerned about nail types, when nails (and structure) are missing completely from the ailerons of most of the Taylorcraft fleet?

As it turns out it doesn't appear to be a big deal. The ailerons seem to make it from one rebuild to the next without the nails and structure, without failing in a dramatic way. Although my aileron spars were cut in every rib location, the real concern (from an imminent failure perspective) was the centre hinge push-rod attach points which were rotten and crushed.

Oh, the photo shows typical aileron rib. You can see the upper flange has buckled under the compression load and the rib web crammed into the spar. Torsional loads then result in the rib web literally sawing into the spar.

Hi Scott,

Perhaps it is attached on the front side?

Also if the rib is attached to the leading edge and the leading edge is attached to the spar top and bottom that can be sufficient. I assume that is the case.

Dave R

p.s. - Actually on second thought the statement now in red is wrong. There needs to be nails in the aileron rib to the aileron spar somewhere.

[Scott]

Re: wing and aileron nails

Yes the ribs are nailed/attached on the front side of the spar and the top and bottom.

Because of the cutout for the spar however, and the fact that they're made of very soft material, we're left with only about 1/2" x 025" of the rib top and bottom to support all the loads aft of the spar. There is effectively no structure, the small amount of rib material left collapses and the rib web ends up "knifing" into the spar.

[Scott]

Re: wing and aileron nails

Just to complete the picture...
This is how the ribs should be IMO;

[PA1195]

Re: wing and aileron nails

Why not apply anti abrasion covering over the spar contact points or rib web metal edge? The rear angle shown would be better.

Gary

[Guest]

Re: wing and aileron nails

Just to complete the picture...
This is how the ribs should be IMO;

very nice

[Scott]

Re: wing and aileron nails

Why not apply anti abrasion covering over the spar contact points or rib web metal edge? The rear angle shown would be better.

Gary

That would protect the spars yes, however would not do anything to improve the structural integrity of the aileron as a whole.

[PA1195]

Re: wing and aileron nails

That would protect the spars yes, however would not do anything to improve the structural integrity of the aileron as a whole.

Yes we should apply your suggested modification. But apparently there are thousands of Taylorcrafts scooting about with possibly compromised controls. In our lifetime I wonder how many have, by the original design, affected airworthiness while flying?

Not everyone can restore an airplane and recover the invested value.

Gary

[Hank Jarrett]

Re: wing and aileron nails

I don't know of any "failed" ailerons, but it was a terrible design. There really should be a solid doubler where bolts go through the spar to prevent crushing and the ribs should have had angles to spread the load and not cut the spar. That said I WILL make the changes at a recover, but I will NOT tear an aileron down just to make the changes.
It is BAD, but not bad enough to get our collective panties in a knot.

Hank

There are a LOT of things on Taylorcrafts that are not the best, but they work and aren't worth changing unless a problem can be shown. That is why it is good to have these discussions.