7A wing bolt orientation

The only drawing I can find in the plans regarding wing bolts is for a 7, not an "A" model. Obviously on the taildragger, having all bolts oriented from front to back is certainly not a problem. But with the gear weldments, some of the bottom bolts must be oriented back to front, right?

Also, I'm torquing the rear spar attach bolt and looking up the proper torque to use. Is this bolt a fine thread or course thread bolt and how does one distinguish the two?

Check out the Fastener Section at Your Local Hardware

U.S. fasteners are specified in "threads per inch". The fine thread versions are the ones with greater Thread Per Inch count. IIRC, there are no coarse threaded fasteners used anywhere in the airframe. Regarding bolts facing fore or aft, the orientation should be to allow the most accessible tightening of the nut. Never tighten the bolt, as you'll get an unreliable torque/clamp results due to the added friction.
Terry, CFI
RV-9A N323TP

Bob,

I had to put some heads forward and some aft. It was not possible to torque the nuts all facing the same direction.

Bob

DWG11 shows all the bolt heads aft. Washers under the nuts for the top bolts and washers under the bolt heads for the lower ones. Be careful inserting the lower outer big bolts. If they go in too far before you get the nut started you will have a problem trying to back them out again. Don't ask me how I know

Jim Talbot
New Zealand
RV7A
Flying!

terrykohler said:

U.S. fasteners are specified in "threads per inch". The fine thread versions are the ones with greater Thread Per Inch count. IIRC, there are no coarse threaded fasteners used anywhere in the airframe.

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Correction...on the -7A, the socket head cap screws that go through the gear leg at the wheel to hold the brake flange, etc., take a 1/4-20 nut. The shank of the screw is 5/16, the threads are 1/4-20. Torque to 1/4-20 specs, not 5/16. Ask me how I know this.

This is the only place I found on the airframe with coarse threads...

jimski9 said:

Bob

DWG11 shows all the bolt heads aft. Washers under the nuts for the top bolts and washers under the bolt heads for the lower ones. Be careful inserting the lower outer big bolts. If they go in too far before you get the nut started you will have a problem trying to back them out again. Don't ask me how I know

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But I don't believe Drawing 11 is referencing an "A", it's referencing a tail dragger without the landing gear weldments.

AN hardware is fine as frog hair

Hey Bob,
It is my understanding and experience that all common AN bolt hardware would be classified as "fine" threads or "UNF".

I know there are exceptions such as engine fasteners and #8 and smaller screws but for AN3 bolts and above, I think they are all fine thread.

Pretty sure DWG 11 applies to the "A" models as well. In fact, I don't see any reason to have the washers under the lower bolt heads on a tail dragger.

jimski9 said:

Be careful inserting the lower outer big bolts. If they go in too far before you get the nut started you will have a problem trying to back them out again. Don't ask me how I know

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This is good adivce!

Final ruling from Van's -- the orientation of the bolt doesn't matter. Whatever makes it easiest to torque the nut.

Think about it / A little more info!

Bob Collins said:

Final ruling from Van's -- the orientation of the bolt doesn't matter. Whatever makes it easiest to torque the nut.

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Thanks Bob,
Vans is correct (no surprise)

When a representative sample of these bolts are destructively tested after manufacture, they are supposed to break at or above a certain tension. The only acceptable failure point is the root of the threads close to the transition area where the unthreaded shank and the threads meet.
That is the tensile test.

The shear test applies the the full cylindrical portion of the unthreaded shank, depending on the fastener it may be cut in two with a special shear jig or put in a special jig to just proof load the shank.

The bottom line is a bolt will be just as strong either way it is installed.

If a nut and bolt combination would fail due to installation direction of the bolt there would be due to a serious mismatch of fastener to structure.

Now I just have to think how on earth to torque those bottom bolts.

Also, with the washer under the bolt head on the bottom bolts, and the width of the landing gear weldment, t'aint many (maybe 1) threads showing.

Bob Collins said:

Now I just have to think how on earth to torque those bottom bolts.

Also, with the washer under the bolt head on the bottom bolts, and the width of the landing gear weldment, t'aint many (maybe 1) threads showing.

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Bob, Be sure that there is AT LEAST 1 FULL thread showing.

Thin washers?

Bob,

I have thin washers NAS1149F0732P was AN960-716L.

PM me I may have some samples.

Could be helpful, especially under the head.

Mel said:

Bob, Be sure that there is AT LEAST 1 FULL thread showing.

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Yeah, I torqued them all yesterday (impossible to get a torque wrench on any of the bottom nuts so had to do via the bolt) and I ended up with almost 3 threads showing on each and realized -- again -- that 400 inch pounds of torque is a LOT!

Bob Collins said:

.....-- that 400 inch pounds of torque is a LOT!

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for a non mechanic maybe. Last week, new bolts were installed our Turbine runner nosecone. I got the pleasure of doing all the torque work to maintain consistency. 270ft-lbs or about 3240 inch pounds gotta make sure you had breakfast when your doing 24 of them.

3 full threads on nas bolts might be bottomed out...

Bob Collins said:

Yeah, I torqued them all yesterday (impossible to get a torque wrench on any of the bottom nuts so had to do via the bolt) and I ended up with almost 3 threads showing on each and realized -- again -- that 400 inch pounds of torque is a LOT!

Click to expand...

you might want to check carefully on this... the nas bolts don't have much extra thread before they bottom out. 3 full threads showing very well could have them bottomed out on the shank. when i did mine recently i had to add washers to keep them from bottoming out and ended up with 1-2 threads showing.

I don't have 3 full threads showing. I have ALMOST a third thread showing.

wings torqued in place....gotta' be a great feeling. WTG Bob

Bob

"Yeah, I torqued them all yesterday (impossible to get a torque wrench on any of the bottom nuts so had to do via the bolt) and I ended up with almost 3 threads showing on each and realized -- again -- that 400 inch pounds of torque is a LOT!"

I echo the concern - there really isn't much spare thread on those NAS bolts. 400 inch-lbs isn't that much - its about a third of what my Porsche wheel nuts are set to - tho it is certainly lot more than one is used to for most aviation requirements.

If you have "nearly 3 full threads" showing I am worried that the nuts are "threadbound" ie have wound onto the unthreaded portion of the bolt. That process can making tightening to the correct torque feel like it is an extremely high setting. How do I know this?

If you put the torque wrench (set at 400 inch lbs) on the bolt heads, can you turn the bolt/washer/nut assembly in the hole? If so, the implication is that altho the nuts are tight on the thread/bolt, the nut and bolt head are not holding the stub spar and socket assembly as tightly together as they should. I had exactly this problem and - once I realised what I had done - had to replace all the bolts. I don't think this part of assembly is well explained in the instructions.

I hope it's all OK for you but it might be good to check.

Good luck!

Chris

Again, I don't have nearly three full threads showing. I have nearly a third thread -- as in the beginning of a third thread -- showing. I have two full threads showing.

Question: Are the the size of the bolts used for an RV-7 bolt, the same as used for an RV-7A bolt? The "A", it seems to me, has an extra "washer" in the form of the landing gear mount. I would think it quite unlikely with that additional amount of material, that the thread has bottomed out.

That would mean that everyone with a non-A model is using extra washers on all of those bolts. Is that happening?

For those bottom bolts, I wasn't torquing to 400 inch pounds, actually. I had to torque via the bolt head, so the big ones varied anywhere from 33 to 37 foot pounds.

I do agree it may be good to check, but I'm reluctant to mess with the bolts more without some firm indication that there's a problem here. I'm not convinced two full threads showing and perhaps the start of a third is that indication without more input.