Ch. 5 - Fuselage sides - Part 7

Landing gear brackets final installation  (1.9 hrs)

Today, I finally put the gear brackets to rest once and for all, by floxing, on top of bolting them to the fuselage sides.

Considering how long I’ve been working on this pieces, the final installation went down rather fast.

Lightly sanding the area that will receive the flox.

Standing the sidewall up, to ease installation.

There are a few accepted practices concerning bolt installation (by Ron Alexander):

1. In determining proper bolt length—no more than 1 thread should be hidden inside the bolt hole. 
2. Whenever possible, bolts should be installed pointing aft and to the center of an airplane. 
3. Use a torque wrench whenever possible & determine torque values based on the size of bolt. 
4. Be sure bolt and nut threads are clean and dry. 
5. Use smooth, even pulls when tightening. 
6. Tighten the nut first—whenever possible.
7. A typical installation includes a bolt, 1 washer, and a nut. 
8. If the bolt is too long, a maximum of 3 washers may be used. 
9. If more than 3 threads are protruding from the nut, the bolt may be too long and could be bottoming out on the shank. 
10. Use undrilled bolts with fiber lock nuts. If you use a drilled bolt and fiber nut combination, be sure no burrs exist on the drilled hole that will cut the fiber. 
11. If the bolt does not fit snug, consider the use of a close tolerance bolt. 
12. Don’t make a practice of cutting off a bolt that is too long to fit a hole. That can often weaken the bolt and allow corrosion in the area that is cut. 

The Long EZ plan already specified the proper nuts and bolts, so I didn't have to worry about choosing the fasteners. 

Bolts being installed

Same thing, other side.

Unfortunately, the plan is mum about how tight they have to be, and searching FAA Advisory Circular 43-13-1b, concerning Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair, I learned that "the importance of correct torque application cannot be overemphasized". 

"Under-torque can result in unnecessary wear of nuts and bolts, as well as the parts they secure. Over-torque can cause failure of a bolt or nut from over-stressing the threaded areas. Uneven or additional loads that are applied to the assembly may result in wear or premature failure".

An important note also specifies that "the torque applied is for the size of the bolt shank not the wrench size".

Bolt and proper torque values highlighted

Given the importance and the amount of information on the subject, I decided to use a torque wrench to make sure all the nuts are properly, and equally tightened.

Torquing the nuts to 60 inch/pound

Small tab installed

Big tab installed

After cleaning up the overflowing flox, both sides were ready to cure overnight.

Both brackets in place

UPDATE #1

The biggest reason for the creation and up-keep of this blog, is the hope that one day someone will see me doing something incorrectly, tell me about it, and save me from a more difficult repair/replacement later on.

That day turned out to be today!

My friend Walter, who from this day on shall be known as Eagle-eye Walter, told me that there might be too many threads showing past the nuts. This might be an indication that the nuts are bottoming out on the unthreaded part of the bolts, a violation of point i on Ron Alexander's list, above.

Looking at other builders' pictures, I didn't think so, but I decided to remove one nut to see if any part of the shank protruded past the washer. 

Unfortunately that's exactly what I found.

Bolt shank extending past the washer (bad!)

This was a weird situation to be in, and required some further investigation, to determine how it could have happened.

The thickness of the washer was 0.032", and the amount of uncovered shank 0.064", exactly double.

Checking online I found the correct thickness for an AN960-416 washer to be 0.064", not the 0.032" mine measured.

So, I went back and checked my old receipts and found out I accidentally ordered the AN960-416L washers, L stands for light, which means half thickness.

Had I used the proper washers on both sides, there wouldn't have been any shank visible past the washers. Mystery solved!

To take care of this problem, I ordered the correct washers from Aircraft Spruce today, and I will install them as soon as I get them.

Good job Walter!

UPDATE #2

The correct washers finally arrived and were put on.

New thicker washer on right, old wrong one on left.

FAA Advisory Circular 43-13-1b gives us guidance about usage of additional washers:

"GRIP LENGTH. In general, bolt grip lengths of a fastener is the thickness of the material the fastener is designed to hold when two or more parts are being assembled. Bolts of slightly greater grip length may be used, provided washers are placed under the nut or bolthead. The maximum combined height of washers that should be used is 1/8 inch. This limits the use of washers necessary to compensate for grip, up to the next standard grip size..."

1/8" is 0.125", and since one washer is 0.064" thick, two of them is the most we want to use.

Using two washers per bolt

A lot less threads showing now

All nuts and bolts properly torqued

All nuts are new, the old ones were not reused.

UPDATE #3

Recently I have been reading the Canard Pushers (all 1400 pages) once again, and on page 13 in CP #25, I found a paragraph of interest, buried between a bunch of pictures.

It reads: "The AN 4-16A bolts require two washers for mounting these brackets. A shorter bolt should not be used, as it results in threads in the bracket."

Case closed!

UPDATE #4

Well, apparently not quite close enough!

An article on the first 2013 CSA newsletter reopened the case.

I guess the word was out in the '90s about using bigger washers on the outside of the fuselage, but this is the first time me, and everyone else I know, ever heard about it.

Central States Association newsletter (Jan 2013)

I now feel that the thin washers I left under the head of the bolts, might be inadequate to handle the landing loads over the lifetime of the plane.

For this reason I decided to remove, and replace them with the much bigger AN970-4.

I will post an entry in the blog about it in the near future.