AN365 in a 7A

Budd Davisson's article in this month's *Sport Aviation says AN365 nuts should not be used on control surfaces on any airplane. RVs , of course, have them all over thfe place on control surface attach points.

Wondering if I should remove them at the next annual and, if so, specifically which ones and what they should be replaced with?

Castle nuts

Hey Bob,

I had to buy a bunch of hardware for the -8 to replace any AN365 and undrilled AN3 bolt that was attached to a moving control surface. I bought various sizes of the drilled AN3 bolts and the castle nuts with a cotter pin kit and matched the length of what was on the plans.

That's one of the requirements in Canada.

Haven't replaced them yet, but will do it before my final inspection.

Cheers,

Don

Hey bob-
Throughout my build, I've been replacing all control system hardware with locking castle nuts & cotter pins... I'm a safety nut. Using nyloc nuts anywhere in the control system freaks me out a little. I know it's proven but it's just personal preference to replace the stock hardware...

There are probably somewhere around 20 to 30 AN365's on each RV's control surfaces, times about 8,000 RV's, so maybe a quarter million of them? Good enough validation for me. As long as neither end of where they are clamped rotates with respect to the bolt/nut, they are fine. I believe this agrees with AC 43-13 as well.

Between a writer and a successful and well respected airplane designer, I'll trust the well respected airplane designer when it comes to hardware selection.

No disrespect to Budd Davisson - I enjoy his articles very much.

This ought to be Good!

I haven't checked the Vans Hobb meter in a while, but aren't we up to almost 8000 flying RV's or close to it. Just checked, 8583 flying according to them. And I'll bet "almost" every one of them, mine included have AN365 lock nuts on the control surfaces group. Pushrods, bellcranks, aileron, rudder, and elevator mounting, you name it. Man that's a lot of nuts!

In that application with a known good nut, how it would ever back off and come unattached would be beyond me. I'm sure Vans or somebody smarter than me will way in on this one. I know for a fact that every time I go out to fly they are always right where I left them the last time. I check during preflight. And I know, there are nuts we cant see during preflight, mainly pushrods. But they are there every annual. So am I safe or just foot loose and fancy free?

If and when Vans issues a SB on this (doubtful), I will reevaluate. I declare those AN365 nuts good little critters for my RV. But I don't use them firewall forward due to the temperature rating.

Okay, so let's pop some popcorn and watch this movie. I know Brantel put the popcorn eatting muppet on a while back and I still chuckle when I think of him.
Fly safe fellows and ladies.

Jeff

The difference is rod end bearings. On the elevator and aileron hinges, control pushrods, etc, the rod end bearing is clamped between two pieces of metal by the bolt and nut. There is no rotation around the bolt at all, only in the rod end bearing. An elastic lock nut is just fine for that location. Now, the rudder cables, brake pedals, and such do see rotation around the bolt, so a cotter pin and castle nut are appropriate.

Perhaps it really is a larger problem than we think, but just not related to RVs?

I looked at a recently purchased Air Cam and all of the control surface hinges were AN3 bolts and self locking nuts.

However, in this case the bolts were the hinges - no rod end bearings. The plane had just had a conditional inspection (aka annual....) and it was not picked up then.

I checked the plans that came with the plane and sure enough they call out for castle nuts and cotter pins.

Again, perhaps it's a large homebuilt problem, just not on our RVs.

I haven't read Bud's article, so I don't know if the OP misinterpreted something that he said, but the bottom line is "what is standard aircraft practice"?
Just because someone well respected writes a mag. article that deviates from long standing and well documented (AC 43.13, Aircraft Standards books, etc.), does that mean everyone should should suddenly change?

It is a long term industry standard (practice) that cotter pin safetied nuts be used on any fastener that is exposed to any level of rotation (a fastener where something that can move is actually pivoting on the fastener).

In almost every example I can think of on RV's where something moves, the rotating part/assembly is pivoting on a bushing or bearing that is captured by the bolt installed with the AN365 nut (the bolt is torqued to normal value and can not be rotated). In the few instances where a bolt is used as a pivot point (fwd and aft ends of rudder cables is a good example), a castle nut and cotter pin is specified.

Tangent - In fact, I would argue that in some instances, a cotterpin safetied nut could be more dangerous than a nylock one. Keep in mind, these airplanes are for the most part built by amateurs, so it is amateur level skills that are installing the cotter pins. How hard can it be you say? It is not. But there are different techniques that can be used to make them safer.
Lets say for example you have cotter pinned bolts on the aileron hing points. They are somewhat low to the ground (particularly the inboard one). Now lets say you are at a remote grass strip and while taxiing you swing you wing through some very tall grass that catches on the legs of the cotter pin (that was installed by an amateur) and bends them open, and at some time later the cotter pin falls out. Given that there is a chance of it occuring, which kind of nut would you rather have installed, if an AN365 is "by standard practice" totally exceptable?
Now I realize that the cotter pin has two legs and they should be bent in different directions, etc., etc., but this is a real scenario. I am aware of cotter pins being lost from rudder cables on tail draggers that regularly get run through tall grass, or on rudder pedals from peoples shoes, because the bolt wasn't oriented to prevent shoe contact.

My main point is "do not become complacent and assume that just because an AN365 nut has been replaced and is now safetied with a cotter pin, that it is automatically safer".

rvbuilder2002 said:

In the few instances where a bolt is used as a pivot point (fwd and aft ends of rudder cables is a good example), a castle nut and cotter pin is specified.

Click to expand...

Yep, far as I recall the flap hinge is the only surface using the castle nut and cotter pin on my 10. But then, the 10 flap is not like the rest of the line.

And, yes, the plans do call out for the correct hardware.

Certified as well

Both of my certified Air Tractors have the same rod end bearing hinge as Van's and they have locking nuts from the factory.

Best,

rvbuilder2002 said:

.......
My main point is "do not become complacent and assume that just because an AN365 nut has been replaced and is now safetied with a cotter pin, that it is automatically safer".

Click to expand...

If you really, really want "belts and braces" then you can use a self-locking castle nut...

http://www.aircraftspruce.com/catalog/hapages/ms17825.php

There have been numerous documented accidents due to a cotter pin that was left out but I can't recall every hearing of a "good" self locking nut departing for no reason.

Walt said:

There have been numerous documented accidents due to a cotter pin that was left out but I can't recall every hearing of a "good" self locking nut departing for no reason.

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My thoughts exactly. There is a trade-off. The only way that nut is going to back out is if the bearings in the rod end-bearing fail or something else causes the rod-end bearing to lock up, then rotation could be applied to the nut. But, the rod-end bearings are supposed to be sandwiched between the adjacent tabs (read: tight). If the bearing fails it should be very, very obvious.

But I too have seen many missing lock nuts. Once even on a rental I was going to fly as a newly-minted pilot. It was a 172 and during my walk-around I noticed that there were no cotter pins on any of the castle nuts holding the right aileron on. Turns out the aileron had been pulled so that part of the wing could be inspected -- two weeks prior. Countless students flew that airplane like that.

I understand about a cotter pinned nut on a rotating bolt, but why do we use a cotter pin on the bolts that hold the engine mount on?
Just wondering if its because of the tensile load instead of the shear load?

Taildrgr said:

I understand about a cotter pinned nut on a rotating bolt, but why do we use a cotter pin on the bolts that hold the engine mount on?
Just wondering if its because of the tensile load instead of the shear load?

Click to expand...

Probably because fiber nuts are not to be used FWF (temp limits).

Bevan

Bevan said:

Probably because fiber nuts are not to be used FWF (temp limits).

Bevan

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Somebody needs to notify Lycoming, then, because my brand new IO-360 from the factory came with (gasp) fiber locknuts on it (e.g., on the Adel clamps holding the fuel injection lines).

I've heard this before about fiber locknuts FWF, and granted there are places in the engine compartment where they probably shouldn't be used (and I used a lot of all-metal locknuts when installing the systems on the engine), but even the fuel injection servo uses fiber locknuts in one or two places, IIRC.

Taildrgr said:

I understand about a cotter pinned nut on a rotating bolt, but why do we use a cotter pin on the bolts that hold the engine mount on?
Just wondering if its because of the tensile load instead of the shear load?

Click to expand...

Engine mounts are also a high vibration joint with rubber in the clamp-up stack. Both vibration and movement can work a nut off a bolt unless mechanically restricted with a cotter pin.

Heck, on my fixed pitched prop, even Sensenich uses self-locking nuts. I was surprised to see this, but that's what their documentation shows.

Cotter pins

I just inspected an RV-10 yesterday with 100 hours on it and NO cotter pins in any of the 4 engine Lord mount bolts.

If it calls for them, they have to be used.

Vic

RV7A Flyer said:

Somebody needs to notify Lycoming, then, because my brand new IO-360 from the factory came with (gasp) fiber locknuts on it (e.g., on the Adel clamps holding the fuel injection lines).

I've heard this before about fiber locknuts FWF, and granted there are places in the engine compartment where they probably shouldn't be used (and I used a lot of all-metal locknuts when installing the systems on the engine), but even the fuel injection servo uses fiber locknuts in one or two places, IIRC.

Click to expand...

I've seen the plastic locknuts melt the plastic right out if the FWF. Regardless of what Lycoming or anyone else does, I'm using AN363's.

AN363

I used AN363 on all fw fwd and control surface attachments and linkages except where castle nuts were specified.

Keep the rod end bearings lubed because Aurora rod end bearings need it.

vic syracuse said:

I just inspected an RV-10 yesterday with 100 hours on it and NO cotter pins in any of the 4 engine Lord mount bolts.

If it calls for them, they have to be used.

Vic

Click to expand...

If what calls for them? If you are saying builders can't deviate from the plans then we probably need to ground the entire RV fleet

I just inspected an RV-10 yesterday with 100 hours on it and NO cotter pins in any of the 4 engine Lord mount bolts....

Click to expand...

One of the things I find fascinating is the difference between a Cherokee 180 and the RV-7A. Pretty much the same engine (mags, carb, etc.).

FWIW - the Cherokee does not have cotter pins on the engine mount hardware.

Dan

No, Walt.

I am far from being the smartest one on the List or anywhere else for that matter.
I was simply stating that if a drilled bolt and castellated nut are used together, then the cotter pin is not optional.

Vic

Technology

I think this is a situation of seeking a solution for a problem that doesn't exist. Van's did this for a reason and has been pointed out, 8000+ flying without control surfaces dropping off.

One of the other interesting controversies is the lace cord vs. zip ties. Many think that lace cord is the only way to go. I see no issues with zip ties but I like the looks of nicely done lace cord.

I was talking to one of the mechanics for our helicopters. He's been with the company for lots of years. I asked why everything is zip tied now instead of lace corded. He said back when lace cord was the only option. Now we have all sizes zip ties for all temperature ranges, stand offs, spacers etc..... He said nothing wrong with lace cord but technology has changed.