Airframe Hardware

gusc · Post by **gusc** » Thu Nov 30, 2006 00:32

Why are AN 310 nuts used on lower lift strut fittings instead of AN365? Do these fittings move enough that they require a cotter pin? It doesn't seem possible that these nuts would ever vibrate loose, kind of a belt and suspenders thing I guess.

Seems strange to me.

Of course it would ruin your whole day if one of those bolts fell out!

Paul Agaliotis · Post by **Paul Agaliotis** » Thu Nov 30, 2006 05:13

Gus,
My opinion is the cost of the hardware in 1945. Why have multiple nut applications when one type will work in all areas. Self locking nuts were pretty new to general aviation and went thru some changes, fiberlocks and boot nuts. I think the current locknuts are good quality and could be used as substitutes in some locations.
Paul

Jay · Post by **Jay** » Thu Nov 30, 2006 09:26

Gus (and Paul),
Two things to remember here. The first is that an AN 365 puts the bolt under tension - it is torqued. An AN 310 does not. Without being the design engineer (I'm not that darn old!) I suspect that there was a reason for not attaching the lower end of the lift strut with a tension bolt. Second thing to remember is that the Champ is a certificated airplane. Unless the parts/service manual or an STC that you are following allows the substitution you are not allowed to substitute - period.

nowlen · Post by **nowlen** » Thu Nov 30, 2006 13:13

its the bolt that is probably the issue. the bolt in loaded in shear and adding tension with a locking nut may lower the shear strength of the bolt. food for though to those engineers out there.

gusc · Post by **gusc** » Thu Nov 30, 2006 17:29

Some interesting thoughts but I don't agree about the tension part.

A lock nut does not have to be highly torqued. A castle nut may be lightly torqued or not. My understanding is that castle nuts are usually used only on moving parts, such as control fittings, where the torque is slight and there may be some movement of the connection.

In this case where the rear lift strut attaches to the main strut I would never leave it loose, this bolt would move and the hole would wallow out if left loose - even more reason to use a locknut.

To me the strange part here is that there is nothing to keep the castle nut from working loose unless you just happen to get lucky with the cotter pin slots when tightening, but the lock nut would never work lose if properly torqued?? Of course anything is possible but I'm assuming a new lock nut each time - on a liftstrut I'll sure use a new nut and bolt every time!

Ron Babos · Post by **Ron Babos** » Thu Nov 30, 2006 19:18

Guys: Just because you use a nyloc or metal lock doesn't mean you have to torque the bolt. It won't effect the shear strenght anyway. All the Champs at my field have lock nuts in these areas.
Ron

gusc · Post by **gusc** » Thu Nov 30, 2006 19:57

The more I look the more mysterious his thing is gets!

The spar to fuselage attach plates use 365 nuts through the spar but not for the fuselage/spar bolt? The outboard spar/lift strut fittings use all 310s.

The spar/rib brackets and aileron hinge plates use 365s. The tail uses 310s for everything. The jury struts use 365s??

If there is any logic to all this it escapes me?? Probably only the original Aeronca engineers know the answer to this. Maybe they got a good buy on AN310s!

Post by **joea** » Thu Nov 30, 2006 23:36

Might it be due to the fact that the tail is not taken off very often but during the delivery of the planes that the wings were often removed to ship the aircraft in a railroad car?

Paul Agaliotis · Post by **Paul Agaliotis** » Fri Dec 01, 2006 00:19

Jay,
Every nut installed on the aircraft will have a specific torque. Some are not very high, but all will put the bolt, screw or pin in a tension condition. This application is a shear condition. Diameter plays the part here, the nut only holds the bolt in position. I,m not saying replace hardware willie-nillie but in this installation the type or style of nut is not of primary concern.
Paul

gusc · Post by **gusc** » Fri Dec 01, 2006 14:29

Which brings up another interesting thing to me, why do some clevises use pins with cotters and some use clevis bolts/

It appears to me that since the clevis is usually not supposed to have tension on it that the clevis bolt is not needed - in fact it is very common to find clevises bent because of short bolts.

I suppose that some applications don't want the bolt to rotate but just to act as an axle, that's the only reason I can think of.

Ron Babos · Post by **Ron Babos** » Fri Dec 01, 2006 16:44

gusc: It's a design issue more than anything else. For example the tail brace wires are tight and so is the pin with the cotter pin. Besides, I don't think a nut would fit in there. Elevator and rudder pins won't allow nuts in the space provided. The strut clevis uses a bolt to take out the slop. If the clevis is bent the opening is too large for the part it slips into and the space should be shimmed prior to snugging it down. This helps stop any movement from wing cycles of take off and landings. Without this the hole would eventually get enlarged from pounding. Things like turnbuckles etc. are always in tension and the pin or bolt won't rattle around.
Some things an these planes would not pass our amateur built standards. One example is the rod end bearing for the aileron on the bellcrank. A clearance issue force them to do it wrong and it's still certified. The accepted practice is to have a penny washer under the bearing to prevent the outer part of the bearing from falling away from the inner ball shoud it fail somehow.
Ron