I use 1/4 20 nylon bolts for my landing gear, but most brands snap off too easily. Any body know of some heavy duty ones that do not break off so easily?

I`m not sure if you can find a stronger nylon bolt.
I use to make my own shear bolts for aircraft tow bars by drilling a hole down the center of the bolt. Making it easier to snap if overloaded. but even if you did this to a 1/4 inch bolt, it would still be stronger than the planes undercarriage structure and would result in more damage than it`s worth.
If your mounting blocks are big enough, you could drill and tap the holes up to the next nylon bolt sizes. after tapping, add a few drops of CA to the threads to harden them. Don`t install the bolts till the CA dry`s LOL.

How many are you using now? Do you have enough room to add an additional nylon bolt, or two? This will provide more strength without having to over-size the current holes.

I boil all my nylon parts in water for 10 minutes or so. This includes control horns, bolts, and any other nylon accessory. This process makes the parts less brittle, more flexible, and less prone to stress snapping.

If you use stronger bolts it would just cause damage to the plane. I don't know how big the plane is, but three #10 nylon bolts are just enough for a .60 plane and only break off when the landing is too rough. Four 1/4 nylon bolts should be more than enough for 1.2 sized planes.

I always was under the impression that the reason for using nylon bolts was so that they would shear if put under stress reather rip the wing or fuse apart. They really are not doing thier job if you hit hard and the bolts are left in the blocks and the bottom of the plane is ripped apart. If you just want strong bolts, use a metal one. That way you can save on the bolt cost and probably repair your plane more often.

The place the bolts are mounted make a big difference. You want the bolts to be mounted as close to the outside edge of the fuselage as possible. If you mount them to far inboard, there is a lot of tensile stress put on the bolt heads (the gear flexes and bow outward on the inside of the mounting holes) and will pop off the bolt heads rather than shear sideways. Typically a 1/4X20 nylon bolt has a single line shear strength of 200 pounds and a tensile strength of 150 pounds.

Another point, is to stagger the bolt pattern, so they are not all in-line, centered down the middle of the LG plate.

If you can make three or four mouintg points; one front, two back [triangular formation] or 2 front & 2 back, you'll get more strength in the structure.

My 4 stars came like that, 3 bolts all alinged along a center line. I've made it so that one hole is near a front (or back) edge, while the other two (outer holes) are the opposite.

I think you will find that those numbers are for a 10-32 or 10-24 nylon screw.
A quarter-twenty has much higher values.

Hopefully, a table of nylon screw data was uploaded here if I did it right.

This topic has been discussed many times here at RCU and many members feel the same way I do.

I use nylon bolts for certain things - like holding the wing on, not because I expect them to break in case of an accident (They won't) but only because they won't vibrate loose like a metal bolt can.

I never use them on landing gear. Here's why:

Imagine that the landing stress on the gear is rated at 1 - 10.

1 is a perfect landing on a paved runway, 7 will snap nylon bolts, and 10 will rip out the gear when held with steel bolts

Now let's look at this senario:

In the course of 50 landings, you get 30 that rate 1-6, 19 that rate 7-9 and 1 that rates a 10

That means that with nylon bolts, you will have 20 repairs (aside from replacing the bolts, don't forget how much damage can occur from the landing gear tumbling under the belly of the plane - and if you have wheel pants, there will be lots of wing damage too).

If you have steel bolts, you will have one repair job. Sure, you ripped the gear out, but 9 times out of ten that's just a matter of slapping it back in with some epoxy.

Need to improve your landings, that's the problem.

I agree with MinnFlyer on this one. I always use steel bolts. As long as the mounting plate is adequately installed, that is all that should be necessary. Have I ever ripped a landing gear out on a bad landing? No!....I usually call those crashes instead.

Mike

True, I can only think of one time (Withing the last 12 years anyway) when I ripped out a set of gear, and that was when I lost a wheel in flight with my 28% Extra 300 and had to land on grass.

Mike, thanks for that explaination. All the oldtimers at the field think I'm crazy because all my gears have steel bolts. They don't get it even when they are walking out to pick up their plane and dettached gear after a decent landing.

Decent Landing and detached landing gear??????????? Never heard of such a thing, if your landing gear comes off on landing you are doing something wrong- Period!!!! Practice your landing skills and if you have steel or nylon bolts won't matter. Many,many,many years ago I had similar bad landings and made the same excuses and then our clubs most experienced pilot asked to fly my plane and he landed it, absolutely picture perfect landing, he handed back my transmitter and told me that there is nothing wrong with my airplane. I learned my lesson and to this day my landings are way better. PRACTICE YOUR LANDINGS, yeah I'm in a grumpy mood tonight.

Hey Grumpy, not all of us have the luxury of flying off a smooth field.

Ditto

For many, it doesn't matter what the surface is.

If you put more bolts and more epoxy at the weak spots the breakage will occur somewhere else.

Bill

I agree with Minnflyer (post #11) on all but one small point. I use aluminum bolts. Enough strength to keep his examples valid but less weight. 1/4"x20 aluminum bolts are available at hardware stores.

The good one is the all thread design. These snap off right where the gap is between the wing and body. What it should do. The threads allow a reliable snap off.

DO NOT use NO THREADS in the joint area.

Might as well EPOXY the wing on.

Gotta agree with Skylane42 here, THe main purpose for nylon is so that it will break. For my own planes I have no problem using blind nuts and steel screws. If I rip the gear off, I probably have other, more serious repairs to make as well. However, as an instructor for a local youth aviation program, where landings are sometimes measured by the damage done and landing gear repairs are common, I recommend (assuming flat stock gear being used), attaching with wood screws. They hold up fine under normal conditions (and we have a very rough runway) but do minimal damage to the plane during the occasional harrier landing. The screws tend to pull out of the wood rather than pull the wood off the plane. I also agree with minnflyer about practicing your landings. Nylon should hold up to even moderately hard landings

There's four reasons nylon screws break off during a ....landing. One is that they were run down too tight and were ready to snap to begin with. Two is that the field is really rough and the gear is getting twisted and turned during a roll out. Three is because the plane is too heavy for the screw size. Four is because it wasn't really a landing, but a semi controlled crash.

Number four is the most common reason for breking nylon bolts on landing gear. Used to fly with a guy that came to the field with a bag of them. Every "landing[:@]" took the gear off. Eventually his planes had so much epoxy on the landing gear plate that they weighed almost a pound more than when they started. Pluds they looked pretty ratty after all the repairs.

Those that learn how to use the throttle to control altitude, the elevator to control airspeed, and use a standard downwind, base, and final landing pattern do better at landing. Don't drive the plane to the ground, but level off about a foot above the ground and lowly raise the nose as it bleeds off speed, permitting the plane to gently sink and finally stall into a nice, soft landing.

More simply put, if you really need "break away" bolts on the gear then you need to learn how to land a plane. You already know how to do a fairly level crash.