I have a Twist that I toss around the sky with some high g maneuvers. It occurred to me that if the single nylon bold failed in flight, it would not be pretty. Can nylon bolts fatigue with repeated installation and removal, eventually to the point of breaking with enough g force?

Yes, nylon bolts can fatigue if overstressed, like everything else. I would be more concerned with the wooden structure of the airframe though. Never over tighten. That said, nylon bolts (1/4"x20) are very strong. Do a simple test and try to break one. Nylon does get brittle over time, usually years, long after the plane itself has expired. Some of the cheap plastic bolts from ARF's I personally would never use. I replace these with true nylon bolts from Micro Fasteners, very cheap in lots of 100.

Safe Flying!

Nylon does not "fatigue" the way a metal bolt will (repeated mechanical stress on metal bolts causes hardening and ductile stretching of the metal). Nylon is not, however, without its faults. Nylon is not a UV stable plastic, which means that overtime, exposure to sunlight will cause the nylon to become brittle (just look at any nylon rope left out in the sun for long periods).

The reason for using nylon bolts in most airplane applications is to get the bolt to fail before the wood does, protecting more of the structure in a crash. For them to operate correctly, they must be prestressed when they are installed. Typically tightened hand tight, and then turned 1/4 to 1/2 turn more to stretch and preload the bolt. Being plastic, it will stretch over time in this condition. Since they're cheap, replacing them occasionally (annually?) is just good insurance.

Brad

Good advice (above). I keep several spares and look them over pretty closely before putting my wing on the plane. The big plus with nylon bolts is that they will shear upon stress and this will usually save a wing. I had (sold it) a Four Star 40 that I did a summer salt with. On the second flip, the bolts sheared right at the base of the bolt head. The wing went left the fuselage went right. All was ok minus a ding on the wing tip. I was lucky. It was going rather slow on landing and I should have gone around.. but.. well, we all were new pilots at one time.

I lost a Venus 40 a few months back. The fuselage was.. well, there wasn't a piece of not-broken wood in the fuselage. The wing, however, which came off (sheared nylon bolt) was totally intact. Strange... but true.

DS.

Last May at a fly in I saw a Big Stick 60 with a Saito .91 loose a wing in a high g turn. The heads of the nylon bolts broke off durning the turn, fuselage became a lawn dart while the wing floated for about 20 sec. The pilot was using a rechargable screwdriver to put the wing on. We think he just had them too tight.

You never need to tighten a nylon bolt more than finger tight. No need to worry about a 1/4-20 nylon bolt breaking in flight. They are good for 200 pounds of shear load and 150 pounds of tensil or stripping strength. For most all of our models, a 10-32 nylon bolt is more than sufficient, they are good for 125 pound tensil or stripping strength and 150 pounds single shear loads. In real dry climates, nylon can weaken some as it dries out but not enough to worry about. That is why, on the old nylon props, it was always recommended that they be boiled in water for 15 minutes at the start of each flying season.

All this is nice to know; I have an old Bud Nosen trainer, the wing bolts on with four 1/4-20 nylon screws. Over time, due to repeated repairs, three or four coats of paint, addition of heavier landing gear and a gas engine, this plane has swollen to 22 pounds. I also increased the wingspan 8 inches (to 96 inches). I was worried whether the bolts could withstand the stresses of loops and rolls to the point that I added functional wing struts to transfer some of the loads to the lower fuse. I still feel better about it, but I guess the blocks that the blind nuts were in would have been pulled out before the screws let go.

Sorry to kinda change the topic, but I have been looking for awhile for a phillips head nylon screw that will work in my Tiwst 40, any thoughts?

Thanks for the help,

Jack.

I've never seen Phillips head nylon screws but you can get socket head nylon screws from several sources. These are much more rugged than Phillips head would be.

I got both Phillips head & socket head nylon screws from Microfasteners.com

Good luck,
Dave Olson

I bought these nylon 1/4 - 20 bolts that have a sort of thumb nerled (spelling) top to them (slotted for a regular screwdriver but has the extended height head that is nerled (spelling again) to be turned by fingers to make them finger tight. That's what I use and they get tight enough not to come out and loose enough to remove easily. This seems to be the best way to tighten these nylon bolts so they are not over torqued. I bought them at the big WRAM RC show in NY last year. A bag of 50 of them cost like 5 bucks or so. Well worth the investment. Same vendor sells the hex-head servo screws, 1/2 inch and 7/16 inch long. They are great.

DS.

One thing i have experienced , is in cold weather (below freezing). I really have to watch my landings, (In summer the same landings or rougher ones have no effect). Just a hair to rough will sheer my 4 nylon gear bolts out (10/32). Mind you this is better than ripping the bottom out of my LT-40 (is converted to tail dragger). But it happens very easily. Will probably add one or two more, So that i will be changing them less ,but still able to sheer off if need be. This thread just gave me a new thought though. What about wing bolts in cold weather? Hope this isn't to far off topic. Not meaning to hijack your thread.

I never changed my wing bolts, and I had no problems to date after 2 yrs... But I asked
this very question on a set that's on my UCD... (and I have to say I am one that always
says... Ahh just a little more...*#%*!!! [:@]... Seems like I'd have learned better after a
few auto wheel stud replacements because of the same thought ) Club members had about
the same answers as above... I get mine from Ace hardware, the price is not bad... So I am
going to start and replace them say twice a year....