To strong nylon wing bolts?!

[Kimble_Schmitz]

Hi all.

Last friday i had this idea about drilling holes in my wing bolts so they would snap when subjected to less force.

I read this post about a Bandit hotliner that crashed and the wing was ripped of in a cartwheal. The bolts didn't snap and the wing and fuse where damaged badly.

So i picked up the calculator and some tecnical books and calculated when my nylon bolts would give way. What came next was a total shock to me. My plane would have to pull over 60 G's for the bolts to snap!

What pilot would fly his plane to 60 G's?!
The wing would surely snap on those forces!

Then i disided i realy needed smaller bolts, but that would mean i'd have to mod my glas fuse. So there my idea of drilling my existing bolt came to me.

I have a one piece wing that is screwed in place with two M4 nylon bolts. In a book i found that the maximum tensile strength that nylon can take is about 60 MPa.

My fuse ways 1,5kg so 10G's would corespond with 150N total on the two bolts. That is 75N on just one bolt. If you divide the force with the area that takes the strain you have MPa.

Adjusting for the threaded part on the bolts that dusnt take eny force i would have to drill out a maximum of 2,5 mm so my plane could withstand 10G's. I drilled out 2mm to be safe.

I have flown today with the hollowed out bolts and they didn't snap even after some extensive G, pullin maneuvres.

Now i ask you, way do manufacturers make their planes with these large bolts when this it not neaded at all. In a crash or a bad landing your fuse will break before the wings comes off.

Enyone did the same to their bolts?!

[avie]

Hi
when your plane gets cartwheeled (or crashed), the bolts don't face tensile forces, but shearing forces (like in scissors). there should be a number in the book;)
except for that, your plane, especially if flown like a hot liner (i.e. hard, fast turns) pulls over 10G. there is a thread about how many G's do hot liners pull. the highest number in some contest formula was 40 G!:eek: !20 was the 'more common':p either way, the threads on the bolt would shear long before you pull 60G's, unless it's bolt all the way up...


Avi

[Kimble_Schmitz]

Your are wright. In a crash the bolts will be subjected to shearing forces rathere then tensile. They can take less shearing force then tensile. But still, less nylon means a more easy snap rather then ripped out fuse nuts :eek:

To use bolts that can take over 60G's is a bit much for my taste. I would like them to snap at a litle over 20 if that is the standerd in F5b flying. Then i am sure in a cartwheal they will come of nice and clean.

After recalculating my current bolts with the 2mm holes, they should snap at around 20 G's if my calculations are correct. But if there are eny imperfections in them i better not lend my plane to a real F5b pilot ;)

Thank you for pointing that out tho, shearing forces are a whole different matter!

[Andy W]

Shearing forces are all that matter here. The tensile strength is far in excess of what we need, but there is no issue there. Better for the wing to stay on in any situation while you're in the air, or else you end up with a 2lb projectile..
That said, I've never had a wing mount bolt shear off either, and I've tried many times! :o However, I prefer to know they are not going to give under flight loads, than worry about what's going to happen if I crash. I use steel or aluminum bolts on my Sirius, Smart, etc.
..a

[Sparky Paul]

You know you've hit hard, when the bolt(s) are sheared, AND the mount they were in has left the area as well! :p

[GordonTarling]

I used three nylon bolts to secure the landing gear to my Hangar 9 Cub - similar thoughts of saving more damage to the model in a heavy landing. They seemed fine until I did the best landing I've ever done with it when, to my utter surprise, the model tipped forward onto its nose and left the gear behind! All three bolts had sheared - don't know why! - so I drilled out the holes to use next size up after that. Originals were 4mm.

[Bill Glover]

I once used nylon bolts to hold the dural u/c on a Club 20 pylon racer (DB Tarka, for anyone with a long memory ;) ). First landing, nice smooth touchdown on shortish grass (Croydon airport) ... the bolts sheared, the u/c swung back,and both spats went in through the bottom sheeting of the built-up wing and came out through the top! Made a right mess of my beautiful sprayed paint job :(

[rcav8r2]

I've heard of drilling out wing bolts for some time now, and used to do this. I started doing this when I was doing full throttle touch and goes out of a split-S with my Kougar. Well one day a wheel got caught in a crack in the runway. The wheel , with the wing stayed in the crack, and the fuse kept going, and going, and... Well the blocks took out a chunk of fuse out with them and were still firmly attached to the wing.
So I started drilling the bolts out. Just a few falls ago I had an elevator pushrod break ( 2-56 rod and about 10 years of vilent snapping manovers must have been too much for it) on my (then repaired) Kougar. It was right after a full power vertical dive, and pull out about 5 foot from the ground. As soon as I leveled out, I went to give it a snapping manover, and it just barrel rolled, and hit the ground at about 100 MPH. It was more of a VERY rough landing than a crash as it landed on the wheels. Well the bolts were perfectly intact, but the bolts, with very large washers, pulled through the wing, and fuse was torn to shreds.

I have resigned to the fact that the bolts aren't gonna break, but use nylon as I'm afraid that the metal ones will loosen as the nylon seem tighter.

TIP: to make the bolts easier to start... After cutting to lenght, grind an angle on them with a belt sander, then run through a die. They almost start themselfs.

BTW.. I 've been holding landing hear on my planes with nylon bolts for years... Have yet to have one break, and I use 6-32 for up to .60 sized planes.

[rorywquin]

When I lived in Holland I once bought hollow nylon bolts - so there is somebody out there making them. I found I had to replace then quite often as the became a little flexible after a while.

[Franck]

I use to drill out all my nylon bolts (I use 6mm) . A bolt should be just strong enough to hold a wing in a steep dive + full up, no more. The bolts out of the box are way to strong for most of my planes. On a cartwheel/rough landing they should give inmidiately.

The T-tail converted Wonder in my avatar crashed several times (cartwheels nosedives etc etc) but the bolt never broke (until I hollowed them out...2mm drill) Never had to glue anything ever since.....used a lot of bolts though :)

Grtz,

Franck

[jrb]

1/4-20 is too, but how about the ARFs that use 4mm metal bolts!

4mm blind nuts can be re-tapped to 8-32, still a a lots of strenth when using a nylon bolt but better than the metal.

Sometime a nylon bolt will pop a head, 3mm on landing with glider or 10-32 on LG on landing with 6+# plane; easier to replace that the fuselage.

Here's a chart with some data for English sized nylon bolts:

[Sparky Paul]

I generally use dowels at the wing front to hold the wing on. Bolts at the rear serve only as locators, as the forces in flight are minimal at the rear of the wing.

[Kimble_Schmitz]

OK, thank you all for the responds, now i know i am not a single lonetic that is drilling his bolts.

A lot of people mentioned that in a crash it dunsn't realy matter if you have nylon bolts that will snap ASAP. They say your plane will come appart enyway :( :eek:
So what is the point in drilling out these bolts?!

Well, i can tell you that when i try to hit a target when landing (competition) i sometimes hit the deck with one wingtip first. This carwheels the airplane and can couse much dammage. If the wing would snap of there would be zero dammage.

That is wy i think i need weak bolts. They need to hold my wings on wile flying but thats about it. To my ammazament, lots of people share my view on this one. :cool:

One quistion does remain, why do people make planes with these large bolts. On my plane 3mm bolts would be more then enouth and i would not feel eny need to drill those bolts.

I think it's wrong for a manufacturer to say "lets be on the safe side and use double the sise needed". Is it that hard to figure out what loads these bolts will have to take?!

Not all of us land pritty everytime, so whats up with the thick bolts?! Just my bleek view on things ;)

[avie]

one thing. when plane cartwheels, what breaks (usually) on a small crash is the tail. if the wing snaps of and only the fuse cartwheels, will it save the fragile tail ?

Avi

[Kimble_Schmitz]

In a matter of speaking, yes

If a wingtip hits the ground or something else, the whole plane is tossed around. If the wing would come of however, the fuse would keep going in a strait line and there should be no dammage to the tail.

Unless ofcourse you hit a tree. If you hit something high above the ground the fuse will plumit down :(

The dammage will be to the nose of the fuse as that hits the ground first. If the tail is not to heavy it might be still ok.
So YES, this should save your tail!

[PeterH]

Anecdote time:

I am flying a 'Doc Mathews' 6-foot Aeronca Defender on e-power, and the wing is held on by a dowel in front and a pair of 6-32 nylon bolts at the rear. One takeoff was punctuated by a healthy gust from the side, and it was cartwheel time. Sheared off both bolts nice as pie, and not a scratch to anything.

A friend of mine uses a pair of 8-32 bolts/front dowel to mount the wing on his Great Planes P-51 Mustang, about 6 pounds of glow powered pleasure. An approach stall/spin entry from 10 feet last weekend got the wing to shear the bolts and depart the fuselage unharmed.

[KillerWatt]

prior to reading these posts, i thought the only reason to use nylon wing bolts was only for the the bolts to snap off during a hard landing or crash and allowing thw wing and fuse to eaisly seperate for less damage to either.....however, the more common american method is to use 1 or 2 Wooden dowels at LE and 2 nylon bolts at wing's LE....now with the previous post comment (and my own opinion) that the wing's TE experiences much less stresses under all conditions, when wooden dowels (which i would think would not break easily as nylon) are used at the LE location, aren't we using the wood (harder to break ?) dowels and the nylon bolts in the reversed locations, if we really want the wing to seperate nicely , or does other stresses occure that i'm not aware of to make using wooden dowels at LE infact function better for real crash seperation results.........i'm in process of modifying an ARF low wing design to bolt on wing method, and i need to decide if the wooden dowel(s) should be located at wing's LE (more commonly seen) or at LE for best crash wing /fuse seperation ???? any thoughts or observed facts comments ...........kw

[Kimble_Schmitz]

That the woaden dowels take most of the strain when flying is a good thing, this means the nylon bolts at the back can be small.

When you cartwheel or just hit somthing, your wing is the part that is stopped cold. The fuse with all the parts inside still wants to go forward.

If you use dowels in front and nylon bolts in the back, the fuse can go forward real easy, only the nylon bolts need to shear of and thats it!

So this is the correct setup if you ask me. Unless you tend to hit a tree flying backwords ;)

When you are designing stuff, make it so that the wing can slide of the fuse travaling backwords. So only the nylon keeps it in the correct position.

Kimble

[rcav8r2]

True, there is a lot more force at the Leading Edge than the trailing edge. On my old 10 year old Kougar I had to replace the LE dowels about 3 times as they became too compressed to trust. They also had burn marks on them...( this also made the wing loose accelearting the wear) I have heard of guys not using nylon bolts on the leading edge of "hot" planes due to the force of friction there ( ANY movement will cause friction at this joint. The more movement, and more violent the manover, the more heat) and the bolts breaking. After seeing the dowels on my Kougar, I am a beliver.:)
Getting back to the wing coming off in a crash.... as pointed out in earlier posts, the bolts are designed to break with a shear force. In this situation the fuselage will continue where the wing won't. With the LE dowels plugging in, IF ( and a big if) the wing bolts break, the wing will "unplug"
Over the past few years, I have been using #8 & 10 nylon bolts on my wings of taimer planes, don't know how they "work" in a crash as I haven't had the misfortune with these planes....yet :D
BUT I just built a new Kougar, and I know what I put this plane through. For this one I used 1/4x20 Nylon bolts. True the TE has less force, BUT this thing can snap VERY violently ( it will actually make a "WOOF" when snapping right after a huge split-S)
This is sure to cause some movement in the wing... I sure would hate to see the wing some flying off in flight :D

[Sparky Paul]

I don't trust bolts at the front of the wing..
There's a lot of force there. A single dowel setup for instance will frequently show evidence of charring on the dowel due to vibration.
I use front and rear wing bolts on my Tiger 60.
One flight it was acting strange when inverted.
Landed, and found the forward wing bolts had departed!
The tuned piped on the motor kept the wing on the airplane.
Front bolts should be metal, not nylon. It's way too easy to torque the head off a nylon bolt, especially when it's cold.

[bjsiegel@texas.net]

I use 6-32 nylon bolts (4) to mount my Phasor 15-4 & MAT 3:1 belted gearbox (H500) to the 1/4" ply firewall on my Big-T.
When I whack it on the nose hard (been practicing "landings"), the bolts shear, saving the gb, etc from a hard hit. Once a Sig glass-filled mount broke instead but that was after a number of hard whacks.
Usually, Big-T is ready to go again in a few minutes.

[avie]

you know, I hate you guys !:p because of you I am gonna DRILL through the wing bolts of my slope glider as a lesson after it cartwheeled during a VERY turbulent fly by over the cliff:rolleyes:

Avi

[Kimble_Schmitz]

I use messing tubes as dowels at the LE. (don't know if that needs to be translated)

I for one don't know what a Cougar is, but me thinks that is not electric but a slimer. Don't know much about slimy planes ;)

But the F5b competition folk use just two nylon bolts and NO dowels. The but them strait thru the main spar and into the sides of the fuse, sorry got no picture.

They sure know what they are doing and man do they pull GGGGGGG's with those planes.

But i know, nylon is a soft material and you can overtighten the bolts real easy. This can lead to a mid air seperation :eek:

Avi, could you explain your post, i don't follow you completely.

[KillerWatt]

ok...i like the explaination of the wing wanting to stop while the fuselage wants to keep going foward as the wing dowels unplug themselves and sheer off the TE bolts .....on the charring dowels, would this happen to a medium speed, electric parkflyer not flying over 30 mph ????? or are you charring guys talking about fast, competion electric or medium to fast glow powered types only...it never occurred to me that that much friction and wing to fuse movement could occure........thanks for the info..........kw

[pullin-gs]

I have a 2-meter Kyosho Soarus that recently had a wing edge "bite" on landing, pretty much pulling out and destroying the wing mount in both the fuse and the wing. The wing was originally screwed down using 2 STEEL 10x24 screws.

I am almost finished with the repair, and am considering using a pair of 8x32 NYLON screws as a replacement. It weighs in at about 45 oz AUW. Is this something that I can rely on? I have some 6x32s abd 10x24s in nylon as well. Opinions?

Thanks

Pullin'

[PeterH]

I suggest using the #8's. This machine will never see a winch, and we use such screws on winch-launched sailplanes, which puts substantially more load on the wing screws than a 'sailplane' with an electric motor will ever see.