Wing bolts plastic or metal?

[martin collins 1]

I am just getting ready to fly my 84" span Bowman Miles Magister which has a 22cc petrol engine on it, it looks like it originally had 6mm plastic wing bolts fitted but bearing in mind the size and weight of the model i am thinking it ought to have metal wing bolts fitted with spring washers under the heads, thoughts from those that fly large heavy models?

[Jon H]

I use 6mm nylon jobs on a number of my big models. Most of the load is on the front of the wing and its not an issue. 

 

I have no idea what the tensile strength of a 6mm nylon bolt is, but i would wager its more than we think. 

[Geoff S]

I never had any problems with 6mm nylon bolts on my Maher's Thunderbird with a Zenoah 26 petrol engine.  Nylon bolts tend not to become loose like steel on steel threads can do unless they're very tight - perhaps tighter than you'd want to on a balsa wing .

[Cuban8]

I've used steel cap heads to secure the wing on my H9 Thunderbolt for years. Not a large model at 63 inches and about ten pounds but I prefer the security that they provide. I don't think it makes much difference if you swap out plastic screws in most cases. Probably overkill on smallish models though.

I'd go for cap heads on your model and intend to use them on my 1/3 scale Turbulent when I get around to finishing it. 

[Adrian Smith 1]

Metal bolts for me as in my experience it doesn't take long to strip the nylon threads if they screw into a metal claw nut. May be if you are less experienced nylon bolts could be an option as they would help avoid more damage on a heavy arrival with the bolt breaking rather than the airframe.

Edited August 1, 2023 by Adrian Smith 1

[Cuban8]

3 minutes ago, Adrian Smith 1 said:

Metal bolts for me as in my experience it doesn't take long to strip the nylon threads if they screw into a metal claw nut. May be if you are less experienced nylon bolts could be an option as they would help avoid more damage on a heavy arrival with the bolt breaking rather than the airframe.

I suppose on a trainer where the wing might tend to slide and break a nylon bolt that would be worthwhile, but where the wing is neatly faired into the rest of the structure, a really duff landing or arrival is going to cause damage whatever you do.

[Paul De Tourtoulon]

29 minutes ago, Adrian Smith 1 said:

Metal bolts for me as in my experience it doesn't take long to strip the nylon threads if they screw into a metal claw nut.

Plastic everywhere for me, just a beech or ply bearer drilled, threaded and a drop of cyano to harden up the threads, no metal claw nuts.

[RottenRow]

I use these on my larger models (around 60” and above). This includes my Bowman Magister.

 

https://www.screwfix.com/p/cross-dowel-bolts-m6-x-50mm-50-pack/78664

 

They have a large flat heat that spreads the load, but can be turned down a bit if required to go into a recess (spin in a drill and hold a file against it). They are 50mm long but are threaded their entire length so can be shortened if necessary (put a nut on first, then cut off and file smooth).

 

Hex socket head so no slipped screwdriver.

 

Brian.

[martin collins 1]

Another Bowman Magister owner 😁 any pictures of said machine Brian? Are you interested in a spare cowl, we are having a batch made.

[RottenRow]

Martin,
 

I don’t have any photos on my phone I’m afraid and am away at the moment but can post a couple later in the week.

 

Mine is pretty old and really needs a refurbishment now, but flies well and has entered a couple of the BMFA Scale Flying Only competitions.

 

I have stiffened up the undercarriage somewhat by reducing the length of the torsion bar part of the piano wire legs (the part in contact with the wings). Ideally they need to be made from heavier gauge wire but I haven’t done that. As standard they spring back and forth too much.
 

I have a spare cowl already thanks, from another model that was broken up.

 

I am slowly building another, the same size as but not a Bowman as I couldn’t find one. This one is from the Hangar One plan, modified a bit.

 

 

Brian.

[Nigel R]

Nylon into tapped hardwood or ply every time, like Paul de t. Never an issue with stripped threads.

 

[Chris Walby]

I have a couple of models (IC) that have or used steel wing bolts, the first I changed back to nylon and the other I have to fit additional bands why?

 

Because steel wing bolts undo themselves! I tried sprung washers and even some very fancy (norlock) and even attaching washers to the screw heads so I could cable tie them. In the end it was just easier and far more reliable to use nylon screws.

 

One other thing and that is in the event of unfortunate incident the nylon screws will probably sheer off whereas the steel screws will certainly cause more damage to either the wing or fuselage or both.   

[Tim Flyer]

I always use plastic bolts threaded into metal inserts for wings and for cowls. Plastic bolts are very strong and less susceptible to loosen with vibration.

 

The reason some modellers may have trouble with plastic “threads wearing out” with metal threads,  is because the threads on blind nuts are often very badly cut.

 

This can normally be easily rectified by running a tap through them. Unfortunately threads cut in modelling hardware by some manufacturers is often of very low quality as many will testify. 
 

Metal wing bolts also can lead to a greater risk of damage from over tightening especially on delicate surfaces.