Using bolts to mount nose coupler??

[emlang93]

First, I apologize if this was already answered in the past, my search turned up no results.

I am currently working on my level 3 rocket build and am facing a few design issues. I have always seen people secure the nose coupler to the nose cone with epoxy. I would like to use 4/40 or 6/32 Button head SS bolts so that I can easily disassemble the nose to add weight, add transmitters, etc.
The rocket is a Mad Cow Mania but I have modified it to a 98mm min diameter.
I am curious to see if anyone has had bad results with mixing bolts and fiberglass. If you have done it and had success what did you do?

I understand that having exterior bolts will affect the air flow and drag of the rocket. To minimize this I will use the smallest button heads I feel are strong enough to take the loads.

Thanks in advance for your help!

 

[FredA]

I do this all the time....no problems.
Just drill the proper hole size and tap.

Another thought if you don't want something in the airstream - use set-screws and to disassemble either remove completely or screw in till they clear.

 

[Worsaer]

I often use PEM nuts in fiberglass, with stainless machine screws to join airframe sections.

 

[smarra01]

The below link will take you to where I have documented my Ultimate
Wildman Punisher build. If you scroll down in the link you will see how I did mine.

I used 1/4-20 bolts that are screwed into t-nuts that where epoxied in.
I didn't mind the extra weight up front.

https://www.radrocketeers.org/forums/viewtopic.php?f=11&t=1630&start=30

 

[markkoelsch]

I often use PEM nuts in fiberglass, with stainless machine screws to join airframe sections.

+1 to pem nuts.

 

[emlang93]

Thank you for all the help everyone. I will look into PEM nuts and the setscrew idea. I was not sure about tapping a laminate such as fiberglass but from the conversation here it looks okay.

 

[cherokeej]

if you use set screws, the only strength you have is the shear strength of the material the screws penetrate. No "clamping" action there. I've got something that might interest the OP, but I need to get the pix out of the camera.

 

[Tim51]

I understand that having exterior bolts will affect the air flow and drag of the rocket.

Why not use countersunk hex socket head screws?

 

[cherokeej]

Well, I've tried twice. Even resized the pix. This thing won't let them upload.

Good luck with your project.

 

[FredA]

Why not use countersunk hex socket head screws

On thin-walled FG...is there any meat left behind the countersink to provide any strength?
Would seem to be very thin.
I know the forces are sheer forces, but you asking for elongation of the holes if they are super thin.

As far as my usage with screws threaded directly into FG.
We've treated some rockets using this method pretty badly and we've bent the 6-32 screws before they came out.
Adding PemNuts or T-Nuts are a lot more work then it is worth.
Drilling holes thought both parts and tapping eliminates all alignment fuss and is all you need plus it takes less than a minute.

 

[degreaser]

Consider using removable nylon rivets. PML has them listed on their hardware page:

https://publicmissiles.com/product/hardware

Amazon has some too:

https://www.amazon.com/dp/B008MP06SG/?tag=skimlinks_replacement-20

They come in various diameters and lengths. McMaster has a wide selection but they are a little difficult to find. Search for "standard nylon rivets", then click on the "Push In" type. Then examine the "Click Lock Shank" type.

https://www.mcmaster.com/#standard-nylon-rivets/=16mhk4d

 

[emlang93]

That is okay. Thank you for trying and thanks for the luck! Really hopping I can get this thing done in a week.

 

[emlang93]

I agree that most of the load is all shear load. Also, if I use 3 screws the odds of all 3 getting striped in one flight are slim, I am guessing.
I agree that countersinking probably wont work even with 100 degree flat heads. Only a 2mm thick airframe so you risk the integrity making it thinner. Great idea for a metal rocket though!

Next thing I am thinking about, if I use exterior truss or button heads, is the turbulence from the heads impacting the fin stability. Would it be best to offset the screws from the fins? Much like wake turbulence when flying behind a jet liner, the turbulent flow would make the Cp change and fins unstable? Is this logic right?

All of this information is great. Feel like I went for no clue to tons of options over night. Now I see why this forum is here. Haha

 

[Steve Shannon]

Why make the coupler removable instead of epoxying in the coupler and making the bulkhead at the bottom of the coupler removable?

 

[emlang93]

Good point Steve. The Reason I am making everything removable is mainly so I can modify the rocket any way I want in the future. I am trying to build a rocket that can fly on J to N so by allowing flexibility I can add and remove parts as needed.

 

[Steve Shannon]

Good point Steve. The Reason I am making everything removable is mainly so I can modify the rocket any way I want in the future. I am trying to build a rocket that can fly on J to N so by allowing flexibility I can add and remove parts as needed.

If you put some kind of shoulder with tee nuts inside the nosecone (or a central threaded rod) you should be able to insert the coupler and have it held in place by the bulkplate. The shoulder would not be removed, but you wouldn't be losing much flexibility.

 

[emlang93]

Steve, That gives me an idea. What if I used threaded rod up to the metal tip? The tip has a 1/4-20 thread and I could use that to hold it all togther through the nose bulkhead plate.

 

[FredA]

tip has a 1/4-20 thread and I could use that to hold it all togther through the nose bulkhead plate.

This is how I typically build my NC's.
The far side of the bulkhead is held with an eye-nut that allows easy attachment of the harness.

However if you don't affix the coupler to the NC, it might continue to move further and further into the NC and the whole assembly might become loose.
Not sure since I've never tried it without a fixed coupler.

 

[manixFan]

Steve, That gives me an idea. What if I used threaded rod up to the metal tip? The tip has a 1/4-20 thread and I could use that to hold it all togther through the nose bulkhead plate.

Like Fred that's how I build my nosecones. I then make a sled with a piece of 1/4" brass tubing to hold my tracker or nose weight if needed and keep it in place with extra nuts. On a few rockets where I did not want extra weight I used aluminum rod instead. It works very well.

I used to use wing-nuts to hold the bulkhead in place but that created an issue when the shock cord snagged on it. So I just use lock washers and regular nuts, with a big fender washer up against the bulk head to spread out the load. I also use a lock washer at the tip to make sure the rod does not somehow unscrew. The only issue I've run into is with holes for shear pins through the coupler. They did not line up the next time I put the nose cone together since I had tightened the nut extra tight and the shoulder moved up into the nosecone a bit. So now I clean up the interior of the nose cone so the shoulder stops reliably or I'll epoxy a very short piece of coupler into the nose cone to act as a stop.

Good luck,


Tony

 

[FredA]

The only issue I've run into is with holes for shear pins through the coupler. They did not line up the next time

I just drill new holes.
Had one NC with about 25 sets of holes....Swiss cheese....still held like a champ.
Would be somewhat a "badge of honor" if it fell apart due to too many holes because it lasted "too many" flights.....

 

[cherokeej]

I guess they fixed it.

Similar problem with a project for a friend. Needs radio gear in the nose of an otherwise all carbon bird, with the antennae up top, where it's not a Faraday cage. But with the large mass, a hard hit could shear attachment. This is one solution. I machined collars to epoxy inside the coupler, and the bulkheads to fit the collars. Countersunk 6-32 stainless flatheads provide shear force as well as clamping force to hold everything together. This coupler will be glued into the n/c, but the sled and both bulkheads come out as an assembly. Add or remove payload mass as needed.

 

[Steve Shannon]

Steve, That gives me an idea. What if I used threaded rod up to the metal tip? The tip has a 1/4-20 thread and I could use that to hold it all togther through the nose bulkhead plate.

Fred, Tony, and CherokeeJ have already answered with better experience than I could. Go for it!


Steve Shannon

 

[NateLowrie]

On my formula 200, I am using 6 #8-32 button head cap screws with PEM nuts to hold the coupler to the nosecone. One could get by with 3 though. Use Grade 8 bolts and nuts and make sure the mating holes on the outer airframe are drilled to close tolerance.
Also, I have used this method to pin the Av-Bay to the fin can on numerous rockets.

 

[Handeman]

I epoxy a small piece of Oak in the coupler and use SST #8 round head sheet metal screws to hold the nose cone and coupler together. There is a small screw head on the surface of the nose cone, but this isn't a MD mach buster looking for altitude records. You could use the pem nuts and machine screw just as well. I just like the oak pieces and sheet metal screws because I have plenty of them and they are a zero cost solution, other then the epoxy.

 

[FerdBerful]

Instead of using bolts from the outside, I've used a thick plywood ring glued into the inside of
the shoulder. (I always use AeroPoxy. I haven't had problems with this coming loose.)





The "real" bulkhead slips over the bolts and is secured with wing nuts:



Sorry it's so recessed in the picture. This is a Nike nose cone which is big
compared to the body space. So to have more room for recovery stuff, I use some
of the nose cone's space.

 

[ksaves2]

On small stuff like 29 and 38mm I use PEM nuts in the coupler and buttonhead socket screws on the nosecone shroud. The bulkheads are too thin to screw in and the
nosecone shroud wall thickness is too thin in my estimation to support countersunk screws without a strength penalty. I keep repeating, "It's only a hobby, It's only a hobby, It's only a hobby." Yeah a slight drag penalty but the MD rockets still fly pretty darned straight and high.

Of course with larger, thicker material, countersunk screws are o.k. and look nicer. Kurt

 

[FerdBerful]

I guess they fixed it.

Similar problem with a project for a friend. Needs radio gear in the nose of an otherwise all carbon bird, with the antennae up top, where it's not a Faraday cage. But with the large mass, a hard hit could shear attachment. This is one solution. I machined collars to epoxy inside the coupler, and the bulkheads to fit the collars. Countersunk 6-32 stainless flatheads provide shear force as well as clamping force to hold everything together. This coupler will be glued into the n/c, but the sled and both bulkheads come out as an assembly. Add or remove payload mass as needed.

View attachment 313769 View attachment 313770 View attachment 313772 View attachment 313771

SWEET hardware!

 

[Steve Shannon]

Instead of using bolts from the outside, I've used a thick plywood ring glued into the inside of
the shoulder. (I always use AeroPoxy. I haven't had problems with this coming loose.)


View attachment 314172


The "real" bulkhead slips over the bolts and is secured with wing nuts:

View attachment 314174

Sorry it's so recessed in the picture. This is a Nike nose cone which is big
compared to the body space so to have more room for recovery stuff, I use some
of the nose cone's space.

That's exactly what I was trying to describe. Thanks!


Steve Shannon

 

[ksaves2]

Whoa Steve, Thanks for posting that. I've done two nosecones like that in four inch diameter with a thick ring like you. I used Cotronics 4525IP to secure
blind nuts on the back side of the ring so I can attach the bulkhead. I didn't use the center all-thread though. Haven't flown them yet. Kurt

 

[FerdBerful]

Whoa Steve, Thanks for posting that. I've done two nosecones like that in four inch diameter with a thick ring like you. I used Cotronics 4525IP to secure
blind nuts on the back side of the ring so I can attach the bulkhead. I didn't use the center all-thread though. Haven't flown them yet. Kurt

Not that it's better, just different, this is how I've done the bolts in the plywood.
This is the back (towards the nc tip). In this case, they are 10-24 machine screws.
I drilled the holes with a #25 bit and then tapped them and then used AeroPoxy
to secure them (Why all that? See my sig ):



Here's what the front looks like:



BTW this is my L3 cert rocket. (That's why I have the pix handy.) It's being built even as
we speak. With any luck (skill?) it'll be ready for Black Rock this summer.