set screws to hold avionics bays?

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Buckeye

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I am working on a Wildman Blackhawk 38. My first fiberglass build - nice material to work with. Since this is a min diameter, I would like to keep protrusions to a minimum for aerodynamic performance. Instead of screws/nuts or removable rivets to hold the av-bay to the airframe (both of which have a head on them), I am considering set screws which can be screwed flush to the airframe. These screws only need to resist shear loads, so the lack of a clamp force should be OK?

To test the set screws, I drilled and tapped 8-32 threads to hold the nose cone. Seems fine to me and can work on av-bays also. The hex head can be covered with clay or tape to make smooth. Any body else use set screws?

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I have used ordinary 6-32 screws countersunk to be flush.
 
Countersinking is another good way to keep the airframe smooth but the set-screws should work. The pictures are 6-32 screws on a 4" airframe with a 1/16" wall thickness. With countersinking, smaller screws might have to be used on thinner airframes.
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I second the suggestion for countersinking. The problem with setscrews is they could vibrate either way (in or out) and you have no "stop" to keep them from overtravel.

Use a countersunk head that is small enough for your wall. I wouldn't suggest countersinking such that your countersink travels into the coupler as you may lose some strength there. May need to use a number of 2-56 or 4-40's instead of just a few 6-32's etc...

Mike
 
Have used set screws all the way up to a 6" P. No issues with the screws....

IMG_1142.jpg
 
I am working on a Wildman Blackhawk 38. My first fiberglass build - nice material to work with. Since this is a min diameter, I would like to keep protrusions to a minimum for aerodynamic performance. Instead of screws/nuts or removable rivets to hold the av-bay to the airframe (both of which have a head on them), I am considering set screws which can be screwed flush to the airframe. These screws only need to resist shear loads, so the lack of a clamp force should be OK?

To test the set screws, I drilled and tapped 8-32 threads to hold the nose cone. Seems fine to me and can work on av-bays also. The hex head can be covered with clay or tape to make smooth. Any body else use set screws?

View attachment 153243

This is a great idea for the smaller airframe size. I may use this for my 38mm min diam build. I am all for sure piece of mind when design and building, and steel beats plastic rivets or shear pins and for aerodynamics this will work nice. I like screw joints in my builds where unscheduled joint separation during flight is a very bad thing.
 
I've posted this before, but it's so handy, I'll post it again. The way I make these connections is with socket screws. These are available in a wide size range. The larger diameter of the socket part makes it very strong (relative to a smaller diameter screw shank or a set screw). Obviously, you have to drill a smaller hole that is deep enough for the whole socket screw and then a larger, concentric hole deep enough for the socket itself. Drilling the larger concentric hole is easy with a bit like the one shown.

Jim

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I've posted this before, but it's so handy, I'll post it again. The way I make these connections is with socket screws. These are available in a wide size range. The larger diameter of the socket part makes it very strong (relative to a smaller diameter screw shank or a set screw). Obviously, you have to drill a smaller hole that is deep enough for the whole socket screw and then a larger, concentric hole deep enough for the socket itself. Drilling the larger concentric hole is easy with a bit like the one shown.

Jim

What do you anchor the socket cap screw in? I like the 6/32 countersunk screws because you can just tap the airframe.
 
What do you anchor the socket cap screw in? I like the 6/32 countersunk screws because you can just tap the airframe.

I prefer to use plywood for my ebay caps (goes hand-in-hand with my high altitude deployment approach). I just drill a hole and screw in the socket screws. I've considered just using larger diameter set screw, which would accomplish the same results. My concern with it is that I think it would require an even thicker piece of plywood (although I can't say I know that for sure).

Jim

DSC04039.JPG
 
Dynacom used this method on all their kits. Fast ebay access and killer looks. You can even get the set screws that are center drilled to help with venting the bay. McMaster has many sizes along with the pem nuts available. SR
 
Dynacom used this method on all their kits. Fast ebay access and killer looks. You can even get the set screws that are center drilled to help with venting the bay. McMaster has many sizes along with the pem nuts available. SR



This is going to sound nutty to some but I use Grimracer Pro Radiobox tape. Its really 3M #5.. Very costly but works great.

I place two wraps around each area needing it.. game on!

Here is a link..

https://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMHP3&P=ML

so you know.. it has NEVER lit go..

Grimracer
 
The set screws and cap screw methods are pretty clean. If you want a completely clean alternative, you can do it by gluing in a coupler into one end, and then clamping your av-bay bulkheads around it using the threaded rods. Each bulkhead gets assembled from opposite ends of the tube.
 
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The set screws and cap screw methods are pretty clean. If you want a completely clean alternative, you can do it by gluing in a coupler into one end, and then clamping your av-bay bulkheads around it using the threaded rods. Each bulkhead gets assembled from opposite ends of the tube.

Now THAT is cool, add some magnetic switching and dun deal!
 
The set screws and cap screw methods are pretty clean. If you want a completely clean alternative, you can do it by gluing in a coupler into one end, and then clamping your av-bay bulkheads around it using the threaded rods. Each bulkhead gets assembled from opposite ends of the tube.

Correct. I know this is how you do the Raven Av-bays. I do the same on my larger diameter rockets where I can get my arm in the payload tube if needed. On this 38mm MD, I need to futz with aligning the sled/screw switch with a vent hole, so that is best done with the entire avbay in my hands, in my mind. Then I can affix the coupler to the payload tube with said set screws. Anyway, I wanted to try something new on this build.
 
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