Shoulder Length

[ssaner]

Does anyone have a theory on how long to make the shoulder of a nose cone or an adaptor that is intended to slide into a body tube, but come apart at ejection? In general, I'm pretty sure that as the body tube diameter increases, you will want the shoulder to be longer, but is there an optimal ratio such that things won't try to work loose or crooked during flight, but yet minimize weight and maximize space inside the tube for payload/recovery device?

Specifically, I'm working on a design for a 3in tube, but I'm interested in a general recommendation if anyone has one.

Thanks

Steve

 

[blackjack2564]

The general rule of thumb is: 1 to 1 1/2 calipers of the tube.

3in tube: shoulder should be 3 -3 1/2 in. minimum. This usually will eliminate chance of wobble.

As always there are exceptions for various applications.

 

[jadebox]

If you do need to reduce the weight or reduce the volume the nose cone takes up in the body tube, you can use a coupler glued to the bottom of the nose cone instead of a solid shoulder. I use this technique on a couple of my larger rockets to allow a couple of more inches of space in the body tube for the parachute.

-- Roger

 

[ssaner]

Thank you. The approx 1 caliber is kind of what I was assuming would be a good starting point.

Also good suggestion on the use of a coupler for a nose cone shoulder.

Steve

 

[jadebox]

Also good suggestion on the use of a coupler for a nose cone shoulder.

I've done that with nose cones made of foam covered with fiberglass. I glue a bulkhead in one end of a coupler and attach a screw eye to it. This assembly is then glued to the base of the nose cone.

I did it mainly because it was easier than forming a shoulder out of foam or some other material. But, it has the advantages I mentioned in the previous post.

-- Roger

 

[ssaner]

I agree. I have turned a few nose cones from balsa on a lathe. Probably the most difficult part of that is getting the shoulder right so that it fits nicely in the tube.

Steve

 

[brianc]

I agree. I have turned a few nose cones from balsa on a lathe. Probably the most difficult part of that is getting the shoulder right so that it fits nicely in the tube.

Put a slice of BT on the spindle with the balsa stock. Test fit without
removing the cone! Works good for drill press turning too.