Modular construction

I am trying to put together a modular MPR and L1 HPR system to stop my incessant "build a dedicated prototype to test things" methodology.

Given that I have three sections of a rocket (motor/fin can, airframe, and payload/NC), does anyone have a recommendation on how to join these sections for flight but still allow the bird to separate at any coupling point for a later flight?

For instance, if I want a rear separation configuration, how might I join the airframe to the payload/NC section for that flight, then be able to do a standard NC eject later on?

I have thought about screws through the body tube-couplers but am concerned about shearing plastic screws or distorting the mounting holes using metal screws.

Right now I am using lightweight fiberglassed or plain BT-80 as the base airframe material.


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Friction fit of course. Some people even add little screws. External tape.

Pardon the tech post!


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Jerry Irvine

plastic rivets (PML)..?

-- Paul. =================================== Expect the worst, hope for the best..... That way dissapointment is easier to handle!! ===================================

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Engine or electronic ejection?

For electronic:

Friction fit... and not even much of that... IF the center section contained payload and recovery gear. Both ends of center section have attach points, as do connection ends of other 2 pieces. No matter which way you mount the center section, you attach the other end of the laundry to one, and a short retainer strap to the other. You would then be able to just flip the center section, and attach the shock lines, depending on which way you want the laundry to exit. You would have to mount and secure the payload for shock and thrust from either direction, and have some kind of access to get inside the center section for payload maintenance.

For engine ejection, or nose-based electronics ejection:

Do basically the same, except cut ejection gas vent hole(s) in the bulkheads of both ends of the center section, so that ejection pressure may be piped to the desired laundry cannon. You might even install a(some) tube(s) between the vent holes to contain and direct the disbursement of gas. And use a tighter friction fit on the couple you don't want to open. All the connecting links would be the same as above.

I have seen all of these methods used.

~Duane Phillips.

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Duane Phillips

I use 3/8" #2 sheetmetal screws. In most cases, the couplers have a small bits of strip wood glued into them to strengthen the coupler and also provide a solid anchor point for the screws. I do this on all my couplers and bulkhead assemblies, and it works very well.

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I'd use small machine screws with the corresponding nut or T-nut epoxied or CA'd on the inside of the coupler. Everyone will have a slightly different suggestion, so in the end do what you think will work best. If you crash & burn, then you learned something!

-- Joe Michel NAR 82797 L1

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J.A. Michel

Thanks for the tips, all.

My current plans are for engine ejection.

I'm concerned about friction fit between fin can and airframe for the nose eject configuration. Never know when you'll get bonus ejection charges. I like positive locks, latches, and retainers; its a control freak thing. ;)

The internal gas piping dual bulkheads sounds promising, MUST play around with that.

Ray, do you reinforce the body tube holes at all? Just wondering if you have a problem with sharp screw threads and enlongated holes. 2,3,4 screws?

Thanks, again.

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I just soak the holes with a bit of thin CA to reinforce it. Works fine. I use

4 screws on each side of the joint. Or you can skip the screws completely and just wrap the joint with a layer of vinyl electrical tape.
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