2 Stage Minimum Diameter High Power How To?

I was thinking about 2 stage high power rockets and realized you can't do it like in low power where the motor serves as a coupler. How do you guys do it? some sort of outside coupler instead of inside coupler? Thats far from ideal, but I suppose it would work.

Of course if you are staging from a larger diameter to a smaller one then you can shove it all into the transition, but I am specifically talking same diameter to same diameter.

Lentamental said:

I was thinking about 2 stage high power rockets and realized you can't do it like in low power where the motor serves as a coupler. How do you guys do it? some sort of outside coupler instead of inside coupler? Thats far from ideal, but I suppose it would work.

Of course if you are staging from a larger diameter to a smaller one then you can shove it all into the transition, but I am specifically talking same diameter to same diameter.

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Every inside coupler has an outside coupler, doesn't it?

Seriously though....the two stagers I've built aren't minimum diameter, so they have a tube coupler that fits into the sustainer second stage .....only problem being you have to reach in further on the sustainer to get a hand on the hardware.....motor retention, etc.

What motor diameter are you looking at....?
Can it not accomodate a regular coupler like you would use for the altimeter/payload bay anyway?

But how can it fit into the sustainer, when the motor can't go up into the tube? The ridge on the motor prevents it from sliding up into the tube, and keeps it sticking out a quarter inch or so.

Do you have a photo?

What I would do in your case is use snap ring hardware to get the job done. Send your hardware to a machinest and have him set the integral thrust ring up on the casing. Then your casing is the coupler. Snap ring hardware is readily avalible from gorilla motor works.

Manny

Use a flush closure with Aerotech or Cessaroni motors and use the motor as the coupler. I'm not sure if flush closures are regularly offered or if they are custom, but I have seen a few people mention them on forums. Better yet, use a CTI tapered closure.

BsSmith said:

Use a flush closure with Aerotech or Cessaroni motors and use the motor as the coupler. I'm not sure if flush closures are regularly offered or if they are custom, but I have seen a few people mention them on forums. Better yet, use a CTI tapered closure.

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CTI tapered closures are not flush with the motor tube. There is still a lip for the motor to thrust against the end of the tube. The taper is to reduce base drag on MD applications. Flush closures are not offered by Aerotech or CTI. I have seen an example of getting them machined down, but it is probably easier to use a snap ring case and remove the thrust ring.

If you can find a Kosdon TRM case, they have no thrust ring at all.

G.D.

Flush closures for Aerotech style are commercially available from Rouse Tech and "legal".

The tapered closures from CTI vary. Check their drawings, as some 38 loads are available special with the tapered plastic and does not have a lip. The Pro29 closure is flush, so it will work. The Pro54 is NOT flush and has a lip.

-Ken

What about sleeves and rods? Integrate a small tube in each fin fillet of the upper stage, and a projecting rod in each fin fillet of the lower stage?

bjphoenix said:

What about sleeves and rods? Integrate a small tube in each fin fillet of the upper stage, and a projecting rod in each fin fillet of the lower stage?

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Do you think that would have enough rigidity? I have a feeling I'd need to use something pretty strong for the rods.

bjphoenix said:

What about sleeves and rods? Integrate a small tube in each fin fillet of the upper stage, and a projecting rod in each fin fillet of the lower stage?

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I had a similar idea as I was reading this. Use a built up fin and integrate a tube and pin into the fins themselves.

You can use the built up fins for your electrical ignition for the sustainer also.

Lentamental said:

Do you think that would have enough rigidity? I have a feeling I'd need to use something pretty strong for the rods.

Click to expand...

That's easy use drill rod.

gdiscenza said:

If you can find a Kosdon TRM case, they have no thrust ring at all.

G.D.

Click to expand...

not completely true, his newer 75mm cases had thrust rings, and even some of his newer 54mm did too.



Braden

If the upper stage is minimum diameter; where/how are you going to fit the staging electronics and battery?

How are you going to route the igniter wires to the upper-stage motor’s igniter?

Ask yourself this; has anybody ever built and flown a minimum dia. high power two stage rocket?

If so, then you need to find said person and pick his brain.

If not, then you have to ask yourself why that is.

Good questions but some are easy to answer.

boomtube said:

If the upper stage is minimum diameter; where/how are you going to fit the staging electronics and battery?

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Electronics somewhere forward of engine to provide good balance (Center of
gravity) and aft of the parachute. The E-bay will also house the timer or
altimeter triggered ejection charges.

boomtube said:

How are you going to route the igniter wires to the upper-stage motor’s igniter?

Click to expand...

Wiring conduit can be hidden in the root of a built up fin.

Motor with flush closure sticks out the rear of sustainer & is used as coupler to booster.

Engine block to hold motor in sustainer, friction fit or threaded plugged forward closure

Sustainer can bit lit with head end ignition. [through the forward closure]. Or with gecko cable. Flat ribbon wire that is attached to outside of motor case

Do like normal, except the interstage couple becomes the av-bay. Treat it like a NC and shearpin it on top of booster. House the electronics inside. Staging is best done with sustainer electronics.

This is Jim Jarvis minimum 98. Motor used for coupler. You can seen the gecko cable used for ignition under the tape on motor for friction fitting.

blackjack2564 said:

This is Jim Jarvis minimum 98. Motor used for coupler. You can seen the gecko cable used for ignition under the tape on motor for friction fitting.

Click to expand...

Actually, this particular rocket is not quite minimum diameter. The tubes are rolled on normal airframes, so they are slightly larger than normal. This is why I can use a CTI motor that has a thrust ring (although they could have removed it for me).

This particular design is somewhat complicated, but it does illustrate a lot of the issues with the minimum diameter two-stagers. I posted additional pictures here a while back.

https://www.rocketryforum.com/showthread.php?p=181334#post181334

The design is a lot easier if you're willing to let the booster be single deploy from the middle of the rocket rather than from the nose as in conventional dual deploy.

Jim

Thanks for all the intelligent ideas. For budgetary reasons I think I am going to back down (for the time being) from my 2 stage 54mm MD rocket idea, and go for mid power 2 stages. That being said, I will see what methods I can do to work on staging. The interstage coupler as electronics bay is a good habit to make.

On a similar note, do you guys know of good, cheep, small, simple, staging timers?

Perfect flight..... 35.00