2 stage to minimum diameter

Hi - can somebody steer me to a link that talks about how to construct an interstage coupler if the upper stage is a minimum diameter rocket (in my case the Madcow Tomach 54)? I've not build anything yet, but the more I draw ideas, the more I think it's just not going to work. Seems like the joint would likely collapse under boost.

Todd

Calling Jim jarvis...

Todd,
Did you think of an external coupler?

If I can make this work, you can make a Tomach 54 work: https://www.rocketryforum.com/showt...-2nd-Stage-Sustainer-Build-quot-and-More-quot.

dixontj93060 said:

If I can make this work, you can make a Tomach 54 work: https://www.rocketryforum.com/showthread.php?29769-Blackhawk-29-aka-2nd-Stage-Sustainer-Build-quot-and-More-quot.

Click to expand...

I am going to try to make my BH 38 a booster.

bzzh8c said:

Hi - can somebody steer me to a link that talks about how to construct an interstage coupler if the upper stage is a minimum diameter rocket (in my case the Madcow Tomach 54)? I've not build anything yet, but the more I draw ideas, the more I think it's just not going to work. Seems like the joint would likely collapse under boost.

Todd

Click to expand...

One way to do this is to use the motor as the coupler. The motor would extend perhaps 3 inches below the bottom of the sustainer. If it's minimum diameter to minimum diameter, then you'd have to use a motor without a thrust ring (an AMW motor is an example). One issue here is that it's helpful to have something inside the top of the booster to protect/cover the chute after the sustainer departs. If it's minimum diameter into something larger, then you could use motors with a thrust ring. in this case, the coupler would look something like a motor mount with the sustainer motor sitting down inside of the booster tube. Here, the coupler would be more like a nose cone, adapted to hold the sustainer motor.

Another issue to deal with is how to light the sustainer motor. If you want to do this conventionally (versus head-end ignition) then you can use a product called Taperwire and run the wire down the side of the motor.

If any of these ideas apeal to you, but you'd like to see some pictures, just let me know. I have lots of examples.

Jim

JimJarvis50 said:

then you'd have to use a motor without a thrust ring (an AMW motor is an example).

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Does aerotech supply flush closures? I think I remember rousetech making a custom one or maybe it was DIY and therefore not a certified motor?

Don't have a website, or any pictures for that matter.

But I turn ISC's out of aluminum. Just finished one for a good friend, to couple a 5.5" booster to a 4", 54mm powered sustainer. The ISC itself houses the booster electronics in that one.

I've also turned two ISC's for projects that staged 98mm MD boosters to 75mm MD sustainers. Sustainer motor retained in the sustainer with piece of all-thread to an internal retainer, also turned from aluminum, and positioned to leave several inches of motor sticking out the bottom. Using a MD type rear closure from Rouse-Tech, the motor seats into the machined receiver in the ISC. Booster electronics are right behind the ISC, and sustainer electronics are where they belong... In the sustainer.

Works quite well.

But it ain't cheap. :y:

Chrisn said:

Does aerotech supply flush closures? I think I remember rousetech making a custom one or maybe it was DIY and therefore not a certified motor?

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Yes, Rouse-Tech now makes a flush rear closure that's certified.

Hi cherokeej,

This rocket will use the bottom section of a 5.5" Madcow DX3 Massive as the booster
and the Madcow Tomach 54 as the 2nd stage. I like the idea of shifting the motor
mount in the 2nd stage a few inches. I can add a pound of lead shot to the nose cone to compensate.
How much would you estimate an iSC for a 5.5" to 54mm ISC with an exposed length of 6"cost?

Todd

PM sent.

Just reread this. An exposed length of 6"? How heavy do you want it to be? I was thinking more like ~1.5" to 2" exposed, with a relatively blunt shoulder angle, and about 3" of 54mm motor case held in the ISC.

Not worried about weight at all, since I'm not trying for 25000 feet or anything like that. As I thought about the ISC being machined out of a solid block of aluminum, you're right, a 6" exposed cone and shoulder could weigh 7-8 lbs, but that's alright.

I am still scratching my head on how the ISC is going to get a hold of the back end of the motor. Maybe a 2"-3" piece of motor mount tube slid on as a spacer (since I'd like to fly the Tomach 54 by itself w/o the motor hanging out). But even then I'd have to build it up till it was a bigger OD that the rear closure with the knurled grip. And I'd have to add probably a a full lb of lead shot to the front nose cone to compensate....

Man, this is a challenge. Has anyone heard of anybody successfully two staging to a minimum diameter before? Jarvis? Anyone? Bueller?

Wadsley and I did it at LDRS; A 76mm 10kNs booster to a 38mm 1.3kNs sustainer. Staging occurred around M2 and the sustainer made it to nearly M4.



The bottom 3" of the 38mm is seated in an aluminum interstage, which extends 3" into the 76mm motor case.

The booster recovery system is inside the motor case above the fwd bulkhead and below the interstage. We used head end ignition on the sustainer.

I'll have some better pictures when I get home tonight.

A while back, I posted some pictures around an interstage coupler that coupled a 4" minimum diameter sustainer to a slightly larger than minimum diameter 4" booster. The sustainer motor had a thrust ring (CTI 98 mm case), so I used a tube to build up the diameter to slightly larger than that thrust ring. This slides into the top of the booster tube. The thread with those pics is here.

https://www.rocketryforum.com/showthread.php?20300-B-Introduction-to-Staging-B

I'm currently working on a new 4" to 3" stage coupler. I'm in the process of coating it with high-temp epoxy (the brown tube is just to hold it during this process). The sustainer motor here is a 75mm AMW motor, and the wires on the motor are how I wire the motor ignitor and separation charge. The thrust ring on the AMW motor can be removed, so no buildup of the tube is required, and the motor just sits down inside the coupler.

For this particular motor, I've filled the thrust ring groove with epoxy, and the little holes you see are for shear pins. Some of you might be able to figure out why I'm doing that.

Jim

Landru said:

Wadsley and I did it at LDRS

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what

Where was I when that happened?

(maybe I was digging out Bare Necessities...)

CarVac said:

what

Where was I when that happened?

(maybe I was digging out Bare Necessities...)

Click to expand...

This was 5 years ago in Argonia. 2008 I believe.

Landru said:

This was 5 years ago in Argonia. 2008 I believe.

Click to expand...

Oh, not at Black Rock.

Landru said:

Wadsley and I did it at LDRS; A 76mm 10kNs booster to a 38mm 1.3kNs sustainer. Staging occurred around M2 and the sustainer made it to nearly M4.

Click to expand...

WOW!! What was apogee?

Cory said:

WOW!! What was apogee?

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Not sure, but simmed to 40Kft. Our parrot browned out igniting the sustainer and we never got data or deploy. The sustainer fence posted about 150' from the rail we launched from, with half the paint burned off.

This is our coupler setup. Probably not going to exactly work for your setup, but maybe it will give you some ideas. Also a little gratuitous Mach damage to the fins.

bzzh8c said:

Not worried about weight at all, since I'm not trying for 25000 feet or anything like that. As I thought about the ISC being machined out of a solid block of aluminum, you're right, a 6" exposed cone and shoulder could weigh 7-8 lbs, but that's alright.

I am still scratching my head on how the ISC is going to get a hold of the back end of the motor. Maybe a 2"-3" piece of motor mount tube slid on as a spacer (since I'd like to fly the Tomach 54 by itself w/o the motor hanging out). But even then I'd have to build it up till it was a bigger OD that the rear closure with the knurled grip. And I'd have to add probably a a full lb of lead shot to the front nose cone to compensate....

Man, this is a challenge. Has anyone heard of anybody successfully two staging to a minimum diameter before? Jarvis? Anyone? Bueller?

Click to expand...

First, forget the knurled rear closure with thrust ring. Not there. You will use a flush rear closure, no thrust ring. Thrust is transferred to the airframe thru the forward motor retainer. Basically, it's a bulkhead held inside the a/f with multiple radial screws, and the motor is screwed to that.

The ISC is a machined fit. The hole down the middle is ~3" deep, has a shoulder at the bottom, and receives the back end of the sustainer motor case. Looks a whole lot like the pics Jim and Landru posted.

As for flying single stage, move the internal retainer forward, and compensate with lengths of all-thread. Example... Single stage flight with long motor uses 1" piece of all-thread to anchor it to the motor retainer. Same case for two-stage configuration will use a 4" length of all-thread, leaving an extra 3" of motor to seat into the ISC.

Examples that used this type of coupling... The Google Team's 100K project that won the Carmack Prize. Same design, but I think their ISC was machined from Delrin.

There's another gent pretty much duplicating that project, only this time using a 98mm Mongoose and a 75mm Mongoose. And he has an aluminum ISC machined by yours truly, made from 6061 T-6.

And you don't want to over-compensate with nose weight until you check the CP/CG. Might not need as much nose weight as you think...

cherokeej said:

First, forget the knurled rear closure with thrust ring. Not there. You will use a flush rear closure, no thrust ring. ...

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Actually, this isn't quite the case. If you're going minimum diameter to something larger than minimum diameter, then you have more options. The easiest way is to use a motor that doesn't have a thrust ring. But, if that isn't in the cards, then you can slip essentially an airframe tube over the part of the motor that sticks out of the sustainer. In many cases, this airframe tube will have a larger diameter than the thrust ring, which allows that tube to slip into the coupler. The problem with this approach is that now you need an off-size tube to receive the airframe tube on the motor. If this isn't evident, imagine you want to make a 75mm to 54mm motor mount, but that the motor size is actually 60 mm. You'd need an off-size motor tube and centering rings, but it's easy to envision the modifications that would be needed. If you carve an adaptor - no problem - you just hollow out the size you need. Or, you can find the odd-sized tube. What i do there is just roll my own using the airframe sheath as a mandrel. Gives a very nice fit because it's custom matched.

When I do these types of rockets, I generally design the sustainer around a specific motor. This accounts for using a thrust ring motor, or not, and for slight differences in the diameters of the cases - which is important for a two-stage coupler. This doesn't mean the sustainer can't be flown on other motors, but it often locks in the type of case that will be used in the two stage configuration.

Jim

Absolutely. It's a custom machined fit, made to stage using one specific case, with no external thrust ring. If he wants to fly in single stage configuration, all he needs is an appropriate piece of all-thread, and he won't need the flush rear closure.

And Todd specified a 54MD sustainer. If he wants to make some sort of adapter to fit in there to hold a 38, or some other odd-ball size, I would think that do-able. Long as it's smaller than a 54.

The design I recently made for staging to a non-MD sustainer is different. Just finished one. Came out pretty sweet. The ISC contains an av bay for booster electronix, all 6061 with a G10 sled, and couples a 5.5" PR booster to a 98mm PR a/f with a 54mm mount, rear c/r set forward against the fin tabs to receive the coupler. During boost, sustainer mass is supported by the front of the coupler tube against that c/r. If that c/r is square, the sustainer will be square under G's. And 1" of the rear of the a/f is captured inside the front of the transition. With some 3.5" of coupler tube inside the sustainer a/f, and 1" of the a/f captured by the front of the transition, it should be held pretty straight. And we've tried it with his airframes. What can I say? It's custom machined. Fits like a Trojan. :blush:

It'll work. :wink:

An example of one of mine is below (from Gerald). This is a sleave over the CTI 98mm motor. The sleave is slightly larger than the thrust ring, so for this, you'd just need an interstage coupler sized to accept the sleave.

And by the way, if you were designing for this motor, you would need to leave space for the nozzle, which extends beyond the end of the case.

Jim