18mm Minimum Diameter / Two Stage Motor Retention

Two models in my stack are the Estes Yankee and Long Tom (instructions linked).

The Yankee is an 18mm MD rocket, and uses masking tape for friction-fit motor retention. Frankly, I don't like this. I know it proabably works just fine, but I was hoping one of you would know a more positive method of retention. I was thinking of just mounting the motor hook in the body tube.

The Long Tom is not a MD model, but as the two motors are placed flush with each other, again no motor hooks are used. Again, I'm looking for better retention suggestions. I could probably work a hook into the booster stage, but the entry end of a hook won't fit in the sustainer.

Thanks

I oppose friction fit motors more than anyone else I know, but I would probably still be doing it in this case.

zanfar said:

The Long Tom is not a MD model, but as the two motors are placed flush with each other, again no motor hooks are used. Again, I'm looking for better retention suggestions. I could probably work a hook into the booster stage, but the entry end of a hook won't fit in the sustainer.

Thanks

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I used a Rocketarium 18mm retainer on my Long Tom. You will need to slightly adjust the sustainer MM forward if you go this route. I decided to use this retainer because I can also fly the Long Tom single stage with 18/20 RMS.

https://www.rocketarium.com/Build/Motor-Retainers/18-mm

sl98 said:

I used a Rocketarium 18mm retainer on my Long Tom. You will need to slightly adjust the sustainer MM forward if you go this route. I decided to use this retainer because I can also fly the Long Tom single stage with 18/20 RMS.

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Thanks, that plus a few standard motor hooks might be exactly what I need. How much space between a booster and sustainer motor can you have before stage ignition becomes a problem?

zanfar said:

Thanks, that plus a few standard motor hooks might be exactly what I need. How much space between a booster and sustainer motor can you have before stage ignition becomes a problem?

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Up to 10 inches with a high probability of ignition (iirc). I have 8.5 inches of space between booster and sustainer motors on my SA-3 Goa scratch build, using two ports to reduce the pressure. It D12-0 to D12-3 no problems with ignition. Its a variant of Passport Staging or Air Gap Staging.
I also prefer not friction fitting motors unless necessary, however when thats the only available method I will put tape tabs between the fins, and down over the section of motor sticking out of the body tube, between the friction fit and the tape the motors don't come out.

There is absolutely nothing wrong with friction fitting the motors. I have a five C6-5 cluster rocket that I tape each motor in. Just isn't room for anything else. Never had a motor even shift, and they can still be pulled out. Yea some might be a bit tight, but not so tight it's stuck. Wooden dowels make great motor ejectors.

With a 18mm min dia it will just complicate things and add weight. Check out the two stage red max I did from the sport rocketry magazine. Not min dia but the retention is great and the design uses techniques that make sense. Der Zwie Dekker Red Max, or even the newst double D Red Max both are built the same just different motor mounts.

What is your plan to couple the booster to the sustainer? Are you using the motor case as the coupler? Will have to plan for that and the safe recovery of the booster. Specially if it is long enough to stabilize and lawn dart. Most boosters are short for that reason they tumble.

Two stage is fun and challenging. Especially with BP. Not knowing if the rocket will stage is nerve racking and when it does it is always a thrill!

See ya,
Rod

Open rocket is your friend for this project, you can work out all the details before you start building.

RodRocket said:

There is absolutely nothing wrong with friction fitting the motors.

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I realize that, as I said in my first post, I just subjectively prefer positive retention.

RodRocket said:

With a 18mm min dia it will just complicate things and add weight. Check out the two stage red max I did from the sport rocketry magazine.

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Thanks, I'll look that up. Not worried about adding weight. I know MD usually implies a performance build, but this just happens to be how Estes designed the rockets.

RodRocket said:

What is your plan to couple the booster to the sustainer?

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The Long Tom (2-stage) isn't MD, it has an "Estes standard" motor mount assembly in both the booster and sustainer. A BT-55 coupler joins the two. So in this case I have a lot of leeway with the design.

Tape has always worked fine for me on MD 18mm rockets. I don't think the ejection charge on the A/B/C motors is powerful enough to disengage the motor from its mount on most rockets of that size.

Give me a few days to work up an openrocket file. Thought about this rocket last night while on the road and think I have an idea on how it might work.

Give me till after weekend. One part of the design will take some tinkering on openrocket.

The idea would be able to launch the two stage on a two motor cluster. One motor is a booster other is standard with delay and ejection. Booster motor mount is actually a stuffer tube ran up to a transition, standard motor mount is done usual way.

Transition becomes nosecone of booster and an internal "funnel" will get booster gasses to light sustainer motor. Booster will have the usual recovery system.

Booster behaves just like any other rocket. Transition has an inside cone and tubing to direct gasses to sustainer motor through a sealed system.

As long as both motors are same ie, C6-5 it might work.

The transition will be the hardest part of the design. Funnel inside transition will be sort of angled to make up for the offset of the booster motor in the cluster. Stuffer tube will seal against the funnel to try and get as much of the gasses to the sustainer motor.

Transition also would have an outside coupler to fit outside the body tube of the sustainer. You would simply slide rocket into a coupler with slots for the fins.

Gotta go for now.

Interesting project!

See ya,
Rod

Couple questions,

Are you planning to keep the Long Tom two stage? Or just use it single as the booster for the Yankee?

Edit--- saw that it is bt-55

I am thinking a wood transition from balsa machine might make the transition/coupler easier. I think balsa machine might have tubing to make the coupler on the transition for the Yankee but will need to dig into their tubing list with measurments.

Did up a quick file to better explain the idea. No rings, no fins

Normally I would have each kit part and measure to get file parts correct.

Remember transition is serving two functions, nose cone for booster and coupler for Yankee.

Had to tinker around with the file parts to get them to do what I wanted but this is the Long Tom booster. Just guessed a length for body tube.

You can do a two motor cluster and then add the inner stuffer tube, but I don't know if you can have two different motors like you would need here. This file is how I would try to build it, just getting openrocket to accept it is the challenge.

You could use standard retainer hooks on all three motors, the Yankee would be done just like the Hi-Flier.

Don't know if openrocket will let this two stage work, but with more tinkering it might be able to work.

Might just work on it some more when I get time.

Both booster motors start, when one motor reaches the delay the other starts the Yankee motor. Yankee starts while booster stage coasts during delay, Yankee separates from booster, booster coasts then deploys chute.

Trick would be to keep the booster together when Yankee motor starts.

If you build this you gotta do a build thread and launch video.

Neat project!

View attachment yankee-longtom.ork

The setup you are using for the motors will not allow any coasting as the C6-0 will immediately ignite the upper stage when it burns through. I'm not sure how the reliability will be affected by having the booster motor gases/particles go around a deflection to enter the upper stage motor the more direct the path between the motors the better. Make sure to add a couple of pressure relief ports into the area directly below the upper stage motor so that when the booster motor burns through it doesn't pressurize the stuffer tube and pop the Yankee off before it ignites. I used a similar method on my SA-3 Goa except my booster was one D12-0 and two C6-3s with two additional tubes for rear deploying parachutes, the staging works great, but both ejection charges going off at the same time ruptured the D12-0s stuffer tube on the second flight.

There are two different motors in the cluster. Booster motor for the stuffer tube, and regular coast, ejection charge motor on other side.

The stuffer tubes job is to get those gasses from the booster motor in the cluster to the yankee motor through the transition.

As I was building it, questions kept coming up about getting gasses to Yankee motor and keeping the two stages from popping apart. There would have to be some sort of funnel carved through the transition to direct gasses to the yankee motor. Hopefully the two cluster motors work together and as the clusters booster motor starts the yankee motor, the other motor is in the coast phase and is along for the ride until the yankee starts and separates and then other cluster motor ejection charge fires.

This project just might make it onto my to build list.

zanfar,

what were you thinking about trying. Wasn't trying to take over your thread. You just brought up such an interesting design thought that I had to run with it since I couldn't quit thinking about it.