Staging different-size BP motors (e.g., 24mm -> 18mm)

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neil_w

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How do you do it exactly? When staging like to like, you tape them together and everything works. How do you "connect" a larger booster to a smaller sustainer, and have the gasses ducted correctly? Must be some obvious way to do it, but not obvious to me.

I'm bouncing around ideas for a 24mm -> 18mm 2 stager, and it would seem useful to understand this detail. :)
 

Gary Byrum

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I've been told many times it's been done, although I've never done it. I suppose you'd prolly do it like I do staging motors. I never tape. I've always used the "pop-n-go" method. Just let the friction of the coupler hold things together. Gasses can escape between the motors and the fire goes up inside the sustainer motor. Works like a charm for me every time.
 

blackbrandt

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Look in the handbook of model rocketry. I've helped lead a rocketry camp for 3 different weeks now, and every 2 stage rocket I've seen has used the gap staging method. Leave a bit of space between the motors (up to about a foot) and put some pinholes through the booster tube above the motor. Essentially, you are venting the hot gasses so the flaming particles (which have enough heat energy to light the motor) can get to the upper stage before it gets blown off. :)

Lemme know if you have any more questions.
 

BEC

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Heck, the currently available Estes ARF models (LGM-0095, Red Rider, Firestorm, Helios, Flying Colors, etc.) with their accessory boosters (Booster-55, Booster-60) are 24mm to 18mm staging models. The stack is gap staged though the gap is not far. Also, if using a C11-0 rather than D12-0 in the booster, some vents in the interstage are recommended so that the sustainer lights before the model stages. The fit between the booster and the "stager" that is used to retain the sustainer motor is pretty loose on these models.
 

kjohnson

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Posts passed in the intertubes. :)

If the design calls for the motors to be touching, an Estes 18mm motor fits inside the end of a 24mm booster motor.

kj
 

neil_w

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24 mm --> 18 mm works just fine because the casings nest into each other. Overlap them by ~1/16" and tape with cellophane as best as you can. I had more difficulty with 29 mm --> 24 mm, but I think I finally figured it out. You can read about the saga here (post #33 is the "solution"): https://www.rocketryforum.com/showthread.php?128250-Magnum-II/page2&highlight=magnum+II
Ah, now that is a magical bit of insight. Seems like it's either that or just gap stage it. Your 29 -> 24 solution seems pretty slick too, but I would be happy to not need to do that when going 24 -> 18.

I am having second thoughts about actually doing 24->18, considering whether I would have any chance of getting the rocket back, but I suppose that even having something like a C11 in the booster will help it jump off the pad a bit more reliably vs. a C6. Will have to see if I come up with a design I like that is heavy and/or draggy enough to justify the 24mm booster.
 

BDB

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Ah, now that is a magical bit of insight. Seems like it's either that or just gap stage it. Your 29 -> 24 solution seems pretty slick too, but I would be happy to not need to do that when going 24 -> 18.

I am having second thoughts about actually doing 24->18, considering whether I would have any chance of getting the rocket back, but I suppose that even having something like a C11 in the booster will help it jump off the pad a bit more reliably vs. a C6. Will have to see if I come up with a design I like that is heavy and/or draggy enough to justify the 24mm booster.
I've had good luck with C11 boosters. They get it off the pad quickly but also burn out quickly. The staging event happens really low. But then again, there really is no substitute for the D12--IMHO the best motor that Estes has ever made!

Just go for it. I think staging 24 mm --> 18 mm might actually be easier than 18 --> 18.

My next LPR challenge will be staging a 3 x 18 mm cluster to a single 18 mm sustainer. I think that should be sufficient complexity to induce anxiety on launch day.
 

BDB

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And I'm sure that John Beans could help you assure safe recovery. That's my plan for the RIMRA launch this weekend.
 

Micromeister

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Posts passed in the intertubes. :)

If the design calls for the motors to be touching, an Estes 18mm motor fits inside the end of a 24mm booster motor.

kj
Exactly: As a matter of fact: 18mm fit inside 24mm motors and 13mm motors fit exactly inside 18mm motors.
I've flown my Magnum for years using D12-0, 24mm boosters to 18mm B6 and C6 motors. without any tape. They simply touch. nothing else is required.

I also fly a 2 and 3 staged UFO. a pair of stacked Stitches with a D12-0 to a C6-0. then I added a third stage a mini mars lander with a 13mm A3-4T motor. All three snuggly fit inside the next Stacked 24mm, 18mm, 13mm. Easy as it can be, Works every time.

069a2-sm_Magnum Goes Loadly 2-Stage_05-17-06.jpg


069b-sm_Magnum Goes Loadly_PhiBetaCatta payload_05-15-06.jpg


NL-12a1-sm_McCoy's Nite Launch Vehicles_09-22-07.JPG


NL-12a2-sm_McCoy's Nite Launch Vehicles_09-22-07.JPG
 

neil_w

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Great pics as always, Micro! That saucer + Mars lander must be a hoot to launch...
 

GlenP

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Vintage Centuri Russian SAM-3 used a D size 24 mm booster with an 18 mm sustainer, check out the instructions here:
https://www.oldrocketplans.com/centuri/cen5355/cen5355.htm
I have fond memories of watching that one fly out of sight to who knows where it is now.

I have made a gap staged 18mm to 13mm with about a 10 inch gap between them and vent holes just below the sustainer nozzle, it is a modified Centuri Excalibur, from SEMROC, split at the transition.

Has anyone staged 24, 18, or 13 mm A, B, C, D low power motors to Micro motors?
 
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BABAR

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No need for tape. If you put the sustainer engine just in front of the booster engine, gap of around 1/8 to say 1/2 inch, with plenty of venting around it, you should be fine. If you gap more than that you will need a tube or chimney to guide the gases forward from booster to sustainer, AND you will need vent holes in the top of that tube to allow the cool gases in the tube "pre-booster burnout" to vacate and allow the hot flaming gases to get to the sustainer engine. If you are going down a level (say D12 to A8), easy to just put a BT-20 with centering rings just in front of your D12 in the BT-50. The BT-20 with the centering rings will act as an engine block for the D12.

The guide tube can be the same diameter as the upper stage sustainer, in which case you just "nest" the sustainer engine in the guide tube above the vent holes. Of you can run the guide tube up inside a larger outer tube (say the same BT-50) and your sustainer engine can be the same size as your Booster. In this case I call the internal guide tube a "chimney."
This I think is more reliable when using long gaps.
These are some examples, not necessarily using smaller engines, but you get the idea.

https://www.rocketryforum.com/showt...Gap-Staging-15-25-inches!&highlight=gap+stage

https://www.rocketryforum.com/showt...ot-gap-stage-Paint-Scheme&highlight=gap+stage

https://www.rocketryforum.com/showt...ged-2-successful-flights!&highlight=gap+stage
 

grapetang

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Vintage Centuri Russian SAM-3 used a D size 24 mm booster with an 18 mm sustainer, check out the instructions here:
https://www.oldrocketplans.com/centuri/cen5355/cen5355.htm
I have fond memories of watching that one fly out of sight to who knows where it is now.

I have made a gap staged 18mm to 13mm with about a 10 inch gap between them and vent holes just below the sustainer nozzle, it is a modified Centuri Excalibur, from SEMROC, split at the transition.
Cool link, thanks! On the Excalibur, how did you recover the booster so it doesn't go ballistic?
 

GlenP

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Cool link, thanks! On the Excalibur, how did you recover the booster so it doesn't go ballistic?
The sustainer keeps the transition with it, it is cardstock, and there is some space between the vented booster coupler, that goes over the sustainer motor mount, and the transition where I pack in a streamer that is attached to the booster. The streamer is rigged by shroud lines in an upside down Y shape to suspend the booster horizontally in a higher drag configuration to compensate for the relatively small streamer that I can fit in there. Recovered it with no damage.

I don't have a picture of the inner workings, but you can see a picture of it here with its little and big brothers.
https://www.rocketryforum.com/showthread.php?27235-Centuri-Excalibur-Gallery&p=1601168#post1601168
 
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scsager

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How do you do it exactly? When staging like to like, you tape them together and everything works. How do you "connect" a larger booster to a smaller sustainer, and have the gasses ducted correctly? Must be some obvious way to do it, but not obvious to me.

I'm bouncing around ideas for a 24mm -> 18mm 2 stager, and it would seem useful to understand this detail. :)
This is an easy to learn skill. The quickest easiest way to learn more about it is to buy this kit >> https://www.estesrockets.com/rockets/kits/skill-3/007245-comanche-3tm
 

grapetang

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The sustainer keeps the transition with it, it is cardstock, and there is some space between the vented booster coupler, that goes over the sustainer motor mount, and the transition where I pack in a streamer that is attached to the booster. The streamer is rigged by shroud lines in an upside down Y shape to suspend the booster horizontally in a higher drag configuration to compensate for the relatively small streamer that I can fit in there. Recovered it with no damage.

I don't have a picture of the inner workings, but you can see a picture of it here with its little and big brothers.
https://www.rocketryforum.com/showthread.php?27235-Centuri-Excalibur-Gallery&p=1601168#post1601168
Nice! Thanks! :)
 

GlenP

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excalibur3_2.jpg
This was earlier this past year, may be the only one of its kind: an Excalibur 3. I tried to capture a video of it, but I lost the rocket as it quickly went out of frame and you could not see it staging, but you could hear the distinct three engines ignite: C6-0 to B6-0 to A10-4T.
 
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