Boosters Not Igniting Another Motor

[altertalk]

Hi,

I am in the process of building the Estes "Geo Sat LV", which has a core with an 18mm motor (up to C) and two fully attached inert boosters. I want to make these boosters live with up to a 24mm motor (D or higher). The question is what to use. I could attach the booster nose with glue and expect a D12-0 to simply burn out but I'd be concerned about it catching the internal booster tube on fire. I could attach the booster nose cones with a small ejection cord, but I'd be concerned about charring on the side of the core. Then there's putting in a side panel that would simply divert the gases out the side of the booster. Has anyone reconfigured a model so that the inert boosters can be live? And if so, what did you do?

 

[teepot]

I put vents in the tubes of the side boosters about half way up the tube. At first I had the vents by the fins. But the fins got scorched so I moved the vents up.

 

[BABAR]

Cool idea.

gonna put a ton of weight on the tail end, may need some nose weight or bigger fins.

easiest solution is to eject the 24 mm motors. IMO it is perfectly safe as long as fire conditions are low, and I’ve been doing it for over a decade without a single incident. Motor ejection varies with field rules, so go with your local rules.

if you go with vents, I would place two equal vents in each tube, 180 degrees around circumference, to balance forces. Otherwise the ejection force may bump the rocket off center. Google “backslider rocket.”. Agree with @teepot, keep them well forward of motors to reduce scorching.

if you get all three motors lit, this baby is gonna get pretty far up there!

presumably you have clustered before, so you know you need a good 12v source.

hope you get three straight trails and a short walk!

 

[altertalk]

Two issues I am going to have to resolve. How to make vents and finding after the launch. To address the stability, I'm using openrocket to determine center of pressure and center of gravity. My hope is for two or more body diameters aft for center of pressure. To get that, I am looking into a low weight low-jack option to place inside the satellite. I figure a small battery and the transmitter should be sufficient weight. Thank you both for the suggestions. Unfortunately, the ranges where we launch are either very grassy (dead dry grass) or a farmer's field. Either way, chucking out a spent motor is not an option.

 

[BABAR]

I gotta question.

WHY are you putting motors in the outboard tubes?

if the answer is, ”I want more altitude” then by all means go with the Ds.

if the answer is, “I want it for realism or just because it looks cool”, I’d go with an 18mm 1/2A or even a 13mm A something-T.

24, 18, and 13mm motors will ALL give you a flame and a smoke trail at lift off and for most of the altitude the rocket is in visual range. if you DON’T want or need the extra OOOOMPH for altitude or payload, the smaller motors give you the visual effects

WITHOUT

as much excess altitude you may not want or need

as much motor cost

As much excess weight in the tail which will require bigger fins or nose weight or both

risk of cattywampus flight if one motor doesn’t light (actually, if the main doesn’t light and your D boosters DO light, you have fecal turbine interaction because that puppy is leaving the rod and unless you ducted the outboards to the main tube, you have no chute deployment and it is coming back ballistic . This is considered poor form [even worse than ejected cases!]. OTOH, if you go with 13mm outboards, particularly a 1/2A or 1/4A, probably won’t even get all the way up the rod. I will take that embarrassment over a ballistic return any day.)

as big size vent holes. I don’t know what size vents are needed for a D motor, but given the outboard motor tube length is short (so not a lot of room for compression) I’d say they need to be pretty big. Are the outboard tubes 24 mm? If they are LARGER, than put your 24 mm mount in with longitudinal balsa strips instead of rings and you can vent out the back. Think Lil Augie spacers
http://www.spacemodeling.org/jimz/eirp/eirp_10.pdf
this is IMO definitely the best way to go if you use 18mm or 13mm motors, run the mount BT-20 or BT-5 almost but not quite to the cone (leave a cm or two). Gases go forward up the motor mount then back down between the mount and the outer tube. No visible vents, and acts as a baffle so if you have plastic tail cones on the outboards, gases should be sufficiently cooled.

Put some JB Weld or other high temp substance on the base of the outboard cones (which are gonna get blasted by the ejection charges, less so but still substantial burn through if you use zero delay) to protect them from the blast.

Another option is to put shock cords on the nose cones, use the same delay on the outboards as the main, example C6-5 and two D12-5s. Since the propellant burn time is similar for Estes 18mm C and D

https://www.rocketreviews.com/compare-estes-c6-to-estes-d12.html
the motors will all fire at approximately the same time. Use long kevlar shock cords with short pieces of elastic for the outboards, and an anti zipper device on all three shock cords. @BlaineS has a great one

https://www.rocketryforum.com/threads/blaines-kevlar-anti-zipper-using-foam-ear-plug.154996/
so what if they don’t go off simultaneously, the rocket is gonna be pretty high up regardless, one or two secoconds shouldn’t matter. This solves your vent problem.

 

[prfesser]

Hi,

I am in the process of building the Estes "Geo Sat LV", which has a core with an 18mm motor (up to C) and two fully attached inert boosters. I want to make these boosters live with up to a 24mm motor (D or higher). The question is what to use. I could attach the booster nose with glue and expect a D12-0 to simply burn out but I'd be concerned about it catching the internal booster tube on fire. I could attach the booster nose cones with a small ejection cord, but I'd be concerned about charring on the side of the core. Then there's putting in a side panel that would simply divert the gases out the side of the booster. Has anyone reconfigured a model so that the inert boosters can be live? And if so, what did you do?

Haven't done it but will make the Interceptor G into a three-motor cluster.

I don't recall where I saw it, long time ago, but there was a bit of instruction on using booster motors in side pods. The burn-thru that ordinarily ignites an upper stage motor simply ejected the empty motor casing.

 

[altertalk]

I gotta question.

WHY are you putting motors in the outboard tubes?

if the answer is, ”I want more altitude” then by all means go with the Ds.

if the answer is, “I want it for realism or just because it looks cool”, I’d go with an 18mm 1/2A or even a 13mm A something-T.

24, 18, and 13mm motors will ALL give you a flame and a smoke trail at lift off and for most of the altitude the rocket is in visual range. if you DON’T want or need the extra OOOOMPH for altitude or payload, the smaller motors give you the visual effects

WITHOUT

as much excess altitude you may not want or need

as much motor cost

As much excess weight in the tail which will require bigger fins or nose weight or both

risk of cattywampus flight if one motor doesn’t light (actually, if the main doesn’t light and your D boosters DO light, you have fecal turbine interaction because that puppy is leaving the rod and unless you ducted the outboards to the main tube, you have no chute deployment and it is coming back ballistic . This is considered poor form [even worse than ejected cases!]. OTOH, if you go with 13mm outboards, particularly a 1/2A or 1/4A, probably won’t even get all the way up the rod. I will take that embarrassment over a ballistic return any day.)

as big size vent holes. I don’t know what size vents are needed for a D motor, but given the outboard motor tube length is short (so not a lot of room for compression) I’d say they need to be pretty big. Are the outboard tubes 24 mm? If they are LARGER, than put your 24 mm mount in with longitudinal balsa strips instead of rings and you can vent out the back. Think Lil Augie spacers
http://www.spacemodeling.org/jimz/eirp/eirp_10.pdf
this is IMO definitely the best way to go if you use 18mm or 13mm motors, run the mount BT-20 or BT-5 almost but not quite to the cone (leave a cm or two). Gases go forward up the motor mount then back down between the mount and the outer tube. No visible vents, and acts as a baffle so if you have plastic tail cones on the outboards, gases should be sufficiently cooled.

Put some JB Weld or other high temp substance on the base of the outboard cones (which are gonna get blasted by the ejection charges, less so but still substantial burn through if you use zero delay) to protect them from the blast.

Another option is to put shock cords on the nose cones, use the same delay on the outboards as the main, example C6-5 and two D12-5s. Since the propellant burn time is similar for Estes 18mm C and D

https://www.rocketreviews.com/compare-estes-c6-to-estes-d12.html
the motors will all fire at approximately the same time. Use long kevlar shock cords with short pieces of elastic for the outboards, and an anti zipper device on all three shock cords. @BlaineS has a great one

https://www.rocketryforum.com/threads/blaines-kevlar-anti-zipper-using-foam-ear-plug.154996/
so what if they don’t go off simultaneously, the rocket is gonna be pretty high up regardless, one or two secoconds shouldn’t matter. This solves your vent problem.

All great questions. First, I am looking for a "stepping stone" for going to Level 3 (L3) High Power rocketry (HPR). The rocketry club I am in offers an option to launch in a 320 acre field a couple times a year, and flights that exceed 5,000 feet. They get an FAA waiver for the day of the launch. According to the club's Launch Safety Officer, there's plenty of power to ignite multiple motors on any of the three different pads they offer, including one with rails. So getting three ignited shouldn't be a problem.

However, I understand your point about building a glorified "lawn dart" if the center core doesn't ignite and I do not have an operational recovery system. I can put in motors with delays and charges to get the boosters to pop a 6" chute each that should not interfere with the 18" chute of the core. It will likely reduce the sink rate and increase the drift distance down range. But with 320 acres, that should permit me to find the rocket. And as I noted, using a low-jack system will also help me in locating it.

As for flight height, having the ability to use D or E motors in the boosters or A thru C motors, gives me options. I can use smaller impulse motors for windy days, or higher impulse for better flying days. As a NASA researcher, I am always looking for options.

Ultimately, I plan to build an L3 HPR Saturn V with 5 operational motors. Though still in the design phase, I am considering a 6 foot rocket with a 6" diameter first stage which approximates a 1:60 scale. While I would like to have 3 stages, I'm still not sure I'd do that. I may opt for a single stage with 5 G's or H's. Time will tell.

 

[KennB]

Find some Estes D11P motors for your outboard tubes.

 

[SharkWhisperer]

Why not just plug the booster motor ends with few mm epoxy or some kitty litter (would need nozzle-fitting tooling for the latter)? Estes BP boosters are just relying on the propellant grain distal end burnthrough for flame generation; goes forward because less pressure than backwards through the nozzle. There's no special booster charge, etc. Just contain it, so it burns out backwards through the nozzle and dies.

No venting necessary. No motor ejection if unwanted...

 

[KennB]

@SharkWhisperer, before you joined the forum, there have been numerous threads about allowable and non-allowable modifications to motors, especially BP motors. Putting epoxy into the end of a BP motor to plug it is considered non-allowable; it is considered a modification that violates the safety code and any resulting problems would not be covered by the group insurance (if you belong to NAR).

An acceptable way to "plug" a booster BP motor would be to pack wadding into the space above the propellant and put some tape over the end to hold it in. As a non-permanent mod, it is allowed.

 

[Johnly]

I'd modify the 18mm motor retaining clip to all for the use of 18mm D impulse RMS motors or change the core motor to 24mm and be able to fly the airframe with G impulse class motor( if you can maintain the CP/GC relationship). With a small BP core motor and D impulse outboards, the rocket has a high probability of pranging if one of the outboard D motors fails to ignite.

 

[SharkWhisperer]

@SharkWhisperer, before you joined the forum, there have been numerous threads about allowable and non-allowable modifications to motors, especially BP motors. Putting epoxy into the end of a BP motor to plug it is considered non-allowable; it is considered a modification that violates the safety code and any resulting problems would not be covered by the group insurance (if you belong to NAR).

An acceptable way to "plug" a booster BP motor would be to pack wadding into the space above the propellant and put some tape over the end to hold it in. As a non-permanent mod, it is allowed.

Ahhh, I see. Momentary lapse there, though a benign stray from the regs, though I cannot for the life of me fathom how an thin epoxy plug could be considered more of a safety hazard than a typical ejection charge and packed clay covering, projectile-wise.

Tape&wadding, epoxy, both come out simply enough... Shoot, a silicate-coated (predried) cardboard endcap stuffed in there would stop the flame. Tis not as though factory-plugged motors don't exist (though I doubt in D size from Estes, at least I've never heard of them...). I'd pay attention to the true fire "resistance" not only of wadding but also your tape selection.

Would ramming an inch of ChoreBoy metal scrub pad in there as a baffle be considered an acceptable modification? Plenty of room remaining in the end of a D12-0. What exactly is the deciding point between allowable/not allowable? I'd wonder if some purists might argue that wadding/tape could be an unacceptable deviation. Just doesn't seem like "research/experimental" topic to me; moreso one of a common sense good or bad idea.....

 

[KennB]

Tis not as though factory-plugged motors don't exist (though I doubt in D size from Estes, at least I've never heard of them...).

https://www.rocketryforum.com/threads/boosters-not-igniting-another-motor.165368/post-2118308

Would ramming an inch of ChoreBoy metal scrub pad in there as a baffle be considered an acceptable modification? Plenty of room remaining in the end of a D12-0. What exactly is the deciding point between allowable/not allowable? I'd wonder if some purists might argue that wadding/tape could be an unacceptable deviation. Just doesn't seem like "research/experimental" topic to me; moreso one of a common sense good or bad idea.....

Ramming may not be a good idea but ChoreBoy (not steel wool) held it with tape would be okay. Check back to the other threads for the back and forth on allowable and sensible. I've been down that road enough.

 

[SharkWhisperer]

https://www.rocketryforum.com/threads/boosters-not-igniting-another-motor.165368/post-2118308

Ramming may not be a good idea but ChoreBoy (not steel wool) held it with tape would be okay. Check back to the other threads for the back and forth on allowable and sensible. I've been down that road enough.

I'll have to review older threads to see what's been discussed before chiming in any further on the topic and risk reader-narcolepsy from my repetition of agreed-upon knowledge. Because I remain "baffled" by the allowable/not allowable distinctions on the topic.

Agree "ramming" as in the way I make my own F+ impules BP motors (research topic) by beating hot BP into a tube with a 3-pound hammer (usual, and acceptable-risk fireworking practice; I'm a hybrid, but a safe hybrid) would not be an ideal way of introducing ChoreBoy (not flammable steel wool) into the backside of a D12-0 motor as a baffle--I should have been more precise in that I meant "stuffing" it in, as with finger pressure. But I maintain that a simple fire-resistant cardboard endcap, perhaps two, plywood-style though one would likely suffice, finger-installed, would have the same flame resistance as wadding/tape or Choreboy/tape, and be similarly resistant to any pressures that might allow hot gasses to get by--the open "back door" of a booster BP grain experiences very little pressure versus what was just milliseconds earlier being forced out through the constricted nozzle for thrust generation. I'll check, but am certain there was much back-n-forth on what tape might be acceptable for this use. Fireproof tape.

But OP, like John above mentioned--I'd probably want my to have a high-power motor as my main, with the outboards similar or lower, but definitely not higher power, in the event of an asymmetrical ignition series. Plus, it just gives you more options to shoot different motors using the central motor alone...

I'll read up the old threads to get myself up to speed here.

Tx, SW

 

[BABAR]

Always a little nervous jumping in here, as I am a lowly L-0 (hey, I launched a G once, and I have launched a couple of Es one at a time!)

you are starting with a cool rocket designed to fly on a single C motor at 15 N max thrust

https://estesrockets.com/wp-content/uploads/Educator/Estes_Engine_Chart.pdf
with 2 additional Ds you go from max thrust of 15 N to 81 N

i am not convinced this rocket is designed to withstand that load, but you can paper the fins or use basswood or plywood if needed.

something a bit strange. On Most clusters with outboards I have seen, the CENTRAL motor is usually as big or bigger than the outboards. Your plan is the opposite, 18 mm core and 24 mm outboard. Since you are going to be putting in two 24mm mounts anyway, why not make it three and put a 24mm mount in the middle (hey, then we go up to 99 N!). But seriously, if you do this, you can always use an adapter to fly it as a single motor C.

I will be curious to see how much nose weight is going to be needed to keep this puppy stable. On the other hand, with three Ds lighting on this little rocket it is going to take off like the proverbial Wuhan Bat out of Hell!

 

[BABAR]

I fly at a local park and routinely eject motor casings up to 24mm Ds on my Helis and AirBrakers. I have never had any problems, but given the practiced is sometimes frowned upon, I have designs that eject the motors with a streamer. I have plenty of room and streamers fold up pretty well and on pop pods attach directly to either the casing or the mount, so no shock cord needed and they take up surprisingly little space (2”x20” streamer can fold-wrap around an 18mm motor easily, a 24” motor even easier.). They look kinda cool, I refer to my modified rockets as HeliBombers (Hey, Estes sold something like this called the Meteor Masher!)

https://www.rocketreviews.com/estes-meteor-masher-donald-besaw-jr.html
How big are the body tubes on the boosters? If they are larger than your 24mm motor mount, you may be able to fit a sizable length of crepe paper streamer folded multiple times and finally with a single wrap around the motor mount, turning the mount into a pop pod. since You are committed to 24mm, I guess going with 18 mm or 13 mm pods is not an option for you.

pluses

should be legal at all NAR launches, I am not macho enough for Tripoli, so I can’t speak for them.

fire risk is no greater than standard streamer recovered rockets

bright color streamers are easily located on flat surfaces, in grown soybean fields or cornfields YMMV (but any small rocket is gonna be hard to find, so not really an issue since you are flying low power anyway.)

no vents needed.

dumps the booster motor mass and actually adds at least a kiss of additional forward thrust to the sustainer as they eject, so more efficient than retained motors

minus:

you got three things to track, so you need dedicated spotters for these cuz YOUR eyes are gonna stay on the sustainer.

 

[neil_w]

According to the club's Launch Safety Officer, there's plenty of power to ignite multiple motors on any of the three different pads they offer, including one with rails. So getting three ignited shouldn't be a problem.

"Plenty of power to ignite multiple motors" is not the same thing as "All motors will ignite every time".

Concur with others that safer practice is to put the largest motor in the center, smaller ones in the outboards.