Clustering using D12-0's

[Fuddrucker]

Hi all,

I have flown my FlisKits Paylord and Starload several times using 3 motors such as C6-7's and D12-7's. I have never used a different combination like 2 C6-0's and 1 C6-7 or the same thing but with D's and was thinging of trying that combination out to try and cut down on the amount of ejection charge heat ect. to make things last longer like the rocket itself and the shock cord, and even the kevlar cord. After a while with three charges going off even the Kevlar cord gets worn out.

I was thinking that on the Estes Snitch, it says to use a B6-0 or a C6-0 and I have noticed when I do that, the top of the Snitch stays much cleaner and does not get all burnt like it does when using a motor with a 3, 5, or 7 designation.

What I was wondering is if anyone has clustered motors with a 0 designation and a 3, 5, or 7 and been successful. I am concerned that there will still be small charge with the 0's that it will pop the nose off. I want to try two motors with a 0, and one with a 7.

Thanks!

...Fudd

 

[Spanerman]

Surly the heat and pressure of the motor burning through will pose more of a hazard to the internals of the rocket rather than a few ejection charges, have you considered a piston system?

Sam.

 

[RoyAtl]

No, the booster motors will not work well in the situation you described because, indeed, when the motors burn through, significant pressure is released forward, resulting in ejection. In the past, certain motors were produced with plugs (D11-P, A10-P, etc) that *would* work the way you want, but they probably limited your design possibilities.

In addition, the problem with depending on only one motor in a cluster for ejection is, what if that's the one motor that didn't ignite? You'd have a lawn dart.

 

[DanFrank]

Hi, You can use booster motors (ie D12-0) in a cluster but you need to put about a 1/8" to 1/4" layer of epoxy in the top end of the motor (not the nozzle end). This does 2 things; it prevents blow-thru which you don't want and it blocks the hole left in the motor after burn-out so ejection gasses don't escape through the spent motor.
Daniel

 

[evil ed]

You might want to go in the opposite direction. Try using a C6-5 and two C6-7 motors. The ejection charges on the longer delay motors would not be confined and may do less damage. Just make sure the shock cord is long enough so that the chute is out of the line of fire from those charges.

 

[RoyAtl]

Hi, You can use booster motors (ie D12-0) in a cluster but you need to put about a 1/8" to 1/4" layer of epoxy in the top end of the motor (not the nozzle end). This does 2 things; it prevents blow-thru which you don't want and it blocks the hole left in the motor after burn-out so ejection gasses don't escape through the spent motor.
Daniel

While this can, and has, been done, it is not an Estes-recommended modification, and will void your warranty with them, and will not (at least should not) be allowed at NAR or TRA affiliated launches, as it is against item #2 in the Safety Code.

 

[shreadvector]

See page 12:
https://www.estesrockets.com/images/uploads/2819_Estes_Model_Rocketry_Technical_Manual.pdf

Lots of hot flaming gas and bits of propellant burst out of the top of a booster motor.

There is no "delay afterburn" which can roast the inside wall of a body tube, but there will be plenty of pressure and gas to blow the nose cone off instantly when the propellant burns through.

 

[Fuddrucker]

Yep, that's what I was thinking Shredvector and RoyAtl. The burnthrough would still cause enough pressure to pop the nose but I just wanted to be sure my thinking was correct. I have seen that blowthrough happen on the Snitch lots of times and that is what concerned me.

I know I could go the other way and use some 5 and two 7's, but the 5's are too short and eject to early.

Thanks for your replies and ideas.

...Fudd

 

[shreadvector]

Quest D5-0P motors are plugged and work great in unusual cluster arrangements, such as clustered with one or more D12-7 or E9-8 motors.

 

[Micromeister]

I'm Truely sorry but I have to completely disagree with most of what others have been posting concerning -0 booster motors.
I've been flying them in combination with other motors for DECADES.

I am particularly surprised reading Roy Green's post. Yes they do burn thur and yes the do expell some forward pressure but generally UNLESS USED in a very tightly confined area (Small Bodytubes) they will NOT cause premature ejection. Many of my Upscale clustered birds (BT-80 & BT-101) are nearly always flown with a combination of D12-3 or 5 motors and D12-0's. Generally in 4 motor clusters I'll use 2 of each, in 5 motor clusters 3 with delays and 2-0's a Great combination in 5 D12 Clustered Crayons. in 3-motor clusters it all depends on how the cluster is set up some get 2 -0 motors others only one or the model flys with matched motors.
In smaller models with B and C 3-motor clusters I'll either vent 2 -0's back thur the centering rings or use a combination that allows the Core motor to have the shortest delay.
Almost all outboard motor pods that are not vented into the model core are flown with -0 motors.

NEVER EVER plug a -0 motor with epoxy it is a direct violation of the MR safety code as you are altering the motor. Not to mention you have no idea of your using to much or too little to actually plug the given motor. The practice is a SUPER NO NO! Please fly safely by not doing such things.

Nearly all of the models in the composite picture below are flown with a combination of D12-3 or 5's and D12-0's.
In some model you may decide to use all the same delay motors or different delays to spread out the after-flame or burnthur. like two D12-3 and D12-5s or 7's.
It all depends on the model and your set-up, but don't let people scar you out of using booster motors in clusters they work just fine.

Another way to extend the life of Clustered birds is to add an second layer of tubing inside the model just ahead of the motor mount. it' only needs to be about 4 or 5 inches long.

Lastly adding a Stainless Steel leader shockcord anchor greatly extends the life of your Kevlar which by the way is only HEAT resistant, Kevlar starts to decompose at temps 800°f and above.
Hope this helps a little.

 

[Fuddrucker]

Yes, that does give me some good ideas for future builds Micromeister. I especially like the steel leader cable idea. I have not had any burn through issues, it is usually just the shock cord / Kevlar Cord attachment point down by the MMT that wears out quick.

Thanks!

...Fudd

 

[powderburner]

If you want to use D12-0s and don't want to take the chance of any damage from propellant blow-thru (or early ejection), you can always make/buy a 24mm plywood bulkhead disc to glue into the front of the MMT. Insert your D12-0 motor as usual (no epoxy or plugs needed) and launch. When the propellant finishes burning and bursts thru the front, the front end of the MMT will pressurize and push the D12-0 motor case out the rear. The disc will plug the spare MMTs and keep the ejection gas from the other mounts from venting out the rear. The other MMTs (holding normal motors with ejection charges) will still push the recovery gear out the front.

 

[spacecadet]

Hi, You can use booster motors (ie D12-0) in a cluster but you need to put about a 1/8" to 1/4" layer of epoxy in the top end of the motor (not the nozzle end). This does 2 things; it prevents blow-thru which you don't want and it blocks the hole left in the motor after burn-out so ejection gasses don't escape through the spent motor.
Daniel

Over here we call that an 'epoxy bullet'. RSOs will frown on it.

 

[adrian]

I'm Truely sorry but I have to completely disagree with most of what others have been posting concerning -0 booster motors.
I've been flying them in combination with other motors for DECADES.

I am particularly surprised reading Roy Green's post. Yes they do burn thur and yes the do expell some forward pressure but generally UNLESS USED in a very tightly confined area (Small Bodytubes) they will NOT cause premature ejection.

By contrast, I have a scratch-built model of the Thunderbird missile which relies on the forward pressure from C6-0s to blow the nose cones out of the BT-55 boosters. Successfully.

The Estes CATO model also relied on the forward pressure from a C6-0 to separate the rocket into its recovery parts.

NEVER EVER plug a -0 motor with epoxy it is a direct violation of the MR safety code as you are altering the motor. Not to mention you have no idea of your using to much or too little to actually plug the given motor. The practice is a SUPER NO NO! Please fly safely by not doing such things.

Agreed. Don't plug the motor, plug the motor mount tube. It's safer, and it saves on epoxy because you only need to plug once, not every time you fly. Vent the motor mount tube too, if you don't want to eject the spent motor.

 

[MarkII]

What about just buying some D11-P motors? They are still in production. You can use two of them in a four-motor clusrter. To use them in a three-motor cluster, the motors would have to be inline so that the thrust would be balanced. D11-Ps have a slightly different thrust profile than D12s.

MK

 

[MarkII]

By contrast, I have a scratch-built model of the Thunderbird missile which relies on the forward pressure from C6-0s to blow the nose cones out of the BT-55 boosters. Successfully.

The Estes CATO model also relied on the forward pressure from a C6-0 to separate the rocket into its recovery parts.


Agreed. Don't plug the motor, plug the motor mount tube. It's safer, and it saves on epoxy because you only need to plug once, not every time you fly. Vent the motor mount tube too, if you don't want to eject the spent motor.

After bursting through the BP "bulkhead" at the top of the grain, wouldn't the thrust chamber pressure just stop at the plug in the motor tube and then escape out through the nozzle? The motor might need to be well-retained for this, but that's not very hard to engineer. The empty motor casing will be strong enough to contain the gas (obviously) and keep the motor tube from rupturing until the pressure is relieved. You would just need a sturdy bulkhead immediately in front of the top of the motor, and good, solid motor retention.

MK

 

[shreadvector]

After bursting through the BP "bulkhead" at the top of the grain, wouldn't the thrust chamber pressure just stop at the plug in the motor tube and then escape out through the nozzle? The motor might need to be well-retained for this, but that's not very hard to engineer. The empty motor casing will be strong enough to contain the gas (obviously) and keep the motor tube from rupturing until the pressure is relieved. You would just need a sturdy bulkhead immediately in front of the top of the motor, and good, solid motor retention.

MK

AVI "Gold" series motors were booster motors with a delay and ejection charge built into a smaller tube that was epoxied into the top of the booster motor. (24mm booster with 18mm delay/ejection module).

They had big problems. At the end of the burn there is only a thin layer of propellant at the top, and this is what ruptures and sends flaming bits up into an upper stage motor. In the "Gold" motors, there was no escape AND the flaming bits had a HUGE surface area along with the entire top surface of the booster motor propellant. The module glues in above kept this massive amount of burning propellant inside with the only outlet the nozzle. Since the nozzle was not sized to handle this much overpressure and since the casing wall is eroded during burn, they would often have a blown aneurysm at the instant of 'burnout'. it was quite loud, too. Their solution was to paint the upper face of the propellant with the same yellow/gold paint they used to mark the top of the ejection charge cap. This inhibited the burn slightly and helped keep the pressure spike to a reasonable level.

That is why people who illegally modify the motors use an epoxy plug, but if done improperly the plug will shoot out the top of the motor like a bullet. The factory plugged motors are the best, as the thick clay cap is pressed in with the propellant and there is no massive increased burning surface at the end of burn.

 

[DanFrank]

Over here we call that an 'epoxy bullet'. RSOs will frown on it.

Pardon me for giving out bad info; I guess I am not keeping up with the times... The "epoxy plug" was used common place years ago and nobody seemed to complain; I guess I am showing my age. Of course this was when Thermalite was commonly used for igniters.

 

[Micromeister]

Pardon me for giving out bad info; I guess I am not keeping up with the times... The "epoxy plug" was used common place years ago and nobody seemed to complain; I guess I am showing my age. Of course this was when Thermalite was commonly used for igniters.

Dan:
Epoxy Plugs were BANNED from use at all Sanctioned NAR launches in the Mid 70's. They were Never that common but were and still are a dangerous and unsafe practice. We (The HOBBY) DO Care and complain whenever it's brought up.
Thanks for Forgetting you every heard of the practice.

But back to the topic:
another thing that is pretty important when flying Clusters where the forward end of adjacent motors are exposed to the burn-thru of the other motors. A single layer of FPwadding will eliminate the potential of back burning motors with or without delay.