D12-0's in a cluster - Need advice

[Ntxrcrc]

Need some advice on D12-0's in a project I am working on.

Some years ago, purchased the plan pack from TLP for a Nike Hercules.
Decided to finally try this project.

There are a few things I am going to deviate from the plans on.
One is using electronic staging instead of the method of micro switches tripping with engine casings ejecting from the rocket.

The design for this rocket uses three D12-0's and one D12-3 in the booster.
Only the D12-3 has engine retention, and is the only one used for recovery ejection.
The three D12-0's are friction fit.
One is purposely designed to eject to trigger the staging ignition.
Remaining two D12-0's are also friction fit, with their engine mounts capped off.
I am assuming they would also be ejected from the rocket.

I do not like the idea of ejecting three casings from the rocket, and intend on using retention for all booster engines.

The design of the booster stage only has provisions for the one D12-3 to vent ejection charges to a BT60 sized parachute compartment located in the interstage coupler.

My experiences with booster engines have all been with igniting the second stage (typical Estes type set ups)

For the requested advice:

How much volume / pressure does a D12-0 put out? Could it be contained in a 2" dia X 15" long tube, or will airframe blow out be an issue.
(Idea being to let the D12-0's vent into the sealed booster tubes, or maybe even having vent holes in the motor mount centering rings to let any pressure exit rear of booster)

Will I just be catching the booster on fire letting the D12-0's vent into the tubes?

Having only one motor for recovery ejection is a risk, especially trying to light a four motor cluster.
Should I redesign the interstage transition to allow the use of four d12-3's, all venting into the BT80 sized tube used to couple with the sustainer?
This would require using a BT80 coupler doing double duty to hold the sustainer stage, and also would eject for recovery system. (BT80 coupler, bulkheads on both ends, with a small band of BT80 body tube - sort of like a DD Ebay)
My only concern would be if this set up would be strong enough to support the sustainer from tipping over under thrust. (Not a lot of length availiable with the coupler due to the design - maybe 2" each side)

Any advice or ideas would be appreciated.

Thanks,
JW

[Indiana]

You could use D11-Ps.

[Ntxrcrc]

Are the D11-P's still in production?

[barone]

Need some advice on D12-0's in a project I am working on.

Some years ago, purchased the plan pack from TLP for a Nike Hercules.
Decided to finally try this project.

There are a few things I am going to deviate from the plans on.
One is using electronic staging instead of the method of micro switches tripping with engine casings ejecting from the rocket.

The design for this rocket uses three D12-0's and one D12-3 in the booster.
Only the D12-3 has engine retention, and is the only one used for recovery ejection.
The three D12-0's are friction fit.
One is purposely designed to eject to trigger the staging ignition.
Remaining two D12-0's are also friction fit, with their engine mounts capped off.
I am assuming they would also be ejected from the rocket.

I do not like the idea of ejecting three casings from the rocket, and intend on using retention for all booster engines.

The design of the booster stage only has provisions for the one D12-3 to vent ejection charges to a BT60 sized parachute compartment located in the interstage coupler.

My experiences with booster engines have all been with igniting the second stage (typical Estes type set ups)

For the requested advice:

How much volume / pressure does a D12-0 put out? Could it be contained in a 2" dia X 15" long tube, or will airframe blow out be an issue.
(Idea being to let the D12-0's vent into the sealed booster tubes, or maybe even having vent holes in the motor mount centering rings to let any pressure exit rear of booster)

Will I just be catching the booster on fire letting the D12-0's vent into the tubes?

Having only one motor for recovery ejection is a risk, especially trying to light a four motor cluster.
Should I redesign the interstage transition to allow the use of four d12-3's, all venting into the BT80 sized tube used to couple with the sustainer?
This would require using a BT80 coupler doing double duty to hold the sustainer stage, and also would eject for recovery system. (BT80 coupler, bulkheads on both ends, with a small band of BT80 body tube - sort of like a DD Ebay)
My only concern would be if this set up would be strong enough to support the sustainer from tipping over under thrust. (Not a lot of length availiable with the coupler due to the design - maybe 2" each side)

Any advice or ideas would be appreciated.

Thanks,
JW
Ok....I think to answer your first question.......I think.......No, I don't know how much volume a D12 will pressurize but you don't want to just vent into a sealed booster tube. One of two things will occur. Either the motor will eject or the sealed booster tube will split open. The gasses have to vent somewhere. The holes in the centering ring to vent aft should work. Of course, even venting the gasses, there is still the possiblity that the tubes could catch fire (do a search for shotgun ejections). :rolleyes:

On a cluster, it wise to have more than one motor for deployment of your recovery device. Using only one, that's the one that probaably won't ignite.

Can't visulize your coupler/BT configuration you're describing. But it sounds like it has a bulkhead to protect the booster from the sustainer ignition as well as acts as a stage coupler. Is there a reason that you can't direct all the other booster tube gasses into the parachute compartment?

[Ntxrcrc]

Don,
Imagine a cardstock bulkhead, 4" X 4" square with 1" radius corners.
This is glued on top of four 2" tubes in a square configuration.
An approx 5" length of BT80 is centered on top of this bulkhead and heavy paper shrouds make up the Nike Hercules trasition.

With the TLP plans, only one 3/4" diameter hole is cut in this bulkhead to vent one 2" tube in the area where the 2" and BT80 intersect. A section of BT60 is glued inside the BT80 offcenter and over the 3/4" hole to act as a parachute compartment.
A BT80 coupler is glued in the BT80 to couple with the BT80 airframe of the sustainer.

The only thing protecting the recovery system is a cardstock cap over the BT60.

Reason for this design?
I'm guessing one is to allow room for a wire and mini plug from the microswitch in one of the booster motor mounts to connect to the bottom of the sustainer.
I will not be using this since I will use a mini timer for sustainer ignition.

I also suspect the designer expects all but one booster engine casing to be ejected, so is only concerned with ducting the one 2" tube.

I'm also expected to cram a 24" chute and recovery harness in this 5" BT60.

If I redesign to use the BT80 as the parchute compartment, there will be no problem venting all four 2" tubes into this section.
What I will have to come up with is a cap for the parachute compartment to both protect from sustainer ignition, and provide enough back pressure to aid in deployment.

One idea is to not glue the BT80 coupler in the transition. Add a bulkhead in the coupler towards to top with a attachment for the shock cord. Use a thin section of BT80 on the outside to support it in the transition and support the sustainer.
This would provide a larger chute compartment.

My concern is having two slip fit joints in such a short length may allow the sustainer to wobble some?
TLP's design does not allow for a very long coupler tube.

Any suggestions for a better transition coupler?

Thanks for the reply on venting the gasses, confirms my concerns!

JW

[Indiana]

Are the D11-P's still in production?

They are listed on Estes's web site, and vendors are carrying them.

[snaquin]

JW,

Do you have any build pics of this model? Sounds like a very interesting design and I'd love to see it!

One thing you may consider if you decide to swap out that cardboard cap that protects the recovery system & blast from the sustainer ignition is that thin FG that ASP sells cut into a small bulkhead disc. It is thin, lightweight and will be more durable than the cardboard or even plywood subjected to repeated sustainer motor ignitions directly on top of that component. ASP offers custom cut fins from this material so you may ask and he might even cut it to size for you .....

http://www.asp-rocketry.com/store/category.cfm?Category=238

Since you mention it would be no problem venting all four tubes into the BT-80 that would be my preferred method using D12's with ejection charges in each of the four booster engine tubes. Maybe even use a D12-3 and three D12-5's for back up. Those 5-sec. delayed engines will fire after the D12-3 (if you have successful ignition of all four engines) and after the chute is deployed. I just wouldn't pick all engines with the same delay time firing all the ejection charges at the same time.

If you only use one D12-3 with three D12-0 (or plugged) engines, if you luck is anything like mine you could almost guess what motor would happen to not ignite out of the cluster causing a first flight prang on your beautiful new model ..... :(

.

[Ntxrcrc]

Steve,
My luck would probably be the same, and the reason I am not building per the plans.
The way it is designed, too many things have to happen just right for a succesful flight.
And like most of TLP's kits, they are made light. So a prang would destroy the model.

No build photos yet, just a plan pack and a bunch of parts I am getting together for the build.
I needed to get the game plan with the deviations firm before I started off in the wrong direction with the build.

I will post a build thread as soon as I start building.

Thanks for the tip on the fiberglass, I will look into that for the bulkhead.
Also on the booster delays. Maybe mix two 3's with two 5's?, redundency you know!

My plan so far (thanks to all the suggestions here) is to vent all four into the BT80 for recovery deployment. Redesign the coupler for dual duty supporting the sustainer and ejecting for deployment.

I will also check out the plugged motors to see if that would be a possibility, but only for two. I think at a minimum 2 should have ejection charges.

In my search for ideas on this project, I saw a number of HPR two-stage builds that use dowels from the transition that slip into small tubes in the sustainer. This looks like a robust design to keep the sustainer in place until seperation.
Would this be overkill in mid power?
Anyone use this sort of set up in LPR or MPR?

Thanks,

JW

[snaquin]

In my search for ideas on this project, I saw a number of HPR two-stage builds that use dowels from the transition that slip into small tubes in the sustainer. This looks like a robust design to keep the sustainer in place until seperation.
Would this be overkill in mid power?
Anyone use this sort of set up in LPR or MPR?

Thanks,

JW

JW,

In case you haven't seen it Sandman produced a couple of very nice Nike Hercules. Search this forum there were a couple of detailed build threads that show a one piece balsa component that Sandman custom made for the transition on his model where the four motor tubes insert, it's really sharp! That may not suit your build, but it is a really cool design. Some of the builders might chime in regarding that model.

I remember an article possibly on Rocketry Planet where someone used carbon arrow shafts with rods for alignment on a similar model. Don't remember for sure.

As far as overkill for LPR or MPR using dowels and small tubes my thinking is use whatever adhesives or materials you think are best for your application. If you're personally satisfied with the outcome, no problem. I choose to use epoxy exclusively for all my MPR builds. Some would deem that overkill but it suits me. To each his own .....

:)

.

[ghrocketman]

I would not mix 3 D11-P's with a D12-3 in a 4 engine cluster due to the fact that you would have issues with assymetric thrust. The D11 does not have the kick of the D12 off the pad and is more like an E9. The initial thrust of the D12 being higher than that of the D11's will cause an un-intended pitch in the flight.
One could use 2 D12-3's and 2 D11-P's however as long as they are arranged properly in the cluster.

[Bob Kaplow]

I would not mix 3 D11-P's with a D12-3 in a 4 engine cluster due to the fact that you would have issues with assymetric thrust. The D11 does not have the kick of the D12 off the pad and is more like an E9. The initial thrust of the D12 being higher than that of the D11's will cause an un-intended pitch in the flight.
One could use 2 D12-3's and 2 D11-P's however as long as they are arranged properly in the cluster.

I've encountered no issues mixing D11s and D12s in clusters regardless of symmetry.

[Ntxrcrc]

Thanks for all the tips, suggestions.

Moving this project over to a build thread in the projects sections.

Thanks,
JW