SRB separation ideas for the Estes Titan IIIe

[Flash]

Just wanted to pick some brains on some ideas of the best way to have functional SRBs on this model which is actually a clone of the original.

I’m not going to use the Estes fin setup, I will be using clear fins through the wall on the main airframe.

Also just B6 or C6-0 in the SRB’s. I’ll compare burn times with the main motor to make the selection.

Two problems right up front are:

1: popping the nose cones is a problem due to the upper cargo bay being in the way.

2: hinging the SRBs is a problem because they will most likey travel into the exhaust of the main airframe engine upon release.

I’ve got some ideas but wanted to here from you all first.

The pictures are to give you a picture of the Rocket, mine isn’t built yet.

 

[Wallace]

Spring loaded pins w/burn string running above "ejection" charge? Elastic "beading string" is my go to for any occasion that requires a burn string. It releases cleanly due to the inherent tension..

 

[Wallace]

And be careful with 0 delay booster motors, tend to produce zipper due to high speed deployment....

 

[Charles_McG]

@Flash I replied over on YORF, but I'll second what @Wallace said.

I've done both things he mentioned - spring loaded pins to push the boosters off when a burn string parted. That was on a 1/100 Shuttle, lots more room, so I had an altimeter fire an ematch to cut the line.
And the high speed deployment is an issue, though I only snapped shockcords. The SRBs are light enough you may get away with only streamers. Or you might try sliding rings on the shroud lines to slow down chute opening.

 

[Wallace]

 

[Wallace]

That was with Mylar streamers and 0 delay motors...Heavy wall tube and probably 100 lb. Kevlar. Probably a lot heavier than what you're proposing though, my strap ons were actually glue ons...

 

[Flash]

Ok, I've given the problem some thought.

Here is what I'm thinking on doing. I am looking at gluing the SRB Nose Cone to 1.5" of BT60 tubing and I mean really gluing it so that it doesn't get blown off. This means cutting the SRB's main airframes which is 10.375" each at their stock length.

Then I would glue the Nose Cone and 1.5" of BT60 to the correct location on the main air frame. This would serve as a solid anchor for the top of the SRBs. Of coarse I would use the assembled full length SRBs to improve alignment while gluing them.

The other 8.875" of the SRT's airframe will connect to the top 1.5" of tubing by BT60 Coupler. One end of the coupler will be butted against the nose cone shoulder forming a anti-blow by seal with the other 1" left over end sliding into the top of the 8.875" SRB airframes.

The bottom of the SRBs will be locked in place by 1/8" launch lugs and dowel rods, two each per boaster.

When the SRB's eject, they will slide straight downward and off the dowels. and the very small parachutes will deploy in a very natural way out of the tops of the boasters much like backfire recovery. The bottom dowels will serve as the bottom anchors during flight with most of the load being on the front 1.5" SRT upper airframe.

I'll have to be careful to have a good fiction fit on the SRB's during flight to keep them from separating at launch that is for sure.

This rocket is for small field launching only, so the SRTs will be most likely using B6-0s and the main motor would be a D12. Burn time for B6-0 is .9 seconds and the D12 is 1.7 seconds.

I added a pic of the Titan IIIe main airframe with both boosters, couplers and nose cones. I didn't add the two dowels and lugs or motor mounts.

So I now open it up to your thoughts.

 

[Bruiser]

Have you seen these?

https://www.apogeerockets.com/Rocket-Kits/Skill-Level-2-Model-Rocket-Kits/Strap-on-Booster-Pods

-Bob

 

[Flash]

They are very nice and I'm sure they are worth the money! I just didn't want to pop the nose cones and also the hing system might cause my SRB's to fall back into the main motor exhaust. On the plus side, the SRB's would operate more like the real ones that is for sure.

 

[Flash]

If anyone has a Rocksim File on this rocket, sure would be nice if you can post it here. It would save me a lot of time and if I can improve on it, I'll post it here also for everyone.

 

[bguffer]

Did you ever find/create a RockSim file?

 

[adrian]

They are very nice and I'm sure they are worth the money! I just didn't want to pop the nose cones and also the hing system might cause my SRB's to fall back into the main motor exhaust. On the plus side, the SRB's would operate more like the real ones that is for sure.

You do want to pop the nose cones, so that the booster is properly secured. If the booster can simply drop off the back, and if there is any delay between main motor ignition and booster ignition, then the booster will fall off as soon as the rocket lifts off. The booster may then ignite and go off on its own, unstable flight.

The hinge system will, if anything, help the booster to get out of the main motor exhaust. If the booster simply drops off backwards then it definitely goes into the main exhaust. If it swings back on a hinge then it can peel away to the side.

 

[Charles_McG]

If anyone has a Rocksim File on this rocket, sure would be nice if you can post it here. It would save me a lot of time and if I can improve on it, I'll post it here also for everyone.

 

[NOLA_BAR]

Have you seen these?

https://www.apogeerockets.com/Rocket-Kits/Skill-Level-2-Model-Rocket-Kits/Strap-on-Booster-Pods

-Bob

I have been looking at these as well. One question, does a booster motor (-0) burn through have enough oomph to blow the laundry? Or, would you need a motor with a true ejection charge?

 

[Charles_McG]

I used C11s in the boosters and had no problems.

You can pour a little extra black powder on top of the booster motor and put in a little dog barf to keep it in place to give it some extra oomph.

 

[Flash]

Sorry for the delay, here is my most up to date rocksim file on the Titan IIIe. I'm working with the idea of using a Estes screw on plastic fin unit that fits the BT60 Crayons that Estes sales. They only come in black but would be a direct fit. I would be able to remove it for the display nozzles when the rocket is on display. I'm also thinking about cutting down and reworking a clear plastic fin unit that fits the Estes 1/200 Saturn V so the fins will be clear since it wouldn't be a direct fit item as is the Crayon fin units. Still have some work to do on this idea, but again, here is what I have so far. Also wanted to mention that all the plastic parts in rocksim were weighted on a digital scales for increase accuracy.

 

[burkefj]

I'm building an original right now, I'm actually mounting clear fins through the wall in each of the boosters instead of the duck feet fins, they are maybe 1/2" further forward than yours, I was surprised how much the CP shifted having the fins further forward, almost directly proportional to how much further forward the new fins were. But if you are adding side motors too you'll need to rely on the rocksim cp calculation to judge your CG requirement anyway since it will be significantly different than the original kit of course.

Frank

 

[Flash]

Burkefj, saw your mods, they look great! Thank you for your post also! The Rocksim file posted above shows the cp and cg points with the 18mm motors loaded. It looks pretty good. I’ll will double check everything when I start the build. Thank you again!