LPR w/ strap-on boosters!

[jetra2]

Hi all,

A coupla night ago, my good friend, rocket buddy, and co-conspirator Eugene (eugenefl) were talking on the phone. Well, somehow the conversation came to a point where we were talking about rockets with strap-on boosters. A light then turned on in my head - I wanted to build a rocket with strap-on boosters! Me and Eugene discussed how cool it would be, and then we decided then and there that we were gonna do it! He was going to rebuild the one he had (pictures of which you can see here) and I would build a smaller rocket with these boosters.

My version would be based on the BT-60 tube, which would have a 24mm mount in it for up to E9-8's, and two BT-55 based strap-on boosters, with 18mm mounts, for motors like the A8-3, B6-2, and C6-3. The reason for the short delay in the boosters is so they'll fall off at around 300-500 feet, creating a nice "ooh, ahh!" effect! LOL...

The BT-60 sustainer rocket will be about 30-33 inches long, using the long PNC-60AH nose, which is used on such rockets as the Der Red Max, Citation Patriot, and Mean Machine. The fin shape is not yet decided, but I'll draw something out till I like it!

The BT-55 boosters will be about 10 inches long, and will use the Goblin nose cone, since I have two extra's! They will be using an attachment method that I'm gonna call the "Hook-n-Dowel" method, and it's similar to Ray Dunakin's design in that the bottom hook hooks into a launch lug spaced off the main body with a small strip of 1/16" balsa, and then attached to the nosecone is another dowel, which slides into another launch lug/receptacle on the main body.

The theory is that the rocket lifts off with all three motors burning (hopefully). Then the booster burn out while the sustainer motor keeps burning, and the delays on the boosters start to burn. Then, after 2 or 3 seconds (dependin on the motor I choose) the ejection charge ignites. This, in theory, pushes off the nosecone on the booster, which pulls the dowel out of the launch lug on the main body, releasing the dowel to fall down the side of the rocket, completely releasing itself from the main body, and coming down under a small chute or streamer. After all this happens, the sustainer *should* be at apogee, deploying it's chute, for a beautiful flight!

Comments? Questions?

Jason

 

[rocwizard]

thats a cool design there Jason, at least it is in my mental image post pics!

 

[n3tjm]

you should make it so the strap ons use B6-0 or C6-0 motors, and have the srap ons pop off on burnout of these motors . Some experiments have to be done, because I don't know if the outgas of the C6-0 motor will be enough...

 

[jetra2]

Well, I didn't waste any time starting, did I? I just went and finished cutting the fins out of basswood. They are a very plain and simple design, since on this rocket I want to keep it ASAP. No, not As Soon As Possible, but As Simple As Possible!

Here's a picture of the fin patterns. I drew a few out to see which one I liked best, then went ahead with the one that you can see I chose and cut out. Sorry the pic is so dark, my flash decided to shut off on me!

Jason

 

[jetra2]

And here's the fins all cut out and ready for shaping! Oh, looky! There's the good-ol "Price Tag Fin!!" LOL!

Jason

 

[dtomko]

Looks excellent! I have plans from the Aug. 1970 Model Rocketeer for a conversion of the Estes Gemini Titan to a Titan III MOL with working strap ons. The strap ons used B-14-0s and the core used 2 B4-4s or C6-5s. The strap ons were held on only by clips in the rear and pins at the front, both made of 1/32" music wire. So there is a loose connection and the strap ons fall off with just a tap. The method was to use the more powerful kick off of the B-14s to keep the strap ons attached; after burn out, they would fall off as the core keeps boosting. The article mentions that the B-14-0s will pop out the nose cones of the strap ons, but recommends the cones have very loose fits. And the strap ons are 18" BT-70s with no stuffer tubes! It's on my list to build, but obviously some different engine arrangement needs to be worked out.
Drew Tomko

 

[astronboy]

Here is my take:

When building a 2-stage model, it is advisable to add vents to the lower stages. Why? Because the gasses released by the burnthrough of the propellant can will seperate the stages before ignition of he sustainer motor. Now, this is not nearly as big a 'pop' as an ejection charge, or we would not have lawn darts when a booster motor is mistakenly used in a single stage rocket.

My thoughts are to use this gas pressure to pop off the booster stages. Perhaps by venting the strap on booster near the top with a single hole directed at the rocket body. The idea is to push the upper end of the booster BT away from the sutainer, just like a full scale rocket like the shuttle sheds it's strap on boosters. Of course, this would require just the right shape pop lug or hook... maybe like a glider pop-pod arrangement.

Any thoughts? Someone must have tried this before...

 

[wwattles]

Ray Dunakin has some interesting ideas on booster separation hardware. Check out his website here for specifics: Ray Dunakin's Booster Pictures Page
Basically, it's a metal pivot point on the back with a forward-facing hook on the front that slips inside the booster just under the nose cone edge, so when the nose cone blows off with the ejection charge, it releases the booster so it falls away, and the chute can deploy for booster recovery.

Ray's hardware is pretty built-up, but you might be able to do it with less.

Or you can buy it from Ray - he sells it as a kit, ya know!

WW

 

[Rocketmaniac]

Jason,

I love the plan...... When I finish my strap-on booster project, we'll have to get together and fly them!!!!!!

 

[jetra2]

Originally posted by astronboy
My thoughts are to use this gas pressure to pop off the booster stages. Perhaps by venting the strap on booster near the top with a single hole directed at the rocket body. The idea is to push the upper end of the booster BT away from the sutainer, just like a full scale rocket like the shuttle sheds it's strap on boosters. Of course, this would require just the right shape pop lug or hook... maybe like a glider pop-pod arrangement.

Any thoughts? Someone must have tried this before...

Well...the problem with this arrangement on my design is that I want the boosters to deploy a recovery system. As in my post above, the boosters fall off upon the time the ejection charge activates.

I think that your idea would work great with smaller boosters. What I would think would work is a hole punched in the side of the booster, about 1/4" or so in diameter, that is pointed directly at the main body tube when they are attached. Then there is a small post that goes right into the sustainer's body, and then, upon burnout and burn through of the boosters, the hole vents all the hot gases directly at the sustainer. This provides enough push to have the booster's post come out of the sustainer, and thus, the booster falls off, and tumble recovers. There are two things to consider with this idea, though. The vent hole is going to put a LOT of hot gases and burning particles right at the side of the sustainer. This has the possibility, after multiple flights, to burn right through the sustainers body. It would be advisable to put a small metal plate opposite the vent hole to one, deflect the gases, and two, protect the sustainer. Then after each flight, you could just wipe the metal plate off, and go again. The other thing to consider is that the boosters should be minimum diameter, and really short to make sure that they tumble recover.

Good idea - somebody try it!

Jason

 

[astronboy]

Jason, I agree. I was thinking of a small tumble designed booster, like a 'traditional' lower stage booter.

For a recovery system, this MAY work, if the 'seperation port' is small. IE: Just big enough to push the top of the booster away from the main BT, but small enough that it allows a recovery system... a streamer maybe, to be deployed.

Fred

 

[dtomko]

I like Ray Dunakin's design with the forward attachment that comes off as the nose cone pops off. However, I would be concerned about the chute tangling or getting scorched by the core as it keeps moving forward. I wonder if rear ejection on the strap ons might work.
DT

 

[jetra2]

Drew,

That's how my design works, also. I just preferred to scratch build my attachment point. You're probably right about the chutes getting scorched a little bit, but I would think that by time the boosters separate, the sustainer should already be burning it's delay, minimizing the risk for a burned chute!

Jason

 

[dtomko]

Jason,
You'll probably be fine, then. In the article for the Titan III, the author says the strap ons pop off at about 50 ft.! Those B-14-0s were all initial kick. I may have to move the Titan III up on my list. I also would like to do a Dyna-Soar version with a working glider.
DT

 

[astronboy]

Oh man, I REALLY want someone to make B14s again!!

We should bug Bill Stine at QUEST....

 

[jetra2]

Ok! Here's some more pics! I finished shaping the fins and making them even, so here's the pics I took.

This first picture is on of the fin cut out of the 3/32 basswood and with the leading and trailing edges ONLY rounded, with a ruler for scale.

Jason

 

[jetra2]

Last picf for now - here's a profile shot of the rounded trailing edge.

I am going to seal these fins with sanding sealer - the grain is so tight on this basswood that I am not going to worry about filling them with Fill-n-Finish!

Jason

 

[eugenefl]

Jason, nice work! I am truly re-inspired to reconstruct my booster rocket. I'm sure Ray will be equally as impressed as I am by yet another great TRF member project.

Just to keep you moving along, here's another picture to "inspire" you. (Shoot, if you want inspiration check out Ray's pictures! I'm sure you've seen 'em!)

 

[jetra2]

Hi all!

NEW PICS!

Betcha that got your attention, huh?

Anyways, I got the chance to cut tubes tonight! I'm still not quite sure how long I'm gonna cut the BT-60, but I did decide that I would cut the BT-55's to seven inches, since with the nosecones, this would give me a 12" booster! Plenty of space in there now for motor, recovery system, and other stuff!

Alrighty, enough crap from me - here's the pics!

This one is a close up shot of the boosters!

Jason

 

[jetra2]

I think that is the first time I've ever done that...I forgot the pic! I wish there was a smiley that had "DUH!" written over it!

Jason

 

[jetra2]

This next pic is a very high profile shot. Where you see the blue tape is where I'm thinking I will cut the BT-60.

Jason

 

[jetra2]

Now here's a picture from the rear of the boosters in position, but with no MMT's. I hope to order the CR's I need next week from Mr. Flis!

Jason

 

[jetra2]

Last one for tonight, here is another close up of the boosters, but with two of the four fins in position, so now you get an idea of what she'll look like.

Tomorrow, I hope to get the hooks built and attached to the boosters, and the receptacles on the sustainer attached, and if I have time, possibly attach the fins!

Jason

 

[wwattles]

dtomko,

I was pondering the rear-ejection idea just last night as I was falling asleep. I think it would work very well if the rear of the booster was simply a side-facing hook that attached to the rear of the main BT, with a very simple attachment point forward, just enough to keep the booster attached during flight. All the thrust would be exerted on the rear of the main tube.
Upon ejection, it would blow the motor out the back, drag the chute with it, and pull the booster free from the back of the main tube. The only danger would be if it didn't detach cleanly, and was left as parasitic drag on only one side of the main rocket...

WW

 

[teflonrocketry1]

Jason,

I made a RockSim version 7 file for your design. I need details to give you a more accurate simulation. What are the exact fin dimmensions and tubing lengths? I could only get approximate values from your photographs. If you send me these details I can make a better simulation file and report a static CP value. I get about 1000 ft AGL for a 2 x B6-2, and core E motor.

Are you really parallel staging this design, where all three motors ignite at the same time? If so, I need to know all the intended motor combinations you will fly; since a unique motor file will need to be created for each parallel staged motor combination.

Bruce S. Levison, NAR #69055

 

[jetra2]

Bruce,

Here's some quick measurements for you!

FINS:

Root Chord: 6"
Tip Chord: 2"
Span: 2.5"
Sweep Length: 4"

BODY:

Sustainer: 28.5" of BT-60 w/ a PNC-60AH nose.
Boosters: 7" of BT-55 w/ Goblin style nose (BNC-55AO, I think)

Oh, here's some planned motor combos:

C11-5, 2x A8-3
C11-5, 2x B6-2
C11-7, 2x C6-3 (unlikely, but it *can* happen. Would be kinda cool!)
D12-5, 2x A8-3
D12-5, 2x B6-2 (first flight, probably)
D12-7, 2x C6-3 (are they still making the D12-7?)
E9-6, 2x A8-3
E9-6, 2x B6-2
E9-8, 2x C6-3

Just tell me if you need any more info. BTW, since I don't have v7 of Rsim, can you either post here or e-mail me ([email protected]) some screenshots of what you have done with it?

Thanks,
Jason

 

[Wingarcher]

I was thinking the other day about ways to "get rid of" the strap on boosters. My sense of style doesn't really like the idea of blowing the nose cone(s)/recovery out of the boosters while they're essentially still attached to the sustainer. It just seems messy. So.....

Put a 3 motor mount in the sustainer (1 24mm, 2 18mm). Stuffer tube the 24mm up for the sustainer recovery. Then with a centering ring around the stuffer tube, create a "chamber" above the 18mm motor tubes that coincides with the top of the boosters. The boosters would attach at the bottom with a hook that has positive engagement under thrust, but drops freely if the top isn't held in. A small plug on the side of the booster would fit into a small hole in the side of the sustainer in the "chamber". When the 18mm motors burn out their ejection charge would fire the boosters off..... where their ejection charges (longer than the 18mm in the sustainer) would deploy recovery. The real question is whether or not an XX-0 motor would have enough "pop" to do the job. Using booster motors would give you earlier booster shedding.

Am I totally crazed? (Maybe, you'd have to get 5 motors to fire at once..)

 

[jetra2]

Alrighty, time for more pics! I finished attaching the hooks to the boosters yesterday and started work on the sustainer's receptacles for the hooks.

This is a picture of the two boosters overall. The line is a reference for only the BOTTOM hook, not the top one.

Jason

 

[jetra2]

Now here's a close up pic of the bottom hooks.

Jason

 

[jetra2]

And the top hooks. These ARE attached directly to the NC's with a 1/16" balsa strip for spacer.

Jason