Strap-on Booster Project

[Rocketmaniac]

Yes, I have started another project (but I am only in the designing / ordering stage) ........ This one involves the use of strap-on booster hardware made by Ray Dunakin...... Right now here is what I am thinking.........

Main body tube, LOC 3.9" with two LOC 2.56" boosters......... A 38mm motor in the main body and then airstart two 29mm motors in the boosters.........

Main body tube section (body tube and nosecone) about 60"
Boosters (booster tube and nosecone) about 36"

Two quick questions.....

1. Should I go with bigger motors? (one 54mm and two 38mm)?

2. Fins...... 3 or 4 fins??? All attached to the main body tube or 2 attached to the main body tube and 1 attached to each of the boosters????

 

[Juerg]

Hi Randy

1) -> you don't want to overload Rays Hardware, did you check the maximum load (=peak thrust *1.5 at least)

2) -> use 4 fins and attach them to the main body. We tried to stabilitze the boosters on our Ariane. Without success, the air is to turbulent to keep them stable after separation.

Cheers


Juerg

 

[Rocketmaniac]

My booster hardware has arrived......... I was reading the info that came with it and now I have some questions.............

It says that the boosters are designed to detach from the rocket when their ejection charges fire....... This means they will deploy their recovery systems while the rocket is moving a fairly high speeds and often is still under thrust.....

Should I;

1. Plan to have a longer burn time on the main vs the boosters?

2. Airstart the booster so that they will burn out after the main is already out?

3. Remove the ejection charge from the booster motors and use an altimeter to fire the ejection charge to release the boosters?


I know there will be more questions later, these are the ones I have been thinking about right now....... As far as matterials, I only have the hardware and the 4" nosecone........ Everything else I will have to order/make, so almost every option is possible right now.........

 

[Justy]

That depends. How much electronic junk can you cram in this thing?

If I had the gear, I'd have a flight computer in the main rocket, timers in each booster, and I'd do it this way:
--> long burn core motor, fast burn booster motors
--> core motor ignited by launch system, boosters airstarted immediately after rocket gets moving (flight computer launch detection)
--> boosters released (flight computer timer or g-sensor detecting booster burnout)
--> boosters falling away from core pulls out a pin, starting the booster recovery timers. Chutes/streamers deploy shortly after (2sec? If they're not stable on their own, they'll tumble, so they'll slow down pretty fast; if they're stable, they'll cruise for a while, so give them time)
--> core continues flight & deploys as normal (flight computer).

Now -that- would be a cool flight.

In summary, in response to your set of options, I choose ALL THREE.

 

[Rocketmaniac]

Originally posted by Rocketmaniac
a longer burn time on the main vs the boosters?

On second thought, would it be better to have the boosters burn longer so when they are done, their ejection charge (and booster separation) will happen when the rocket is moving slower?

 

[Rocketmaniac]

Originally posted by Justy
If I had the gear, I'd have a flight computer in the main rocket, timers in each booster

What flight computer would you use? Is there one the fires 3 separate charges? What about timers? What is the best one?

 

[Ray Dunakin]

Originally posted by Rocketmaniac
My booster hardware has arrived......... I was reading the info that came with it and now I have some questions.............
It says that the boosters are designed to detach from the rocket when their ejection charges fire....... This means they will deploy their recovery systems while the rocket is moving a fairly high speeds and often is still under thrust.....

Should I;
1. Plan to have a longer burn time on the main vs the boosters?
2. Airstart the booster so that they will burn out after the main is already out?
3. Remove the ejection charge from the booster motors and use an altimeter to fire the ejection charge to release the boosters?

Generally, I use a shorter burn on the boosters and a longer burn on the main. The boosters need to get the full weight of the rocket moving quickly to provide stability. Here are some additional suggestions:

1. You can fold the booster's shock cord in a "zigzag" fashion, then put a small rubber band around it. Doesn't have to be real tight, just enough to hold it together. This will absorb a lot of the force when the chute opens. I did this last August when I flew a 2.6" diameter rocket with two Pro38 three-grain boosters, and it worked pretty well.

2. It's possible to use a timer to fire a small charge that will release the boosters, then use the booster's motor ejection to deploy the chute. You can use either a small electronic timer (such as from PerfectFlite) or use gray "Thermolite" timing fuse from www.pyrotek.org. Here's a drawing showing how to set this up:

https://albums.photo.epson.com/j/ViewPhoto?u=3009006&a=30072909&p=66242597&f=0

I haven't had a chance to try this myself yet but I see no reason why it wouldn't work.

 

[Ray Dunakin]

Originally posted by Rocketmaniac
Should I;
1. Plan to have a longer burn time on the main vs the boosters?
2. Airstart the booster so that they will burn out after the main is already out?
3. Remove the ejection charge from the booster motors and use an altimeter to fire the ejection charge to release the boosters?

I forgot to add a couple more comments to my previous reply...

The easiest thing to do is ignite the boosters and main simultaneously, with a short delay on the booster ejection charge and let the booster ejection separate the boosters as their chutes are ejected. Alternately, you can ignite the boosters first, then ignite the main after booster burnout. Igniting the main first and lighting the boosters after burnout of the main is also possible but (I think) may be less efficient.

Optimally, you want the boosters to separate as close to booster burnout as possible so that the rocket is no longer carrying dead weight/drag. However, it may be desireable to time the booster separation for after burnout of the main motor to prevent possible scorching of the booster chutes by the main's flame. (Depending on motor size/type.)

Igniting the boosters first, deploying them after they burn out, then igniting the main is probably the coolest method. It's also probably the trickiest. If you're using the booster's ejection to separate the boosters, you need a really short delay to prevent the rocket from arcing too much prior to ignition of the main. If you use a timer (fuse or electronic) you can separate the boosters right after they burnout, then ignite the main before the rocket has a chance to slow down or arc over.

 

[Ray Dunakin]

One more comment about strap-on boosters...

I have a couple different types of booster mounting hardware. The "mini-hardware" can be used for boosters up to 29mm diameter. I use them a lot, usually with Estes D12-0's and streamer recovery. Nothing fancy, just let the motor ejection separate the booster as it pushes out the stream. The streamers sometimes get torn (it's cheap plastic surveyor's ribbon) but the boosters are light enough that it doesn't do 'em much harm.

Sometimes I'll cluster several boosters on a rocket, and alternate D12-0's with D12-3's. Looks cool to see one set of boosters drop off, then the rest drop off three seconds later.

 

[Ray Dunakin]

Oops, yet another comment about strap-on boosters...

If you use an altimeter in the main rocket, it's probably a good idea to keep the vent as far away from the boosters as possible. There's bound to be some turbulance around the boosters, and having the boosters eject near the vent would probably not be good either.

 

[Rocketmaniac]

Ray,

So much good info....... I am starting to get a plan in my head......


First off, use H180s in the boosters and a I161s in the main

Can I do the following.....

1. Lite the boosters on the pad...... (1.3 sec burn time)
2. Eject the boosters with a timer in each booster (nosecone still on)
3. Airstart the main....... (2.2 sec burn time)
4. Booster ejection charge ejects the nosecones and deploys chutes.
5. Main burns out and has normal dual deployment altimeter in control....

Now, a few more questions.....

Can I eject the booster without ejecting the nosecone and deploying the chute? If so, how can this be done? If I understand things right, normally the booster is "locked" into place with the nosecone or coupler..... so when the nosecone is ejected, it "unlocks" the booster.....

If this is not possible, I gues I would just modify step 2, say "eject booster with timer in each booster" and delete step 4 as this would happen during step 2

 

[Ray Dunakin]

Originally posted by Rocketmaniac
Ray,
Can I do the following.....
1. Lite the boosters on the pad...... (1.3 sec burn time)

Yes.

2. Eject the boosters with a timer in each booster (nosecone still on)

No. The boosters must eject their nosecones in order to be released from the main rocket.

3. Airstart the main....... (2.2 sec burn time)

Yes.

4. Booster ejection charge ejects the nosecones and deploys chutes.

See below.

5. Main burns out and has normal dual deployment altimeter in control....

Yes, with this caveat: I haven't used an altimeter in a rocket with strap-on boosters, so I don't know for sure what effect they may have. But I think as long as the vent is not too close to the boosters it should be ok.

Can I eject the booster without ejecting the nosecone and deploying the chute? If so, how can this be done? If I understand things right, normally the booster is "locked" into place with the nosecone or coupler..... so when the nosecone is ejected, it "unlocks" the booster.....

That is correct. When using this type of hardware, the nosecone must be ejected in order to separate the boosters.

If this is not possible, I guess I would just modify step 2, say "eject booster with timer in each booster" and delete step 4 as this would happen during step 2

Yes, it is possible to eject the nosecone without ejecting the parachute, using the methods. The timer fires a charge located above the parachute, which blows off the nose and releases the booster. Then the booster motor's ejection charge ejects the chute after the booster has been released.

 

[DPatell]

I doubt that there would be an issue with the altimeter. Barometric altimeters should be fine, while accelerometers would be cool as heck because you could see the lighting of the central motors in the report.

Ray had a good point, as long as the altimeter is not around the boosters, it should be fine. The boosters would cause abnormal airflow if the vent hole was below the booster cones. Otherwise, seems like a great idea to me!

 

[Rocketmaniac]

I got most of the tubes I need to start construction....... I have changed my mind and will put a 54mm motor mount in the main body tube and 38mm motor mounts in the two boosters..... I can always use adapter to reduce them down to 38mm and 29mm.......

 

[teflonrocketry1]

Are you interested in a good RockSim (version 7) simulation of your design and its flight? Send me the details (dimmensions, motors etc.) and I will put one together based on my side pod simulation article that Apogee just published in their newsletter:

https://www.apogeerockets.com/education/downloads/Newsletter119.pdf

I also helped Tim Van Milligan write the newsletter article on parallel staging.

Bruce S. Levison, NAR #69055

 

[Rocketmaniac]

Ray, (or anyone else)

I was wondering if there was a way to "lock" the boosters in and not allow them to separate? Meaning, can I design a rocket / system where I can separate the boosters on some flights and on some not have them separate from the main body tube? I am going to have 54mm motor mount and will be able to use a hybrid motor for a cool low and slow flight?

 

[Ray Dunakin]

Originally posted by Rocketmaniac
Ray, (or anyone else)

I was wondering if there was a way to "lock" the boosters in and not allow them to separate? Meaning, can I design a rocket / system where I can separate the boosters on some flights and on some not have them separate from the main body tube? I am going to have 54mm motor mount and will be able to use a hybrid motor for a cool low and slow flight?

With my system, the booster motor's ejection charge blows the nose, releasing the booster. So you'd just have to use plugged motors with no ejection charge when you don't want the boosters to come off.

 

[wwattles]

Ray,

Correct me if I'm wrong here, but your booster kits use a hard-mounted, forward facing hook to hold onto the nosecone rim, so when the ejection charge fires to release the nosecone, the booster loses its connection point to the main rocket, right? What if a builder changed out that forward hook with something that would be hinged on the inside to swing in and out of the rocket? It would be a mechanism similar to what Estes uses on their F-14 Tomcat swing-wing kits.
Granted, this system might not be optimal, since it involves moving parts inside a rocket, and those tend to get jammed with ejection charge residuals after a few flights, but it may work.

Any thoughts, Ray?

WW

 

[Ray Dunakin]

Originally posted by wwattles
Ray,

Correct me if I'm wrong here, but your booster kits use a hard-mounted, forward facing hook to hold onto the nosecone rim, so when the ejection charge fires to release the nosecone, the booster loses its connection point to the main rocket, right? What if a builder changed out that forward hook with something that would be hinged on the inside to swing in and out of the rocket? It would be a mechanism similar to what Estes uses on their F-14 Tomcat swing-wing kits.
Granted, this system might not be optimal, since it involves moving parts inside a rocket, and those tend to get jammed with ejection charge residuals after a few flights, but it may work.

Any thoughts, Ray?

WW

Yeah, that's definitely a possibility. I've thought about that myself but haven't tried it yet because it would take a lot of time and effort to work out the design and build it.