inexpensive, yet "exotic" idea?

Ouch - that sounds painful. My first ever DD flight was in a high-distraction area (all kinds of people asking questions, big launches going off, etc). It was successful, but I started preparing the rocket at 10:00AM, and it flew at 4:45 in the afternoon . Kept having stupid problems, getting distracted, etc, but when it flew, it was beautiful (and a real relief).

Yeah, I mean... L1 is pretty scary, I was nervous for L2, but nothing beats the added excitment of your first dual deploy, seeing that awesome R9C pop out of our thor at 1300' was pretty cool... Our first K and second dual deploy, a 5.5" nike smoke, was also pretty cool and scary... I was literally shaking before the launch of freedom won

Well I am almost done cutting out the 4 1/8" G10 fins... CF tube is slotted, two forward rings are glued to the motor tube... tonight I am just going to fondle all these rocket parts, but tomorrow I plan on gluing in the motor mount tube, then when I get a chance to give the fins a nice bevel I will glue them in... What is the best airfoil/bevel design for speed and altitude? I have a 60% router bit, I was just going to have that go around the leading and trailing edge... whats the best way to get a true airfoil (no part of the fin is flat, it is like two bevel's that meet in the middle of the fin... For example, the acme fin canisiters have it)?

that would be two 45 deg cuts, one on each side.

Here is a picture of the rocket, dry fitted of course... This is how the outside will look, minus beveling the fins and without the strap on boosters. First here is a picture of all the parts except for the fins. It is a little blurry

Here is a picture of the entire rocket, without the strap on's, dry fitted. It is capable of flying like this (without the boosters) but is a little over stable, around 2.25 calibers loaded.

Here is a picture showing the fins dry fitted, and it also shows how the 54mm aeropack retainer butt's up against the airframe.

Here is a picture showing the fins dry fitted, and it also shows how the 54mm aeropack retainer butt's up against the airframe. What do you think? Showed it to my dad, he said it looks pretty cool the way it is, but I think it will look pretty awesome with those strap on boosters, and it has the ability to start out with two boosters, like I am doing, and "upgrade" to 4 boosters in the future. Still needs some ideas on booster seperation. I am going with electronics seperation now, after figuring out that it can be at the same time as the main motor is airstarted.

I think for my booster design, I have a preliminary design. There will be two attachment points to the main tube, per booster. The top will be a PVC attachment, there will be a PVC tube glued into the tube (as flush as possible). Then a connecter will be attached to the booster. A small BP charge (what size would you recommend?) will be used to seperate this point. The aft attachment point will be some sort of pivot point, I was thinking maybe a magnet, or something like that.

I was thinking the "cleanest" way to mount the PVC tube into the main rocket section would be just below the most forward centering ring. Then the wires to blow the charge would be external. But if I could find a way to seal off the PVC tube, I could mount it just below the alt bay (in the drogue chute compartment) and that way the wiring would all be internal, but I cant really think of a way to have the wire go to the PVC tube, without the risk of the BP explosion seperate the drogue compartment. So the simple way to do it would be external wiring (and the sustainer motor is already externally wired anyway's). Feedback on the PVC design, or what would be a good aft pivot point would be great... I am going to go sim it with some smaller central motors and see what size AT motor would be a good test platform for the boosters. Having them not seperate when a K185W lights (or having only one seperate) would be bad but if it is a 38mm H or I then it wont do much. Jraice

Originally posted by jraice
A small BP charge (what size would you recommend?) a [/B]

Click to expand...

Have you used BP charges before? Made them before? Look up InfoCentral and follow the BP chart on airframe volume for BP charge sizes. I would not know what size of BP to use, no one could without knowing your airframe volume. It is easy.
Mark

I have flown 3 dual deploy rockets, I was refering to the BP charge that will seperate the boosters from the rocket. After talking about it with my dad, we think the easiest and most clean system would be a drag seperation of the strap on boosters. They could be in a channel that allows them to fall down but not go up (motor thrust cant break them free but after they burnout they can just fall off). This would probably be done with a wood block or two holding them in place, when they light the force will keep them in place and at burnout they will fall free.

Ok, if you were using drag to make the boosters fall off,,, what about when it is on the pad with the motors in the boosters,,, would the weight make the boosters fall off too?
If the rocket were to slow down after burn out(drag) the boosters would have forward momentum,,, it would not work because at ignition the boosters will have forward momentum to lift the rocket, right?
The other way around would be,,, it troubles me on how you are planning to do it. It has to have a pyro device to unlock the boosters to release them after burn out.
Mark

I have read of it being done before, they will be on a sled, so they can slide back, but not forward... they will be resting on the pad so they wont slide off before launch. At ignition the thrust will keep them on and at burnout the drag on the booster will force them down and off. Why wouldnt that work? I am talking about added drag on the boosters, and if that isnt enough, when the central motor (K impulse, lowest average thrust would be a K185) lights that will make a lot of drag on the boosters and they wont stay attached for long...

This is the same idea as drag seperation on a standard multi stage rocket...

What happens if they don't come up to pressure at the same time?

Any boosters that light late are going to fall off the rocket, and then proceede to landshark in whatever direction they fell in.

Originally posted by strudleman
that would be two 45 deg cuts, one on each side.

Click to expand...

wouldn't that end up awfully thick?
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But it is going to be just as dangerous as any other clustered rocekt in which one motor is late to come up to pressure. Hmm... what if a nylon screw (like in the titan rocket project) was used to hold the boosters it place, but they were still mounted with a sliding release system. Then after the screw blows apart they can fall backwards. Any ideas on this or how to make a drag seperation reliable enough to be ok? (without using electronic release). I am not trying to stay away from electronics because of the actual electronic aspect, it is the way that electronics would have to make the boosters seperate that is complicated.

How much construction of this thing could I do (the main section) before designing and attaching a booster release system? It is just sitting in my room just calling out to me to mix up some epoxy! If someone could think of a safe way to have them "drop away" without electronics, like with a sled. But it would still be safe if one motor was a little slow to light, then please speak up. I would LOVE to not have to use the timer for the boosters, because I want them to fall right at burnout (so they are easy to find) but I may want the central motor to light, say 2 seconds after burnoutn.

I suggest you get some electronics appropriate for what you want to do and quit trying to hack a solution.

Get an altimeter that has good support for staging. One that senses motor burn out(s) and knows what to do.

I strongly suggest you buy a Defy Gravity or AFC-877 as both of these offer superior handling of staging compared to others on the market.

GUESSING when to stage, drop boosters, etc. with timers is crude at best and very error prone....especially when applied to an odd-roc that won't sim well.

You apear to have to budget to buy whatever motors you want...time to spend some money on infrastructure.

I have heard of using a burn string to secure a drag-seperated booster in place, and have it placed so it burns when the engine ignites. That way, if the engine doesn't ignite, you simply take the booster along for the whole flight. Of course, this was only for an LPR bird, but a similar technique should work for a larger rocket.

Fred, it isnt that I dont want to use electronics, but there doesnt seem to be a great solution (or atleast nobody has pointed it out) for a way to use electronics to jettison the booster. The burn string idea is interesting... but I am not sure how reliable it would be (could iterfer with a perfect dual motor ignition, something could get caught on it). Plus I dont know how well it would hold to the forces being put on it if it's corrosponding motor doesnt light. I have plenty of $$$ to spend on this rocket, but cant find a resonably priced option for electronic boostre release. Only commercial item I have seen is a booster dropper and that is very expensive, plus I dont think it would work with a rocket like mine (to close to minimum diameter, couldnt access the back to insert nylon screw). You guys seem to think electronics is the way to go, so bring on the options that go along with electronics... i have heard of using super magnets, but I dont think my battery's could magnitize an electronic magnet without loosing all of their power (must power MAWD alt as well). Believe me, I am not neglecting this rocket from electronics, it will have an alt, timer and transmitter on board, as well as an audio beeper.

Jordan,

The booster drop off is your baby...

You've decided you want to do it....you know your rocket's configuration and limitations...so figure out how.
That's the part of the "joy" of this hobby.

Don't sit there and hope that somebody hands you a solution.

My suggestion about electronics addresses your questions about how to CONTROL their drop-off and the ignition of the other motor(s).

This is a complicated and potentially dangerous rocket.
Do it right.....or don't do it.

Ok, I guess I will go back to the drawing table of electronicly controlled designs.

While, walking the dog with my dad, I think we may have come up with an idea, it still needs some finalizing but it is a start. It is based off Ray's design (nose cone comes off and allows booster to seperate)... Picture this, you have a 20" length of 38mm tube, this houses the 6 grain J motor, recovery harness and a streamer. Then, attached with a coupler and bulkplate is a 4" section of tubing, then the nose cone. Electronics blow the nose cone off (attached with a 6" harness to the main rocket) and using Ray's method that seperate the booster from the main rocket. At the same time electronics will light the central (main body) motor. Then, the CTI motors full delay will burn as the unstable booster slows and falls, and eject the streamer. The joint for the actual recovery device for the boosters will have to be pretty tight, might even use two shear pins, to make sure that when it seperates the force doesnt seperate it prematurally. All we need to figure out now is the specifics, and how to make the wire going into the booster (wire that fires BP to eject nose cone) seperate as the booster seperates. EDIT: Wow, I thought Ray (HAKO ballistics) only sold mini hardware and nose cones, now I see the really light weight booster cones! The standard 38mm is cool, but it might be pretty cool looking to use the cone that isnt straight (flat on one side, curved on the other) for a real SRB look. It will still lower the CP though, right (apogee say's nosecones on booster lower the CP, in turn making the rocket more stable). And they even have 38mm booster compatible hardware. I might even be able to start working on the main rocket now that I know how the booster seperation will work.