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BJCK1990

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I read a review about Public Missiles CPR3000 dual deployment system which discouraged the use of the system for rockets which used K sized motors or larger. Has anyone had issues with this system for this type of motor or anything larger?

The rocket which I am considering this system for will use a K1100 sized motor, have a diameter of about 4.0 inches, and will be weighed down enough such that apogee is at approximately 1500 ft.

Thank you for your comments.
 

ben_ullman

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I would ditch the CPR at all costs. Its expensive and hard to work with.

Ben
 

sylvie369

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I think that the comments in that review about not flying it with K motors are more a matter of airframe than of the CPR system itself. I'm also not sure I agree - the author of the comment seems to think that fiberglass is a must if you're flying K motors, and that's simply false. Regardless, your airframe decisions are mostly independent of your decisions about what kind of altimeter bay to use.

That being said, I agree with the other response - I wouldn't bother with the CPR system, and instead learn to make your own altimeter bay and mountings. That's what the vast majority of dual deployment fliers do. It'll save you money, give you a much more straightforward system, and probably give you a better system. I've seen a CPR system in action exactly once, and I attend a LOT of HPR launches.

I'm curious - what in the world are you flying, that you're going to keep a 4" rocket to 1500 feet on a K1100?
 

ben_ullman

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I'm curious - what in the world are you flying, that you're going to keep a 4" rocket to 1500 feet on a K1100?
It must be pretty wild. a 1/38th scale Saturn V with 28lb nosecone went 1k feet on one.

Ben
 

BJCK1990

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Thank you for your responses. The rocket is for a competition where the challenge is to design the heaviest rocket to reach a minimum altitude of 1500 feet. However, I do not have any previous rocket experience. I am given a decent budget though so money isn't an issue. I haven't decided what I am going to use to weigh it down yet (maybe sand or lead shot).

My back up option was to use an RRC2 mini and build my own duel deployment system, or maybe single deployment. Does anyone have a good recommendation on a design for a system?

Thanks again.
 

ben_ullman

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Thank you for your responses. The rocket is for a competition where the challenge is to design the heaviest rocket to reach a minimum altitude of 1500 feet. However, I do not have any previous rocket experience. I am given a decent budget though so money isn't an issue. I haven't decided what I am going to use to weigh it down yet (maybe sand or lead shot).

My back up option was to use an RRC2 mini and build my own duel deployment system, or maybe single deployment. Does anyone have a good recommendation on a design for a system?

Thanks again.
Just go single deployment. at 1500 its not that big of a deal. Just make sure you don't have ALL the weight in the nose. You will make it quite overstable. Try and disperse some of it throughout the main part of the rocket.

Ben
 

BJCK1990

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Alright, guess ill keep it with the good old "Keep it simple stupid" method. A reliable, safe recovery is more important then how far we have to chase it.
 

Handeman

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When you add the weight to keep the flight to 1500 ft, make the weights removable. Then you can get rid of the lead and really fly the rocket!
 

ben_ullman

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Alright, guess ill keep it with the good old "Keep it simple stupid" method. A reliable, safe recovery is more important then how far we have to chase it.
The chase won't be that bad. Estes rockets hit 2200' on some motors and those are single deploy. You will be fine.

Ben
 

bassdoc

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Thank you for your responses. The rocket is for a competition where the challenge is to design the heaviest rocket to reach a minimum altitude of 1500 feet. However, I do not have any previous rocket experience. I am given a decent budget though so money isn't an issue. I haven't decided what I am going to use to weigh it down yet (maybe sand or lead shot).



I was just wondering if you can fly on a K if you have no previous rocket experience. Do you have a level 2 or is this part of a group thing where someone else is certified?
 

Mike Di Venti

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Thank you for your responses. The rocket is for a competition where the challenge is to design the heaviest rocket to reach a minimum altitude of 1500 feet. However, I do not have any previous rocket experience. I am given a decent budget though so money isn't an issue. I haven't decided what I am going to use to weigh it down yet (maybe sand or lead shot).



I was just wondering if you can fly on a K if you have no previous rocket experience. Do you have a level 2 or is this part of a group thing where someone else is certified?
You took the words right outta my mouth.
 

Mike Di Venti

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I have used the CPR 3000 for sometime. Until it broke.
What a pain to fix. I just made a regular av-bay that could transfer rocket to rocket.

For what you want to do, the CPR would not be a good idea. I think there would be too much stress at that joint. I can vision it breaking at the CPR.

I say this because you're going to build a 4" rocket that'll have to weigh around 50#. That's a lot of weight to fit in a small rocket to keep it near 1500'.

You'd be better off tying a rope to it and hold it back!:eyepop:
 

ben_ullman

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I have used the CPR 3000 for sometime. Until it broke.
What a pain to fix. I just made a regular av-bay that could transfer rocket to rocket.

For what you want to do, the CPR would not be a good idea. I think there would be too much stress at that joint. I can vision it breaking at the CPR.

I say this because you're going to build a 4" rocket that'll have to weigh around 50#. That's a lot of weight to fit in a small rocket to keep it near 1500'.

You'd be better off tying a rope to it and hold it back!:eyepop:
now that would be hilarious. enter a 1k foot contests or something and just ancor it to the ground! :roll:
 

JDcluster

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How do you find these gigs? I'd love to have a budget provided by someone else to build & fly rockets.....




JD



Thank you for your responses. The rocket is for a competition where the challenge is to design the heaviest rocket to reach a minimum altitude of 1500 feet. However, I do not have any previous rocket experience. I am given a decent budget though so money isn't an issue. I haven't decided what I am going to use to weigh it down yet (maybe sand or lead shot).

My back up option was to use an RRC2 mini and build my own duel deployment system, or maybe single deployment. Does anyone have a good recommendation on a design for a system?

Thanks again.
 

sylvie369

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This wouldn't happen to be the Wisconsin Space Grant Consortium competition, would it? If so, I'll probably see you at the launch, and probably at the presentations the evening before. I mentored a team in the second and third contests (I think this is roughly the sixth?).

If that's the contest you're in, you won't be able to use single motor-based deployment. Among the rules you'll see

"All parts of the rocket must be recovered together using an electronically deployed parachute recovery system"

That doesn't mean you can't just pop a parachute at apogee, but you'll have to do it electronically, not through the motor's ejection charge. In fact, with that much weight at 1500 feet, I think you can be sure that the successful teams will be ones that simply use an altimeter to blow the main at apogee. That's going to make your altitude bay design a little easier, at least. You might think about using the altimeter's main deployment output as a backup charge.

In fact, if you've got a lot of weight in the rocket, an altimeter-based apogee deployment is going to be far better than motor ejection, because with motor ejection you have to estimate the proper delay so that you eject while the rocket is traveling fairly slowly, at apogee. If you miss, and deploy early or late, with all that weight (/momentum) things will come apart dramatically. If you use an altimeter instead, you don't have to guess at when the rocket will be at apogee: the altimeter will simply detect the right time to fire the deployment charge, and fire it. There's another thread on this forum about when to use dual deployment: this is a perfect example of a situation in which you want to use altimeter-based deployment even though you're not concerned about how far the rocket will drift.

Placement of the weight is going to be really important. Are you using RockSim on this project? Be sure to put some wind in your simulations. If you're too nose-heavy, there's a risk of weather-cocking too much into the wind, and not reaching your 1500 feet target. I think you'll want to be careful to keep the stability margin right there in the 1-2 caliber range.

A big challenge is going to be recovery design (obviously). If that 50 pound estimate (above) is right, that IS a lot of weight to put in a 4" rocket. It has to go somewhere, and so does your parachute, and it's going to have to be a pretty large parachute. When your charge blows, the weighted part is going to stay put, and everything else (the remaining 10 or so pounds of rocket) is going to be blown off of that part. It'll be important to think about what's where when that happens.

Don't worry at all about drifting away - from 1500 feet with significant weight, that's not going to happen to anyone. Anyone who lands in the trees or ponds, it'll be because they didn't boost vertically: get that part right, and you'll come down on or near the runway.
 
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