20 replies to this topic

[Caramanos2000]

Ok its been a while since I made anything. Want to make a nice rocket. Would a D sized rocket engine be ok to lift a nice 2" cylinder shell? Its going to be a beraq or a lampare, havnt decided yet.

[portfire]

Ok its been a while since I made anything. Want to make a nice rocket. Would a D sized rocket engine be ok to lift a nice 2" cylinder shell? Its going to be a beraq or a lampare, havnt decided yet.

Don't just put a 2" cylinder shell on top of a commercial motor (make your own BTW,it's much more rewarding) and hope it's going to lift it.

My advice is to lift 'dummy headers'. Which is basically tubes (In fact your better off using plastic bags, as the ejection charge on the motor will disperse the sand making testing SAFER) filled with sand, and adjusting the weight. They are other factors, but I won't go into them as your using commercial motors

Read the 'rockets with headers' thread.

[Arthur Brown]

If you plan to use a rocket to lift something, you need to do some tests and calculations.

First you need a thrust/time plot for your motor, for this you need to do tests!

You then find the trajectory times and speeds for the motor (with its decreasing mass as consumed) and the payload.

You should be able to determine the thrust, mass, acceleration, time of burn, speed and height reached under power, total height to apogee total time to apogee.

Using all these you should be able to produce something that will fly, carry a load to a safe height, and burst at the apex of it's flight.

Seeing a device that launches, Goes to height and falls back bursting close to the ground is no fun if you happen to be standing (running!) in the burst diameter.

All the info you need will be found by searching the rockets with headers thread.

[karlfoxman]

If I was you I would look into making a 1lb core burner to lift a 2" cylinder. They will weigh roughly the same as a 3" ball shell. As the others say test your motors before you use live headers, I have seen motors not lift, burn too long and come to the ground, cato and be very unstable! Its not a good idea to put a live header onto any untested rocket motor as it can quickly make accidents happen. Its nice to see someone trying beraq, how are you making them?

[portfire]

He uses commercial motor's, wouldn't that give thrust/time etc Arthur ? Then all he as to do is test how much it could lift, obviously to a SAFE height.

As said, make your own motors!! You'll get more thrust, more lifting capability and with plenty of tests, you'll get accurate timing so your header breaks at apogee.

[Arthur Brown]

Thrust - mass = lifting force

Lifting force / mass = acceleration

Acceleration for burn duration gives total height and final velocity -- at end of powered flight

add deceleration to turn over point in free flight to get total height and time

This is the height/time for the burst to happen.

A commercial rocket motor may give you all the data, may not. However as you are using it outside its intended purpose you should test adequately first. Having a two or three inch ball head break after a low lift or during freefall after apogee means a 20 metre zone of burning stars firing into the crowd.

The damage caused by a beraq breaking low and pushing inserts into the crowd to cause flash burns etc doesn't bear thinking about.

remember that the force doing the lifting is the rocket thrust less the all up weight of the assembly.

500g for the shell, 500g for the rocket inc stick the thrust must exceed 1000g for it even to move.

Do the calculations carefully -especially for units SI, mks, cgs whatever you are comfortable with. Then do tests, then fire live shells.

If you have access to commercial products, look (without dismantling) See how they are made -well what you can determine from the outside anyway. Then check that what you design is not too far from commercial practise. --If it looks wrong it may be wrong.

[portfire]

Sorry Arthur, forgot to mention he's using Estes motors

http://www.rocketsto.......=1&P_ID=864

Although you could use them for firework rockets, their designed for model rockets. I doubt this engine will lift a 2" shell

[Pretty green flames]

Arthur, respect man, you seem to know a lot about rockets BUT don't you think that going through all this trouble of calculating stuff is a bit much for attaching a shell to a rocket?

Dude, simply make a rocket, stick a dummy payload on it and fire it then work on from there. Pyrotechnic rockets are more or less trial and error. Even if you do all those calculations you WILL get a CATO eventually.

Keep it simple

[portfire]

If I've got my calcs right (very much doubt it) those D12 motors will lift around 100g...Arthur ?????

[Arthur Brown]

Arthur, respect man, you seem to know a lot about rockets BUT don't you think that going through all this trouble of calculating stuff is a bit much for attaching a shell to a rocket?

Dude, simply make a rocket, stick a dummy payload on it and fire it then work on from there. Pyrotechnic rockets are more or less trial and error. Even if you do all those calculations you WILL get a CATO eventually.

Keep it simple

Thanks!

However It's a LOT safer to do the calculations than to pick the beraq casings out of someones face!

Brief calculations, then remote tests. THEN you can try to produce the device - assuming your legislation permits.

Experimenting with rocket lift when you have a beraq filled shell on top is foolhardy until you have tried to predict performance, the checked the performace

If your shell is too heavy for the motor it will be sitting there in launch tube as the motor stops then it will burst at ground level -- second class option.

Trial and error is a poor design procedure for energetic things! Do some basic calculations to ensure that you stay safe without injuring people. Trial and error is too close to doing a Darwin!


Added

Looking at the motor spec that motor contains 21g powder so the tube will weigh 20 ish grams too add a stick that's 50g You have 50g to put on top before it just sits there or just makes a very slow, low flight. 50g is nothing for a ball shell!

Added 2

If you use a commercial motor where are you going to get the burst ignition from? Ball head fireworks often have a fuse port in the closure plug this contains either a pressed delay or a precision cut time fuse. It's this delay that lets the rocket coast from powered flight to burst at apogee.


Perhaps a beraq is the worst, most dangerous head to top an experimental rocket with. When you have sorted out lifting the mass to height and burst some dry sand. Then tried a shell with stars, then you could try a shell with beraq on your rocket. Remember that a single beraq is a small M-eighty -better fired at a distance.

Edited by Arthur Brown, 19 April 2008 - 01:17 PM.

[Pretty green flames]

Thanks!

However It's a LOT safer to do the calculations than to pick the beraq casings out of someones face!

Brief calculations, then remote tests. THEN you can try to produce the device - assuming your legislation permits.

Experimenting with rocket lift when you have a beraq filled shell on top is foolhardy until you have tried to predict performance, the checked the performace

If your shell is too heavy for the motor it will be sitting there in launch tube as the motor stops then it will burst at ground level -- second class option.

Trial and error is a poor design procedure for energetic things! Do some basic calculations to ensure that you stay safe without injuring people. Trial and error is too close to doing a Darwin!

Arthur, I agree, safety comes first as I also suggested with the use of dummy headers to determine lift capacity and the height the rocket goes with a certain ammount of payload.

Firing a "live" rocket which has not yet been tested for it's lift capacity is certainly an irresponsible and stupid thing to do.

I merely suggested that doing those calculation may not be absolutely neccessary. It was not my intention to convince anyone that putting a header on an untested rocket was safe or even sane.

[Arthur Brown]

We both agree!

A quick calculation and some dummy tests may well give a satisfactory product and retain your liberty.

Personally I doubt that the indicated motor is adequate for much of a ball shell, and underlifting a beraq doesn't seem good.

[sui]

Well, i agree with you guys on doing some dummy lift tests first, just to be on the safe side. Esp if you dont have an exact idea what the motor is going to lift. Sure its useful to do your math , but for my part dont think its really nessecary.. IF you have the right place (without the crowd which could get injured..) to do your tests, it doesnt matter much if your rocket goes upward or crawls to the launch tube..you´ll see what happens. I dont see that trial & error is such a bad thing esp with homade rocket motors. If the motor isnt pushing your shell high enough, adjust it ..till it does .Of course adjusting the power of your motors with live shells is indeed stupid, but you dont really need much tries to get em right. Simple rammed bp motors can lift alot.. why to do the overkill with the calcs ? Is that really needed ?

Sui

[Caramanos2000]

I have used B-6 motors to lift some nice stuff. They fly really really high without some sort of effect it would be almost impossible to spot. Using commercial motors for now because I cant risk a cato as my testing area is not large enough. BTW the crowd will be me myself and I with a camera lol. I have had some limited success with nickle rockets but not much besides that as my tools and chems arnt the proper ones for making rockets.

[portfire]

Using commercial motors for now because I cant risk a cato as my testing area is not large enough.

I don't want to sound like i'm having a go, but if your test site doesn't have enought area to test rockets, I wouldn't be trying to lift a 2" can shell with a D impulse motor. Even if the motor did lift the shell, the report from the shell will be louder than a CATO from a small rocket.

Edited by portfire, 21 April 2008 - 05:16 AM.