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Necessary thrust / SI?

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hyadub

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It was suggested I post this question here:

We are wanting to launch a payload, hopefully less than 10lbs. None of us has formal training in this field but are educated in other areas (like bio, law, etc).

How do we determine the necessary thrust/SI (and thereby figure out what sort of motor we'll need to buy/build?) to reach our goal? Assume we know the weight of the payload and our target speed and/or altitude?

Appreciate any advice, and especially the necessary equation! I'm sure we'll be back with questions about motors once we figure out whether this is feasible and what our thrust requirements are. Thanks!
 

Handeman

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There are a lot of simulation software programs that will allow you to enter the basic configuration and weight of your rocket and simulate the flights on various motors. WRasp, RockSim, etc.

The equation is out there, but I don't know anyone that doesn't use the computer and simulations to determine flight profiles for these things.

I guess the first question is, is the 10 lbs just the payload, or the complete rocket weight? Either way, you are probably looking at a level II rocket and motor.

What is the minimum diameter for the payload, that will determine the configuration of the rocket and affect motor size.
 

hyadub

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I guess the first question is, is the 10 lbs just the payload, or the complete rocket weight? Either way, you are probably looking at a level II rocket and motor.
thanks for the reply. it would just be the payload. We're thinking we'd like to have some flight controls, a good strong transmitter, digital camera, storage (probably flash?), and i guess some rudimentary avionics. The idea is to get the sucker way, way up there and be able to produce some rather stunning images. We're aware that at some point you may need various FAA clearances etc, but for now we're hoping to figure out how seriously to take ourselves and what kind of thrust we can expect to be able to produce (or will become necessary).
 

blackjack2564

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A direct answer : The standard ratio is 5 to 1, thrust to weight. Soooo.....if your rocket is flight ready and weighs 15lbs. You will need 75lbs of thrust.

Most motors are rated in newtons, to convert, divide by 4.45, that will give you thrust in lbs.

We are talking 5 to 1 average thrust. Not total. This will give a safe flight.

For example : a 4in rocket weighing 17lbs, flying on a motor in the K-700 range, will fly to around 9-10,000 feet.

The rocket kit will cost around 150-225.00, the motor case 200.00, fuel 160.00 and the electronics, parachute, and misc. another 200.00 .

This should be a pretty good cost est. with off the shelf parts.
 
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lkal32

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Why not look into using a weather balloon??? Much simpler and cheaper...
 

n5wd

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For example : a 4in rocket weighing 17lbs, flying on a motor in the K-700 range, will fly to around 9-10,000 feet.

The rocket kit will cost around 150-225.00, the motor case 200.00, fuel 160.00 and the electronics, parachute, and misc. another 200.00 .
Of course, that's the cost for JUST THAT FLIGHT. To be able to get to that point, you'll have to jump through certain hoops - such as certification. You didn't say where you are... so if you're in the US, one of your crew will have to be certified by either the National Association of Rocketry or the Tripoli Rocetry Associaton as a Level 2 High Power flier. To get that certification, you have to have been a Level 1 High Power flier, and pass the certification test.... activites which will increase your overall cost (but definitely will provide a bit of fun, as well).

If your interest is merely in lifting a payload to some reasonable height, you might employ the services of someone local who is already certified to fly the high power motors you're going to need, and who can offer mentorship as well.

Either way, there's a bit of a learning curve to get where you want to be, but your crew seems like they're not adverse to learning, and hey.. it's only rocket science! :D
 

cherokeej

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It was suggested I post this question here:

We are wanting to launch a payload, hopefully less than 10lbs. None of us has formal training in this field but are educated in other areas (like bio, law, etc).

How do we determine the necessary thrust/SI (and thereby figure out what sort of motor we'll need to buy/build?) to reach our goal? Assume we know the weight of the payload and our target speed and/or altitude?

Appreciate any advice, and especially the necessary equation! I'm sure we'll be back with questions about motors once we figure out whether this is feasible and what our thrust requirements are. Thanks!
Hi there. Any interest in this?

http://www.arliss.org/

Every September, and we're expanding the program to include a launch in June, to help accommodate US schools.

Bottom line is that with a ten pound payload, if you want serious altitude, you're going to need some serious impulse.

BTW, the 5 to 1 thrust to weight ratio is a minimum... You really do want more than that...

James
 

FROB

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My suggestion is to downscale - With modern electronics, you can get your payload down in weight significantly- I'd expect to get all those functions into a package of less than a pound, and with some effort, less than 1/2 Lb. It's really worth the effort there as the weight savings there has a drastic domino effect on the requirements and cost of the rest of the rocket. If you put that into a 3" dia minimum diameter carbon-fiber airframe with the biggest 3" dia motor (maybe an 'N' ) you can get your hands on, you can probably get beyond 35,000 feet. Much more complex, but doing a 2-stage 3" to 2" min-dia has the potential to make it past 50,000'.
By the way, if your aim is to get video of the curvature of the earth, the edge of the atmosphere, and a black and starry sky, you really want to get to 70,000' or more where it starts to be really apparent. Weather balloons routinely get to 100,000' or more with a payload, and a modest budget, an altitude thats extremely difficult to achieve with rockets at the hobby-amateur scale, and only with great expense, and a lot of luck.;)
 

bobkrech

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It was suggested I post this question here:

We are wanting to launch a payload, hopefully less than 10lbs. None of us has formal training in this field but are educated in other areas (like bio, law, etc).

How do we determine the necessary thrust/SI (and thereby figure out what sort of motor we'll need to buy/build?) to reach our goal? Assume we know the weight of the payload and our target speed and/or altitude?

Appreciate any advice, and especially the necessary equation! I'm sure we'll be back with questions about motors once we figure out whether this is feasible and what our thrust requirements are. Thanks!
You need a BATFE explosives permit to purchase a high power rocket motor motors that is capable of launching a 10 pound rocket, and you also need a FAA waiver in order to launch it.

It's a lot simpler to find your local rockety club by going to http://www.nar.org and http://www.tripoli.org and talk to the folks there about what you really need to do your project.

Bob
 

dave carver

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I posted minutes, and I mean minutes, after the first post and it's not here:(

Might be a few bugs left around here :p
 

judo

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We're thinking we'd like to have some flight controls, a good strong transmitter, digital camera, storage (probably flash?), and i guess some rudimentary avionics.
Flight controls and avionics sounds like a guidance system. I don't know if that's even legal. What, exactly, is your payload?

I suggest checking YouTube for rocket videos. Some cameras look out, some down, and some both.
 

Peartree

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If you want to build a rocket, there is a learning curve and certification.

If you only want to loft the package, you could probably work with someone who is already certified.

If you only want the pictures, there are a bunch of folks who have probably already done what you want to do or who could do it with their equipment at the launch of your choice (if the FAA wiaver was high enough) for the cost of a motor.

What is it you really want to do?
 
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