# Help out a few (smart) beginners? Thanks!

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Some friends and I have an ambitious goal but are not quite sure how to get started. We're sort of rocketry newbs but we are educated in other disciplines (biology, law, etc).

We're developing a fairly light payload / instruments package. All in we're hoping under 10 lbs. (avionics, digicam, storage)

We know our target velocity. What equations can we use to determine whether a prefab motor will be appropriate, or if we will have to do something custom? (And whether our target Vf is feasible?)

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Google WRASP and in their data base is a varity of rockets in assorted diameters and weights with parameters you can change and motors of different sizes and impulses and you can, with a little practice, ball park just about anything you need.

Hope this helps.

Welcome to TRF, hyudab (and friends). It's pretty quiet here during the day but the troops should come out in full force later.

Have you hooked up with a local launch group?

Have you hooked up with a local launch group?
e-mailed a local club and he provided some useful information. As soon as we can get the right equations together to know whether our goal is attainable we'll start looking into NAR/FAA/ATF rules etc.

Right now we're still trying to figure out how to solve for thrust/specific impulse when we know the target speed, altitude, and weight.

I haven't made the jump to high power yet but I am working in that direction. A payload package of ten pounds is nothing new around here and some of the large birds tip the scales near a hundred pounds (and more). Likewise, there are folk around here that fly complete avioncs packages complete with redundant flight computers, ham radio frequency GPS locator beacons, digital video and more.

Feel free to be more specific but I suspect the people with the answers will be hanging out in the high power forum. You might also want to download the 30 day trial of Rocksim. That will be able to account for your specific geometries as well as your weights and locations of your payloads and will also let you play with various sizes of commercially available motors.

thanks. i've posted there too, now. I'm thinking that, at its most basic, I'm just asking for an equation. I've tried googling around but a lot of what i find is way more complicated that what i'm looking for. Thanks for your reply!

If you are asking what I think you're asking, the physics are far more complex than you may realize. There isn't just one flight equation that can simply be done as a "plug and chug" math problem. The physics of rocket flight (greatly simplified as opposed to doing a complex finite element analysis) are described by the Barrowman equations. These can be done by hand but are also the basis for WRASP and Rocksim. These simulations will do days of hand calculations in minutes and let you "play" with the variables and experiment with actual thrust curves of commercially available motors.

thanks. i've posted there too, now. I'm thinking that, at its most basic, I'm just asking for an equation. I've tried googling around but a lot of what i find is way more complicated that what i'm looking for. Thanks for your reply!

Go to Apogee's site.

https://www.apogeerockets.com/

Try out the RocSim demo.

Not an equation, you just plug in what you want to build and see what it can do.

Welcome! One thing I might add, I'm not sure how much experience with rockets yall have, but from the sound of your post perhaps not as much as would be preferable for a project this advanced. Perhaps I'm wrong in that presumption, but the tone of your question and self professed "noob" status tends to reinforce it.

Remember you have to crawl before you can walk. Get together with a local club, fly some rockets, talk rockets, learn from others and by your own experience before committing months of work and perhaps hundreds of dollars of electronic equipment and rocket and motors to flight, only to learn the hard way that some simple mistake or omission tripped you up. Experience is a good thing, hard won, and usually expensive, so it's best gained on cheaper, smaller rockets first. If you're attempting your own design, I ESPECIALLY recommend starting smaller first, and learning the ropes. Once you get some experience and make a few mistakes, you'll start figuring out what works and what doesn't, and what are good tradeoffs and what isn't.

Good luck! OL JR

Yeah, a 10 lb. payload isn't "light" by everyone's standards. To me, that's "high power."

For the gory detailed equations presented in a relatively simple format.

https://www.rocketmime.com/rockets/rckt_eqn.html

To predict the apogee of most hobby rockets fairly accurately, all you need to know is rocket weight, airframe diameter, drag coefficient (assume 0.6 to 0.75) and motor thrust curve. This is a simple on-line calculator that does exactly that.

https://www.markworld.com/

Why don't you let us know a little about your project. There's a lot of folks here that could help determine what you need, but without a bit more info, we can't be too helpful.

Bob