Hi There from me & my son

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Hi There from me & my son

Postby camacd » Wed Apr 01, 2015 9:11 pm

My Son Harry and I have recently discovered rocketry. I bought him a ready to fly rocket for Christmas. After a few misfires and some frustration for a day or so, we worked out that the Estes ingiters were a bit dodgy and that you need a good battery to make them fire.
Anyway, we then went to a Qld rocketry launch day at Cedar Creek and learned about Thunda Down Under. We decided to try building out own rockets for the big weekend.
The rockets flew ok but after a few flights they were both damaged, and our learning curve continues. We are now building the next design, looking for more altitude, as well as reliability.
I need help with the mathematical side. I'm an engineer so I can grasp most concepts but I need to know where I can get the right formulae, what are the types of assumptions to be made, etc.
So I'm keen to chat to anyone who can help.
Cam MacDiarmid
"He who says it can't be done is liable to be interrupted by somebody doing it". - My Mum

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Re: Hi There from me & my son

Postby Fadge » Wed Apr 01, 2015 9:57 pm

Welcome to the forum. You will find plenty of useful info here.

With regard to the maths, it is best to download a copy of Open Rocket, which is free. It is very easy software to use and you can create your rocket design and simulate flights with different motors.

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Re: Hi There from me & my son

Postby SpaceManMat » Wed Apr 01, 2015 11:13 pm

Hi Cam welcome to the world of rocketry. With regards to Open Rocket you can find files for most of the rocket kits out there. http://www.rocketreviews.com/ is a good resource for simulation files and also pictures, flight logs etc. Keep in mind that Open Rocket will read RockSim files as well with few issues.
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Re: Hi There from me & my son

Postby martymonsta » Thu Apr 02, 2015 5:58 am

Hi Cam and welcome to the forum. Probably one of the most critical factors in designing a rocket is the relationship between the center of pressure (CP) and the center of gravity (CG). The CG is relatively easy to find, just balance the rocket on your finger, the CP is harder to find as it is the point where aerodynamic lift is centered, some kits will have it marked but if not use a program like Open Rocket to find it. Their relationship to each other gives a fair indication as to whether they rocket will be stable in flight. The CG as a rule of thumb should be at least 1 body tube dia. forward of CP with all motors and parachutes installed, if it is less then the flight may become unstable. I hope that helps.
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Re: Hi There from me & my son

Postby CATO » Thu Apr 02, 2015 6:17 am

Hi Cam (and Harry), welcome to the forum.
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Re: Hi There from me & my son

Postby Lamp » Thu Apr 02, 2015 8:39 am

Hi Cam and Welcome.

Open rocket if free and is a great program for everything from small low power rockets to large high power ones. It does require the latest version of Java but is well worth learning how to use. If you design a rocket in it, it will tell you CP, CG and your stability margin. If you then run a sim of your rocket in the program it will give you altitude, velocity, acceleration and all sorts of other parameters...and these are quite accurate.
I recently used it to design a 2 stage N to M powered rocket...
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Re: Hi There from me & my son

Postby october sky » Thu Apr 02, 2015 9:41 am

Hi Cam and Harry and welcome not only to this great forum but awesome hobby of rocketry ! :D

You are in the right place and what the guys have already told you is the way to go. Just keep asking questions as that's the way we have all learned. :wink:

I'm sure to catch up with you in one of the QRS launches in the near future. BTW, enjoy the ride, don't rush and your rockets will get bigger and bigger in time. :mrgreen:

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Re: Hi There from me & my son

Postby Ironside » Sun Apr 05, 2015 10:48 am

Cam and Harry,

It can be a little daunting to get started. There are plenty of fellow rocketeers at the QRS launch days who can assist. In the meantime, the following reading may be of interest:

QRS web site members section has an articles section that can provide some interesting articles particularly the Barrowman papers.

Also on the web site there are info packs for LPR and MPR that are useful.

Australian Rocketry web site has a Getting Started section that is worth a read as well.

Or you can browse through the hundreds of articles on the Apogee [i]Peak of Flight[i] site
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Re: Hi There from me & my son

Postby camacd » Thu Apr 09, 2015 8:16 pm

Thanks everyone for the welcome.

I've located a number of useful papers on the web and found drag formulae, barroman equations etc. I've created a spreadsheet using these principles to determine total mass, CG, CP, and also to do an incremental flight analysis. I can put in different motors and it will spit out the revised outputs.

I've built a couple of rockets with D/E motors and I'll try them out this weekend. I'll see whether my calculations are taking me anywhere near the truth.

I'll also track down open rocket and see if it gives comparable results.

Hopefully see you on Sunday.
"He who says it can't be done is liable to be interrupted by somebody doing it". - My Mum

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