Sascha Grant posted images of his square rocket build (built around a BT-50 body tube) on the MAKE Flickr pool.
16 thoughts on “Square rockets? Why not?”
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Square rockets? Why not?
Sascha Grant posted images of his square rocket build (built around a BT-50 body tube) on the MAKE Flickr pool.
Comments are closed.
Well, they’ve always been cylinders because that was the best compromise between aerodynamics and the body weight encapsulating the fuel. That was necessary because the ability to overcome the ratios was so marginal. As we get more efficiency from the fuel, then being completely efficient with the body weight vs volume and airflow isn’t as crucial, and we can experiment.
So before, the “why not?” answer was “our engines and fuel aren’t good enough.” Now they might be.
Back in the Day, a couple of rocket buddies made triangular-cross-section rockets from FedEx mailing “tubes!” The through-the-wall fins emerged from the edges, not the faces.
I forget what the nose cones were, but I suspect they were cardboard as well . . . three triangular bits.
I think a non round rocket will cause more problems when there is wind.
Weathercocking, or the rocket nosing into the wind is usually caused by insufficient initial launch speed, and/or an over-stable design. The overall shape of the rocket is a factor, but only in the context of the CP/CG relationship, which is the crucial bit. The additional area does induce additional drag, which could aggravate the former case of too slow, but a larger or faster burning motor can solve that. Rockets in flight are all about relative wind, and since they generally are travelling much faster than any crosswind, the effects aren’t usually significant with a reasonable design.
It all just depends on what the goal is. If it’s to have something showy and fun, sure you can do all sorts of shapes. (But be sure to do your stability checks with rocksim or something similar before you launch it).
If you’re going for altitude, then a minimum diameter round airframe with a Ogive or similar nose is going to be your best bet. Well, conical for supersonic flight if you’re going that big.
One of my favorite insane-looking rockets is the A.C.M.E. Spitfire, which was inspired by the Gary Larson cartoon (You’ll see the resemblance) “we’re not rocket scientists”.
http://www.fliskits.com/products/01prod_fs.htm
He asymmetrically balances the airframe (Mr. Flis IS a rocket scientist). It’s a time-consuming build, but it just looks so insane I found it irresistible.
So if you do decide to build your own 3 or 4 sided rocket ala “fedex express”, just be aware of the extra drag and make sure you have enough initial thrust to have a safe launch.
Happy skies-
-RG
The actual link is: http://www.fliskits.com/products/rocketkits/kit_detail/acme.htm
Corners and edges tend to be weak spots–also the cylinder uses the least material. All this is less important at the small scale though.
Round (cylindrical in this case) things hold the most volume for the least amount of surface area (material in this case). Surface area is expensive in both materials cost and in aerodynamic drag. Cylinders are also less likely to buckle than other shapes -something that is important in rocketry.
Also, some designs actually have used the body of the rocket as part of the pressurized fuel tank system. Imagine a square/prismatic propane tank!
-Bob