Once you're making a really big rocket, other constraints, like how high your factory roof is or how wide your train tunnels are, start to come into play, and you may have to get longer and skinnier than the aerodynamically optimal shape as well. So that's where the basic familiar rocket shape comes from. Keeping the bottom end of the Sears-Haack shape cylindrical, or even flaring it out slightly, rather than boat-tailing, improves stability dramatically. For stability, you want to keep the center of pressure behind the center of gravity - this is why darts, arrows, and many rockets have fins at the back the fins add drag at the base, moving the center of pressure back and keeping the projectile stable. The tapered "boat-tail" at the back of the Sears-Haack shape, though, moves the center of aerodynamic pressure forward. The nose cone usually has a shoulder a section that fits inside the air-frame to keep it centered on the rocket and a place on the bottom where the recov-ery system can be attached. (Note that the proportions of this particular example aren't part the definition of the Sears-Haack shape for minimal drag you'd have to have an impractical body of infinite length and infinitesimal cross section.) Nose cones come in many shapes: round-ed, elliptical, parabolic, ogive, and conical, to name a few. Sears-Haack is pretty similar to the German V-2 rocket body. So what am I missing? Where in my broad estimations / calculations have I made naïve assumptions?įor supersonic flow, the Sears-Haack body offers less drag than the shorter teardrop that's optimal in the subsonic regime.
Now, rocket designers are reasonably smart folks, and have probably thought of this So, for a single stage rocket, I would assume a bullet shaped rocket with something like a 3:1 length to diameter ratio would be ideal for an Earth launched rocket.Īnd for a multistage rocket, the top stage would have something like a 3:1, and the lower stages something like 1:1 - 2:1 length to diameter ratios.
Shapes ready? Now it’s time for the little ones to get creative and learn!Ĭreate a shape craft activity kit. Use scissors to cut out the traced shapes from the coloured craft paper. Take a coloured craft paper and place a shape cut out on it simply trace around the sides of the shape. Print and cut out the shapes from the template. You can either do freehand drawing or use the template. If you are going this with younger children then prepare the shapes beforehand but it is great scissor practice for older children. If you cut the shapes in felt then you can reuse them over and over again on a felt board without glue.
You could also use craft foam or even felt to practice on scissor skills. For younger children, you can precut all the shapes, but for older ones, you could make a stencil and get them to trace the shapes and cut them out. I love how simple activities like this shape rocket can be adapted to the age and ability of children. In fact, it is a really fun, simple activity that can be used lots of ways and is really inexpensive.
This build a shape rocket is a brilliant preschool activity for shape recognition, working on scissor skills and also for colour recognition.