Originally posted by Hospital_Rocket
I have a couple of ideas for some scrarch builts that I am tossing around and want to know how geometry affects performance.
In general, nose shapes like conical, ogive, secant ogive, and the other 'pointy' ones are the best choices for transonic and supersonic flight. On the real sounding rockets they want to reach high altitudes efficiently so these shapes are often selected unless a specialized payload requirement steers the design in some other direction. For some missiles (usually military) the nose shape is a radome (cover for the guidance system antennae) and the nose shape is often influenced by seeker-head function and sensitivity.
In general, nose shapes like elliptical, parabolic, hemispherical, and other 'round' configurations are the best choices for subsonic flight. When given a smooth finish these shapes offer the lowest drag coefficients, and a short (~2:1) elliptical NC also minimizes wetted surface area. Serious NAR competition models will frequently use these shapes unless some other design requirement prevails (such as the hinge mechanisms of HD models).
There is nothing inherently wrong with using supersonic shapes in subsonic model rockets. You will pay a small performance penalty for the (unnecessary) extra surface area. If you turn your own NCs out of a relatively heavy wood (basswood, poplar, etc) the added volume will result in a heavier nose cone, unless you perform some additional step to hollow out part of the nose. The nose shape selection is basically just a matter of style. Obviously, if you are making a scale model of a supersonic design then you have to use the original nose shape.
In general, in all cases you would prefer to avoid sharp corners and mathematically-hard lines oriented perpendicular to the airflow. Shapes like the Gemini crew capsule are a perfect example: the flat nose (and sharp corner), the crease where the main capsule shape flares out, and the base of the capsule (another sharp corner to transition to the Titan booster shape) are all 'bad' aerodynamically. (In the case of the Gemini design, it would have been worse to add an aerodynamically optimized fairing over the whole thing because the weight would have reduced performance unacceptably.)
