An elliptical nose with at least 3:1 length to width ratio is ideal. Notice that this is pretty low on the list, however. A lot of ink has been spilled on the ideal nose shape, but for subsonic rockets it's far from your biggest concern.
Conical nose cones have the highest drag of any commonly used shape.
As mentioned earlier in the thread, the rules are very different for subsonic and trans- or supersonic. For the latter a conical nose cone is good. For subsonic, an elliptical nose is much better, as nose cones go. Von Karmin is better yet, as others have said, but also, as Jeff said, the nose cone is far from the most important factor. So on the question of Von Karmin vs. long elliptical, I suspect you're not looking at the last percent of speed but rather at the last tenth of a percent.
- round the leading edge and taper the trailing edge of your fins to form a smooth airfoil cross-section. fins with square edges have much more drag than ones that have been shaped.
That's a pretty good approximation for an ideal airfoil. If you're still after that last tenth of a percent, it should be curved all the way, like a symmetrical airplane wing.
Also, tapering the fins so they are thinner at the tip than they are at the root helps even more. Make the airfoil profile the same all the way out except for scaling down as you go, in chord and thickness together.
- Use a minimum diameter body, that is make the rocket body the same diameter as the engine. Going one tube size up roughly doubles the drag on your rocket.
Which means, you can get lower drag with an 18 mm tube than a 24 mm one. Since you want to use a D motor, go with an 18 mm composite, like the Q-Jet D20. Of all that I'm adding here, this is the most important bit. Realistically, this is the only important bit that I'm adding.
EDIT:
I was ninjad by this. I thought all of the 18 mm motors with the Arotech brand were discontinued to make room for the Q-Jets. Yeah, the D24 sure looks like the way to go. The D21 is also better than the D20, so use whichever you can get. (See graph at the bottom).
- put good smooth fillets on your fin roots. A smooth transition between the body and fins reduces drag.
There is an ideal fillet size. I don't remember what it is, but it's smaller than you probably think visually.
- Launch lugs add drag, if you're really serious consider making a piston launcher instead of using a launch rod. They're a pain in the butt, however, so only do this if you're really serious about getting the last few percent of performance.
Another option is fly away rail guides. That requires launching off of a rail, and it's probably not as good as a piston, but it's surely better than carrying a launch lug along, and it's easier than a piston.
If you're trying for maximum speed, lighter is always better. If you're trying for maximum altitude, there's actually an optimum weight for your rocket that you can find through simulation
And just to amplify that a little, drag is always your enemy either way.
Totally disagree on the "no paint" idea. A mirror-finish paint job (like a Nathan build) is WAY less draggy than raw cardboard/FG/CF/whatever.
Don't do a pretty paint scheme or any decals. Filler primer, sand smooth, then gloss clear coat.
Or you could just borrow/modify Tim Van Milligan’s competition style design for his Frit kit - the RocSim file link is on the online catalog page
And speaking of Tim, there was a series of
Peak of Flight articles a couple three years back about building super light. He used a home made composite body tube made from epoxy and a single layer of tissue paper, I kid you not.
