High Altitude Rocket Project (HARP)

I recently read an article published by Apogee in their Ezine about someone who is trying to reach an altitude of 100km using a 2 stage rocket. In the same 'Zine is a discussion of the nose cone shapes that work for the sort of mission HARP is to accomplish. The outcome of the discussion is that drag varies not just with altitude (less air friction, of course) but also with Mach number. That is we can expect our rocket to go supersonic for this sort of mission, but it would travel at Mach 1.5 for half of the powered flight envelope. The nose cone suggested is one known as 'hypersonic optimum' which is a 'pointy' type of cone, that is less rounded and far narrower in profile than, say the sort of nose you see on an anti-aircraft or anti-ship missile. The nose cone is effectively a 'blunted' cone, aka 3/4 power. It's side elevation makes it less of a pure triangle, but not much further so. There is no gradual transition from square to angled sides. It's just angled. Interestingly, this shape is the one I use most when I use TinkerCAD to design nose cones, not because I think I am doing it 'right' but because it happens to be a convenient default shape in TinkerCAD. Oh happy co-incidence.

I've also been putting more thought as I built HARP 4. Yes there are design issues, and documentation and planning and so on. But to get to that point some experimentation in practical construction techniques is necessary (I felt):

Since we are talking requirements, I'd like to introduce 5 new requirements:

The rocket must be built out of readily available materials
The rocket must fly on readily available motors or propellants (no backyard fiddling with stuff that goes BOOM!)
The rocket must be subject to the safety rules of the NAR to the maximum extent possible
The rocket must launch from a tower (no launch lugs) to limit parasite drag
The rocket must have a minimum of protrusions (like pods) to limit parasite drag

If we are to build a HARP, we are really looking at metal (Aluminum) or Fiberglass. Since our rocket will experience some serious skin friction, we know paper rocket tubes are just not going to survive unless we cover them in something like fiberglass, which still keeps the rocket within the NAR requirements that the rocket crumple if it goes ballistic and crashes. It is likely better to use thin walled fiberglass tubes, however, as those are commercially available and so adheres to the first of our requirements. If we were to use Aluminum, we would again use commercially available tubing, but that may bump up against the self destruct requirement the NAR has.

It is very likely that at the next High Power launch at Great Meadows next Spring (2015) we will be flying a Fiberglass tubed rocket. I also am wondering if our glider should be folded inside the main tube and pop out at Apogee, open its wings (perhaps scissor wing style) and come down that way. That would again meet the requirement to limit protrusions and limit parasite drag. I will spend a good part of the winter looking at design concepts. HARP 4 however is meant to test engines and payloads more than the airframe, even though on November 1 I will be launching a 5 foot tall rocket with a quad engine cluster as the potential carrier for the HARP glider.