On Wed, 30 Apr 2008 21:31:02 -0500, Dan wrote:

It seems to me using solid fuel rocket engines would make more sense
for racing. Each airplane would have two engines, one high impulse for
take off and the other a long duration burn for the race. It seems to me
rapid engine changes would be possible.

It's an interesting idea, but has some technical drawbacks.

A liquid rocket motor, like they're using now, gets fuel just like a recip:
Fuel and oxidizer are stored in tanks and fed to the engine via pipes. It means
that you can install the motor itself in the best location and put the fuel
tanks on the CG so that the aircraft's balance doesn't change during.

However, a solid rocket is a single, self-contained unit. If you put (for
example) a Star 17A solid rocket where the Velocity's engine normally goes,
there'll be ~280 pounds in the engine compartment when the motor lights off, but
only ~30 pounds left when the motor burns out 20 seconds later. This is the
equivalent of having a recip engine completely depart the airframe in flight.

It's not insurmoutable...you could put a small water tank for ballast way up
front and drain it at the required rate. If you could get five times the moment
arm (which is probably pushing it) you'd only need a six gallon tank. But with
both a boost and a sustainer engine, you'd have to have a larger tank with
variable drain rates. And if the water drain system fails, the plane will
shortly become uncontrollable...no way to shut down a solid rocket short of
blowing it up.

If your solid rocket motor were slim and long, you could install it so that half
the casing was forward of the CG. But that does push it into the cabin.

Due to the heat, I doubt a composite Velocity airframe could stand the motor
near the actual CG. The only remaining solution would put twin engines on the
wings. You'd have to beef up the wing structure to handle it. You'll also need
to ensure the aircraft has enough rudder authority to handle it when one motor
burns out a little earlier than the other.

It would probably be a lot easier to mount a second liquid-fueled sustainer
motor in the current vehicles. In fact, a better solution would be to install
multiple small motors instead of the single large one they're doing now. This
would give the pilots a "throttle" that would be a significant tactical factor
in the event of an actual race.

I have always thought a replica Me163 with a solid fuel engine would
be a rather nice air show draw.

The guys up in Everett manufacturing the Me-262s are building an ME-163. No plan
to fly it, though. Pity....

Ron Wanttaja