Herb Schaltegger wrote:

Good points; on the other hand, don't the two passengers sit
side-by-side behind the center/forward pilot's seat?

I assume that's the case; you wouldn't want the passengers interfering
with his field-of-view out all the circular windows.

The NO2
tank, however, appears to be situated very damn nearly at the center of
lift of the wing or perhaps a bit forward of that point, probably right
at the CG as well.

It would make sense if the whole oxidizer tank/ fuel cylinder assembly
was as close to the CG as possible, so that propellant depletion
wouldn't shift the CG at all during ascent; since the oxidizer tank is
in front; I assumed the cylinder full of the fuel material would be
mounted in back of the CG to keep the propellant weights consumed during
motor burn in front and back of the CG similer...if it was going to be
off-balence, then you would want it nose-heavy during ascent, to add to
it's "arrow stability" as it accelerates toward the supersonic regime;
once it goes supersonic, the center of lift should move aft of the CG,
and stability increase.
snip

Thus, if they have a rocket failure of some type and
terminate boost, the CG won't change too much. Note that Scaled has
already demonstrated cold-flowing the oxidizer in-flight; I would
suspect that with the tank where it is, it has little impact on vehicle
stability either full or empty. I also see from Scaled's data sheet
that in addition to elevators on the tail for pitch and roll control,
the entire horizontal tail surface is electro-servo actuated for
supersonic flight control and overall vehicle trim. I would suspect
that that control surface, as far back as it is, can do very well at
trimming out the effects of two passengers (total weight of what? 350
pounds?) just a few feet forward of the CG.

You could certainly do this; but you are going to pay a price for it-
this means keeping the horizontal control surfaces at a angle of attack
different from the wing, and that's going to generate drag (you are also
going to have to adjust the angle that they are at at varying speeds).
During the early non-powered Spaceship One tests it once tumbled out of
control during a test drop at full aft CG limit; this was probably
related to the pilot only/pilot-passengers flight profile options- I
assume the design was optimized to fly with the pilot and weight of
passengers as it's normal flight condition, as that is what is needed to
win the prize.


Hmmmm . . . this very much sounds like something for Mary to comment on.


You know what _she'll_ want to know.....'Does it have extensible "Dog
Peckers" on it?'

Pat