In article ,
Pat Flannery wrote:

Herb Schaltegger wrote:

That would depend on the inherent stability/flying qualities of the
vehicle and the degree of control authority provided, I should think.
That big plank of a wing and featherable tail would seem to have a
pretty decent margin.



But the passengers would be sitting up in the nose of the ship; which
would put them pretty far forward of the CG;
I assume that the rocket motor sits just astern of the CG and the NO2
tank just forward of it, so as to keep the aircraft's balance correct as
the fuel and oxidizer are expended- if that is the case, then you are
going to need to carry ballast in the crew compartment to represent the
passengers if the aircraft is not to stall on the return glide- the only
other thing you could do is fly it in a controlled dive via fly-by-wire
to compensate for its tail-heaviness; this would make a landing flare
very tricky. Besides, knowing that it has to carry the ballast for the
prize flights, you would want to carry it during the envelope expansion
flights so as to get a true measure of the aircraft's handling and
velocity capabilities at operational weight.


Good points; on the other hand, don't the two passengers sit
side-by-side behind the center/forward pilot's seat? Or am I making
that up out of poor memory combined with how I would arrange the thing
internally? (I thought I'd seen a sketch of that layout somewhere but I
could be wrong.) Because if so, they would be seated closer to CG of
the vehicle and thus have smaller impact to the CG, at least compared
the impact of the rocket fuel and oxidizer in the rear and the single
pilot perched up closer to the nose.

The data sheet from Scaled isn't terribly clear about crew seating, but
it appears that they are all three seated fairly far forward. 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. 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.

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

--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
Columbia Loss FAQ:
http://www.io.com/~o_m/columbia_loss_faq_x.html