Just idle fun speculation, of course. Clearly, a conventional rudder like
the Genesis wouldn't work with a 31 meter span. But, it would take only a
tiny amount of drag at the wing tip acting through a 15 meter moment arm to
produce huge yaw moments. I've run this calculation a few times and the net
drag of tip drag rudders would acutally be less than a conventional rudder.
A trailing edge elevator would work fine regardless of the span. The
Genesis "T" tail is actually a hinderance.

As for the control moments to control engine thrust and "P" factors, yes,
that is a challenge. A few prople have suggested lowering the thrust line
so it passes through the CG and aerodynamic center. The rear propeler could
fold back somewhat like a Carat and be pulled into a tube in the rear
fuselage. Not sure how the landing gear would work with a low thrust line.

Obviously there would be some weight reduction to the 'non lifting parts'
that would roll through the wing spar calculations allowing a lighter wing.
Probably not a huge weight reduction but every bit helps the wing bending
moment.

Turning flight might be easier. The short fuselage could be kept aligned
with the local airflow easier than the very long one of the ETA.

Obviously, something like this isn't a 'cut and paste' sort of design. Each
aspect of the design would break new ground and have to be carefully thought
through. Each design change would affect everything else.

Bill Daniels


"Eric Greenwell" wrote in message
news:nmkji.6642$wu5.6324@trndny03...
Bill Daniels wrote:
I think this incident may have an influence on future designs. The
Genesis
obtains excellent handling and quite respectable performance without a
tail boom which forces the question, " Why have one?" The 18 meter and
larger gliders would obtain even greater relative performance and damage
resistance since the fuselage size need not increase in porportion to
wing span.

I suspect the increase in wing span might still require a commensurate
increase in rudder/fin and boom length, just to control yaw, even it
wasn't needed for the elevator. Also, flapped gliders have relatively less
drag from the elevator than aileron-only gliders, so I think they would
have still be better off because the wing could be more easily optimized
for performance.

I wonder what the ETA would be like with the Genesis fuselage.

A further complication with the ETA is controlling the glider under power.
I have no idea how it would work out in practice, but I'm guessing any
advantages of the Genesis type design would be lessened by the control
requirements under power. Add in the problems of stabilizing a floppy,
high-aspect ratio wing, and I'm willing to believe the nod for performance
still goes to the conventional tail.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org