QUESTION:
Is Nasa currently conducting any research
and development on the Joined Wing design?
I flew one for the original designer,  Julian 
Wolkovitch. 

ANSWER from Steve Smith on May 18, 1998:
It happens that my group did a huge amount 
of work on Joined wings.  We worked 
somewhat in collaboration with Wolkovitch's 
company.  They got an SBIR phase 2 contract
to build a flight demonstrator.  They spent 
the entire value of the contract building the 
design capability and performing a detailed 
structural design for the joined wings.  Their
ultimate structural design capability for 
joined wings was really quite good, but
unfortunately, there was no money left to 
actually build it. The aerodynamic design was 
done here, by me. I also did a wind tunnel test
on the design.

In house here at Ames, we focused on truly 
answering the question of whether a joined 
wing would make a better transport.  We 
chose a 150 passenger, 1500 NM mission, 
and designed both conventional and joined 
wing designs. We used sophisticated structural
design optimization methods and good non-
planar aerodynamic models coupled to a 
mission simulation.  The mission simulation 
allows you to provide the right weighting of 
design point and off-design performance, and 
insures that you satisfy all mission 
constraints.

To give you an idea of the complexity of the 
simulation, the constraints were take-off and
landing field length, nose-wheel unstick, 
static stability margin, engine out climb 
(2nd segment climb), Range with IFR
reserves, 4 different structural loading 
constraints for gust and maneuver at 
different points in the flight envelope,fule 
volume, elevator control power at max dive 
mach number, and probably a few others 
I've missed.

The mission variables as well as 
configuration variables were optimized, so
cruise mach and altitude were variables, as 
well as thrust, span, aspect ratio, joint 
location, sweep, airfoil thickness, wing and 
tail taper, and all the aerodynamic twist 
variables to optimize the trimmed cruise 
drag, and all the structural variables to 
optimize the structure for minimum weight.
All these were determined using a numerical 
optimization package called NPSOL that 
solves constrained optimization problems 
using what's called "Sequential Quadratic 
Programming." The optimization objective 
was minimum direct operating cost (DOC) 
for each airplane.

As we went through the development of all 
this, we were continually adding more 
sophisticated analyses, and each time we did, 
some of the potential benefit of joined wing 
was lost.  Finally, we included a structural
constraint on rear wing (tail) buckling, and 
the weight increase required to prevent 
buckling was small, but enough to remove the
last of the advantage of the joined wing...it 
ended up having about 3% higher DOC for 
the same mission, compared to a DC-9-like 
airplane.   This isn't to say that a different 
mission might better exploit the joined wing 
to advantage. I also think there were some 
limitations on the designs that might have
hurt the joined wing...if we did it again, we 
might get a slightly different answer.  But 
not vastly different - it's going to be a small
margin either way.  Joined wing suffers most
from short tail moment arm, so the tail down
-load to trim at CL max is large, so the wing 
area was bigger, quite a bit bigger.  I think 
we could help this some by tailoring the flap
deflections and increasing the wing sweep, so
there was less download on the tail for a given
static stability margin (c.g. position).

All this work generated one PHD thesis 
directly, and contributed to two others, as 
well as generating about 10 archival journal 
papers and nasa data reports.  If you do a 
search for joined wings with authors John
Gallman, Steve Smith, Ilan Kroo, you will 
find our papers.  John Gallman's thesis also 
includes a flutter analysis of the joined wing.

Since then, Boeing has done some interesting 
work on the joined wing as a platform for 
phased-array radar, with the goal of 
replacing the AWACS dish on top of the 
airplane with a radar array built onto the 
wings. The diamond planform gives all-aspect
coverage, and as long as the performance is 
only adequate, they have a much more 
mission-capable airplane than current 
AWACS type airplanes.  The first candidate 
airplane would be carrier based and replace 
the E-2 Hawkeye. We gave them our 
joined-wing structural design code, but I 
don't know to what extent they used it.

Also going on now is some work at Lockheed 
on Box Wings.  I extended some of our joined 
wing structural analysis to box wings several
years ago on a consulting job. I found the box 
wing to be much heavier, and it also has
some odd structural dynamic modes that 
might hurt the flutter speed. Anyway, 
Lockheed is hot on the idea, and I gave them 
the structural design code too.