Gerolf writes: "Exactly my point, Petr - better handling is the
REAL performance gain on modern topless hang gliders."

Steve Pearson writes:

The current competition hang gliders from all manufacturers are
very refined with few opportunities for performance improvement. In terms of
configuration, we’re between two poles that each offer compelling
advantages—rigid wings with extreme aspect ratios have extraordinary aerodynamic
efficiency but it’s paragliders, at the other end of the spectrum, that have
been much more effective at expanding the soaring and cross country envelope. So
hang glider designs are evolving consistent with the same optimization problem
that resulted in a corresponding diversity in nature from the albatross to the
eagle.

To naive observers, it often seems that ‘more glide’ is the answer to our
performance aspirations, and an incremental improvement is as simple as
increasing the aspect ratio. Who hasn’t looked at the glider specifications
expecting those numbers to somehow characterize the  aircraft? I know I did
several times over the last 40 years with design decisions. 15 years ago I built
a number of progressively higher aspect ratio T2s that flew great and it’s still
hard to appreciate how something that looked so promising didn’t perform better.

There are a few issues that constrain the design problem. The first is handling,
which is largely influenced by wing span. Handling and control authority are
fundamental to performance and progressively diminish with bigger spans. The
second is stall speed which depends primarily on glider area, so with increasing
AR constrained by span you end up with a higher stall speed which compromises
the ability to climb in small thermals. The third is weight which is related to
glider span, and heavier gliders are generally undesirable. So, in our
development program the test glider that we flew ended up with a little more
span than the T2 154 and the area of the T2 144. The handling was similar to a
154, the stall speed like a 144, and the weight was 5 pounds heavier than a 154
(because it required a stiffer airframe to control twist at higher speeds) by
the time it was configured for comparable performance. In short, the effective
performance was diminished. The other implications of this example are that even
the best design intensions offer no guarantee of meeting expectations, and that
it’s often easier to screw things up than improve performance.

The question remains, how do we improve performance? Comp and record flying
happens more in climb and racing than at best glide speeds. Climb depends more
on handling and low stall speed than minimum sink rate. Racing at speeds 1.5x
best glide or higher depends on low twist. So there are probably better
opportunities for improving performance than increasing aspect ratio and the
associated reduction in induced drag, and it seems that we should look more to
improving low speed performance.

We use 2 launch elevations at our test fly site—the 750' for Falcons and Alphas
and the 1500' Regionals for S3s and above. The interesting thing is that at the
lower launch, the performance metrics are inverted. The model that is most
likely to soar and climb out is the Alpha and the least likely is the T2. The
handling and slower speed of the Alpha allow it to exploit lift that you can’t
manage in a T2. The T2 has a much lower sink rate than the Alpha but it’s
hopelessly disadvantaged in this task. From my perspective, I’d rather improve
the ability of the T2 to work challenging lift to match the Alpha than gain a
bit of glide performance.