On Friday, May 28, 2021 at 8:13:48 AM UTC-4, Christoph Barniske wrote:
The Twin 1 is available with a retractable gear or as a trainer version (fixed gear, no water ballast). The RG version suffers from too large geardoors which are torn off easily in outlandings. Although the gear is fixed, the trainer version also has the box for retracting the gear in the fuselage..

The Twin 1 has slightly better performance than the II (which is already better than the ASK21) and a higher payload. But it's heavy on the controls and the backseat is quite uncomfortable. There's also a noteable lack of control harmony compared to other glass gliders. These are the main reason for their low price. We sold it after a few years and nobody really missed it. In my view, if you get a Twin II with reasonable payload, it's a much better choice.

As for the single-seat Grob gliders, there's also a technical note on applying turbulator tapes on Twin 1 and 2 wings. It improves handling in thermals, but doesn't help with the lack of harmony and stiff controls on the Twin 1.

The technical note actually allows for turbulator tape in front of
all flight control surfaces. This is separate from the Aero Kurier
article which described under wing turbulator tape to anchor
laminar separation bubbles and improve performance.
Adding Z-Tape to the vertical fin just in front of the rudder actually
makes a very noticeable difference in rudder effectiveness on a
Twin 1. This in turn makes the controls much more harmonized
and in turn more pleasing to fly. People in the USA that have a
Twin II with no damage history and high payload know what they
have and are not selling. I would expect that if a unicorn like that
appeared on the USA market, the asking price would be in the
$50K-$60K range. Most clubs that used to operate L-13 Blaniks
before the wing spar A.D. just don't have that kind of cash
available.

Mike Opitz
RO