On Wed, 26 Oct 2011 09:59:26 -0700 (PDT), soartech
wrote:

Reading that many lethal accidents are caused by stalls I thought that
a stall warning indicator might be a nice thing to have. After
searching a bit I found this really interesting but sad story on the
subject written by someone at DG sailplanes:
http://www.dg-flugzeugbau.de/ueberziehwarnung-e.html

.... text deleted

In the interests of not "reinventing the wheel", few likely recall
that the late Dick Johnson published his design for a vane-based stall
warning indicator in the June 1990 (page 25) issue of SOARING
magazine. Dick showed full constructional details of his design in
this article.

The design was the result of a design competition OSTIV announced in
1987, a "Competition for Development of a Special Flight Instrument
for Stall Warning of Sailplanes". The design Dick developed finished
2nd in this competition. While the instrument never found a wide
following, Dick continued to fly with this instrument on his Ventus up
to his untimely death in 2008.

I have reproduced a short note Dick wrote on his instrument, as well
as the winning Polish design, several years before his death.

Bob

======================

SAILPLANE STALL WARNING SYSTEMS

Because of concern about sailplane stall accidents, during early 1987
OSTIV announced that they would sponsor a "Competition for Development
of a Special Flight Instrument for Stall Warning of Sailplanes". We of
the Dallas Gliding Association decided that entering that competition
was certainly a worthwhile project. The offered prize for 1st place
was 2,550 DM, and 1,000 DM for 2nd place. Those prizes were awarded
after flight-testing judging and during the 1989 OSTIV Congress at
Weiner Neustadt in Austria.
Over a 2-year period we studied various candidate configurations, and
performed developmental flight-testing with 5 or 6 different
experimental stall warning systems. While most of the flight-testing
was performed with my Ventus A, several other sailplanes ranging from
a Schweizer 1-26 to a Nimbus 3 were included. Flight testing included
flying into moderate rain showers, and flying with many natural bugs
along the wing leading edges.
We judged our best overall stall-warning configuration to be a small
floating vane mounted well aft on the top surface of the wing, and
entered that configuration into the 1998 OSTIV Competition fly-offs at
Weiner Neustadt. The Polish entry was judged to be the winner there,
but our configuration placed 2nd. The weakness in our design was that
its external mounting was subject to damage during club use.
The Polish design used the differential pressure measured between the
fuselage nose pitot tube and a small flush orifice located on the
bottom of the nose several inches aft of the pitot. It is essentially
an angle-of-attack indicator, and I believe that it is still marketed
today.
Although its external mounting makes it subject to handling damage,
the DGA design performs well in my opinion, even in rain and with bugs
and various flap settings. I have used it on my sailplanes
continuously since its development, and feel my flying is safer for
that. Its design is shown in the 7/90 issue of Soaring, and I believe
it was also published Sailplane & Gliding about that time.

Richard H Johnson