There are always a bunch of Thorps at Oshkosh. In 1963
the late John Thorp designed the classic all metal Thorp T-18.
Of more than 1500 plans sold, about 400 were completed. Although designed
for an O-290 it could take up to an O-360 the latter
of which gave an "honest" cruise speed of about 185 mph. In 1984 Lu Sunderland
designed the S-18 as an improvement over Mr. Thorp's design.
The S-18's new wing lowered the stall speed by 7 kts over the Thorp
T-18. The new wing also provided a more gentle stall with
more pre-stall buffet. The S-18 fuselage is 2" wider and
5" longer than the standard T-18. Cruise speed is similar
to the T-18.