44
Speed Performance Indicator (SPI)
As a cross country glider the SIGMA 7 is designed to fl y in accelera-
ted fl ight in turbulent air. These days, accelerated fl ight plays an im-
portant role for the part-time pilot who is interested in performance,
and a high average speed is a decisive factor in successful long
fl ights. This calls for continual choices of speed-to-fl y, depending on
headwind, sink rate and expected future climb rate, so as to achie-
ve the best glide across a valley, or the shortest time to cloud base.
That’s why the SPI is very important for a SIGMA 7.
Based on accurate polar curve values fi ve positions are indicated on
the back of the D-risers, each with values of current headwind ,
sink rate (vario reading in unaccelerated fl ight) and expected climb
rate (vario reading in unaccelerated fl ight). The red markers on the
speed system can be set exactly to the chosen SPI position.
Each SPI position is correct for each one of the three fl ight values in-
dicated at that position, when that value is considered by itself. The
principle of the SPI is based on a simplifi ed and extended McCready
speed-to-fl y theory.
08290300_Advance_HB_SIGMA7.indd 44
08290300_Advance_HB_SIGMA7.indd 44
04.06.2008 14:27:47 Uhr
04.06.2008 14:27:47 Uhr
