2001 November 18
Ref 16195
Gene Mechtly;
My supersonic airplane has an air data computer which gives air
temperature, indicated air speed, true air speed, speed of sound and
Mach number. This combined with ground speed from a doppler radar
gives wind speed and drift angle. For display, it shows wind speed
(may be a vector) , ground speed and Mach number along with
"time-to-go" to the next way point.
Time to go is in minutes. The speed of sound is 20 sqrt T. So, at
-55 oC, the speed of sound is 300 m/s. At Mach 2 along with a tail
wind of 100 m/s, the ground speed is 600 m/s + 100 m/s = 700 m/s.
This is 42 km/min meaning the top of the display scale is 50 km/min.
As we come down in altitude, the speed of sound goes up to
330 m/s but we can not make Mach 2 so 50 km/min is high enough.
Now, the display may not be analog so it may not look like that
in my car.
Robert Bushnell
