I guess a small clarification would be appropriate here. The airspeed indicator doesn't show how fast your are going - it only shows something called indicated airspeed. The indicated airspeed (IAS) varies with altitude, barometric pressure, and temperature. Other factors, such as angle of attack, have a lesser effect on the IAS. I have noticed differences of over 10% between indicated airspeed and true airspeed in single engine aircraft operating at or below 12,500 feet. Aircraft that fly at higher altitudes keep track of two relative speeds - indicated airspeed and mach - their speed as a fraction of the speed of sound. At higher altitudes the speed of sound can be reached at indicated airspeeds much lower than at sea level. These aircraft have two "redline" airspeeds - the red line on the airspeed indicator and a maximum mach operating (MMO) speed. Stall speed will remain constant on the airspeed indicator. The Cessna 150 I learned to fly in would stall at about 47 kts indicated airspeed regardless of how fast I am actually going. The last speed of relevance is ground speed - the speed of the aircraft over the ground. This is generally the aircraft's true airspeed plus or minus any movement of the air mass the plane is flying in. In the Cessna 150 I flew I recorded ground speeds of 50 to 170 knots at different times when doing a cross country flight, even though my indicated airspeed was constant at about 90 knots. The U2 operates at altitudes high enough to have as little as a 10 knot IAS difference between stall speed and MMO speed. Because of the thin atmosphere at these altitudes there isn't much going into the airspeed indicator's pitot tube so, although the plane has a very high true airspeed, it has a very low indicated airspeed. If we assume an indicated airspeed of 120 kts, a density altitude of 70,000 feet and a temperature of -50C, the true airspeed would be about 504 kts. This hopefully explains the difference between the U2's ridiculously low (indicated) airspeed and ridiculously high groundspeed. Brian -----Original Message----- From: Derek Boyer [mailto:[EMAIL PROTECTED]] Sent: Tuesday, October 12, 1999 7:38 PM To: '[EMAIL PROTECTED]'; [EMAIL PROTECTED] Subject: [RCSE] U-2 and UAV's at Edwards Memory tells me that at operational altitude (way beyond 'speck') the U2 fly's in a sort of a coffin: a few miles per hour IAS slower, it stalls; but a few miles per hour faster and it comes apart. I also remember that airspeed was ridiculously low and groundspeed was ridiculously high up there. RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
