What does "KNOTS" mean on the HSI (right upper corner)?
From FlightSim
Q:
WHAT DOES "KNOTS" MEAN ON THE HSI (RIGHT UPPER CORNER)?
A:
I assume that you are not asking what "knots" mean. The knots on the B737-400 and other jets that use the same HSI means the speed of closure to the VOR being received. The other side has the distance to the VOR. Both of these are from the airplane at altitude to the beacon on the ground. So you could be several miles from the beacon when you pass over it.
The speed of closure is in actual ground speed, but it is measuring the rate at which the distance to the beacon is increasing or decreasing. If you are far enough away and flying direct to the beacon, this will be close to the true ground speed, which will be much higher than the IAS of the airplane. If you are not flying direct to the beacon, the speed shown here will be something less than the true ground speed since a line from the airplane to the beacon will shorten or lenghten disproportionally to the movement of the airplane. Probably more than you wanted to know, but I'm an old guy and I ramble on.
Bob Fiedler
I haven't looked at the HSI recently, but KNOTS is basically an abbreviation
for nautical miles per hour (a nautical mile is 6080 feet, about 15% larger
than a stature mile -- 5280 feet). So you're looking at the speed readout.
Modern aviation uses knots almost exclusively (except for a few places that use
kilometers per hour).
Larry N.
