How to measure the airplane instantaneous velocity?

Question

without GPS or Radar

Answer 1

Um, airspeed indicator?
OR DME (distance measuring equipment) will give you current ground speed, DME is neither GPS or radar.......

Answer 2

There is a Vertical Speed Indicator (VSI) that gives you speed (in feet per minute) of climbing or descending. It uses the slight change in Barometric pressure to indicate a climb/ descent.
It has a very slight lag in real time indications.

You have an airspeed indicator that uses ram air to determine the air speed indicated (in Knots per hour or miles per hour)

Answer 3

nor gps nor radar give instantaneous speed, but average speed per amount of time/ between two samplings of aircraft position. they derive the speed from position, they dont measure speed itself. tahts is to be done and is done by measuring differential between static and total air pressure, thus deriving the ram pressure and stating the speed of aircraft. equipment is named pitot probe.

Answer 4

I believe that would be a calculation not measurement. Any speed measurement has to be over a period or moment, of time, albeit very brief. You also have to combine three axis.