Real Time Air Speed or post flight
i don't have the ability to make a finely tapered tube or the wotsit accurate enough. i got the idea watching a program about airships and a machine used to test the ability of the material to hold the gas in. they force air through it, and a series of tubes give a reading, 10's 1's, .1's 01's ect
it would have to be damm accurate to measure 0 too 300 mph, and then find a way for the wotsit to stay put. either no gap around it, or a marker of some sort