to measure velocity of sounding rocket

Question

How to measure velocity of sounding rocket?? is using a pitot tube an efficient way to measure and how exactly to measure speed of sounding rocket using a pitot tube ???are there any other method to measure speed of sounding rocket

Answer 1

Pilot tube is an okay method if you're free to put it on exposed parts of the rocket - nose cone, leading fin edges, etc, wherever your reading won't be disturbed by laminar flow along the rocket surface - the tube facing into "inert air".

You perform the readout using a relative pressure sensor (differential barometer) chip. The device has two pipes, you connect one to the pilot tube, and the other to a shielded air intake measuring static pressure (say, a pipe with tip embedded in a piece of sponge). Your control board will read the difference in pressure as either current/resistance/voltage, or a digital signal like SPI, depending on what sensor you use.

You can either perform calculations of how the airspeed converts to pressure differential, or (preferably, because manufacturing inaccuracies may make your calculations useless) calibrate it, by driving a car (or motorcycle) on a windless day, putting your sensor in airflow (out the window) at specific speeds, and recording the readouts, to get parameters for the pressure-speed function.

Of course the first limitation: "exposed location" is usually a no-go for this solution, nose cone usually ejected to release a parachute, the fins located near the engine, making the connection a huge hassle, etc. In this case you use alternatives.

Andrew suggests GPS. This is a very common solution, and quite precise although slow (most GPS receivers provide readouts once per second) plus needs extra initialization time ("get the fix"). Also, all civilian GPS receivers will cut off at 18,000 meters (this is to prevent unauthorized military use). You need dedicated GPS receiver for aerospace (and to cut through a lot of red tape) to get GPS readout anywhere above that.

Uwe suggests a doppler sensor. I don't know of any doppler sensors to measure airspeed with no ground reference. Laser sensors are okay for measuring ground distance up to a couple hundred meters, above that professionals will use aircraft radar systems (ground radar stations), amateurs... will use other means than doppler shift.

An absolute pressure sensor (normal barometer chip) with shielded intake can be used to measure air pressure and derive altitude from that - and vertical speed from altitude change.

Still, unless your rocket is meant to go above 18km, a common GPS is probably the most sensible solution. And if you plan to fly it higher... get an airspace GPS.