The pitot tube is a small L shaped tube (usually) that protrudes from underneath the surface of the wing. It measures total air pressure through a small hole in the front of the tube. There is another tiny opening called a static port, usually positioned on the side of the aircraft, which measures static pressure. The difference between total pressure and static pressure is dynamic pressure, which equates to airspeed. This drives the airspeed instrument in the cockpit. You will often see aircraft have a “pitot heat” switch in the cockpit, which is used when you get in icing conditions, because if the pitot gets iced up then you get an incorrect pressure reading and hence an incorrect indicated airspeed.

A very good explanation. A couple of glosses – on older aircraft (pre 50s?) the pitot was a double tube end – one open, the other closed, the closed being the static. This was rather than having it on the fuselage, a more sophisticated system. Look at the outer leading strut midway up on most pre W.W.II biplanes to see one. It looks like two black finger size tubes pointing forward.

On some DH Moths, you can see a primitive alternative. A flat plate facing the airflow on a sprung wire, held by a quarter circle of metal. This was graduated with mph (or knots) and the airflow pushed the plate back, thus showing the airspeed if the pilot squints at this thing on the outer strut. The principle was known to, and demonstrated by Leonardo da Vinci, a few years earlier. (!) (See pic)

If you want unfortunate G- regos, there was a photo published a few years back of G-SEXY parked next to Tiger Moth G-AIDS (ouch)

Cheers