Many commercial airliners have car-like window-wipers. I would presume this is for taxiing only, as the wind would surely keep the windows free from water when airborne, or do they turn them on in flight?
Also, don't these wipers cause a lot of drag, and wouldn't it be more economical to have some kind of air-jet blowing from nozzles to keep the windshield clear?
In the Falcon 50 and 900, we have windshield wipers that we are allowed to use in flight (up to 205 KIAS), but I have never used or seen them used in the eight years that I have been flying them because they simply aren't needed. They are usually stowed out of the wind stream so don't really cause much drag.
The Learjet's on the other hand DO have hot air that blows on the windshield and we sometimes used it to blow water droplets off of the windshield when on the ground. However, the primary purpose of the hot air was to heat and defog the windshield.
On a larger airplane, the additional piping, valves, etc. required to get the hot air all of the way up to the windshield actually weighs and costs more than just putting the windshield wipers up there along with electrically heated windshields to keep them from fogging up.
In the EMB-145 we could use the wipers below 170 KIAS. Wipers are really only useful on or near the ground, so this was not a limitation that really mattered. Our windscreen wasn't the best at deflecting rain, so in heavy precip we would use them inside the FAF when looking for lights/the runway and during taxi to the gate. On departure we would use them in heavy precip to taxi and takeoff, turning them off in the after takeoff flow.
Other airplanes, as Lnafziger points out have better flow characteristics over the windscreen or blown air and are not equipped with wipers.
In any airplane, the wipers are only potentially useful for ground ops, takeoffs and landings and serve no purpose at altitude.
In addition to the wipers, we were also equipped with an electric defroster to keep the windscreen free of fog and ice, and this was used during the descent from cruise to landing.
On the 747-100 and -200 airplanes we had windshield wipers which we occasionally used on short final in heavy rain. The switches were on the overhead panel on the captain's side, but the usual procedure was to ask the flight engineer to turn them on but to stand by to turn them off if the visibility was worse with them on than off, which was sometimes the case. I only remember leaving them on for the touchdown a couple of times.
We never used them while taxiing that I recall.
They were very noisy, distractingly so.
