Why do propellor airplanes have variable pitch propellers?
Variable-pitch propellers — Aircraft with variable-pitch propellers do have adjustments that serve much the same purpose as transmissions in an automobile, which in an airplane is to vary the speed of the vehicle by the bite (angle of attack) of the propeller blade.
Can a propellor airplane have a geared engine?
The simplest ones do not. However even some basic general aviation aircraft have geared propellers, permitting engines to operate at higher rpm for greater power output, while keeping the propeller RPM within acceptable tip-speeds.
When did they start using propellor in airplanes?
By the time WW2 happened, most high-powered airplanes (and a few small ones, but not many, yet) for both the airlines and the military had been equipped with a constant-speed prop.
Why does my car make a low pitched hum?
While driving, you hear a low-pitched hum. As you accelerate, the noise gets louder—maybe it sounds like an airplane taking off—but after a certain speed the volume is consistent. When you make a turn, the noise gets louder; but if you turn the other way, it disappears.
Why do propeller planes suddenly make noise when they fly?
Probably what you hear is caused by the variation in noise (and dominant frequencies) while the plane flies overhead. Directivity plot of propeller noise. The details depend a lot on the specific aircraft and propeller type.
When does a plane make a howling noise?
Every A320 series aircraft emits a signature howling noise while approaching to land. It is heard most when the plane is travelling at around 160 knots, and the frequency is around 500-600Hz, which is close to peak sensitivity of the human ear.
What causes descending aircraft to make a noise like a whistle?
That being said, there is apparently a fix to that problem, as both the aforementioned links describe. As Euractiv.com explains, the fix is a vortex generator: a 5-cm triangular piece of aluminium sheet metal upstream of the two vents on each wing, in order to divert the air flow and stop the whistle.
Why does a propeller change speed so quickly?
It is unusual to change prop speed quickly and only briefly, so I would suggest two possible explanations: On the ground: The pilot tests the propeller pitch control. This he/she does by revving up the engine while the propeller is at a low pitch setting.