Why can headwind assist planes when taking off and landing? Why does tailwind not help with takeoff?
In: 11
The same phenomenon applies to helicopters. Imagine a scenario where a helicopter takes off with a 20 knot tailwind from a runway:
The pilot lifts the helicopter into a 10 foot hover. The aircraft isn’t moving over the ground, but from the perspective of the air mass, it is flying backwards at 20 knots. This speed does reduce the power needed to hover slightly. However, once the aircraft starts the departure/takeoff, it needs to slow down back to 0 knots from the air masses’s perspective. The air mass sees the helicopter going backwards, then as the helicopter starts moving forward, it will eventually be going forward at the same speed as the air mass., which is a zero airspeed hover, which means power required just went up. In addition, the helicopter is now no longer outrunning it’s dirty air and power required will go up due to that as well.
From this point, a more normal takeoff and flyout will commence. But how far down the field or runway is the helo at this point? To get back to the normal no-wind position, the aircraft had to go from flying backwards at 20 knots to a zero airspeed hover. That took some distance.
If you flip the scenario around:
When the helo lifts into a hover, the wind is already pushing the dirty air away from the rotor, and power required is less because the aircraft already has 20 knots of airspeed. As the aircraft starts moving forward, it will require much less room to do a normal climb out profile, because it will hit these speeds much sooner.
Latest Answers