Power needed for slow SAL vs hover...

[Nick]

Is it true that a helicopter requires less power for slow straight and level
flight than for hovering? If so, anyone know any figures for say an
R22?......or even hazard a guess?

Cheers

[John_F]

Hover out of ground effect requires the most power.
If you are in ground effect you get a small boost in rotor efficiency
due the down wash being obstructed by the ground.

If you are hovering and slowly increase your speed forward at about 15
knots you enter ETL (Effective Translation Lift) which gives you about
a 15% increase in rotor efficiency due to the change in the way air
enters the rotor.

This can get you in trouble if it is hot and/or high and you are real
heavy.
You may only have enough power to barely hover in ground effect but
not enough power to hover out of ground effect. So you hover barely
off of the ground and slowly increase your forward speed until you get
to ETL at which time you have enough power to climb due to the
increased rotor efficiency. The problem comes when you try to stop.
If you come to a stop too fast you will find that you don't have
enough power to hover 5 to 10 ft in the air at the end of a quick stop
and the rotor rpm decreases. If it decreases too much you either have
a real HARD landing or worse the blade stalls on one side and you roll
over and meet the ground quickly as parts of the rotor fly off after
trying to beat the ground into submission.




On Sat, 30 Dec 2006 16:17:06 -0000, "Nick"
> wrote:

>Is it true that a helicopter requires less power for slow straight and level
>flight than for hovering? If so, anyone know any figures for say an
>R22?......or even hazard a guess?
>
>Cheers
>