View Full Version : V mp


nodrama
30th Jun 2010, 15:35
Could someone please explain V mp (minimum power airspeed)?



thecontroller
30th Jun 2010, 16:44
http://www.pprune.org/flying-instructors-examiners/55854-power-curve-diagram.html

Helicopter Power Required (http://www.griffin-helicopters.co.uk/note/helicopterpower.htm)

http://www.google.co.uk/url?sa=t&source=web&cd=1&ved=0CBYQFjAA&url=http%3A%2F%2Fwww.stlouishelo.org%2FSchool%2520of%2520Aviation%2520Safety%2520-%2520Power%2520Available%2520vs.%2520Power%2520Required.pdf&rct=j&q=helicopter+power+curve&ei=6WUrTNfeKqH-0gTtxMzkAg&usg=AFQjCNFa3gZ-gP9ccWk7gzyX4lh6znHseg

John R81
30th Jun 2010, 17:23
Or....

It is the airspeed at which the machine uses minimum power to remain in flight.

As airspeed increases the blades get more efficient and so less power is required to sustain flight. The blades continue to get better as airspeed increases, but drag on the blades and the body of the helicopter also increase as you gain speed and these require power to overcome.

At lower speeds the improvement in blade efficiency (less power needed) outweighs the combined increase in drag (more power needed) and so the total power required to keep the helicopter in the air falls as speed increases. However, the rate of increase in drag gets higher as the speed gets higher, so there comes a speed when either increasing speed (increasing drag more than blade efficiency) or reducing speed (reducing blade efficiency more than reducing drag) will mean that the total power required to stay in the air will increase.

Simples!:ok:

The technical explanation you have above, or is available from any Principles of Flight training manual for PPL(H). The curve for any particular helicopter can be found in the POH.

John

nodrama
30th Jun 2010, 17:44
It is the airspeed at which the machine uses minimum power to remain in flight.

Great. That, plus the curves is all I really needed.

So is V mp also the minimum airspeed that determines the minimum height (for a particular helicopter), where if the engine(s) went quiet, the rotors will have enough energy to get the thing on the ground relatively safely?

Pofman
30th Jun 2010, 18:06
Vmp is not an abreviation I have ever come across in 50 years of helicopter flying. We usually refer to that point as endurance speed as in piston minimum fuel consumption is at minimun manifold pressure so it will be located at the bottom of the power required curve.
You need to get Wagentendonk's Principles of Helicopter Flight from ASA as he explains this well and it is the basis for all the JAA PPL(H) POF exam questions.:ok:

Shawn Coyle
30th Jun 2010, 19:25
Normally it's labeled V(sub)Y.