Vx Vy again

[OneIn60rule]

What happens to the speed of Vx and Vy with increasing altitude?

A) Both remain the same
b) Vx remains const. and Vy increases.
C) Vx Inc. and Vy remains const.
d) Vx remains constant and Vy decreases.

Correct answer is D but is it because ROC would decrease for increase of altitude and Vx is basically BEST angle of climb which is least amount of ground covered for every vertical unit achieved? (since Vx doesn't care about time it takes compared to ground)

Barking up the wrong tree am I?


Other question

With which conditions would one expect Vmc to be the lowest?

A) Cold temp,low altitude, low humidity
b) hot temp, low pressure altitude, high humididy
c) hot temp, high pressure altitude, high humidity
d) cold temp, high altitude, low humidity

Answer given is C but that doesn't seem to make much sense to me. Anyone care to clarify?

By the way, Merry X-mass and a happy new year!:}

[NineEighteen]

For your first question, see this thread (http://www.pprune.org/forums/showthread.php?s=&threadid=92520&highlight=decreases) :rolleyes:

For the second one, I recall the question concerning Vmcg and answer (c) is correct.

If conditions are hot, high and humid the air is less dense. This reduces thrust and means when you lose the critical engine on takeoff there is less yawing effect from asymmetric thrust than there would be in denser air.

Vmcg concerns the calibrated airspeed for minimum control on the ground (i.e. using primary aerodynamic controls only to correct the yawing tendency). We know that flying surfaces are more effective the faster air flows over them so, if the yaw is less pronounced, the required airspeed for counteracting it need not be so high.

As elevation and temperature increase (Hot High and Humid) Vmcg decreases.

0918

[OneIn60rule]

For the thread link and the Vmc question.:ok: