Vmc and weight

[Swen]

I would greatly appreciate if someone could give a thorough, but short explanation of how max gross weight affects Vmc. Such an explanation that a DE would like to hear.

Im preparing for my AMEL checkride and this is the only Vmc related topic that I am having trouble with. Thanks for any input.

 

[ananoman]

In general, a heavy object is harder to displace than a lighter object. A heavier object is more 'stable' due to it's higher inertia.

A heavy aircraft will resist the yawing force due to a failed engine more than a light aircraft. This will tend to decrease Vmc. But there is a tradeoff, as the heavy aircraft will also have poor climb performance compared to the light aircraft.

 

[aviategw]

From the ATP Piper Seminole Training Supplement.

"In a given bank, the heavier the aircraft, the greater the horizontal component of lift that adds to the rudder force. As weight increases, the horizontal component of lift increases, which added to the rudder, decreases, Vmc. As the center of gravity moves forward, the moment arm between the rudder and the CG is lengthened, increasing the leverage of the rudder. This increased leverage increases the rudder's effectiveness and results in a lower Vmc speed."

 

[chris]

For any given bank angle, the heavier a/c will have a greater horizontal lift component (as mentionned above). That is, the heavier the a/c, the greater the amount of lift that is being produced (lift = weight).

The HCL is what offsets the sideslip during an engine failure. Since the HCL is greater for any given bank angle for the heavier a/c, Vmc will be slightly lower.

 

[chris]

For any given bank angle, the heavier a/c will have a greater horizontal lift component (as mentionned above). That is, the heavier the a/c, the greater the amount of lift that is being produced (lift = weight).

The HCL is what offsets the sideslip during an engine failure so that the sum of forces is 0 and the sum of moments (torques, from a physics standpoint) are also 0. Since the HCL is greater for any given bank angle for the heavier a/c, Vmc will be slightly lower.