The maximum endurance with a helicopter is achieved by flying at...
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A
a lower speed than for maximum range and at the lowest altitude that is safely possible.
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B
the same speed as for maximum range and at optimum height.
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C
a lower speed than for maximum range and at the service ceiling.
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D
a higher speed than for maximum range and at the lowest altitude that is safely possible.
Refer to figure.
The power required curve can be described as a fuel flow curve. Where the power required is high, fuel flow is high:
1. At the bottom of the power required curve (Point 3), the power required is at a minimum and fuel flow will be at a minimum as well. The corresponding TAS is the minimum power required speed, VMP, which is also the maximum endurance speed, VMAXEND and the best Rate of Climb speed, VY.
2. At the tangent of the origin to the power required curve (Point 4), the maximum range speed, VMR, is found, which is also the minimum angle of descent speed and the minimum drag speed, VMD (Best Rotor thrust / Rotor drad ratio).
As shown in the figure, the maximum endurance speed is always lower than the maximum range speed.
Additionally, flying at the lowest safe altitude can reduce the power required to maintain flight, as there's a decrease in aerodynamic drag and often more efficient fuel consumption due to higher air density.
So, if flying at maximum endurance speed at the lowest possible altitude, then the duration the helicopter can remain in the air can be maximized.
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