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You are approaching your destination aerodrome, but due to a delay, ATC has requested you to hold. You want to perform the hold at the maximum endurance speed. As you are flying a jet, which speed should you use?

  • A

    VMD, and there is no effect of wind on this speed.

  • B

    VMP, and there is no effect of wind on this speed.

  • C

    Fly faster than VMD on the outbound leg and slower on the inbound leg.

  • D

    Fly slower than VMD on the inbound leg and faster on the outbound leg.

Refer to figure.
The best endurance speed in a jet aircraft is the speed at which the engines need to produce the least thrust, as thrust is directly proportional to fuel flow, and we want to make our fuel flow the lowest it can be. The speed of minimum thrust required is the speed of least drag (as thrust is directly opposed by drag). We call this the minimum drag speed (VMD) and it is the speed that aircraft fly in the holding pattern, when it is time in the air that is most desirable, rather than distance travelled.

It occurs at the bottom of the "total drag" curve as shown in the annex above, where the combination of induced and parasite drag equals the lowest value.

In a jet aircraft, VMD gives us the Best Endurance and Best Angle of Climb (VX).

Unlike range, endurance is not affected by the wind conditions, since it is only affected by the airspeed selection and availability of the fuel onboard so the Maximum Endurance Speed, as an airspeed, remains unchanged regardless of the wind.

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