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Which of the following combinations require the most hover-taxi fuel for a twin-engined turbine helicopter?

  • A

    Low taxiing airspeed and a high density altitude.

  • B

    High taxiing airspeed and a low density altitude.

  • C

    Low taxiing airspeed and a low density altitude.

  • D

    High taxiing airspeed and a high density altitude.

Density Altitude is the pressure altitude corrected for non-standard temperature, the ISA deviation. In other words, it is the altitude in ISA, which gives the same air density as the prevailing non-ISA combination of temperature - pressure altitude and is used to establish helicopter's performance, as it is a figure that expresses where your engine "thinks" it is, as opposed to where it actually is. As density altitude increases, the air density reduces. This causes the thrust and therefore the output power or performance to decrease at all phases of flight.

A high density altitude means that the density is low, so the performance of the helicopter is degraded, i.e. more power is required to maintain the same performance and as a result more fuel.

In a low taxi-hovering speed more induced drag will be generated and as result the power required will be higher, which in turn requires more fuel.

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