TM 1-1520-238-10
7A-16
subtract change in torque from torque required for the pri-
mary mission configuration. Enter the cruise chart at re-
sulting torque required, move up, and read fuel flow. If the
resulting torque required exceeds the governing torque
limit, the torque required must be reduced to the limit. The
resulting reduction in airspeed may be found by subtract-
ing the change in torque from the limit torque; then enter
the cruise chart at the reduced torque, and move up to the
gross weight. Move left or right to read TAS or IAS. To de-
termine the airspeed for maximum range for alternative
wing stores configuration, reduce the value from the
cruise chart by 2 knots for each 5 square feet increase in
drag area, DF, or increase maximum range airspeed 2
knots for each 5 square feet reduction in drag area. For
example, for 16 Hellfire configuration DF = 9.6 square
feet, from figure 7A-18. Therefore, maximum range air-
speed would be reduced by 2/5 x 9.6 = 3.84 knots, or
approximately 4 knots.
7A.20.7 Additional Uses.
The low-speed end of the
cruise chart (below 40 knots) is primarily to famil-
iarize you with the low-speed power requirements of the
helicopter. It shows the power margin available for climb
or acceleration during maneuvers, such as NOE flight. At
zero airspeed, the torque represents the torque required
to hover out of ground effect. In general, mission planning
for low-speed flight should be based on hover out of
ground effect.
7A.21 CONDITIONS.
The cruise charts are based on 100% rotor rpm, ATF or
ETF = 1.0, ENG INLET ANTI-ICE switch OFF, JP-4 fuel,
and dual-engine operation. Engine inlet anti-ice and rotor
blade de-ice effect are as follows:
a. With ENG INLET ANTI-ICE switch ON, fuel flow
will increase approximately 85 pounds per hour; maxi-
mum continuous torque available could be reduced by as
much as 24.5%; maximum torque available, 30 minute
limit could be reduced by as much as 20%; and maximum
torque available, 10 minute limit could be reduced by as
much as 18.6%.
b. With rotor BLADE de-ice switch ON, fuel flow will
increase approximately 30 pounds per hour, and torque
required will increase 1.4%.
For example, with ENG INLET ANTI-ICE and rotor
BLADE de-ice off, torque required, from cruise chart is
50%, and maximum continuous torque is 92%. With ENG
INLET ANTI-ICE and rotor BLADE de-ice switches ON,
torque required will be 50 + 1.4 = 51.4%, and maximum
continuous torque will be approximately 92 – 24.5 =
67.5%.
