Rotorcraft Flying Handbook, FAA-H-8083-21

the entire flight operation. Being able to hover at the takeoff
location with a certain gross weight does not ensure the
same performance at the landing point. If the destination
point is at a higher density altitude because of higher elevation,
temperature, and/or relative humidity, more power
is required to hover. You should be able to predict whether
hovering power will be available at the destination by
knowing the temperature and wind conditions, using the
performance charts in the helicopter flight manual, and
making certain power checks during hover and in flight
prior to commencing the approach and landing.
TAKEOFF PERFORMANCE
If takeoff charts are included in the rotorcraft flight manual,
they usually indicate the distance it takes to clear a 50-
foot obstacle based on various conditions of weight,
pressure altitude, and temperature. In addition, the values
computed in the takeoff charts usually assume that the
flight profile is per the applicable height-velocity diagram.
SAMPLE PROBLEM 3
In this example, determine the distance to clear a 50-
foot obstacle with the following conditions:
Pressure Altitude..................................5,000 feet
Takeoff Gross Weight.....................2,850 pounds
Temperature .................................................95°F
Using figure 8-4, locate 2,850 pounds in the first column.
Since the pressure altitude of 5,000 feet is not one
of the choices in column two, you have to interpolate
between the values from the 4,000- and 6,000-foot
lines. Follow each of these rows out to the column
headed by 95°F. The values are 1,102 feet and 1,538
feet. Since 5,000 is halfway between 4,000 and 6,000,
the interpolated value should be halfway between these
two values or 1,320 feet ([1,102 + 1,538] 4 2 = 1,320).
CLIMB PERFORMANCE
Most of the factors affecting hover and takeoff performance
also affect climb performance. In addition,
turbulent air, pilot techniques, and overall condition of
the helicopter can cause climb performance to vary.
A helicopter flown at the “best rate-of-climb” speed
will obtain the greatest gain in altitude over a given
period of time. This speed is normally used during the
climb after all obstacles have been cleared and is usually
maintained until reaching cruise altitude. Rate of
climb must not be confused with angle of climb.
Angle of climb is a function of altitude gained over a
given distance. The best rate-of-climb speed results in
the highest climb rate, but not the steepest climb angle
and may not be sufficient to clear obstructions. The
“best angle-of-climb” speed depends upon the power
available. If there is a surplus of power available, the
helicopter can climb vertically, so the best angle-ofclimb
speed is zero.
Wind direction and speed have an effect on climb performance,
but it is often misunderstood. Airspeed is
the speed at which the helicopter is moving through
the atmosphere and is unaffected by wind.
Atmospheric wind affects only the groundspeed, or
speed at which the helicopter is moving over the
earth’s surface. Thus, the only climb performance
TAKE-OFF DISTANCE (FEET TO CLEAR 50 FOOT OBSTACLE)
Gross
Weight
Pounds
Pressure
Altitude
Feet
At
–13°F
–25°C
At
23°F
–5°C
At
59°F
15°C
At
95°F
35°C
2,150
SL
2,000
4,000
6,000
8,000
373
400
428
461
567
401
434
462
510
674
430
461
494
585
779
458
491
527
677
896
2,500
SL
2,000
4,000
6,000
8,000
531
568
611
654
811
569
614
660
727
975
613
660
709
848
1,144
652
701
759
986
1,355
2,850
SL
2,000
4,000
6,000
8,000
743
770
861
939
1,201
806
876
940
1,064
1,527
864
929
929
1,011
1,017
1,102
1,255
1,538
– –
1,320
Figure 8-4. Takeoff Distance Chart.
8-5