ROTORCRAFT FLYING HANDBOOK1(49)

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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
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
TAKE-OFF DISTANCE (FEET TO CLEAR 50 FOOT OBSTACLE)
373

400

428

461

567

 

531

568

611

654

811

 

743

770

861

939

1,201
401

434

462

510

674

 

569

614

660

727

975

 

806

876

940

1,064

1,527
430

461

494

585

779

 

613

660

709

848

1,144

 

864

929

1,017

1,255

–
 –
2,150

 

2,500

 

2,850
458

491

527

677

896

 

652

701

759

986

1,355

 

929

1,011

1,102

1,538

 

1,320
SL

2,000

4,000

6,000

8,000

 

SL

2,000

4,000

6,000

8,000

 

SL

2,000

4,000

6,000

8,000
Figure 8-4. Takeoff Distance Chart.
8-6
affected by atmospheric wind is the angle of climb and
not the rate of climb.
SAMPLE PROBLEM 4
Determine the best rate of climb using figure 8-5. Use
the following conditions:
Pressure Altitude................................12,000 feet
Outside Air Temperature ...........................+10°C
Gross Weight ..................................3,000 pounds
Power ...........................................Takeoff Power
Anti-ice ..........................................................ON
Indicated Airspeed .................................52 knots
With this chart, first locate the temperature of +10°C
(point A). Then proceed up the chart to the 12,000-foot
pressure altitude line (point B). From there, move horizontally
to the right until you intersect the 3,000-foot
line (point C). With this performance chart, you must
now determine the rate of climb with anti-ice off and
then subtract the rate of climb change with it on. From
point C, go to the bottom of the chart and find that the
maximum rate of climb with anti-ice off is approximately
890 feet per minute. Then, go back to point C
and up to the anti-ice-on line (point D). Proceed horizontally
to the right and read approximately 240 feet
per minute change (point E). Now subtract 240 from
890 to get a maximum rate of climb, with anti-ice on,
of 650 feet per minute.
Other rate-of-climb charts use density altitude as a
　
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