FLIGHT MANUAL BO 105 CB-5/CBS-5
EUROCOPTER
5 - 10
LBA APPROVED
Rev. 0
5.3 DENSITY ALTITUDE
The density altitude chart (see Fig. 5-4) expresses density altitude in terms of pressure
altitude and temperature. The less dense the air the higher the density altitude. For stan-
dard conditions of temperature and pressure, density altitude is identical to pressure alti-
tude.
A high density altitude affects the performance of both rotors and engines. When density
altitude is high, less lift is developed by the rotor blades for any given power setting than
at standard conditions and the power output of the engines is reduced below the output
for standard conditions.
Each takeoff and landing must be separately evaluated as density altitude may change
considerably in a short period of time.
The true airspeed factor value
1
s
Ǹ
is a conversion factor used to obtain true airspeed from
calibrated airspeed by correcting for density altitude.
EXAMPLE
: (see Fig. 5-4)
Determine: Density altitude (DA)
True airspeed factor
True airspeed (TAS)
Known: OAT –14 °C
Pressure altitude 5000 ft
CAS 100 kt
Solution: 1. Enter chart at known OAT (–14 °C).
2. Move vertically up to known pressure altitude (5000 ft).
3. Move horizontally left and read density altitude = 2630 ft
.
4. Move horizontally right and read true airspeed factor = 1.04.
5. Multiply the known calibrated airspeed (100 kt) by true airspeed factor
(
1
s
Ǹ
= 1.04) to obtain true airspeed.
TAS = CAS x
1
s
Ǹ
= 100 x 1.04 = 104 KTAS
Rev. 1
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