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elect to carry on to forward flight,
you should be able to clear the
landing spot during the steep dive
you have to make to achieve flying
speed, which is why the CDP is
about 40 feet high. Once you're
happy about the power, gently
accelerate level, to VY.
All this is not without its critics,
though, since prolonged hovering at
high engine power is not necessarily
good engine handling. Not only that,
it may be impractical on an oil rig if
there are accommodation blocks and
cranes around.
Unofficially, therefore (from a rig
anyway), one school of thought
suggests a level acceleration to best
rate of climb speed, then going up to
a safe altitude, whereas others
advocate getting to best angle of
climb speed, climbing to a safe
height and then accelerating to best
rate of climb. The first is supposed
to keep you in the H/V curve less,
but the second gets you higher
sooner, so you lessen the chances of
hitting the water if an engine fails,
especially if the deck is only 50 feet
high (most major platforms are 100
feet off the water).
One technique might be to hover
over to the front of the deck with
the rotors not overhanging (the front
is where the wind is coming from).
Check the Ts & Ps as usual, then
pull power and head upwards,
rotating while there is a positive rate
of climb to a few degrees nose down
(10 is OK initially - you might lose
height with more), to get the tail up
and clear. After rotation, maintain
the collective while looking for
takeoff safety speed and accelerate.
As to which technique is best, you
have to make some choices yourself,
Techie Stuff 117
like whether you want to hit the
water or the deck, or would rather
be low with rotor RPM, or higher
with less, and little airspeed.
To get back on to the ground, you
will not be surprised to hear there is
a landing profile as well, for the
Twinstar being something like this:
For a clear area, you arrive at the
100' point at 40 kts (it's actually
difficult to get them both at the
same time, so you would first hit
one, then the other). For a helipad
(that is, not within the definition of a
clear area), the figures are 90' and 30
kts, for a semi-vertical arrival.
Factors Affecting Performance
Density Altitude
This is the altitude at which the ISA
density is the same as that of the air
in question or, in other words, your
real altitude resulting from the
effects of height, temperature,
pressure and humidity, all of which
can make the air thinner and which
are mentioned below. The details
will be in the Flight Manual,
although humidity is usually ignored
in the average performance chart,
because it has more to do with
engine power than aerodynamic
efficiency, and high air density and
humidity do not often go hand in
hand. However, if the air is humid,
say after a good shower, you would
be wise to be careful.
Anyhow, the idea is that the more
the density of the air decreases for
any reason, the higher your aircraft
thinks it is. If you look at the lift
formula, you will see that the lift
from a wing or thrust from a
propeller is directly dependent on air
density, as is drag, of course. The
effects are as valid at sea level as they
are in mountainous areas when
temperatures are high – for example,
90° (F) at sea level is really 1900' as
far as your machine is concerned. In
extreme circumstances, you may
have to restrict your operations to
early morning or late afternoon.
Here is a handy chart:
°F/C 60/15.6 70/21.1 80/26.7
1,000’ 1300 2000 2700
2000’ 2350 3100 3800
3000’ 3600 4300 5000
4000’ 4650 5600 6300
5000’ 6350 6900 7600
6000’ 7400 8100 8800
7000’ 8600 9300 1,0000
8000’ 9700 10400 11100
9000’ 11,000 11600 12400
1,0000’ 12250 13000 13600
11,000’ 13600 14300 15000
12000’ 14750 15400 16000
It shows that, at 6,000 feet and 21°C,
for example, you should enter
performance charts at 8100 feet.
TODR will increase by 10% for each
1000-foot increase in aerodrome
altitude and 10% per 10o C increase
in temperature (factor by 1.1).
LDR will increase by 5% for each
1000-foot increase in pressure
118 The Helicopter Pilot’s Handbook
altitude and 10o C increase in
temperature (factor by 1.05).
Aircraft Weight
Greater mass means slower
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(78)