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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).
252 Operational Flying
LDR will increase by 5% for each
1000-foot increase in pressure
altitude and 10o C increase in
temperature (factor by 1.05).
Aircraft Weight
Greater mass means slower
acceleration/deceleration and longer
distances. TODR will increase by
20% for each 10% increase in weight
and LDR 10% per 10% increase in
weight (factor by 1.2 and 1.1). Very
few aircraft allow you to fill all the
seats with full fuel.
Some manuals give take-off and
landing weights that should not be
exceeded at specific combinations of
altitude and temperature, thus
ensuring that climb performance is
not compromised. These are known
as WAT limits (Weight, Altitude and
Temperature)
Dynamic Rollover
This occurs when your helicopter
has a tilted thrust vector with respect
to the C of G, commonly
encountered with some side drift
when you have one skid or wheel on
the ground acting as a pivot point,
but you can also get a problem when
your lateral C of G falls outside the
width of the skids or wheels. Every
object has a static rollover angle, to
which it must be tilted for the C of
G to be over the roll point, for most
helicopters being 30-35°. As your
lateral cyclic control at that point is a
lot less effective than if you were
hovering, because it is not rotating
around the C of G, but the rollover
point, you have less chance to get
out of trouble, and the only effective
control is through the collective (do
not raise it). In other words, the lift
from the rotor disc that should be
vertical is inclined and converted
into thrust, above the centre of
gravity, so trying to use the cyclic to
level, and the collective to get you
off the ground is wrong!
Dynamic rollover is worst with the
right skid on the ground (counter
clockwise main rotor) and with a
crosswind from the left, with left
pedal applied and thrust about equal
to the weight (i.e. hovering). A
machine can roll upslope if you
apply too much cyclic into it, or
downslope if you apply too much
collective, enough to make the
upslope skid rise too much for the
cyclic to control. Avoid it by keeping
away from tail winds, and landing
and taking off vertically.
Engine Failure and
Autorotations
This part is not meant to cover
(again) the basic stuff you learn in
flying training, but to offer advice
that would be useful to a working
pilot, who is very often over trees, or
in remote places that the student is
routinely taught to avoid. In short, it
talks about surviving a potential
crash, because you won't always find
yourself over the clear areas you
need for training.
Engine failure in a helicopter is
detected by a noticeable decrease in
engine noise (!), yaw in the same
direction as blade rotation, loss in
　
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