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point), the conditions under which
you operate determine how heavy
Techie Stuff 115
your aircraft can be and, as a result,
your payload. Over a whole trip, the
weight could be dictated by:
· Maximum weight
· WAT limits (see below)
· Space available
· Obstacles
· The route
· Hovering OGE
Individual machine performance will
vary due to such variables as the age
of the airframe and engines, the
standard of maintenance, or crew
skill and experience, without the
engines being adjusted for several
seconds after the initial failure. What
you can do on one day under a given
set of circumstances may well be
impossible another time.
Performance is therefore a set of
average values—particular machines
may be better or worse.
The original testing, of course, is
done with new aircraft and
experienced pilots, which are known
as unfactored. Fudge factors are
applied to unfactored figures to
produce net performance (and gross
performance when they're not), so
there is a margin if you have a tired
engine, or a new pilot. Occasionally,
performance data (as amended) in a
flight manual will already be
factored, but you will have to check
the small print on the chart, in case
they surprise you (JAR does not
make a distinction between the two,
except for a 1% margin for IFR).
Also, figures and graphs are based
on Standard conditions which allow
for fixed reductions in pressure and
temperature with height. As we all
know, the real world isn't like that,
so these assumptions may not always
be true and due allowance must
therefore be made for them (if your
aircraft is performing sluggishly, you
may find it's not the machine, but
the conditions it has to work under
that are at fault).
Profiles
A profile is a series of target steps to
be achieved on takeoff or landing,
designed to give you the best chance
in an emergency. For example, with
a TwinStar in a clear area, you would
go up to 6 feet, then nose forward to
10 feet and 30 knots, (CDP)
accelerate to 40 kts (VTOSS) up to 550
feet, level out and accelerate to 55
kts (VY):
In practice, with both engines
performing normally, you would
accelerate as quickly as possible
through CDP and climb away as you
would with a single – only if an
engine fails would you decelerate to
VTOSS, or Takeoff Safety Speed (the
equivalent to V2 in a plane, for the
best angle of climb, then adopt VY at
the prescribed height, for the best
rate of climb.
The CDP is the only point where
you have a choice of action – before
then, you reject. Afterwards, you
carry on. The LDP is a similar point
for landing, where the idea is to hit a
speed and height combination from
where you can make an approach
that will allow you to land safely
116 The Helicopter Pilot’s Handbook
(most people get to one first, then
creep up on the other).
There can be many variations on the
Cat A theme:
· Airfield, or Clear Area, with
distances around 1000-1500 feet
to play with, accelerating to
where you can climb even at
max weight, usually close to VY.
· Reduced Field Length, climbing
vertically or even backwards, to
land in a much smaller area if
you have to, say 300-500 feet
long, usually at about 85-90%
max weight.
· Vertical, which speaks for itself,
but you may have the option of
a dip below heliport height or
not (i.e. at ground level). The
former allows 90% max wt, the
latter around 80%
Class 1 helipad take-off procedures
involve climbing vertically at first,
then going upwards and backwards
to a predetermined height (the
Critical Decision Point, or CDP) before
going forward (actually, ICAO now
call it the Takeoff Decision Point, or
TDP). This could be up to 150 or
200 feet above the helipad, after
going vertically to about 50 feet first
(if you've got the power on a hot
day!). For the TwinStar, you start
going backwards from about 15 feet,
at around 200 feet per minute,
keeping the helipad in sight, and at
TDP (90 feet) select max power and
10° nose down at the same time, so
your tail doesn't hit anything.
In theory, having moved backwards,
you still have the take-off spot in
sight and it's therefore available for
landing. At CDP (or TDP), if you
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本文链接地址：
The Helicopter Pilot’s Handbook(77)
