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the curve a second time). The best
rate of climb speed gives the maximum
40 Canadian Private Pilot Studies
altitude in the shortest range, and
because the maximum power is also
available then, is the same as the
endurance speed. In other words,
the best ROC is obtained when there
is the greatest difference between the
power required for level flight and
that available from the engines.
Blade Sailing
High winds and gusts will cause the
main rotor blades of helicopters to
flap up and down and be both a
danger to people near them and the
helicopter itself, as the blade stops
could be damaged, or a particularly
flexible blade could hit the tail
boom. At certain critical speeds (50-
100 RPM), blades will pass in and
out of the stall. Holding the cyclic in
the direction of the wind will keep
the pitch of the advancing blade to a
minimum and stop it lifting in the
first place.
Other ways of minimising the effect
include parking the helicopter away
from the downwind side of
obstructions or the downwash or
slipstream of other machines,
keeping the collective down, or
accelerating and decelerating the
blades as quickly as possible. In
addition, point the nose out of wind,
so that the lowest deflection is away
from the tail boom (exam question):
Having the wind from the rear helps
you keep an eye on the low blade at
the front, but this means landing
downwind in the first place.
Do not use pitch on the collective to slow the
blades down –droop stops depend on
friction for proper operation, and all
you will be doing is lightening the
load where it ought not to be.
Some Questions
1. What factors affect the amount of
lift produced by an aerofoil?
2. Why does an increase in all-upweight
lower speed in a helicopter?
3. If its propeller rotates
anticlockwise, which way does the
aircraft yaw on takeoff?
4. Which way does the nose pitch if
you turn right with a right hand
propeller?
5. Why does the RPM of a fixed
pitch propeller increase during
takeoff?
Some Answers
1. The angle of attack, air density,
velocity of airflow, surface area.
3. More collective pitch is required
and the retreating blade stalls earlier.
3. To the right (the downgoing blade
has the higher angle of attack). Blade
rotation is viewed from the cockpit.
4. Down, due to gyroscopic effect.
5. The blade angle of attack is more
efficient.
Engines & Systems
Engines, turbine or piston, all work
on more or less the same principle –
a quantity of air is sucked in and
mixed with fuel, compressed, set on
fire and slung out of the back (suck,
push, bang, blow in other words or,
more technically, induction, compression,
power and exhaust). The difference is
that the power comes from the
ignition stage in the piston, and the
exhaust stage in the turbine, which is
always ignited, whereas the piston
only does so when the spark plugs
operate. The jet is also a whole lot
lighter, and spins a lot faster. In
short, engines convert heat energy
into mechanical energy, and not very
efficiently at that (if they were,
exhausts would be cold – the
thermal efficiency of a piston engine
is only 30%, although it does
increase with altitude). The
mechanical energy may be used to
drive electrical, hydraulic and
pneumatic systems as well, which is
why engines are also called
powerplants.
For short range aeroplanes, the
propeller is the most economical
method of propulsion, which can be
driven by a piston or turbine engine
(piston-driven ones are generally
found on aircraft below 5700 kg).
Because of inefficiencies in design,
there is a loss of energy in the
process, and the thrust horse power is
about 80% of the shaft or brake horse
power actually coming out of the
engine. Sometimes, engine output is
too great for the transmission, so the
manufacturer will derate it to make
sure it doesn't damage anything.
Reciprocating Engines
A typical piston engine consists of a
series of identical cylinders which can
be arranged in many ways, according
to what the engine is going to be
used for. The Beaver, for example
had a Pratt & Whitney R985, which
was a radial engine that had the
cylinders in a circle, attached to the
crankshaft in the centre (with the
propeller bolted to it). In this case,
the cylinders stayed still, and the
　
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