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a third to a quarter of the size of the
stalling angle. It never changes, but
without an angle of attack indicator,
you need an indirect method of
guesstimating it, such as speed,
which may have to be increased
slightly with aircraft weight, reducing
your range, as you will be using more
power, and hence fuel, to attain it.
The biggest factor concerning your
range will be the wind, which will
reduce your groundspeed when on
the nose, causing you to use more
fuel. However, a slight increase in
airspeed, say 5-10%, will get you
there sooner with only a slight effect
on fuel consumption.
Maximum Endurance Speed
This gives you the most time in the
air for least amount of fuel, which is
useful when waiting for the weather
to clear, or when asked to hold clear
of a control zone, but, in practice, it
gives you little or no controllability,
so there will be a recommended
endurance speed in the flight manual,
which is a few knots above.
The endurance is longer the lower
you can fly (allowing for safety, of
course), and turbulence and flaps
will affect the speed considerably.
There is more drag with endurance
speed than there is with range speed,
which is higher.
Load Factor
The total lift divided by the total
weight, the ratio being 1:1 in level
unaccelerated flight. In other words,
the weight carried by a wing
expressed in terms of "G".
Principles of Flight 25
When you turn, the aircraft tries to
continue in a straight line, and a
force is needed to point it towards
the centre of the turn – this would
be Centripetal Force, which must be
generated by extra lift from the
wings. In effect, the (upwards) lift
vector is reduced by the same
amount, which needs to be
compensated for. In a 60° banked
turn, therefore, the amount of lift
you need is doubled, so the load
factor becomes 2. This can also be
increased temporarily by sharp
manoeuvres or gusts and turbulence
(a gust with a speed of 66 feet per
second will change the angle of
attack at 200 kts by as much as 11°,
which will either lift you very quickly
or cause a stall).
Here is a chart expressing angles of
bank against load factors:
Angle Factor
0° 1
15° 1.04
45° 1.41
60° 2
75° 4
The point to watch is that the load
factor may increase so much that the
maximum weight of the aircraft is
exceeded, and the wings won't be
able to do their job properly.
Propellers
These are just aerofoils with a twist
in them (washout) to spread the lift
evenly over the whole length, as the
tips run faster than the center and
need less angle of attack (the word
pitch is sometimes used loosely to
describe this). The basic propeller is
averaged to cope with many flight
conditions, so is not perfect for
them all, particularly the takeoff. The
real problem is that you have to
make the engine run faster for more
performance from the prop, and
engines work best within a certain
speed range.
Officially, a propeller's function is to
convert the crankshaft's rotary
movement into thrust, by moving a
large column of air backwards, to
propel the aircraft forward. As a
propeller is an aerofoil, the thrust it
creates is the same as the lift from a
wing – it's just used differently.
A tractor (at the nose) will propel fast,
turbulent air over the lifting surfaces,
whereas a pusher (somewhere behind
the fuselage) provides better high
speed performance because it
doesn't produce so much drag. On
the other hand, the tractor bites into
clean air, while a pusher spins in air
that is already disturbed.
A rotating propeller creates various
forces which may be allowed for in
the design stages, including gyroscopic
precession (see Instruments), where
lifting the tail tends to make the nose
yaw to the left. Torque results from
the airframe going the opposite way
to the direction of rotation:
The effect is to produce a roll, which
is countered by washout on the
upgoing wing.
26 Canadian Private Pilot Studies
The blade going down pulls more at
high angles of attack, resulting in
asymmetric thrust (also known as the P
factor). Where the propellers rotate
the same way on a multi-engined
aircraft (as with the PA 23), the
failure of one engine may cause
more problems than the other
because of this – in the case of the
　
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