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pressure and speed.
Dynamic hydroplaning is the basic sort,
arising from standing water. Viscous
hydroplaning involves a thin layer of
liquid on a slippery surface, such as
the traces of rubber left on the
landing area of a runway (one reason
why it's dangerous to drive after a
rain shower in Summer).
166 Canadian Private Pilot Studies
Reverted Rubber Hydroplaning happens
when a locked tyre generates enough
heat from friction to boil the water
on the surface and cause the
resulting steam to stop the tyre
touching the runway. The heat
causes the rubber to revert to its
basic chemical properties.
A rough speed at which aquaplaning
can occur is about 9 times the square
root of your tyre pressures, 100
pounds per square inch therefore
giving you about 90 kts (7.7 times if
the tyre isn't rotating)—if this is
higher than your expected take-off
speed you're naturally safer than
otherwise. The point to note is that
if you start aquaplaning above the
critical speed (for example, when
landing), you can expect the process
to continue below it, that is, you will
slide around to well below the speed
you would have expected it to start if
you were taking off.
Under-inflating tyres doesn't help—
each 2 or 3 lbs below proper
pressure will lower the aquaplaning
speed by 1 knot, so be careful if
you've descended rapidly from a
colder altitude.
Grass
For dry short grass (under 5"), the
TODR will increase by 20%, a
factor of 1.2. When it's wet, 25%—a
factor of 1.25. For dry, long grass (5-
10"), TODR will increase by 25%,
and 30% when wet (it's not
recommended that you operate
when the grass is over 10" high).
For dry short grass (under 5 inches),
the LDR will increase by 20%, a
factor of 1.2. When it's wet, 30%—a
factor of 1.3. For dry, long grass (5-
10 inches), LDR will increase by
30%, and 40% when wet. For other
soft ground or snow, the increase
will be in the order of 25% or more
for take-off and landing.
Obstacles (The Climb)
The best Rate of Climb speed is
obtained when there is the greatest
difference between the power
required for level flight and that
available from the engines. In
turboprops, this will coincide with
the speed that gives the best
lift/drag ratio, since power output is
relatively constant. Turbojets,
however, produce more engine
power with speed, which is enough
to overcome the extra drag, so the
maximum differential between
power required and available
happens at a higher speed. There will
be performance tables to find time
and fuel required for climbs.
Remember that headwind and
tailwinds will change the distance
figures. To cope with this, work out
the groundspeed with no wind and
apply the corrections then. You can
use the whizzwheel to find out the
distance and time.
The Cruise
That part of the trip from the top of
the climb (TOC) to the top of the
descent (TOD.
For most trips, fuel management
revolves around getting the
maximum range for a given amount
of fuel or, looked at another way,
how little you can get away with on a
fixed distance. However,
occasionally you must hold, and the
question of how long you can stay
airborne arises, namely endurance.
Flight Planning 167
Speed
Peculiar to landing is speed—a
higher one than specified naturally
requires a longer distance, not only
for slowing down, but the FAA have
also determined that being 5 knots
too fast over the threshold is the
equivalent of being 50 feet too high.
Miscellaneous
Low tyre pressures increase distances
required.
V-Speeds
Significant aircraft speeds, calculated
for every takeoff, and varying with
aircraft weight or mass. Some, like
V1, are found in tables in the
Performance section of the Flight
Manual. Typically, you would enter a
table at the appropriate PA, then go
across until you reach the relevant
temperature range (making sure you
use C or F). Then apply gross weight
and flap settings and read the speeds
off. On the 727, V1 and VR are
always the same. Here are some:
Speed Meaning
VNE Never Exceed speed, around
90% of Dive Speed (VD). On a
turbine, the equivalent is VMO
or MMO.
VNO Normal Operations
VTOS In a single, a target speed to
be achieved when becoming
airborne. It allows safe control
with a margin over stalling
　
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