Real-Life Math -- Solution
The following method was used to calculate the speed of the aircraft
at the time the blades struck the ground.
Nominal rotational speed
of the Main Rotor Head (MRH) = 330 revolutions per minute (RPM).
Therefore,
the number of times a blade passes a point on the ground =
330
(RPM) x 4 (4 blades on the main rotor) = 1320 (per minute)
Time
between strikes = 60/1320 = 0.045 seconds
Distance between the
first three strikes = 1 meter
Distance/Time = Speed
1 meter/0.045
= 22.22 meters per second
22.22 x 60 (seconds in one minute)
x 60 (minutes in one hour) / 1000 = 79.99 km/h
To convert to
knots:
79.99 x 0.54
= 43 knots
The speed of the
aircraft at the time the blades struck the ground was 43 knots.
"Math
plays an extremely important part in my work," says George Carney. He is part
of a two-person team that investigates all British army air accidents throughout
the world.