Pilot Hughie provides a helicopter lesson for the crew (and us)
by Guest Blogger
July 15, 2005
People have been asking me about maneuvers with the heli, noticing that
when in what (seems to them) the same situation, different maneuvers
are sometimes conducted. To answer some of your questions, here is a
basic introduction to what can become a very deep subject. If I told you
that aircraft are in fact sucked up by a vacuum above the wings, and
then went on to explain it, you might be a little bored. So, lets go
with the KIS (Keep It Simple) approach.
Individually, the blades at the top of a helicopter are called the main
rotor blades; collectively they form the rotor disc, which for all
intents and purposes is a rotating, flying wing. When in flight, the main rotor blades
of our helicopter (Tweety) turn at 480 rpm (revolutions per minute. Changing the angle of attack (pitch) of the rotor blades
collectively, changes the amount of lift – how much they dig into the
air. Digging them in less (by making them more horizontal) causes the
heli to descend, digging them in more causes it to rise and requires
more power. Tilting the entire rotor disc causes the heli to go in the
direction of tilt. How the disc is ’tilted’ is a complex explanation
that would take more writing, than you probably have to time to read.
When flying, the primary concerns are weight and
balance. You have a certain amount of
power available, and if you exceed that, you will trash the
engine – this can happen in about two seconds. The repair bill will
resemble a lottery payout. This situation can be monitored at take off,
and if you ‘red line’, you don’t fly until you have got rid of some
weight. Self-unloading cargo (i.e. people) is usually the answer.
When lifting from the deck you are in ‘ground effect’ for about the
first six feet. This is when your down-wash is stopped by the surface
and cannot dissipate quickly. This gives you more lift. Keep in mind that the rotor blades provide
both upward lift, and directional propulsion so if you can get more of
either from someplace else then you’re working the blades, and thus the
engine, less hard.
One method of gaining lift, is to get over about 40 knots (46 mph),
that’s when some aerodynamic wizardry takes over, and generates lift for
you, but, in order to get there you have to stay in ‘ground effect’.
There are various ways of doing that, depending on the situation.
Dropping off the side of the ship, and using the water surface, to
generate ground effect, is one method used to achieve this. If I can get
into a headwind situation, that helps enormously (for example a 10 knot
head wind means I only need another 30 knots of ground speed to reach 40
The other method, which is also used to escape from small areas in
forests etc., is a ‘towering departure’. In Tweety, the blades rotate
anti-clockwise. Naturally, the rest of the helicopter wants to rotate
with them, but is prevented from doing so by the tail rotor. If, when
lifting, I rotate the helicopter in the same direction as the main rotor
blades, I decrease the torque effect, thereby diverting power from the
tail rotor to the main rotor. I can use this power to increase the
pitch of the main rotor blades, and generate more lift. When a
reasonable height has been gained, I tip the nose over, and head
downwards, using gravity to reach that magic 40 knots. Scary for first
time passengers, especially if they don’t know what’s going on!
Now that we have taken off, we have to land. Take offs are optional –
landings, on the other hand, are mandatory. Finding level ground is not
always possible. If you land on a steep slope you have the worry of
blades hitting on the high side, or worse still, one of your passengers
taking a stroll up the hill, instead of down – this generates a lot of
Another problem with landing on a steep slope is that if the top of the
rotor head goes past a vertical line with the skid (that is if the heli
is tilted too far over to the side), a situation known as ‘dynamic
roll-over’ occurs as the gyroscopic effect of the rotor pulls the heli
the rest of the way over. This will result in a hole being dug by the
main rotors, providing a storage facility for the rest of the ensuing
scrap, that is about a tenth of a second behind, to be buried in.
A method of avoiding this is to rest one skid on the ground (keeping the
heli level, with the other skid in the air), and have people disembark.
I like to know when people disembark, because, as you can imagine, the
‘weight and balance’ of the aircraft will change dramatically. It is
important that crewmembers communicate very clearly with the pilot –
especially if it’s me. BUT – please remember to take off your headset as
you disembark, people do forget – believe me
Balancing on logs, rocks, or ice – with the heli’s skids perpendicular
to the thing you’re landing on – is another method. The basic weight of
the machine is supported, and I am just balancing the mass, but again,
as in the previous scenario, I like to know when people are departing –
that way there are no ‘surprises’!
A last mention, about something I am a bit anal about – DOORS. When you
leave the aircraft they must be closed properly behind you, with the
seat belt INSIDE, and clipped together. If I am flying along, and a
door ‘pops’, I have to land. This may not be convenient. It also scares
the living daylights out of me. And if a loose item were to get sucked out,
and go into the tail rotor… lots more paperwork, but perhaps not
for me and my crew.
I hope these facts and explanations have been helpful. Briefings
are given to crews before a flight, but, if in the meantime you want to
know anything, just ask, I will try and think of an answer.
– Hughie the pilot
[Hughie, a native of Scotland, has been flying fixed wing aircraft for
10 years, for Greenpeace and commercially. He
put himself through helicopter training eight years ago with the idea of
being a Greenpeace heli pilot, and has logged nearly 4,000 hours flight
time. He has never lost a passenger, and in person is an
easygoing kind of guy, except when it comes to helicopter safety.]