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

knots total).

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

paperwork.

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.]

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