How helicopters fly (1/2)


Uploaded by OUlearn on 10.09.2009

Transcript:
Pilots need incredible skill to get the best out of these machines
but even a complete novice like me can take the controls.
However, a little knowledge of the science of flight is a lot of help
as anyone who dares to take the controls will soon discover.
I don't really know how it's going to be, to be honest with you.
I think it will be exciting but I think it will be really scary.
Scary but exhilarating.
When you're floating around in a ton of metal,
it's reassuring to know a bit of the science that keeps you up there.
The theory of flight covers some really important stuff
like, how do you get up in the air?
What keeps you there? What happens if the engine breaks down?
Useful stuff for passengers to know, but essential for pilots
as two complete beginners are about to find out.
Marie and Tracy both work in the Royal Berkshire
ambulance control room in Wokingham.
When an emergency call comes in,
it's up to them to decide which ambulance to send
and that doesn't always mean one with wheels.
I've actually been up in the air ambulance.
I thoroughly enjoyed myself in that.
Obviously I had no part in flying the thing
but it was just amazing what they can actually do.
When we first found out we were going to get the air ambulance
we all had to go up to give us an idea of what it was about.
I was just amazed by the experience, how far you could see.
In fact I was so taken with it that when I went back to work
I handed in my notice to my boss and said I was going to be a pilot.
Tracy hasn't actually given up her day job
but she and Marie do want to find out what it's like to be pilots.
I'm looking forward to it.
Actually sitting in the driver's seat and taking over control
and actually how it works.
I am a little bit concerned because Marie is a very fast driver.
I'm concerned that perhaps that's going to transfer
to her being a very fast helicopter pilot.
Anyone who wants to be a pilot has to study the science of flight
and the first question is always how does it stay in the air.
I don't know how they stay up there.
I know that they do and I'm quite relieved that they do
but I don't know a lot about it.
To get into the air you have to overcome the pull of gravity.
To do that the rotors send a huge amount of air rushing downwards.
Believe me, I can feel it!
This creates an equal and opposite force pushing up on the rotors.
So the helicopter goes up.
And for pretty obvious reasons this effect is called lift.
As far as we're concerned lift is what we produce
to get two and a half tons of helicopter up off the ground
and accelerate it into forward flight.
The blades are responsible for producing, in a helicopter,
both the lift and the thrust to give it speed.
The basic thing about a helicopter
is that it's much more simple than you probably thought.
We just fly by using a wing and we push our wings around in a circle
in a rotary motion, so they're called rotors.
And the big secret with a wing
is that you've got to keep it moving through the air.
If you've ever stuck your hand out of a car window
you'll know exactly what a wing is doing.
If you put it out of a window and it's really flat,
then it slides through the air quite easily,
and if you increase the angle of your hand,
it's harder to push it through the air
but also you feel some lift as well.
Rotors are like the wings on an aeroplane
and if you look at the end of a rotor
it's got this streamlined shape called an aerofoil.
It's the curvature on this aerofoil
that gives a smooth flow of air over the rotor.
Whether it's a rotor or a wing,
it's the aerofoil that generates the lift.
The shape and angle of the aerofoil in flight
makes the air flow faster over the top surface than underneath.
The faster the air flows, the lower the pressure.
The difference in pressure between the top surface and the bottom
means that the aerofoil lifts up.
Because of the conservation of energy
that faster flow has to get the energy from somewhere
and it gets it from pressure.
So the pressure goes down to enable the faster flow over the top
and the differential in pressure gives you the lift.