We have detected that you do not have the latest version of Flash player installed.
Please click here to download the Flash plugin

If you do not wish to download the latest version of Flash player please click here to bypass detection.

Is it a bird? Is it a bloke? no is Jetman!

So you want to fly high in the sky with nothing but a pair of wings strapped to your back and four tiny jet engines? Easy!

Jet Man!

Well, actually, not very easy at all. Let’s have a look at how you can make a man fly like a bird. At least a very large bird with its bum on fire.

Jet Bird

How do you make a heavier than air machine fly?

The key is to generate lift. This is where the aerofoil comes in. This is the special shape that aircraft wings (and helicopter rotor blades) are made with. The shape produces an upward force whenever it moves through a fluid. A fluid can be either a liquid or a gas. This happens because the speed at which a fluid moves changes the pressure it exerts.

If a wing is stationary the air exerts its normal atmospheric pressure equally on both sides. There is no resultant force so the wing stays firmly on the ground. If the wing moves forward through the air the special shape means that the air that hits the leading edge of the wing must split in two. Some must go over the top, some must go underneath. Both airstreams must get to the back edge of the wing at the same time.

This means that the air going over the top must move faster, as it has a greater distance to go, because of the curved top surface. The air taking the direct route underneath has got to move more slowly. The fast air going over the top exerts a lower pressure than the slower air going underneath. The two forces are unbalanced. This produces a resultant force, called lift, directed upwards.

Generating lift

Phew! If you want to see this in action just hold a piece of A4 file paper against your lower lip and blow over the top. Watch what happens!

What can we do to maximise the lift?

There are two main things:

  • You can make the wing move faster, this will generate more lift, like in a jet fighter
  • Use a wing with a larger area, like in a glider
  • Or, both, like in an air liner
Planes

The next problem is to how to make the wing more forward. Most modern aircraft, and jet men, opt for gas turbine engines. Jets!

How does a jet engine work?

The principle is surprisingly simple. It basically consists of two sets of fans, or turbines. The ones at the front suck air in and squash it down into a very small space. They are known as the compressor fans, because they compress the air. The compressed air is passed into a combustion chamber where fuel is added. This is in fact paraffin, usually known by its American name, Kerosene.

Jet Engine

The fuel air mixture is ignited. The explosion causes the gasses to push out of the back of the engine through another series of fans. These fans are connected by a strong shaft to the compressor fans at the front, which suck in more air which is mixed with more fuel and so on. The process is continuous: sucking cool slow air in at the front and pushing hot fast air out of the back. Bingo! Continuous controllable thrust. Simple idea, rather harder to do in reality

A jet engine spins at around 60,000 revolutions per minute, about ten times as fast as a car engine, with the turbine blades glowing red hot. A Rolls Royce Trent engine has 92 turbine blades in its output fan. Each one produces about 800 horse power, the same as a Formula 1 car. The whole engine produces about 74,000 horse power and yet weighs only about as much as a family car. Amazing stuff! What’s more it does it for many hours at stretch, day in, day out with pretty well flawless reliability.

Jets and Cars

What’s more it does it for many hours at stretch, day in, day out with pretty well flawless reliability.

So how does all this knowledge help jet man?

Yves Rossy initially started out wanting to enhance the sky diving experience by being able to glide under control using a winged back pack. It wasn’t until later that he thought he might actually be able to achieve a secret dream of flying like Superman or the Rocketeer.

Small wings mean not much lift, unless you are moving very fast. To give enough power and still be light in weight a jet engine is the logical choice. All jets made for conventional aircraft are way too big.

Yves and his team decided to use the tiny jet engines used in model aircraft. These produce about 20hp each so four of them gives about 80hp. This is enough to push Yves along at over 193km (120mph) at an attitude of over 5000ft! Impressed?

Project

Construct a rocket powered skate board using a 2 litre bottle of Diet coke and a packet of mentos. Google ‘diet cake and mentos experiment’ for inspiration. The winner is the team that makes the skate board travel the greatest distance on level ground. Pictures of the most successful attempt will be posted on the site.

Beware the pressures generated can be very high, safety goggles must me worn!

The big questions:

A modern jet can fly a passenger across the Atlantic at with a fuel efficiency of around 50 miles per gallon per passenger. Short flights are less fuel efficient. Why?

Do you the benefits of cheap flights out weigh the pollution costs?

Could the modern world function without cheap mass transportation?