Have you ever wanted to fly? To soar above valleys and mountains, cities and oceans, feeling the wind whipping against your face? Flight has fascinated humans for as long as we have looked skyward and seen birds soaring gracefully above the trees. What is it to fly? How do we explain flight?
We know birds and insects fly. Bees fly, bats fly. Planes and helicopters do. You might say gliders, kites, hang-gliders and boomerangs fly as well.
Is flight about things moving through the air?
People – including scientists and engineers – have their own ways to define flight.
- Some have a narrow definition: things that fly are things that can stay in the air for a period of time with controlled movement and have their own power source.
- Others insist that only things with wings can truly fly.
- Others are more inclusive: if it doesn’t fall out of the sky because of gravity, it must be flying.
What do you think flies? Planes? Birds? Bumble-bees? Rockets? Thistledown? A stone that has just been thrown? How would you define flight?
For our purposes (because we have limited space and flight is such a huge topic), ‘things that fly’ refer to things with wings.
Things with wings
- Birds that fly have wings. They also have streamlined bodies, light internal or external skeletons, a large heart and strong flight muscles. Find out more in the article How birds fly.
- Planes also have wings and streamlined bodies. Instead of a large heart and strong muscles, they have powerful motors that make up for their weight through speed. Find out more in the article Principles of flight.
- Gliders also have wings and streamlined bodies, but they don’t have a motor. Their power comes from slowly descending as they move forwards, like a skier going down a slope.
- Hang-gliders have wings that can generate lift. They also get their power by descending.
- Well made kites are aerofoil wings, but they need to be tethered for controlled lift.
The awesome flight of the godwits
For explanations of key concepts, see Investigating flight – key terms.
Nature of science
Some scientists have very definite views when defining what flight is. Other scientists just as passionately disagree with their rigid definitions. There are often conflicting views between scientists. Such arguments show that science is a process of intense criticism and that it has a subjective aspect as well.