Lift force

Illustration: Anna Sanchis

The Wright brothers -Wilbur and Orville- finally did it. It was in Kitty Hawk (North Carolina) on December 17, 1903. Their airplane Flyer flew. It did not glide, but, driven by a 19 horsepower engine, it remained in the air under control for 12 seconds and 37 metres at 48 km per hour on average. While it is true that it was initially helped by a catapult, it was Orville, the pilot, who really manned the device, which flew on its own. Two years later, on October 5, 1905, the Wright brothers managed to keep the device flying for 40 minutes and 39 km. From 1908 they did not need a catapult for takeoff.

There had been many previous attempts to fly with a machine heavier than air. All of them failed. Engravings, photos and even early films captured the picture of those monstrosities that tried to emulate birds. Some even had feathered wings. The great success of the Wrights was dissociating lift and impulse. Inventors before them beat the wings of their machines trying to replicate birds. But what holds birds in flight in the air is not the motion of their wings, but aerofoil. In fact, we only need to observe the flight of vultures to notice it.  Flapping does not hold the birds in the air, it only provides impulse.

Birds and planes remain suspended in the air thanks to the differential that exists between the speed of the air flowing over the top surface of the wing and the speed of the air flowing under it. That is why wings are curved at some point, so that it takes longer running over them than under them. This differential results in a vector that tightens the wing upwards. It is called lift force. The bigger the curvature, the greater the lift force. But also the greater the drag force, of course.

Impulse force is the one that produces motion. This is the task of the engine or, in the case of birds (and to some extent also in the case of helicopters), flapping, which is a form of rowing similar to that of Gondoliers, produces motion. Impulse cannot hold a plane in flight, but it causes the wings to move in the air mass, that is, it triggers lift. The engine makes the plane advance when it is moving slowly (when rolling down the runway) and take  flight when it goes pretty quickly, and the lift force lifts it up (when taking off or flying).

Impulse force is the one that produces motion. This is the task of the engine or, in the case of birds (and to some extent also in the case of helicopters), flapping, which is a form of rowing similar to that of Gondoliers, produces motion. Impulse cannot hold a plane in flight, but it causes the wings to move in the air mass, that is, it triggers lift. The engine makes the plane advance when it is moving slowly (when rolling down the runway) and take  flight when it goes pretty quickly, and the lift force lifts it up (when taking off or flying).

«We have many rigid gas balloons with no rudder and we lack easy-to-handle aircrafts. We need the new Wright brothers of economy»

It is a very interesting case of correlative physical phenomena. Something similar happens with bikes. The gyroscopic effect keeps it standing, but only by pedalling and making it move can we get this gyroscopic effect. So planes and bicycles stand and advance with motion, but not only because of it. Only with engine or pedals can cars run; bicycles also depend on the gyroscopic effect of the wheel (to keep the balance) and aircrafts on the wing’s lift force (to remain airborne). It is not intuitive and we tend to forget it. And we project this misrepresentation on other similar correlative phenomena. Perhaps the clearest case can be found in economy. Without growth (engine) there is no progress, but without a supporting system (a lift force), it collapses. At a hundred km per hour, a bicycle is very stable, but mostly it is very dangerous. Immersed in the post-industrial era, keeping on growing, and more and more intensively, is also nonsense. We need to uncouple lift and impulse because turbulence in speeding weakens the lift force. Therefore we are unsustainable. We have many rigid gas balloons with no rudder and we lack easy-to-handle aircrafts. We need the new Wright brothers of economy. Urgently, I think.

© Mètode 2015 - 85. Online only. Living with climate change - Spring 2015
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PhD in Biology, socio-ecologist, and president of ERF (Barcelona, Spain).