In this article I will give a breif summary on different types of aerofoils and why a wing produces lift. This article is mainly based at people who are just getting into the hobby and maybe don't know all that much about the basic principles of flight. This may also apply to people who are intermidiate in the hobby and want to start scratch building but don't know anything about how to make a wing which will produce a descent amount of lift.
Why a wing produces lift:
A wing produces lift because of it's shape, specifically because, in it's most basic form, it's curved top and it's flat bottom. The curved surface on the top produces low pressure.
This is because the air travelling over the top of the wing has longer to travel around the wing than the air which flows underneath, and this means that the air will decrease in pressure as stated in Bernoulli's principle, 'an increase in the speed of the fluid occurs simultaneously with a decrease in pressure'. This is all that lift is, a low pressure area above a high pressure area, this causes the high pressure to push up, and thus lifting your plane off the ground.
Different aerofoils:
There many different aerofoil types, all with there different purposes. I won't go into to much detail on these rather just outline the main different shapes. Underneath there are a series of examples:
Flat bottomed aerofoils are the most simple aerofoil shape and produce quite a lot of lift but aren't the most slippery. They are used a lot in scratch building as they are very easy to reproduce.
Semi-symmetrical aerofoils are probably the most commonly used airfoils on planes as they produce less drag than flat bottomed aerofoils but still a lot of lift.
Symmetrical aerofoils are used on 3d, precision aerobatic and racer planes. They are used on 3d planes as they produce lift inverted and upright and track very straight and are used in racers as they are very slippery in the air. This type of wing generates lift by flying at a slight angle of attack as if it was horizontal, equal amounts of low pressure would form over the top and bottom of the wing.
Under-cambered aerofoils are used in high load planes and slow flyers as they produce a very large amount of lift but a lot of drag.
I hope this article was helpful and if there is anything else you would like to know, comment.
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Try to explain ground effect using you explanation. You can't.
You see, the reason there is ground effect is the reason airplanes have 'lift'.
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"In fixed-wing aircraft, ground effect is the increased lift and decreased drag that an aircraft's wings generate when they are close to a fixed surface ... When an aircraft is flying at an altitude that is approximately at or below the same distance as the aircraft's wingspan or helicopter's rotor diameter, there is, depending on airfoil and aircraft design, an often noticeable ground effect. This is caused primarily by the ground interrupting the wingtip vortices and downwash behind the wing. When a wing is flown very close to the ground, wingtip vortices are unable to form effectively due to the obstruction of the ground. The result is lower induced drag, which increases the speed and lift of the aircraft." (Wikipedia - the "ground effect" to knowledge)
Also the reason why I so often stall-smash the nose of my planes, I do not take this effect in mind when planning my approach and overshoot...
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Now it might be confusing since the route over the top equals the route over the bottom if the airfoil is horizontal
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Thank you !
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You can easily test this in a moving car - put a wing section out of the window (when safe to do so) - see how much more lift (and drag) is created when the section is tilted.
You can also do this with a flat board to show even a flat section can give lift or even your hand.
You can also ponder these questions:
Why can air craft with aerofoils fly upside down?
Why can aircraft with symmetrical aerofoils fly?
Why can aircraft with no aerofoil fly?
Why does the KF step improve on the flat board.
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To answer some of your Q's:
An aircraft flying upside down commonly needs quite a lot of "down stick". It counters the lift from the wing (now driving it into the ground) with AOT.
Symmetrical is already answered. In short, a main reason for 100% symmetrical wings is less drag. A totally flat wind (e.g. FT Flyer) flies on the same principal, but a flat wind has more turbulence and thereby drag. A sym-wing is much more slippery. (Most real planes with aerobatic capability have semi-sym-wings so that they can fly distance more economically).
No airfoil: see above.
KF step generates an airfoil due to the turbulence after each step. These swirl pockets effectively produce an airfoil, even though much less slippery (i.e. more drag) than a proper airfoil.
Your arguments are all true, but don't negate the effect of an airfoil.
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When writing an article about lift one should at least mention Newtonian lift, as the contemporary understanding of lift is more based on this principle than Bernoulli's principle.
Cheers
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