This is quite fascinating: There was research into this as early as 1941?
https://www.nasa.gov/centers/dryden/pdf/88792main_Laminar.pdf
https://www.nasa.gov/centers/dryden/pdf/88792main_Laminar.pdf
Laminar Flow Control
- Thread starter Zipper730
- Start date
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swampyankee
Chief Master Sergeant
- 3,962
- Jun 25, 2013
The idea of sucking away a turbulent boundary layer predates 1935 (see Schrenk, O, "Experiments with suction-type wings", Aug 1935 originally published as "Versuche mit Absaugeflugeln," Luftfahrtforschung. Vol. 12, No. 1, pp. 10-27, March 28, 1935. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930094644.pdf This is one of many examples of aeronautics' internationalism before WW2) or look at this list: NASA Technical Reports Server (NTRS)
Can someone explain to me in a simple way how a laminar wing lifts an airplane? I always thought an airplane wing had to be convex at the top and flat at the bottom. This causes a difference in air velocity at the top and bottom. And that causes the pressure difference. But when I look at the P-51 wing, I have the impression that it is equally convex at the top and bottom. See figure:
http://historynet.com/wp-content/uploads/2015/07/air_flow.jpg
http://historynet.com/wp-content/uploads/2015/07/air_flow.jpg
Just the angle of attack generates lift.
drgondog
Major
The NAA/NACA 45-100 airfoil has camber also but the first statement above is correct - positive AoA generates the lift/pressure distribution
Unfortunately, I still don't understand how it works. Where does the pressure difference over the wing and under the wing come from?
The speed of the aircraft, as trodom posted, try holding a piece of card out of a car window at 45degrees. A plane like a P-51 is doing circa 100MPH at take off at normal flying speeds around 300MPH you get a lot of lift from a small angle of attack. When I was a kid some of my friends had static line aircraft, some were just a thin and narrow plywood board with a prop and motor, the "wing" had no aerofoil shape at all, not even pointed leading and trailing edges.
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The distance over top of the wing is great than the difference under it. With symmetric airfoils via AoA.
How do symmetrical airfoils generate lift?
When I was a kid I used to think that this is how an airplane wing works. But then in school during the lesson I heard that the "lift" of the plane is the result of the difference in airspeed over the wing and under the wing. And that for the same reason a strong wind lifts the roofs of houses (because they are convex at the top). So ... something must be wrong with school education.
I always thought that was how a rocket's "fins" worked. The rocket cannot change the direction of flight because it "wants" to have the lowest possible resistance in flight. And these "fins" force it - as long as the rocket is flying very fast. But the wings of an airplane - as they taught me in school - are quite a different matter than the "fins" of a rocket.
"the exiting airstream is deflected downwards." - it reminds me more of a rocket fin or elevator fin on the tail of an airplane. If I understand this text correctly (maybe wrong). George Cayley explained the phenomenon of flight in a different way. Or maybe I get it all wrong.
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That depends on the type of rocket, a simple childs rocket using water goes up because of its centre of gravity and the drag of the tail fins. A fire work needs a wooden stick to move the centre of gravity behind the centre of thrust. On a proper rocket like a V2 or Saturn V the thrusters steer the rocket they are adjustable and move based on info from gyroscopes and computers. On the first stage of Saturn V it had 5 rocket motors, the 4 outside steered only the centre motor was fixed. Anything moving very fast has momentum but also has massive forces on it. A Sidewinder missile only has small "wings" but they generate the lift to keep it flying horizontal and turn at up to 25G if required. The wings of early aeroplanes had classic aerofoils using a differential in air pressure to create lift, many airplanes in the supersonic era have wings like a blade.
With due respect to the great George Cayley, he was writing years ago and was actually discussing gliding, though he did have ideas on propulsion, he could only theorise about it. Cayleys "glider" did not use a cambered aerofoil, there is a replica at "The Yorkshire Museum" picture from wiki
At school they were perhaps teaching the whole subject of relationships between pressure volume and temperature (Boyles Law etc), generating lift by increasing velocity over the top of the wing and therefore reducing pressure is one example of it.
You are only discussing lift, the other issue is producing lift without producing drag in two structures (wings) that can contain 180 gallons of fuel, 6 machine guns and ammunition and have the beams strong enough to support 9 times weight of the plane when making a tight turn. If you stick a card out of the car window at the same time as pushing your hand up it pushes it backwards, that is the drag. The P-51 wing was incredibly sophisticated and took years of wind tunnel research into plastic flow, pressure gradients and other "stuff" I barely understand about gases and thermodynamics.
It is definitely a complicated matter. As I heard, the PZL.37 was used partially symmetrical airfoil by accident and out of necessity. The constructor had to fit the bombs inside the wings. But he was highly skeptical. He believed that an airplane with symmetrical airfoil would fly worse. As it turned out, he flew quite well, but his "father" didn't understand it. So - before that people had to think that symmetrical airfoil was a bad idea. What's more - the Germans captured PZL.37, the Soviets captured PZL.37 and ... they did not copy this idea. And they certainly had smart engineers too.
