Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Misconceptions: Physics of Flight

On Wed, 11 Aug 1999, Michael N. Monce wrote:

Ok, but doesn't Bernoulli still generate lift (i.e. pressure
differential) even at zero angle of attack??


Yes, and that's the usual argument offered by those who support the "wing
shape" explanation. This debate has occurred over and over again on
internet forums and newsgroups, and it usually follows the same
sequence, therefor I have some rapid comebacks already prepared!

:)


Here is a counter-argument. Imagine a very thin, cambered (curved)
airfoil where the upper and lower surfaces have the same path-length. This
airfoil generates lift at zero angle of attack. Why? Imagine a flat thin
wing at zero attack angle, then imagine "bowing" it a bit so it has a
camber. This creates lift, even though the angle of attack is changed.
Why?

As far as I can see, inertia is the answer. When air flows off of the
trailing edge of any wing, it keeps going in the same direction: angled
downwards. At the leading edge of the wing the air-flow pattern is
different. Vacuum-cleaners are similar: "sucking" creates a radial
pattern of flowing air, while "blowing" creates a narrow jet. When air
flows past a wing, the trailing edge of the wing has a large effect on
directing the air at a certain angle, while the leading edge has a far
smaller effect. Even if the front of the wing is a mirror-image of the
back, the front and back will behave differently because air has inertia.
Another way to say it: the mass of the parcels of air is the key to
understanding flight. But we already knew about this, since any airplane
must fling mass downwards if it wants to remain suspended against gravity.

At zero angle of attack, if the trailing edge of the wing is effectively
tilted downwards, then it directs the flow of air downwards. Curved
airfoils do this. SO do airfoils where the top is curved and the bottom
is flat. These airfoils behave as if they have a positive attack angle.

See FIGURE 4 on this collection of GIFs:

http://www.amasci.com/wing/airgif.html


Huge, bloated article on similar topics:

http://www.amasci.com/wing/airfoil.html


Explanation of flight which doesn't talk about pressure or pathlength:

http://www.amasci.com/wing/rotbal.html


((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com http://www.amasci.com
EE/programmer/sci-exhibits science projects, tesla, weird science
Seattle, WA 206-781-3320 freenrg-L taoshum-L vortex-L webhead-L