Okay... now explain how a cheap balsa glider with flat wings flys so well.
You know the type, I think Guillow.
Thanks for the detailed explanation!!!
>From: "Matt Gewain" <[EMAIL PROTECTED]>
>To: "Dana Falconer" <[EMAIL PROTECTED]>, <[EMAIL PROTECTED]>
>Subject: RE: [RCSE] aerodynamic question
>Date: Wed, 1 Nov 2000 06:28:19 -0800
>
>A symmetrical airfoil is exactly the same shape on the top as on the
>bottom.
>When air flows over a wing there is a point on the leading edge of the wing
>where air above that point flows over the top of the wing and air below
>that
>point flows over the bottom of the wing. This point is called the
>stagnation point. Similarly there is a stagnation point at the trailing
>edge where these streamlines of air flow back together. Aerodynamicists
>have a rule called the Kutta condition that says that the rear stagnation
>point is always at the trailing edge of the wing ( for normal attached
>flow). This means that at a Zero angle of attack The forward stagnation
>point is at the exact center of the leading edge of the wing, and the
>distance between the forward and aft stagnation points is the same over the
>top and bottom of the wing. By Bernoulli's law this means that you get the
>same velocity and pressure profile over the top of the wing and the bottom,
>and create no lift.
>
>When you put the wing at a positive angle of attack the forward stagnation
>point moves down on the leading edge making the distance over the top of
>the
>wing greater and the distance on the bottom of the wing less between the
>forward and aft stagnation points. This increases the velocity and reduces
>the pressure over the top of the wing and reduces the velocity and
>increases
>the pressure over the bottom of the wing. This is how a wing creates lift.
>If the Angle of attack is negative (nose down with respect to the wing)
>then
>you create negative lift. This is what happens in inverted flight, because
>we flip the wing and negative lift vector upside down so it opposes
>gravity.
>
>When you have a non symmetrical airfoil you have added camber to the wing
>so
>the zero lift angle of attack is no longer zero. A positive camber airfoil
>has a negative zero lift angle and generates more lift in the positive
>direction at the same angle of attack. But if you want to fly inverted the
>positive camber wing will require a large negative angle of attack to
>generate much negative lift and will stall at quickly.
>
>Matt Gewain
>
>
>
>
>
>I have always wondered this and I bet all of you out there know the answer.
>Okay here goes...
>
>Considering a symmetrical airfoil:
>Is a symmetrical airfoil used primarily for aerobatics/inverted flight?
>
>If so doesn't the top of the wing create less pressure therefore helping to
>create lift. I realize that newton's 3rd law is also involved with a wing
>producing lift.
>
>So if the top of the wing creates less pressure due to the bernoulli effect
>then when inverted the less pressure the top of the wing creates is working
>against you right?
>
>I assume this is compensated by increasing the angle of attack and newton's
>3rd law then starts to play into maintaining altitude when inverted.
>
>With a symmetrical wing the curve on top is almost the same as on the
>bottom. Therefore the upward force the top of the wing creates is almost
>the same as the downward force that the bottom of the wing creates (upward
>being greater). The difference is the lift. So why have a symmetrical
>wing? Why not have a wing with a flat bottom and a top that a little lift?
>What I am getting at is, what does the symmetrical wing buy you
>aerodynamically?
>
>Thanks!!
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