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general_kalle
06-14-2008, 02:20 PM
two physics questions.
somebody call raaaid http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

as i understand it a wing profile forces the air to travel farther above the wing than below the wing. that creates some pressure difference (not completly sure about that)
the faster travel of the wind below the wing lifts the plane up.

but what about when the plane is inverted. how come it continues to have lift?
If you invert your plane it will start nosing down but isnt that just because of the shape of the plane. I mean if you counter it by moving the stick forward you can fly level inverted.

Why is it that the wing still produces lift even though its inverted?

The Heinkel Lerceh as we all know have cirkular wings.
if say the lerce flyes forward the buttom of the wing cirkle will have to have the wind traveling faster at below it...but so does the top part of the wing. that means that the shape of the top part of the wing would have to be the opposite as the bottom part?
what about the parts on the side? how are they shaped?

is these points the reason that the lerche did not fly in real life? does it mean that it is not really thought about?


Hope you can understand it. As English is not my native language i might have some problems explaning exaktly what i mean. Just ask me if im unclear.

Regards

general_kalle
06-14-2008, 02:20 PM
two physics questions.
somebody call raaaid http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

as i understand it a wing profile forces the air to travel farther above the wing than below the wing. that creates some pressure difference (not completly sure about that)
the faster travel of the wind below the wing lifts the plane up.

but what about when the plane is inverted. how come it continues to have lift?
If you invert your plane it will start nosing down but isnt that just because of the shape of the plane. I mean if you counter it by moving the stick forward you can fly level inverted.

Why is it that the wing still produces lift even though its inverted?

The Heinkel Lerceh as we all know have cirkular wings.
if say the lerce flyes forward the buttom of the wing cirkle will have to have the wind traveling faster at below it...but so does the top part of the wing. that means that the shape of the top part of the wing would have to be the opposite as the bottom part?
what about the parts on the side? how are they shaped?

is these points the reason that the lerche did not fly in real life? does it mean that it is not really thought about?


Hope you can understand it. As English is not my native language i might have some problems explaning exaktly what i mean. Just ask me if im unclear.

Regards

LovroSL
06-14-2008, 02:37 PM
when you fly inverted, plane moves at an high angle of attack so a part the thrust vector (force of the propeler or a jet engine) is used as lift. This perpendicular component is in horizontal flight the size of negative lift that the wings are causing + weight of the plane.

Jambock_Dolfo
06-14-2008, 05:25 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by general_kalle:


If you invert your plane it will start nosing down ... I mean if you counter it by moving the stick forward you can fly level inverted.

Regards </div></BLOCKQUOTE>

Exactly.
In short, AoA.
All aerobatic propeller planes I flew had a more pronounced "nose up" attitude when flying inverted. So basically to go inverted you first pull the nose up, roll inverted and re-trim for inverted flight. Or you may move around the "sacred circle" using rudder and elevator to coordinate the maneuver with the ailerons. Result will be the same "nose-high" inverted attitude.

Maybe it is better explained here:
http://www.newton.dep.anl.gov/askasci/phy00/phy00640.htm


-dolfo

Tully__
06-14-2008, 11:38 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jambock_Dolfo:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by general_kalle:


If you invert your plane it will start nosing down ... I mean if you counter it by moving the stick forward you can fly level inverted.

Regards </div></BLOCKQUOTE>

Exactly.
In short, AoA.
All aerobatic propeller planes I flew had a more pronounced "nose up" attitude when flying inverted. So basically to go inverted you first pull the nose up, roll inverted and re-trim for inverted flight. Or you may move around the "sacred circle" using rudder and elevator to coordinate the maneuver with the ailerons. Result will be the same "nose-high" inverted attitude.

Maybe it is better explained here:
http://www.newton.dep.anl.gov/askasci/phy00/phy00640.htm


-dolfo </div></BLOCKQUOTE>

Also in a great deal more detail but without requiring a physics degree to get the gist of it: See How it Flies (http://www.av8n.com/how/)

general_kalle
09-03-2008, 01:35 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The Heinkel Lerceh as we all know have cirkular wings.
if say the lerce flyes forward the buttom of the wing cirkle will have to have the wind traveling faster at below it...but so does the top part of the wing. that means that the shape of the top part of the wing would have to be the opposite as the bottom part?
what about the parts on the side? how are they shaped?

is these points the reason that the lerche did not fly in real life? does it mean that it is not really thought about?


Hope you can understand it. As English is not my native language i might have some problems explaning exaktly what i mean. Just ask me if im unclear.

Regards </div></BLOCKQUOTE>

WTE_Galway
09-03-2008, 01:52 AM
You are basically talking about what is termed wing camber.

Camber makes a wing stronger and adds a bit more lift at the expense of some drag.

Camber is not essential for lift. Look at toy model aircraft with perfectly flat wings. They still fly.

Providing you have sufficient angle of attack even a flat board can generate lift.

Stingray333
09-03-2008, 08:42 AM
A large portion of the lift generated by the wing is due to Newton's second law (or is it his first law?) that for every reaction there is an equal and opposite reaction. As the wing moves through the air, the air passing under the wing is deflected and pushed downwards (assuming the wing has some positive angle of attack, or a flap surface angled down). Equal and opposite to this, the air pushes the wing upwards.

There is some aspect to lift due to pressure differential between the top portion and bottom of the wing due to the Bernouli principle, but I do not believe it to be the larger component of the lift (I would like to be corrected on this matter if this is not the case if someone is more knowledgeable)

As an experiment to yourself, when you are a passenger in a car traveling down the highway put your hand out the window and try to simulate an airfoil. Just by putting your hand at a very slight angle of attack you can feel a tremendous force acting upwards on your hand. I have also tried cupping my hand in such a way to emulate a chambered wing, but I do not feel any upwards force, but this is obviously just the case that it is hard to emulate the proper shape of the wing with your fingers.. nevertheless, it is fun to try!

Stingray

M_Gunz
09-03-2008, 12:23 PM
Oh my.....

The difference between top curve and bottom isn't usually all that much and in some cases
there is NONE, the airfoil being symmetric. Look it up if you think I make it up, I don't.

Reason for lift is because of angle of attack +and+ sharp trailing edge. Look that up too,
search on Kutta Condition and you find more, what results and how.

Biggest part of the nose pitch angle difference between flying rightside up and upside down
is that the wings are tilted upward with respect to the roll axis of the plane, this is called
the Angle Of Incidence and runs about about 5 degrees on many WWII fighters. So you have to put
the nose twice so far up when you fly inverted, once to overcome AOI and once again to get
the same AOI to your flight path.

All these things can be looked up here. (http://www.av8n.com/how/)

If you want to say this guy doesn't know what he writes then look over his credentials which
include:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">John Denker is certified as a Commercial Pilot, Flight Instructor, and Ground Instructor. He is an FAA Aviation Safety Counselor. He is a past member of the board of trustees of the Monmouth Area Flying Club, and a past member of the National Research Council Committee on Commercial Aviation Security. </div></BLOCKQUOTE>