Basic Principles

[jetset737]

Is it higher pressure on the top of the wing and lower pressure on the underside of the wing that enables an aircraft to fly or is it the other way around?
I'm always getting that mixed up!!

Is there anything else I kneed to konw appart from flying a circuit, ailerons, spoilers, flaps, and that the larger the wing area the slower the aircraft is able to go when landing.

I need to know ASAP!!

[Autofly]

High pressure will always move to low whether it be air/water/etc....... therefore the high pressure beneath the wing keeps the aircraft in the air. I'd read your tech book again if I were you. The fundamentals of flight is the last thing you'd want to forget.

Autofly

[Superfly]

Autofly,

:confused: Steady, steady when you're talking about books 'cause mine say: this the lower pressure on top of the wing that enables the wing to be "sucked" and therefore counter-balance the effect of gravity upon the Aircraft. you could maintain flight with a wing that doesn't have a lower surface > Imagine a wing with a conventional top surface and beneath, just the ribs with no fabric or whatever material to cover them : I guaranty you that it would fly. JEDELSKY type of wings perfectly illustrate what I'm saying.

[TheNavigator]

Another way of looking at it:

Pressure is just force per unit area.

Higher pressure means more force per unit area.

A wing generates lift because there is a resultant force (upwards) that equals weight (downwards force). This upwards force arises from the lower pressure/force on the top side of the wing with regards to the higher pressure/force on the lower part of the wing. Both these forces are exerted towards the wing.

This is what is possible to write in a few lines.

For more info check this excellent link http://www.monmouth.com/~jsd/fly/how/

Hope this helps!

PS - Autofly is right about something. Air flows from a high pressure region to a low pressure region and it is this that causes the vortices formed at the end of the wings when air moves from the upper side of the wings to the lower side.

[ 18 July 2001: Message edited by: TheNavigator ]

[Delta Wun-Wun]

The way I remember it .....The top of the wing is curved so the air has farther to travel,therefore it is going faster so is at a lower pressure than the slower air underneath....I think :eek: :eek:

[Kermit 180]

The camber or shape causes an acceleration of air over the upper side of the aerofoil, causing a difference of lower pressure on top. This drop in pressure on the upper side of the aerfoil causes a total reaction, which is comprised of two forces, known simply as lift, and drag.

(That's if you believe the Bernoulli-based theory).

Kermie :D

[mr.smith]

another pespective for ya-

as the Relative AirFlow passes over a venturi(the upper wing camber) then the speed of the RAF increases as the pressure decreases.
This reduced pressure sucks the wing upwards - two thirds of the total lift is created this way.
The remaining one third is produced by the RAF striking the lower surface, which is typically inclined at an angle of 4 degrees - called flat plate effect.
Bob's yer uncle and yer flying, man.

hope this helps,
smithy.
;)

[Manflex55]

The 2 flies (Auto & Super) & mr smith are right : it has been demonstrated that the vacuum created @ the top surface of an aerofoil produces 2/3 of the total Lift, compliments of Dr Bernoulli & his venturi effect. The high pressure developed below the aerofoil produces the remaining third.

MF

[ 19 July 2001: Message edited by: Manflex55 ]

[RVR800]

Is the sharp bit at the front end of
the wing or at the back - its all so
confusing isnt it?

:p

[Teroc]

Aww Jetset C'mon... Pull the other one.

[scroggs]

Ok, so how does an aircraft fly upside down? And how does a wing with little or no camber work (there are many)?

[Rod Eddington]

well done scroggsy, that's an old favourite of mine. i don't think anyone i've asked about the upside down thing has been able to come up with anything half-decent. my a-level physics teacher rapidly changed the subject when i asked him!

another question though, could a plane take-off upside down?? (obviously it'd need wheels on the top)

anyway i'll stop thinking now, it's hurting my head!

cheers, rod

[Teroc]

A combination of all 3 generally accepted theories cause the wing to generate lift.
1. Bernoulli
2. Newtonian Physics
3. Pressure differential
We all know bits of the 3 common theories answer some questions but on their own dont answer all the questions. The 3rd theory is probably the least understood. Heres a good explanation I found on the net which explains why an aircraft can still fly upside down.

Air approaching the top surface of the wing is compressed into the air above it as it moves upward. Then, as the top surface curves downward and away from the airstream, a low-pressure area is developed and the air above is pulled downward toward the back of the wing.
Air approaching the bottom surface of the wing is slowed, compressed and redirected in a downward path. As the air nears the rear of the wing, its speed and pressure gradually match that of the air coming over the top. The overall pressure effects encountered on the bottom of the wing are generally less pronounced than those on the top of the wing.

[Trislander]

Delta Wun Wun, Exactly the way I remember it.

Just remember that to lift anything, a pressure is required underneath the object that is greater than the force pulling it down to the earth- in the case of a box full of junk: In order to lift the box, you must apply pressure with your hands/arms underneath the box. This pressure must be more than the gravity force pulling it down to the ground. But think of gravity as a pressure on top to make things easy. The more pressure you add under the box controls the speed at which you lift it, as in an aircraft climbing in the sky.

Got it?

As for the upside down aircraft- The aircraft being upside down has no effect on the lift process. For the plane to remain at a set altitude while inverted, you must push forward on the control column just enough to hold the aircraft at the correct attitude: on the line between pulling the second half of a loop and the beginning of an outside loop.

Got that too?

Great!

Trislander.

------------------
http://www.aurigny.com/images.gb%20/trislander.jpg
"Ayline 221 airbourne"

[scroggs]

Trislander, a neat precis of some generic handling notes, but you've missed the point slightly. Teroc is on the right lines, I fancy. My point was that the Bernoulli explanation of lift begins to break down when your high-camber wing is inverted. The application of negative angle of attack doesn't adequately cover the problem caused by the curvature of the wing. Obviously a degree of flat-plate effect is involved ('Newtonian physics'), but the 'pressure differential' thing is Bernoulli under a different name. There was a very educational argument about this in Tech a few months ago which suggested that the more advanced courses (aero eng, etc) are beginning to explain the phenomenon of real-world lift in rather more detail than we've been used to, and which allows sensible explanations of the two situations I postulated in my earlier post.
I'm not ridiculing anyone here; when I did the RAF Central Flying School course in the late '80s, the basic aerodynamic package relied entirely on Bernoulli. The high-speed flight aerodynamic package brought in many of the factors which are now assumed also to work in conventional (below 400kt TAS) flight.
It's an interesting, if esoteric, subject which I'm afraid defeats me after now 36 hours awake, but I'm glad you guys brought it up.
Now, is anyone any wiser?