Tilting wings to create lift

[TomcatMVD]

both laws generate lift, its really that simple. Bernoulli is slightly wrong, as air from the top and bottom doesn't meet up at the back, but it generates lift. but so does forcing air down. both theories contribute.

Well... the Bernoulli explanation does not demand that both airflows meet at the trailing edge, that's just a misconception resulting from ages of teaching it that way in order to simplify its understanding. The acceleration of the particles is most often explained by the Venturi effect, whereby the narrowing of the passage between the airfoil and the undisturbed air accelerates the particles of air. It is through Bernoulli that this acceleration generates a decrease in air pressure.

[Festivefire]

The most annoying thing about this argument: when i use the fin tool in gmod, i have to pick between laws of lift when i want to make a prop a wing, and i can't integrate both, without double layering it, even though using both is more accurate.

[FlamedSteak]

Man, I always wanted to do CFD at school. The best we could hope for in the 90's was a 2d design program that crapped out every 20 minutes.

[Nao]

Ok. So while we agree on the fact that the flow above the wing remains crucial to generate lift, it is the reason for such behavior that we can find a disagreement on. When I mentioned spoilers I wasn't referring to the drag they generate but rather the disruption of the airflow over the wing, which decreases lift quite drastically. Now, if the reason for that decrease in lift is the prevention of the downwards motion of the upper flow rather than the lack of "suction" from the lower pressure of the faster air particles, then I could see the Newton explanation taking relevance over the Bernoulli one. All in all, the explanations I've found online sort of point out to a combination of both phenomenons. This has been quite enlightening, I am a private pilot myself, and have gone through my whole training praising Bernoulli and only him for the magic of flight Granted it always struck me as "funny" when thinking about inverted flight, but I guess I just always kind of thought it was too complicated for me to understand xD

Haha, just noticed that i misread your post, in polish we call slats - "spoilery" That's why I remembered about them and brought that CFD picture.

For me the inverted flight works quite similar to standard when we try using Bernoulli's principle. It's just that the air takes "longer path" around the upper side even if the wing is flat there, because of where it splits at higher AoA (kind of like in my CFD picture).

And that venturi effect you also mentioned really feels like right on spot.

Also looks like foilsim is working again http://www.grc.nasa.gov/WWW/k-12/airplane/foil2.html. It works in browser and can simulate variety of airfoils. Quite fun learning tool.

[zzz]

Regardless all this laws and how exactly this works - can wings maintain real aircraft in air at the same height(or even elevate) at zero angle of attack(with bottom plane of wing parallel to direction of moving)?

Edited June 25, 2013 by zzz

[TomcatMVD]

Regardless all this laws and how exactly this works - can wings maintain real aircraft in air at the same height(or even elevate) at zero angle of attack(with bottom plane of wing parallel to direction of moving)?

IIRC it is only possible at very high speeds, but in most aircraft, level flight is achieved by maintaining an AoA of 3 to 6º depending on the airspeed.

[Comrade Jenkens]

Regardless all this laws and how exactly this works - can wings maintain real aircraft in air at the same height(or even elevate) at zero angle of attack(with bottom plane of wing parallel to direction of moving)?

I'm guessing that it depends on the wing, weight of the aircraft and its speed. I'm pretty sure that plenty of aircraft can fly with their wings at zero angle of attack though.

[earth]

very few do, because even if you make a wing with a very curved back, thus with great bernouilli lift, you have to deal with other crap like phugoid motion, which increases when AoA decreases.

[zzz]

but in most aircraft, level flight is achieved by maintaining an AoA of 3 to 6º

I'm pretty sure that plenty of aircraft can fly with their wings at zero angle of attack though

Hm. Something inconsistent here.

So

In RL aircraft don't need to have wings tilted

actually, in real life, they do have a bit of tilt.

Only if they need to have a tilt. If the lift coefficient of the wing is high enough in a horizontal position then there's no need to tilt.

And they need it isn't it? Because lift of the wing in horizontal position is not enough, especially at low speed. To tilt plane or wings on plane is not big difference, as I understand, it's about wich way is more handy for this plane

Edited June 25, 2013 by zzz

[TomcatMVD]

Hm. Something inconsistent here.

So

And they need it isn't it?

Wings need a positive AoA, whether that means a relative tilt compared to the airframe, I believe that is something different. AoA pertains to the angle at which the wing meets the incoming air (or rather air meets the incoming wing ), it is entirely possible to have a wing with 0 tilt in reference to the airplane's longitudinal axis and still keep a level flight AoA by maintaining a slight nose-up attitude.

[zzz]

it is entirely possible to have a wing with 0 tilt in reference to the airplane's longitudinal axis and still keep a level flight AoA by maintaining a slight nose-up attitude.

But they need to tilt it some way anyway. This is what op said - he don't need to fly nose up so just tilt wing to create some positive angle. From which there was a dispute about in RL it's not needed, wing produse lift even if parallel to air stream because of shape and Bernoulli. But no matter how right Bernoulli real aircraft still need some angle because "lift coefficient of the wing is" not "high enough in a horizontal position".

Edited June 25, 2013 by zzz

[Comrade Jenkens]

The book I am currently reading. (The Anatomy of an Aeroplane) talks about both mechanisms creating lift and so the aircraft can fly on either. Many aircraft can fly with zero angle of attack but some aircraft have symmetrical aerofoils and so must use the other mechanism.

[Nao]

The book I am currently reading. (The Anatomy of an Aeroplane) talks about both mechanisms creating lift and so the aircraft can fly on either. Many aircraft can fly with zero angle of attack but some aircraft have symmetrical aerofoils and so must use the other mechanism.

I think even symmetrical wing uses the Bernoulli's effect as the air splits below the wing nose, and travels longer distance above the wing.

Also on topic of zero aoa. This type of airfoil can generate half of its lift at 0 aoa, and is used on commercial airliners to fight the wave drag at speeds close to 1mach.

[TomcatMVD]

But they need to tilt it some way anyway. This is what op said - he don't need to fly nose up so just tilt wing to create some positive angle. From which there was a dispute about in RL it's not needed because of shape and Bernoulli. But no matter how right Bernoulli real aircraft still need some angle because "lift coefficient of the wing is" not "high enough in a horizontal position".

I get your point, the way I see it though, the "tilt" of the wing when compared to the fuselage is not really necessary. Usually when on the ground, airplanes would tend to have a slight nose-high attitude (when on the runway, most airplanes will start flying on their own just a bit after rotation speed). Once airborne, the higher speed means a smaller AoA is enough for level flight. As a matter of fact, one pic is worth a thousand words:

This is a Cessna 172. The most common single engine piston airplane. Those wings are definitely not parallel to the ground, however they seem more or less level with the airframe (if there is a tilt, it's not noticeable). Once in flight, the airplane's attitude is quite different as the nose drops down a little bit.

It's all relative though... I mean we're talking about 3º here. The wings could be perfectly aligned with the body and you'd be maintaining level flight by keeping a 3º nose high attitude, which for all intents and purposes, you can hardly call a pitch up attitude. As a matter of fact, your pitch must be corrected as you change your speed, in order to maintain an AoA that would keep the airplane flight level, so whether there is a "tilt" of the wings in comparison with the airframe, is beyond the point and would only serve a design purpose (i.e. if the wings are level with the airplane maybe the cockpit floor does have a little tilt so passengers won't feel discomfort by the most common cruise attitude of the airframe).

Edited June 25, 2013 by TomcatMVD

[WestAir]

Fun Fact: Did you know most horizontal stabilizers (the wings on the empennage) are upside-down?

Not all of them - a lot of sports and acrobatic aircraft have symmetrical wings (In fact, most acrobatic aircraft have both their main wings and the horizontal stabilizers built with perfect symmetry on the top and bottom.) In those aircraft, all that's needed for flight is a positive angle of attack, inverted or otherwise. Airshows would be boring if Bernoulli had his way.

[zzz]

Well, OK. I just always imagine this little differently. Underestimated the shape, I thought it mostly for help with drag and stream(all this vortexes and such). After all even some pieces of plywood or paper planes are flying.

Edited June 25, 2013 by zzz

[SourMonkey]

Don't know what the fuss is about, we can all agree that the angle of attack required for an airfoil to produce sufficient lift depends on the airfoil design, speed, and the A/C's weight. Also, Bernoulli's principle is, in a nutshell, stating that as the fluid speeds up the static pressure decreases; and he wasn't wrong.

It's all relative though... I mean we're talking about 3º here. The wings could be perfectly aligned with the body and you'd be maintaining level flight by keeping a 3º nose high attitude, which for all intents and purposes, you can hardly call a pitch up attitude. As a matter of fact, your pitch must be corrected as you change your speed, in order to maintain an AoA that would keep the airplane flight level, so whether there is a "tilt" of the wings in comparison with the airframe, is beyond the point and would only serve a design purpose (i.e. if the wings are level with the airplane maybe the cockpit floor does have a little tilt so passengers won't feel discomfort by the most common cruise attitude of the airframe).

You also have to remember that there is a bit of wing washout, in which the angle of incidence decreases as you move out to the wing tip. This lets you stall at the wing root first. It is also why it is a bit less noticeable if you are comparing the angle of the wing tip to that of the aircraft (not that it is greatly noticeable to begin with).

Fun Fact: Did you know most horizontal stabilizers (the wings on the empennage) are upside-down?

Provides stability