Tilting wings to create lift

[Comrade Jenkens]

Hi

I've recently discovered that if I tilt the wing pieces by 5degrees so that the leading edge is slightly higher, the wings will work better than if they are simply placed on normally. This stops the aircraft having to fly slightly nose up all the time as they do currently and is more fuel efficient.

How many other people use this trick already?

[leax256]

yep. used it alot, I say used because I hate making spaceplanes.

[Scarecrow88]

Most aircraft designers use that trick. It's called the angle of incidence.

[Comrade Jenkens]

In RL aircraft don't need to have wings tilted in such a way as their shape allows them to create lift while level. In KSP the wings don't create lift while the aircraft is perfectly level and so my aircraft have always been flying slightly nose up.

[Nao]

I go a step further and go with 30 deg inclination

There are around 200-300 small delta winglets (part with best lift/mass ratio) hidden inside the hitchhiker pods all at 30 deg inclination. It flies quite realistic for a KSP physics

Btw as we increase inclination wings provide more lift until around 30deg and then lift starts to go down. On the other hand control surfaces increase lift until close to 90deg (with a plateau at 30-35deg).

[IvanTehFennec]

In RL aircraft don't need to have wings tilted in such a way as their shape allows them to create lift while level. In KSP the wings don't create lift while the aircraft is perfectly level and so my aircraft have always been flying slightly nose up.

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

[Nao]

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

Seeing B-52 on final approach always gets me as the wings point upwards while nose point downwards (B52 has quite bit of wing inclination) ... and then there is F-8 crusader also haha.

But there are planes with symmetrical wings like in KSP. They require nose up flight to generate lift. Extra 300 is a nice example. It's pure KSP design: a brick, pair of boards, powerful engine and a madman inside.

[DisarmingBaton5]

Seeing B-52 on final approach always gets me as the wings point upwards while nose point downwards (B52 has quite bit of wing inclination) ... and then there is F-8 crusader also haha.

But there are planes with symmetrical wings like in KSP. They require nose up flight to generate lift. Extra 300 is a nice example. It's pure KSP design: a brick, pair of boards, powerful engine and a madman inside.

I think the Extra 300 has symmetrical wings so it can fly upside-down.

And the B-52 looks awesome.

[Epthelyn]

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. Symmetrical wings do need to tilt though, because the airflows above and below them will be equal in velocity. Make the air move faster over the top and the plane lifts whether than be by shaping the wing or tilting it.

I don't think KSP obeys the wing shape thing; if you have a model with a curved top it will act like a flat rectangular panel (not entirely sure, but the aerodynamic model is bad )

"I think the Extra 300 has symmetrical wings so it can fly upside-down."

Pretty much.

In other words, this does not happen in KSP:

[Ralathon]

In other words, this does not happen in KSP:

It doesn't in Real Life either. The whole "air on the topside of the wing goes faster" is nonsense, a wing generates lift because particles moving along the top of the wing experience more curvature. The particles curve because of a force towards the wing (surrounding air pressure causes this), Newton's 3th law shows that this results in an upwards force.

[Epthelyn]

It doesn't in Real Life either. The whole "air on the topside of the wing goes faster" is nonsense, a wing generates lift because particles moving along the top of the wing experience more curvature. The particles curve because of a force towards the wing (surrounding air pressure causes this), Newton's 3th law shows that this results in an upwards force.

A force acting down on a wing and providing, by N3L, an equal an opposite force wouldn't actually result in lift. It would be a balanced force, therefore no change. At least a change in pressure makes some sense.

The whole "air moving faster over the topside of the wing" is "air moving faster over the topside of the wing results in less pressure over the wing" and

[Rickenbacker]

It doesn't in Real Life either. The whole "air on the topside of the wing goes faster" is nonsense, a wing generates lift because particles moving along the top of the wing experience more curvature. The particles curve because of a force towards the wing (surrounding air pressure causes this), Newton's 3th law shows that this results in an upwards force.

That, and the MAIN reason wings create lift: They force air downwards, which results in an equal force upwards on the wing, lifting it.

[Nao]

It's true that wings create lift by forcing air downwards, but the main reason air starts to flow downwards is because of pressure difference and not because wing is physically deflecting them downwards.

For example with this basic experiment, there is no direct force of moving air on the paper, it rises due to lower pressure of moving air above it.

Also about the wing inclination, even the best wing profiles provide biggest L/D at small positive angles of attack. (around 4-6 deg) (L/D - lift to drag ratio, the plane flies most efficient at its maximum L/D) so most planes have some positive wing inclination.

[m4v]

It doesn't in Real Life either. The whole "air on the topside of the wing goes faster" is nonsense, a wing generates lift because particles moving along the top of the wing experience more curvature. The particles curve because of a force towards the wing (surrounding air pressure causes this), Newton's 3th law shows that this results in an upwards force.

Is not nonsense, the air on top of the wing does go faster. What is nonsense is the equal transit time theory taught in schools for explain why it goes faster. Edited June 23, 2013 by m4v

[rdfox]

Augh, the whole "Bernoulli" argument. Wish they didn't teach that in schools at ALL.

Listen, you want to find out what's most important in generating lift? Go out on the freeway, driving at 70 miles an hour, and stick a hand out the window and "fly" it up and down by adjusting pitch. The human hand is a TERRIBLE airfoil shape, but you'll still get huge amounts of lift.

The primary source of lift is the pressure on the underside of the wing due to its being pitched upward to the relative wind (i.e., positive angle of attack). The airfoil shape takes advantage of Bernoulli's principle to make the lift more efficiently, by reducing the upper surface pressure and thus increase the pressure differential. It does allow the wing to generate lift even at zero or slightly negative angle of attack, but very little--this is why airliners cruise in a somewhat nose-high attitude, to maintain a positive angle of attack for efficient flight.

While the airfoil was a critical item in making flight possible in the early days, these days, power-to-weight ratios are high enough to make them merely an efficiency issue. As Peter Garrison (aviation journalist who has also designed and built at least three different light airplanes of his own, from scratch) once put it, "these days, there's enough engine power available to be able to make a plane fly with a couple of two-by-twelves for wings."

[Nao]

Bernoulli isn't the best way to describe airfoils, but so is the hand argument.

Airliners have nose up attitude because they use fuselage to generate additional lift, also you can't really compare a flow of standard wing to an airliner which flies right on the boundary of supersonic flight which is quite different animal to standard model and the fact that the range of speeds the wing needs to be working is quite big.

I would say that now days airfoils are as important as ever, just look at the complex mechanization in the wings of modern airliners. The power is there of course but civilian transport is and it always will be about efficiency, and you can't have that while powering through air on a board (except maybe in Russian engineering )

The wing deflection matters yes but so is the fact that most low to medium speed airfoils at 3-6deg aoa have almost no change in pressure at the bottom and have quite big one at the top.

Another important thing is the laminar flow. That's what really differentiates wings from boards. Board or hand can generate lift almost purely from air deflection at bottom side, and the air on the top side is turbulent creating lots of drag. Wing on the other hand has (ideally) a laminar (non-turbulent) flow over the top, not only does this reduce drag by a lot. It also makes the air "glue" to the wing as it goes downwards on the top side, inviting more air above the wing to move downward.

Also i wouldn't say that wings generate low amounts of lift at 0deg AoA. They work best at 3-6 (mostly) but if you going faster, they can provide plenty of lift at even negative angles. (for example competition gliders, that have to use negative flaps to reduce lift while cursing).

rdfox, If you have any sources about "the primary sources of lift" of an wing, please share. As it does not sound right.

[Luna Lovecraft]

Kind of funny to see this still be pervasive. You'd have thought schools would have done away with that and the whole "blood in your veins is blue" thing.

[GOOMH]

I think this thread needs a little veritasium to clear up some things about wings

[Montieth]

In RL aircraft don't need to have wings tilted in such a way as their shape allows them to create lift while level. In KSP the wings don't create lift while the aircraft is perfectly level and so my aircraft have always been flying slightly nose up.

Look at a B-52 in level flight.

[doggie015]

I think this thread needs a little veritasium to clear up some things about wings

So THAT's how they work!

[TomcatMVD]

Although I can agree with an explanation that combines both Newton's third law and the Bernoulli effect, I wouldn't disregard the latter as such a minor player in the creation of lift, after all, a stall occurs when the airflow separates from the top of the wing, so the lift created by that airflow is vital. Not to mention the use of spoilers, which deliberately disrupt the flow over the wind in order to reduce lift. So while we can explain a "pushing" force as understood by Newton's third law of motion, there is also a "pulling" force being exerted on top of the wing that cannot be explained by it and plays a major role in the creation of lift. At least that's the way I see it.

[Nao]

On the subject of spoilers ...

This is a model that I've done on my CFD class (it's not a turbulent flow because it would take hours to compute on standard PC's) but it shows how the air actually flows.

My CFD picture is kind off crappy ... I would be able to better demonstrate it if not the damn nasa blocking their browser based "foil sim" application >_<.

As you can see the blue air - that goes under the wing is deflected downward, but after the end of the wing, due to interaction with the air that goes above, it stops it's flow downward. That shows that the top side of the flow has similar amount of energy as the bottom one (to be able to stop it's flow downward). So even at such high angles of attack the low pressure effect above the wing is comparable in strength to the mechanical deflection of air at the bottom. For lower AoA's the low pressure above the wing has even bigger effect in generating lift.

The air that flow downwards after the plane passes it is actually mostly the one that was above the wing, not below.

There is a problem with Bernoulli's law application here because, while it looks like it applies, it doesn't really. As the low pressure area above the wing is created mostly because of laminarity of the flow. As the air goes up first then goes down as it sweeps the wing - and the fact that it goes down creates low pressure area. As the wing moves away, there is a significant volume of air that were above the wing that is going downwards.

If we loose laminarity of the flow above the wing there is not only an increase in drag, but a significant loss of lift due to turbulent air that doesn't want to move downwards and create low pressure area above the wing.

Look for example at how "big" the speed brakes on a gliders are:

They don't really create much drag, (speed decrease is almost non visible) what they do is kill laminar flow over the top of the wing that significantly lowers lift, and that requires the pilot to pull up the nose so that the whole wing generates more lift and drag.

(I'm actually a glider pilot, and i can tell you first hand that during landing you just keep nose steady - to keep speed constant, and control the descent rate by operating the brakes, that's how important the flow above the wing is).

And there is also the moment of stall. Even at high AoA lift still comes from air passing above, and stall creates a huge mess there that kills lift, that makes plane go down like a brick.

The conclusion here would be that, most lift comes from air passing above the wing, but not because of Bernoulli's effect but rather the way wing is shaped, having a downwards sweep at the top.

Also another obligatory B52 picture! (i love how they land almost nose down) http://files.air-attack.com/MIL/b52/b52_andersen_2.jpg (picture is too big to post without spoilers )

Edited June 24, 2013 by Nao

[TomcatMVD]

On the subject of spoilers ...

This is a model that I've done on my CFD class (it's not a turbulent flow because it would take hours to compute on standard PC's) but it shows how the air actually flows.

My CFD picture is kind off crappy ... I would be able to better demonstrate it if not the damn nasa blocking their browser based "foil sim" application >_<.

As you can see the blue air - that goes under the wing is deflected downward, but after the end of the wing, due to interaction with the air that goes above, it stops it's flow downward. That shows that the top side of the flow has similar amount of energy as the bottom one (to be able to stop it's flow downward). So even at such high angles of attack the low pressure effect above the wing is comparable in strength to the mechanical deflection of air at the bottom. For lower AoA's the low pressure above the wing has even bigger effect in generating lift.

The air that flow downwards after the plane passes it is actually mostly the one that was above the wing, not below.

There is a problem with Bernoulli's law application here because, while it looks like it applies, it doesn't really. As the low pressure area above the wing is created mostly because of laminarity of the flow. As the air goes up first then goes down as it sweeps the wing - and the fact that it goes down creates low pressure area. As the wing moves away, there is a significant volume of air that were above the wing that is going downwards.

If we loose laminarity of the flow above the wing there is not only an increase in drag, but a significant loss of lift.

Look for example at how "big" the speed brakes on a gliders are:

They don't really create much drag, (speed decrease is almost non visible) what they do is kill laminar flow over the top of the wing that significantly lowers lift, and that requires the pilot to pull up the nose so that the whole wing generates more lift and drag.

(I'm actually a glider pilot, and i can tell you first hand that during landing you just keep nose steady - to keep speed constant, and control the descent rate by operating the brakes, that's how important the flow above the wing is).

Also another obligatory B52 picture! (i love how they land almost nose down) http://files.air-attack.com/MIL/b52/b52_andersen_2.jpg (picture is too big to post without spoilers )

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

[Fuzzy Dunlop]

It's always seemed quite simple, the air follows the trailing edge, which is angled towards the ground - hence upwards lift. The interesting part for me is persuading the air to flow over the wing without slowing it down too much.

[Festivefire]

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.