Questions tagged [lift]

The force acting on an aircraft in opposition to gravity which keeps the aircraft in the air.

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56
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11answers
36k views

How do wings generate lift?

Just the basic question that every aviation enthusiast must be curious about: exactly how does a wing generate lift?
45
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8answers
11k views

How complete is our understanding of lift?

I'm currently studying for my PPL and one of the accepted textbooks contains the following disclaimer at the end of the Principles of Flight section on lift: It is important to note that the ...
19
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7answers
18k views

Does lift equal weight in a climb?

This subject keeps coming up in the discussions and questions such as this one, which asks if lift equals weight in level flight. Good answers there, pointing out that upwards force has many sources. ...
28
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2answers
16k views

What is vortex lift?

In a recent question I asked, I was given an answer by Peter Kämpf and he described something about lift being created by a vortex used on delta wings and the Bird of Prey wing. How exactly does ...
8
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1answer
3k views

What is the aerodynamic centre and how does it relate to the pitching moment?

Okay so I have been trying to get my head around the Aerodynamic centre and the Pitching moment. Wikipedia really isn't helping much but from what I can gather the Pitching moment is a force caused by ...
13
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2answers
30k views

What is the method to calculate a finite wing's lift from its sectional airfoil shape?

I am struggling to get my head around a concept that I believe should be fairly simple to understand. Lift versus drag and AoA data of many airfoils are freely available, for instance the NACA 4-...
6
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2answers
3k views

Why is induced drag less on a high span wing?

I have a basic question and sorry if it is a well known fact. I understand that the induced drag is due to the tip vortices changing the effective angle of attack (downwash). I searched some ...
18
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5answers
5k views

Why is lift larger than thrust? [duplicate]

It's been a while since I tried to read a little about flight mechanics and aerodynamics, but I remember one question I had back then: Is the thrust of a common passenger aircraft (A320, B737) ...
31
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8answers
7k views

Is excess lift or excess power needed for a climb?

As answered in this question, aircraft need excess power - not excess lift - to climb. This is plausible when the aircraft's thrust vector has a vertical component (its nose and engine points upwards),...
11
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3answers
2k views

What are the physical laws for upscaling an RC model to 1:1?

What are the laws of physics for upscaling an RC model from a smaller to larger scale or even to a full sized 1:1 aircraft? I guess the basic thing may be lift/weight ratio which was nicely described ...
13
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2answers
6k views

What is the actual air speed over and under a wing due to Bernoulli's Principle?

Bernoulli's Principle states that as a fluid speed increases, its pressure decreases, and vice versa. Air flowing over the wing of an aircraft flows faster than its neighboring air flowing under the ...
11
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3answers
3k views

How is lift provided by a wing affected by propeller wake?

Does the lift of that section of the wing which is in the wake of the propeller increase (because the airspeed in that section is higher)? If yes, is this fact used actively to improve the lift ...
4
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4answers
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Descending on a given glide slope (e.g. ILS) at a given airspeed— is the size of the lift vector different in headwind versus tailwind?

We had a discussion with friend and we were talking about if the airplane is on approach and the one is landing with tailwind and the other one is landing with headwind, so both have the same value of ...
30
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4answers
7k views

Principle of aerodynamic lift: are misconceptions also taught in flight schools?

Describing lift as the result of "equal transit time" on both sides of an airfoil is a fallacious theory widely found in technical books and articles for general public (see below for details about ...
4
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1answer
2k views

What is the pressure on the pressure side in relation to the freestream?

The following [edited] images are from a network post: The top image states on the pressure side, the pressure is greater than the freestream. On the bottom image, the $C_p$ varies. According to ...
25
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5answers
13k views

Is there a maximum lift to drag ratio?

If I recall correctly, the best competition gliders have a L/D ratio as high as 60:1. What imposes this limit? Is there a maximum theoretical L/D ratio, or could sufficiently advanced materials allow ...
8
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3answers
4k views

Is the low air pressure on top of the wing the major contributor to lift?

I am kind of old time flyer. Started to fly with those primitive hang-glides with titanium frame and the yoke control, around 1966 and then after a few close calls and getting older I switched to ...
7
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1answer
2k views

How much lift comes from the fuselage on modern jets?

I understand this question is broad, but specifically referencing modern jets where composites are used a lot to get complex surfaces (such as in the Beechcraft Premier 1), how much of the total lift ...
4
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1answer
669 views

Where does upward momentum come from in leading edge vortex?

I believe I am beginning to understand how a leading edge vortex creates lift. Faster air creates a lower pressure above the wing making lift. But I am hoping to get another view of this in terms of ...
0
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1answer
624 views

Do wingtip vortices cause a decrease in the lift component of aerodynamic force, and do planes need to pull more AoA to compensate?

So, from what I know about wingtip vortices, they shift the angle of the relative airflow to where the effective angle of attack of the airfoil is lowered. Since the aerodynamic force is always ...
90
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14answers
16k views

Are wings any more efficient at creating lift, versus orienting the engine's thrust downwards?

As I understood from this article, wings on an airplane basically create lift by pushing air down. Maintaining the lift force expends energy because air needs to be continually accelerated downwards. ...
6
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3answers
11k views

What is the effect of flow separation on lift, pressure distribution and drag?

Consider an airfoil (a wing) in an airflow. When angle of attack increases, at some point the flow start to separate from trailing edge. By increasing the angle of attack more, this separation area ...
5
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5answers
26k views

What is the highest possible thrust generated by 15cm ducted fan?

I recently developed a sudden interest in flying. I'm wondering whether a pair of small ducted fans could lift a person off the ground. Lets say the ducted fan is 15cm in diameter. What would be the ...
10
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3answers
12k views

What is the lift force per unit span?

I got Aircraft Design: A conceptual approach for Christmas, and I'm having a hard time with lift coefficients because I honestly have no idea what "lift force per unit span" means, so can someone ...
8
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1answer
637 views

Do software simulations and wind-tunnel tests accurately predict Cd and Cl in real-world conditions?

Will the lift coefficient (Cl) and drag coefficient (Cd) I obtain by using software simulations or subsonic wind-tunnel tests be the same as on an actual aircraft while cruising? Or will there be some ...
4
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1answer
13k views

How are Cd and Cl calculated from Cp data?

Given pressure coefficient data for corresponding x/c (position along chord) values on a wing, I am looking to calculate coefficients of drag and lift. Here's what I have: b, MAC, S, sweep angles at ...
28
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8answers
4k views

Does a sudden drop of the velocity of the headwind affect the airspeed by lowering it?

I had a discussion about air speeds with one of my instructors recently. He is claiming that there is a sudden drop in the wind velocity as you get closer to the ground (which is absolutely true, due ...
10
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3answers
4k views

What is the physical meaning of circulation found in Kutta condition?

The Kutta–Joukowski theorem is applicable for 2D lift calculation as soon as the Kutta condition is verified. When this is the case, there is a circulation $\small \Gamma$ around the airfoil. My ...
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2answers
3k views

For a large commercial plane on landing, does the L/D ratio increase, decrease, or not change much?

Consider a large commercial aircraft coming in for landing. The exact part I'm interested in is the flare (where the aircraft noses up yet does not actually go higher above the ground), with flaps ...
7
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3answers
10k views

For the elliptical wing, which property is actually elliptically distributed?

A well-known "elliptical" wing: One of the 50 Spitfire still flying in the World. Source My questions What is elliptical in the elliptical wing? What is regularly distributed: lift? drag? something ...
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1answer
267 views

Why is subsonic lift at 25% of chord? [duplicate]

I pretty much understand the way a wing works and the different ways of explaining it, what I don´t understand is why the lift on a subsonic wing manifest itself at the 25% chord.... The 50% chord ...
14
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1answer
625 views

What amount of lift would be created in the fallacious “lift from equal transit time” theory?

Context A wrong --but simple to understand-- theory for lift states: Air molecules that were close before being separated at the leading edge must be close again after they join back at the trailing ...
10
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1answer
9k views

Does lift coefficient vary with the wind velocity for a given angle of attack?

I have this question in my mind. I have been trying to look for this in different books about aerodynamics and I couldn't find the answer. I know I could check the answer experimentally, if I had a ...
14
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3answers
15k views

How much thrust is needed by an aircraft to have vertical takeoff?

In some airshows, I have seen some big aircraft (like 737) takeoff almost vertical. Generally, fully-loaded passenger/cargo planes don't do that, I guess due to safety issues but I think there needs ...
4
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2answers
4k views

How to calculate the Glide Ratio from Drag & Lift?

I know that $c_{d}=0.03 + 0.095c_{l}^2$. What is the glide ratio?
3
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2answers
1k views

Are high lift wings bad for faster speeds

I notice a trend in many aircraft designs. If the aircraft was designed to go slowly but have shorter takeoffs/landings they use airfoils with a high lift. However for long endurance flights they use ...
3
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2answers
1k views

How much lift do planes produce before rotation?

In the takeoff roll, I'm pretty sure planes produce some lift before rotation, but how much? Is it insignificant compared to post-rotation, or is it large compared to the post-rotation lift?
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5answers
11k views

Where can I find data tables for lift and drag coefficients of airliners?

I'm teaching an introductory course in fluid dynamics and I'd like to show some "real" data regarding drag and lift forces on an airfoil. It is easy to find data on the geometry of typical airfoils, ...
11
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1answer
18k views

How to calculate the Lift Coefficient for the A320?

I'm trying to figure out the lift coefficient of an A320. What I'm doing is the following: during cruise, the lift is equal to the weight of the aircraft ($mg$) so that I used the cruise table taken ...
4
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3answers
16k views

How does the aspect ratio of a wing impact its lift?

The wing lift formula shows that lift of a wing is proportional to its area. $ L = {\dfrac 1 2 \times \rho V^2 \color{magenta}S C_L} {\small \begin{align} &{} &&\text{where:} &&L =...
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2answers
3k views

Why did the Solar Impulse flight take so long?

The Solar Impulse just made big news for flying from Japan to Hawaii on a solar-powered plane in five days. But five days seems really long. Let's do the math on that. The distance from Japan to ...
6
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1answer
904 views

How does rudder size influence its ability to produce lateral lift?

Does anyone know how the area, height and width of a rudder affect how well it provides lateral lift? I've heard that the most effective rudders are around 35% of the vertical stabiliser MAC but is ...
27
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2answers
4k views

How exactly can an airship lose lift?

On this wiki page (under 'Comparison with heavier-than-air aircraft'), the altitude record of the L-55 Airship states: The ultimate altitude record for a rigid airship was set in 1917 by the L-55 ...
17
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4answers
2k views

Why do planes not fly “backwards” (up from the planes POV) when in a vertical climb?

As suggested by a user in this question, I'd like to ask this question: One of the most basic aerobatic maneuvers is a vertical climb. This can be achieved by just pitching up to what appears to be ...
15
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2answers
2k views

What phenomenon causes the increase of drag with rain?

I know that rain generally worsens the aerodynamic propeties of an aircraft. I'm wondering what processes cause the increase in drag. I'm mostly interested in General Aviation, thus relatively low ...
7
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2answers
4k views

What are the conditions for an airfoil to be a “thin airfoil?”

I know about the theory differences between regular airfoils and thin airfoils, but is there any condition for saying a given airfoil can be analyzed as if it is thin? The extreme case of infinitely ...
7
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5answers
749 views

How to recognize the horizontal winglet in the Horten design, or the experimental glider in this video?

Comments below the NASA Armstrong Flight Research Center video Proving Prandtl- With A Twist! incclude: This video is entirely a hidden jewel in youtube, it deserves much more attention than what it ...
7
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3answers
2k views

Is induced drag caused because of the tilt of the wing backwards?

In this question: Why is induced drag less on a high span wing? In the answer it was stated that wing tip vortices do not cause induced drag. If this is the case then what causes the induced drag. ...
3
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4answers
363 views

How much of an airplane's forward energy is lost to lift?

An airplane needs to move forward to generate lift, and because energy isn't created from nothing, all the kinetic energy of lift comes in the form of drag, where air (air resistance) turns forward ...
12
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2answers
2k views

Why do the outer parts of wings generate less lift?

In this Wikipedia page it says: Constant chord: parallel leading & trailing edges. Simplest to make, and common where low cost is important, e.g. in the Piper J-3 Cub but inefficient as the ...