# What is Airfoil: Definition and 89 Discussions

An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of a wing; blade of a propeller rotor or turbine; or sail as seen in cross-section.
A solid body moving through a fluid produces an aerodynamic force. The component of this force perpendicular to the relative freestream velocity is called lift. The component parallel to the relative freestream velocity is called drag. An airfoil is a streamlined shape that is capable of generating significantly more lift than drag. Subsonic flight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, often with a symmetric curvature of upper and lower surfaces. Foils of similar function designed with water as the working fluid are called hydrofoils.
The lift on an airfoil is primarily the result of its angle of attack. When oriented at a suitable angle, the airfoil deflects the oncoming air (for fixed-wing aircraft, a downward force), resulting in a force on the airfoil in the direction opposite to the deflection. This force is known as aerodynamic force and can be resolved into two components: lift and drag. Most foil shapes require a positive angle of attack to generate lift, but cambered airfoils can generate lift at zero angle of attack. This "turning" of the air in the vicinity of the airfoil creates curved streamlines, resulting in lower pressure on one side and higher pressure on the other. This pressure difference is accompanied by a velocity difference, via Bernoulli's principle, so the resulting flowfield about the airfoil has a higher average velocity on the upper surface than on the lower surface. In some situations (e.g. inviscid potential flow) the lift force can be related directly to the average top/bottom velocity difference without computing the pressure by using the concept of circulation and the Kutta–Joukowski theorem.

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1. ### Aerodynamics: flow separation's effect on lift and drag

In aerodynamics, how does flow separation reduces the lift and drag of a wing at the same time?
2. ### Shape and 2D Lift Relationship

I’m aware that this is a simple question to a very complex question. However, I’m curious as to how to calculate a lift coefficient simply using a 2 dimensional equation or a series of 2 dimensional equations, such as the NACA equations. I’m somewhat familiar with the lift line theory, but to be...
3. ### Clarifications about the aerodynamic centre of an airfoil

Hello, when dealing with longitudinal stability calculations of an aircraft/airfoil we are considering all aerodynamic forces relevant to the generation of moment around the c.g.(lift) as acting at a point we call aerodynamic centre which is, by definition, a point where the pitching moment of...
4. ### Is ideal fluid flow around an airfoil the Lambert W function?

NOTE: By "ideal", I mean incompressible & inviscid (the forum doesn't allow a long enough title). I was looking at this Wikipedia article, and the graph of this function struck me as looking exactly like ideal fluid flow around an object. https://en.wikipedia.org/wiki/Lambert_W_function...
5. ### Wall to wall airfoil in a wind tunnel

Does wall to wall airfoil produce downwash in wind tunnel ?
6. ### I (Airfoil) Why do boats have a pointy bow?

A (displacement) boat hull has a design goal of making as little water resistance as possible with the required volume for load carrying capability. To achieve this the hull is given the shape similar to a vertical symetrical airfoil. But as the leading edge of a boat (it's bow) seems to be made...
7. ### Force components acting on an airfoil

Hi, I have a simple question but I want to be 100% sure that my reasoning is correct. Take a look at this picture showing forces acting on an airfoil: Green forces (X and Y components) are known from CFD software but I need the values of blue components (lift and drag). Of course for zero...
8. ### High CFM Fan Airfoil: Expert Guide

Hi airfoil experts, I brought two high speed fan for magnetron cooling, and upon destroying one due to my mishandling of the stuff, I found out these fan have surprising nice airfoil. See the pictures and you will understand their construction. The rotor part looks just like a normal air flow...
9. ### Aerospace Engineering: Predicting Airfoil Drag in 2D Potential Flow

Hi, My other post got deleted because it was flagged for spam, but it was just a link to a pdf. So I'm uploading the pdf instead. I am working on a model to predict drag on airfoils in 2D potential flow (e.g. vortex panel methods). Currently, XFOIL uses a semi-empirical wake-momentum-thickness...
10. ### Calculating the cl_max of a wing from airfoil characteristics

Hi, is there an appropriate method to get the maximum lift coefficient (cl_max) of a wing from the polars of the section airfoils? The background is that I cut a arbitrary wing into a certain number of sections. After that I use Xfoil to compute the local cl_max. Since this approach neglects...
11. ### Airfoil drag prediction in incompressible and inviscid flow

What is the most elegant way of predicting drag on an airfoil in inviscid and incompressible flow? Or is this still an open problem? It seems like the consensus for airfoils in incompressible and inviscid flow is that they cannot produce drag; or at least, we are not able to predict it...
12. ### Flow Quality Impact on airfoil pressure distribution

I have collected velocity data for a 3-D grid of test section of a low speed wind tunnel.I have tested airfoils for pressure distribution in the same test section for similar free stream conditions. How do I calculate the impact of flow quality in the test section on the test results of pressure...
13. ### Lift and Drag force in a Wind Tunnel

Hello guys, I am trying to calculate the lift force and drag force in a wind tunnel at my school as a part of a project that i am doing. I am varying the length of the airfoils and trying to measure the lift force and drag force. I have 3-d printed 7 airfoils. However, I am not able to find any...
14. ### How Do You Calculate the Area of an Airfoil Cross-Section?

Not really sure if this thread belongs here but I am supposed to figure out the radius of gyration, section modulus, and Q values at the neutral axis for this symmetric wing cross section. The only problem is that I am not even really sure how to find the area of the cross section. i know that...
15. ### No drag thin airfoil theory / Pressure drag

Hello everyone. I have a question about the fact that there is no drag in the thin airfoil theory. I have read that it comes from inviscid and incompressible flow (potential flow) but what i can not understand is why there would be no drag from pressure differences ? The skin drag is of course...
16. ### How to replicate a realistic Reynolds number for an airfoil

Homework Statement Hi I am doing a project of designing and testing a wing in a wind tunnel, the wing is based a cessna 172 skyhawk wing and I am trying to determine what chord length it should be to try and replicate similar reynolds numbers that a cessna 172 wing would experience in real...
17. L

### Predicting the behaviour of a closed circular airfoil

I was out and about today and observed a dog walker playing frisbee with their dog. I noticed the frisbee gliding gracefully through the air as the dog jumped to grab it, clutching the ring-like disc in its mouth. It got me to thinking about airflow over the disc, the lift and drag properties...
18. ### Is an Avocado Shaped Like an Airfoil?

Homework Statement Hi everyone. Is an avocado technically an air foil? like if you cut an avocado in half, it wold be the right shape right? see and if so, would you leave the pit in or not? Why? Homework EquationsThe Attempt at a Solution I am pretty sure that they are. I am giving a...
19. ### Determination of Static Presssure on an Airfoil

I'm working with data across an airfoil and need some help. We've got Kulite sensor data along 3 chord lengths of a certain NACA airfoil. The case is of an incompressible flow. I need to determine the coefficient of pressure at these sensor locations using total pressure measured and I...
20. ### Perturbation Methods + Airfoils

First of all, thanks for reading. I'd like to ask if some of you here can suggest a reference text concerning perturbation methods on thin airfoil? I'm using the text of Katz and Plotkin as well as Van Dyke but for now, I find it challenging to follow their discussion. I hope that finding a...
21. ### Exploring the Possibility of Multi-Wing Aircraft Designs

I played around with various parameters to air foils using Foilsim http://www.grc.nasa.gov/WWW/k-12/airplane/foil3.html What I found was that for a given wing length, a smaller chord gives a better lift/drag ratio. This will make the wing area small, hence the total lift will be small and there...
22. ### Discover Post Stall Airfoil Data for High-Angle-of-Attack Calculations

Hello all, Where can I find post stall airfoil data? I'm writing a numerical methods program and need lift coefficient data for airfoils at very high angles of attack. Books or websites would be great. Thank you for any help
23. ### B Can Reversing an Airfoil on a Prop Plane Still Create Lift?

Hi was trying to figure out what would happen if you reversed the wing of a standard prop plane? for example...the thinner wedge is towards the front. Would you still get lift? I suppose not since there is a reason the rounded/thicker edge is facing towards the front. but why not?
24. ### Airfoil Explained for 16-Year-Old Confused By It

Go easy on me I'm only 16 ;) I am utterly confused with the concept of "Airfoils", I have been doing some research on the web and so far all I have found is confusing descriptions that I do not understand and people arguing over which aerodynamics model for Airfoils is correct. The arguing and...
25. ### When is Lift on an aerofoil proportional to velocity?,

Hello, I was doing my physics coursework, and blew a hairdryer at my makeshift aerofoil across distances of about 10cm and wind velocities of 8-11 m/s, then measured the lift off of a balance. I found they were proportional, exactly (!?), after doing some research I found drag is proportional...
26. ### Boundary layer at airfoil stagnation points

I was reading this: http://www.creatis.insa-lyon.fr/~dsarrut/bib/Archive/others/phys/www.mas.ncl.ac.uk/%257Esbrooks/book/nish.mit.edu/2006/Textbook/Nodes/chap06/node29.html Under the first figure it states "Figure 6.20: The boundary layer at a stagnation point on an airfoil has a constant...
27. ### Airfoil question about camber and thickness

Hello everyone! I wanted to ask if the wing thickness is the same meaning as camber? Thanks in advance
28. ### Circulation Around an Airfoil and Starting Vortex

Homework Statement Using Kelvin’s circulation theorem, find the qualitative and quantitative relation between the circulation around an airfoil and the circulation of the starting vortex. Homework Equations Kelvin's circulation theorem: DΓ/Dt=0 The Attempt at a Solution I don't really know...
29. ### Concerning the Airfoil of Variable Pitch propellers

Hello, I am not an expert in aerospace engineering, merely a hobbyist so bear with my ignorance. lately I have been thinking of creating my own propeller and variable pitch system using a CNC machine as a longer term goal. This desire arose due to the fact that there are no commercially...
30. ### How does airfoil design affect wind turbines?

I understand that when wind hits the blades straight on it spins for the same reason a pinwheel spins when you blow straight at it. But when wind is hitting the "cutting" parts of the blade how does air foil design help there? Wouldn't the lift generated by the air foil not matter since the...
31. ### Selection of airfoil and sizing of propeller

Two problem to solve. 1) I have 4 propellers built with different airfoils. I have the graphs of coefficient of thrust and efficiency in function of advance ratio. There is a mathematical method to select which one is the best or the only way is just look at graphs 2)I know the maximum thrust...
32. ### Calculate Lift from a full-blown-circulation airfoil?

Hello everyone! I am interested in roughly calculating the lift from an airfoil that has air circulating around its full circumference, (can be done by a treadmill skin but probably best done in practice by blowing air from slots around the entire circumference as seen in Fig.1) As...
33. ### Stress analysis on spars for an airfoil

Homework Statement If I have two spars running through an airfoil, which can be assumed to be two dimensional, which method would I use to find the stresses at the points where the spars are fixed? The loads would be lift and drag and what I need are the bending and shear stresses. Because I...
34. ### Understanding Airfoil Ceiling Fan Blade Velocity Diagrams

Anyone can show me how the velocity diagram at the inlet and outlet of a airfoil section ceiling fan blade?
35. ### Guidance in Gambit 2.4 -- How change airfoil chords in Wells turbine model?

hi my dear friends, Wells turbine is the subject of the my Thesis: http://www.upload7.ir/imgs/2014-10/37346220310608280524.jpg i make below model in gambit 2.4 ,But now I want to make the upper airfoil cord bigger than the bottom one. below model is constant,attention to third pictures(...
36. ### How to Design an Airfoil for High Altitude Using XFLR5?

Hey Everyone, so I have just started Aerodynamics and having completed a number of exercises I'm being asked to design an airfoil. I'm a bit outta my dept as I've transferred into this course from a diff field. 1. Homework Statement To design an airfoil, using the knowledge you've acquired in...
37. ### Airfoil design and optimization

Friends, I want to know the methods involving the airfoil design and optimization. from initial step onwards...how to start my works.
38. ### How Does the Angle of Incidence Affect Lift and Drag in Small Aircraft?

For a given airfoil, the amount of lift and drag and thus the L/D ratio vary depending on it's angle towards the airflow. In general, for small aircraft with a straight wing shape (I say so because that seems to be the simplest case since the airfoil shape will be constant throughout the...
39. ### Airfoil Mechanism: Exploring Lift & Drag Forces, Angle of Lift & VAWT

Hello, I read about airfoil mechanism that there happens to be pressure difference created above and below the airfoil which result in lift force. My questions are: 1. What actually happens in the speed of air. I mean how can one side of the air travels with greater speed when they have the...
40. ### Shape of Airfoil: Analysis & Design

Homework Statement See attachmentThe Attempt at a Solution Im not sure how to solve c and d...
41. ### Airfoil - NACA 64a416/4416 mod

Hello, I am looking for coordinates data for the airfoil NACA 64A416/4416 mod. This airfoil was used on the DeHavilland DHC-2 Beaver. While the airfoil is listed on various manufactures lists no data, or image, of the airfoil is available. Can you tell me whether there is a reason this...
42. ### Airscrew Thrust and Resistance Calculations?

I want a general idea of how much thrust an airfoil will produce at a set speed with a set shape I would also like to know how much resistance it has in a set density gas I know the math exists for liquids but wikipedia say that for gasses the math is to long and it thusly isn't shown there I...
43. ### VAWT Airfoil Design: Learn How to Calculate Power Output

hello folks, I am in mechanical stream & am working on a project of VAWT of power 300 watt. I found a link where i can calculate power output for different parameter. Here's the link: http://usvawt.com/cgi/windpower.cgi where i took height as 2m and width as 3m. Now need to design...
44. ### How Can You Accurately Bend Aluminum Tubing for an Elliptical Airfoil Shape?

Hello all, I'm in the process of building an ultralight glider. (to be piloted by me) As part of the construction process, I need to bend some aluminum tubing into an airfoil shape. This tubing will form the top of the wing. The bottom of the wing is flat. The shape of this particular...
45. ### Supersonic Airfoil + Bow Shocks

Homework Statement Hey all, In my Gas dynamics class we need to find the lift and drag coefficients of a supersonic airfoil (diamond shaped) for a range of AoA and Mach numbers. I can easily handle any situation where oblique shocks or Prandtl-Meyer expansions occur, but I'm unsure how to...
46. ### Stagnation Pressure on Airfoil

First, let me say I am not a engineering student but just a average person trying to get his pilots license and enjoy working with aerospace problems. My problem is: “An aircraft is flying at 150 mph. The atomspheric pressure is 14.1 lbs./sq in and the temperature is 50 degrees F. Find the...
47. ### Dynamic behaviour of a rotatable airfoil, at constant and variable flow field

Homework Statement While I was learning about drag and lift on airfloils, I imagined a special airfoil which is fixed at a certain elevation and cannot move vertically (y axis) but can be rotated around its axis (z). Let's assume the direction of the flow to be the x axis. I try to predict...
48. ### The Mathematics of Airfoil Design

My question is kind of simple, does the calculus of variations find its way into the design of the shape of an airfoil? I'm interested in what kind of mathematics gets used in basic airfoil design. I suspect the calculus of variations must be involved, but I know nothing about deriving the...
49. ### Suitable mechanism for changing the angle of attack of an airfoil

I have to conduct wind tunnel test on a naca0015 symmetric airfoil at different angles of attack and I am in search of a suitable mechanism to change the angle of attack of the airfoil.Please help.
50. ### Flow Separation of Airfoil in terms of Reynolds Number

Hi I know that for an airfoil, it's typical to describe stall in terms of angle of attack. I'm wondering, how does Re play a role in flow separation of an airfoil (and for objects in general such as a plate, sphere, or cylinder)? One Wikipedia (http://en.wikipedia.org/wiki/Flow_separation) it...