Questions tagged [airfoil]

The 2D shape of a section of aircraft wing.

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13
votes
2answers
26k 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-...
26
votes
8answers
4k views

Is there an aerofoil that gives reasonably good lift for both air flow directions: forward and backward?

Could an aerofoil be designed to give reasonably good lift for both flow directions? I was motivated by this related question on Aviation SE: Can a plane fly backward if its propeller is in reverse? ...
11
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4answers
3k views

Why do airfoil's trailing edges point downward?

The trailing edge of and airfoil is mostly pointing downward. Is there any reason for that? Down wash increases drag and down wash is due to the direction of air pointing down. If the trailing edge is ...
15
votes
4answers
24k views

What is the performance of a flat plate wing?

By flat plate I mean this: Source: Physics.SE Low performance indeed, but how much low? How would: The angle of attack, The speed range, The turn capability, The fuel consumption, Or other ...
8
votes
3answers
4k views

Can a steady flow have stagnation points?

I am confused by this idea. If a flow is steady, its streamlines are unchanging. Taking the typical example of an airfoil, there is (at least) one streamline which will hit the leading edge of the ...
4
votes
1answer
1k 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 ...
10
votes
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 ...
14
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3answers
15k views

Are NACA airfoils used in modern aircraft design?

I know that NACA is famous for its ducts: Gratuitous Ferrari F-40 from Wikipedia. Mmmm... pretty... It is also well known for its airfoils, and many planes in the early years of aviation used NACA ...
9
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3answers
15k views

What is the difference between a leading edge flap and a slat?

I always thought that the definition of slat was: "Lift modifying and adjustable wing element on the leading edge of main airfoil." and the definition of flap was: "Lift modifying and adustable ...
6
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3answers
10k 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 ...
11
votes
4answers
925 views

Why does the aerodynamic center exist?

I am a glider pilot and instructor with a master’s degree in actuarial mathematics. I teach aerodynamics every winter for upcoming glider pilots. As you surely know, the aerodynamic center is the ...
9
votes
1answer
8k 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 ...
7
votes
1answer
2k views

What are the disadvantages (if any) of using a supercritical airfoil?

The title sums up my question pretty well. I've searched all over this site, having read many of the questions and answers to various supercritical wing topics, but I haven't found any mention of ...
6
votes
2answers
606 views

Which design method is used for super critical airfoils?

How is an Airfoil categorized as super critical or not super critical? What are the ways to design a super critical airfoils?
0
votes
1answer
545 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 ...
9
votes
4answers
5k views

How to go about designing a custom airfoil?

I am familiar with the NACA 4-digit and 5-digit airfoil design system where airfoils, but I was wondering if anyone had some good reference material or software for designing a completely custom ...
3
votes
1answer
802 views

What does leading edge radius mean?

What does leading edge radius mean amongst these parameters of a st cyr 24 airfoil?
3
votes
2answers
708 views

Why is the critical AoA of most flaps 40° when most airfoils stall at 15°?

A plain flap deflected 40 degrees is largely stalled (...) Flaps stall at 40° according to an answer on Quora, why is this so when typical airfoils stall at 15°?
5
votes
1answer
2k views

How to determine if flow transitions or separates from a Cp plot?

I came across this image: My question is: given a general Cp plot, how does one tell from the shape of the curve if flow transitions or separates? Specifically, what features on the plot do I look ...
3
votes
2answers
6k views

How are empennage airfoils chosen?

Empennage airfoils are usually symmetric. What is the process behind choosing the airfoil used in the tail of the airplane? Is it related to the stability? And then how would the angle of attack of ...
3
votes
1answer
420 views

What's the theoretical background of the critical angle of attack?

The critical angle of attack seems to be at all (most?) airfoils around 15-20°. Why is that? Why is it in this range and not lower or higher? Is it just the result of optimizing airfoils? Or is it ...
6
votes
1answer
18k views

How do I choose the correct NACA airfoil for my requirements?

How do you find the correct NACA airfoil to use when you already know the requirements? All of the research I have done on this has shown how to determine what kind of camber/chord/aspect ratio etc. ...
55
votes
4answers
10k views

Why do solar planes have many small propellers instead of fewer large ones?

Many solar planes, like NASA's Helios (pictured above), NASA's Pathfinder, and to a lesser extent Facebook's Aquila employ the use of many small motor propeller sets instead of one or two engines like ...
7
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1answer
1k views

Is drag coefficient lowest at zero angle of attack?

The drag coefficient of a symmetric airfoil is lowest when its angle of attack is zero. I'm not sure if this is true in general.
12
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4answers
4k views

Why isn't there a single best airfoil for subsonic flight?

Why does airfoil used by modern subsonic aircraft (this is true for transonic airliners too) vary from plane to plane? Haven't we figured out a single best airfoil shape, with the highest lift to ...
10
votes
2answers
1k views

Do airliners like Boeing and Airbus use airfoil variation along the span for their wings?

Airfoil variation will make a significant difference in airflow over the wing, thus proper variation according to the lift profile should improve the overall aerodynamic performance. But by how much? ...
7
votes
2answers
3k 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 ...
6
votes
2answers
5k views

How to pick a good airfoil based on Cl and Cd

Let's assume I have 10 different airfoils graphs of Cl x Aoa, Cd x Aoa and Cl/Cd x Aoa. How do I pick the best one that will give me the most efficiency (the longest flight time)? I understand the ...
6
votes
3answers
9k views

Should the pitching moment be up or down?

I had a question regarding the direction of the pitching moment. To make sure we are on the same page, here is what I know so far (please correct me if I am wrong). Lift acts through center of ...
5
votes
2answers
2k views

Is the Reynold's number a function of the fluid flow stream or the obstruction?

I am slightly confused with this notion of the Reynolds Number. Specifically, I am looking at airfoil performance at very low Reynolds number. I am reading a lot of papers saying things like ...
3
votes
1answer
831 views

Are there any reference values for Cl and Cd of a NACA 0012 airfoil to verify CFD simulations?

I am having trouble finding the established results of inviscid flow CL and Cd variation over NACA 0012 airfoil, for the transonic region. I need the data to verify the results I am getting through my ...
3
votes
1answer
8k views

How do symmetrical airfoils generate lift? [duplicate]

It is widely understood that the curved shape of a typical airfoil (such as a Clark Y) causes a pressure difference that creates lift. How do symmetrical airfoils do this when the top and lower ...
3
votes
2answers
2k views

What is the best airfoil for Edge 540 Style Aircraft?

I need help picking an airfoil. I'm an artist and have limited knowledge of such things. It's for a game with an aircraft similar to an Edge 540 / Extra 300. Unfortunately I have a limited selection ...
2
votes
1answer
2k views

How to calculate variable pitch propeller parameters?

I'm carrying out a project on Variable Pitch Propellers for UAVs and especially self-adjusting or Passive Variable Pitch Propellers that change pitch due to aerodynamic forces and Pitching Moments. ...
2
votes
2answers
2k views

Is airfoil thickness proportional to drag coefficient?

Does increase in the thickness of a camber airfoil mean more drag will be produced? Why do slow flying planes have thick airfoils when it will just slow them down even more?
2
votes
1answer
658 views

How does airfoil thickness affect the Mach number at which it experiences transonic flow?

Roskam (book: Airplane Aerodynamics and Performance, Subparagraph: 2.5.2 HIGH-SPEED AIRSPEED INDICATORS (COMPRESSIBLE FLOW)) affirms: [...] Airplane with no sweep and thick airfoils become ...
1
vote
1answer
171 views

How to find the static stall angle of attack for a given airfoil at given Re?

For vertical axis wind turbines applications I'm wondering how one would find the static stall angle of an airfoil at a given Reynold number? Is it just the critical angle of attach (AoA) where ...
0
votes
2answers
799 views

Winglet design and airfoil selection

I'm currently in the process of designing a winglet for my low speed aircraft in xflr. While researching about winglets I read in a Boeing article that if the baseline outboard wing is relatively ...
-1
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1answer
3k views

How can I calculate airfoil thickness?

Given this information... ... how can I find the thickness for a "NASA/Langley LS(1)-0417MOD general aviation airfoil" at 90% and 99% chord?
8
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3answers
4k views

Why should the leading edge be blunt on low-speed, subsonic airfoils?

I have read that is to help the flow remains attached, but I do not understand the physical principle.
8
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5answers
3k views

Why are the wings of some modern gliders tadpole shaped?

Why are the wings of some modern gliders tadpole shaped, rather than teardrop shaped? An example is the Schleicher ASG 29. Or did they just add a flat plate at the trailing edge for the flaps and ...
8
votes
1answer
502 views

Can a Kline-Fogleman airfoil be used for engine turbines?

I am currently working on the Kline-Fogleman airfoil for NACA 23015 variant at Reynolds number 208800 with the configuration of the backward facing step of 50% thickness at 50% chord on the bottom ...
6
votes
3answers
4k views

Why the dynamic pressure is not mentioned in the explanation of lift by Bernoulli's principle?

Usual "explanation" of lift using Bernoulli principle This theory is: Air over the wing is accelerated, its dynamic pressure increases with velocity. The static pressure over the wing decreases (due ...
5
votes
4answers
4k views

How do I choose the correct airfoil?

I am currently working on a personal single seat, piston aircraft that I would fly myself and I am currently in a bit of conundrum when it comes to my wing design. In this project, I assigned us in 2 ...
5
votes
1answer
300 views

Where can I find articles about Handley Page multi element segmented airfoils?

Can anyone direct me to a source containing the complete article on Handley Page's 6 and 8 element airfoils from Flight magazine Feb 24, 1921 (PDF) or further more detailed information on this subject....
5
votes
4answers
2k views

Can this design provide more lift force than thrust from engine?

The problem is depicted in the picture: Generally, why we don't use engine blow wings to fly? Can we use wind-tunnel-like wing to generate lift force? Can it generate more lift than thrust? If it ...
4
votes
1answer
900 views

Does the Airfoil Tools Cd/Alpha Curve include both induced and parasite drag?

I'm looking at Cd / Alpha for the SD7062 Profile: http://airfoiltools.com/airfoil/details?airfoil=sd7062-il Wondering if it includes both induced and parasite drag. How does one tell?
3
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1answer
764 views

What is decalage and how it affects airplane performance?

What is decalage in airplanes and how important is it in respect to airplane performance?
3
votes
1answer
5k views

How to select the most efficient airfoil for low speed flight?

What airfoil (or family) has the highest $C_L/C_D$ ratio at speeds in the $50\:km/h$ range. The use case would be an ultralight with a max speed of $50\:km/h$
3
votes
2answers
716 views

Is flow turning different from the Magnus Effect? If so, how?

The production of lift is much more complex than a simple differential pressure between upper and lower airfoil surfaces. In fact, many lifting airfoils do not have an upper surface longer than ...