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40

Early biplanes did use similar airfoils. Not as extreme as the Eppler 376, but still very thin and highly cambered. When Otto Lilienthal started his glider experiments, he tried to copy storks. He experimented with different airfoil shapes by using exchangeable ribs on the gliders and by testing model wings on a rotation test stand (Rundlaufapparat). There ...

36

This is called stall hysteresis. You have two different situations and the flow reacts differently in each of them. When increasing the AOA The flow is attached to the wing and the boundary layer is resisting the adverse pressure gradient as much as possible. At some point the flow detach from your profile and you have stalled let's say at 18°. At this point ...

15

This is more an addendum than an answer, regarding "birdlike" airfoils. Ignoring the fact that birds can modify geometry, chord and camber of their wing when required, what can at best characterize a bird's wing airfoil, in addition to camber, is maximum thickness' location, very close to the leading edge, and constant minimal thickness between ...

13

There certainly are airfoils that are patented. Here is an example. Here is another airfoil by the famous aerodynamicist Richard Whitcomb. I think it is tricky in practice to obtain a patent in that you need to define the airfoil in a way that isn't so narrow as to be useless for protection. Just claiming a series of coordinates would provide very little ...

10

Patenting an airfoil would be difficult- the owner of the patent would need to show that they had invented something new that wasn’t obvious, and to enforce the patent they would have to prove that somebody else’s airfoil was identical and not an improvement on the original design. Given the NACA system for describing airfoils it would be difficult to claim ...

9

Assymetrical wings on missiles/guided bombs do exist. However the goal of all missiles/guided bombs is to hit or come close to its target, which mean different things for various missiles. This drives their design: Symmetrical airfoils on missiles are used in order to guarantee uniform turning capability. This enables the missile to immediately turn in ...

8

The difference is that one figure looks at 2D flow around an isolated airfoil, where L/D ratios of up to 200 can be reached, while the other figure is for the 3D flow around a whole airplane, warts and all. The additional sources of drag which are absent in 2D flow around airfoils are: Induced drag. This will double the total drag right at the polar point ...

7

Amazing! British pioneer JW Dunne proposed this as a propulsion system around 1901 but Sir Hiram Maxim told him it would not work. (ref. unpublished documents in the Science Museum Archive's Dunne collection). Nine years later Henri Coanda built a ducted "jet" plane on broadly similar principles, which failed miserably (The Wikipedia article is not ...

7

The Boeing 737 predates the use of supercritical airfoils at Boeing (which again predate the work of Whitcomb, but I digress). In order to keep changes to a minimum, the 737 wing airfoils only got the equivalent of a "nose job" over the years to bring their drag divergence Mach number up. Note that regional airliners fly a bit slower than ...

6

It has to do with the Birnbaum distribution. The center of its area is at one quarter. In potential flow theory, lift can be calculated as the linear superposition of a contribution from camber and one from angle of attack. While the camber-related part of lift is constant, the angle-of-attack related part varies linearly with this parameter. This means that ...

6

Landing phase would benefit from high lift but low lift-to-drag ratio. At most phase of flight you need about the same amount of lift to keep the plane in the air. However during landing you need to slow down to landing speed. Hence you lower lift-to-drag ratio by keep the same amount of lift but increase amount of drag. This is usually accomplish by ...

6

Normally, you would pick a symmetric airfoil. The thickness should be between 9% and 15% to find a good compromise between structural efficiency and maximum side force. Choose a thicker airfoil at the root, a thinner one at the tip and interpolate linearly between them. Of course, for supersonic designs a thinner airfoil should be selected. In some special ...

5

In cruise: No. Less drag means less thrust, which is always beneficial for the practical operation of an airplane. There is only one condition except for approach and landing where high drag helps, an that is also not during cruise: In aerobatic airplanes during vertical maneuvers. If, for example, the aerobatic display includes a vertical dive, high drag ...

5

Simple answer: The pressure difference between lower and upper side on an uncambered airfoil or a flat plate can be summed up in a force acting at the quarter point, independent of angle of attack. Only when separation starts will this pressure distribution change shape and the force will move backwards. Since a flat plate has a sharp leading edge, ...

5

Most missiles fly at such high speeds and manoeuvre so violently that "up" means very little to them, it is simply a mild error to be corrected for. Cruciform wings and tails are designed solely for manoeuvrability in whatever direction the missile needs at that moment. After a bit of that, there is no predicting which way up the missile will be by ...

5

Answer to the implicit question: Yes, the more recent airliner airfoils are indeed secret. Look for reports like this to see what is out there. Answer to question 1: Try the linked NASA Technical Paper 2969. Answer to question 2: Your viscosity is for sea level. Try to use the value for the tropopause and it will be only ⅓ as large.

4

Wind tunnels are stingy with the data they reveal. They only give the total value but not neatly split into its contributions. Therefore, any such table needs to be calculated. Since XFOIL, which is now around for more that 30 years, we have such a tool and it does output the single contributions. However, I know of no publicly available collection which ...

4

No, it's not possible to have them simultaneously. Here's a proof by contradiction: Assume that there are two points on the airfoil that have constant pitching moment, located at $x_0$ and $x_1$, each having constant moments $M_0$ and $M_1$, respectively, and that $\frac{\partial{M_0}}{{\partial\alpha}}=\frac{\partial{M_1}}{{\partial\alpha}}=0$ (which make ...

4

Normally, supersonic fighter wings for which airfoil information is published use a very thin NACA 6-series section with very little camber, such as Aircraft root airfoil tip airfoil McDonnell Douglas F-15 NACA 64A006.6 NACA 64A203 General Dynamics F-16 NACA 64A204 NACA 64A204 Lockheed-Martin F-22 NACA 64A?05.92 NACA ...

4

Yes. Lift and Drag are both obtained by multiplying the CL & CD by the same factors (1/2 rho V^2 S); the ratio L/D cancels out those factors, leaving CL/CD.

3

The Benedek 10355 clearly stalls with separation starting from the trailing edge. There is some discussion whether a laminar-to-turbulent transition due to rising pressure will always involve a laminar separation bubble, however short. But that bubble does not constitute a leading edge stall. XFOIL is not meant for flow simulation deep into the stall region. ...

3

The laminar "bubble" on the bottom is caused by the wavy contour. There is a pressure rise at about 25% on the lower side which causes the boundary layer to thicken, but the subsequent flat pressure profile keeps the boundary layer laminar until it separates at the trailing edge. Here is the plot from XFOIL and I placed a green circle over the spot:...

3

The flow of a viscous fluid can be described using the Navier-Stokes equations. This includes describing flow of air around an airfoil. Your assumption about conservation of momentum or energy is correct, both of these enter in the derivation of Navier-Stokes, together with conservation of mass: [The Navier-Stokes Equations] describe how the velocity, ...

3

The technical report NACA-TR-824 has been digitized. The digitized version includes Cl and Cd for 118 airfoils at 3 Reynolds numbers. To get it, create an account on x-plane.org. (It's been online sporadically elsewhere over the decades, e.g. here. People associated with the digitizing include Gregory Peter, Gregory Siemens, and James Sonnenmeier.) ...

3

High lift at the expense of even higher drag means that the plane will not be able to fly very fast, as drag rises sharply with speed. But the extra lift is still useful in several situations and is often provided by drag-creating high-lift devices. Some of these situations include: STOL (short takeoff and landing) and low-speed flight performance, where ...

3

This is due to the Coandă effect. https://www.britannica.com/technology/fluidics#ref129652 In the 1930s Henri Coandă, a Romanian scientist, described what is now known as the Coandă effect, a major contribution to fluidic technology. He observed that as a free jet emerges from a jet nozzle the stream will tend to follow a nearby curved or inclined surface. ...

3

Draw a line from the leading edge to the trailing edge. This is the chord, and it has a positive angle of attack as the shape is oriented. Therefore your premise that this has zero angle of attack is incorrect. Since you can produce lift with a positive angle of attack using a flat plate, it is reasonable to assume that this shape, as drawn, should produce ...

3

Camber directly affects the amount of circulation an airfoil can generate, adding camber will always generate a higher zero alpha lift coefficient (intersection of the lift coefficient curve with the x=0 axis) up until a point that there is too much camber to sustain attachment. This leads directly to the question asked - does camber increase CL_max? For any ...

3

Designing an aircraft to travel at mach 1 and beyond presents a whole host of challenges that must be overcome. For example, beyond the obvious issue of airfoils, turbojet engines generall need to solve the problem of supersonic intake - slowing the air down as it enters the engine to speeds below mach 1 before compression and ignition. The considerations ...

3

Yes, you chose the wrong airfoil. While the NACA 6-digit series was among the first set of airfoils computed from a design pressure distribution, they will suffer from shocks when operated above their critical Mach number just as any other airfoil. Comparison of drag rise over Mach for 6-series and early supercritical airfoils from NASA Technical Paper 2969....

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