Find the ideal wing cross-section

 1.Drones need wings! 　

     It seems that demonstration tests of transportation systems using drones are progressing all over the world. 　 

     However, the type without a wing that gains the lifting force with the propeller and tilts the entire body or only the propeller to provide the propulsive force for lateral movement is too inefficient.      

     When moving laterally after climbing, the propeller should be used only for propulsive force, and the upward force should use the lift force of the wings, and if that is not possible, it is efficient to use the lift of the wings to fly even a little. 

 （from Wikipedia) 　

     In other words, the “Osprey” VTOL (Vertical Take-Off and Landing Aircraft) type is very efficient. 

 　No matter how dramatically battery performance, motor performance, weight reduction technology, etc. will evolve in the future, increasing cruising range and payload are eternal challenges as long as we pursue performance improvements. 　

     As long as the aircraft moves in the air, there is no reason not to use the wings. 　 

     If a wing of a sufficient size is not possible, even if a part of the airframe is made into a wing shape, it should be shaped so as to obtain a little lift. 

 2.Current wing cross section is not optimal 　

     I noticed that the cross-sectional shapes of the wings of airplanes in the world are slightly different. That means that the ideal shape has not been found yet. 

     Therefore, I wanted to know what the cross-sectional shape of a wing with a large lift-to-drag ratio was, and made models of various shapes to measure the lift and drag. 

     This kind of experiment is a comparative test. 　

     And what is important is that the magnitude relationship of the numerical values ​​measured by the small model does not change even if it becomes the size of the actual size. 　

     The key to proceeding with the experiment is what to read from one test result and what test to perform next. 　

     I knew that before I experimented, that the relationship between the cross-section shape of the wing and the lift&drag ( physical reason) gradually becomes clear, and I eventually reach the ideal shape. That's what a comparative test is. 　

     Then, in the process of pursuing the optimum shape of the wing section, there were some cases in which the experimental results could not be explained by the conventional way of thinking of the lift generation mechanism, so I decided to consider my own mechanism of lift generation. 　

     Since my personal opinion of the lift generation mechanism obtained from the experiment is separately posted, here I will introduce the optimum shape of the wing cross section of the airplane.

 3.What I learned from my experiment 

1)The drag force is smaller when the cross-sectional shape of the tip of the wing is sharp rather than round.

     It has been said that the "ideal shape with the smallest drag when an object moves in a fluid is a streamlined shape.” 　

     All the dictionaries I see explain that way, but it wasn't. 　

     I wanted to know how much the drag would be reduced by eliminating the stagnation point that occurs at the tip of the so-called streamlined type, and I confirmed it through experiments. 

     Even with a streamlined shape, stagnation occurs at the tip. In order to eliminate it, it is only necessary to lose a flat surface that faces the flow, so the tip should be sharpened to divide the flow into upper and lower parts. 　

     The tip of the model P has a semi-circular shape of 10R, and the drag force of the model O only with a 90° tip angle is reduced by 12%. 　

     With such a small shape change, a large drag reduction can be achieved. 　

     The tip of model F with a tip angle of 30° is a semi-circle with a radius of only 2R, and if you eliminate the stagnation point that occurs linearly here and use it as model E, the drag force is further reduced by 8.8%. 　

     I would like you to pay your attention to the magnitude of these effects. 　

     Needles to say, the smaller the tip angle is, the smaller the drag force is, but the graph below shows what the relationship between the tip angle and the drag force is. It was found that the effect fades below 20°.　

Tip angle and drag.

    The shape of the tip of the Chuo Linear Shinkansen is a design that still has a flat surface that faces the flow.In other words, I think it's a design that can still reduce air resistance. 

     Once again, the streamlined shape with a round tip was not the optimum shape with low drag.

２）Is it easy to stall if the tip is sharpened? 

     It is well known that jet fighter flying at supersonic reduces drag by sharpening the tip. However, it seems that the drastic reduction in subsonic aircraft has not been studied much because the streamlined image was too strong. 　

     Furthermore, it is said that sharpening the tip of the wing makes it easier for the air flow to separate and stall, and the shape of the wing is viewed as taboo, and it seems that no experiment has been done. 

     Most of the explanations for “stall” are that the lift disappears when the angle of attack is around 10°, but in my experiment, there is astern lift force even if the flow separates on the upper surface of the wing. This is also most dictionaries have the wrong commentary.

     The graph above is a model R (an example of a wing section) that measures how the lift and drag changes with changes in the angle of attack. 

     Even if the flow separates on the upper surface of the wing, the lift will not be lost. 　

     Isn't such a graph possibly badly affected? 

     This is a plot of lift-drag ratio on the vertical axis and angle of attack on the horizontal axis from the data of my experimental results. 

    It is a big mistake to judge from this graph that the airplane will stall at an angle of attack of 14°.

３) The drag is smallest when the sharp tip is at the center of the projected height of the wing. 　

     It was found that sharpness of the tip reduces the drag force and that the lift does not disappear even if the flow separates. 

     Where is the most effective position of the pointed wing when there is the angle of attack? I wanted to know. 

 (from Wikipedia) 

  ＊Notice the white misty stream blowing the engine in these photos. 

     In both cases, the attitude of the aircraft at the time of takeoff was slightly raised, but form these photographs it can be seen that the divergence point between the flow on the upper surface and the flow on the lower surface of the sing is considerably below. 

  ＊ The figure below shows the result of the measuring the lift-drag force by changing the position of the wing tip because I wanted to know where the branch point was. 　

     From the result of this experiment, it was found that the drag was smallest when the tip of the pointed wing was located at the center of the projected height of the wing. When the tip of the wing was on the line where the branch point of the flow existed, the reading said that there would be no stagnation on the front side. 

 4,Find the optimum shape of the wing section 

     So I wanted to know what shape is most efficient for the entire wing. 　

     The figure below shows the results of the typical three existing shapes and the optimal shape model in my opinion. 

     The result is a lift and drag force with an angle of attack of 0 to 10°. 

・ Model N (general shape):                The wing thickness is small, so the drag force is small. 

・Model U (Zhukovsky wing): 　　　　Drag force is the second smallest among 4 models. 

・Model W (Super Critical Wing):         The lift-drag ratio is extremely small when the angle of attack is small.

・ Model T(shape with emphasis on lift) 　This has a large lift-drag ratio. 

＊Model T has a minimum drag near the angle attack of 4 to 6 degrees. This is the feature of my patent. A thinner wing reduces drag overall but also lift. 　

     You can see how high performance the shape “ModelT” derived from my patent is. 　

     The angle of attack is 8° when the lift-drag ratio of T is maximum. Therefore, considering cruising, if the aircraft’s attitude is horizontal and the wing angle of attack is set to 8°, the wing profile will have the highest efficiency. 

     T is a model that aims to increase the lift by increasing the blade thickness, and you can also aim to reduce the drag by decreasing the wing thickness. 

     The wing thickness will be determined by the blade strength, fuel tank, etc. 

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 (Aside) Depending on the model, isn't it annoying that the passenger is in a nose-up posture even if the passenger is ready to cruise? That means the aircraft is generating extra drag. I think it should be horizontal. 　

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    The drag increases as the wing thickness increases, but if the part indicated by the red line is made straight, the tip angle can be made smaller and the drag can be reduced relative to the wing thickness. 

      The basic of the most efficient wing cross section shape (wing optimum shape) that I recommend is the shape of the model T. 

     You can fly to higher wing with the same thrust, you can fly at high places at high speed, and if you fly at high speed, the cruising range will increase. 

     Furthermore, awing with a large lift-drag ratio, etc., which can increase take-up capacity or enable takeoff and landing on a short runway, will bring great benefits. 

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