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Because they are very lightweight and fragile. Therefore, thrust and propulsion mass must be distributed over span - a single, large propeller and motor would put too much force into the structure loc …

He experimented with different airfoil shapes by using exchangeable ribs on the gliders and by testing model wings on a rotation test stand (Rundlaufapparat). … In order to combine fast flight with high lift for take-off and landing, the thick airfoil is better. …

The X-Wing actually used an elliptical airfoil and forced the Kutta condition by directed blowing. … This is indeed the only sensible application of an airfoil that works in both directions. …

Take symmetric airfoils - here the trailing edge runs parallel to the airfoil chord. … But - as always - too much is not good: The Eppler 417 airfoil of the SB-7 glider was an extreme layout with too much rear camber. …

Your typical four-digit NACA airfoil will have a maximum lift coefficient of 1.2 to 1.6, depending on camber and Reynolds number (picture source). … The stall speed of an aircraft with a flat plate wing will be approx. 50% higher than with a proper airfoil on the wing, and drag will increase much more at high lift coefficients than usual, which translates …

So there is a different airfoil for every design Reynolds number, even at the same lift coefficient. … The short and stubby wing will need a different airfoil than the long and sleek one. Also, ideally you should vary the airfoil within one wing, depending where along the span you look. …

Again, molecules flowing along the wall of the airfoil will be slowed down by the stagnation point pressure the closer they are to the trailing edge. …

to use anything newer than an airfoil from the 1920s. … The excellent Polish aerobatic glider Swift S-1 uses indeed a NACA 6-digit airfoil, the $64_1412$. …

Flow separation on the suction side, but it would still produce lift like a regular airfoil. The L/D ratio would be lousy, however. … The inclination of the airfoil will already be enough to cause this acceleration, regardless which side faces forward. …

First propeller use: A highly cambered airfoil would cause high pitching moments and twist the propeller blade. … Adding slots between segments will make those work even better than a solid airfoil and allow to use more camber. …

However, increasing the flow speed will result in a thinner boundary layer and a slightly different shape of the airfoil - boundary layer combination as "seen" by the outer flow. … See below for a plot of the venerable NACA 4412 from Abbott and Doenhoffs collection of airfoil data (picture source): Note that the lift coefficient is plotted for Reynolds numbers R of 3, 6 and 9 …

The fist decades of aviation used empirically determined airfoil shapes which usually had most camber near the nose. … Simply put, almost any airfoil is a laminar airfoil at low Reynolds numbers but performs better with a turbulent boundary layer in the pressure recovery region. …

Here are a few older ones: Type Root airfoil Tip airfoil Boeing 377 Stratocruiser Boeing 117 (22%) Boeing 117 (9%) Douglas DC-7 NACA 23016 (16% … This also means that no stock airfoil is used, and most modern designs have their custom-made airfoils. …

All points you mention are correct (for the nitpickers: Point 5 is only true below transsonic speeds). That the pitching moment of the wing is drawn nose-up is probably because it is positive this way …

Then the lift curve slope increases up to $c_{L\alpha} = 2\cdot\pi$ for $AR = \infty$ (and zero airfoil thickness and no friction effect), as shown by the blue line. … If you know your airfoil lift curve slope, modify the result from the plot above by the ratio between the airfoil lift curve slope and $2\pi$. …