# Tag Info

55

Same reason gliders keep their wings waxed. It wasn't the camo per se, it was the dull matte field-applied paint finish that included all sorts of imperfections, and to a small degree, the weight of the paint vs natural finish. At a microscopic level, the surface of the matte finish was much rougher than a gloss or unpainted metal surface. The ...

33

If the cables break on an elevator (and the safety brakes fail), you won't be in true freefall. You'll still have friction from wind resistance, from the guide rollers on the rails, etc. The same is true in an airplane. Even if you're falling straight down, you'll still have wind resistance. In addition, lift doesn't just drop straight to zero when the wing ...

19

It's primarily all about matte vs glossy finish. Normally a camo paint scheme would not be finished in a glossy finish as this might flash in the sunlight. A matte finish is rougher and thus has more air resistance than a glossy finish. The roughness is on a scale that is much larger than microscopic, but not obvious to the naked eye.

12

First propeller use: A highly cambered airfoil would cause high pitching moments and twist the propeller blade. Of course you can pre-twist the blade so it will assume the correct shape in the desired operating point, but a propeller needs to work over a wide range of operating points, from take-off roll to high speed flight at altitude. In off-design points ...

11

The force that pushes a glider is a component of its weight. More precisely, it's the projection of the vector weight W on the glide path. It's exactly of the same value of drag D, if the glider is flying at a constant airspeed, with no accelerations. In the picture, all vectors are forces except for U, V and w, that are horizontal-, total-, and vertical ...

11

Airplanes do not fly because of their engines. Airplanes and gliders both fly because their wings turn thrust into lift and drag. That simplistic answer, of course, just begs the question "how can you generate thrust without an engine?" A glider is constantly trading altitude (potential energy) for airspeed (kinetic energy). Energy over time equals force, ...

10

It's important not to overthink it. I'll keep it simple. A coordinated turn means you are keeping the tail lined up with the nose in the airstream. If you are uncoordinated, you are flying sideways in the airstream to some degree or another; the side of the fuselage is being presented to the airflow. If you learn to fly in gliders, it's obvious because ...

10

You can't just cherry-pick aerodynamics and exclude everything else when it comes to aircraft design. But let's entertain flight dynamics alone for this instance, and use Selig S1210 or S1223 as examples. Selig-S1210 (for Re 0.2e6, 0.5e6 and 1.0e6) characteristics: First, notice that the linear range of the airfoil extends from $C_l$ 0.5 to 1.9, which ...

10

Is a “stalled” aircraft free-falling? No! If I was in an elevator in a sky-scraper, and the cable broke, I would free fall and feel weightless (until hitting the ground of course). When I stall an airplane(power-off) and the wings stop producing lift, why doesn't the same effect occur? Because in a stall, the aerodynamic force component acting against ...

7

Can someone tell me which force during an uncoordinated turn is too big or too small and literally what makes a turn uncoordinated in terms of forces? The slip-skid ball (inclinometer ball) will be off-center whenever the component of the net aerodynamic force that we see when looking at the airplane in a head-on view is tilted "sideways" in the ...

6

For the same wing span, an elliptical wing planform is the most aerodynamically efficient compared to any other flat wing planform because it has the lowest induced drag. Note that we are comparing only aerodynamics here. Things get much more nuanced once you couple structural weights, stability & control for a global efficiency (also see @Peter's answer)...

5

The inefficiency is the result of a comparably high weight in relation to the possible lift. However, for small aircraft that disadvantage is not very pronounced (this is true especially for braced wings and biplanes) and is outweighed by very favorable stall characteristics. Also, a rectangular wing is very easy to build. Compare with what has been built so ...

5

If you are asking about the forces involved in an uncoordinated turn, Thrust, Drag, Lift, and Load (weight) still apply. But, let us define Lift as acting perpendicular to to the wings in a direction opposite Load. While Load is acting perpendicular to the wings in the direction of gravity plus the aircraft’s momentum. When you are banked, or you are in a ...

5

The X-57 should show the highest gain in lift from the props. They will wrap the full wing in accelerated flow. XFLR is not capable of capturing this effect, since the pressure distribution should be similar to the case without props, only the reference dynamic pressure is higher than that of the prop-less wing. Of course, swirl effects will add a spanwise ...

4

Short answer: Yes. Maximum speed is correlated with wing loading. A high wing loading shifts all speeds up. A flying wing will always have a lower wing loading in comparison to a conventional design when payload, range and landing speed of both are identical. So you will start at a disadvantage. Due to the high lever arm of the conventional tail, the ...

4

I'll use the following diagram for illustration: Intuitively, a hard surface resists fluid flow via shear stresses; these shear stresses tend to rotate fluid elements (i.e. vorticity). Therefore, we can regard a hard surface as filled with vortex sources. In actual fact, only the boundary layer contains vorticity, and there is usually no fluid element ...

4

Let's do a Gedankenexperiment. Fly a glider on a horizontal flight path. It will slow down and stall. Now fly the same glider in a vertical dive. It will accelerate downwards, pulled down by gravity. Now think of gliding flight as a superposition of both states. Mostly horizontal flight with a bit of vertical dive on top. Shouldn't it be obvious that ...

4

From A.C. Kermode; Mechanics of Flight, London, Pitman, 8th Edn, 1972, p.75 (his bold): "We call the angle between the chord of the aerofoil and the direction of the airflow the angle of attack. "This angle is often known as the angle of incidence; the term was avoided in early editions of this book because it was apt to be confused with the riggers' ...

4

It is just angle of attack. Most anything can have an angle of attack. If you must be specific, you mention 'angle of attack of ...' Due to complexity of aerodynamics, most external elements of an airplane have their own local angle of attack. AoA sensors measure their angle of attack, and it is usually not even converted to 'wing' or 'fuselage'; it is ...

4

Under incompressible potential flow and at small angles of attack, one of the most celebrated results of Thin Airfoil Theory is that all airfoils have their aerodynamic centre at 1/4 chord; and for symmetrical airfoils, the centre of pressure coincides exactly with aerodynamic centre. If you look at the plot in the OP, the variation of Cm between -3 and 3 ...

4

When we designed the SB-13, we also thought that it's not so much different from a regular layout. Boy, were we wrong. It starts with ground handling: Regular aircraft have some distance between front and main wheels, and even more between main wheels and tail skid in taildraggers. This makes them fairly stable in pitch on uneven surfaces. When both wheels ...

4

Most supersonic aircraft have points where the cross-section suddenly changes, such as the fuselage nose, the wing root leading edge or the wing trailing edge. The points of sudden change produce sharp changes in air pressure, i.e. loud sonic booms. Concorde was one example. By designing the plane's cross-section to vary smoothly from end to end, the ...

3

Enbin Zheng is correct, the gravity force is vertical, always vertical, and cannot account for horizontal motion at all. What does? Let's take the bicycle first. On flat ground it has a gravitational force of 1 G, but does not move vertically. There for, it has an equal upwards 1 G force of terra firma (the ground) holding it at "ground level". Taxiing ...

3

There is little to be gained by twisting the horizontal stabilizer in terms of efficiency. First, the span of a typical horizontal tail is much smaller than the wing (see A320 illustration below for example). Apart from the small outboard portions, the downwash behind most of the wing is fairly constant. This makes the simplification of a uniform downwash ...

3

Compared to a turbojet engine, the heating (from cylinder fins) of the working fluid (air) in an radial engine is relatively small, and so will be the possible thrust augmentation via the Meredith effect. Better results can be had by dumping the engine exhaust into the cooling air stream exiting the engine, and directing this blend of spent engine cooling ...

3

If one can handle a little abstraction, a half maple leaf seed is perfect. The main driver of an established spin is lift and drag asymmetry, resulting in a helical spiral downwards. While fuselage shape and weight distribution are contributing, difference in lift between the two wings results in a slip towards the lower lifting wing. Once the aircraft ...

3

As a partial answer following up on those to date, here is an image from Where is the spanwise flow? How does the span wise flow point the air towards the wingtip?, showing a snaking in-then-out flow over the wing. Note the inward flow over the leading edge and wing section, which is just the point where wing fences are located. On sharply-swept deltas ...

3

@George already gave a correct answer, but I'll expand it a bit and show the source. Indeed, the lower load limit is for trans- and supersonic flight (formally M > 0.85) and the higher limit is for subsonic conditions. The AoA redline at 15° also relates to M > 0.85. At subsonic speeds, the max AoA is 26°. I can only speculate why it is not shown on the ...

3

I found your exact question a little confusing, so let me answer with a quote from a current British PPL exam preparation book: The wing's angle of incidence - the angle between the wing chord-line and fuselage - is fixed by the construction of the wing and the angle at which it is bolted onto the fuselage Source: AFE Book 4 - Aircraft General Knowledge ...

2

In order for a glider to fly, it must generate lift to oppose its weight. To generate lift, a glider must move through the air. The motion of a glider through the air also generates drag. In a powered aircraft, the thrust from the engine opposes drag, but a glider has no engine to generate thrust. With the drag unopposed, a glider quickly slows down until it ...

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