# Tag Info

56

What you saw is called a speed brake, which is one of the functions of the spoilers. From the Boeing 737 NG FCOMv2 (9.20.5 Flight Controls - System Description): Flight Spoilers Four flight spoilers are located on the upper surface of each wing. Each hydraulic system, A and B, is dedicated to a different set of spoiler pairs to provide isolation ...

38

In theory they can stop moving relative to someone standing on the ground. In practice this does not occur. Aircraft fly through the air and, yes, below a certain airspeed, an aircraft will stall. Let's take a super-simple example to explain the situation: You are standing on the ground on a very breezy day. It's quite windy on the ground, and blowing ...

38

Because manufacturing processes are not perfect, and the minute differences between parts as-designed and as-produced are amplified by the high rotational speeds and large diameters of modern jet engines. Take a following back-of-the-envelope calculation: disregard incoming airflow velocity and assume a hypothetical fan with a 1 meter diameter rotates at ...

34

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 ...

31

Your misunderstanding lies in your thought that lift is smaller than thrust, while in fact, lift is much larger than thrust. The lift is provided by the wings. Their purpose is exactly to create a lift force (upwards force) while requiring relatively little thrust (forwards force). How well they do this is expressed by their lift-to-drag ratio (L/D ratio). ...

25

If you can forgive my limited Paint skills: It's the variable/constant speed that makes the difference. Weight changes endurance (time to ground) and not range (distance to ground) if speed is adjusted to match the new weight. Weight changes the speed for best L/D, but does not ever change the best L/D ratio (and thus best range) For gliders (which are ...

24

Unequivocally: no. Big airliners (or passenger planes of any size for that matter) do not hover in air. From a moving car, train or such it is possible to have an illusion that an airplane hovers midair, but someone who was claiming that they were standing still and witnessing an airliner hover in the air, was most probably deceived by one's senses. It ...

23

This would be possible with other fighter jets that are of similar design to the F-15, i.e. have a low aspect ratio, much of their lift produced close to the centerline, and a lot of control authority. They would also need the other two key ingredients for a landing of this kind: a strong aviator at the controls and a bit of luck. Specific contributing ...

13

You ask: If the engine can spin the propeller fast enough, why does it need power behind it? Good question. However, the answer is in the if of your question. A propellor does work - it pulls (or sometimes pushes) the aircraft through the air. In order to move the aircraft at a useful speed (or even at all) it has to spin pretty fast. The faster it ...

12

There are a couple of sources of loss throughout the process, as indicated in the figure from an old paper format uni book. I've had to translate the labelling, open to suggestions there. The percentages are valid for a high bypass turbofan manufactured in the late 80s. The total energy input starts with the fuel flow: chemical energy per second. Combustion ...

12

Though your photos refer to a specific commercial airliner, your question is general, so I will describe a more specialized use case for speed brakes. A glider (also known as a sailplane) has no engine, and it is designed to have a very high glide ratio so that it can travel further between sources of lift. If a glider were to come in for a landing without ...

12

There are advantages in the blades not being "perfectly identical". If all the vibration frequencies were exactly the same, when the blades were assembled to make the complete fan the vibrations would be coupled together and the blades could resonate with a large amplitude, causing increased noise and potentially reducing the life of the blades because of ...

10

Maybe wings never mattered... Altitude: The answer depends a bit on the design of the craft in terms of control surfaces/wings. Atmospheric reentry begins at the Karman line at an altitude of 100 km (62.14 mi / ~ 54 nautical mi) (327,360 feet) above the surface. Which is generally when air resistance starts to matter but that does not mean control surfaces ...

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

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 ...

8

Two of the given answers - choices (2) and (3) - are correct in different reference systems. It depends on the reference system of the observer: In a non-accelerated reference system, centrifugal forces do not exist. Increasing angle of attack increases the centripetal force, that increases the turn rate. The reaction force of the centripetal force is the ...

7

Turning Rate All planes flying a turn in line-abreast formation are turning at the same rate $\omega$. A standard turn is commonly defined as $\omega_1 = 3°\frac{1}{\mathrm{s}}$. Full Circle Time Period If planes are turning at the same rate, the time period to complete a complete circle will be the same as well. Time period: $$T(\omega) = \frac{360°}{... 7 While it is true that copper is 1.6 times more conductive than aluminum per volume, Conductivity in \frac{\mathrm{MS}}{\mathrm{m}} = \frac{\mathrm{10^6}}{Ω\,\mathrm{m}}: copper: 56 aluminium: 36$$\frac{56}{36} = 1.56$$aluminium is 2.1 times more conductive than copper per weight. Density in \frac{\mathrm{g}}{\mathrm{cm^3}}: ... 7 I'll do this without most of the math since your target audience won't want to read equations in your story. In the simplest terms, the maximum speed of an airship occurs when the maximum thrust generated by its engines is equal to the drag it experiences while being pushed through the air at that speed. That drag depends on the diameter and length of the ... 7 As a partial answer to your question, air moving over a stationary (relative to the ground) wing will generate lift. There have been several weather related incidences where aircraft were picked up off the ground by significantly strong winds. Videos of these incidents showed that it was lift and not force from form drag that lifted the aircraft off the ... 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 A meaningful numeric value is going to be hard to calculate, because so much depends on the aircraft you're working with. In practice, if I can pull off power at the calculated Top of Descent point, descend, meet any ATC crossing restrictions, fly the approach, configure as late as possible, and push up the power right at the point where I'm required to be ... 6 the further apart the engines are, the worse becomes the yaw in an engine-out situation. but spacing them (and their fuel tanks) further apart along the span of a wing allows more even distribution of load stresses. 6 I think what you seek is called the stagnation pressure, which is the pressure rise experienced in a given parcel of air if all the kinetic energy associated with that parcel's velocity were to be converted without losses into potential energy (stored work) of compression according to the ideal gas law. The equation for stagnation pressure is$$ \frac{P_\...

6

As you can see on the photo, the flaps are slightly extended, allowing the aircraft to fly at a lower airspeed. This is common for aircraft to do during an approach, to keep a constant distant between incoming flights. An aircraft flying into an airport, can perform a continuous descent or a step down decent. Illustrated in the figure below: From the figure ...

6

Before I get into the question about the turning fighter jet, a few words about airplanes' being extremely sensitive to gusts during final stages of landing. If this was actually true, I'd be dead by now. Seriously. Airplanes are sensitive to gusts during landing, I'll give you that, but I think it's exaggerating beyond reason to say it is extreme. Now, ...

6

A plane requires air moving over the wings to generate lift. If there is no air movement, there is no lift, and the plane will fall. Note that this requires that the plane is moving relative to the air, but not necessarily relative to the ground. In theory, you could have a plane pointed into a very strong wind that would have an airspeed sufficient to ...

5

I know those things as squirrel cage blowers. As the video says, they are a good choice if you want to move a moderate amount of air without exposing rotating blades. Impeller, by the way, was initially the word for a sort of airscrew that is moved by the flow. The small thingy in the nose of the Me-163 rocket interceptor was an impeller and needed for ...

5

Let's first address OP's first question: What is an acceptable settling time for the phugoid mode in a large aircraft? Phugoid is a hands-off (i.e. pilot and autopilot off) rigid-body mode, with or without Stability Augmentation System. MIL-STD-1797B specifies a damping ratio of at least 0.04 for Level 1 handling quality. The typical phugoid period is ...

5

The $I_{xz}$ moment of inertia is a measure for how the weight is distributed in the xz plane. You can obtain it by multiplying a unit of mass $dm$ by its distance in $x$ and $z$ from the center of gravity and taking the negative of it. For discrete masses (blocks of mass) it looks like this:  I_{xz} = \{-(x_1 \cdot z_1) \cdot m_1\} + \{-(x_2 \cdot z_2) \...

Only top voted, non community-wiki answers of a minimum length are eligible