54

It generally means that the hydraulic actuator (power control unit) driving the surface has an "idle" facility that allows fluid to move internally between the two sides of the actuator piston, or just circulate in the pressure/return lines, and when unpressurized it acts more or less like a hydraulic damper even though the input spool valve is at its "null" ...


20

Surfaces sticking out ahead of the Centre of Gravity act in an unstabilising manner: any dissymmetry will want to amplify itself. A dart thrown with the feathers first is in an unstable equilibrium and will very quickly turn around 180º. Surfaces behind the CoG act as stabilisers, keeping the nose pointing forward. An aeroplane has vertical and horizontal ...


18

@John K's answer is perfect. However, in other mechanical systems such as elevators, fork-lifts, factory machines, etc and also NON hydraulic systems (and also possibly Jets) it is designed to be so so that when the machine is idle/switched-off the system is in a 'non-stressed' state or in a 'safe state'. The keywords are 'design' and 'requirement'. As @...


16

Acme screw type screw jacks with the square threads, as used in stab trim systems (as opposed to a recirculating ball screw), are usually inherently irreversible because of the higher friction of the direct sliding contact of the square sided threads vs a rolling ball interface (as a sliding interface, it's totally dependent on the grease to keep friction in ...


15

Screws can be either self-locking or overhauling. Jackscrews used for stabilizer control are designed to be self-locking, since their purpose is to make the stabilizer adjustable, but prevent it from moving by itself. A jackscrew (or screw jack) is pretty much by definition a self-locking screw. It should be noted that vibrations can induce travel in ...


13

The bungee is just a bidirectional spring that tends to hold the elevator at position x, and if you move the stick you are stretching the spring in one direction or the other. They are used in the elevator control circuit to provide an adjustable centering force for trim purposes, and on gliders with all flying tails, a measure of stick free static ...


13

A Boeing 737 has a movable horizontal stabilizer for pitch trim with elevators for pitch control (also known as a THS – Trimmable Horizontal Stabilizer). This is true for all 737 variants, including the MAX. Note: The term stabilator is typically used when the entire tail is rotated for pitch control, like e.g. on a Piper Cherokee. The following image (...


13

A trim tab is operated by an independent control to a variable position that is normally fixed once set, unless readjusted, and is done to cause the control surface to aerodynamically want to hold a position that is different from its normal "trail" position, without any input from the cockpit end. Think the typical elevator, aileron, or rudder trim used to ...


11

From Wikipedia: The Rockwell B-1 Lancer has small canard vanes or fins on either side of the forward fuselage that form part of an active damping system that reduces aerodynamic buffeting during high-speed, low altitude flight. Such buffeting would otherwise cause crew fatigue and reduce airframe life during prolonged flights. Having a traditional ...


11

In general, an engine fire in a modern jet airliner should not cause a loss of control. Even though engine fires are rare, pilots are highly trained in dealing with them. Once detected, pilots are able to cutoff the supply of fuel and hydraulic fluid to the engine, and then discharge fire extinguishing agents. Even if the fire was not extinguishable, it ...


10

This is a safety feature. You don't want the airplane to blow over in a strong wind. With the elevators down (as you see them in the pictures), a gust from the front will push the plane's nose down and keep the main wing from generating lift. A gust from behind will push the nose up, but in this case, the main wing will present its top surface to the gust,...


10

Yes, that will work. If the entire wing tip pivots, it simply acts as an aileron that takes up the entire chord of the wing. Other alternatives to ailerons include: Weight shifting. If you can shift the aircraft's center of mass left and right a significant amount, thus will cause the aircraft to roll in the same direction. This is how hang gliders turn. ...


8

We don't know - until we hear about such a case! A positive answer would require a trace of MCAS action sufficient evidence that the pilot could not have handled the (near) stall without MCAS. This information could come from a pilot who notices the trim interference, and perceives the situation as dangerous, and reports the event or a flight ...


8

There is more to it than just looks. One immediate benefit is a more backward location of the center of pressure on the backwards swept surface. But that effect is small and has to be bought with a lower lift curve slope, i.e. lower effectivity at low angles of attack rsp. sideslip. But once sweep is big enough, it will extend the useable range of sideslip ...


8

Yes, that is correct. Moving any control surface until you hit the stops is considered "full deflection". For the purpose of maneuvering speed, this is the speed at which any single control surface can be fully deflected without risking damage to the control surface or structure. Pitch is full back/forward on the yoke or stick, which is where the elevator ...


7

As per the A320 flight manual (§127.20 p3), the maximum permitted total pitch alteration in normal law depends upon speed, aircraft mass, CoG, and other factors: Pitch Attitude Limitation: Pitch attitude is limited to: 30º nose up in conf 0 to 3 (progressively reduced to 25º at low speed) 25º nose up in conf FULL (progressively reduced ...


7

The top wing is always the most efficient, as the lower ones suffer reduced lift due to interference from the air flowing beneath the one above. Ailerons will therefore be most effective on the top wing. If they do the job OK then there is no need for any more. Reasons for adding more below include: The upper set are likely to be (or found to be) inadequate....


7

You have to have some way of holding the surface at other than where it wants to naturally trail in the airstream. Your options: Hold it yourself with control pressure. Becomes a pain after a while. Some very simple homebuilt designs don't have any pitch trimming device and they have only one trim speed where they will fly hands off, the trim speed more ...


6

The details will depend on the exact aircraft type, so I will answer for the Bombardier Dash-8 Q400 as an example. The autopilot does not have rudder authority on the Dash-8 (source: FCOM Autoflight chapter): 12.3.7 Autopilot The Autopilot (AP) couples the FD commands to the flight control surfaces using pitch and roll servos for automatic control ...


6

1. Aeroelasticity Unlike a tailplane, a delta wing is more rigid due to its much bigger chord and multiple spars, so control reversal due to aeroelasticity isn't a special concern. Big subsonic jetliners typically lock the outer ailerons at high speeds. Concorde featured a similar function for the outer elevon, but only if $V_{MO}$ is exceeded by 25 knots ...


5

The main downside of flaperons is you can't lower them as much as a regular flap because it has to still do its aileron function when "flaps down". This means the downgoing flaperon has to be limited to its "lift generation" range when the flaperon mixer is moving it to full down flap plus full down aileron, and can't exploit the "drag generation" range of ...


5

JohnK is right, they are helping to trim the aircraft. But there is more to them. Ideally, if you want to modify the hinge moment of a control surface, you would add a Flettner tab (in order to decrease control forces, like done on the SB-10 rudder) or an Anti-Flettner tab (in order to increase them, like on the Diamond DA20 Katana elevator.). No bungee or ...


5

That would be the correct control response for a combined roll to the right and nose up pitch command from the pilot. It looks like that photograph was taken while the pilot was in the middle of doing a check of their control services prior to taxi. You can see similar results in the tower buzz sequence out of Top Gun. The final bit shows an F-14 from the ...


5

The pilots do not manually trim an Airbus in pitch. The flight control computers provide automatic trim: The normal-law flight mode is a load-factor-demand mode with automatic trim and protection throughout the flight envelope. Following normal law, the sidestick controllers set the elevators and THS to maintain load factor proportional to stick ...


5

Different aircraft and manufacturers take very different approaches. 1. Boeing 777 The B777 has three Primary Flight Computers (PFC) that are responsible for flight control laws computation and four Actuator Control Units (ACE) that are responsible for the closed-loop control of their responsible flight control surfaces. The ACE is primarily an analog ...


5

Thankfully, aerodynamics in the usual flight range is linear. Therefore, there is a gradient of lift over angle of attack and another one over the flap deflection angle. Both are constant over a range of maybe ±15° and can be combined. The angle of attack is referenced to the fixed part of the flight surface and the deflection angle to the moving part ...


4

There are different degrees of control. The plane could at least be made to crash in a different debris pattern than if the input was not made, and even that's a form of control. As the whether the plane could be controlled enough to land, and do so, as the question states, with all of its control surfaces disabled, let's see. You get considerably pitch ...


4

Most airlines have a Flight Data Analysis section which uses the routine download of the FDR to automatically flag deviations from the normal flight profile for investigation. The kind of maneuvering that would activate MCAS would vastly exceed the typical limits and be subject to a detailed investigation. Most of the 737 Max FDR do have provision for ...


4

Can't speak for the Lear, which I believe has manual controls anyway, but the CRJs DO NOT have manual reversion. The RJs are designed to a technical level similar to the Boeing 767. The control surfaces are purely hydraulically operated. For elevator and rudder, which have 3 PCUs each, you'd have to lose all 3 hydraulic systems to lose the surfaces. For ...


4

The maneuvering speed is the maximum calibrated airspeed at which - starting from straight and level flight - you can safely move any single flight control from the neutral position to the maximum deflection possible at that airspeed. What constitutes full deflection varies from aircraft to aircraft, and also - frequently - with airspeed. At low speeds, it ...


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