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" ...


35

The Dunne D.8 used a pair of levers, each controlling one elevon.


32

A cruise missile is rocket or jet powered and flies to its target within the atmosphere, using lift to stay up. Most have wings, although a few may use lifting body designs. They maneuver using control surfaces on the wings and tail like an airplane. Mission profiles can include big course changes, to evade air defenses, or to hug terrain to stay hidden. ...


28

Short answer: Canards make most sense with negative static stability and high maneuverability. Commercial aircraft don't need either, so a conventional layout works best. For a statically stable aircraft, the conventional layout gives most efficiency with sufficient damping. Static stability requires that the forward lifting surfaces create more lift ...


27

Good question! There's a bit of a misconception: when the elevon moves up, it actually decreases lift. It pushes air up which pushes the wing down. This explains the roll behaviour, but how does decreasing the lift make the plane go up? The key here is that the lift is reduced only at the rear of the plane. In other words, the rear of the plane is pushed ...


25

What is better and easier for small-scale models is not necessarily better for larger aircraft. First, you can't say that the fixed part "does nothing". The tail is primarily a stabiliser; without it, a normal airplane will not fly at all. Only then it is a control surface, which allows it to fly well and how you want it. Consequently, the size of the tail ...


23

Short answer: Rudder and ailerons have different purposes and control rotation about two different axis, but their use is coordinated since a rotation about one axis induces a secondary rotation on the other one. The rudder use is mostly to prevent unwanted yaw movement for safety and comfort, or to force yaw against the aircraft tendency to keep the ...


23

They look like spoilers but are more precisely called drag rudders. They are not meant to reduce lift like regular spoilers, but increase drag in order to create a yawing moment. Regular aircraft have a vertical tail for yaw control. Without this, you need some force acting at a lateral distance from the center of gravity for yaw control, and this is what ...


23

It isn't done because a moving control surfaces is easier to design and build than an engine mount that rotates. Plus the associated structure needed to accommodate the thrust, p-factor, and gyroscopic loads is going to be a lot heavier than ailerons, spoilers, moving tail plane, etc. Another issue is if one loses one or both engines, your roll and pitch ...


22

Cruise Missile : Uses thrust for the whole trajectory Uses aerodynamic forces by moving control surfaces to move. May use thrust vectoring Ballistic Missile: Uses thrust to reach very high altitude. After that, no thrust, only potential energy is used and converted to speed. Uses aerodynamic forces (for a limited extent) to move by deflecting control ...


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

Theoretically it could work that way. A maneuver that needs a certain control surface deflection for a certain amount of time could be done with full 30 degree deflection in a shorter time. Fine control and trimming would be more difficult. Small adjustments would require a very short time at full deflection. Control laws would have to take into account the ...


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

You basically have the answer right inside of the question (as was mentioned in the comments). In order to make the plane pitch up and down you have the ailerons move up or down in unison (usually called an elevon at that point, again, as noted in comments.) Here's a handy diagram to give you some idea of what we're on about: In the second image the ...


16

The canards on the Tu-144 weren't canards technically. They were static surfaces, not moving. They were purely lift devices to improve low speed handling (and thus help reduce landing speed which was excessively high). These were added because low speed handling was found to be deficient, due to the inferior (as compared to Concorde) wing design.


16

The early wright glider (1902) had its rudder connected to the wing warping system. they connected the rudder control cables to the wing-warping hip cradle, so a single motion by the pilot operated both controls. They also changed the original double rudder to a single rudder, as shown here. The wrights also used a hip cradle to move the wing ...


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 ...


15

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 ...


13

Cruise missiles have rocket or jet engines that are powered during the entire flight. It allows the missile to cruise low through the atmosphere, sometimes just above ground level. Lift and guidance of the missile are achieved by aerodynamic forces. Ballistic missiles on the other hand are not powered during most of their flight. During the launch they ...


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 ...


12

Control authority is a function of the local dynamic pressure (the product of air density and speed squared), geometry (the product of control surface area and lever arm), local angle of attack $\alpha$, the angle of deflection $\eta$ and the relative flap chord. Generally, the control surface works fairly linearly in a range between $-15° < \eta < 15°$...


12

Because it is not aerodynamically efficient. To achieve stability the forward surface has to fly at higher angle of attack than the rear. So the canard has to fly at rather high angle of attack which leads to high drag and disrupts airflow for the main wing further reducing it's efficiency. It is not a chance that most modern jets have the same layout. It is ...


12

Please let me assume that you wonder about control surface effectiveness rather than their efficiency. Both are closely related, but I prefer to address their effectiveness - doing what the pilot demands them to do. The aerodynamic forces are proportional to the dynamic pressure $q$ of the flow, which is density times velocity squared, as in $$q = \frac{\...


12

The aerodynamic forces resulting from surface deflections are orders of magnitude larger and faster (in their rate of change) than the gravitational forces obtainable by shifting the centre of mass. Additionally, as OP seems to realize, yaw control would not be feasible with this method. So overall it would not be impossible, but it has no clear ...


12

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 ...


11

For statically stable aircraft, the canard is a spoiler in disguise. It will create a strong downwash right behind itself, coupled with an upwash outward of $\pi$/4 of its semispan. With changing angle of attack and lift coefficient, the vertical position and the strength of both up- and downwash will change, so the wing incidence variation over wingspan can ...


11

Yes it is a viable way for roll control - aerodynamically that is. The mechanism you describe is a proper servo tab, where the aeroforces on the tab are fed back, and the tab acts like a lever on the main control surface. This was the way the post WW2 airliners were controlled, before they got too big and fast and only hydraulics could do it. However, as ...


11

I once had a very cheap electric ducted fan styrofoam RC plane that I found for sale at Woolworths sometime in the 90s that had "bang bang" flight control surfaces and throttle. In lieu of servos, it had a very light, weak solenoid with the control rod as its core. I was a novice, but was able to get it to 'fly' a maximum distance of 20ft, bank either left ...


11

It depends on the aspect ratio of the wing and the lift coefficient. Short, stubby wings at low angle of attack will not create much adverse yaw with aileron input, especially when the ailerons have differential linkage (more deflection on the trailing-edge-up side and less on the opposite side). Differential gearing is also beneficial in reducing stick ...


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