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" ...


39

Those are called "Lightening Holes". The name refers to the weight reduction brought about by removing part of the material—lightening—and should not be confused with anything to do with electrical discharge—lightning. From the FAA's AMT Airframe Handbook, in Chapter 4, page 4-82: Lightening holes are cut in rib sections, fuselage frames, and other ...


31

Surface 1 is a horizontal stabilizer with elevator, just the same as on any other aircraft with a T tail arrangement. Surface 2 is called a rear strake or a tail fin. There is one on each side of the fuselage. They provide extra stability during operation at high angles of attack when the fuselage is disturbing the airflow to the vertical tail. They are ...


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 ...


19

All quotes in this answer are from the English translation of the BEA accident report. The elevator cable broke at "an altitude estimated at between three and four hundred feet",(p. 7) and there were eleven seconds between that time and the point of impact. If it had happened higher, the pilot would potentially have had time to figure out what happened and ...


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 @...


14

There are five sets of pitot tubes on the 737, organized into two groups, the pitot tubes on the nose are used for airspeed measurements, independent for the pilot and copilot and one as a backup. There are two pitot tubes on the tail that are for the "elevator feel and centering unit" (pdf; page 8). The elevator feel computer provides simulated ...


13

There is no "horizontal stabilizer" on the Concorde like other commercial aircraft, the wing performs that duty because it is a delta-wing. The elevators for the Concorde are combined with the ailerons into something called "elevons" which perform both functions (Think stereotype paper airplane). Note: Elevators and Horizontal stabilizers are not the same ...


13

Flaps which only extend over part of the wing will cause lift changes mainly over that part of the wing, which will result in a lift distribution over span which is far from the elliptic ideal once the flap is deflected. Therefore, it makes sense to move the ailerons in the same direction, especially when the inboard flaps are simple camber-changing flaps. ...


11

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

Several good reasons depending on the design and intent of the aircraft: Mechanical simplicity. In your case of "flaperons", having a single set of control surfaces do two things decreases the number of moving parts the plane has. Simple is best; the simpler your aircraft, the less can go wrong (and the lighter it is, and when you're trying to get something ...


8

Of course it creates a pitching moment! Now we need to define around which reference point this moment should be measured. If the reference point is the center of gravity, it is even equally strong as the pitching moment of the elevator, it only has the opposite direction. If you use the aerodynamic center as the reference point, the moment will be less ...


8

MCAS uses stabiliser input to retain full elevator authority in both directions for pilot input. MCAS is set up as an Inner Loop autopilot: it controls behaviour around the CoG of the aeroplane without displacing the cockpit flying controls. For aeroplane pitch control there are indeed two options: the stabiliser and the elevator. If the elevator is chosen ...


8

Moving each part has different effect on drag: Moving just the elevator increases camber, producing large force which is useful for manoeuvring, but it also produces more drag. Moving the whole stabilizer, keeping the camber low, produces less drag for the same force, which is good for cruise efficiency. That's why the elevator is used for control and the ...


7

An All-Moving control surface is a surface where the complete structure acts as a stabilizer. For example, in case of a horizontal tailplane which can be completely moved to work as an Elevator - instead of just the trailing edge of the horizontal tailplane moving to work as a control surface. In such cases, it is called a Stabilator (Stabilizer + Elevator). ...


7

For a small RC plane that travels at slow speeds your design would work great. However these type of designs have structural limitations. For an all movable vertical and horizontal stabilizer setup all the forces exerted on the control surfaces would be transferred to a movable bearing. This would be a single point of failure if the bearing were to fail. ...


7

There are many factors going into the sizing of elevators, and they are all interconnected with other considerations such as CG envelope, static margin, flight controls, etc. Here are some factors that will influence up-sizing the elevators. Usually, the minimum elevator sizing is determined by low speed requirements: Ability to perform early rotation in ...


7

When I was type rated in the CRJ200 with hydraulic controls and a THS, directly coming from light aircraft, the differences in technique are significant and it was definitely something new to learn. With a THS, column neutral is always the same spot. This means trimming to a speed is not a case of moving the control to location X and trim until it stays at ...


7

The tabs themselves are not locked -- that lock you mention is upstream: an input lock. Next time you sit next to the wing, watch the aileron as the pilots check the controls and notice how the tab moves opposite (alternatively, and rewindable, you can watch it here). With the input locked, the tabs are free to move without directly feeding back into the ...


6

There are a number of scenarios that I can see happening, most of which depend on the aerodynamics specific to the aircraft. Scenario 1: Nose Down Force > Up Force I believe this to be exactly what happened in this instance. What happens is that the downward deflected elevator overpowers the upward deflected elevator creating more down force than up force....


6

You need more than the correct elevator incidence. Natural longitudinal stability works by distributing lift over the flow direction such that forward surfaces create proportionally more lift than rear surfaces. Now it is important to know that only pure supersonic lift will be evenly distributed over the chord length of a wing. In subsonic flow the center ...


6

Yes, both are equal for small angle changes. Exceptions do apply, especially in transsonic flow. Both changing the stabilizer incidence and the elevator deflection will change the lift distribution between wing and tail surfaces and will trim the aircraft for a different angle of attack. Changing the incidence gives the empennage a new angle of attack while ...


6

Incidence is the angle at which an aerodynamic surface is mounted to the remaining structure of an aircraft. Variable means that this angle can be changed in flight. Normally, a control surface is split between a forward part, called the stabilizer, and the rear part, called the elevator. On aircraft with less powerful wing flaps, the stabilizer incidence is ...


6

Drag is one main reason, as outlined in @JanHudec's answer; the other one is maneuverability given the fairly wide CG range that exists on modern transport category aircraft. Without horizontal stabilizer, elevator may be insufficient for maneuvering at forward CG. One probable limitation would be the compliance with 14 CFR 25.107(e)(3) and (4), where prompt ...


5

Normally not; details depend on the control system and by how much the aircraft is out of trim. The force produced by the empennage will be the same in the trimmed state and when out of trim, only the control forces are different. Let's examine the different possibilities: Adjustable spring (as used on some light aircraft and gliders): The elevator ...


5

In my checklists, I am required to "set trim for takeoff" in the engine run up. What is the point of this step if that trim setting doesn't hold the proper attitude for not falling out of the sky? A major cause of accidents on take-off and landing is a stall followed by a spin. A wing stalls when it reaches the critical angle of attack, which is much ...


5

Further speculation: Fewer control surfaces overall means fewer moving parts, less mechanical complexity, less weight, possibly less drag, and so forth. The downside is that the control system must allow the combined control surfaces to be controlled in a way that makes sense to a pilot. This can be done mechanically, but especially in aircraft that are fly-...


5

You're absolutely correct, camber equals curvature. The camber of the horizontail tail is changed by deflecting the elevator, not the camber of the elevator itself. And yes the local angle of attack changes when the elevator deflects, resulting in an aerodynamic moment.


5

The angle of attack is lower for the faster flying aircraft. More speed means more dynamic pressure, and in order to create the same lift (weight did not change, after all), less angle of attack is needed to create the needed amount of lift. Now it is important to know that the angle of attack (more precisely, the difference between the actual and the zero-...


5

It depends, partially on what you precisely mean with "trim". Pilots use a rather narrow definition where trimming means to zero the control forces for a specific control surface deflection and speed. This is achieved by tabs or springs in the control linkage. Engineers use it more broadly and include the ability to deflect control surfaces such that the ...


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