54
votes
Accepted
Why do military jets sometimes have elevators in a depressed position when parked?
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 ...
- 117k
47
votes
Accepted
Why were the Space Shuttle's elevons reversed, early in re-entry?
For an explanation let me first explain hypersonic flow a bit. In super- and hypersonic flow, when a body moves through a fluid what changes foremost is not speed but density. At the high angle of ...
- 225k
37
votes
In the early days of flight, were there any cockpit control schemes other than the modern one?
The Dunne D.8 used a pair of levers, each controlling one elevon.
- 18k
33
votes
How are cruise missiles different from ballistic missiles?
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 ...
- 52.1k
30
votes
Accepted
Are the functions of ailerons and rudder similar?
Short answer:
Rudder and ailerons have different purposes and control rotation about two different axis. However a rotation about one axis induces a usually unwanted rotation on the other one. In ...
- 68.6k
27
votes
Accepted
How do elevons work to roll a flying wing?
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 ...
- 12.6k
26
votes
Accepted
Why don't commercial aircraft use all-movable tail surfaces like my RC plane?
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,...
- 8,855
24
votes
Accepted
What is the purpose of these odd "control surfaces" on the BAE Taranis?
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 ...
- 225k
24
votes
Accepted
Why aren't tilting propellers used as an alternative for ailerons or elevators?
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 ...
- 69.4k
24
votes
Accepted
Why do the ailerons of this flying wing work oppositely compared to those of an airplane?
Most likely the adverse yaw effect (due to the induced drag of the increased lift on the down-aileron side) is causing the wing to yaw the opposite direction from the intended roll, and the yaw causes ...
- 16.5k
23
votes
Accepted
How are cruise missiles different from ballistic missiles?
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....
- 784
23
votes
Why are the grid fins on Starship pointy and sharp?
Such design, with hyperbolic leading edges, has been invented by MBDA (Airbus branch for missile systems) represented by BAE Systems (defense contractor), and is described in the European patent 3 599 ...
- 68.6k
20
votes
Accepted
Is the location of an aircraft spoiler really that vital?
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 ...
- 60.7k
19
votes
Accepted
How are control surface problems in wings having high bending dealt with?
Flaps and ailerons are weak in bending and have multiple hinges along the span. Also, as you can see in the photo, the flaps are segmented which not only helps to optimize the deflection angle over ...
- 225k
18
votes
Can an airplane fly with on-off control surfaces?
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 ...
- 70.3k
18
votes
Why do military jets sometimes have elevators in a depressed position when parked?
@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 ...
- 281
18
votes
Accepted
Why are the red/white control surfaces under the wing extended during a take off?
These are not control surfaces, but a special type of split flap. In a split flap, the rear part (20% to 30%) of the lower wing panels is hinged at the front and can be lowered, thus increasing wing ...
- 225k
17
votes
In the early days of flight, were there any cockpit control schemes other than the modern one?
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 ...
- 98.1k
16
votes
Accepted
How is pitch controlled in a flying wing?
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 ...
- 23.9k
16
votes
Accepted
Do jackscrews suffer from blowdown?
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 ...
- 117k
16
votes
Why do the ailerons of this flying wing work oppositely compared to those of an airplane?
In some aircraft, such as the Canadair CP-107 Argus, the control yoke is not actually connected to the ailerons. Rather, they are connected to servo tabs, which are basically small ailerons attached ...
- 11.9k
15
votes
Do jackscrews suffer from blowdown?
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 ...
- 25.5k
14
votes
How are cruise missiles different from ballistic missiles?
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 ...
- 77.1k
14
votes
Accepted
What are the pros and cons of having canard control surfaces versus a horizontal tail control surface?
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 ...
- 225k
14
votes
Can all airliners be turned without rudder input?
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 ...
- 225k
14
votes
Accepted
How exactly do the Beechcraft 1900's stabilons work?
This Flight Safety Training Manual describes them as improving "deep stall" characteristics and C of G range.
The stabilons are fixed surfaces that add effective stabilizer area to improve ...
- 117k
14
votes
Accepted
Could a trim system conceivably manipulate only primary surfaces?
I assume by "primary surface" you mean the elevator, not the stabilizer, so we are not talking about moveable stabilizers.
Most gliders with stabilzer/elevators, and a lot of homebuilts and ...
- 117k
13
votes
Has anyone researched or built an aircraft that controls pitch and roll by pumping liquid within the airframe?
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.
...
- 8,498
13
votes
What kind of horizontal stabilizer does a Boeing 737 have?
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 ...
- 51.4k
13
votes
Why do gliders have bungee cords in the control systems and what do they do? Are they on all control surfaces? What about ultralights?
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 ...
- 117k
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