53 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 ...
John K's user avatar
  • 131k
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 ...
Peter Kämpf's user avatar
36 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.
Pilothead's user avatar
  • 20.1k
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 ...
Sanchises's user avatar
  • 13.3k
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,...
Zeus's user avatar
  • 9,063
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 ...
Romeo_4808N's user avatar
  • 73.7k
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 ...
Zeiss Ikon's user avatar
  • 17.1k
24 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 ...
mins's user avatar
  • 72.9k
21 votes

Why isn't the rudder below the tail?

It is bad to put things below the tail because they might hit the ground. Even with nothing below the tail sometimes there is still a tail strike. http://avherald.com/h?article=42b2d053
Anonymous Physicist's user avatar
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 ...
Koyovis's user avatar
  • 61.7k
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 ...
Peter Kämpf's user avatar
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 ...
Peter Kämpf's user avatar
17 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 ...
fooot's user avatar
  • 73.2k
17 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 ...
Mr. de Silva's user avatar
16 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 ...
Dave's user avatar
  • 101k
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 ...
John K's user avatar
  • 131k
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 ...
HiddenWindshield's user avatar
16 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 ...
John K's user avatar
  • 131k
16 votes

Why isn't the rudder below the tail?

The MQ-1 Predator does have a V-tail ruddervator below the tail. Does the Predator drone's design make a tail strike more likely on takeoff and landing? The MQ-1 is already at high risk of a rear ...
Anonymous Physicist's user avatar
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 ...
Jpe61's user avatar
  • 28.7k
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 ...
Peter Kämpf's user avatar
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 ...
John K's user avatar
  • 131k
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. ...
AEhere supports Monica's user avatar
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 ...
Bianfable's user avatar
  • 55.9k
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 ...
John K's user avatar
  • 131k
13 votes

What is the difference between a trim tab and a servo tab?

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 ...
John K's user avatar
  • 131k
13 votes
Accepted

How do tailless aircraft yaw?

Technically the B-2 bomber has rudders, they are "drag rudders" (or split rudder) and are located on the outer portion of the wing: Source: Quora The rudders open in a clamshell ...
Ron Beyer's user avatar
  • 36.2k
13 votes
Accepted

Under what circumstances does the F-16 and possibly similar fighters deploy leading edge slats?

Technically, F-16 and "similar fighters" have leading edge flaps (LEF) (or droop flaps), rather than slats. The difference is that they don't form a gap between themselves and the main ...
Zeus's user avatar
  • 9,063
12 votes
Accepted

Will control surfaces on a plane be less efficient at a higher altitude?

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 ...
Peter Kämpf's user avatar
12 votes

Can an airplane fly with on-off control surfaces?

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 ...
slomobile's user avatar
  • 123

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