Balanced rudders are used by both ships and aircraft. Both may indicate a portion of the rudder surface ahead of the hinge, placed to lower the control loads needed to turn the rudder. For aircraft the method can also be applied to elevators and ailerons; all three aircraft control surfaces may also be mass balanced, chiefly to avoid aerodynamic flutter.
A balanced rudder is a rudder in which the axis of rotation of the rudder is behind its front edge. This means that when the rudder is turned, the pressure of water caused by the ship's movement through the water acts upon the forward part to exert a force which increases the angle of deflection, so counteracting the pressure acting on the after part, which acts to reduce the angle of deflection. A degree of semi-balance is normal to avoid rudder instability i.e. the area in front of the pivot is less than that behind. This allows the rudder to be moved with less effort than is necessary with an unbalanced rudder.
Balanced rudders were probably first used in the early 15th century, in Ming China's treasure ships [1] , and were reinvented and first used in modern ships by Isambard Kingdom Brunel on the SS Great Britain, launched in 1843. [2]
Control of aircraft is complicated by their motion in three dimensions, yaw, pitch and roll, rather than one but there is a similar need to reduce loads, tackled in the same way as on a ship with some part of the surface extending forward of its hinge. This is referred to as aerodynamical balance. In addition, because aircraft control surfaces are mounted on flexible structures like wings, they are prone to oscillate ("flutter"), a dangerous effect which can be cured by bringing the centre of gravity (c.g.) of the control surface to the hinge line. This is called mass balancing. [3]
The principle is used on rudders, elevators and ailerons, with methods refined over the years. Two illustrations of aircraft rudders, published by Flight Magazine in 1920, [4] illustrate early forms, both with curved leading and trailing edges. Both are mounted so that the area of the balancing surface ahead of the hinge is less than that of the rudder behind. Various layouts have been tried over the years, generally with smaller balance/rudder areas. Most fall into one of two categories: horn balanced, with small extensions of the control surfaces ahead of the hinge lines at their tips, or inset balanced with extension(s) of the control surface into cut-outs in their supporting fixed surface. Frise ailerons use a variant of the latter balance, with the nose of the up-going surface projecting below the wing, but not vice versa, to provide both balancing and asymmetric drag. Irving balanced ailerons have no projections but harness the aileron deflection induced change of pressure above and below the wing, sensed via the hinge gap, to assist the motion. [3]
Flutter occurs when the control surface is displaced from its intended deflection. Because the ailerons are on the long, narrow wings which can twist under load, they are the surface most prone to oscillate. If the centre of gravity is behind the hinge, the surface can move like a pendulum and undergo forced simple harmonic motion with increasing amplitude. Adding balancing weights which make the centre of gravity and hinge line coincident solves the problem. These weights may be in the nose of the surface, or lighter masses attached further ahead of the hinge externally. [3]
A tailplane, also known as a horizontal stabiliser, is a small lifting surface located on the tail (empennage) behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed-wing aircraft such as helicopters and gyroplanes. Not all fixed-wing aircraft have tailplanes. Canards, tailless and flying wing aircraft have no separate tailplane, while in V-tail aircraft the vertical stabiliser, rudder, and the tail-plane and elevator are combined to form two diagonal surfaces in a V layout.
An aileron is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll, which normally results in a change in flight path due to the tilting of the lift vector. Movement around this axis is called 'rolling' or 'banking'.
Aeroelasticity is the branch of physics and engineering studying the interactions between the inertial, elastic, and aerodynamic forces occurring while an elastic body is exposed to a fluid flow. The study of aeroelasticity may be broadly classified into two fields: static aeroelasticity dealing with the static or steady state response of an elastic body to a fluid flow, and dynamic aeroelasticity dealing with the body's dynamic response.
In flight dynamics a spin is a special category of stall resulting in autorotation about the aircraft's longitudinal axis and a shallow, rotating, downward path approximately centred on a vertical axis. Spins can be entered intentionally or unintentionally, from any flight attitude if the aircraft has sufficient yaw while at the stall point. In a normal spin, the wing on the inside of the turn stalls while the outside wing remains flying. It is possible for both wings to stall, but the angle of attack of each wing, and consequently its lift and drag, are different.
Aircraft flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude.
A conventional fixed-wing aircraft flight control system (AFCS) consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. Aircraft engine controls are also considered as flight controls as they change speed.
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's pitch, and therefore the angle of attack and the lift of the wing. The elevators are usually hinged to the tailplane or horizontal stabilizer. They may be the only pitch control surface present, and are sometimes located at the front of the aircraft or integrated into a rear "all-moving tailplane", also called a slab elevator or stabilator.
The empennage, also known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow. The term derives from the French language verb empenner which means "to feather an arrow". Most aircraft feature an empennage incorporating vertical and horizontal stabilising surfaces which stabilise the flight dynamics of yaw and pitch, as well as housing control surfaces.
Aircraft flight mechanics are relevant to fixed wing and rotary wing (helicopters) aircraft. An aeroplane, is defined in ICAO Document 9110 as, "a power-driven heavier than air aircraft, deriving its lift chiefly from aerodynamic reactions on surface which remain fixed under given conditions of flight".
Trim tabs are small surfaces connected to the trailing edge of a larger control surface on a boat or aircraft, used to control the trim of the controls, i.e. to counteract hydro- or aerodynamic forces and stabilise the boat or aircraft in a particular desired attitude without the need for the operator to constantly apply a control force. This is done by adjusting the angle of the tab relative to the larger surface.
A servo tab is a small hinged device installed on an aircraft control surface to assist the movement of the control surfaces. Introduced by the German firm Flettner, servo tabs were formerly known as Flettner tabs. Servo tabs are not true servomechanisms, as they do not employ negative feedback to keep the control surfaces in a desired position; they only provide a mechanical advantage to the pilot.
A vertical stabilizer or tail fin is the static part of the vertical tail of an aircraft. The term is commonly applied to the assembly of both this fixed surface and one or more movable rudders hinged to it. Their role is to provide control, stability and trim in yaw. It is part of the aircraft empennage, specifically of its stabilizers.
An aircraft stabilizer is an aerodynamic surface, typically including one or more movable control surfaces, that provides longitudinal (pitch) and/or directional (yaw) stability and control. A stabilizer can feature a fixed or adjustable structure on which any movable control surfaces are hinged, or it can itself be a fully movable surface such as a stabilator. Depending on the context, "stabilizer" may sometimes describe only the front part of the overall surface.
Adverse yaw is the natural and undesirable tendency for an aircraft to yaw in the opposite direction of a roll. It is caused by the difference in lift and drag of each wing. The effect can be greatly minimized with ailerons deliberately designed to create drag when deflected upward and/or mechanisms which automatically apply some amount of coordinated rudder. As the major causes of adverse yaw vary with lift, any fixed-ratio mechanism will fail to fully solve the problem across all flight conditions and thus any manually operated aircraft will require some amount of rudder input from the pilot in order to maintain coordinated flight.
An aircraft in flight is free to rotate in three dimensions: yaw, nose left or right about an axis running up and down; pitch, nose up or down about an axis running from wing to wing; and roll, rotation about an axis running from nose to tail. The axes are alternatively designated as vertical, lateral, and longitudinal respectively. These axes move with the vehicle and rotate relative to the Earth along with the craft. These definitions were analogously applied to spacecraft when the first crewed spacecraft were designed in the late 1950s.
In flight dynamics, longitudinal stability is the stability of an aircraft in the longitudinal, or pitching, plane. This characteristic is important in determining whether an aircraft pilot will be able to control the aircraft in the pitching plane without requiring excessive attention or excessive strength.
A flight control mode or flight control law is a computer software algorithm that transforms the movement of the yoke or joystick, made by an aircraft pilot, into movements of the aircraft control surfaces. The control surface movements depend on which of several modes the flight computer is in. In aircraft in which the flight control system is fly-by-wire, the movements the pilot makes to the yoke or joystick in the cockpit, to control the flight, are converted to electronic signals, which are transmitted to the flight control computers that determine how to move each control surface to provide the aircraft movement the pilot ordered.
The Junkers J 29 was a two-seat, single-engined experimental training monoplane, built in Germany in 1925. Its significance is that it was the first aircraft to fly and test the Junkers Doppelflügel control surfaces used very successfully on the later Junkers Ju 52.
The Caudron C.25 was a large, three-engined, biplane airliner, designed and built in France soon after the end of World War I. Its enclosed cabin could accommodate up to eighteen passengers.
The Naleszkiewicz JN 1 was an experimental tailless sailplane designed in Poland to explore the aerodynamic properties of a proposed powered tailless aircraft. It proved hard to fly and a crash led to its abandonment after only a few months of limited testing.
Oscar Parkes British Battleships ISBN 0-85052-604-3