Rudder Calculations and Manoeuvrability

Rudder Maneuverability 4


Structurally, empennage contains entire tail assembly including tailplane, tailfin, and fuselage. The front part of the tailplane provides pitch stability. The elevator controls changes in pitch. In some cases, aircraft employ all moving stabilizer, and, the elevators contained in one unit called the stabilator. The vertical structure of tail has a fixed front section known as vertical stabilizer, which is used to restrict yawning. The rudder in the rear section of the vertical stabilizer used to turn the aircraft’s nose to one side.

Trim devices introduce maintenance of constant pressure on the rudder controls in some aircraft. The trim devices act to change the aerodynamic load on the surface. In aircraft that have multi-engine trim tabs on the rudder reduce the effort of a pilot required to keep it straight in asymmetrical thrust situation in single engine operations. Some elevators and stabilators are trimmed by anti-servo tab to increase the feel of control force as suggested by (Spyrou, 1994). The configuration of the fin and tail empennage of the aircraft leads to further classification. Also, the individual shape of the tail surface is similar to the surface of the wing platforms. The V-tail and X-tail designs contribute to pitch and yaw. The control surfaces act together to provide the control of the yaw. Indeed, the V-tail is lighter than a conventional tail to generate less drag. X-tail is fitted with a wheel to allow the craft sit on its tail to land and take off vertically.

Advantages of conventional rudder configuration

The tail is lighter in structure to have less wetted surface area compared to the conventional configuration of the tail reducing the drug. To some extent, they increase stealth. The engine of V-tail is placed outside the fuselage to improve safety and reduce noise of the cabin.

Limitation of conventional rudder configuration

The rudder requires more complex control system as both the surfaces has to be linked together. The surfaces have to be robust in their structure due to the increased load to reduce the elimination of the controlled surface.

A rudder is a device that is used for steering and maneuvering a vessel. Rudders are located behind propellers at the stern to produce a transverse force and steering moment about the center of gravity for the ship; this deflects the flow of water to the foil plane direction. Five different types of rudder include:

  1. Spade or Balanced rudder

A balanced rudder is a rudder plate fixed to rudderstock at the top of the rudder. This type of rudder does not run down alongside the span of rudder. The rudder stock position alongside chord of rudder determines whether the rudder is balanced. According to (Spyrou, 1994) the rudderstock in balanced rudders is at a position such that forty percent of the rudder area is at the forward of the stock and the rest is at its aft. The position at the chord is chosen because; the gravitational center of rudder is placed near the location. The torque that is required to rotate rudder will be lesser than the required force to move it. The energy required to steer the gear equipment reduces, hence lowering the consumption of fuel.

Rudder Calculations and Manoeuvrability

  1. Unbalanced Rudders

Unbalanced rudder has attached stocks at the forward most point of the span. The rudderstock runs alongside the length of rudder. For this case, the torque required in turning the rudder is higher than the required corresponding rudder. In this juncture, the topmost part of the rudder has fixed to the spintle to prevent vertical displacement from its position.
Rudder Calculations and Manoeuvrability 1

  1. Semi- Balanced Rudder

In the modern industry, the rudders mostly used are semi-balanced rudders. In this category, the rudder is partly balanced and partly unbalanced. The top part of the conventional rudder is un-balanced to help in acting like a structural support to the rudder in vertical displacement. Conversely, the balanced part will render less torque in swinging the rudder. Semi balanced rudder returns to the orientation of the centerline resulting to failure of the steering gear when making a turn.

Rudder Calculations and Manoeuvrability 2

  1. Flaps Rudder

In flaps rudder, the flaps are not retractable and they have their essential effects in giving the rudder some angle of attack. Flaps rudder, change effective angle of attack of the aero foil wing section. During the take-off, the flaps are deployed completely to help maximizing the lift force by obtaining the angle of attack.
Rudder Calculations and Manoeuvrability 3

  1. Pleuger Rudder

Pleuger rudder has a smaller propeller located within it. The propeller generates a thrust in a direction oriented alongside the rudder, hence, allowing effective maneuver in a slow speed condition.

Rudder Calculations and Manoeuvrability 4


Spyrou, K. (1994) “A New Approach for assessing ship maneuverability based on decisions analysis and its practical application”, Journal of the society of naval architects of japan vol. 167, pp 267-280