Business Travel Solution - Helicopter Anti-Torque Systems

Counteracting the effects of torque can be accomplished in one of three ways, for single rotor helicopters. The action of the rotors creates an equal and opposite reaction (the fuselage spinning opposite the direction of the main rotors), according to Newton's Third Law. When the helicopter becomes airborne the force of friction is removed and if nothing is present to counteract the torque force the fuselage will rotate in a direction opposite the rotors. If the helicopter is on the ground the friction between the helicopter's landing gear and the surface will prevent the torque force from spinning the fuselage. This rotation causes a torque (a rotational force). Which turns the rotor, the engine turns the drive shaft, in relation to helicopters. Torque is a measure of how much force acting on an object will cause that object to rotate. To understand torque and its effect on helicopters we need to reference Newton's Third Law of Motion which states for every action there is an equal and opposite reaction.

The tail rotor is comprised of two or four small airfoils that the pilot is able to control in the cockpit by manipulating the rudder (anti torque) pedals. The purpose of the tail rotor is to reduce the effect of torque and the yaw motions inherit in helicopter flight. A tail rotor is situated on the tail of a conventional helicopter. The first way to counteract torque is with a tail rotor.

Helicopters that use dual-rotor systems do not require the use of a tail rotor as the two rotors are designed to spin in different directions canceling out the yaw created by one another without the need for a tail rotor.

Which makes it much safer and also means less noise is generated, this system removes the tail rotor. NOTAR is a fairly new form of anti-torque system developed by McDonnell Douglas. The second way to counteract torque is with a NOTAR (No Tail Rotor) system.

Hughes Helicopters has since been acquired by McDonnell Douglas. However it wasn't until 1981 that a prototype helicopter made its first flight using the NOTAR system; in 1975 this concept was initially created by Hughes Helicopters.

Which creates lift and so adds to control, this fan forces air at high speeds through the back of the craft. The NOTAR system uses a variable pitch fan driven by the transmission of the main rotor.

By removing the tail rotor you remove this possibility and there is a significant reduction in the helicopter's vibration. Safety - the tail rotor striking something causes many accidents. Its advantages include: Reduced noise levels - around 60% of the noise from conventional helicopters normally comes from the tail rotor. NOTAR has advantages and disadvantages, as with any system.

NOTAR's disadvantages are it isn't as efficient as a tail rotor and helicopters that use a NOTAR system will have a loss of maneuverability.

A fenestron performs the same as a conventional tail rotor but there are design differences, in application. A fenestron is a tail rotor which is fitted within a housing. This is actually a form of tail rotor commonly known as a Fantail. The last way to counteract torque is known as a fenestron.

More protected - less likely for foreign objects to get into the tail rotor and cause damage and reduced noise. The advantages include: Safety - these are much safer for ground operations because the tail rotor is enclosed in a housing. Compared to a standard tail rotor having merely 2-4 blades and offers many advantages and a few disadvantages over a normal tail rotor, a Fenestron has between 8 and 18 blades.

Fenestrons are also more expensive to produce and less efficient The disadvantages include: Higher weight and higher air resistance which leads to increased fuel consumption.

Regardless of the type of system used, anti torque systems are vital to the safe operation of a helicopter.