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Engine & Transmission


A helicopter is powered by its engine(s). There are two types of engines in use: combustion and turbine. The combustion engine can be separated into the piston and the wankle sub-types. Piston engines are almost exclusively used in (very) light helicopters, although some which are turbine powered have recently come onto the market. Turbine engines are more expensive than their combustion counterparts. The main advantage of turbines is their high power to weight ratio. They are also more reliable than the combustion engine.

Due to the weight of a combustion engine, it is placed below the main rotor shaft in order to balance the machine. A turbine engine is often placed at the roof of the hull.

Helicopter turbine engine

Piston helicopters essentially come in two types: carbutor or turbo charged. The latter has the advantages of a slightly higher power to weight ratio, an output power that is less dependent on altitude, and the lack of a requirement for carbutor de-icing (as there is no carbutor). The price of these advantages is higher costs and increased complexity (with a higher probability of failure). More recently, some helicopter designs are exploring the use of diesel engines.

Helicopter with piston engine

Some models use a wankle engine. Its main advantage over a piston engine is its compact and light-weight design, and it is capable of delivering a smooth, high RPM power. A wankle motor works by rotary design, which converts pressure into a rotating motion. It is quiet (compared to piston engines).

When a helicopter has to be able to fly with a single engine failure, more than one engine must be employed. Helicopters that are to be operated in crowded areas (cities) or above the sea always use 2 engines. In some rare instances, three engines can also be installed.


The first and primary function of the transmission is reduction gearing, since engines turn much faster than the main rotor shaft; for example, a combustion engine turns approximately 10 times faster than the main rotor shaft. The gear reduction of a turbine powered helicopter is in the order of 100:1. The transmission must be able to cope with the high torque values produced when driving a rotorsystem. The second key function is the transmission of the main rotor thrust to the hull.

An important aspect of the transmission is its free-wheeling unit. This unit guarantees that when the engine stops (due to a failure), the main rotors can continue to rotate freely, preventing a sudden rotor RPM decrease. This is an important feature, which makes it possible for a helicopter to go into autoration when the engines fail. In this situation, the helicopter 'wind mills' down in a controlled manner.

Helicopter turboshaft and transmission

The transmission also drives the tailrotor. Because the requirements of an operating tailrotor are still mandatory in autoration, the transmission must connect to the tailrotor from the main rotor shaft site, and not from the engine site, which will not be running in these circumstances.

   Next topic > Tailrotor, Tail Rotorhead, and Tailboom

Cyclic & Collective

  • The title of this book leads me to wonder what more it will teach me in addition to its content about these two, most frequently used, helicopter input controls. As it turns out, the answer is: a lot more. Of course, all of the obligatory subjects like basic physics, rotor aerodynamics and helicopter performance are dealt with as well, as are piston engine and basic helicopter manoeuvres. Yet the scope of this book is actually much wider than one might initially think. Firstly, it is divided into a 'beginners’ and an 'advanced’ section. This means that the book can treat more complex concepts in depth, even though the focus in the first section is directed more towards newcomers to the field. Secondly, subjects like turbine engines, multi-engine helicopters and autopilots are also examined. This is particularly helpful, since these topics are not usually covered in the majority of helicopter books aimed at this target audience. Thirdly, the book deals with many things that you will not normally find in a text book: helicopter related experiences and a great deal of interesting detail. This is the sort of information that can only be provided if you have flown a lot of different helicopters and have been working in this industry for some time. What’s more, this tone is amplified by the consistently narrative style of the book.
  • 536 pages

Art of the Helicopter (Hardback)

  • Well structured text that covers many technical aspects. It starts with an introduction to helicopters, followed by a treatment of the technical background needed when studying them. Thereafter, dynamics, rotor systems, engines and transmission are explained in detail. The book concludes with a section on performance and other types of rotorcraft. Its main asset is that the text is technically and theoretically very accurate, and rather than mathematics, its focus is always on enabling the reader to achieve an understanding of helicopters from a technical or engineering point of view. The more technically orientated reader will love this work.
  • 416 pages

Principles of Helicopter Flight (Paperback)

  • If you are wondering how a helicopter flies, and really want to comprehend the process, you have no choice but to delve into aerodynamics. This means not only understanding which forces play a role and the laws of physics, but also being able to put it all together and apply your knowledge to a rotating system consisting of a number of rotor blades. This is a demanding task and requires some very hard work. It is, undoubtedly, worth the effort though, and will help you to become a better pilot. There are many books out there to help you with this task of exploring the principles of helicopter flight, but they tend to fall into two camps: populist and taking a rather simplistic approach, or highly technical and assuming the reader has a degree in mathematics. This book is different, because it clearly explains the principles of flight in a step by step way that is easy for most readers to follow. Further benefits are that a lot of attention is paid to flight manoeuvres and operations, and every chapter concludes with questions as a study aid.
  • 320 pages

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