Wide chord
Encyclopedia
A wide chord
fan
engine
is a term to describe a modern turbofan
jet engine
having a ducted fan
with a specific blade geometry - In layman's terms, they would be described as having wider blades than other jet engines. The technology was pioneered by Rolls-Royce
in the 1970s and development from a variety of manufacturers continues today.
mounted at the rotational center on the fan disk
, and as the engine core rotates the fan blades accelerate an air mass
and create the force to move forward which gives thrust
(in accordance with Newton's Third Law).
In theory the larger the fan diameter (the line from the tip of one fanblade to its opposite member) the greater the thrust. In practical applications, fansize is limited by the weight, the space available around the aircraft and by the increased drag
(resistance) generated by the larger frontal area.
In the race to achieve better fuel economy, more thrust and less weight & noise from jet engines, designers have refined the blade design and materials to extract more thrust for any given fan disk
area. One significant improvement is to make blade chords wider and, more recently, alter the blade geometry to give it a scimitar
-like shape. Further refinements include making the blades from a light material such as titanium
and to manufacture them with a hollow cross-section.
Modern jet engines such as the Rolls Royce Trent 900 engine which powers the Airbus A380
and the Engine Alliance GP7000 are examples of wide chord fan engines.
and as such, there is no single optimum design. As with most mechanical components, the blade is a compromise in trying to achieve as large a blade area as possible within the practical constraints: Widening the blade chord will increase the blade drag while lengthening the blade will increase tip speed (and noise) plus it may make the fandisc impractically large. A larger blade is also heavier, which when taken together with increasing tip speed as the fandisc gets larger, puts a point of diminishing return between weight and blade length (tip speed.)
A wide chord engine addresses this by having fewer, wider, blades meaning a wide chord fan engine will have fewer, but more effective, fanblades compared to a regular jet engine. To address the weight issue, blades are often hollow and made from titanium
. Finally, blades are often given a scimitar
shape to achieve higher flying speeds.
The Rolls Royce Trent 900 wide chord jet engine
Chord (aircraft)
In aeronautics, chord refers to the imaginary straight line joining the trailing edge and the center of curvature of the leading edge of the cross-section of an airfoil...
fan
Fan (mechanical)
A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air.A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually, it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing...
engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
is a term to describe a modern turbofan
Turbofan
The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan...
jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
having a ducted fan
Ducted fan
A ducted fan is a propulsion arrangement whereby a fan, which is a type of propeller, is mounted within a cylindrical shroud or duct. The duct reduces losses in thrust from the tip vortices of the fan, and varying the cross-section of the duct allows the designer to advantageously affect the...
with a specific blade geometry - In layman's terms, they would be described as having wider blades than other jet engines. The technology was pioneered by Rolls-Royce
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....
in the 1970s and development from a variety of manufacturers continues today.
Overview
The main fan on a jet engine consists of a number of aerofoilsAirfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
mounted at the rotational center on the fan disk
Fan disk
A fan disk is the part of a turbofan jet engine that contains the fan blades. It is considered one of the most critical components of the engine and has four main functions:...
, and as the engine core rotates the fan blades accelerate an air mass
Air mass
In meteorology, an air mass is a volume of air defined by its temperature and water vapor content. Air masses cover many hundreds or thousands of square miles, and adopt the characteristics of the surface below them. They are classified according to latitude and their continental or maritime...
and create the force to move forward which gives thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
(in accordance with Newton's Third Law).
In theory the larger the fan diameter (the line from the tip of one fanblade to its opposite member) the greater the thrust. In practical applications, fansize is limited by the weight, the space available around the aircraft and by the increased drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
(resistance) generated by the larger frontal area.
In the race to achieve better fuel economy, more thrust and less weight & noise from jet engines, designers have refined the blade design and materials to extract more thrust for any given fan disk
Fan disk
A fan disk is the part of a turbofan jet engine that contains the fan blades. It is considered one of the most critical components of the engine and has four main functions:...
area. One significant improvement is to make blade chords wider and, more recently, alter the blade geometry to give it a scimitar
Scimitar
A scimitar is a backsword or sabre with a curved blade, originating in Southwest Asia .The Arabic term saif translates to "sword" in general, but is normally taken to refer to the scimitar type of curved backsword in particular.The curved sword or "scimitar" was widespread throughout the Muslim...
-like shape. Further refinements include making the blades from a light material such as titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
and to manufacture them with a hollow cross-section.
Modern jet engines such as the Rolls Royce Trent 900 engine which powers the Airbus A380
Airbus A380
The Airbus A380 is a double-deck, wide-body, four-engine jet airliner manufactured by the European corporation Airbus, a subsidiary of EADS. It is the largest passenger airliner in the world. Due to its size, many airports had to modify and improve facilities to accommodate it...
and the Engine Alliance GP7000 are examples of wide chord fan engines.
Key design considerations
The geometry of a jet engine blade is essentially that of an airfoilAirfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
and as such, there is no single optimum design. As with most mechanical components, the blade is a compromise in trying to achieve as large a blade area as possible within the practical constraints: Widening the blade chord will increase the blade drag while lengthening the blade will increase tip speed (and noise) plus it may make the fandisc impractically large. A larger blade is also heavier, which when taken together with increasing tip speed as the fandisc gets larger, puts a point of diminishing return between weight and blade length (tip speed.)
A wide chord engine addresses this by having fewer, wider, blades meaning a wide chord fan engine will have fewer, but more effective, fanblades compared to a regular jet engine. To address the weight issue, blades are often hollow and made from titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
. Finally, blades are often given a scimitar
Scimitar
A scimitar is a backsword or sabre with a curved blade, originating in Southwest Asia .The Arabic term saif translates to "sword" in general, but is normally taken to refer to the scimitar type of curved backsword in particular.The curved sword or "scimitar" was widespread throughout the Muslim...
shape to achieve higher flying speeds.
External links
The Rolls Royce wide chord fan bladeThe Rolls Royce Trent 900 wide chord jet engine