The notion of aircraft generations, a term that applies to only jet rather than propeller driven fighter aircraft, appeared in the 1990s and attempted to make sense of the leap-frogging improvements in performance to jet fighter aircraft brought about through major advances in aircraft design, avionics, and weapon systems. While the rationale that constitutes a generational shift is debatable, a generational shift in jet fighter aircraft occurs when a technological innovation cannot be incorporated into an existing aircraft through upgrades and retrospective fit-outs.
The first generation of jet fighters such as the F-86, MiG-15and MiG-17, had basic avionic systems with no radars or self-protection countermeasures, and were armed with machine guns or cannons, as well as unguided bombs and rockets. A common characteristic of this generation of fighter was that the jet engines did not have afterburners and the aircraft operated in the subsonic regime.
In addition to the improved fuel burn requirements, the 787 propulsion system also had to meet more stringent noise and emissions requirements. Finally, in order to maximize the capital value of the airplane, Boeing decided that the propulsion systems should be designed for full interchangeability between the two engine types.
The common motor start controllers (CMSCs) are used to control the VFSG start function and properly regulate torque during the start sequence. Once the engine is started, the CMSC switches over to controlling the cabin air compressors, thereby performing a second function.
During normal operation of the airplane, the flight crew monitors engine data on the primary flight display (see fig. 6). The display can be set to show the full normal display, both primary and secondary engine parameters, or an abbreviated compact display with only primary parameters.
General Aviation Aircraft Design, Second Edition, continues to be the engineer's best source for answers to realistic aircraft design questions. The book has been expanded to provide design guidance for additional classes of aircraft, including seaplanes, biplanes, UAS, high-speed business jets, and electric airplanes. In addition to conventional powerplants, design guidance for battery systems, electric motors, and complete electric powertrains is offered. The second edition contains new chapters:
Written by an engineer with more than 25 years of design experience, professional engineers, aircraft designers, aerodynamicists, structural analysts, performance analysts, researchers, and aerospace engineering students will value the book as the classic go-to for aircraft design.
Dr. Snorri Gudmundsson served from 1995-2009 at Cirrus Aircraft. He served in various engineering roles in the development of several aircraft, including the Cirrus SR20 and SR22 aircraft. From 2005-2009, he served as the Chief Aerodynamicist, where he was responsible for the aerodynamics of the SF50 Vision jet (recipient of the 2017 Collier Trophy). He had two appointments a Designated Engineering Representative (DER) for the FAA, as a Structural and Flight Analyst. He has contributed to the certification of several aircraft. This includes development and certification flight and structural testing. He has conducted load analysis, stability and control evaluation, and performance analysis on a variety of single and multi-engine aircraft. In 2010, Dr. Gudmundsson joined the faculty at Embry-Riddle Aeronautical University, where he is currently an Associate Professor of Aerospace Engineering, teaching aircraft design and aerodynamics. Dr. Snorri has a Youtube channel on Aircraft Design:
When it comes to making a new aircraft, engine design is at the top of the list for any manufacturer. Powerful and efficient engines can allow aircraft to travel longer distances with a lower fuel burn, a key factor for airlines. So which are the most powerful aircraft engines today, and what planes are they found on?
As expected, the most powerful commercial plane engines are found on widebody aircraft. The most powerful engines are also found on twin-engine jets rather than four-engine ones due to the need for more thrust on twin-engine planes. With that, let's jump into the list!
The current leader in the engine market is the upcoming GE Aviation GE9X. While not in commercial service yet, the engine will feature on the upcoming Boeing 777X and has already flown a number of test flights. The engine is based on the design of the GE90, which is found on the older 777.
Coming in at second place is another GE engine, the GE90, which can be found on the popular 777 aircraft lineup. The engine first came into service in 1995 with British Airways' 777-200s. As the 777 family grew, so did the GE90 variants, with the third-generation engines being the most powerful to date. These are the GE90-115B and -110B, which are found on the 777-300ER and 777-200LR and 777F, respectively.
The PW4000-112 went to be re-engineered to fit the Airbus A380, as a part of the Engine Alliance GP7000 project with GE. While the PW4000 has since been replaced on newer widebodies, it remains a popular engine on older aircraft and will be in service for years to come.
Similarly, four-engine aircraft also have multiple high-efficiency engines rather than higher thrust engines. The most recent quadjet, the 747-8 comes with four GEnx engines, with the older A380 comes with four GP7000 engines (with a maximum thrust of 74,700 lbf).
Engine development almost goes hand-in-hand with aircraft design, with the pair needing to work in harmony to produce the best results. In recent years we have seen a shift toward manufacturers working with a single engine maker for their projects to optimize the results. While this leads to fewer choices for airlines, it has yielded exceptional results in terms of efficiency, such as the 777X and A350.
For aircraft jet propulsion there are in general four distinct designs: the turbojet, turbofan (or bypass engine), turboprop and turboshaft. This post will address the layout and design of the two most common engines used in modern aircraft, the turbojet and turbofan, and explain how their characteristics make each engine applicable for a specific task. Specifically, two important topics are addressed. The first is the multi-shaft engine with separate low-pressure and high-pressure spools and the second is the bypass engine, in which most of the air compressed by a fan bypasses the core combustor and turbine of the engine.
For sustained supersonic speeds a turbojet engine remains and attractive option for aircraft propulsion. The Rolls-Royce Olympus 593 is a two-shaft example that was used to propel the Concorde to twice the speed of sound.
The propulsive or Froude efficiency of a jet engine is defined by the power output divided by the rate of change of kinetic energy of the air. The kinetic energy of the air represents the power input to the system. The power output P is the product of force output i.e. the thrust F and the resulting air speed . Although this is an approximation this equation summarises the essential terms that define aircraft propulsion. The force F required to accelerate the fluid is given by the momentum equation,
For a fixed airspeed , can be increased by reducing . However decreasing decreases the thrust unless is increased. Thus, for civil aircraft when the economy is important is increased using high by-pass ratios of the turbofan, while for military engine where thrust is important low-by pass engines with large exit velocities are employed.
When optimising the jet engine performance two parameters are typically considered: the specific thrust (ST) of the engine, and specific fuel consumption (SFC), the mass flow rate of fuel required to produce a unit of thrust. Generally speaking turbine designer have two thermodynamic variables to optimise these two entities: the compressor pressure ratio (R) and the turbine inlet temperature (TET). The effects of these two variables on SFC and ST will be considered in turn.
This optimisation of R and TET can of course not be separated from the mechanical design of the engine. Driving up TET requires the use of much more expensive alloys and cooled turbine blades, which invariably lead to an increase in cost, mechanical complexity or otherwise a reduction in engine life. Increasing R will require larger compressors and turbines that incur weight, cost and mechanical complexity penalties.
As revealed above the high exit velocity of turbojet engines does not allow high propulsive efficiencies required for civil aircraft. To raise the propulsive efficiency a bypass engine, often known as a turbofan engine, is used.
The core of the turbofan engine is essentially the same as the turbojet featuring a compressor, combustion chamber and power turbine as shown in Figure 2. However the engine features a second turbine that drives a large fan at the front of the engine. This fan delivers air to a bypass duct that channels air to the exhaust nozzle without passing through a combustion chamber. For this reason designers often refer to the cold flow in the bypass duct and hot flow through the core. Mixing the colder bypass air with the hot exhaust gases from the core results in higher propulsive efficiencies and lower noise levels. Early bypass engines typically had bypass ratios (the mass flow rate of bypass air divided by the mass flow rate of air going through the core) of around 0.3 to 1.5. The arrangements for modern airliners are High-Bypass-Ratio (HBR) engines with a bypass ratio of 5 or even more. In the Rolls Royce RB211 and Trent families the fan is driven at low speed by one turbine, and two internal compressors driven by another two separate turbines to give a triple spool engine.
For turbofan design engineers have four major variables to consider: the bypass ratio (BR), overall pressure ratio (OR), fan pressure ratio (FR) and TET. Similar to the turbojet high TET is required for increased thrust. As the FR is increased the thrust contributed by the cold flow is increased while that of the hot flow decreases since more power is required to drive the fan. There is an optimum value of FR for which the total thrust is a maximum. In actual fact the optimum value of FR when F is a maximum automatically produces minimum SFC if OR and BR are fixed. 2b1af7f3a8