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Take off aborted at KDAB due to multiple bird strikes. Pilot Steve Barber is reported to have done a magnificent job getting the plane on the ground. In the House of Taters. Written by a customer while visiting nutrisystem. United Fly's great, doesn't drive so well once on the ground in Houston. The Champion of Tattoos.
We sure hope that at least some buyers have racetrack club memberships because this rig digs track time. During a hot 2: The comparatively modest 0. Indeed, after two three-lap sessions, the reported electric range only dropped from 23 to 19 miles. And with no cars to pass, Lars never pressed the Sport Response press-to-pass button, which maximizes E-boost for 20 seconds. Might this E-Hybrid eclipse the Turbo's 'Ring time? It weighs pounds more, but the weight-to-power drops from 8.
Speaking of modes, the others mirror those on the 4 E-Hybrid: E-Power, the default which prioritizes electric driving and depletes the battery most freely; Hybrid Auto mode, which blends gas and electric power most efficiently; and the two Sport modes, which both keep the engine on and prioritize electric assist with the non-plus mode maintaining a constant battery level instead of maximizing battery charge.
Later this summer we'll take the helm ourselves to determine whether the Turbo S E-Hybrid is more four-door or crazy-pricey Panamera Turbo. This new hot-vee twin-turbo 4. Its two twin-scroll turbos spool out 1. Those inlet valves enjoy variable timing and lift the exhaust valves get variable timing only , and enabling cylinder deactivation between and 3, rpm greatly reduces throttling losses under light loads lb-ft max.
The sand-cast aluminum block gets a new type of atmospheric plasma-sprayed micron-thick iron coating applied. This, in combination with chrome-nitride-coated piston rings, greatly reduces friction.
The basic architecture is shared with the EA V-6 also employed in the Panamera. Developed by Porsche and built by ZF, this box is now standard on all Panameras. It adds an extra cog and the option of hybridization in essentially the same package envelope as the seven-speed PDK box it replaces with mass increasing by only 3 pounds. The gear ratio spread is an impressive Internal power loss in the transmission is said to be 28 percent less, thanks to friction reductions, a demand-driven lubrication system, the wide gear ratio spread, and optimized electronic control of the gearbox.
This box helps improve fuel economy by 1. This pack features eight modules of 13 prismatic lithium-ion battery cells each on two levels cooled by a dedicated coolant circuit.
Operating voltage is volts, and its peak output is kW hp for 10 seconds. The system is designed to utilize The pack weighs about pounds and measures It's water tight, and it rides outside the bodywork under the rear deck in the space where unelectrified Panameras package a well containing the volt battery and sound-system subwoofer.
These items move into the auxiliary storage cubbies off to either side of the rear of the cargo area, reducing Euro DIN cargo volume from A bypass flow can be added only if the turbine inlet temperature is not too high to compensate for the smaller core flow.
The resulting turbofan, with reasonable efficiencies and duct loss for the added components, would probably operate at a higher nozzle pressure ratio than the turbojet, but with a lower exhaust temperature to retain net thrust. Since the temperature rise across the whole engine intake to nozzle would be lower, the dry power fuel flow would also be reduced, resulting in a better specific fuel consumption SFC.
Some low-bypass ratio military turbofans e. F have variable inlet guide vanes to direct air onto the first fan rotor stage. This improves the fan surge margin see compressor map. An afterburner is a combustor located downstream of the turbine blades and directly upstream of the nozzle, which burns fuel from afterburner-specific fuel injectors.
The variable geometry nozzle must open to a larger throat area to accommodate the extra volume flow when the afterburner is lit. Afterburning is often designed to give a significant thrust boost for take off, transonic acceleration and combat maneuvers, but is very fuel intensive.
Consequently, afterburning can be used only for short portions of a mission. Unlike the main combustor, where the downstream turbine blades must not be damaged by high temperatures, an afterburner can operate at the ideal maximum stoichiometric temperature i.
At a fixed total applied fuel: However, a high specific thrust turbofan will, by definition, have a higher nozzle pressure ratio, resulting in a higher afterburning net thrust and, therefore, a lower afterburning specific fuel consumption SFC. However, high specific thrust engines have a high dry SFC. The situation is reversed for a medium specific thrust afterburning turbofan: The former engine is suitable for a combat aircraft which must remain in afterburning combat for a fairly long period, but has to fight only fairly close to the airfield e.
However, the pilot can afford to stay in afterburning only for a short period, before aircraft fuel reserves become dangerously low. To boost fuel economy and reduce noise, almost all of today's jet airliners and most military transport aircraft e. Modern combat aircraft tend to use low-bypass ratio turbofans, and some military transport aircraft use turboprops. Low specific thrust is achieved by replacing the multi-stage fan with a single-stage unit. Unlike some military engines, modern civil turbofans lack stationary inlet guide vanes in front of the fan rotor.
The fan is scaled to achieve the desired net thrust. The core or gas generator of the engine must generate enough power to drive the fan at its design flow and pressure ratio. Reducing the core mass flow tends to increase the load on the LP turbine, so this unit may require additional stages to reduce the average stage loading and to maintain LP turbine efficiency.
Reducing core flow also increases bypass ratio. Bypass ratios greater than 5: Further improvements in core thermal efficiency can be achieved by raising the overall pressure ratio of the core. Improved blade aerodynamics reduces the number of extra compressor stages required. With multiple compressors i. The lower the specific thrust of a turbofan, the lower the mean jet outlet velocity, which in turn translates into a high thrust lapse rate i. See technical discussion below, item 2.
Consequently, an engine sized to propel an aircraft at high subsonic flight speed e. Low specific thrust engines tend to have a high bypass ratio, but this is also a function of the temperature of the turbine system. The turbofans on twin engined airliners are further more powerful to cope with losing one engine during take-off, which reduces the aircraft's net thrust by half.
Modern twin engined airliners normally climb very steeply immediately after take-off. If one engine is lost, the climb-out is much shallower, but sufficient to clear obstacles in the flightpath. The Soviet Union's engine technology was less advanced than the West's and its first wide-body aircraft, the Ilyushin Il , was powered by low-bypass engines.
The Yakovlev Yak , a medium-range, rear-engined aircraft seating up to passengers introduced in was the first Soviet aircraft to use high-bypass engines. Turbofan engines come in a variety of engine configurations. For a given engine cycle i.
Off-design performance and stability is, however, affected by engine configuration. As the design overall pressure ratio of an engine cycle increases, it becomes more difficult to operate at low rpm, without encountering an instability known as compressor surge.
This occurs when some of the compressor aerofoils stall like the wings of an aircraft causing a violent change in the direction of the airflow. However, compressor stall can be avoided, at low rpm, by progressively:. Most modern western civil turbofans employ a relatively high-pressure-ratio high-pressure HP compressor, with many rows of variable stators to control surge margin at low rpm. As the HP compressor has a modest pressure ratio its speed can be reduced surge-free, without employing variable geometry.
However, because a shallow IP compressor working line is inevitable, the IPC has one stage of variable geometry on all variants except the , which has none. Although far from common, the single-shaft turbofan is probably the simplest configuration, comprising a fan and high-pressure compressor driven by a single turbine unit, all on the same shaft. Despite the simplicity of the turbomachinery configuration, the M53 requires a variable area mixer to facilitate part-throttle operation.
Hot gas from the turbojet turbine exhaust expanded through the LP turbine, the fan blades being a radial extension of the turbine blades. One of the problems with the aft fan configuration is hot gas leakage from the LP turbine to the fan. Many turbofans have the basic two-spool configuration where both the fan and LP turbine i. The BR is typical of this configuration. At the smaller thrust sizes, instead of all-axial blading, the HP compressor configuration may be axial-centrifugal e.
Higher overall pressure ratios can be achieved by either raising the HP compressor pressure ratio or adding an intermediate-pressure IP compressor between the fan and HP compressor, to supercharge or boost the latter unit helping to raise the overall pressure ratio of the engine cycle to the very high levels employed today i.
All of the large American turbofans e. The high bypass ratios i. Rolls-Royce chose a three-spool configuration for their large civil turbofans i. The first three-spool engine was the earlier Rolls-Royce RB. As bypass ratio increases, the mean radius ratio of the fan and low-pressure turbine LPT increases.
Consequently, if the fan is to rotate at its optimum blade speed the LPT blading will spin slowly, so additional LPT stages will be required, to extract sufficient energy to drive the fan. Introducing a planetary reduction gearbox , with a suitable gear ratio, between the LP shaft and the fan enables both the fan and LP turbine to operate at their optimum speeds.
Most of the configurations discussed above are used in civilian turbofans, while modern military turbofans e. Most civil turbofans use a high-efficiency, 2-stage HP turbine to drive the HP compressor.
The CFM56 uses an alternative approach: While this approach is probably less efficient, there are savings on cooling air, weight and cost.
Because the HP compressor pressure ratio is modest, modern military turbofans tend to use a single-stage HP turbine. Modern civil turbofans have multi-stage LP turbines e.
The number of stages required depends on the engine cycle bypass ratio and how much supercharging i. A geared fan may reduce the number of required LPT stages in some applications. Consider a mixed turbofan with a fixed bypass ratio and airflow. Increasing the overall pressure ratio of the compression system raises the combustor entry temperature.
Therefore, at a fixed fuel flow there is an increase in HP turbine rotor inlet temperature. Although the higher temperature rise across the compression system implies a larger temperature drop over the turbine system, the mixed nozzle temperature is unaffected, because the same amount of heat is being added to the system.
There is, however, a rise in nozzle pressure, because overall pressure ratio increases faster than the turbine expansion ratio, causing an increase in the hot mixer entry pressure.
A similar trend occurs with unmixed turbofans. So turbofans can be made more fuel efficient by raising overall pressure ratio and turbine rotor inlet temperature in unison. Increasing the latter may require better compressor materials. If the latter is held constant, the increase in HP compressor delivery temperature from raising overall pressure ratio implies an increase in HP mechanical speed.
However, stressing considerations might limit this parameter, implying, despite an increase in overall pressure ratio, a reduction in HP compressor pressure ratio. However, this assumes that cycle improvements are obtained, while retaining the datum HP compressor exit flow function non-dimensional flow.
In practice, changes to the non-dimensional speed of the HP compressor and cooling bleed extraction would probably make this assumption invalid, making some adjustment to HP turbine throat area unavoidable. This means the HP turbine nozzle guide vanes would have to be different from the original.
In all probability, the downstream LP turbine nozzle guide vanes would have to be changed anyway. Thrust growth is obtained by increasing core power. There are two basic routes available:. Both routes require an increase in the combustor fuel flow and, therefore, the heat energy added to the core stream. The cold route can be obtained by one of the following:.
Alternatively, the core size can be increased, to raise core airflow, without changing overall pressure ratio. This route is expensive, since a new upflowed turbine system and possibly a larger IP compressor is also required. Changes must also be made to the fan to absorb the extra core power. Early turbojet engines were not very fuel-efficient as their overall pressure ratio and turbine inlet temperature were severely limited by the technology available at the time.
Turbomachinery testing, using an electric motor, had started on 1 April The British wartime Metrovick F. The original low-bypass turbofan engines were designed to improve propulsive efficiency by reducing the exhaust velocity to a value closer to that of the aircraft. The Rolls-Royce Conway , the world's first production turbofan, had a bypass ratio of 0.
It was followed by the aft-fan General Electric CF engine with a 2. There were at one time over CF aircraft in operation around the world, with an experience base of over 10 million service hours.
The airflow past the blades has to be maintained within close angular limits to keep the air flowing against an increasing pressure. Otherwise the air will come back out of the intake. During development of a new engine type a relation is established between a more easily measured temperature like Exhaust gas temperature and the TIT. The EGT is then used to make sure the engine doesn't run too hot. Exotic alloys , sophisticated air cooling schemes and special mechanical design are needed to keep the physical stresses within the strength of the material.
The high-temperature performance of fan blades has increased through developments in the casting manufacturing process, the cooling design, thermal barrier coatings , and alloys. Cycle-wise, the HP turbine inlet temperature is less important than its rotor inlet temperature RIT , after the temperature drop across its stator. Originally standard polycrystalline metals were used to make fan blades, but developments in material science have allowed blades to be constructed from aligned metallic crystals and more recently single crystals to operate at higher temperatures with less distortion.
These alloys and Nickel -based superalloys are utilized in HP turbine blades in most modern jet engines. HP turbine inlet is cooled below its melting point with air bled from the compressor, bypassing the combustor and entering the hollow blade or vane. Fan blades have been growing as jet engines have been getting bigger: Advances in computational fluid dynamics CFD modelling have permitted complex, 3D curved shapes with very wide chord , keeping the fan capabilities while minimizing the blade count to lower costs.
Coincidentally, the bypass ratio grew to achieve higher propulsive efficiency and the fan diameter increased. Rolls-Royce pioneered the hollow, titanium wide-chord fan blade in the s for aerodynamic efficiency and foreign object damage resistance in the RB then for the Trent. GE Aviation introduced carbon fiber composite fan blades on the GE90 in , manufactured today with a carbon-fiber tape-layer process. Engine cores are shrinking as they are operating at higher pressure ratios and becoming more efficient, and become smaller compared to the fan as bypass ratios increase.
Blade tip clearances are harder to maintain at the exit of the high-pressure compressor where blades are 0. Geared turbofans and further fan pressure ratio reductions will continue to improve propulsive efficiency. The weight and size of the nacelle would be reduced by a short duct inlet, imposing higher aerodynamic turning loads on the blades and leaving less space for soundproofing, but a lower-pressure-ratio fan is slower.
Modeling advances and high specific strength materials may help it succeed where previous attempts failed. For GE Aviation , the energy density of jet fuel still maximises the Breguet range equation and higher pressure ratio cores, lower pressure ratio fans, low-loss inlets and lighter structures can further improve thermal, transfer and propulsive efficiency. CMCs will be used ten times more by the mids: Rolls-Royce Plc aim for a Nearly stoichiometric turbine entry temperatures approaches the theoretical limit and its impact on emissions has to be balanced with environmental performance goals.
Open rotors, lower pressure ratio fans and potentially distributed propulsion offers more room for better propulsive efficiency. Additive manufacturing could be an enabler for intercooler and recuperators. Closer airframe integration and hybrid or electric aircraft can be combined with gas turbines.