# Tag Info

39

It's simple. Cheap (development costs amortized decades before) and reliable. They made money for airlines. Or, you know, they wouldn't have bought them. There's more to operating costs than fuel burn, and in any case, fuel prices in the mid 90s were cheaper than at any time since the 20s in constant dollars. Fuel was so cheap that Air Canada was ...

38

This 'party trick' is covered nicely on metabunk.org. [It's the Su-30's] ability to inject unburnt fuel into the exhaust plume via the afterburner system. The super hot air of the exhaust instantly evaporates the volatile fuel, and then when it mixes with the cold air behind the plane the fuel reforms as a fine mist, essentially a fuel smoke cloud. (...

34

A start on a TF all the way to idle is about 20-40 seconds depending on the engine, and the fan itself won't do more than creep a bit until the core actually lights off which is 5-10 seconds, so they'll have lots of time to get down and get away as per @ymb1's diagram, once the wheeEEEEEEEEEEtickticktickticktickticktick starts.

33

I analyzed a Pratt & Whitney F100 turbofan last semester in my aerothermodynamics course, so allow me to answer this question. The short answer: the un-compressed air provides the majority of an engine's total thrust since the compressed air powers the engine. Correction: I forgot to mention that the fans also compress entering air. That is, all air ...

33

(Airbus) The suck zone ahead of a CFM56 on an A320 is less than 5 meters. The couple have enough time to take a leisurely walk toward the cockpit window. The engine start time takes upwards of a minute (the starter is limited to four 2-minute bursts, followed by a 15 min cool down). Newer engines take longer to start. On the neo with PW1000G engines it's ...

32

Image source The generators are usually driven from the Accessory Gearbox. This CAD drawing is from the company that makes accessory gearboxes for the Rolls Royce Trent engines driving the A330 and A350, and it shows the connection of the accessory gearbox to the high pressure rotor. This picture from the book The Jet Engine by Rolls Royce shows the ...

31

From: Forum post - "Trails from the back of Fighter Jets", Metabunk.org Jets practicing for air-shows (or actually in air-shows) sometimes use smoke to create trails. This is made by injecting something like paraffin into the hot exhaust where it vaporizes and condenses as smoke. And the accompanying image Looks a lot like the image in your question.

29

Ultimately what you want from all three types of engines is quantification of thrust available to push an airplane through the sky. The turbofan/jet engines are self contained and produce thrust directly but a turboprop engine requires the addition of a propeller, which may have differing characteristics based on the installation. Since thrust is not known ...

28

The bleed will be tapped from one or two of the 3rd, 4th, 5th or 6th High Pressure Compressor stages. Usually there are two bleed ports. The highest pressure port will supply really hot air for things like anti-icing. The lower pressure port farther upstream will supply air for air conditioning/pressurization and other pneumatics. Some systems combine ...

27

Short answer The longest shaft (N1, low pressure spool) which rotates with the large fan, the LP compressor and the LP turbine is centered at each end by a stationary frame with struts. Frames are known as fan frame and low pressure turbine rear frame, due to their positions Left: Fan frame of a CF6 (source). Right: Rear frame of a CFM56-7 (Safran). ...

27

The blades are loose in their "Fir Tree" blade mounts so that they can self balance. They are called "fir tree" because they are v shaped. As the rotation speed and centrifugal force increases, they move in the mounts and establish individual lead/lag positions to achieve a balanced disc. It will be understood that turbine wheels rotate at very high ...

26

It's not military vs civilian, but subsonic vs supersonic-capable Note that subsonic military aircraft use the same engines as civilian aircraft, even if their names might be different. The KC-135 used initially the J-57 which was called JT-3C when used in the Boeing 707-120. Now they fly the CFM-56, which is used on the Boeing 737 and the A320. The C-5 ...

25

Both aircraft seem to have the same purpose Not entirely. The RAF see the C17 as a strategic airlifter, the A400 is seen as a tactical airlifter replacing the turboprop C130. Strategic airlifters are more likely to make longer, higher-altitude journeys. Where jets are more fuel efficient. They are more likely to operate between airports with concrete ...

25

Location The general design is to group elements that need to be driven by the engine around one "accessory gearbox" which is located away from the engine centerline. A driving axial shaft in therefore required. In some cases, there are multiple accessory gearboxes. Usually the accessories are located at the bottom of the engine fan case, making them and ...

25

Yes in principle, but some modifications are advisable. What limits the maximum operating altitude of a jet engine (besides the thrust needed to climb up there) is the length of the combustion chamber and the absolute pressure of the air entering it. Since the atmospheric pressure drops with altitude and the compression ratio of the compressor stays ...

25

Production turbofans just weren't available. Once they came on the market and were mass-produced, jetliners switched to them. While turboprops did exist at the time, they were (and are) a turbine engine driving a propeller in place of a piston engine, a straightforward combo of two techs. Turbojet engines were fairly complex machines for the era on their ...

24

This answer needs some background information. What became the A400M started as the Future Large Aircraft or FLA in 1983. Airbus was worried what to do with their engineers after work on the A320 was completed, and the next projects, soon to be called TA9 and TA11 (TA for Twin Aisle; they would eventually mature into the A330 and A340), were still far, far ...

24

Because the LP turbine extracts power for the fan, which requires the most power. The HP and IP turbine only extract power for their connected compressors - the LP turbine extracts power for the fan and the LP compressor. The fan does work on all airflow through the engine, the compressors only on a fraction (10:1 for a high bypass like the Trent 1000). The ...

24

Turbojets and turbofans are very similar indeed: both are turbine engines; both create thrust form jet exhaust; and both have a rotating implement in front that can be called a fan. Although in the case of the turbojet, it isn't called a fan but the compressor first stage. $\$ Junkers Jumo 109-004 So what is the difference? There are four types of ...

23

Jet engines directly produce thrust by exhausting gas (and in a modern turbo fan also moving a lot of air around them), so fuel flow rate is directly related to the thrust that is generated. In a turbo prop the engine produces power which, via a gear box spins a propeller that generates the thrust. Since most turbo props have the ability to adjust the ...

23

There are basically 3 limits that the engine faces, temperature (maximum turbine entry temperature or maximum compressor exit temperature), pressure (maximum compressor exit pressure) and stress (maximum stress in the blades as a result of spool speed). Varying the OAT for a specific engine design will hit one of these limits. When the OAT increases, the ...

21

In a turbojet, all the air goes through the engine proper, through the combustion chamber and all the stages of compressor and post-combustion turbine blades. In a turbofan, some of the air is just pushed by a fan around the rest of the engine. This is the "bypass". As Harper points out, it's not fundamentally different from a turboprop or extracting ...

20

The inlet angle is a compromise between cruise, when the aircraft has a low angle of attack, and the take-off and climb phase, when the engine runs at maximum thrust, and the angle of attack is several degrees higher than during cruise. Especially right after rotation, when the aircraft is heavy and slow, the angle of attack might reach into the lower two-...

20

Struts. Lots of them, and with an aerodynamic shape so they don't cause too much drag. Some of those struts double as stator vanes and reduce the swirl of the internal flow. By doing this they add a little thrust. Others house the driveshafts by which rotational energy is taken from the shaft to spin pumps and generators. Maybe it helps to watch this ...

20

The simple answer that covers the majority of engines is that a fan has a shroud. The possible exception are unducted fans or Open Rotor Engines, which are a hybrid between a turboprop and a fan engine. A more scientific answer is based on the difference in disc loading: How much power per disc area can be pumped into the fan for propulsion. For propellers, ...

19

On modern turbojets the bypass air provides (at least) two things Thrust The air does bypass the engine core, but it is accelerated by the N1 fan and provides thrust as it is expelled rearward out of the engine. Thrust from the bypass air can contribute more than half of the total thrust produced by the engine (upwards of 80% of the total thrust for some ...

19

I's like to expand the answers on how this could reduce vibrations, as it was mentioned in a comment. Therefore, I'd like to look at something completely different: When computers were equipped with faster and faster CD-ROM drives, the reduction of vibrations caused by small imbalances in the discs became more and more important. The solution is is shown ...

19

This is one of the four Variable Frequency Generator (VFG) of the Airbus A380. It's apparent power is 150 kVA. Rotor, source: Safran The total power available from the engines is 600 kVA. Seen from the other side: Stator, source: Thales The A380 is a one of these "more electrical" planes, where hydraulics tends to be replaced by electric devices, and ...

19

Thermal efficiencies are very rarely quoted for aviation gas turbines. The metrics of interest are specific fuel consumption, and power to weight ratio. While a higher thermal efficiency will increase these, SFC and thrust/weight are performance terms that are easier to comprehend, and describe the performance in terms that can directly be used in ...

18

WHAT??? I CAN'T HEAR YOU I said, let's get away from this loud engine! Before it can even start to turn the fan, the noises the engine must make will be so deafening as to force the people in that location to flee. And even before that, there would be clunks, shakes, and vibration that would be very noticeable, and put even deaf people on notice to ...

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