# Tag Info

59

Modern high-bypass turbofan engines work by pulling in immense volumes of air and accelerating it. A screen as proposed would make that task far more difficult, which would ruin the efficiency of the engine. It's also pretty well unnecessary. Jets worldwide take plenty of birdstrikes every day. Unless the pilots see it (hitting the windscreen will do ...

41

I'm not an engineer (which might be better suited to answer this) so this is from simplified things they feed pilots: Jet engines take much longer to spool up (i.e. increase RPM) than piston engines, especially at low RPM because of the pressure ratio/increased airflow necessary to keep the compressor from stalling/surging/blowing up every time when ...

37

Torque is less of a problem due to the effective roll damping of a wing, but gyro effects and prop wash are important. Gyro effects first became an issue with rotary engines in WW I. A rotary engine has its crankshaft fixed to the airplane, and both the cylinder block and the propeller rotate. This gives better cooling at low speed and produces a flywheel ...

37

The means of starting most turbine engines is high pressure bleed air. This bleed source typically comes from an APU but may also come from an already running engine (crossbleed start) or an external huffer cart. In some airplanes the start is completely FADEC controlled and need only be initiated and monitored by the flight crew, and in other airplanes ...

31

Engines on airliners turn the same direction. The torque isn't as much an issue on jets as it is on props. A lot of multiengine prop planes have propellers that turn in opposite directions. In turbine engines this can be done in a gearbox to allow the same engine to be used on both sides. Some turbine engines, such as the PT6, have two turbines turning in ...

29

What is this turbine part? This assembly is part of the turbine used to rotate the compressor section of a Pratt & Whitney PT6, a free turbine turboprop. It's known as compressor turbine or just CT. Where is it located? The compressor turbine is located at the exit nozzle of the annular combustion chamber, and is the first component which enters in ...

25

Titanium is unsuitable because it will react with oxygen and carbon at high temperature, well below its melting point, making it very hard and brittle. Welding titanium is very complicated because it needs to be shielded extremely well from any oxygen when hot. Ti$_3$O will form above 500°C, and Ti$_2$O above 600°C. Initially turbine blades were made of ...

25

Not all turbine blades are made of nickel alloy, some blades are made of such family of alloys but clearly not all. Some blades are actually made of ceramic materials. The turbine is always located after combustion chamber and the temperature which the first stage of turbine blades is able to resist is a proof of high technology engine. Those blades are ...

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

Yes, indeed the plan to build a hydrogen-powered jet laid the groundwork for using hydrogen in the Centaur rockets and the upper stages of the Saturn 5. While hydrogen was used only experimentally in test rigs, the Soviet Union built a derivative of a regular airliner, the Tupolev 155, for testing hydrogen and natural gas in flight. EDIT: NACA also did in-...

22

Modern jet transport category aircraft have APUs and they will be running if no engines are. Batteries on jets do not work very long with all electrical buses energized and the first thing you do after turning the batteries on is seeing that they are working correctly and then starting the APU (assuming no GPU is hooked up, if there is a GPU then starting ...

21

As a side comment, there is a type of engine researched in the 80's/90's, but never marketed, where an unducted fan is driven directly by the turbine shaft without a gearbox: The propfan. It's close to your idea, albeit the unducted fan is not exactly a propeller. Safran has restarted researching on this design, end of 2017, for an operational use after 2030....

20

The first photo shows the engine air intake screen. Its basically a screen to prevent FOD ingestion, as you noted. From CH-47 Theory of Operations: Engine Inlet Screens An engine inlet screen which maximizes foreign object damage (FOD) is installed on each engine. The reduction in engine power available with screens installed is negligible. The ...

19

There are a few very practical reasons why turbine engines use inner shafts/spools. First, jet engine spools are very high speed rotating parts, this means they are subjected to high amounts of centripetal force. Centripetal force is calculated by $F=mr\omega ^2$ were F is Force, m is mass, r is radius of gyration and $\omega$ is angular velocity. So ...

18

Screens were actually used on the first prototypes of the Me-262, but soon abandoned when they were found to be more of a burden than a help. If you look carefully at the picture of the Me-262 V3 below, you can see the spherical screens on both engine intakes. Today, screens are used only in ground tests. See the picture below for the Rolls-Royce version: ...

18

For fuels intended for use in aircraft, the key performance parameter is the energy density of the fuel: how much potential work is stored in how many liters of stuff. High energy density means the fuel tanks will be small and the energy released upon burning a liter of it will be large. The problem with using hydrogen as aircraft fuel is that its energy ...

17

If you would like to know about jet engines, please read @casey's answer. It's very detailed and good. There are some turbine engines which are started a different way. We are talking about turboprop or turboshaft engines. A famous example is the PT6 turbine, delivering power to many small turbine-powered propeller airplanes like Beachcraft's King Air ...

17

A few Russian/Soviet fighters had retractable FOD screens on their engine intakes (MiG-29 and Su-27 IIRC). The assumption was that they would operate from damaged runways or roads and the engines would need protection against Foreign Object Damage (FOD). Right air intake of a MiG-29 with main doors closed and louvres on the wing root opened.

16

There are three problems with this idea: (1) To make a screen strong enough to withstand the body of a 15-to-20 pound bird hitting it at 500 miles per hour, would require thick wire which would significantly block air flow. (2) Such a screen would be very liable to collect ice, so it would have to be heated to high temperature. This would be expensive and ...

15

Propellers in some form are really the only option. It is currently the only efficient way to generate thrust with air as a medium. Even jet engines are in some sense just a very elaborate system of propellers. The reason for the turbine is to create an environment to efficiently burn fuel (suck, squeeze, bang, blow) to generate as much thrust as possible. ...

14

Their main advantage is higher strength at elevated temperatures. With elevated I mean temperatures up to 1200°C, which is what you will find in modern, film-cooled high-performance turbines where the gas temperature is even a few hundred centigrades higher than that. Steel would melt and other materials like titanium would quickly oxidize, and only nickel ...

14

It can be done, but the better specific fuel consumption does not compensate for the extra weight. We all know that aero engines have to be as light as possible. In land, stationary installations, where weight matters but little, regeneration, intercooling, and even combined-cycle (in electricity generation, using a gas turbine that drives an alternator, but ...

13

The fan section of a turbofan engine is driven by the low pressure (LP) spool. This means that it is connected to two parts of the engine: The LP compressor, which must compress the air before it enters the high pressure (HP) compressor The LP turbine, which must receive the air after it exits the HP turbine The problem is that the HP section is efficient ...

13

Turbofan engines are designed and tested to contain a fan blade failure. However, this is a violent event and will cause serious damage to the engine. The engine and surrounding components are subjected to large forces and vibrations, and the engine can ingest debris from the damage to the fan, causing further damage. There will likely be an investigation, ...

13

engineer and pilot here - formerly of JPL. I've seen blade loss tests and any modern high performance engine will violently destroy itself if a blade is lost. You can see tests of this on youtube for example at that link or by searching on "jet engine blade-out test" (without the quotes). (User fooot gave a longer example video as well.) In these tests they ...

13

A rotating drum will have a higher inertia. When the pilot commands a thrust increase, spooling up the drum will take longer than spooling up a shaft. Also, a big drum is harder to balance well than a thin shaft. However, what you propose is not so far from general practice: The high pressure spool on modern engines is quite big already, but it is still on ...

13

Turbine Blade The turbine blade (part number 1475M35P01) is from the High Pressure Turbine (HPT) a CFM56-3 according to this ATSB report on performance testing of the engine. The report contains several images of blades which look similar to your photos. Compressor blade A search on locatory.com for the part number (B778503) lists the description as C-3 ...

12

Airliners.net is the photo directory of aircraft on the internet, a quick search turns up this beauty :) You can also diversify your search to A318, A319 and A321 since it's in principle the same equipment. Aidyn Iskakov - Almaty Spotting Club http://www.airliners.net/photo/Air-Astana/Airbus-A320-232/2419974/ (source: airliners.net)

12

Jet fuel is seldom if ever pure hydrocarbon molecules. It's got a lot of other stuff mixed into it to improve the properties. I'm going to quote Shell for the sake of examples: Antioxidants (gum inhibitors) must be used in Avgas to prevent the formation of gum and other antioxidation products. Jet fuels, which are inherently more stable than gasolines,...

12

tl;dr They're pretty much all considered turbofans with a few exceptions from the '70s such as this experimental Britten-Norman Islander. They key difference is a prop can be considered a separate entity (add-on) to the turbine for a turboprop, but a fan is an integrated component for a turbofan. Slightly longer answer After a fair bit of thought and ...

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