42

Yes, large turbofans can be turned by hand without too much force. On smaller aircraft this is regularly done as part of the preflight walkaround. You can see an example in this YouTube video of an A320 walkaround: Admittedly, the pilot turns the engine with four fingers here, but you can see that not much force is required. Turning it with a single finger ...


26

Turning the engine with one finger is not necessarily recommended, because the leading edges of the fan blades are quite sharp. But it is possible. For some experimental vibration measurements, it is preferable to keep the rotors turning slowly to avoid the bearings "sticking" in one position and confusing the results. A common way to do this is ...


16

High Pressure Turbine Active Clearance Control (HPTACC) is a system that controls the temperature of the shroud of the high pressure turbine rotor (HPT). It can cool or heat the shroud support structure using bleed air from the 4th (relatively cool) or hot bleed air from the 9th stage to control the (tip) gap (or tip clearance) between the rotor (rotating ...


10

The turbine blade clearance is the gap between the tip of a turbine rotor blade and the turbine shroud: CFM56-7B HPTACC principle, adapted from Airbus engine systems manual The blade is part of the rotor, and the shroud is part of the stators assembly. The length of a blade and the diameter of the shroud vary with the temperature of gas from the combustion ...


9

No Turbojets were mainly used in the Fourties and Fifties. As soon as pressure ratios had become high enough to allow adding a fan stage, turbofans replaced them. And the distinction is less between civilian and military engines but between low-bypass-ratio and high-bypass-ratio. Civilian jets which used the same engines as military ones did so because there ...


8

Almost all jet engines will have one or more "resonance" conditions where the combination of turbine RPM, mechanical elasticity and aeroelasticity constructively reinforces to cause mechanical or aerodynamic vibration. Think of it this way: If you have a slinky spring (mechanically elastic) toy you can hold it by one end and let the rest drop ...


8

Pretty much all "jet" aircraft designed since the 1960s (if not the late 1950s) have used turbofan engines, and bypass ratios have tended to increase over that time frame, as higher bypass tends to produce more thrust for a given specific fuel consumption. The Boeing 707 and older versions of the B-52 bomber (both introduced close to 1960) are ...


7

All three engines you show are for fighter jets flying at supersonic speeds. These engines need a low bypass ratio: Why do military turbofan engines use a low bypass ratio? To achieve more thrust at lower bypass ratios, the bypass air needs to be accelerated more, which requires more than one fan stage because axial compressors can only add a limited ...


7

Both-engine-out glide performance isn't accounted for and isn't a certification requirement (of any airplane that I'm aware of). Airliners have good glide performance as a happy side effect of design optimization for cruising at high altitudes. What does have to be accounted for is single engine performance issues; things like departure performance with an ...


6

The final report notes: At the time of each TAI [thermal acoustic imaging], the inspectors attributed the indication to a defect in the paint that was used during the TAI process and allowed the blade to continue the overhaul process and be returned to service. [emphasis mine] The paint being referred to is used for the inspection. Its function is to ...


6

Most jet nacelles contribute little or no lift, but there is at least one highly notable exception. The airflow inside the nacelle is dominated by the engine and any chance to create differential pressure between upper and lower leading sections is kept negligible in order not to disrupt the intake flow. The outside is more of a stubby fuselage than an ...


6

Did Dassault have some magic trick up their britches It was an era of innovations. Have you seen the Vickers VC10 thrust reversers? The clamshell / target doors can be made internal within the nacelle. Literature is lacking on the Mercure, but there is a nice hint from a cutaway drawing: Source: Air Enthusiast magazine, via aviadejavu.ru The highlighted ...


6

Valves open at low speed to prevent the blades to stall. At low spool speed, or a low power setting (low power setting => less fuel added to the cycle => less power in the turbine and as such less power available for the compressor), the volumetric flow through the fixed geometry compressor passage becomes too large (with respect to the design value, ...


5

Almost any sort of body, conveniently oriented in a fluid flow, can produce lift. A ball is one of the few exceptions... Please note that lift and drag do never cancel out, because they are –by definition– vectors at 90º... There are wingless, heavier-than-air aircraft, like this one, for example: https://en.wikipedia.org/wiki/Wainfan_Facetmobile


5

Smaller airplanes with both rear-mounted and under the wing engines used to have "bucket" type reversers, which captured both hot and hold exhaust. However, a bucket is not a tenable solution for large diameter engines. Fortunately, in modern turbofans the cold thrust is the vast majority of the trust, so there's no point in trying to create a ...


5

Tip speeds do not actually stay the same, turbofan (and turbojet) blade tip speeds can exceed the speed of sound, up to Mach 1.3 (actually stated M1.4 in the link, my experience is M1.3 but also my professor used to mention M1.4) as seen in link. As they are enclosed, the negative effects of the shock are much smaller than if it were an open propeller. Open ...


5

A fan blade at the front or turbine blade at the back of a jet engine is a small aerofoil surface which is fixed to the main shaft and spins with it. By contrast, a stator vane is a similar aerofoil surface fixed to the outer casing and remains static. Why do that? The spinning blades of a given stage cause the airflow to start spinning, and that slows the ...


4

The amount of current flow produced by a seebeck effect device is tiny relative to their size. You would need a plane load of them just to power the lighting system in a passenger jet.


4

When engine or wing anti-ice are needed, the required amount of bleed air increases. In order to provide enough bleed air at the required pressure, the engine idle speed must be increased. That way, the compressor runs faster, which provides more high pressure air to the bleed valves. Note that this will result in more idle thrust as well, which can have an ...


4

Aha! finally found the answer. Based on this and this F-15 uses an APU named Jet Fuel Starter (JFS) which is fitted centrally between the two engines. See 15 on the figure below Another figure of the intake and exhaust of the JFS from bottom of the fighter: The below figure shows the danger area of the JFS: And finally here is an image of this JFS: Hope ...


4

Both shafts are not connected directly. But there are still ways to transfer rotation from one to the other. The most obvious one would be the airflow generated by N2 turning the LPT. But also the bearings between both are not totally without friction and so will also transfer some rotation.


3

You can't escape the tyranny of the law of conservation of energy and the second law of thermodynamics (with it's corollary limiting thermodynamic cycle efficiency). The energy taken from cooling in a reciprocating engine is truly wasted, so the thermal gradient there can be further used without affecting efficiency of the engine itself. But turbines have ...


3

This is most likely some kind of a test where high speed photography (as in 5,000 - 10,000 frames/second) will be used to capture the detailed motion of the fan blades. Types of tests that might require this type of video include fan blade out testing, bird strike testing, and icing / hail testing. There may be others but those are the most common. Why the ...


3

The core is the Internal Combustion Engine - it has intake (of air), compression (of air), combustion (of the fuel/air mix), and exhaust (water vapor, CO2, air) that provides the motive force to rotate the turbine (N2) and provide perhaps 25% of the actual thrust of the whole engine when it exhausts out of the tailpipe. From How Do Jet Engines Work? on this ...


2

You're asking about turbine (hot) reversers of early high-bypass turbofans. 747 flickr.com and twitter.com It had the same mechanism as the cold bypass (blocking doors), similar to what the C-17 (right image) uses nowadays. L-1011 Lockheed L-1011 TriStar - Airliner Tech Vol. 8 It had target-type, but only during development. DC-10 Design Features of the ...


2

From this answer, on the B737NG bleed air tap point: Compressed air is tapped from the engine 5th and/or 9th compressor stage. Air supply is regulated according to demand and varies according to flight stage - during flight stages with relatively high engine power (take-off, climb, most cruise), 5th stage compressed air only is used. During low engine power ...


2

The context is that commercial airplanes make up most of the traffic. Let's take the A320 as an example of commercial airplane. http://a320dp.com/A320_DP/electrical/sys-3.7.1.html The main AC electrical power sources are: Left and right engine integrated drive generators (IDGs) (90-KVA each) KVA is kiloVolt-Ampere, roughly equivalent to KW. So we need ...


2

Based on my reading, the biggest disadvantage of hydrogen as an engine fuel is its low density. Even when stored as a cryogenic liquid, it take up more than ten times the space as the same mass of kerosene, which means the same size tanks will hold only about a third as much energy (even though hydrogen has about three times the energy content per kilogram ...


2

The « cone exposition » is a result from nacelle engine design, and the choice to mix flows or not. The two main strategies are called: Mixed exhaust engine resulting to long nacelle hiding exhaust nozzle and plug. Separate exhaust engine which is shorter and then allows a view of nozzle component. The reason to choose one type of exhaust is made by ...


2

First off, all civil airliners nowadays use turbofans, not just "most". Second, almost all civil airliners still in service use specifically high-bypass turbofans, with a bypass ratio1 of 5:1 or greater. With these engines, the vast majority of the engine's thrust comes from the cold bypass air, not the hot core air, so, even if you reverse both ...


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