# Tag Info

30

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 ...

25

Turbojets and turbofans are very similar indeed: both are turbine engines; both create thrust from 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 five 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 ...

22

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 ...

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 ...

19

Centrifugal is easier to make. It's just a big vacuum cleaner with a kerosene burning furnace behind it instead of an electric motor. You have a one piece impeller, as opposed to numerous little blades and discs, and can be cast or machined from a block of metal. It's not dependant on the aerodynamic lift of blades to force air from a large space into a ...

15

Completely different design philosophies They are both turbine engines, and that is where the similarity ends. In a turbojet, the compressor-burner-turbine package is optimized to make thrust. A turbofan engine is a type of turboshaft engine. These use a compressor-burner-turbine core, but use a secondary set of turbine blades to convert its thrust ...

11

Yes, they can. In service today: The Canadair CL415 is a turboprop water bomber with water landing capabilities (typically, water skimming capabilities, to skim across a lake and refill). The Shin Maywa US-2 is the latest in a series of rescue/maritime patrol aircraft that have been in service for some time. The design uses the engines and wing of a C-...

10

To expand on what Dave said, the term Power is used for turboprops because the thrust produced by the prop is a function of horsepower applied to the prop, that is, torque @ RPM. The gas generator of a turboprop - the jet engine part - has its output indicated as a percentage of maximum torque it can apply to the propeller gearbox, whereas a pure jet ...

10

Propeller planes already existed, and turboprops were an answer to a question that was not asked in times of war. The main driving factor behind development of the turbojet was to provide great climbing power and high airspeed for intercepting enemy bombers, which the turboprop would not have been able to do. Fuel economy and engine life were of secondary ...

8

Yes. The Rolls-Royce/Snecma Olympus 593 [Wikipedia] were pure turbojets and they had thrust reversers. Source: Wikimedia Also, T/R on Concorde were also used in flight (If I remember correctly, only the inboard ones were used in flight) because Concorde didn't have spoilers. Being a civilian aircraft, with the engines mounted under the wing, Concorde ...

8

If it was to leak, it's still going through the intake to the compressor or bypass duct. This is incorrect. A "leak" would cause the compressed air to circle around the fan and exit again from the front, reducing the efficiency of the fan, because part of the power would be used to compress air that does not do any useful work in the engine. The circling ...

8

The development of turboprops and jets were going on more or less concurrently before and during the initial stages of WWII -their first test runs were within years of each other. You have to understand that there was a war going on- any (significantly) better aircraft engine would be the difference between life and death; and that would be the one that ...

7

The Aermacchi MB-339 was developed from the -326 and it is also powered by one Rolls-Royce Viper Mk. 632 turbojet. From its aircraft manual, the relight button is for the in-flight re-ignition: Premuto - Attiva il sistema di riaccensione in volo. Pressed - Activates the re-ignition system in flight. The start button in your picture is for activating ...

7

Yes, but the classification is not a matrix. A turbofan by definition needs a fan, but at its core it can have a centrifugal compressor. A good example is the Pratt & Whitney Canada PW600 series. This allows a compact design, at the expense of compression ratio. It works well for low-thrust applications such as the Cessna Mustang. The advantages are the ...

5

The main way to convert a gas turbine to provide thrust rather than shaft horsepower is to attach a large fan or propeller in place of the previous load. For example, the GE CF6, which powers aircraft such as the 747, 767, and A330, has a gas turbine variant called the LM6000 that provides around 50 MW of power. If you want to provide thrust from the ...

5

To start the engine, the fan blades have to be spun up. This is typically handled by either blowing air through them from some outside source, and/or by using an APU to generate power to drive the shaft they're connected to. Once the engine is running, it sucks in enough air to keep going on its own.

4

And, if you want a turbojet without any air flowing through the engine around the core, the 707-120 and DC-8-10 used Pratt & Whitney JT3C turbojets with thrust reversers. Slightly-later models (the 707-220/-320 and DC-8-20/-30) used P&W JT4A turbojets, also with thrust reversers. Over in Europe, the Caravelle VI-R used Rolls-Royce Avon 533R/535R ...

4

The real reason is that, by definition, a jet engine does not output any kind of power but outputs the thrust force instead. Turbopropeller engines do not output a thrust force but rather output a mechanical power through a shaft and gearbox supplied by said power by either a power turbine or the gas core itself. That arrangement has to do more with how ...

4

You wrote in a comment on Dave's answer: why you wrote that turboprop engines generate power, whereas while writing for jet engines you wrote that they generate thrust. This was my actual question? I understand mechanics of both, but why is it intentionally written different? Am I missing something? So it sounds like the main question you're trying to ...

4

Yes, if it's designed to do so. There have been several jet seaplanes over the years, and one feature common to almost all of them is that the engine intake(s) are mounted above the wings or high on (or above!) the fuselage (sometimes on an auxiliary pair of high-mounted stub wings) to avoid ingesting water. Martin P6M (intakes - and engines - on top of ...

4

Turboprops and turbojets - or, more broadly, jets - produce thrust in somewhat different ways. First of all, let's address the way thrust is produced. Per Newton's 2nd and 3rd laws, force equals acceleration times mass, and an action (accelerating the air) produces an opposite reaction. After canceling out the variables (the math is easy to find), thrust is ...

3

It's not a cut and dried single figure but this SR-71 PROPULSION SYSTEM - P&W J58 ENGINE (JT11D-20) seems to have enough information to allow you to arrive at a reasonable figure with 'some work'. If I had to choose one information source to get a feel for the answer this would be on the short short list (so far :-) ). Unlike most other sources, the ...

3

The final turbojet-powered aircraft to carry passengers was an Aerotours Dominicano Boeing 707-020 (early name for the Boeing 720). Registration N8711E. Retired sometime between 1986 and 1996. The final turbojet-powered aircraft to carry cargo was an Airborne Express Caravelle 6R. Registration N902MW. Retired in 2002. Hope this answers your question!

3

As far as the T-104, Aeroflot retired the Tu-104 from civil service in March 1979 however it wasn't until after the Pushkin crash in February 7th 1981 that killed 52 people that the type was permanently removed from service. Follow-up / safety actions The remaining military Tu-104 aircraft were grounded following this accident. Source: https://...

3

This is kind of half an answer, but the difference between active tip clearance control and passive tip clearance control is in the definition of “active” and “passive”. An active system has some way of determining the clearance, and then making adjustments to achieve a desired gap. So, it has a feedback loop in the control system. A passive system has no ...

3

Oau, a lot of answers and almost nobody touching on the real issue. Propellers will produce a thrust that decreases with increased speed. Since power= thrust x speed, this means the engines will produce (more or less) an (almost) constant power throughout the speed range of the aircraft. Given a specific fuel flow, it will produce a specific (calculatable) ...

3

Going back further to the early 40's to the de Havilland Goblin turbojet: There is an in-depth article from Flight from February 21st, 1946. The first page is here, but you'll need to download the rest of the pages from the navigator on the left. It even comes with this diagram showing the forces on the different parts. Materials Reading through the ...

3

You certainly can. The equivalent to overtorquing is called overboosting and is defined as an exceedance of the primary thrust setting parameter, N1 or EPR. Modern FADEC engines contain software protection, but it is certainly possible in mechanically controlled engines. Thus, older aircraft, such as the DC-9 have mechanical or electronic controls which set ...

3

$v_0$ is the airflow speed through the engine, not the airspeed. As per @Bianfable’s comment. How the engine works at standstill: the compressor sucks air into the inlet, it initiates the flow through the engine. Axial compressor blades similar to a propeller, centrifugal compressors by slinging air out towards the compressor outlet. Maximum thrust at ...

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