Questions tagged [engine-design]

Questions about the process and principles used when designing aircraft engines. Use "jet-engine" and "piston-engine" tags to specify a certain type of engine.

Filter by
Sorted by
Tagged with
20 votes
2 answers
3k views

How do turbofan nacelle lengths compare?

For example, compare the JT9D and the PW4000 below (both from Pratt & Whitney, both on a 747): (Left, Right) The PW4000 has a longer forward nacelle, and a covered exhaust cone. On the inside—...
user avatar
23 votes
2 answers
15k views

Where is the generator in a large turbofan of a commercial airliner?

So, where do you put the electrical generator? If it's gonna be coaxial, the only place is the rear (it will be burnt) or the front (it will get in the way of intake). If it's gonna be coupled to a ...
DrZ214's user avatar
  • 17.7k
4 votes
3 answers
2k views

In high-altitude piston aircraft, what type of forced induction (boost) is used?

In high-altitude piston aircraft, what type of forced induction (boost) is used? Turbocharger or supercharger?
Andrea Ghilardi's user avatar
40 votes
9 answers
34k views

Why increase the number of cylinders in an engine instead of increasing their volume?

I've been reading about WW2 planes lately. Some of them have 12 or even more pistons in their engines. But if your goal is to increase power, why would you add more pistons instead of simply ...
DrZ214's user avatar
  • 17.7k
25 votes
3 answers
4k views

Why are turbofan inlets leaned/angled forward?

(Image Source: Wikipedia) Seeing that everything is radially symmetric (apart from the nacelle mount, naturally), I wonder why the inlet (the front part of the nacelle) is usually skewed?
Pavel's user avatar
  • 909
21 votes
5 answers
13k views

Why do airplanes use an axial flow jet engine instead of a more compact centrifugal jet engine?

Axial flow jet engines take up a lot of space. Centrifugal jet engines create high pressure. Can you create a centrifugal air pump that pushes as much air as a axial jet engine. Centrifugal air ...
Useruuu's user avatar
  • 341
10 votes
7 answers
11k views

Why are contra-rotating jet engines so rare?

Why are contra-rotating jet engines so rare? Such a jet engine would have contra-rotating turbines, or contra-rotating compressors, or both. In fact I cannot think of even one aircraft that has this. ...
DrZ214's user avatar
  • 17.7k
6 votes
1 answer
8k views

How do exhaust cones affect the performance of turbine engines?

I've seen explanations stating that it creates uniform stream of exhaust gas towards the exhaust duct, however without the cone wouldn't it still be considered a uniform stream? Also since a ...
ApolloMission4's user avatar
9 votes
1 answer
9k views

How is the central hub / shaft casing of a two-spool jet engine assembled?

This is the usual view of a two-spool turbine engine: (From source) I don't know if shaft casing or hub are correct names, this is the external skin of the volume around the N1/N2 shafts. I can't ...
mins's user avatar
  • 71.8k
8 votes
1 answer
9k views

How does a labyrinth seal work when the engine isn't rotating?

I believe I understand how a labyrinth seal in a turbine engine works when a the engine is running. Any oil that makes it past the first part of the seal is thrown outwards due to the centrifugal ...
Notts90's user avatar
  • 3,559
8 votes
1 answer
4k views

In a turbofan, why are there no stators behind the fan?

Why are there no stators behind the fan? At least, I've never seen any turbofan design that has stators right behind it. (Here is the latest turbofan I've looked at, the CFM56. Cutaway part starts ...
DrZ214's user avatar
  • 17.7k
5 votes
1 answer
10k views

What is the difference between single and dual annular combustor?

CFM56 uses single annular and GEnX uses dual annular combustion chamber. somebody please explain with pics.
Pritam's user avatar
  • 548
4 votes
2 answers
4k views

Why are turbofan inlets circular- or oval-shaped instead of square-shaped?

Source: materialsengineeringconsultant.com and initious.blogspot.com. Most of the engines are circular except for some that are oval. The oval shape provides a better ground clearance. Why aren't ...
Ethan's user avatar
  • 9,329
40 votes
11 answers
18k views

Why do new jet engines cost billions to design?

This question might come off as crude because it involves people's salaries, but I do not understand why new designs of large turbofans cost many billions of dollars to design. For example, the Pratt &...
DrZ214's user avatar
  • 17.7k
38 votes
4 answers
5k views

Can supersonic conditions be replicated on the ground?

In a previous question the P&W J 58 engine for the SR-71 was discussed. The engine was a new and innovative design combining the characteristics of a turbojet and a ramjet. Before flying with ...
TomMcW's user avatar
  • 28.4k
15 votes
6 answers
9k views

Why does the B-52 outboard engine nacelle have a sharp change in shape?

The outboard engine nacelle of a B-52 appears to have a change of shape too extreme for just blending to the center-line of the engine pod. Why is the B-52 outboard engine nacelle shaped the way it is?...
jwzumwalt's user avatar
  • 11.4k
10 votes
4 answers
4k views

Is the bleed air passengers breathe tapped from the engines before or after it comes in contact with fuel? And why? Isn't this unhealthy?

Passengers are often surprised to hear that the air they breathe comes from inside the engines. This sounds unhealthy. Can you explain, why it is not ? Is bleed air tapped (for cabin pressurization) ...
summerrain's user avatar
  • 3,364
8 votes
5 answers
10k views

Why is there a pressure drop in the combustion section of a jet engine?

This image, referenced in this question, shows in green the pressure value in a jet engine: The combustion section between compressor and turbine is where fuel is injected, mixed with air, and ...
mins's user avatar
  • 71.8k
8 votes
1 answer
2k views

Why does the CF6 have a lower bypass ratio than the TF39?

The General Electric TF39, which powered the original C-5 Galaxy, was the very first high-bypass turbofan brought into mass production, with a previously unheard-of 8:1 bypass ratio. Yet, when it ...
Vikki's user avatar
  • 28.3k
6 votes
7 answers
3k views

Are there Hybrid Electric-Combustion Turbine Engines where only the compressor is electric driven?

So, from what I could understand about conventional Turbine Engines and its various types is that normally the combustion chamber ignites fuel with compressed air, rotating a low pressure fan which ...
mandiokai's user avatar
  • 562
5 votes
2 answers
941 views

Are there any ducted propeller or fans without a shaft in the centre?

Are there any propeller or fan designs that hold the propeller or fan in the duct and do not have a boss or propeller shaft? This could reduce the drag of the centre. Are there any other advantages?
SRawes's user avatar
  • 1,211
5 votes
3 answers
2k views

How much weight does a thrust reverser add?

How much weight does a thrust reverser add to an engine? Let's take the CFM Leap 1B as an example, which powers the new version of the Boeing 737. This engine can produce up to 130 kN of thrust for ...
DrZ214's user avatar
  • 17.7k
4 votes
4 answers
540 views

What changes are needed for a piston-prop aircraft to withstand saltwater environment?

I'm interested in WW2-era piston-prop aircraft. I want to know what changes are needed to make the aircraft withstand saltwater corrosion. Presumably these are different and more expensive than the ...
DrZ214's user avatar
  • 17.7k
4 votes
3 answers
2k views

Why does the Trent XWB have intermediate compressor stages?

I realized that the Rolls-Royce Trent XWB on the Airbus A350 has intermediate compressor stages. Why is that? Other engines like the CFM56 or IAE V2500 that power most of the A320-family have low ...
Gary Zenger's user avatar
4 votes
2 answers
1k views

What modifications are required for automotive fuel STC?

What actual engine modifications are required to allow certificated piston engined general aviation aircraft to run automotive fuel under an FAA Supplemental Type Certificate (STC)?
Michael Hall's user avatar
  • 25.7k
4 votes
1 answer
786 views

Why does the spool speed increase with altitude for a turbofan engine (single spool & double spool)?

So, I want to see the effect of altitude on the compressor characteristic of a single spool & double spool turbofan engine at constant flight speed and TIT (turbine inlet temp). I am aware that ...
Topcatmki's user avatar
  • 163
3 votes
4 answers
3k views

What drives the shape of an engine's intake on a fighter jet?

Rectangular intakes have more corners which might increase subsonic pressure losses and would weigh larger than a pitot (Semi-circular) type intake. Are the designer drivers solely based on supersonic ...
jetlight's user avatar
1 vote
1 answer
2k views

What would be the best fan duct design to achieve maximum thrust?

I have a few brushless motors and I am trying to get the best thrust out of each motor. I am busy doing some research but can't get a clear answer. What would be the best fan duct design to achieve ...
Marc Uberstein's user avatar
1 vote
3 answers
555 views

Can a gas turbine be able to switch from torque to thrust?

Can a turbine engine be switched from providing torque (like a helicopter) to the rotor to transfer power to provide exhaust thrust (like a jet plane)? Related: BV-347 upgrade this way?
Muze's user avatar
  • 1
56 votes
6 answers
26k views

Why do most radial engines use an odd number of cylinders?

To help suppress vibration, most 'V' and 'horizontal' engines use an even number of cylinders as closely opposed as possible. Radial engines are well known for excessive vibration. For some reason ...
jwzumwalt's user avatar
  • 11.4k
46 votes
4 answers
14k views

What is this hole at the front of the engine pylon on a Boeing 707?

Images of the Boeing 707 show a hole at the front of the engine pylon just above the engine. Can someone please tell me what is the purpose? Also why do images show the hole absent on the left outer ...
Paul Howard's user avatar
43 votes
6 answers
11k views

What is some of this extra "stuff" on jet engines?

At the risk of sounding too broad, I want to better understand the complications of jet engines. This time, I'm asking about extra "stuff", which unfortunately I have no better name for ...
DrZ214's user avatar
  • 17.7k
23 votes
1 answer
3k views

How much weight does a blisk save?

A Blisk is a bladed-disk, all one monocoque component. So the blades do not have to be inserted and secured, and they are not removable. No nuts and bolts either. The downside is that any serious ...
DrZ214's user avatar
  • 17.7k
20 votes
1 answer
9k views

Why did Boeing remove the engine chevrons on the 777-X?

From the most recent renderings on Boeing's site, it looks like the engine chevrons found on the 787, 747-8 and 737-Max have been removed from the 777-X. Is there a good reason for this?
lchike's user avatar
  • 303
18 votes
6 answers
9k views

Why do large turbofans generally have many more LP turbine stages than HP turbine stages?

In almost every large turbofan I see, the LP turbine stages outnumber the HP turbine stages by a factor of at least 2. Here's a photo of the RR Trent 900: The Trent 900 (like most Rolls-Royce ...
DrZ214's user avatar
  • 17.7k
17 votes
2 answers
4k views

Why don't NK-12 powered contra-rotating propellers turn in equal rpm?

The Kuznetsov NK-12 is a Soviet turboprop engine of the 1950s, designed by the Kuznetsov design bureau. The NK-12 drives two large four-bladed contra-rotating propellers, 5.6 m (18 ft) diameter (NK-...
Jpe61's user avatar
  • 28k
10 votes
2 answers
1k views

Why were turbojets the first kind of turbo-engines, instead of turboprops?

During WW2, the first jet engines appeared en mass in combat aircraft. Britain and Germany made the first ones. But why were turbojets first? Why not turboprops, which are easier since the turbo-...
DrZ214's user avatar
  • 17.7k
10 votes
4 answers
10k views

How are turboprops and other propeller planes pressurized?

I know how most turbofan jets are pressurized: But it can't be the same with turboprops, as I don't understand how propellers can take in the air. Yet, planes like Q400s can fly above 8000', all the ...
Air Canada 001's user avatar
10 votes
3 answers
3k views

Why do many large turbofans have a gap (of turbine blades) between the LP turbine and HP turbine?

After browsing around a while, I noticed that many...I think almost all...large turbofans have this gap between the LP turbine and HP turbine. I took some screenshots and put a red circle around the ...
DrZ214's user avatar
  • 17.7k
9 votes
3 answers
7k views

What are the advantages and disadvantages of mixing the bypass flow with the core flow?

Many Aircraft engines mix the bypass air with the core gases before exhausting to atmospheric pressure through a propelling nozzle. However, some do not mix and have separate nozzles for the flow of ...
Abhishek Verma's user avatar
9 votes
7 answers
3k views

Why don't bypass ducts in jet engines narrow down the flow to accelerate it?

Since decreasing the flow area increases flow velocity, why don't turbofan bypass ducts narrow down to produce more thrust?
Francis L.'s user avatar
  • 2,524
9 votes
2 answers
3k views

What is the operating temperature of a turbofan engine, and how is it kept at that temperature?

What is the operating temperature of a turbofan engine? If advancements were made to materials through material science for the internal components would increasing the operating temperature result in ...
securitydude5's user avatar
8 votes
1 answer
727 views

How difficult is it to design a high bypass turbofan given a military derived core?

Suppose one of the big-threes is given a military low-bypass turbofan core, how difficult would it be to produce a design centered around this core that matches the competitive performance of a ...
Meatball Princess's user avatar
7 votes
1 answer
1k views

What are the "beta lines" of a gas turbine engine component?

For a compressor in particular, what do the beta lines represent? I know for a compressor map you have the lines of constant spool speed, and the contours of isentropic efficiency. I also understand ...
Buran_'s user avatar
  • 73
7 votes
5 answers
15k views

Why do jet engine fan blades have a twisted shape?

I'm thinking: as the blades rotate, the tip moves faster than the hub. So to make the blades efficient, the blades are usually twisted. The angle of attack of the blades at the tip is lower than at ...
D. Frederico's user avatar
7 votes
3 answers
1k views

Why don't turbofan engines have shrouds affixed to the fan blades?

For a turbofan to be efficient the gap between the blades and the shroud has to be extremely small. Why don't we just attach the shroud directly to the blades and let it spin as one? Would that ...
Francis L.'s user avatar
  • 2,524
7 votes
1 answer
2k views

What is the purpose of the air inlets on an A320neo's pylon (LEAP-1A)?

What is the purpose of the air inlets on an A320neo's pylon (LEAP-1A)? Passive cooling, air bleed like in the 707, or something else?
JML's user avatar
  • 73
7 votes
3 answers
2k views

Is this image of Compressor aerodynamics correct?

Image Source: Air Gas Turbine Technology by Treager, Chapter 5 The rotation direction of rotor shown seems opposite. If it is correct, these are the questions I would like to ask: Why the Y vector is ...
Noorul Quamar's user avatar
7 votes
1 answer
489 views

Which compressor is more like to surge and stall - axial or centrifugal?

I am studying about stall and surge in rotodynamic compressors and want to understand which one is more prone to these phenomena.
Aditya Shiva Appalla's user avatar
6 votes
2 answers
533 views

Why is a turbofan engine less efficient when air leaks over fan blade tips?

Image source I understand part of the reasoning for minimal clearance between the casing and the fan blades, is to have the larger fan blade possible, which generates a larger low pressure area to ...
ApolloMission4's user avatar