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.

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8
votes
2answers
233 views

How does the engine wash improve engine performance?

According to maintenance manual, we usually carry out engine wash (CFM56) with pure water as scheduled task. Pure water is injected into the engine from the LP compressor inlet while the engine is ...
35
votes
10answers
14k 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 &...
0
votes
0answers
27 views

What is the flow rate through the bypass tubes on the J58 engine?

Does anybody know how large the mass flow rate through the bypass tubes on the Pratt & Whitney J58 engines at subsonic and supersonic conditions is? Also is there any information available to find ...
4
votes
2answers
264 views

Do thrust reversers only have idle and full modes or are there intermediate settings?

Are there any intermediate thrust reverser settings? If so, how often do pilots use these intermediate settings?
5
votes
1answer
153 views

PBY-5A exhaust modification?

What is the function of these “tubes” that cover the outboard exhaust stacks on some PBY-5A and PBY-6A aircraft?
4
votes
2answers
117 views

How is lift transferred from rotor to chassis (or weight, the other way around)?

I am trying to find out how a helicopter rotor's lift is transferred to the chassis. Equivalently, how is the weight of the helicopter transferred to the rotor blades? While looking for this online, ...
-3
votes
2answers
185 views

What is the Angle of Attack of this Propeller?

Photo 1 and photo 2 from here, photo 3 is from here. Here are three propellers. As in my understanding, the AoA or the pitch of a propeller should be close to its rotation's direction, around 15 ...
5
votes
3answers
359 views

Do contra-rotating propellers have the same RPM?

Image source Here is a contra-rotating propeller. The front propeller rotates counterclockwise while the back propeller rotates clockwise. My questions are: Do they rotate at the same speed (RPM)? ...
43
votes
5answers
9k views

Why are two-stroke engines nearly unheard of in aviation?

Almost all aircraft piston engines are four-stroke engines, with one power stroke per piston every other crankshaft revolution and a great deal of intricate moving parts which are only too happy to ...
3
votes
1answer
169 views

Why are liquid ring compressors not used in a jet engine?

A question has been asked here before whether sliding vane compressors could be used in place of axial compressors on jet engines since they have a high compression ratio per stage (Why were rotary ...
3
votes
1answer
200 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 ...
0
votes
1answer
133 views

How do you design a NACA intake?

What are the construction guidelines to geometrically build a NACA intake (submerged intake) for aircrafts? The relationships between the aerodynamic performance parameters (ram recovery, drag, and ...
3
votes
2answers
250 views

From which stages is the bleed air from a GE90?

I'm doing a university project on the GE90-115b engine and I'm having a hard time understanding this EASA type-certificate data sheet. In particular I can't figure out the air bleed extraction section ...
4
votes
2answers
217 views

Are there any safety features to prevent reversible-pitch props from reversing in flight?

Some aircraft have propellers capable of reversing pitch, which is also known as beta angle. The example I saw was an Aviat Husky. (Youtube demonstration) I want to know if there are any safety ...
3
votes
1answer
397 views

Topics for high school chemistry project (IB Chemistry IA)? [closed]

I have to do an IB Chemistry IA and I wanted to relate it somehow to aviation; however, I can't do anything super complicated though because I'm only a high schooler. Here are some possible topics ...
1
vote
0answers
109 views

Do rotating deflagration engines exist?

Pulsejets (which could have been called pulse deflagration engines) rely on pulsed deflagration to generate energy and thrust. Their pulsed mode makes them hideously loud and rather inefficient, but ...
3
votes
2answers
165 views

What are the relative efficiencies of the various stages of a counter rotating propeller?

After going through the CFD results of a drone project I am involved in, I noticed that the data shows significantly increased (+10%) thrust generation at the second stage of a counter-rotating, 2-...
1
vote
3answers
269 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?
3
votes
2answers
146 views

Can an S-duct fit a turbofan exhaust instead of the intake?

Can an S-duct fit a turbofan exhaust instead of the intake? The idea here is to merge 2 exhausts into one at the exact center of the tail. This would be for twin-engine aircraft that have both engines ...
1
vote
1answer
149 views

On a centrifugal compressor impeller what is the difference between the radial vanes and rotating guide vanes?

I thought the radial vanes were a machined part of the impeller that just force the airstream radially? And that another name was rotating guide vanes as they are rotating with the impeller disc.. But ...
0
votes
1answer
169 views

Why is the intake of the 757 (RR) engine slanted? [duplicate]

I'm sitting looking at a 757 with Rolls-Royce engines and just noticed that the intake is slanted forward by 5-10 degrees. Anyone know why? (wikimedia.org)
18
votes
4answers
4k 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 ...
1
vote
2answers
122 views

Could a Dyson fan displace more air without increasing the fan size?

So the Dyson Fan is cool. But it has a thrust to weight ration of 0.6. Not very efficient for flight. Its great at sucking large amounts of air but not at a very high velocity. Thrust is small amounts ...
6
votes
1answer
454 views

How does the CFM LEAP-1B engine achieve the same efficiency as the LEAP-1A despite its lower bypass ratio?

The CFM LEAP engine comes in 3 variants (1A, 1B, 1C). The larger LEAP-1A and LEAP-1C variants have bypass ratios of 11:1, while the smaller LEAP-1B only has a bypass ratio of 9:1. For turbofan ...
4
votes
2answers
179 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)?
3
votes
1answer
152 views

Why do the Diamond DA-42 and DA-62 have a minimum fuel temperature requirement?

On the turbo diesel DA-42 and DA-62 aircraft there exists a minimum fuel temperature limitation where you may not start or operate the aircraft below that. Does anybody know why this is? It seems ...
0
votes
0answers
46 views

Oultlet vane guides

I have looked around the web and I could not fine this information. How many vanes are there for the CF6-80 and the CFM-56? Is the count dependant on anything particular, such as fan diameter?
29
votes
2answers
4k views

What features enable the Su-25 Frogfoot to operate with such a wide variety of fuels?

It is widely attested* that the Su-25 Frogfoot's engines (the Turmansky R-95Sh and later the R-195) were designed to function using a wide variety of fuels, including diesel, gasoline, petrol, ...
0
votes
1answer
149 views

Any unique characteristics to identify aircraft engine? [closed]

I love to find out the engine manufacturer and make, used in all of the aircraft I fly. Can anyone provide hints on how to identify an engine uniquely? The CFM56 on a Boeing 737NG is easy. It has a ...
0
votes
0answers
147 views

Does any modern jet engine have blow-in doors, if not, why? [duplicate]

Are the blow-in doors concept on some engines like the JT3D used on modern jet engines, or not? If they are unusual, please explain why?
0
votes
3answers
384 views

Why is carburetor heat unnecessary at full throttle?

Questions like How does aircraft design affect carburetor ice? show how carburetor mount point affects the relative passive heating of the carburetor by the engine, but I've never learned why full ...
1
vote
1answer
149 views

Are turbofans compensated for gyro effect?

In a multi-spool design is the gyro effect canceled or mitigated by having the two or more spools spinning in different directions?
4
votes
1answer
292 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 ...
4
votes
1answer
246 views

Are all engines fan blades made out of titanium?

I was wondering if all engine fan blades are really made out of titanium.
11
votes
2answers
1k views

Are centrifugal turbojets easier to make than axial ones?

Looking at the history of jet engines, I noticed that the British first made centrifugal-types, but the Germans went straight into axial-types. Which type is easier, if any? By that I mean, which ...
4
votes
1answer
583 views

How is the F-22's nacelle/engine bay ventilated?

How is the aircraft skin around the engine bay in the F-22 cooled? As in the F-35, there are scoops below the wings, which provide ram air around the engine bay, but you don't see any scoop around in ...
0
votes
2answers
105 views

Why can't ramjet diffusers be stacked to achieve a good overall pressure ratio?

The problem with ramjets is that they only gain efficiency similiar to turbojets at speeds above mach 2. However, ramjets can operate at speeds of a few hundred km/h. Why therefore cant ramjet ...
2
votes
2answers
301 views

What is the minimum size of a ramjet?

Having recently learned that 155 mm ramjet artillery shells are now a thing, I wonder how much ramjet engines can be miniaturized. Could we see ramjet tank shells? Man-portable recoilless guns? ...
2
votes
1answer
235 views

Who should design the nozzle of jet engines on aircraft?

There is a question in my mind that which company should design the nozzle of jet engine - the aircraft designer or the engine designer? If you watch this documentary: BBC Documentary Rolls Royce ...
3
votes
1answer
339 views

How does propellers' pitch change during the use of reverse thrust in turboprop/propfan propelled planes?

Which way do proplellers turn during the use of reverse thrust in turboprop/propfan propelled planes: A) Do the leading and trailing edges of propellers remain the same or... B) Do the propellers ...
3
votes
4answers
292 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 ...
0
votes
0answers
65 views

What % of horsepower in a turbine is used by the compressor section? [duplicate]

If a turbine generates 10,000 shaft horsepower, I am trying to understand how much horsepower has been used to compress the air. So the turbine that generates 10,000 hp must in fact generate 10,000 ...
3
votes
3answers
169 views

Would there be a purpose for a set of compressors in an electric turbo fan?

This is actually a two part question. Would there be a purpose to a compressor in an electric turbofan where there is no need for a combustion chamber, and if not, is there then a purpose for a bypass ...
0
votes
2answers
123 views

How do engines cope with various intake airflow speeds?

On a recent trip out of Washington Dulles to San Francisco, our B777 met with 200+ mph headwinds (as per the passenger entertainment system) at 35,000 ft for the first half of the route, before ...
2
votes
1answer
86 views

Is there a good online source on rotating detonating pulse engine?

I can't find a clear presentation that would explain the workings of a rotating pulse detonation engine graphically, only useless (to a layman) cfd simulations of the combustion chamber. Please share ...
0
votes
1answer
184 views

How does the debris rejection system in the CFM LEAP engines work?

How does the debris rejection system in the CFM LEAP engines work? LEAP - The debris rejection system
0
votes
2answers
201 views

Could a jet engine be made from cast aluminium?

What materials are used to make the high temperature-high pressure bearing parts in a jet engine? I'm asking about the combustion chamber, combustors, nozzle and diffuzers (as in ramjets) rather than ...
3
votes
0answers
91 views

Could injectors be used as an alternative to turbopumps in jet engines?

Could injectors be used instead of turbopumps in aeroengines? Are there jet engimes that already use them? https://en.m.wikipedia.org/wiki/Injector
2
votes
1answer
196 views

Why and how can a fume event occur?

« A fume event occurs when bleed air used for cabin pressurization and air conditioning in a pressurized aircraft is contaminated by fluids such as engine oil, hydraulic fluid, anti-icing fluid, ...
9
votes
3answers
3k 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) ...