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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0
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0answers
6 views

What is the engine shell temperature?

What are the highest temperature locations in the outer shell on an aircraft engine? Particularly, modern turbofans like the Trent 900 for example. I'm interested in the temperature constraints of ...
7
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7answers
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?
3
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1answer
114 views

How has afterburner design changed since it's inception?

I came across a NACA summary paper on the past 5 years of afterburner development and started reading cause it seemed interesting. However, a couple of pages in I scrolled back up and realized that it ...
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1answer
106 views

What is the temperature range of engine mounts connected to the pylon?

I want to know what is the temperature of the engine mounts in modern turbofan engines for example, Rolls Royce Trent 900. Also, what are the temperature considerations you need to make while ...
12
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4answers
3k views

Why hasn’t the Wankel rotary engine seen more use in aircraft?

The Wankel rotary engine seems to have several advantages over traditional reciprocating cylinder-and-piston designs. In general, they have a much higher power-to-weight ratio, less vibration, and ...
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0answers
105 views

How hot is the outer casing of a turbofan engine?

I am able to find temperatures inside different components of turbofan engines, but I can't seem to find what would be the temperature of the external casing/shell of the engine. For example, ...
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0answers
39 views

How to determine the number of copression stages given a compression ratio?

I have a personal project to design a gas turbine engine, the main problem that nags me is how do I determine the pressure rise in each stage of an axial compressor? Say, I'm planning on a 38:1 engine ...
8
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2answers
1k views

What is the purpose of a freewheeling unit in an helicopter, if a centrifugal clutch is already present?

Some helicopters such as the Bell 47 are fitted with a centrifugal clutch. Centrifugal clutch will engage only at certain engine RPM. If the engine fails, the engine RPM will reduce and the ...
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1answer
64 views

Why are inlet vanes used instead of variable geometry inlets to prevent compressor surge/stall?

Jet engine core axial compressors (that of subsonic turbofans anyway) are designed to keep air flowing the right way at max RPM(or close to it). Below that, the airflow slows more and more, and ...
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0answers
47 views

How to avoid shock (particularly Oblique shock) inside Cd nozzle?

Using the Area ratio (A/A*) and for the desired exit Mach number I have designed a cd nozzle. The Inlet total pressure (Po) and the total temperature (To) is calculated using Isentropic relations for ...
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4answers
8k 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 ...
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1answer
32 views

Considering a piston engined aircraft, what resistance pressure would be generated within its engine bay against its cooling intake?

Consider a piston engine with all its coolers and components within an aircraft engine bay. To cool this engine, cooling intakes are positioned facing the direction of flight. Now, the condition at ...
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0answers
16 views

Effect of Exhaust Mixer on the temperature of Core Exhaust

After the core exhaust leaves the turbine section (having a temperature of about 900 C ), and it mixes with the by-pass air via the exhaust mixer , what will be the resulting temperature of the ...
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3answers
220 views

Why weren’t large, high-power radial engines built to take advantage of the Meredith effect?

Most aircraft piston engines fall into two general categories:1 Radial engines (radials for short2) have their cylinders radiate out from the crankshaft in a star pattern; they tend to have a blunt, ...
3
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2answers
146 views

How do turbofan internals handle the load from the thrust?

To my understanding, turbofan engines get the majority of their thrust from the fan in front of the engine, up to around 70-80% while the core flow generates around 20-30%. Forward movement is ...
12
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2answers
688 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-...
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0answers
46 views

Jet Engine Cooling, HTC and cooling calculations

Right now I am working on a project about cooling systems in jet engines. And I don't have a supervisor to ask anything. I would like to know what is the most useful resource (book, analsys programs ...
5
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1answer
332 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?
7
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1answer
96 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.
3
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1answer
124 views

How to calculate the number of blades?

Inspired by building a new drone, I got lost in curiosity. What if I have a fixed length of rotor blades and a target amount of lift I want to, well, lift. How do you calculate the number of blades? ...
1
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1answer
58 views

Could high density abrasion-resistant ceramic turbine blades allow for the use of borane fuels?

In the late 1950s the U.S Air Force searched for a fuel with similar characteristics to jet fuel but with higher energy density allowing longer flight range for bombers. In 1947 the British had ...
20
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6answers
8k views

Do turbofan engine cowlings dilate during spool-up?

I was watching this Youtube video, portraying a Fokker 70 taking off. I wouldn't have noticed if it weren't for a comment, but during spool up (~ 3:24 in the video), it appears as if the engine ...
13
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4answers
9k views

Are jet engines designed in a way to make an explosion result in the least damage possible?

I know most engines are super reliable today, but do manufacturers do anything to at least make an explosion result in the least damage possible?
35
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1answer
7k views

Do the Mt. Everest rescue helicopters have modified engines to operate at high altitudes?

There are so many climbers on Mt. Everest today that there is now a helicopter rescue service there. They operate rescue up to 21,000 + ft. Because this is essentially stationary service it seems that ...
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1answer
56 views

Are solid fuel rocket engines designed differently and how? [closed]

How do solid fuel (Hydrazine, UDMH) and oxidizer (N2O4) differ in design from cryogenic rocket engines such as LH2 and LOX? Are there differences related to temperature, material design, turbopumps, ...
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2answers
120 views

How is a stator like a diverging passage?

I've read in a lot of places that stators in an axial compressor are responsible for diffusing air and removing the radial velocity to make the flow parallel to the shaft. What I don't understand is ...
8
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3answers
458 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 ...
36
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10answers
15k 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 &...
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0answers
33 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 ...
5
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2answers
613 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
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1answer
171 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
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2answers
130 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, ...
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2answers
248 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 ...
6
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5answers
631 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)? ...
48
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6answers
11k 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
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1answer
184 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 ...
4
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1answer
265 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
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1answer
217 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
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2answers
652 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
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2answers
390 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
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1answer
711 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 ...
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0answers
116 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
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2answers
194 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
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3answers
322 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
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2answers
235 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 ...
2
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1answer
281 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
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1answer
199 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)
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5answers
5k 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 ...
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2answers
138 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
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1answer
1k 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 ...