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Questions tagged [propulsion]

Questions about the various methods used to propel aircraft.

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I'm having a hard time conceptualizing this statement from "The Jet Engine" by Rolls-Royce

This is taken from section 21 of Chapter 3, Compressors that discusses axial flow compressors in turbine jet engines. The more the pressure ratio of a compressor is increased the more difficult it ...
shrimp's user avatar
  • 41
1 vote
2 answers
107 views

Why does adding heat to the subsonic flow increase the speed of the flow?

In Rayleigh flow, adding heat to the subsonic flow increases the speed and adding heat to the supersonic flow decreases the speed. But what is its physical cause?
alireza's user avatar
  • 113
0 votes
2 answers
72 views

How do tubojets compare to afterburning turbofans in terms of efficiency?

Turbojets used to be more common in the 40's and 50's but once jet engine design matured they pretty much went extinct in favor of the more efficient turbofan. I know one advantage of the turbojets is ...
shrimp's user avatar
  • 41
-1 votes
3 answers
190 views

What is the most efficient design for an aircraft designed only to hover? [closed]

What could be the most efficient propulsion solution/design for an aircraft (weighting less than 25 kg) designed only to hover (at a height of 100 m) ? No horizontal flight intended other then ...
BobC's user avatar
  • 51
1 vote
3 answers
150 views

Could an air-breathing electric propulsion (ABEP) or other form of ion propelled aircraft fly on Mars?

I'm currently in a class for aircraft propulsion and I became interested in Ion propulsion. It seems there hasn't been many developments for a few years as far as viable aircraft utilizing the ...
thewanderingsophist's user avatar
-2 votes
1 answer
123 views

Are Hybrid-Electric Propulsion Systems the only avenue to achieve the range and speed equivalent to current airliners? [closed]

Airliners like the A320neo and 737-800 use HBP Turbofan engines to achieve cruise speeds of around 0.8 mach, and have ranges around 6,300 km. Therefore, is the only means of achieving similar numbers ...
Carvman's user avatar
0 votes
1 answer
132 views

When doing calculations with TSFC of multiple engines, do we add all TSFCs together?

I'm doing an assignment at the moment where I need to evaluate FOMs based off some characteristics of an aircraft. One of the parameters I need to evaluate is the best milage, which I'm doing like so: ...
amca5333's user avatar
0 votes
0 answers
40 views

If you could put multiple smaller ejector pumps in the same space, would it work better than one larger ejector pump?

I saw somewhere how, for Dyson bladeless fan systems to work for hovering, you'd need an entire grate of ejectors rather than a single ring. However, if you had five ejectors in the same space, each a ...
Geoffrey Williams's user avatar
5 votes
3 answers
920 views

How does momentum thrust mechanically act on combustion chambers and nozzles in a jet propulsion?

I'm asking this question since I can't intuitively understand how the acceleration of mass flow and therefore the increase of its momentum can actually mechanically act on the combustion chamber ...
MK.s's user avatar
  • 65
0 votes
1 answer
81 views

Can engines with a fixed nozzle in the angle of attack have the same effect as the thrust vectoring?

If the figure above represents a missile at the angle of attack and we vector resolution the thrust output from the nozzle, we can see that the thrust is divided into sine and cosine parts. Does the ...
alireza's user avatar
  • 113
8 votes
3 answers
622 views

Could entrained air be used to increase rocket efficiency, like a bypass fan?

Could entrained air flow could be used to increase thrust in the similar way to how a bypass fan works? - The total thrust is √(2𝜈𝑃) where 𝜈 is the total exhaust effective mass flow straight ...
Dylan Menzies's user avatar
3 votes
2 answers
247 views

How is the power gained from exhaust of an engine calculated?

Ryan XV-5 Vertifan used exhaust gas from engine to rotate the fan inside the wing. If I want to design an aircraft using this propulsion system how can I calculate how much power I can get from a ...
Eaza's user avatar
  • 121
3 votes
1 answer
567 views

Why does Engine Pressure Ratio (EPR) rise as thrust levers are pushed forward?

I'm looking for an answer that at least addresses the fundamental thermodynamics of a jet engine. Jet engines use a Brayton cycle to get useful work out of a heat source. An ideal Brayton cycle engine ...
youguysfail's user avatar
2 votes
1 answer
394 views

What are the exit temperatures of bypass flow

Consider a typical high bypass turbofan designed for cruise at approximately mach 0.8, with a separate nozzle for the bypass air. Ideally, the bypass air would be compressed adiabatically by the ...
Ögmundur Eiriksson's user avatar
0 votes
0 answers
42 views

Is the same working principle of a vacuum ejector (fluid eductor, pressure ejector or "motive flow") viable to be used as a propulsion system? [duplicate]

Some time ago I've made a question involving Jetoptera bladeless propulsion, and got a comment saying they didn't know how that method of propulsion would make any difference. But I forgot to ask more ...
Fulano's user avatar
  • 121
0 votes
1 answer
152 views

Are there any aircrafts that use the same "ballooning effect" of spiders to fly?

For those that aren't aware, the "ballooning" effect that spiders use to glide (not necessarily fly) explaining in a simple way, some small invertebrates throw a bunch of long strings (in ...
Fulano's user avatar
  • 121
8 votes
2 answers
2k views

Could ducted propellers improve efficiency in small drones?

I have seen that a new electric airplane design has decided to a choose ducted propeller design somewhat similar to the one of jet engines, explaining this design choice with the fact the ducted ...
AndreaF's user avatar
  • 181
0 votes
0 answers
182 views

Why does adding more blades to a propeller/fan not show a decrease in efficiency?

According to this answer increasing blade solidity increases the blade area by either enlarging chord or increasing blade count both of which reduce efficiency via reducing the lift coefficient and ...
usernamechecksout's user avatar
5 votes
3 answers
4k views

What is a spool in any jet engine, what is its funtion?

I am a student and I'm trying to determine how a spool works in an engine. What effect does it have depending on the number of spools on the performance of the engine? I tried to find it on Google but ...
Karandeep Singh's user avatar
3 votes
5 answers
3k views

Is it possible for a ramjet to start from 0 velocity?

I was wondering if it is possible for a ramjet to start from 0 velocity. I know its working principle and all, but is there any missile or aircraft that completely uses ramjet, with no rotating part ...
J. Brown's user avatar
0 votes
1 answer
906 views

What are the advantages and disadvantages of fluidic thrust vectoring on aircraft?

The Rockwell XFV-12 was a research project for combining supersonic speed with Vertical Take-Off and Landing, From wikipedia: The XFV-12 used a thrust augmented wing concept... in which exhaust would ...
Fulano's user avatar
  • 121
3 votes
1 answer
319 views

Could small ramjets on the tip of propellers allow for supersonic spin of turbine blades?

Well, of course, if it was practical, someone would've already done that, but I'm still curious. As you can imagine, I'm an illiterate on the matter of aerodynamics, and even though supersonic ...
Fulano's user avatar
  • 121
4 votes
1 answer
1k views

Thrust varaition of a Turbofan engine with altitude and mach number [duplicate]

my classmates and I are trying to find a mathematical model for a low bypass turbofan engine, we ended up finding a model given by Snorri on "General Aviation Aircraft Design", but the ...
AlejandroArias's user avatar
0 votes
1 answer
769 views

How to determine the length of the CD nozzle?

I am designing a convergent nozzle as well as a CD(Converging-Diverging) nozzle. How do I find out the length of those nozzles? If the throat of the CD nozzle has 0 length then what should be the the ...
Twisampati Roy Chowdhury's user avatar
3 votes
2 answers
4k views

What is a ram recovery point?

As aircraft speed increases, thrust tends to decrease somewhat; as the aircraft speed reaches a certain point, ram recovery compensates for the losses caused by the increases in speed. The inlet must ...
Noorul Quamar's user avatar
3 votes
3 answers
3k views

Why does a rocket engine increase power with speed if the burn rate is constant?

A rocket produces constant thrust with speed, and that means increasing power with speed. Where does this increase in power come from if the fuel burn rate is constant? How can we explain this in the ...
22flower's user avatar
  • 1,958
14 votes
1 answer
2k views

What makes an engine suitable for supersonic flight?

I would like to know for example if someone can take the "core" of an CFM56 used on A320, redesign it by adding a supersonic intake, a convergent-divergent nozzle, and reduce its bypass ...
AlejandroArias's user avatar
0 votes
0 answers
61 views

Which would be the best placement of an engine for a supersonic buisness jet that has an intake of 2-D ramp? [duplicate]

I would also like to know if possible which would be the advantage/disadvantage of placing the engine under or over the wing for example.
AlejandroArias's user avatar
4 votes
3 answers
526 views

Is a ducted fan considered a jet or propeller for the performance parameters?

Right now I am working on a UAV design which will use ducted fan. But the performance calculations are a bit troublesome. For some calculations jet and propeller results are almost same but for the ...
J. Brown's user avatar
0 votes
0 answers
174 views

Do aircraft using the push pull configuration always use the same engine?

I am currently doing research for a “white paper design” aircraft and I have always been interested in push pull aircraft as they seem to be rare and I wanted to see some challenges in making a very ...
Aidan.T's user avatar
2 votes
0 answers
208 views

How are Fan pressure of and Static pressure in the turbofan engine related?

If the fan air is ducted to the rear, the total fan pressure must be higher than the static gas pressure in the primary engine's exhaust, or air will not flow. By the same token, the static fan ...
Noorul Quamar's user avatar
4 votes
1 answer
88 views

Performance metrics of a propulsion system - optimising a propulsive fan system [closed]

I'm designing an electric fan propulsion system for a hybrid-electric business jet. The hybrid business jet uses a series hybrid configuration and distributed electric propulsion. The electric fan ...
wannabe-engineer's user avatar
-6 votes
1 answer
337 views

Relation between weight of the aircraft and mach number [closed]

Is there any formula that relates weight of the aircraft with mach number?
Nawaz Sharif's user avatar
1 vote
1 answer
169 views

Is there a limit to a subsonic ramjet's pressure ratio?

Subsonic ramjets have high specific fuel consumption. This indicates to me they must have a low pressure ratio. Is there a limit to how high pressure ratio one can achieve with subsonic air? Why can't ...
Francis L.'s user avatar
  • 2,514
0 votes
2 answers
230 views

Can thrust be produced only using the forward speed of a nozzle?

Why can't a nozzle that is already in relative motion to the air produce thrust by speeding up the air that passes through inside it? So let's pretend you're in a glider with two converging nozzles (...
Joe's user avatar
  • 1
-8 votes
1 answer
283 views

What is the reason for different number of front nozzles on commercial aircraft? [duplicate]

As we observe in commercial aircraft, that there are four or two front end nozzles for gas emission in the air. What is the reason for this variable of 4 or 2 nozzles? Why is it not a constant?
Prashant Akerkar's user avatar
6 votes
1 answer
2k views

Why is thrust said to be constant over speed for a jet engine?

I'm just interested in some basic facts regarding flight. On reading the rather "low level" book "Understanding Flight, David F. Anderson, Scott Eberhardt), I recently came up to the ...
MichaelW's user avatar
  • 251
2 votes
1 answer
102 views

Is hybrid propulsion widely used by UAVs?

Is it common to have hybrid propulsion in UAVs used for terrain mapping with long endurance, short range and altitude? Is the technology and research mature enough to make hybrid propulsion? ...
Auberron's user avatar
  • 1,567
1 vote
1 answer
351 views

How can jet engines be more efficient than propellers? [duplicate]

If jet engines are smaller in diameter than propellers, is it fair to say that propellers accelerate a lot of air a little while a jet engine accelerates a little air a lot? Basically, a jet engine ...
Jonah's user avatar
  • 113
1 vote
1 answer
92 views

What are some first-order drag approximations for airframe/propwash interactions?

What are some first-order drag approximations for airframe/propwash interactions, both for dynamic flight and for static thrust, in a traditional tractor configuration?
Kenn Sebesta's user avatar
  • 5,142
1 vote
0 answers
362 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 ...
Neanic's user avatar
  • 33
2 votes
1 answer
2k views

Does jet engine exhaust velocity relative to itself remain constant despite speed changes?

Maybe this is a stupid question. I seem to have been told, the velocity of the exhaust leaving an airbreathing jet engine relative to the engine, is constant despite changes in airspeed. However, to ...
Abdullah is not an Amalekite's user avatar
1 vote
3 answers
539 views

Are there any aircraft powered by tip jets in the propeller blade?

I am familiar with tip jet powered helicopter experiments. Is there any aircraft that use/used this mode and would it be useful to use a tip jet driven prop on aircraft instead of piston or turbine ...
Opusci's user avatar
  • 31
4 votes
1 answer
555 views

why some airplanes have their exhaust gases vectored above the wing?

I was looking at images of the SkyCourier shown below and i have noticed the asymmetrical exhaust pipes in both engines (one pointing up and one is straight), doing my research on the internet, i ...
Ibrahim Jaafar's user avatar
3 votes
2 answers
634 views

What is wrong with my understanding about total pressure for a rocket nozzle?

I’m using the ideal rocket equations and isentropic flow but cannot determine what is wrong in my understanding about total pressure. Can anyone explain where I am wrong using the following example? ...
waterdragon's user avatar
2 votes
2 answers
393 views

How to select and electric propulsion system for my experimental Ultralight?

I've been trying to design and build, my experimental Ultralight using electric propulsion system, My plane designed base on Slaler and Gensis ultralight , following is the primary calculation Empty ...
Hamid s k's user avatar
  • 131
3 votes
1 answer
242 views

Which is better: a rotor / prop followed by a stator, or contra rotating rotors / props?

It is all in the title. I'm interested in power absorbed/used for a given thrust, or thrust generated for a given power (same diameters of course). Just thrust and power. Ignore materials, electric ...
toshi ba's user avatar
  • 411
2 votes
2 answers
317 views

Is a chambered fan more efficient than a ducted fan?

A chambered fan is not exposed to the oncoming airflow in forward flight. I am working on a VTOL design that uses a chambered fan. There will be a wing attached to top of the thrust arms. Could it ...
Tom Daily's user avatar
0 votes
0 answers
228 views

Why are some exhaust cone exposed?

Some engines have an exposed tail/exhaust cone at their exit, protruding aft the nozzle. how does that affect the overall thrust and pressure distribution along the walls of the cone? is it's role ...
toshi ba's user avatar
  • 411
2 votes
0 answers
262 views

Are subsonic nozzle fully expanded?

this is about converging subsonic nozzles. Are they fully expanded? meaning exit pressure=ambient pressure? What about diverging subsonic nozzle? Are they fully expanded? what would happen if the ...
toshi ba's user avatar
  • 411