Questions tagged [propulsion]
Questions about the various methods used to propel aircraft.
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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 ...
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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 ...
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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?
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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 ...
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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 ...
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Are there modern airplanes with two propellers driven by one single engine?
Except 1903 Wright flyer, are there any other airplane using one single engine driving two coplanar propellers?
Coplanar means push-pull and coaxial designs are not in the question's frame.
Tilt ...
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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 ...
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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 ...
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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:
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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Are ducted fans more efficient?
As far as static thrust, does a shrouded/ducted propeller outperform an un-shrouded propeller? It seems that the guide blades on the bottom of the duct would allow little more thrust to be extracted ...
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Why is max endurance different for jet and props?
Max endurance speed is not the same for gliders, propeller planes (also for turbo prop, right?) and jet planes.
While for for jet planes max endurance is at the minimum drag speed ($V_{md}$), for ...
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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 ...
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Why aren't thin, delta-shaped wings used for fighter aircraft?
In the past, we used thin, delta-shaped wings (ogival wings) such as those on the Concorde.
These wings can be used up to mach 2.2. Due to high fuel consumption, these wings are no longer used ...
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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 ...
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Would it be feasible for a typical passenger jet to carry along its own Oxidizer?
We know that many Space Shuttles / Rockets etc. carry their own oxidizer with them. This is partly because at the heights they operate the atmosphere is too rarefied to have enough oxygen to sustain ...
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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 ...
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Is there any engine that doesn't use a propellant to produce thrust?
As far as I know, all engines used in aircraft produce thrust by means of some propellant: kerosene, hydrogen peroxide etc. Maybe I've missed something, but could you tell me, are there any engines ...
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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 ...
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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 ...
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What are the mass flow rate and exhaust velocity for a CF6 or GE90 turbofan?
For a typical turbofan jet engine (two examples given in the title), what is the exhaust velocity and mass flow rate of air at sea level and cruising altitude (~ FL350)?
Also, does the specific ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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.
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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 ...
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Can a pulse jet be used on a light GA aircraft?
I have an idea for designing a light, cheap and fast 2-seated private airplane... I was thinking about using a pulse jet engine which is simple to design and build, and is cheap too.
Noise is not an ...
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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 ...
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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 ...
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How much thrust is gained from placing a propeller in a duct?
Assuming that the power and diameter are the same, how much extra thrust can be gained by placing a propeller in a duct? How does it influence the RPM?
To clarify: take any prop, place it in a well-...
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Relation between weight of the aircraft and mach number [closed]
Is there any formula that relates weight of the aircraft with mach number?
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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 ...
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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 (...
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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 ...
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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?
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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 ...
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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 ...
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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?
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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 ...
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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?
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