Questions tagged [propulsion]

Questions about the various methods used to propel aircraft.

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4 votes
1 answer
786 views

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 ...
-2 votes
1 answer
121 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 ...
3 votes
2 answers
242 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 ...
0 votes
1 answer
83 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: ...
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 ...
5 votes
3 answers
846 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 ...
0 votes
1 answer
80 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 ...
8 votes
3 answers
619 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 ...
2 votes
1 answer
323 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 ...
4 votes
3 answers
475 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 ...
16 votes
3 answers
42k views

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 ...
18 votes
4 answers
9k views

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 ...
3 votes
1 answer
453 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 ...
0 votes
0 answers
40 views

Pusher vs Pull prop [duplicate]

Probably a pretty simple question, but what exactly are the pros and cons of pull and push propellers, and is there a reason why pull propellers are a lot more prevalent in planes than pusher ones?
2 votes
3 answers
2k views

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 ...
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 ...
6 votes
2 answers
591 views

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 ...
0 votes
1 answer
148 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 ...
2 votes
4 answers
1k views

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 ...
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 ...
0 votes
0 answers
178 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 ...
8 votes
1 answer
12k views

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 ...
5 votes
3 answers
3k 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 ...
3 votes
5 answers
2k 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 ...
0 votes
1 answer
848 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 ...
3 votes
1 answer
295 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 ...
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 ...
0 votes
1 answer
684 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 ...
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 ...
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 ...
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 ...
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.
0 votes
0 answers
168 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 ...
12 votes
3 answers
3k views

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 ...
2 votes
0 answers
201 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 ...
4 votes
1 answer
86 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 ...
10 votes
2 answers
3k views

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-...
-6 votes
1 answer
322 views

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

Is there any formula that relates weight of the aircraft with mach number?
1 vote
1 answer
158 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 ...
0 votes
2 answers
216 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 (...
3 votes
1 answer
236 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 ...
-8 votes
1 answer
280 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?
4 votes
1 answer
524 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 ...
5 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 ...
2 votes
1 answer
100 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? ...
1 vote
1 answer
346 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 ...
1 vote
1 answer
90 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?
1 vote
0 answers
342 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 ...
2 votes
1 answer
1k 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 ...
1 vote
3 answers
518 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 ...