Questions tagged [propulsion]

Questions about the various methods used to propel aircraft.

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0answers
52 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 ...
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0answers
114 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 ...
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3answers
2k 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 ...
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0answers
38 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 ...
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1answer
74 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 ...
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2answers
2k 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-...
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23 views

how to calculate power required for engine of duct fan? [duplicate]

I need 600 N thrust for my aircraft. I am planning to use duct fan. according to calculation of duct fan: T=Ct.ro.A.V^2 Ct=0.03 ro=1.09 (in my place) A=(0.26^2)*3.14=0.21225 m^2 v=300 m/s then T=624 N ...
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1answer
112 views

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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1answer
70 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 ...
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2answers
122 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 (...
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1answer
184 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 ...
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1answer
220 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?
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32k 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 ...
4
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1answer
316 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 ...
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1answer
369 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
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1answer
67 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? ...
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1answer
233 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 ...
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1answer
51 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?
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0answers
85 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
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1answer
366 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 ...
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3answers
899 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 ...
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3answers
216 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 ...
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2answers
402 views

Engines more powerful than the brakes?

This might be more of an anecdotal question, but are there any aircraft where under full throttle (with afterburner in worst-case) where the wheels wouldn't provide enough friction against the runway ...
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2answers
250 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? ...
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2answers
163 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 ...
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1answer
231 views

Why can’t electric motors be used in aviation [duplicate]

Why can’t electric motors be used in aviation? Is it a problem with batteries, torque, or what? From what I’m aware motors at high torque are expensive and need a massive footprint, than a high rpm ...
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4answers
2k views

Are fixed wing aircraft with gimbal thrust feasible?

Elon Musk has suggested that he'd look at implementing VTOL electric aircraft with a "gimballed thrust" system similar to the one used in rockets. Aircraft have all these unnecessary things like ...
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1answer
583 views

How do you maximize an electric engine's thrust?

I've been recently looking for answers to this question on the internet but the jungle of propellers, fans and electric motors didn't quite get me an answer. How would I have to design an electric ...
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1answer
242 views

Propeller effect on the L/D of an aircraft (Pusher Propeller configuration)

I recently performed an aerodynamic analysis of a fixed-wing UAV with a pusher propeller configuration. I found out that the L/D reduced by about 15% when compared to the body alone without propeller. ...
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2answers
201 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 ...
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0answers
107 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 ...
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0answers
137 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 ...
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3answers
727 views

Why aren't tilting propellers used as an alternative for ailerons or elevators?

I was wondering what are the reasons for not using tilted propellers fixed to ailerons/elevators/elevons? Or even on wings with no control surfaces at all? Wouldn't the 2nd way of thrust vectoring ...
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2answers
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 ...
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0answers
170 views

what is the physical explanation for additive drag?

from what i understand, additive drag is not really drag. it is a way to account for the variation of inlet condition due to conservation of mass. but i still don't get why it create drag(negative ...
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3answers
2k views

What is a biplane propeller and how efficient is it?

Lazair ultralight series II used biplane props to absorb more power from the engine....so my question is what really is a biplane propeller and are they efficient in comparison to a four bladed prop?
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2answers
6k 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 ...
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1answer
231 views

Why don't we see diverging nozzles or diffusers?

When it comes to fully subsonic propulsion, all outlets are converging nozzles (I did say fully subsonic so no converging diverging). From what I understand, they are flow regulating devices (changing ...
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2answers
2k views

Would injecting water into a jet engine’s exhaust increase velocity?

Can high pressure mist of water be sprayed into jet engine exhaust, to create steam, to increase velocity? Would the steam generated from high pressure water being injected into the jet engine exhaust ...
3
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1answer
277 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 ...
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2answers
229 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-...
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2answers
3k views

What do I need to know to design contra rotating propellers for a powered paraglider?

I wonder if anyone has any technical information that would assist in using the correct Size & Pitch Contra rotating Propellers (CRP) on this Foot launched Powered Paraglider engine ? We are ...
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6answers
1k views

What are the advantages of using a ramjet in an air-to-surface missile?

Which are the advantages of using a ramjet compared to a rocket engine in an air-to-surface missile? I suppose the cost rises a lot, so why do some countries use ramjets as a way of propelling ASM ...
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5answers
2k views

How does the nozzle diameter affect the thrust of a ducted propeller?

I currently do some experiments with ducted propellers in which I try to figure out which effect a nozzle has on the thrust produced. My theory goes like this: If I reduce the exit diameter of the ...
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2answers
399 views

Is the Meredith effect utilized in the cowling design of air-cooled engines?

The P-51 is famous for its advanced-for-its-time aerodynamics, the prime example of which is the radiator design under the belly which utilizes the Meredith effect to, in effect, turn it into a mini ...
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1answer
492 views

Is there a way to avoid fuel loss caused by vaporization from engine heat?

Concorde had engines directly attached to the wings, close to the fuel tanks. Some fuel was evaporated due to heat. What were the reasons to not use pylons or some cooling system to limit this effect?
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1answer
714 views

How fast do four Tire-Propellers have to rotate to lift 2000 lbs? [closed]

I just saw this come out, Goodyear's Tire-Propeller Concept – a combination tire that can also act as propeller (well, more like a ducted fan I guess). There's a neat video that goes with it, ...
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3answers
21k views

Could a Dyson fan scale up to be used as a bladeless aircraft engine?

Dyson has been making bladeless fans for a few years now that accelerate a consistent stream of air without exposed blades. If this concept were applied to aircraft engines, it could potentially ...
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2answers
337 views

Why Engine Exhaust Nozzle can not be totally buried in aircraft fuselage? [closed]

Why The CD nozzles of the fighter aircraft are always outside the fuselage, Why the whole engine is not buried in the fuselage?? If engine shroud also can be made variable area and varies with CD ...
3
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1answer
203 views

Can a turbofan engine have less noise so that it doesn't disturb our ears?

A few years back I have seen that Pratt and Whitney 's Geared Turbofan Engine(GTF) has reduced it's noise levels to about 50%. But recently I was having a discussion with a friend and he told me that ...