Questions tagged [propulsion]
Questions about the various methods used to propel aircraft.
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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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1answer
48 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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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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1answer
92 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
153 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 ...
2
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1answer
173 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 ...
3
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2answers
169 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
88 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 ...
2
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1answer
135 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 ...
2
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2answers
158 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
85 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
58 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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96 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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1answer
143 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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46 views
Non-dimensional variables choked nozzle
I understand that a choked nozzle removes the dependance on the static pressure $p_a$ because if M>1 in a choked nozzle then waves cannot travel upstream in the nozzle (as explained in the paragraph ...
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1answer
238 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
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-...
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1answer
140 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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1answer
203 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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1answer
501 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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2answers
265 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 ...
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1answer
190 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 ...
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1answer
999 views
Hydromechanical/Electronic fuel control system [closed]
Can someone explain the picture below which represents hydromechanical/electronic fuel control? What's the function of the solenoid on the picture below? What are the differences between solely ...
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2answers
348 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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6answers
879 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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1answer
252 views
How does the debris rejection system in the CFM LEAP engines work?
How does the debris rejection system in the CFM LEAP engines work?
LEAP - The debris rejection system
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2answers
694 views
How is a propeller diameter for given application determined?
let's say I need 1000 N of thrust for a given aircraft and flight velocity. I have available a fixed pitch propeller with a given shape, and thus given performance to advance ratio curves. Let's say ...
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2answers
660 views
Can motorjets be a viable means of propulsion?
A motorjet is a very early type of jet engine where intake air passes through a compressor driven by a separate piston engine, and is then mixed with fuel and burned to provide thrust. They were used ...
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1answer
319 views
How does the load transfer from a prop to the airframe?
I was just watching this video...
Restoration and startup of a Wright 1820 Cyclone
...and it got me thinking: a propeller shoves back air, and this creates a forward force on the prop. The prop ...
7
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1answer
382 views
Why divide the blades of a 9 blade propeller into 3 groups?
In a youtube video an airboat is featured with two contra-rotating propellers, each holding nine blades. Interestingly those nine blades are not spaced evenly, but grouped into three groups. I've ...
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1answer
454 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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3answers
18k 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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0answers
121 views
How does a partially covered air intake affect the thrust of a propeller ?
does a partially covered air intake of a ducted propeller significantly affect its thrust?
If so, will it be like 10 or rather 90 percent less thrust ?
Thanks for your answers!
Simon
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3answers
1k 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
3k views
Why does the diffuser section generate thrust in a jet engine?
I am studying the thrust distribution of jet engines.
But I'm now a bit confused.
In Rolls-Royce's "The Jet Engine" book,
http://aeromodelbasic.blogspot.com/2012/05/thrust-distribution-distribution-...
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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
149 views
What are technical and aerodynamical limitations to blown wings main propulsion?
Why wouldn't some blown flap or blown wing device (suppressing propeller or fan or jet exhaust from aircraft design) produce sufficient thrust needed for takeoff and cruise flight, opposed to "only" ...
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2answers
351 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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1answer
579 views
In what way are the airfoils used for a propeller different from the ones used in turbofan engine?
Airfoils are used in the blades of a propeller as well as the blades of the fan, axial compressor and turbine in a turbofan engine. Thus, the airfoils used in above two applications have different ...
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116 views
Alternate for jet fuel [duplicate]
At some point maybe after around 8 to 10 decades we may end up with a situation where the crude oil wells get drained up due to massive extraction and increasing demand for gasoline and ATF. What ...
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0answers
40 views
What are the effects of angle of attack on turbines in composed delta wings with jets in upper side?
: a layperson doubt. What would happen during take-off and landing of a machine as Boeing X-48, because of the high angle of attack, the steep attitude of the airplane: would this difficult air supply ...
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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 ...
6
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1answer
912 views
Can an airliner land safely using only propulsion control?
In this amazing story ,after losing all hydraulic power of the aircraft , Captain Al Haynes guided the plane to the Sioux city, crashed but saved 185 of the 296 lives (United Airlines Flight 232-Sioux ...
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2answers
2k 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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1answer
490 views
What prevents miltiary jets and turbo-props from being refitted with a turbofan?
What prevents military jets and turbo-props (such as P-3 Orion) from being refitted with a high bypass turbofan?
3
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1answer
984 views
When is jet engine thrust maximum?
Assuming we have a convergent nozzle I've read that the maximum thrust is achieved just in the moment the nozzle exit -minimum area- is chocked, i.e., the nozzle is adapted in the sense the pressure ...
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830 views
Shaftless propeller vs duct fan [duplicate]
If both have the same dimension, same amount of fan blade, and supplied by the same amount of energy, which one would product bigger thrust and less total drag (the drag on the blade and the "tube" ...
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1answer
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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3answers
572 views
Why do some fighters have two engines?
Some countries (e.g. Russia) develop fighter aircraft (e.g. Sukhoi) with 2 engines.
Is it for maneuverability, or is it because they can't build an engine that would meet the power requirement?
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240 views
Where does this integral for a 'aerospike nozzle' come from?
Today I was reading about the aerospike nozzle and found this image:
(from section 10.3.1 of this lecture)
This image tells us how to measure the thrust of this kind of nozzle. I can understand all ...
