Questions tagged [propulsion]
Questions about the various methods used to propel aircraft.
81
questions
0
votes
0answers
55 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 ...
0
votes
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 ...
2
votes
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 ...
4
votes
1answer
75 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 ...
0
votes
0answers
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
...
-6
votes
1answer
113 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
1answer
71 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
2answers
126 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 (...
-8
votes
1answer
223 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?
5
votes
1answer
392 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
1answer
69 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
1answer
234 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
1answer
52 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
0answers
87 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
1answer
386 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 ...
0
votes
3answers
224 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 ...
4
votes
1answer
328 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
votes
2answers
256 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?
...
2
votes
2answers
171 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 ...
3
votes
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 ...
2
votes
2answers
202 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 ...
0
votes
0answers
108 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 ...
2
votes
0answers
138 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 ...
1
vote
0answers
180 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 ...
1
vote
1answer
237 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 ...
3
votes
1answer
278 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 ...
3
votes
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-...
1
vote
1answer
249 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. ...
2
votes
1answer
232 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 ...
2
votes
1answer
723 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, ...
-2
votes
2answers
341 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
votes
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 ...
-1
votes
1answer
2k 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 ...
1
vote
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 ...
5
votes
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 ...
0
votes
1answer
362 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
1
vote
2answers
1k 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 ...
4
votes
2answers
1k 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 ...
3
votes
1answer
418 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 ...
8
votes
1answer
426 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 ...
1
vote
1answer
594 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 ...
52
votes
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 ...
1
vote
0answers
128 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
14
votes
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?
3
votes
2answers
4k 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-...
5
votes
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 ...
1
vote
2answers
214 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" ...
4
votes
2answers
404 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 ...
1
vote
1answer
726 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 ...
0
votes
0answers
120 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 ...