Questions tagged [propulsion]
Questions about the various methods used to propel aircraft.
3
votes
1answer
150 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
32 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
3answers
146 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
83 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
0answers
40 views
Does Froude Efficiency represent an upper bound for propellers in certain flight / aircraft conditions?
I used the Simple Propeller Theory to calculate the Froude Efficiency for my theoretical propeller-driven craft (at 65k feet). Here are the results: https://ibb.co/kPPqzU.
My results were that, for ...
1
vote
2answers
107 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 ...
3
votes
2answers
263 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
165 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
votes
1answer
202 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 ...
0
votes
1answer
198 views
How do you maximize an electric engines 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 anwer.
How would I have to design an electric ...
51
votes
3answers
13k 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
99 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
6
votes
3answers
398 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?
2
votes
2answers
807 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-...
3
votes
3answers
408 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
110 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" ...
7
votes
2answers
546 views
How did Northrop Grumman propose to make the Global Hawk nuclear powered?
Reading further after receiving this answer, I saw the section on nuclear power in the Wikipedia article on the Northrop Grumman RQ-4 Global Hawk:
Nuclear power
Sandia National Laboratories ...
1
vote
1answer
219 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
104 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 ...
47
votes
9answers
20k views
Why don't aircraft use nuclear propulsion?
Nuclear propulsion research for aircraft was abandoned during the 50's.
Why wasn't it revived ever?
1
vote
0answers
38 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 ...
6
votes
2answers
1k 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
votes
1answer
866 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 ...
3
votes
2answers
1k 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 ...
7
votes
1answer
422 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?
14
votes
2answers
4k views
What is this plane and what are the rockets on the back used for?
While reading this question I saw an image of a plane marked as a US Marines plane of some sort with thrusters or rockets of some sort attached to the sides just past the CG. What plane is this and ...
3
votes
1answer
709 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 ...
1
vote
0answers
533 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" ...
9
votes
1answer
1k 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-...
4
votes
3answers
497 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?
1
vote
1answer
192 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 ...
10
votes
2answers
3k 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 ...
6
votes
1answer
5k 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 ...
3
votes
3answers
2k views
Why are the top speeds for jet engines higher than for propellers?
I realize turbines are more efficient than piston engines, but if that were true, then why don't turbo-props reach jet speeds?
0
votes
1answer
229 views
All Electric Jets [duplicate]
I've been researching electric jets, and I have seen a number of schemes. What is the most likely way to build an all-electric jet engine, assuming that the power source is available and practical?
4
votes
1answer
331 views
Are flame holders made of a special material other than that used in combustion chamber?
Are the flame holders made of materials which have higher friction coefficients than the combustion chamber in order to create turbulence?
0
votes
1answer
93 views
How does one determine the freestream and ultimate slipstream velocities to estimate thrust?
The task before me is estimating the thrust of a propulsion system (a ducted fan) using this equation for thrust (Eq. 2.1.1)1:
$$T = (mass\; flow\; rate)\;(slipstream\; velocity - freestream\; ...
7
votes
1answer
551 views
How much do the fan blades of a GE90-115b stretch when the engine is spinning at maximum RPM?
I've always wondered what kind of stresses and resulting deformations jet engines are subjected to when running.
7
votes
3answers
1k 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 ...
-2
votes
1answer
227 views
Where can I find an example of a propulsion maintenance task card?
I'm looking for an example of a task card for aircraft propulsion maintenance, e.g. propeller or engine maintenance. I've found examples for wings and airframes, but not for propulsion.
9
votes
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 ...
1
vote
2answers
402 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 ...
10
votes
2answers
16k 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 ...
2
votes
3answers
532 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 ...
6
votes
2answers
313 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 ...
8
votes
2answers
3k views
How do you choose engine placement for under wings engines?
I'd like to know how you choose the location of the engines under the wings, in the case of a 4-engines aircraft with low wings (and therefore with engines under the wings).
Concerning the ...
1
vote
2answers
794 views
Why wasn't a scramjet used for the Concorde?
Why didn't Concorde use a scramjet engine for supersonic flight, but it is used in the Airbus and Skreemr hypersonic flight concepts to achieve supersonic speeds?
4
votes
1answer
280 views
How did Wilbur Wright create and use the formulas he mentions in his letter to Octave Chanute?
In a letter written by Wilbur Wright and addressed to Octave Chanute, dated 1903/06/18, I have found two things that I do not quite understand.
Our engine develops at the brake 15.6 horse power and ...
5
votes
2answers
2k views
How is mass flow rate computed?
I have been wondering how the mass flow rate is determined by the area of the engine air intake surface and the incoming speed of the air.
In still air, it is understandable that a stationary engine ...
9
votes
1answer
299 views
What is the purpose of those casing treatments and how were they designed?
The images show a kind of casing treatment used in Russian aero-engines.
From what I have found out the first engine featuring this kind of casing treatment was the Tumansky R-13. Since then it was ...
