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Questions tagged [propulsion]

Questions about the various methods used to propel aircraft.

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57 votes
3 answers
34k 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 ...
Geoff's user avatar
  • 1,443
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 ...
yankee's user avatar
  • 1,073
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 ...
Daniel Caoili's user avatar
14 votes
3 answers
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?
David Teahay's user avatar
  • 2,895
14 votes
3 answers
25k views

How does turbojet thrust change with altitude?

I am studying the rate of climb of turbojets, I don't know how the thrust varies with altitude and in particular which are the differences between necessary thrust and effective thrust. Hope being ...
Davide's user avatar
  • 773
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 ...
AlejandroArias's user avatar
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 ...
mohsen dehghani's user avatar
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-...
White Knight's user avatar
10 votes
1 answer
539 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 ...
rul30's user avatar
  • 1,547
8 votes
4 answers
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 ...
FloatingRock's user avatar
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 ...
AndreaF's user avatar
  • 181
8 votes
3 answers
623 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 ...
ddddmmmm's user avatar
8 votes
1 answer
554 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?
gatorback's user avatar
  • 357
8 votes
1 answer
13k 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 ...
flextempers's user avatar
8 votes
1 answer
566 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 ...
flawr's user avatar
  • 724
7 votes
1 answer
1k 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 ...
no more sigsegv's user avatar
7 votes
1 answer
900 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.
flextempers's user avatar
6 votes
2 answers
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 ...
Tom Daily's user avatar
6 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 ...
MichaelW's user avatar
  • 251
6 votes
2 answers
601 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 ...
curious_cat's user avatar
  • 8,456
6 votes
2 answers
5k 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-...
Jono's user avatar
  • 161
5 votes
3 answers
5k 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?
yippy_yay's user avatar
  • 7,375
5 votes
6 answers
2k 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 ...
JoseDo's user avatar
  • 257
5 votes
3 answers
946 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 ...
MK.s's user avatar
  • 65
5 votes
3 answers
849 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?
kcihtrak's user avatar
  • 431
5 votes
5 answers
3k 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 ...
Simon Henn's user avatar
5 votes
2 answers
4k 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 ...
tzy's user avatar
  • 283
5 votes
3 answers
4k 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 ...
Karandeep Singh's user avatar
5 votes
2 answers
2k 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 ...
Vikki's user avatar
  • 28.4k
5 votes
1 answer
815 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?
kcihtrak's user avatar
  • 431
5 votes
1 answer
447 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 ...
Robert Werner's user avatar
4 votes
2 answers
632 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 ...
Milwrdfan's user avatar
  • 1,789
4 votes
2 answers
2k views

I'm having a hard time conceptualizing this statement from "The Jet Engine" by Rolls-Royce

This is taken from section 21 of Chapter 3, Compressors that discusses axial flow compressors in turbine jet engines. The more the pressure ratio of a compressor is increased the more difficult it ...
shrimp's user avatar
  • 41
4 votes
1 answer
2k 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 ...
XF-91's user avatar
  • 2,096
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 ...
AlejandroArias's user avatar
4 votes
1 answer
88 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 ...
wannabe-engineer's user avatar
4 votes
1 answer
566 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 ...
Ibrahim Jaafar's user avatar
4 votes
1 answer
908 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 ...
user avatar
4 votes
3 answers
529 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 ...
J. Brown's user avatar
3 votes
3 answers
873 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 ...
FlegmatoidZoid's user avatar
3 votes
5 answers
3k 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 ...
J. Brown's user avatar
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 ...
22flower's user avatar
  • 1,958
3 votes
1 answer
360 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 ...
sai teja's user avatar
  • 437
3 votes
1 answer
835 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 ...
MichaelK's user avatar
  • 2,377
3 votes
2 answers
356 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-...
AEhere supports Monica's user avatar
3 votes
2 answers
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 ...
The Raptor's user avatar
3 votes
1 answer
581 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 ...
youguysfail's user avatar
3 votes
1 answer
321 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 ...
Fulano's user avatar
  • 121
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 ...
Noorul Quamar's user avatar
3 votes
2 answers
642 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? ...
waterdragon's user avatar