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Questions tagged [propulsion]

Questions about the various methods used to propel aircraft.

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1answer
225 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
155 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
164 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
115 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
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2answers
213 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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3answers
195 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
117 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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0answers
50 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 ...
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2answers
201 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
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2answers
306 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
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1answer
177 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
243 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
229 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 ...
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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 ...
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0answers
106 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
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3answers
433 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
1k 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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3answers
605 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
116 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" ...
6
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2answers
600 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
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1answer
259 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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0answers
105 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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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?
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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
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
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1answer
874 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 ...
7
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1answer
437 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?
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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
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1answer
754 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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0answers
575 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
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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-...
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3answers
506 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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1answer
204 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 ...
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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
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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 ...
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3answers
3k 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?
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1answer
236 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?
5
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1answer
368 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
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1answer
115 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\; ...
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1answer
577 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
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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 ...
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1answer
254 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.
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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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2answers
414 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
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2answers
18k 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 ...
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3answers
565 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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2answers
322 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 ...
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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 ...
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2answers
831 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?