Questions tagged [propulsion]

Questions about the various methods used to propel aircraft.

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6
votes
1answer
936 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
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 ...
8
votes
1answer
506 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
1k 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
899 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" ...
10
votes
2answers
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-...
5
votes
3answers
629 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
253 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 ...
17
votes
2answers
6k 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
9k 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 ...
6
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3answers
4k 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
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1answer
336 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
613 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
515 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
721 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.
8
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4answers
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 ...
-2
votes
1answer
339 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.
12
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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 ...
2
votes
3answers
722 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 ...
13
votes
3answers
31k 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
886 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
432 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 ...
1
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2answers
1k 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
348 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
3k 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 ...
10
votes
1answer
406 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 ...
1
vote
1answer
489 views

Is there a way to avoid fuel loss caused by vaporization from engine heat?

Concorde had engines directly attached to the wings, close to the fuel tanks. Some fuel was evaporated due to heat. What were the reasons to not use pylons or some cooling system to limit this effect?
1
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2answers
2k views

Why aren't thin, delta-shaped wings used for fighter aircraft?

In the past, we used thin, delta-shaped wings (ogival wings) such as those on the Concorde. These wings can be used up to mach 2.2. Due to high fuel consumption, these wings are no longer used ...
13
votes
3answers
18k 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 ...

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