Questions tagged [propulsion]

Questions about the various methods used to propel aircraft.

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16
votes
2answers
5k 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
8k 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
votes
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
votes
1answer
325 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
votes
1answer
553 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
309 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
695 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
votes
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
334 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.
11
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 ...
2
votes
3answers
688 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 ...
12
votes
3answers
27k 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
816 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
401 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
vote
2answers
989 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
332 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 ...
9
votes
1answer
376 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
470 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
vote
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 ...
12
votes
3answers
14k 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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