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8 votes
Accepted

How does momentum thrust mechanically act on combustion chambers and nozzles in a jet propulsion?

It all comes down to where you draw your control volume. At one extreme you can draw your control volume as a simple rectangle box 'around' the engine, but with a good bit of space between the ...
Rob McDonald's user avatar
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8 votes

What is the most efficient design for an aircraft designed only to hover?

This is the most efficient type of aircraft designed only to hover. Tethered, sealed helium balloon. Unlike a hot air balloon, it doesn't require any propulsion, and altitude control is possible by ...
Therac's user avatar
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5 votes

How does momentum thrust mechanically act on combustion chambers and nozzles in a jet propulsion?

how does the reaction force actually act on combustion chamber/afterburner or nozzle walls? Let's first clarify what the reaction force is: It is the force which accelerates a mass of burning fuel-...
Peter Kämpf's user avatar
5 votes

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

Variable pitch propellers can help explain this. When the aircraft speed is slow, the blade pitch is finer. At faster air speeds the blades must be opened more in the direction of the airstream. This ...
Robert DiGiovanni's user avatar
2 votes

Can engines with a fixed nozzle in the angle of attack have the same effect as the thrust vectoring?

The pitching moment from thrust vectoring comes from the trust axis' position relative to the center of gravity of the rocket or aircraft's body. If the rocket motor, or jet engine, is rigidly ...
John K's user avatar
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2 votes

What is the most efficient design for an aircraft designed only to hover?

If this is for a station-holding drone, for minium power you probably would go with a coaxial helicopter with the longest rotor blades you can live with, to get the highest L/D from the rotor (imagine ...
John K's user avatar
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2 votes

Are Hybrid-Electric Propulsion Systems the only avenue to achieve the range and speed equivalent to current airliners?

The premise of this question - that hybrid systems can compete with jet fuel on range in the first place - is unproven and likely incorrect. I would however direct anyone interested in understanding ...
Therac's user avatar
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1 vote

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

Picture 3.9, which is related to the text you copied in your question, is helpful in understanding the concept: First of all note that with "inlet" they mean the beginning of the axial ...
sophit's user avatar
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1 vote

Why does adding heat to the subsonic flow increase the speed of the flow?

Let's take as an example the brayton cycle, as used in turbojets. in the combustor section, heat is added to the flow by burning fuel in it at constant pressure. Adding heat to the flow makes it want ...
niels nielsen's user avatar
1 vote

How do tubojets compare to afterburning turbofans in terms of efficiency?

How do tubojets compare to afterburning turbofans in terms of efficiency? The 5th slide from this presentation (original plot from Daniel P. Raymer, Aircraft Design: A Conceptual Approach), shows a ...
sophit's user avatar
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1 vote
Accepted

What is the most efficient design for an aircraft designed only to hover?

The key here is disk loading ($T/A$). For most efficient hover, you want as low a disk loading as possible. Small thrust (but must equal weight) and a huge disk. When throwing a gas to make thrust (...
Rob McDonald's user avatar
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1 vote
Accepted

When doing calculations with TSFC of multiple engines, do we add all TSFCs together?

The thrust-specific fuel consumption (TSFC) is a measure of how efficient an engine is. It tells you what fuel flow rate is required to generate a certain amount of thrust. If you have two engines, ...
Bianfable's user avatar
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