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87 votes
Accepted

Could a Dyson fan scale up to be used as a bladeless aircraft engine?

No. Not a useful propulsion engine. The first problem is power. The air stream from Dyson's fans is weaker than what you can get from a conventional fan the same size, and jet engines need a very ...
Therac's user avatar
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25 votes
Accepted

Why aren't tilting propellers used as an alternative for ailerons or elevators?

It isn't done because a moving control surfaces is easier to design and build than an engine mount that rotates. Plus the associated structure needed to accommodate the thrust, p-factor, and ...
Romeo_4808N's user avatar
  • 73.8k
23 votes

Can a pulse jet be used on a light GA aircraft?

In principle yes. But some details will turn most potential operators off. Noise is the obvious first one. You might not mind, but cockpit noise and vibration in operation will certainly put an ...
Peter Kämpf's user avatar
21 votes

Why is max endurance different for jet and props?

Difference between engine types That different engine types cause the optimum loiter speed to be different is due to the amount of air used for thrust creation. Propellers accelerate a lot of air by ...
Peter Kämpf's user avatar
21 votes

What makes an engine suitable for supersonic flight?

Yes. This is more or less exactly what had been planned for the (now defunct) Aerion supersonic business jet. The engine was to be developed by GE, with the core of a CFM56, the fan replaced with a ...
Daniel K's user avatar
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19 votes

Are ducted fans more efficient?

there is a lot going on here. Short answer is that a ducted fan (what you have pictured) can produce a lot more thrust (experiments from one paper say twice as much) than an open rotor of the same ...
Marius's user avatar
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17 votes
Accepted

What is a biplane propeller and how efficient is it?

It is essentially two propellers stack on top of each other. You can see it in this picture of a Lazair. As for why they were chosen for the Lazair, Many have asked why Ultraflight opted for ...
Dave's user avatar
  • 101k
16 votes

Would injecting water into a jet engine’s exhaust increase velocity?

Spraying water into the exhaust stream will cool down the exhaust flow. The energy needed to heat and evaporate the water needs to come from somewhere, after all. The cooler and denser exhaust flow ...
Peter Kämpf's user avatar
13 votes
Accepted

Are fixed wing aircraft with gimbal thrust feasible?

Could you create an aircraft using an jet engine/propeller/ducted fan on a gimbal? Sure you 'could'; it is feasible by the laws of physics. But just because you can does not mean that you should. ...
Romeo_4808N's user avatar
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13 votes

Is it possible for a ramjet to start from 0 velocity?

No, a ramjet can't be started at zero speed. Yes, there are missiles that use ramjet propulsion without any rotating parts: they use a rocket to accelerate the missile to high enough speed for the ...
Zeiss Ikon's user avatar
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13 votes

Could entrained air be used to increase rocket efficiency, like a bypass fan?

It's called an air-augmented rocket. They add a lot of weight, but yes, they work. They've been discussed on SE here: Limits of bypass ratio in air-augmented (ejector-jet/ducted) rocket
Therac's user avatar
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12 votes
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Why are the top speeds for jet engines higher than for propellers?

The thrust of a propeller is proportional to the inverse of airspeed, while the thrust of a pure turbojet is roughly constant over airspeed in the subsonic region. This means that two airplanes with ...
Peter Kämpf's user avatar
12 votes

Is there any engine that doesn't use a propellant to produce thrust?

Yes there are. Although they are not for commercial aviation. One example are solar powered engines: Source Wikipedia Alternatively, there are other means of storing energy - rubber bands, but this ...
Alexus's user avatar
  • 746
11 votes

Why does a rocket engine increase power with speed if the burn rate is constant?

Put simply, the variation in power is due to the distinction between the exhaust jet power and mechanical power added to the vehicle. The power of the exhaust gas stream measured in the rocket-fixed ...
Liriodendr0n's user avatar
11 votes

Could ducted propellers improve efficiency in small drones?

If the ducted propeller really increases efficiency, we would see more of these Rhein Flugzeugbau Fanliner (picture source) and fewer of these: Socata TB-9 (picture source) The ducting has benefits ...
Peter Kämpf's user avatar
10 votes
Accepted

Can an airliner land safely using only propulsion control?

Some airliners have in fact landed more or less successfully using only engine power for control. The 2003 DHL attempted shootdown incident is an example. A major difference between United 232 and ...
Fred Larson's user avatar
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10 votes
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What are the advantages of using a ramjet in an air-to-surface missile?

A rocket-powered missile carries both fuel and oxidiser and oxidiser is the heavier part. For example a gram of jet fuel needs almost 3.4 grams of oxygen to fully burn! Increasing the fuel load ...
Jan Hudec's user avatar
  • 56.3k
10 votes

Could ducted propellers improve efficiency in small drones?

It is actually suprisingly easy to give a lower boundary and therefore an estimate of the power consumption in hover for any thruster. It is given by momentum theory which correlates the size of an ...
U_flow's user avatar
  • 3,815
8 votes

Can a pulse jet be used on a light GA aircraft?

This question is pretty close. And you should read here as well as here Generally pulse jets are not great at low speeds (and can be hard to start when stationary). These are key aspects of small GA ...
Dave's user avatar
  • 101k
8 votes

Would injecting water into a jet engine’s exhaust increase velocity?

Water injection in the exhaust could work if: The water is fully evaporated before it exits the engine exhaust. The fuel injected in the combustion chamber must also be fully evaporated for effective ...
Koyovis's user avatar
  • 61.8k
8 votes

Why is thrust said to be constant over speed for a jet engine?

There are several effects which in combination make constant thrust a good approximation at subsonic speed. Thrust is created by accelerating a working mass in opposite direction. Net thrust is the ...
Peter Kämpf's user avatar
8 votes

Is it possible for a ramjet to start from 0 velocity?

No. A ramjet relies on stagnation pressure at the inlet in order to compress air prior to combustion. They are typically not effective until the speeds get quite high, somewhere in the Mach 2+ range. ...
Romeo_4808N's user avatar
  • 73.8k
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
  • 12.5k
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
  • 27.4k
7 votes
Accepted

Is there any engine that doesn't use a propellant to produce thrust?

No matter which kind of engine, you need some way to supply the engine with energy and you need some way to store that energy until you need it in flight. Short of going nuclear (and there are some ...
hmakholm left over Monica's user avatar
7 votes

Engines more powerful than the brakes?

Many small 4 to 6 seats propeller airplanes can overcome their brake/wheel holding capability, on concrete and ashpalt. My Cessna Cardinal is 180HP, I do engine pre-takeoff runup checks at 1700-1800 ...
CrossRoads's user avatar
  • 8,795
7 votes

How does the nozzle diameter affect the thrust of a ducted propeller?

Welcome. I'm afraid your theory wasn't actually working. Reducing the duct's exit diameter led to an increase in its internal pressure, increasing load on the propeller, and likely even causing some ...
Therac's user avatar
  • 27.4k

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