84 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 ...
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  • 17.6k
24 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 ...
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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 ...
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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 ...
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  • 5,228
18 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 ...
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  • 3,551
18 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 ...
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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 ...
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  • 95.9k
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 ...
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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. ...
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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 ...
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  • 14.3k
12 votes
Accepted

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 ...
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11 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 ...
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  • 716
11 votes

Why wasn't a scramjet used for the Concorde?

A supersonic ram jet (scramjet) requires a fuel with a very high flame speed, so the combustion doesn't take place after the fuel-air mixture has left the engine. Aviation fuel would be completely ...
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11 votes
Accepted

How does turbojet thrust change with altitude?

The thrust variation with altitude would be highly engine specific, but the general trend is nicely depicted in the image below: Read this for further details.
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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 ...
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10 votes
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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 ...
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  • 2,418
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 ...
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  • 54.1k
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 ...
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  • 95.9k
8 votes

How does turbojet thrust change with altitude?

Thrust is produced by accelerating air. The exhaust air leaves the engine nozzle at a fairly fixed velocity, so the acceleration is mainly controlled by the difference between the exhaust and incoming ...
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  • 171
8 votes

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

Yes, it is. It was used on may 2nd generation designs already mentioned by habu, and it is returning now in the 4.5th generation, now with canards: Eurofighter Typhoon: JAS-39 Gripen: Dassault ...
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  • 54.1k
8 votes

Why wasn't a scramjet used for the Concorde?

The Skreemr at the present time is only an advertisement idea, so comparisons are not really meaningful. Nevertheless, the difference with the Concorde is the expected range of speeds: at Mach ~2 a ...
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  • 31.5k
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 ...
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  • 57.7k
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. ...
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7 votes

How is mass flow rate computed?

The short answer is: No. One cannot calculate the inlet mass-flow based on the velocity alone. However in order to "know" the velocity ( $v$ ) you most likely would have measured everything you need (...
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  • 1,537
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 ...
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  • 8,689
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 ...
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  • 17.6k
7 votes
Accepted

How does the load transfer from a prop to the airframe?

The engine mount is an important component that transfers the prop thrust to the airframe. It's clearly visible in this photograph of a fast and powerful plane, a Bf109. Of course, bearings transfer ...
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  • 10.4k

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