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 ...
- 30.2k
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 ...
- 237k
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 ...
- 237k
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 ...
- 5,586
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 ...
- 102k
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 ...
- 237k
13
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 ...
- 237k
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.
...
- 75.1k
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 ...
- 17.3k
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
- 30.2k
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 ...
- 306
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 ...
- 237k
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 ...
- 2,688
10
votes
Accepted
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 ...
- 56.5k
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 ...
- 5,044
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 ...
- 102k
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 ...
- 62.9k
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 ...
- 237k
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.
...
- 75.1k
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 ...
- 16.9k
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 ...
- 30.2k
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 ...
- 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 ...
- 30.2k
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 ...
- 11.2k
7
votes
Can a turbofan engine have less noise so that it doesn't disturb our ears?
Turbofans already produce much less noise than the turbojets used in the 1960s. In general, the higher the bypass ratio, the lower the noise level.
It's difficult to silence a jet engine: any ...
- 10.3k
7
votes
What is a spool in any jet engine, what is its funtion?
A spool in a gas turbine consists of a compressor (or fan), a connecting shaft and a turbine, see this answer. The purpose of the spool is to compress air driven by combustion gasses through the ...
- 1,817
7
votes
Where can I find prof. Wittenberg's TU Delft aircraft propulsion notes?
Um - yeah the handout in question, VTH-D 14, dates from quite a while before the start of the internet. And it is in Dutch.
I have a treasured paper copy (with an imprint of a cup of coffee), which ...
- 62.9k
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