85
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 ...
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 ...
- 72.8k
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 ...
- 230k
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 ...
- 5,508
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 ...
- 3,671
19
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 ...
- 230k
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 ...
- 100k
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 ...
- 230k
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.
...
- 72.8k
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 ...
- 17k
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
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 ...
- 230k
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 ...
- 736
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 ...
- 230k
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 ...
- 230k
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 ...
- 2,468
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 ...
- 56.2k
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 ...
- 3,272
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 ...
- 100k
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 ...
- 32.4k
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 ...
- 61.3k
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.
...
- 72.8k
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 ...
- 7,244
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 ...
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 (...
- 1,547
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 ...
- 8,765
Only top scored, non community-wiki answers of a minimum length are eligible