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Dyson has been making bladeless fans for a few years now that accelerate a consistent stream of air without exposed blades. enter image description here

If this concept were applied to aircraft engines, it could potentially reduce the number of bird strikes, engine complexity/part count, danger for ground crews, etc. That said, it has not been done (or has it?). What are the major roadblocks prohibiting engineers from scaling this technology to large aircraft applications?

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    $\begingroup$ The Dyson is just an ejector pump using a electrically driven centrifugal compressor to create the jet, and arranged in an artful way. It would seem to be a very inefficient way to make thrust, with all the friction losses and such, but it would be interesting to see if the Dyson uses more or less wattage per cfm of air moved than a regular bladed fan (because it's the air being moved that is the thrust). Dyson's marketing tries to portray his inventions, like the particle separator vacuum design, as groundbreaking, but those things have been used in industrial processes for decades. $\endgroup$ – John K Jul 24 '18 at 16:00
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    $\begingroup$ Humorously, turbulent airflow is generally perceived as more cooling to the human skin, than smooth or laminar flows too. $\endgroup$ – RomaH Jul 24 '18 at 18:48
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    $\begingroup$ In theory, yes, but it'd cost you £300M and only hipsters could fly on it $\endgroup$ – Richard Jul 24 '18 at 21:06
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    $\begingroup$ @RomaH is not an impression. Turbulence increases mixing, and thus heat transport away from the surface. $\endgroup$ – Federico Jul 25 '18 at 6:34
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    $\begingroup$ @Agent_L Your safety claim is incomplete. The Dyson fan has a small enclosed high-speed fan: higher speed makes things more dangerous but more enclosure makes them safer (in general). You're only considering one of the competing factors. $\endgroup$ – David Richerby Jul 25 '18 at 12:24
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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 powerful stream. You'll notice they're quite heavy as well; Dyson AM-06 has a thrust-to-weight ratio of just 0.06, 100 times less than a jet engine.

The second reason is they're very inefficient at high speeds. Dyson's fans use the Venturi effect, which is also used in aircraft evacuation slides, to turn a narrow stream of fast air into a wide stream of slow air. This happens through friction simply pulling slow air alongside the fast stream.

Current airliner engines do the same thing, but better. There, high-energy air spins a turbine, which then spins a fan. The conversion efficiency of this process is 3x-5x better and produces uniform velocity - important when you're close to the speed of sound. The fan approach also results in a smaller, lighter engine.

Jet engines imitating Dyson's fans would need cores and core intakes as least the same size as current ones. The reason Dyson chooses to protect their intake with a grate and Rolls-Royce or GE don't is Dyson fans produce on the order of 50 W of power, jet engines 50+ MW. No one cares about a few watts, they do about a few megawatts, which translate into a couple ocean tankers full of oil over a plane's lifetime.

If you want, you can protect a jet's intake with a grate too - see F-15SE, Su-57 (PAK-FA) with radar blockers, Mig-29's "dirt runway" top intakes. This has nothing to do with using an ejector or not. Dyson's design does remove the slow fan, but at the cost of a lot of weight and efficiency, and it's core damage that is the worst scenario in bird strikes.

The third reason is that Dyson's fans would not scale. To fly at Mach 0.8, the ejector stream would have to be highly supersonic, which is a problem in itself. To use them for hovering, where they are reasonably efficient, you'd face the problem of Venturi effect fading with distance - requiring an entire grate of ejectors, not one simple ring. Helicopter blades do the same thing better, while being far lighter and easier to fold.

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    $\begingroup$ +1 for a very well done and comprehensive answer! $\endgroup$ – Mat Jul 24 '18 at 17:31
  • $\begingroup$ I recall reading about someone using this technique to make a flying saucer. Maneuverability was impressive, but as you note, efficiency was abysmal. $\endgroup$ – Mark Jul 24 '18 at 19:11
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    $\begingroup$ So, in general - a "dyson engine" would weigh much more and be a much more inefficient means of thrust. Both are good reasons NOT to make one. If only "looking totally awesome" were a more meaningful design parameter :D Thanks for the insight @Therac $\endgroup$ – Geoff Jul 24 '18 at 19:26
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    $\begingroup$ I found some data on a Dyson fan vs regular fans for CFM per watt, and the Dyson is considerably more efficient than a regular fan, but this is at gentle breeze fan speeds. The efficiency advantage drops off as you increase the velocity. This suggests that an "annular ejector thruster" device that could move enough air to be of use to propel an airplane would be a lot less efficient than driving the air directly. I would guess that the static thrust of such a device would be not so bad but would drop off a lot as speed increases, pretty much the opposite of a regular jet. $\endgroup$ – John K Jul 25 '18 at 1:31
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    $\begingroup$ @JollyJoker Another comparison point could be helicopters. The de Bothezat had to deliver at least 120 N/kW, more than the Dyson's fan. Everything newer is closer to 80 N/kW - but at much higher thrust speeds, even toys start at 6 m/s. So, at static thrust, Dyson's fan is not better than helicopters; it only turns out efficient when compared to cheap desk fans. $\endgroup$ – Therac Jul 25 '18 at 11:36
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Actually, the principle exploited by the Dyson fan is used in some gas turbines, just not quite the way your question expected.

See the section here on “ejector nozzles”.

Here is a picture of the J58 engine. When the tertiary doors are open, air is entrained through them, adding mass flow to the engine. In theory, the extra mass flow gives extra thrust. But, the extra air flow was entrained by the core airflow, so in reality the conservation of energy probably means no extra thrust occurs, because you have a higher mass flow, but some of the velocity from the core flow has been transferred to the tertiary flow, so the average velocity will be lower.

(@John K almost got there when he mentioned “annular ejector thruster”.)

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The underlying concept in the Dyson fan may be considered similar to that called: 'Trompe' (See Wikipedia), where a jet of water drags a flow of air. You can have a look in ESPACENET at Patents FR935340: 'Flow enhancer for jets and compressors'; US2946540: 'Jet propelled aircraft'; CA611861, for a 'Flying Disc', all by Henri Coanda, and US2918233: 'Aerodyne', by Alexander Lippisch, all in the same line, thus, I'd consider as best option to accept or reject Dyson fan as an alternative to propellers, ducted fan, or turbofans, conducting some experiments, with the design adapted to propulsion, not cooling or moving air, the Dyson fan data provided in a link in answer by JollyJoker is promising. Not?

The concept in Dyson fan was in some aircraft designs, the Avro Canada Flying Disc never went airborne and was uncontrolable, but the P Moeller disc m200x -

- flew with multiple fans, and was transposed into a toy named: 'Magic UFO', a variant drone.
See patents: US3065935, J Dubbury; GB383408, C E Johnson; US3022963, JCM Frost, showing the concept in Dyson fan was considered in Aircraft, calculations and experiments have the last word, but if an arrangement moves more air, meaning more mass, at similar speed, meaning more thrust, and this done with less power, men, you have an idea worth testing at airplane scale. Salut +

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  • $\begingroup$ please do not post two answers when you want to add informations to another answer of yours $\endgroup$ – Federico Jan 14 at 12:59

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