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Old 04-11-2018, 04:17 PM   #1 (permalink)
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Defying gravity, the flying future.

I must confess, putting science and mathematics for side for a moment, and by watching and judging with the heart, that I get puzzled with the drones transportation for passanger that are comming.

When kid I had a domestic fan that could be pointed 90 degree to top or to bottom. I put it to maximum speed and waited it could fly away, but it didn't, and I imagine that a electric motor wasn't powerfull enought even to fly itself.
Today small electric motors are flying a air taxi away.

Some machines looks like are defying the gravity law. Some with proppeler blades small, remembering a PC cooler fan.



I ask myself. How is that possible ???

-Low weight due carbon fiber?
-Extra high power electric motors ?
-Lithiun bateries of low weight ?



If science manage to create electric motor with power density even higher (more KWs per Kg) and could develop batteries with 10x more energy density than lithium batteries, these vehicles would change a lot of things.

Despite the science advances we will see in next years, they still could not drive close like car, and would still require a lot of space between each other to avoid crashs, since they alter the air flow near itselve generating a lot of turbulence.

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Old 04-11-2018, 04:28 PM   #2 (permalink)
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For one thing, ducted or shrouded fans are a lot more efficient than open ones.

Ducted fan - Wikipedia

Quote:
In some cases, a shrouded rotor can be 94% more efficient than an open rotor. The improved performance is mainly because the outward flow is less contracted and thus carries more kinetic energy.[2]
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Old 04-11-2018, 04:42 PM   #3 (permalink)
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Uhhnnn... like guns with longer tube have more power ?

But this first air taxi in the video, even with the total propellers together, don't look like have a huge area. It still puzzles me...

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Originally Posted by jeongyun View Post
For one thing, ducted or shrouded fans are a lot more efficient than open ones.

Ducted fan - Wikipedia
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Old 04-11-2018, 08:02 PM   #4 (permalink)
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Guns with longer barrels are more accurate. Ammunition with more gunpowder are more powerful.
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Old 04-12-2018, 03:56 AM   #5 (permalink)
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A propeller creates forward thrust because the pressure on the leading side of the propeller blade is lower than at the trailing side.
The air around the propeller tries to equal out the pressure differences. The funnel avoids side access so the pressure difference on the blades remains higher.

Also, a slight taper on the funnel entry can harvest some forward thrust as the intake side does have low pressure, further enhancing efficiency.
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Old 04-12-2018, 12:15 PM   #6 (permalink)
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Thank you folks. Smart community .

Well... Why propeller airplanes don't have a sort of case (duct) around the propeller, like some propeller used in scale model planes (electric ducted fan) that trys to mimic a turbine's look ?




I found a intesting thing about human power vehicles. Helicopter powered by humans :



A solar powered attempt :

(should had put solar cells in the propeller's blades )


You only need to be strong and slin lightweight at same time, and enjoy trips of 10 seconds. But it's impressive anyway.

Why bikes used in record breacking don't also use arms power, like this human powered helicopter ?

Last edited by All Darc; 04-12-2018 at 12:38 PM..
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Old 04-12-2018, 01:29 PM   #7 (permalink)
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My opinion, the problem with flight is that it's far less efficient than ground travel, all else being equal. You expend energy staying aloft that tires do for free. I don't foresee flight as being common for every-day and short-range travel until energy becomes significantly cheaper.

And you bring up a good point about batteries. There ARE battery powered airplanes already, but they have relatively small payloads and short range.

https://newatlas.com/electric-aircra...stralia/52846/

Quote:
A single charge can reportedly keep the plane in the air for up to one hour, with 30 minutes of extra power in reserve.
Although the article is very optimistic (and it's quite an achievement to have a working electric plane at all), it's important to note that this airplane cruises at less than 100mph, with A 100 mile range in perfect conditions. The interior volume is limited to two cramped passengers and zero cargo.

On the flip side, operation costs are lower and it's probably a lot more reliable/safe.
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Old 04-12-2018, 01:49 PM   #8 (permalink)
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Also, many smaller propellers are less efficient than fewer large propellers. You need many propellers for redundancy, but it's very inefficient, and batteries already suffer from low energy density.
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Old 04-12-2018, 03:13 PM   #9 (permalink)
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The most efficient transport will be hyperloop, vehicles in vacuum tubes, and the few required energy it's produced by solar panels. Not sure if it can have a good use for cities, since it will be very expensive.



For flying maybe in future people will need to have solar panels and get credits of produced energy to be allow to fly in electric vehicles. A week or so to produce energy to a short flying trip.

Personal dirigibles could be a alternative, but heliun it's going to shortage soon, and hydrogen it's dangerous.


But even if energy wasn't a problem, the flying vehicles took far more space to navegate than road cars, since the require distance for safety it's giant. If 0,1% of people in big cities had a helicopter, there sould be no enough space on air.

Is the reported sodiun batteries, that promissed a 10x more power density than lithiun bateries in a very close future, a true or just a scam ?

Quote:
Originally Posted by Ecky View Post
My opinion, the problem with flight is that it's far less efficient than ground travel, all else being equal. You expend energy staying aloft that tires do for free. I don't foresee flight as being common for every-day and short-range travel until energy becomes significantly cheaper.

And you bring up a good point about batteries. There ARE battery powered airplanes already, but they have relatively small payloads and short range.

https://newatlas.com/electric-aircra...stralia/52846/



Although the article is very optimistic (and it's quite an achievement to have a working electric plane at all), it's important to note that this airplane cruises at less than 100mph, with A 100 mile range in perfect conditions. The interior volume is limited to two cramped passengers and zero cargo.

On the flip side, operation costs are lower and it's probably a lot more reliable/safe.

Last edited by All Darc; 04-12-2018 at 03:21 PM..
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Old 04-12-2018, 03:19 PM   #10 (permalink)
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It's strange how this vehicle (small propellers) have a total propeller area looking smaller than human transport drones with fewerm and larger propellers.

The Skydriver looks really impossible, since I see no compartment for batteries :



Quote:
Originally Posted by redpoint5 View Post
Also, many smaller propellers are less efficient than fewer large propellers. You need many propellers for redundancy, but it's very inefficient, and batteries already suffer from low energy density.


Last edited by All Darc; 04-12-2018 at 03:50 PM..
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