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Oh No! Another multicopter!

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D Hillberg

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MULTI COPTER CRASH CLAIMS 28 LIVES NEWS AT 10!

A flying chain saw High blades you get to swap heads,

Mid blades an assortment of legs & pieces

Low blades get you piles of mush and stinky feet.

A tree chipper at least has a discharge chute to put the mess in a dump truck.

The odds of a failure mode are high and the results in a crowded city is sushi
 

Jay Kempf

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A lot of styling went into that. Love the fender bulges like a 90's M3 and the 2000 F1 nose windscreen, scoop, rollover hoop, helicopter skids, rear diffuser, tesla emblem tail light.... That is a lot of female molding for a first hover test. Very Manga.
 

Alessandre

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I think the big issue with quad or more copter is the efficiency, the demands for energy is high and any lb more has a big cost in energy, the safety they could solve with innovates design. The conventional helicopter all the fuselage is hanging on a rotor with big blades and when it moves forward generate extra lift because the rotor disc behavior became like a wing and it's auto rotation capable, in a 3, 4, 6 or 8 copter are hanging on motors that once the energy is cut off the rotation stop almost immediately, for hover they have a high consumption, to forward flight 2x more. Maybe with a portable nuclear power-plant they can be viable. Maybe the Avenger's flying carrier could be more feasible because it can use nuclear energy.
 
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Dusan

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The food processor octo-copters (rotor blade plane of rotation at testicle height) are the same as rap music. I'm sitting here gritting my teeth waiting for the whole fad to go away, and it just never does.
It will not go away, the media is exploiting the public for "where is my flying car?" craze. Same for investors, everybody wants to be the first to commercialize a flying car, taxi, VTOL or whatever, see big players as Uber, Joby and Lilium. The public want will be even more after this covid experience, not liking being stuck in traffic again after comfortably working from home for so long.

My experience in aircraft design tells me is that this is the wrong approach to personal flight. A comparable size single rotor helicopter is outperforming a hovering multi-rotor in all flight conditions. Furthermore, from aerodynamic efficiency point of view, nothing can surpass wing-borne flying mode and that's why even helicopters cannot compete with fixed wing aircraft, as a mode of transportation. A personal aircraft will need to transition to an efficient wing-borne flight mode, especially if propulsion is electric, to counteract the limited battery specific energy. This opens another can of engineering problems that are not solved yet.

Just tilting the rotors will not do for the following reason: To be hover efficient, a VTOL aircraft needs large rotors - having low disk loading, otherwise the power demand is very high. However, large rotors are detrimental to wing borne cruise performance, a conundrum of all VTOL concepts, since the creation of the first VTOL aircraft. This was recognized early by NASA and other corporations, a representative study in the field is "Dynamic Model Wind Tunnel Tests of a Variable-Diameter, Telescoping-Blade Rotor System (TRAC Rotor), Evan A. Fradenburgh, Robert J Murrill, Edmond F Kiely" link: https://apps.dtic.mil/dtic/tr/fulltext/u2/771037.pdf Another document having a nice explanation of why the efficiency of the tiltrotor is low in cruise mode, and why a variable-diameter rotor is beneficial is here: NASA Technical Reports Server (NTRS)

A variable telescoping blade is hard to engineer, proved not feasible for tilt-rotors as V22 and AW609, maybe it works for smaller, personal aircraft. I think a better approach is to use a wing specially designed to generate lift in hover, the conventional wing is dead weight in hover anyway, to augment the rotor hovering lift as in these aircraft concepts: Aliptera
 

Victor Bravo

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OR... you could just put back all of the thousands of small airports in cities around the world, that were removed by the greedy-assed real estate vermin to put 10 million cookie cutter shopping malls, and have a simple, low-cost, efficient little Cub sized airplane to commute in. And C-130 sized short-haul commuter airplanes operating like Metro trains, but without the trillions of dollars in infrastructure cost. A 2500 foot airstrip in the center of a city takes up a lot less real estate than 100 miles of freeway and parking structures.
 

pictsidhe

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Multicopters are a dead end for safety reasons. Fixed wing and helicopters can glide to their crash site. Total power failure is frequently survived. A multicopters will just fall. It's only way to limit impact speed is a BRS. They suck at low altitude.
Even if they could be made safe, giving Joe public flying cars for city use seems like a dreadful idea to me, way too many idiots out there. A fender bender in a car would be a lot more serious in the air.
 

Dusan

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OR... you could just put back all of the thousands of small airports in cities around the world, that were removed by the greedy-assed real estate vermin to put 10 million cookie cutter shopping malls, and have a simple, low-cost, efficient little Cub sized airplane to commute in.
This will never work for two reasons: You'll need runways at every mall, business and street ends so people can reach every endpoint in their little Cub. Think like residential air-parks expanded everywhere. It is not feasible. Second reason: using small airports in cities, you need to get there from your location and get from there to your final destination, and when using your personal car it's actually faster and cheaper to go directly with your car to the final destination if it's under 200-300 miles. What I'm saying is that transferring from one mode of transportation to another takes a lot of time and infrastructure, it is much better to have a single mode of transportation, 'door to door' directly.
 

Dusan

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Multicopters are a dead end for safety reasons. Fixed wing and helicopters can glide to their crash site. Total power failure is frequently survived. A multicopters will just fall. It's only way to limit impact speed is a BRS. They suck at low altitude.
Even if they could be made safe, giving Joe public flying cars for city use seems like a dreadful idea to me, way too many idiots out there. A fender bender in a car would be a lot more serious in the air.
There are some fallacies here:
- fixed wing can glide - true, but you need to figure a landing spot; if there is none you're screwed.
- helicopter auto-rotation - if you're low and slow, the energy is not available for safe landing, see the height–velocity diagram, you're screwed.
multi-rotors have this perceived notion that if one or two rotors fail there are more to take the slack and perform a safe landing.
 

pictsidhe

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Total power loss turns a multicopter into a brick, at any altitude. There are more things that can go wrong than a single motor failure. Fixed wing and helos can still glide. Yeah, options are limited, especially at low altitude. But there are at least options to choose from, or avoid. Hit the school, or pancake the playground?
 

Dusan

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Total power loss turns a multicopter into a brick, at any altitude. There are more things that can go wrong than a single motor failure. Fixed wing and helos can still glide. Yeah, options are limited, especially at low altitude. But there are at least options to choose from, or avoid. Hit the school, or pancake the playground?
With separate motors, controllers and batteries, the estimation is that there is less chance of total power loss (except emp, lightning strikes and other unforeseen conditions) Anyway, I'm not defending or saying that multi-copters are better, far from it, actually I think they are less efficient aerodynamically - see my previous post, but they could be equipped with BRS parachute. As proved by small fixed wing aircraft equipped with parachutes, safety and peace of mind increases, and usually helicopters, due to the large rotor cannot be provided with a parachute.
 

Aerowerx

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Instead of a ballistic parachute, has anyone considered a helium balloon that would be deployed as needed? This would work even at low altitudes, I think.
 

pictsidhe

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Instead of a ballistic parachute, has anyone considered a helium balloon that would be deployed as needed? This would work even at low altitudes, I think.
It would be rather interesting watching the necessary size balloon getting inflated in very little time
 

Aerowerx

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It would be rather interesting watching the necessary size balloon getting inflated in very little time
Automotive airbags do it, so the basic technology already exists.

And remember you would only have to limit the ground impact to 3-4 g or so (just guessing).

Another idea. Like the proposed Mars lander. Surround the thing with airbags. So it just bounces along upon impact.
 

pictsidhe

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Surround a multi death scythe with an airbag? Really?
A helium balloon would need to be huge. Hundreds of cubic yards, and you it want to inflate that in say one or two seconds?
 
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