Aircraft

Rotor X's quad-rotor eVTOL promises extreme efficiency and autorotation

Rotor X's quad-rotor eVTOL pro...
The RX eTransporter claims extremely impressive range, payload and endurance figures for a non-transitioning eVTOL air taxi
The RX eTransporter claims extremely impressive range, payload and endurance figures for a non-transitioning eVTOL air taxi
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The RX eTransporter claims extremely impressive range, payload and endurance figures for a non-transitioning eVTOL air taxi
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The RX eTransporter claims extremely impressive range, payload and endurance figures for a non-transitioning eVTOL air taxi
Large-diameter rotors produce very efficient lift, although there are other factors to consider
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Large-diameter rotors produce very efficient lift, although there are other factors to consider
Small wings on the top and tail improve the eTransporter's range at speed
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Small wings on the top and tail improve the eTransporter's range at speed
Rotor X will be building combustion-fueled versions of this airframe as well, and Advanced Tactics will be developing it for military applications
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Rotor X will be building combustion-fueled versions of this airframe as well, and Advanced Tactics will be developing it for military applications
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Arizona's Rotor X wants to step up from being the world's biggest kit helicopter manufacturer and get into the eVTOL game, and to do so, it's put forth a design it claims is "dramatically more efficient and less expensive than all other eVTOL concepts being proposed or developed today." Its huge blades could also make it one of the safest eVTOLs in the sky, since they give it the capacity to autorotate in the case of motor failure.

Rotor X's design is called the RX eTransporter. It's a relatively simple quad-rotor multicopter, with a helicopter-like cabin that seats up to nine, including pilots, or carries up to 1,600 lb (726 kg) of cargo. These guys are not interested in the complexities of tilt-rotor design or the hover inefficiency of small-diameter rotors; this thing offers four of the biggest rotors you'll see in the eVTOL space, extended out from the cabin on long poles.

Where most transitioning vectored-thrust or lift-and-cruise eVTOLs rock a large wing for efficient forward flight, the eTransporter has a T-tail and a small top wing. This looks to us like a clever way of compensating for some of each rotor's retreating blade stall as airspeed increases, but this still won't be one of the faster air taxis in the sky. Cruise speed is listed at 140 mph (225 km/h), with a max speed "over 160 mph" (257 km/h) – vectored thrust designs are aiming at more like 200 mph (322 km/h).

This is the opposite approach to the ultra-small rotor concept used by Lilium, and its advantages, disadvantages and mission profiles will tend toward the other end of the spectrum. The Lilium jet is horribly inefficient in a hover, but highly efficient on the wing, so Lilium is looking to position itself as an inter-city longer-range transport service.

Large-diameter rotors produce very efficient lift, although there are other factors to consider
Large-diameter rotors produce very efficient lift, although there are other factors to consider

The eTransporter, on the other hand, will be among the most efficient eVTOLs on the market in a hover – indeed, Rotor X says it'll be able to hover on the spot for more than 45 minutes if necessary on a single charge. Moving through the air at speed will develop enough lift from the small wings and the body design to double its endurance figure to more than 1.5 hours, and the company is claiming a max range up to 230 miles (370 km) running on battery power. That's an incredibly impressive figure for a straight-up multicopter, and a testament to just how efficiently larger rotors like this can produce lift.

There are some possible downsides to this approach. One could be blade tip noise, which could prove a limiting factor for a given eVTOL's ability to operate in densely populated spaces. That said, Rotor X president Don Shaw tells us that the company is currently working on quiet rotor technology, and expects this design to make less whooshy downwash than small-rotor competitors. Another is footprint, although Shaw says the eTransporter's four wide arms will fold in to make it easier to garage.

And then there's redundancy. Lose one of the rotors on a typical quadcopter and you've got yourself a one-way ticket to tumble town. According to Shaw, however, each of the eTransporter's rotors is powered by multiple electric motors, allowing multiple failures before you lose a single prop. And even if you do completely lose power to a rotor, these large blades will also make the eTransporter one of the very few eVTOL market entrants capable of autorotation, a process in which an unpowered rotor can be spun up by the ambient air as the aircraft descends, effectively allowing the pilot to use a dead rotor a bit like a parachute, making for a controlled and cushioned landing.

In forward flight, Shaw says the total failure of a single rotor will be even less of an issue; the pilot will be able to choose to continue the flight or land, whatever's safest. "The eTransporter," he says, "will be one of the safest means of transportation by far in the eVTOL air taxi market."

Rotor X will be building combustion-fueled versions of this airframe as well, and Advanced Tactics will be developing it for military applications
Rotor X will be building combustion-fueled versions of this airframe as well, and Advanced Tactics will be developing it for military applications

Still, it'll be interesting to see how the quad-rotor configuration goes when it comes to certification, even if the rest of the design is a lot less complex than most of the bigger players in this field; redundancy upon redundancy is the mantra with which other eVTOLs hope to rock the regulators (and their investors) to sleep.

Either way, an aircraft tailored toward super-efficient hovering could make a lot of sense for quick cross-town transport, deliveries and industrial operations. Rotor X says a number of mining companies, for example, are "already showing serious interest" in pilot-optional cargo lift versions of this thing.

The company is working on this project with Advanced Tactics (AT), makers of the Black Knight VTOL "flying truck" for the US Military. AT will be developing a military version of this aircraft as part of the US Air Forces AFWERX/Agility Prime programs. There will also be a longer-range, heavier-lift version built using either a fully combustion-fueled or hybrid powertrain.

Rotor X says it expects to start testing an experimental-class prototype in Alaska next year. It's expecting commercial FAA air taxi certification by 2024.

Editor's note: This article was amended on 29 June, 2021, to include additional information provided by the Rotor X president Don Shaw.

Source: Rotor X

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9 comments
9 comments
dan
bigger rotor = smaller disc load = more efficiency = good approach. but why not use a single rotor? disc area would double at least. batteries still could be used as energy source, e.g. with a NOTAR system or an independent tail rotor/e-motor. even coax designs (with an e-motor in the rotor shaft) would outperform complicated not-fish-not-bird-designs. to you readers: is it correct that recently eVTOL companies have increase their disc surface, constantly? From very cool but inefficient as Lilium to this design, maybe not so fancy but maybe with a chance it could fly commercially one day?
Chris__
This thing is going to be LOUD like a helicopter with those big rotors... and probably no more efficient in hover... and not much faster... wouldn't any prospective customer just buy... a helicopter?
dan
@ Chris, maybe a good point... Though efficiency NEEDS big rotor/prop area. That collides with speed. But at least this design - maybe - could take off one day as this design certainly is several times more efficient than extreme designs like Lilium and alike. Speed maybe secondary as we loose more time in security checks and boarding in particular in shorter flights. So you might be right, just by a helicopter... Cheers!
Primecordial
Could the rotor pod arms not be configured to generate lift, and thereby lose the odd-looking beanie prop-like wing?
Arcticshade
@Chris

No A helicopter has got a complicated head that is exactly why multicopters will be so popular, its direct drive, no gears, and linkages that wear out and fail and sophisticated maintenance is a thing of the past. This idea is superb !
doc
A wonderful concept lets have this go forward and get some real life testing done.
A single rotor is too complicated, and a soingle point of failure can bring a helicopter down,

With this craft you have redundant rotors, with which there are no mechanical parasitic loads (ie gearboxes etc) to leech of the main power source. Furthermore the electric system is super efficient, and super easy to support, a motor/rotor swap could probably be done in 20 minutes ! and maintenance on a rotor in 5 ! (which would like just consist of a bearing change. Astonishing how far we have come since the age of the helicopter. Well done RotorX team !
dan
@doc: enthusiasm is a great feeling, right? But you surely are aware that the bigger rotor or horizontal "props" only do work with a collective pitch control. on a toy quadcopter, the uneven forces (forward moving/retreating blade) are small enough to be supported even by plastic props. Manned aircrafts including this design however, must eliminate (by adjusting the pitch) theses uneven forces. (Consider why helicopters need them...) So this design will not fly like this. Sorry.
Graeme S
Dan, that is why these rotor heads have a teetering head, this is common amongst helicopters, has been that way for 50 years, the teetering head automatically adjusts the retreating blade by increasing it AoA and conversely decreases the advancing blade AoA. This dissymmetry of lift in forward flight is the main reason that the speed at which helicopters can fly, that said more rotors, all doing the same thing means that each rotor head produces part of the overall lift component thus its individual teeter capacity is also less therefore it can accommodate a faster forward speed than a single rotor system. It will get to a speed / lift capacity same as all helicopter rotor heads but the overall speed of the aircraft will be a lot faster than a single rotor helicopter
Laszlo KRUPPA
The eVTOL arena used to be a place for the competition of batteries. Nowadays it is turning more and more into a rotor/propeller competition. Old limitations of the props shall be broken. It is mainly the speed range that is less than 1/3 of a Mach today. (For a VTOL design speed – middle point of the speed range - must be below 200 km/h to perform well in vertical takeoff and also remain silent enough for the urban environment.) Embracing the new morphing blade propeller technology can help winning the race. The first party to make it, is in for a big sensation.