Aircraft

Blainjett's hemi-rotor concept promises unprecedented VTOL performance

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Blainjett believes its extraordinary hemi-rotor drone concept will deliver unprecedented power, speed and efficiency thanks to its unique propulsion systems and airframe
Blainjett
Blainjett believes its extraordinary hemi-rotor drone concept will deliver unprecedented power, speed and efficiency thanks to its unique propulsion systems and airframe
Blainjett
The hemi drone in various stages of flight. Leftmost is hemi-rotor mode for slow speed forward flight. Second is low drag swept-wing mode for high speed. Third is a high-lift winged configuration for slow cruise, and on the right is hover/VTOL mode, with the bodywork slats opened up to allow vertical airflow
Blainjett
The split system allows the swashplate to tilt, while also letting you raise the entire average height of one side of the disc
Blainjett
Blainjett's dynamic variable pitch blade system in prototype form
Blainjett
Large hemispherical lift rotors rapidly flatten out their blades as they pass back under the body of the hoverbike
Blainjett
The hoverbike is designed to seat as many as three people. The hemispheric rotors give it two-three times more power and efficiency, says Blainjett, than a series of smaller ducted fans
Blainjett
In slow-speed hemi-rotor mode, the bodywork is closed and the lift rotors only pitch up as they move out into clean air
Blainjett
In high-speed flight, the wings are swept back into a low-drag configuration
Blainjett
In normal cruise flight, the lift rotors turn and lock outwards to act both as wings and as control surfaces
Blainjett
In VTOL/hover mode, the bodywork opens up to allow vertical airflow for maximum lift
Blainjett
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This wonderfully odd idea appears to have genuine potential to radically improve the power, speed, efficiency, payload capacity, range, endurance and ground footprint of a wide range of VTOL aircraft and drones. We've never seen anything quite like it.

Blainjett's fascinating hemispheric rotor concept is a totally unique and left-field approach to VTOL flight. The company (no relation to me, for the record!) came up with the bones of the idea while working on the Horizon eVTOL hoverbike, which we covered back in January, and trying to solve the problem of how to generate lots of efficient vertical thrust without taking up large amounts of space or exposing bystanders to fast-spinning propellers.

You could use a bunch of small ducted fans, something like what Lilium is doing in the air taxi segment. But small fans are extremely inefficient in VTOL lift and hover mode – Lilium is banking on its design making more sense in longer-range flight, where its low drag might give it an advantage over large-prop competitors. The hoverbike would be spending all its flight time in hover mode; small fans would kill its endurance, bigger ones would end up something like the treacherous Hoversurf Scorpion, which looks like a great way to cut down on limbs if you feel like you've got too many.

Blainjett's solution was to go with big, variable pitch rotors for efficiency, but to tuck the entire retreating half of the swept disc away under the bike's bodywork. Using a split swashplate, adapted from the helicopter world, they devised a system that would immediately ramp the blade pitch down to fully horizontal every time it went into its slot in the bodywork, then ramp it back up to a positive lift pitch when it emerged on the other side.

Large hemispherical lift rotors rapidly flatten out their blades as they pass back under the body of the hoverbike
Blainjett

The result, according to Blainjett president Cary Zachary, was a system that took up about as much space in the aircraft's top-down footprint as a set of smaller, ducted fans, but with huge advantages in thrust output and efficiency – a factor of two to three times better on each metric.

That was on a hoverbike. Now, the company is designing a hemi-rotor, cruise-capable drone to take maximal advantage of the idea, and it adds a couple of interesting wrinkles to make things even more effective.

"If our lab testing continues on its current trajectory," Zachary says in a new press release, "we believe our [hemi-rotor-configured] prototype will boast the most efficient hover and forward flight profile of any rotor-borne VTOL aircraft."

Them's some fightin' words, alright, but the new machine certainly appears to up the ante. It runs just two lift rotors, but they're disproportionately huge compared to what you'd see on a typical drone, and they can presumably handle all the micro-corrections and nuances of VTOL flight thanks to their variable-pitch blades.

In VTOL/hover mode, the bodywork opens up to allow vertical airflow for maximum lift
Blainjett

For VTOL and hover operations, the drone's top and bottom bodywork opens up in a series of slats, exposing a greater percentage of the rotors' swept area to airflow and deriving maximum lift. Then, as it begins to move forward under the power of a large rear pusher prop, these slats close up, and the lift rotors begin operating in hemi-rotor mode, flattening out as they pass through the bodywork and pitching back up when they're out in the air.

In slow-speed hemi-rotor mode, the bodywork is closed and the lift rotors only pitch up as they move out into clean air
Blainjett

At a certain airspeed, the lift rotors are able to stop altogether, pointed out to the sides, and begin acting as wings. The drone's bodywork itself is designed to act as a wing as well when it's closed, and the ability to change the pitch of the blades on the lift rotors lets them operate as control surfaces in cruise flight.

In normal cruise flight, the lift rotors turn and lock outwards to act both as wings and as control surfaces
Blainjett

That's a neat trick – we haven't seen anything like it before. But there's something else up Blainjett's sleeve here, too, because at high speeds, wide wings can cease to be an advantage and start causing more drag than they're worth. These are not ordinary wings, though; with full control over their orientation, this design can treat them as swing-wings, like the ones on the F-14 Tomcat ol' Thomas Cruise turned into a movie star in the first Top Gun. Angled sharply back, they offer a low-drag cruise option.

In high-speed flight, the wings are swept back into a low-drag configuration
Blainjett

So what you've got is a vertical lift system with two enormous rotors instead of four or more much smaller ones, in a very compact ground footprint. If the air can move smoothly through the slats in the bodywork, I can see this being a super-efficient machine in VTOL and hover operations. And then in forward flight, you've got another sizeable propeller, a lift-generating body, and a uniquely tuneable set of wings that can be finely managed both in terms of blade pitch and their sweep angle relative to the body.

I wasn't so sold on the hoverbike back in January, but the way this remarkable concept is put into practice on this Hemi drone, I can totally see how it might be far and away the most efficient use of energy we've seen in the VTOL world to date – and one of the fastest drone designs in cruise flight as well. That's a combination with dynamite potential, as electric drones and eVTOL aircraft begin to proliferate in a multitude of different business models.

Blainjett says it's built small-scale prototypes and tested them in different phases of flight, achieving results that validated its expected lift and drag profiles. The company has entered a partnership with Fenris Electric Systems to develop the complex and custom flight control systems it'll need to operate all the bells and whistles on this bad boy.

As testing continues, Blainjett is looking to set up non-exclusive development and manufacturing partnerships to commercialize the technology, Zachary telling Unmanned Systems magazine that he's hoping to accelerate development by requiring any partners that further improve the technology to share their innovations with the wider group.

It's a wonderfully odd idea, but one with genuine potential to radically improve the power, speed, efficiency, payload capacity, range, endurance and ground footprint of a wide range of VTOL drones – and potentially manned aircraft as well. But it's early days yet – as you'll see in the video below, a marvellous nine-second piece of cinema packing in a mighty 127 freezable frames to give us a glimpse of the prototype. These guys are amazing, they've even managed to radically boost the speed of promotional videos.

Mind you, it sure doesn't seem like these are going to be on the quieter end of the drone spectrum, and that's not nothing when it comes to urban use cases.

Source: Blainjett

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18 comments
paul314
I hope they've thought through the debris issue. Anything blocking one of those slots could be an unfortunate surprise.
stevendkaplan
If this design actually works like they say then I imagine the US military is going to be very interested!

I wonder if you could make an attack helicopter using this system for lift?
mediabeing
The 'video', if you can call it that, is an unpleasant tease. It smacks of dishonesty. Bad move.
guzmanchinky
Very cool, but I see a lot more complexity than a standard drone like setup. Complexity is the enemy of reliability and safety in aviation (and elsewhere)...
michael_dowling
Just when I thought I had seen it all,this shows up! Brilliant idea-I wish them well. Wonder how it stacks up on noise ?
MarylandUSA
I'm sure this article was written as clearly as possible. But a lay reader like me still puzzled over several passages, wondering whether it was suggesting "A" or "B". I'll will need to watch a complete video to "get" how the VTOL mechanism works.
Demosthenes
The video presented was very impressive.
Username
It's amazing how well drawings perform!
riczero-b
As Paul says the integrity of operation depends on slotting the rotors through the bodywork, and that could fail mechanically or electronically, leaving no redundancy. In aero engineering terms could fail unfortunately means WILL fail.
Ralf Biernacki
It has a curiously insectlike look to it---with the return stroke hidden from view, it looks like a fly buzzing its wings back and forth. Cool. 8-D