The Tethered Uni-Rotor Network: Eternal Flight UAV (opens in new tab)

How would it respond to gusts?

How strictly does it need to maintain angular velocity as it goes around?

What would the maximum speed in still air be? Some fraction of the rotor tip speed?

Does the tilt-wing configuration (presumably for landing and perhaps takeoff) set the constraint on payload mass fraction, as that will require more structure than the tension-stabilized rotary mode? Or is the payload mass fraction relatively insignificant compared to the battery and solar cell mass?

Safety: is there a way for it to gracefully fail? Transition from 4 blades to 3, and let the failed one dangle down as you descend? Would this be even remotely possible?

Cool concept!

1. Any preliminary numbers for total weight and/or disk loading?

1a. How much weight budget is left for payload while still being past the break-even point, considering you'll need enough battery to weather nights and clouds?

2. What kind of numbers are you assuming for flux on the wings? In my experience these numbers are always supremely disappointing compared to theoretical maximum once you take into account angle of irradiance due to time of day, season and latitude, plus the unpredictable effects of cloud cover.

3. Is there any particular benefit to having each of the wing sections decoupled from the structure and attached by tether vs. just extending the airfoil and meeting at a hinge or universal joint?

4. Controllability during takeoff looks like it's going to be a shit show :) Any proof-of-concept results there? Does the h-stab span the entire wing section, or only just behind the props? If it's the former, does that mean the solar cells have to flex?

5. I don't know if the illustration right above the Flight Operation heading is representative, but if it is, I expect a pretty big drag hit from those tethers. (Brings me back to q3 - why not just make that more airfoil?)

6. How fast are we expecting this thing to spin?

Does it scale down? Could I use RC-scale technology, build my own, and use it to provide services to my own local network?

Sure, we all have the eye on the industrial horizon here.

But what would a "the streets have their own uses for things" application of the TURN concept look like?

For instance, I build RC planes for fun, and am a huge fan of Kline-Fogleman airfoils, for their simplicity if not economy .. and I can imagine a low-cost TURN implementation based on KF airfoils which might be more viable at the LoRa/WAN levels of scale. Something easily deployable, cheap/disposable/replaceable, on a much smaller scale of industry - yet widely available.

Can you generate lift from the tether. Maybe using the magnus effect?

How does it take off?

The research is using a spiral development process, where flight data from small scale prototypes are used to validate existing simulation and dynamic models, and then those models are used as design tools for the next largest embodiment. So right now, there are three different scale systems which serve different demographics.

The smallest scale system is purely battery power, but offers flight endurance well beyond what conventional fixed-wing can achieve. Traditional 10-ft wingspan drones carry 5-pounds for about 90 min. A comparable weight/payload TURN system can fly closer to 7 hours. This prototype is being used as a minimum viable product for an upcoming product launch.

The company was awarded an SBIR research grant from the Air Force which considered an internal combustion engine TURN embodiment. While not eternal fight, it again offers significantly extended flight endurance. The best research aircraft can fly a 250 pound payload, drawing 2000 watts of power for about five days. My research shows that an IC TURN system could remain aloft for over 30 days.

Finally, the largest scale system is striving for eternal flight while operating within the stratosphere. At 65k feet, the system is above most weather and commercial airliner traffic, and the air is thin enough to warrant a large wing fitted with solar panels. By getting the power requirements low enough, the energy collected during the day is enough to remain aloft throughout the night, thereby eliminating the need to land and refuel.

>Can anyone here call out whether or not this looks like a viable thing?

For the solar, truly eternal case (which isn't strictly possible because sooner or later you're going to lose a bearing or blow a capacitor or something), I think the limiting factor would be less on the aerodynamic side and more on the power-to-weight ratio you're able to achieve with solar.

A lot of that is going to depend on things like power system efficiency, latitude, and altitude which makes it hard to give a definitive yea or nay on whether this is feasible. I'm not really an expert in power systems but from an aerodynamic perspective it seems at least within the realm of possibility.

Like anything, the details of the implementation are going to make it or break it but there's not enough concrete info in the video.

They're only at the beginning of development, and they're starting at a small scale, so it's not clear whether the smaller scale drones can't achieve perpetual flight or whether that was simply not a necessary goal at this point to monetize the idea and get their business off the ground.

But, assuming that there's some point as you scale down at which perpetual flight becomes impossible, my first guess would be the surface area for solar cells at being a limiting factor.

The text mentions that the smaller version has no solar cells.

The wing generates lift, the engines on the edge of the wing generate thrust. That thrust is at a tangent to the circle the wings travel. Essentially the wings are pushed forward but cabled at the side.

Seems that the four wings rotate around the central unit creating centrifugal force that will keep the cables tight.

It probably wasn't a good choice for them to use the word "tethered" in the name.

It might not be incorrect, but tethered means you are connected to something. In this case, that something is the aircraft itself. Self is not the first thing most people are going to think of when they hear the word tethered. Especially since, as you point out, there are already aircraft that are tethered to the ground.

It's not tethered to the ground. It's a group of rotating "wings" tethered to each other in the centre, wherein the centrifugal force of the rotation give structural stability. That way they get away with using less structural material, which means more of the weight can be batteries or fuel.

These plan to operate much higher at 60k feet and won't be tethered to the ground. The additional height will give them better coverage than the radar aerostats you mention. I think removing the tether might be required for them to be used a lot because the tether seems like it'd a) weigh a lot requiring much larger stats and b) if they're dense enough the tethers could pose a danger to air traffic (at the very least you'd have to route planes to avoid them). Both of those get worse as the stat operates higher and the forces on the cable get higher. It may become an issue where the increased strength required increases the cable weight beyond the point where an cabled aerostat becomes viable.

The use-cases discussed in TFA all seem pretty low-power, mostly recon-type stuff. That said, it'd be interesting to contemplate what the right proportions would be to actually run a hungrier payload.

At a certain point, "perpetual" also starts to run into problems of mechanical failure. Then again, if these things are cheap enough and/or able to limp home in the case of a snapped cable or failed prop motor, maybe it still works out.

Regarding your second point: https://www.airbus.com/defence/uav/zephyr.html

"The first unmanned aircraft of its kind to fly in the stratosphere, Zephyr harnesses the sun's rays, running exclusively on solar power, above the weather and conventional air traffic. It is a HAPS: a High Altitude Pseudo Satellite, able to fly for months at a time, combining the persistence of a satellite with the flexibility of a UAV."

This isn't a new idea, at all. You have to go back to the late 1780's to find a time before the use of balloons as recon platforms: https://en.wikipedia.org/wiki/History_of_military_ballooning

It's not at all COTS, but the Rutan Voyager [1] spent 9 days in the air on it's round-the-world flight.

[1] https://en.wikipedia.org/wiki/Rutan_Voyager

it'll be really interesting to see how this performs in extreme weather. i wonder if the cables would result in a much higher tolerance for shear, etc.

Lol I just asked the same question without seeing your response. I was thinking hollow canvas tubes radiating out from a central hub, slowly unspooled in flight. Some mechanism would use the mechanism of rotation to draw air outward along the tubes to keep them inflated, combined with rotation induced from the central hub. No idea if that would work...

DARPA already looked at that through ISIS. The problem is the massive volume of gas within the airship. Even the lightest winds require a substantial amount of power to travel or station-keep. Google is using weather balloons, but they don't have any active controls, so they drift aimlessly away from the equator, and then need to be manually picked up after about a month.

There's an image. https://static1.squarespace.com/static/5901f9f12994ca40051ae...

Basically, the whole thing takes off like a helicopter, before turning the wings on their sides.

Not really sure how those ideas are all that similar to the TURN here. Those are long flying and involve tethering, but the flight systems are quite different and they're tethered to the ground.

Sorry about that. It's all I had to work with. The TURN concept recently won a local business pitch competition, with a video posted on their website. Slightly (just slightly) better production quality.

https://757pitch.org

I don't think that building (maybe) better solar glider UAVs falls in that category.

They basically combine the existing principles of control-surface based helicopter blade pitch control (e.g. Kaman K-Max) and blade tip propulsion, then drive them to the UAV-exclusive extreme where the individual blades gain complexity until they are a coordinated team of autonomous planes while the "body" of the helicopter along with all the complicated mechanical linkages to the blades is reduced to simple tethers between the blades and a central connection point where a stationary payload could be attached.

I suspect that they are overestimating the structural savings relative to something like the helios glider (where mass was already distributed along the wing) and underestimate tether drag.

The big difference is that a new type of aircraft won't fly at all if it's as bad an idea as solar roadways, whereas the latter could be built mile after mile until the world runs out of stupid money, no matter how bad it really is. If nothing else, the idea of "tethered uni-rotors" deserves a place in the canon of cool sci-to technologies that could theoretically work. They would fit in quite nicely in the future segment of Seveneves for example.