
The Tethered Uni-Rotor Network: Eternal Flight UAV - bennylope
https://turnuav.com/
======
gene-h
Another interesting idea in this domain is to use wind power rather than solar
power. Wind gradients can be harnessed through dynamic soaring although this
can be a bit limiting. One way we might get around this is by flying two
airplanes connected by a long tether.[0][1] One airplane flying at a different
altitude where the wind is significantly different can be used like a kite
sail to pull the other airplane. Although it has been shown to be a pretty
nasty control problem at least for a human[2].

[0][https://www.nasa.gov/feature/flight-demonstration-of-
novel-a...](https://www.nasa.gov/feature/flight-demonstration-of-novel-
atmospheric-satellite-concept)
[1][https://www.nasa.gov/sites/default/files/atoms/files/14-2015...](https://www.nasa.gov/sites/default/files/atoms/files/14-2015_phase_i_william_englom_virtual_flight_demostration_stratospheric_dual_aircraft_platform.pdf)
[2][https://arc.aiaa.org/doi/10.2514/6.2018-1492](https://arc.aiaa.org/doi/10.2514/6.2018-1492)

------
jselfridge
I'm the originator of the TURN concept, and owner of the company. I can answer
any questions you guys have about the vehicle.

~~~
CarVac
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?

~~~
jselfridge
In steady wind, it needs to spin faster to maintain its wind robustness, which
does consume more power... but that's common to all aircraft. Generally
speaking, the it is robust to wind gust velocity about 25-30% of the wing
speed.

It's more important that each wing maintain equal spacing between one another.
But the angular rate of the entire system can be adjusted to accommodate the
current operating condition.

I've evaluated models that can travel at 68 knots. Not terribly fast, but the
intended application is to stay in one spot for as long as possible.

The tilt-wing configuration is actually dated. The L/D ratios of the wing
would require the motors to be excessively oversized for takeoff and landing
only. The design has been revised to have a single motor on the outboard
section, and the system begins its rotation while on the ground prior to
takeoff.

With three rotors it is still possible to stabilize the central hub, assuming
the three can support the additional weight of the lost rotor arm. And with my
controls background, I can't wait until I have more time to investigate this
failure mode mitigation option!

------
upofadown
Not sure I understand the images. The cables seem to be connected to the end
of the wing units. A wing can't normally generate force longitudinally. So how
is the wing generating cable tension?

Added: OK, it is all generated by the centripetal force caused by the mass of
the wing units. So fast spinning and lots of cable/parasitic drag to get the
wings reasonably level. Seems like a lot of wing area for a small payload. How
is this better than just a wing large enough to support the payload with
cables to distribute the load across the wing length?

Added2: This scheme still has the problem that the downwash from each wing
will affect the other wings, just like in the helicopter case.

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

~~~
samstave
Wouldnt a single wing being buffetted by a downdraft or sudden turbulence
cause catastrophic loss of tension between all wing tethers and the whole
thing collapse?

What if instead of teathers, you just had two large circles of composit, as a
hub and a rim, that were stiff enough to keep all wing positions but stiffer
than a flimsy string - and thus keeping formation?

~~~
Aarostotle
I'm a paraglider pilot, not an aerospace engineer, so take this with a lot of
salt... but:

Paragliders can have asymmetric collapses of the airfoil due to turbulence,
but usually it's no big deal (other than being a little scary). Catastrophic
loss of tension is avoided because there's still airflow over the rest of the
glider, which remains pressurized. All the pilot needs to do is maintain safe
directional control until the full wing re-pressurizes. You feel a sudden loss
of pressure and then an abrupt surge of pressure, then things normalize.

My _guess_ is that something if similar happens here, it'll happen
asymmetrically, and the props might keep airflow over the other 3 wings, which
are still flying. They maintain stability while the wing that went floppy
drops, regains its tension, and then resumes normal flight.

Last: I'd wager that they plan on deploying these in stable air, at very high
altitude.

------
sargun
This is very interesting. I'm a little confused though. The page talks at
length about eternal flight, and how the turn system is supposed to enable
them. Then, in the "Smaller Scale Commercial Drone" section (which I imagine
is a smaller scale version of TURN), it states that the endurance is only
4.5-7.5 hours. What does scale do, which enables eternal flight? Is it just a
matter of having more power on board?

In addition, what are these eternal flight numbers based on in terms of
latitude, and season? In the video, he states that they were looking at
internal combustion @ 30 days. What about the solar approach? Would 18 hours a
day of light be enough? 12? 6?

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

~~~
jselfridge
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.

~~~
ChuckMcM
This is a really neat project. I noted in the discussion that by rotating with
end tip motive power you eliminate the need for stiffening the wing, however
doesn't this increase the need for better tensile strength along the wing? (in
order to prevent it from pulling itself apart, something "regular" wings don't
get a lot of stress on).

Also, in typical rotor craft the lift is highest on the outer edge of the
rotor and least in the center where the airfoil speed is slowest. Does that
affect where you put the payload? Is it on the edges of the wing or still in
the center? At the center, if the wing is supported by the centripetal force
of the wingtip motor's angular momentum, there is a huge torque in the middle
if you pull it down. (much like pulling down on a suspended cable). How much
deflection before you have the same problem as the stiffened wings of current
efforts?

~~~
bigiain
Increasing tensile strength is super easy compared to improving bending and
twist resistance, especially when the aerodynamics not only constrains the
thickness of the wing but also rewards high aspect ratios (the tip-to-tip
length of a wing compared to its front/back dimension).

Imagine a wing that's 20+ times longer than it is deep, and is only 5% as
thick is it is deep (so, for example, a 20m wide wing, that's 1m deep front-
to-back, and 5cm thick top-to-bottom) - that's really hard to get stiff in
bending along it's long axis, and in twisting stiffness around that long axis.
This is why - as the article mentions, a sailplanes long thin wings account
for 40+% of the airframe weight, when a stubby-winged but less aerodynamically
efficient wing (like, say a Cessna 172) the wing might only account for
10-20%$ of the total airframe weight.

This TURN design minimises bending/twisting forces by replacing the load
bearing and alignment forces with mostly end-to-end tension ones - which are
much easier to resist (just load the structure up with "axial" carbon
fibre...).

------
yathern
Very exciting project! Love the idea, and can't wait to see some proof of
concepts eventually. It obviously has the potential to be revolutionary in the
aerospace industry, though time will tell if it's as effective as claimed of
course.

They compare the TURN concept to satellites in the beginning, mentioning only
positives by comparison - of which there are indeed many (cheaper, better
comms). One thing I didn't see mentioned was the failure mode between the two.
A satellite that ceases to function will stay in orbit, until this orbit
decays enough for it to burns in the upper atmosphere. If one of the rotors on
this device fails, it will just come crashing down to earth.

And also, in typical neo-luddite fashion, I'm fearful for the surveillance
applications of this device. Even if staying airborne isn't eventually
completely free (eternal flight) with this system, the ability to stay up for
9 hours at a time on a few Li-Ion cells opens up a world of possibilities, not
all of which are great. If NOAA can afford to put a number of these out in the
Atlantic to get better atmospheric readings, surely cities, states, city-
states, and others can afford to put a number of these above their populace.

However, progress is inevitable, and the technology can't always be blamed for
it's potentially negative applications. I think this is an amazing project -
but it will require some self-control to not let this push us further into a
surveillance state.

~~~
Mtinie
Regarding your second point:
[https://www.airbus.com/defence/uav/zephyr.html](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](https://en.wikipedia.org/wiki/History_of_military_ballooning)

~~~
daveFNbuck
You'd have to go back before humans to find a time before facial recognition
was used to track individuals, yet people get upset about when facial
recognition is used to automatically track and record all of your movements
through ubiquitous cameras.

There's a big difference between a person going up in a balloons for a few
hour to scout a military locations and a swarm of drones constantly monitoring
a city in peacetime.

~~~
Mtinie
I was not making a judgement about whether or not there's a difference between
a single balloon and a drone swarm (there is), but addressing the comment:

> And also, in typical neo-luddite fashion, I'm fearful for the surveillance
> applications of this device. Even if staying airborne isn't eventually
> completely free (eternal flight) with this system, the ability to stay up
> for 9 hours at a time on a few Li-Ion cells opens up a world of
> possibilities, not all of which are great.

~~~
daveFNbuck
It looks a lot like you were saying these are similar. I'm not sure what else
your comment could mean. What was your intended meaning?

------
reaperducer
Perhaps I just didn't understand the web page, but this seems unnecessarily
complicated.

The Department of Customs and Border Protection already operates a fleet of
tethered airships. These seem to be a much simpler solution to "eternal
flight."

[https://en.wikipedia.org/wiki/Tethered_Aerostat_Radar_System](https://en.wikipedia.org/wiki/Tethered_Aerostat_Radar_System)

~~~
adrianmonk
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.

------
sargun
What's the current longest endurance, COTS (commercial off the shelf) flight
platform?

~~~
curtis
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](https://en.wikipedia.org/wiki/Rutan_Voyager)

~~~
digikata
Similarly not-COTS, but a series of UAVs, a Zephyr "7" made a record 336 hour
flight - 14 days, with an unofficial runs of three minutes (!!) short of 26
days aloft for a recent Zephyr S.

[https://en.wikipedia.org/wiki/Airbus_Zephyr](https://en.wikipedia.org/wiki/Airbus_Zephyr)

~~~
curtis
The Zephyr is using Lithium-Sulfur batteries, which have a better energy-to-
weight ratio ("Currently the best Li–S batteries offer specific energies on
the order of 500 W·h/kg" according to Wikipedia [1]).

These aren't commercially available though. Twice the performance of currently
available automotive batteries is a major advantage for aircraft applications.

Pretty cool.

[1]
[https://en.wikipedia.org/wiki/Lithium%E2%80%93sulfur_battery](https://en.wikipedia.org/wiki/Lithium%E2%80%93sulfur_battery)

------
goda90
I wonder if the development of thinner, flexible solar panels and batteries
would make a lighter than air UAV a better choice for eternal flight. That way
it only needs to power rotors for positioning instead of maintaining flight.

~~~
jselfridge
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.

------
crowbahr
I have to wonder what the maximum translational velocity would be for these
hovering platforms. How well could they deal with high winds? Gusts? How
quickly could they change their position?

To make a comms network you'd need them relatively evenly spaced out to
maintain coverage over a wide area. You'd also need them to have beefy and
power hungry broadcast/receiver systems. How well can they scale with the
solar energy?

Overall a very cool idea though!

~~~
mikepurvis
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.

~~~
crowbahr
Seems like the video talked about wanting to make it into an internet
communication network, which just doesn't seam feasible to me.

Then again, I'm just a programmer. I recognize I have no grasp of the power
requirements for that kind of project.

The inexpensive nature of them seems a major draw. I wonder if they can detach
cables and have the wings fly home on their own while having the center
parachute down?

------
gpm
This seems like a really cool idea. What I can't figure out is the bootstrap
process. How do you launch/start the wings rotating?

~~~
RandallBrown
There's an image.
[https://static1.squarespace.com/static/5901f9f12994ca40051ae...](https://static1.squarespace.com/static/5901f9f12994ca40051ae59d/t/590346c9f5e2316bee3d0122/1493387276592/TURN.jpeg?format=2500w)

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

------
zackmorris
I think there is merit for the last idea in the article - some kind tethered
drone array as a windmill using something like autorotation:

[https://en.wikipedia.org/wiki/Autorotation](https://en.wikipedia.org/wiki/Autorotation)

Similar ideas have been suggested using balloons:

[http://latesttechnology-world.blogspot.com/2013/07/magenn-
ai...](http://latesttechnology-world.blogspot.com/2013/07/magenn-air-rotor-
system-mars_18.html)

[https://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=134023](https://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=134023)

[https://en.wikipedia.org/wiki/Airborne_wind_turbine](https://en.wikipedia.org/wiki/Airborne_wind_turbine)

An array of wind-powered drones could scale well beyond what's possible with a
traditional wind turbine, since most of the torque gets applied at the
wingtips. There might be advantages with inconsistent wind gusts too, since
the rotor could wind up in strong wind and unwind in weak wind. Startup costs
would be negligible since a few drones could start the rotor and more could be
added as needed. It might even by safer for birds if a drone array turns
slower than a fixed rotor.

~~~
bennylope
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.

------
peter_d_sherman
Utterly Brilliant!

Something like this is sorely needed for bringing broadband to other parts of
the world. Best of luck to Justin in this endeavor. I hope he succeeds wildly!

------
mLuby
Is the cable portion essential? I'd think a semi-rigid structure (like they
talk about with helicopter blades or glider wings) when under load would
survive longer.

~~~
gfodor
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.

~~~
nradov
There's not much weather up at the planned operating altitude.

------
carapace
Er, use the Magnus effect. (Cf. "Magenn Power, Inc." company, now apparently
defunct.)

[https://en.wikipedia.org/wiki/Magnus_effect](https://en.wikipedia.org/wiki/Magnus_effect)

I've been playing with geodesic cellular kites, and "eternal" flight is
certainly possible. If the ratio of surface area to mass is great enough it's
actually hard to stay on the ground. Cellular kites scale. I would like to
eventually make flying buildings, etc...

~~~
plutonorm
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...

~~~
carapace
Sorry for the delay. I don't know if that would work either, but it sounds
good. ;-)

Check out "Tensairity"
[https://en.wikipedia.org/wiki/Tensairity](https://en.wikipedia.org/wiki/Tensairity)

------
vpribish
clever design, but that video was awful. It came across as either ill-informed
or misleading - and the beige - oh my, the beige.

~~~
jselfridge
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](https://757pitch.org)

------
everyone
Why not use a balloon? or dirigible or something like that?

------
JackFr
Balloons?

------
opless
Is this "solar freaking roadways", but for UAVs ?

~~~
usrusr
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.

