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?
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!
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?)
1. The payload likes to stay around 5-10% of the total vehicle weight (otherwise the tether sags to steeply). I've generated sizing models from 5 pound payloads on up to 250 pound payloads for the Air Force SBIR research.
2. I have a look up table that plots energy capture for various latitudes vs day-of-year. It accounts for azimuth angle of the sun and duration of sunlight, where the integral of the area under the curve accounts for reduced collection at sunrise and sunset. To put it in perspective, operating on the worst winter day at 55 deg latitude is 15x harder than flying at the equator.
3. That produces triangular span loading (common to helicopters) which is not nearly as optimal as an elliptical span load distribution (common to gliders). Inboard sections just add weight and drag, without generating that much lift. The tether also has drag, but it's only 6% of the total system drag.
4. Agree. Takeoff has been completely revised and the transformational component has been abandoned. Now there is only a single motor on the outboard tip, and the system spins prior to takeoff. So the control laws for the retracted state are nearly identical to the extended state, just with a different set of gain values.
5. To build upon Q3, the tethers do have a very high Cd value (circular cross section is about 1.2), but they are extremely thin (small frontal area), and because the system rotates, the average velocity is 40% of the wingtip (which makes a huge deal for the V^2 in the drag equation).
6. At the largest scale, it takes nearly 40 seconds to make a full revolution. This slow rotation really helps to reduce the overall power requirements (P=VD).
Great answers, thanks for the insight! Responses to the responses:
2. Definitely squares with what I remember of the problem. Seems like accommodating the most extreme operating conditions would compromise the design so strongly that it's better to just constrain the envelope it's intended to work inside. If you can reach continuous operation at "reasonable" latitudes during a large portion of the year, that could still be a strong value proposition.
3+5: Gotcha, so I just wasn't appreciating how small the tether cross-section really is.
4. Ah, makes sense - that sounds much cleaner. 4 flying wings trying to do a VTOL while attached to a weight seemed a little crazy.
1+ 6. Wow! So this is one big boi. Pretty cool. I would have pictured a much faster rate of revolution.
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.
The video on the linked website mentions that smaller scales are potentially useful but implies they are not capable of indefinite flight.
(It mentions a unit with a five pound payload flying for around four hours, comparing it to a conventional platform with a similar on-board battery which was able to remain aloft for around an hour.)
Comments
I'm the originator of the TURN concept, and owner of the company. I can answer any questions you guys have about the vehicle.
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?
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!
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?
1. The payload likes to stay around 5-10% of the total vehicle weight (otherwise the tether sags to steeply). I've generated sizing models from 5 pound payloads on up to 250 pound payloads for the Air Force SBIR research.
2. I have a look up table that plots energy capture for various latitudes vs day-of-year. It accounts for azimuth angle of the sun and duration of sunlight, where the integral of the area under the curve accounts for reduced collection at sunrise and sunset. To put it in perspective, operating on the worst winter day at 55 deg latitude is 15x harder than flying at the equator.
3. That produces triangular span loading (common to helicopters) which is not nearly as optimal as an elliptical span load distribution (common to gliders). Inboard sections just add weight and drag, without generating that much lift. The tether also has drag, but it's only 6% of the total system drag.
4. Agree. Takeoff has been completely revised and the transformational component has been abandoned. Now there is only a single motor on the outboard tip, and the system spins prior to takeoff. So the control laws for the retracted state are nearly identical to the extended state, just with a different set of gain values.
5. To build upon Q3, the tethers do have a very high Cd value (circular cross section is about 1.2), but they are extremely thin (small frontal area), and because the system rotates, the average velocity is 40% of the wingtip (which makes a huge deal for the V^2 in the drag equation).
6. At the largest scale, it takes nearly 40 seconds to make a full revolution. This slow rotation really helps to reduce the overall power requirements (P=VD).
Great answers, thanks for the insight! Responses to the responses:
2. Definitely squares with what I remember of the problem. Seems like accommodating the most extreme operating conditions would compromise the design so strongly that it's better to just constrain the envelope it's intended to work inside. If you can reach continuous operation at "reasonable" latitudes during a large portion of the year, that could still be a strong value proposition.
3+5: Gotcha, so I just wasn't appreciating how small the tether cross-section really is.
4. Ah, makes sense - that sounds much cleaner. 4 flying wings trying to do a VTOL while attached to a weight seemed a little crazy.
1+ 6. Wow! So this is one big boi. Pretty cool. I would have pictured a much faster rate of revolution.
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.
The video on the linked website mentions that smaller scales are potentially useful but implies they are not capable of indefinite flight.
(It mentions a unit with a five pound payload flying for around four hours, comparing it to a conventional platform with a similar on-board battery which was able to remain aloft for around an hour.)
Can you generate lift from the tether. Maybe using the magnus effect?
How does it take off?