A 20kg hybrid drone that can fly at 50kmh for 4 hours | Hacker News Reader

A 20kg hybrid drone that can fly at 50kmh for 4 hours

quaternium.com

I don't understand anything in aerodynamics, so pardon my stupid question: planes are the most wide-spread flying machines because they are vastly more efficient than a rotary-wing aircraft due to the lift generated by wings. Why then a quadcopter is the default shape for smaller drones? Is it because small wings don't generate enough lift for the drone to make a difference? But they surely provide additional stability and won't hurt at a glance.

Not an aeronautic engineer, but to compare to a similar mass like a bird, having wings would make the hobby-sized drones quite a bit bigger. I assume there's also the ease of changing direction / altitude that comes from having the paired motors, controlling tiny planes would take tiny ailerons and flaps (which, like you say, may not scale down effectively).

Not an expert, but I'd guess quadcopters are much easier to pilot. You press a button and they go that way. Taking off and landing on wings is very difficult in comparison, requires more space, more facilities, more organization.

But they have tiny wings (arms) and if they were airfoil shaped then it would give some lift in straight and level flight. Then at start/landing/low speed, they would just do nothing.

Perhaps the air is so turbulent around the wings due to the propellers that wings just don't get any airflow to create lift, or would need to be much longer to be out of the way of the propellers, that it's not worth it?

Adding foldable wings would be a massive complexity and weight increase relative to the standard scheme which pretty much boils down to 4 motors + an IMU, with the rotors being the only moving parts.

The closest thing in the real world to the hybrid that you describe would probably be the tiltrotor, where the same engines which supply lift can turn 90 degrees to become forward thrusters on wings: https://en.wikipedia.org/wiki/Tiltrotor

I don’t mean foldable I just mean airfoil shaped cross sections that still fit within the normal “wingspan” of the multirotor.

Amazon have made at least two designs, one that flies “tilted” and uses the boundary ring as wings, another with more separate wings and forward propulsion

Version 1: https://techcrunch.com/2020/08/31/amazons-prime-air-drone-de...

Version 2: https://www.amazon.jobs/en/teams/prime-air

Actually it is not easier at all, the complexity is obscured by an onboard computer, which constantly helps to keep position, not to flip upside down and lose control completely. By applying differential thrust on different propellers it executes commands from operator to tilt and rotate. If the computer fails, operator, even with a direct control of the propellers, will not be able to maintain a stable flight.

From aerodynamic standpoint planes are much easier to pilot (all but military, same story with computers for better maneuverability) since they are designed to be inherently stable. So if all power is lost and you still have control of aerodynamic surfaces, there is not problem to land a plane after planning for some tens or even hundreds of kilometers (depends on initial altitude). This is obviously not the case with quadropters, loss of a single propeller leads to complete loss of control.

It leads to loss of six-dimensional control, though interestingly you can still maintain five-dimensional control (losing yaw) with only three or even just two props, see demonstration from ETH Zurich: https://www.youtube.com/watch?v=t369aSInq-E

Yes, indeed, though this seems to be an experimental drone. Most common commercially available DJI drones fall if single motor or propeller fails, though in future they may gain such functionality, which would be great for safety.

A nice example of a different approach is a variable angle of attack propellers which are driven by a single motor [1]. See after 0:52 and 7:13. In case battery is dead since all the propellers are synchronized they auto-rotate and stabilize the drone (near the earth the pilot activates the motor just to land softly, but likely similar effect can be reached by properly adjusting the angle of propellers in proper time, like in case of auto-rotation landing for helicopters).

[1] https://youtu.be/TnGhEInTXYc?t=52 (this video was posted below by @jcims)

Oh yes, it's for sure an experimental thing, and probably patented out the wazoo. My point is just that it's physically possible, as I don't think that is well known.

(Note also that doing this outside of a mocap arena would probably require a pretty high-quality IMU since you need very accurate yaw and you're constantly integrating your gyro to get it, with only the magnetometer and maybe the camera providing any kind of absolute reference.)

For the end user it’s easier and that’s what matters. You can just hover the drone, but you need to constantly look after an RC plane.

I know, but the computer just has to do local corrections, i.e., varying a little bit the input on the propellers to keep the drone stable. On the other hand, there is no local correction that enables you to hover a winged plane (it always has to move at a minimum speed in the air to generate lift), so you can only drive them automatically if the computer can globally control your trip, which is much more inconvenient for a human driver.

The aerodynamic stability is an interesting topic, but useless here. If you assume your computer is dead, you won't control neither a remote quadcopter nor a remote winged plane.

Planes with wings, by and large, do none of the following: hover, fly sideways, fly backward, fly straight upon or down, land or take off vertically.

I say by and large because there are exceptions, but they are complex, expensive, and compromised.

Well, yes, this is true I guess. However, this drone is advertised not for those things, but for long range predominantly. This is what I find a bit strange.

As for complex and expensive the first google result for "rc plane vtol" for me is this one [1] and it costs around $50. And then there are things like [2]...

[1] https://www.youtube.com/watch?v=xFISwEQbaz0 [2] https://www.youtube.com/watch?v=MDxHamYEQNU

I'm surprised. The first vtol plane you linked works so well I don't even understand why quadrocopters even exist at this point. So quadrocopters are just a modern fad and will disappear eventually.

It looked really unstable and the shape meant that even a smallest wind will screw it up.

It really depends on the application. For most industrial applications, they are really apples and oranges, with planes being unsuitable for many missions.

There is no shortage of fixed wing drones and commercial operators are not idiots. They buy what they need for their application.

Quadcopters are equivalent to helicopters in terms of performance. VTOL-planes fly as a plane, they do not have hovering endurance, barely a few minutes at the most, just for take off and landing. So they cannot perform missions that require hovering capabilities. A hybrid multicopter has the advantage of longer-endurance, traditionally exclusive of planes, while still keeping all the advantages in simplicity, ease of use and versatility of multicopters.

I think yet another factor (that I haven't seen mentioned already) is the payload platform orientation.

On a quadcopter you have a horizontal plane on which you can mount cameras or other sensors. Suppose you want to do some mapping, which is a pretty common scenario for these kind of industrial drones. With a quad, you can easily mount a camera which is mostly pointing in the same direction, regardless of air speed. With a gimbal you can direct it pretty freely.

With a VTOL aircraft like your [1], the ground angle would shift 90+° degrees depending on airspeed (nose-up hover vs nose-forward flight). It would require a pretty aggressive gimbal to just keep the camera pointed towards the ground, and some angles would be impossible to get in hover mode.

But for some industries like AG/large scale mapping, range is so important and you are basically always just interested in looking straight down and fly in simple pattern, that fixed vings are a thing: https://wingtra.com

>Well, yes, this is true I guess. However, this drone is advertised not for those things, but for long range predominantly.

It is implied. Costumers shopping for $20,000+ industrial drones already know the tradeoffs between fixed wing and quadcopters.

That's not true of fixed-wing drones. I've seen fixed-wing drones, made of really cheap parts, just act like helicopters. Hover, translate in arbitrary horizontal directions, VTOL, etc. I dunno if they were "flying backwards", but they did reverse flight direction. I think it's mostly just a matter of power-to-weigh ratio, which small aircraft have in spades.

I would expect the efficiency would be severely compromised by these maneuvers.

Sort of like fly 20 minutes or take off vertically for 30 seconds.

For efficiency, I think the best bet might be to take off from the top of a downhill slope gaining momentum and flying. To land, return facing up the slope killing momentum.

sort of like this: https://youtu.be/vscvM8ysAwM

That's the point. Even though some fix-wings or convertible drones are able to do certain maneuvers similar to multirotors, their endurance is extremely limited then. A hybrid copter like HYBRiX is able to hover for hours, but it would be even more efficient on translational flight. Here you can see to which degree we can control the drone when we push it to its limit: https://www.instagram.com/p/CHIZgQPgLtZ/

This means an outstanding resistance to wind, which fix-wings do not have.

> I've seen fixed-wing drones, made of really cheap parts, just act like helicopters.

> I think it's mostly just a matter of power-to-weigh ratio, which small aircraft have in spades.

Yeah! These small aircraft parts actually provide a respectable amount of thrust. The low weight of drones and model aircraft usually means they have massive thrust-to-weight ratio. T/W > 1 means the engine alone is able to propel it straight up. The larger the ratio, the more it acts like a rocket.

https://en.wikipedia.org/wiki/Thrust-to-weight_ratio

Quantum Systems makes drones that do this, and they get massively longer flight times than standard quadcopters. Their Vector drone can fly for 120 minutes, comparable to this fossil fuel powered quadcopter, on batteries alone:

https://www.quantum-systems.com/project/vector/

Just guessing (in addition to what others already mentioned - btw. I was wondering the same thing hehe):

maybe one big part involves the landing & takeoff:

for plane-like drones both are a lot more dangerous (therefore more difficult to be automated) and need a lot more space than quadcopters (and the likes). Saying this because I remember that, when I was a kid, my RC-plane (which took weeks and $$ to build) crashed 1.8 seconds after the first take-off attempt (damn, I got so angry & depressed...).

I guess that soon or later we'll see mixed designs that can take off & land like a quadcopter but which can increase their range/efficiency by "transforming" in mid-air into an airplane-like form? (something similar to https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey or maybe just a passive design that works by changing the fixed orientation of the whole drone from horizontal to almost vertical, or the opposite depending on the form of the drone?) In any case complexity would increase, therefore more specific demand for long-range capability is probably needed to go towards developing something in this area?

I remember how depressed I was when I crashed my RC plane on its maiden flight. Took a turn that was too sharp and didn't have the piloting skills to avert the subsequent nosedive.

I crashed my first Phantom drone as well since I didn't know you have to warm up the batteries in cold weather. Live and learn I guess :)

Hybrids already exist in a variety of forms and it’s not beyond hobbiests to crank them out: https://www.youtube.com/playlist?list=PLj3Bh6Krv9CXC8L8c3bPg...

Most commercial versions opt for simplicity and use a separate set of propellers for quad and forward flight configurations.

Thx - maybe there are some additional complexities related to the payload/cargo (center of gravity, can the payload be rotated yes/no and if not then how to keep it level without increasing too much the weight, etc...)?

The problem with that is that, in the end, you are carrying a multirotor on your plane. It is not so efficient as a fix-wing or plane and it does not perform like a multirotor, because it lacks hovering endurance. That convertible concept does make sense for some specific applications, but they are not the perfect-for-all solution either.

> Saying this because I remember that, when I was a kid, my RC-plane (which took weeks and $$ to build) crashed 1.8 seconds after the first take-off attempt

This made me wonder if a drone gyrocopter might be a useful compromise, since they're inherently very stable. They do seem to exist but are rare[0][1].

According to the few discussions I could find on the topic, gyros are also less efficient than helicopters, so I guess that doesn't really make it a useful compromise in the context of drone range[2].

[0] https://www.youtube.com/watch?v=TPbQlRm_lvI

[1] https://www.rc-airplane-world.com/rc-autogyros.html

[2] https://www.rotaryforum.com/threads/gyro-vs-helicopter-cruis...

Drones are usually copters so they can do vertical takeoffs and hover.

They're quadcopters rather than single mainrotor + tailrotor because it greatly simplifies the mechanics.

Single rotors need a cyclic mechanism to vary the blade pitch depending on where the blade is in the rotation and the control inputs. This is VERY complicated with a lot of moving parts that have to maintained and adjusted. (See https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Si... for one example)

Quads (and hexes, etc) can have full control authority via RPM only, using a simple injection molded constant pitch prop.

You have to admire the balancing effect of the torque on quad-rotors. Two CW and CCW rotors cancelling out the yaw (or introducing it, when required).

Quadcopters take simple hardware and control it elegantly with complex software. The beauty is that you only need to write the software once. All other tech requires more complicated hardware.

To underscore the relative simplicity, you can make a quadrotor with just 4 moving parts. Each electric motor has only one moving part, the rotor, and the prop is attached directly to it without even any gears.

Just noting cheaper quads often use geared props to compensate for their under-powered motors.

I used to fly gas RC helicopters and the joke was that RC helis are collections of small expensive parts desperately trying to get away from each other.

Well, full-ish control authority. They have to angle themselves in a certain direction in order to accelerate in that direction. Though perhaps that isn't so different from a helicopter.

whats the benefit of a single rotor then and why arent we seeing quad rotor configurations for combat or transport helicopters?

The main reason is that multirotors are a much more recent solution, and they started as small unmanned vehicles because the regulation is much simpler (the requirements for airworthiness certification for multirotors are not standardized yet). But I believe that we will see more and more applications for multirotors in the future. As a concept, they are safer than helicopters, with much simpler mechanics.

Single rotors are easier to fly, and more efficient. Also fewer things that can fail.

Basically with a quad if you lose any of the 4 engines you're going down.

This is much less of an issue with an unmanned aircraft.

With a single rotor if you lose any of them you're going down too :)

Controls got easy, batteries got good.

Computer-controlling a fixed-wing plane requires a lot of sensors, and a lot of math, and a lot of space, and forward airspeed.

Computer-controlling a quadcopter requires a lot of sensors, and a lot of math, and a lot of power.

Arduplane exists alongside arducopter, and it's easy enough to build both, but I can't fly a fixed-wing model in my backyard. I can fly a quadcopter just fine.

With wings, you have to be moving forward to stay in the air. With rotors, you can hover if the control circuitry is up to the task

> I don't understand anything in aerodynamics

Same here.

> Why then a quadcopter is the default shape for smaller drones?

Large fixed-wing planes are expensive. Piloting them requires jumping through many high-hanging and heavily regulated hoops. The most dangerous parts of the flight near the airports happen in well-known space, according to pre-defined paths known to all parties.

In many places of the airspace, pilots are guided by data from the ground. Optical from visual approach slope indicator (these weird light arrays around airports which are visible as 0-4 red circles depending on whether you’re too high or too low). Radio from beacons. Most importantly humans, the job title is “air traffic controller”.

For the scale of a conventional airplanes, accurate map data is available. GPS data+SRTM height map is accurate enough for most cases. Also, real-time weather data is pretty accurate at that scale.

None of the above applies to small drones. They’re cheap, most are piloted by amateurs and no licensing is required. They can take off and land whenever. No ground control is available. At their scale, no offline map data is available, and ground-induced wind turbulence is borderline unpredictable.

This might change in a few years.

We might get chips smart enough to reliably do right things based on the limited input data despite the unpredictable factors.

We might get sensors sensitive enough to generate much better data for these chips. E.g. if you have spatial data for 1x1x1km space around the drone, with 1mm spatial precision, and 20ms refresh rate consistent over the whole volume, today’s mobile chips will do mostly OK in good weather.

We might get good enough sensors to cover all airspace with them, and make robotic equivalent of air traffic controllers, a software that detects future collisions and tells the drones to do something about it. Or broadcast current wind conditions at 1m^3 resolution.

Least likely but still, we might get good enough actuators & power sources to combine these two. Birds do OK, many of them can hover, glide, and arbitrarily combine hovering with gliding. When you can stop flying and hover, or land almost everywhere, collision avoidance becomes way simpler. That’s one reason how birds and modern-day small drones are functional.

The wings help for covering longer distances efficiently but make hovering and vertical takeoff tricky, tail-sitters combine positive features from both types of aircraft https://en.wikipedia.org/wiki/Tail-sitter

I think there will be a large market for plane-like drones with very malleable wings for exactly the reason you state.

The cost (in terms of both price and structural integrity) of gratuitously dynamic wings (think turning the whole wing 45 degrees to horizontal, bending the wing to 90 degrees at it's half way point) are much smaller for small aircraft.

Such gratuitously dynamic wings give more degrees of freedom for automated piloting software to work with when it comes to optimizing near vertical take-off and landing when compared to a fixed wing aircraft, while retaining fixed wing efficiency advantages during elevated flight.

Why the quad set up over the classic single rotor seen in helicopters?

A hybrid drone like HYBRiX has power redundancy. If the engine stops for some reason, it still has some minutes of endurance in electric-only mode, for an emergency landing. With an unmanned helicopter, if the engine fails, the crash is mostly warranted, even with the autorotation function.

Besides, the mechanics are simpler and therefore more reliable. And the propellers are smaller than a helicopter rotor, which is safer. Multirotors are also much simpler to operate than a helicopter. Most industrial customers do not want to operate unmanned helicopters because of their complexity.

Mechanical complexity. A collective pitch helicopter requires a bunch of expensive moving parts and linkages to run the swash plate. The most traditional design requires 3 relatively powerful linear actuators of some sort as well as a spherical bearing at the swash plate, then 2 linkages to the rotor head and 2 more bearings on the rotor head itself. A quadcopter requires brushless motors (usually with 2-3 typical sealed ball bearings each) and props. Less moving parts, broadly generalizing, means fewer ways to fail.

TL;DR: It's because they can hover.

They have a stable and basically stationary anywhere in 3-space mode (until the juice runs out). Human and automated control is much simpler as a result.

Small wings are less efficient particularly when things get really small but at this weight there are a lot of fixed wing UAVs. This is also not terribly small at 1.6m long.

Fix wings are amazing for some applications. The problem with them starts when you want to carry heavier payloads. Taking-off and landing gets more and more complicated as they scale-up, while you only need 10 sq. meters to take-off HYBRiX drone. In the end, the different drone types are suitable for different purposes.

Yeah most obviously this is useful if you need to land and then take off again somewhere where you don't have infrastructure to relaunch a fixed wing UAV. For example collecting something. Although that presents its own challenges in terms of how non-experts safely handle attaching the payload to the UAV.

I think its a super interesting piece of kit so I hope you find success with it!

To add to all the other responses, multirotors are the least power efficient setup by far. And fixed wing the most, and regular helicopter somewhere in the middle.

Several hours of flight time is trivial with a battery powered fixed wing model airplane.

> Why then a quadcopter is the default shape for smaller drones?

Because somebody, somewhere published the first opensource autopilot code, and that first code was for the quadcopter.

a stupid nit to pick about an obvious off-the-cuff statement, but the whole drone hobby is older than quadcopters, as are open-source 'drone' solutions with route planning/loitering/all the stuff you'd expect a drone to do.

But before quadcopters we used large-wingspan EPO foam / balsa / plastic planes.

It's still common place.

Yes, but I say that the quadcopter boom was almost singlehandedly due to appearance of the single firmware which was "copypasteable," and suitable for garage factories.

Fixed wing aircraft must have air moving along the wings in order for them to generate lift. In other words, the aircraft must always be moving through the air. If its speed drops below some minimum value, it will stall and drop out of the sky like a rock. This is also why they need runways in order to take off. They need to accelerate to a minimum speed in order to even get airborne.

https://en.wikipedia.org/wiki/V_speeds

Rotary wing aircraft use their engines to constantly move the wings through the air instead of moving the aircraft itself. So the wings are always generating lift and the aircraft is free to move in much more flexible patterns. A very useful maneuver is hovering in place: the aircraft is able to simply hold its position in the air. Since only the wings need to move to generate lift, the aircraft itself does not need to accelerate in order to take off and therefore a long runway is not necessary.

Civilian drones usually have rotary wings because this allows people to do useful things like having the drone stay in one place in order to film or photograph something. A fixed wing aircraft would have to establish a loitering pattern around an area in order to do the same thing. In other words, rotary wings can just hover in place while a fixed wing would have to fly around in circles.

Fixed wing aircraft are more fuel efficient. Rotary wing aircraft must constantly spend fuel in order to keep their wings spinning. They lose lift otherwise. A fixed wing aircraft would probably be able to glide great distances and even land safely even if it lost all engines in the middle of its flight.

There are also unpowered rotating wings.

Maybe it is possible to combine a "normal" quadrirotor (for vertical takeoff and hovering) with a rotating wing aircraft, the autogyro:

https://en.wikipedia.org/wiki/Autogyro

to save a lot of energy when traveling horizontally.

There is actually this thing here that is already a sort of cross-breed between a helicopter and an autogyro:

https://airialrobotics.com/

https://airialrobotics.com/gt20-gyrotrak/

That's really cool! I've read about the use of autorotation but only in the case of emergencies. I had no idea there were entire aircraft based around the concept.

Since the rotary wings are unpowered, the autogyro loses many of the properties that make the helicopter so valuable. It requires forward motion in order to move air through the unpowered rotary wings and maintain lift. Looks like they have propellers providing forward thrust just like fixed wing aircraft. The article also states that they're not capable of vertical take off and landing. They need a runway to accelerate just like fixed wing aircraft.

Yep, but you can still power (when needed) the rotating wing and un-power it when it is not needed (forward travel), that is the "breakthrough" (if it works) of the mentioned GT20:

>Helicopter mode for hovering and slow forward flight any time

>Gyrocopter mode for fixed wing fast flight and long distance

See also gyrocopters:

https://www.youtube.com/watch?v=a882megKhVM

Now, in scale for drones, it may also be possible to have an always unpowered rotor (rotating wing) AND 4 (or 5/6[1]) more conventional small rotors for vertical take off/landing and hovering.

[1] just thinking aloud, but it would probably be simpler to have four horizontal small rotors, like a "common" drone and an additional one or two vertical to provide trust forward like a traditional airplane or autogyro.

Having involved in UAV development projects for agriculture monitoring and have used both rotary-wing and fixed-wing UAVs, I'm now firmly believe that neither of them is fit for purpose in aerial monitoring.

The rotary-wing UAV is a power hungry gussler while fixed-wing UAV is not that versatile (e.g. for hovering, etc). The best compromise will be Gyrocopter or Autogyro since it is both energy efficient and flexible. It can also easily fly at sustain high speed wind of more than 50 knots.

[1]https://en.m.wikipedia.org/wiki/Autogyro

Yeah I've wondered for quite a while why autogyro drones aren't popular. They should be efficient and safe - since one problem with autogyros was the noise they made due to large rotor size, drone sized ones shouldn't have that problem.

Planes work similarly well at small and big scales. They are more efficient than quadcopters even at small scale.

Quadcopters are just much safer and easier to control. Compare "fall down at random without input" vs "stop without input".

As for why quadcopters aren't used at big scale - moment of inertia scales with cube of the propeller radius. And to control a quadcopter you're constantly speeding up and down each propeller. That's a huge loss of energy when your propellers are big enough.

So instead at big scales we use very complicated mechanically designs like helicopter. It uses a propeller that rotates at constant speed (so moment of inertia doesn't matter), and instead changes the angle of attack to control the aircraft.

BTW moment of inertia is also why nobody in their right mind would build huge mech robots like in sci-fi. Wheeled vehicles move forward without fighting inertia - wheels spin at constant speed and you just add the energy lost to friction. Mechs constantly swing their huge legs back and forth fighting the whole inertia twice with each step. Fine for toys, not fine for big vehicles.

So it can carry 10kg with the 32" propellers basically about 120 miles (call 50km/h for 4 ours so 200 kilometers) and you can refuel it quickly. That is also about $1M weighs in $100 bills. Only about $200K in 20's :-)

So this could presumably deliver goods to remote places where it might be difficult, or perhaps unsafe, to drive to. Seems like there is a market for that.

We already have Bitcoin to help criminals move money.

When I buy my illegal narcotics, I never use something as volatile and traceable as Bitcoin.

What do you use

I barter for my drugs.

All joking aside, though, I've actually never met a "drug dealer" that accepted anything but cash.

"I can’t afford it, I would never buy drugs I get drugs free" MLWTTKK

Most of the darknet shops accept bitcoin just fine

I believe they are discussing large transactions. Maybe Monero is a better alternative.

There is a reason El Chapo had 2 Billion in cash stashed away in his mansions. Cash is still king.

Converting millions/billions into cash from bitcoin is WAY too easy to see. And the time it takes to get the billions out would give you a big problems with liquidity and volatility of assets.

It is the hard goods, that are so difficult to move though ...

So it does with quadrotors what Zipline does with wingborne drones (although Zipline is faster and purely electric, so fewer systems to maintain and to go wrong).

Site is down, here is google cache: https://webcache.googleusercontent.com/search?q=cache:KiJcBe...

Seems to be in a similar product category as Anduril’s Ghost sUAS - https://www.anduril.com/ghost

Less capacity, but longer flight time. Seems similarly marketed towards industrial/military use tho.

Interesting.

It is surprising to me (but probably it is some aeronautics specification/need) that its 2-stroke engine uses 95 octane+4% oil mix, it is years that using synthetic oil you can use 2% or even 1% oil.

I think it’s something like the engine of a chainsaw, or similar “gardening engine”, that can use up to 4/5% of oil

Sure, but the whole point of reducing the oil percentage in two stroke engines has been (since like 40 years) to reduce the formation of carbon in the combustion chamber and - particularly - to have cleaner spark plugs (which imply better ignition) besides better combustion.

Less oil in the mix (as long as lubricating is sufficient) is better.

The traditional 4-5% is for mineral oils.

Synthetic (totally or partially) oils can usually go on 2% (or 50:1) and in some cases as low as 1% (or 100:1).

Modern chainsaws and similar are already at 2%, see (examples):

https://www.stihlusa.com/information/how-to-guides/mixing-oi...

https://www.husqvarna.com/au/forest/when-working/usage/how-t...

https://www.amsoil.com/p/outboard-100-1-pre-mix-synthetic-2-...

Ignition in an engine for airplanes/drones/etc. is - obviously - much more important than in a common 2 stroke engine (chainsaw or similar), a "common" 2-stroke engine used in ultralights is the Rotax 582 (an earlier model was the 532) check its "limitations":

https://en.wikipedia.org/wiki/Rotax_582

The 582 has twin sparks (two spark plugs per cylinder) and runs on 50:1 mix:

https://www.flyrotax.com/produkte/detail/rotax-582-ul.html

Might be for safety reasons, an engine seize in a flying drone would be catastrophic and dangerous compared to merely inconvenient as in most small engine applications.

OTOH, piston scoring from burning oil will probably increase the chance of a lock up over time.

Except the onboard combustion engine is just to generate electricity, no? An engine sieze means you just have to land quickly.

That is true for HYBRiX, but there are other hybrid multirotors, which do not have a design well-balanced enough to being able to stay aloft on just batteries (batteries to lift a 25kg MTOW drone are heavy, so the drone needs to be very light, while still robust, to work properly.. it is tricky ;)

For reference, the Stihl chainsaw I just purchased had a 50:1 gasoline to oil mix. That is 2%, of course there are probably 25:1 or 20:1 engines out there as well.

Wild guess: The engine is an off-the-shelf part and that just happened to be the specs for whatever fit the size/weight/power/cost requirements.

Could be duty cycle or cost of synthetic, either way 2-strokes are extremely dirty emission wise due to unburnt fuel in the exhaust.

https://www.pegasusaero.ca/

This company designed hybrid engines for retrofitting onto drones

Nice.

Their generators are amazing, 1-1.5 KW generator in less than 3 kg, or 3 KW in less than 4 kg, really packed power.

(BTW they use 2.5% or 40:1 mix)

It's because of the duty cycle of the engine, we put it at a constant rate of 12000 RPM for hours. It is not the standard setting for that engine.

Be nice to get a price on this, I hate 'ask for quote'.

This could serve as an example of the insane energy density that fossil fuels pack.

They do, but one of its selling points is its case "fits in the trunk of a standard car." that suggests it's a pretty big drone and I default to imagining copters that fit in a hand, size in picture[2] more than I understand what 20kg means in drone size. No wonder it can fly a long way if it's massive.

For energy density comparison, check the Wikipedia list of energy density of various things[1], starts with Antimatter highest, then nuclear fuels, Hydrogen[3] at the top of the chemical fuels with ~140 MegaJoules per Kilogram, then all the hydrocarbon fossil fuels hang around 45-55 MJ/Kg, body fat comes in around 38, coal around 30, wood around 18, glucose around 15, Lithium-air battery at 9, household waste at 8, and the highlight of our modern electronics lifestyle Lithium-ion battery at 0.3-0.9, barely ahead of flywheel at 0.3-0.5.

[1] https://en.wikipedia.org/wiki/Energy_density#Tables_of_energ...

[2] https://www.armytimes.com/resizer/-965_SXAhPeD1LTlB-xZuQwJvJ...

[3] the catch with Hydrogen is a kilogram of it is 11 cubic meters, and a lot of that energy advantage has to go into compressing or cooling it to make it usefully dense, and maintaining the infrastructure to store and transport that safely.

That actually makes me hopeful. If we can get a lithium air battery working the a 10x jump in density is possible.

That’d be a game changer!

Bit rich to call it "low pollution" in their list of benefits. Depends what you put in it and what you compare it to I suppose, but per kilo transported if using fossil fuels, I doubt it compares well to an electric (assuming electric means renewable, which obviously also varies).

Of course it does not compare to electric multirotors in that aspect, but its performance is much more advanced. We aim to replace combustion manned helicopters in first response applications, among others. HYBRiX can provide similar operational flight time with 100 times less fuel consumption per hour. Electric multirotors, with up to 30 minutes of flight time, are not suitable for searching missions for example.

One of the interesting things about this UAV is that it’s using Ardupilot which is quite advanced and flexible and one of the only autopilots (there are like two) that use a copy left license. This means we might see more hybrid drones supported by Ardupilot.

It's probably the single biggest strike against it, honestly.

Why is that?

Hi all! thanks for sharing the news! At Quaternium we are very excited to see that our project is raising so much interest! There are already many accurate comments on this thread. But just to give you some context. Quaternium was the first company in the world to demonstrate a hybrid power system for a drone, with a flight over 3 hours back in 2015. Right now, our latest record is over 10 hours of hovering flight with HYBRiX multirotor (with an experimental setting with more fuel and no payload). A key element of this news is that the drone is <25 kg MTOW, (bigger aircrafts have obviously longer flight times). The fuel engine acts as a range-extender, it is a series hybrid, like the BMW i3. And we develop the power system, in collaboration with Löweheiser company (https://loweheiser.com/) using a 2-stroke Zenoah engine that we adapt to the drone needs. Our product uses the engine on a very different duty-cycle, comparing to the standard application, so we do a lot of work on it and got a much better performance compared to other competitors. Multirotors are the most popular drones for several reasons, that some users have already mentioned. They are much more versatile because they can hover, do not need launching platforms and are quite easy to operate. They are also mechanically simpler than helicopters, reducing failure points. Our goal with HYBRiX is to being able to replace manned helicopters for aerial imaging operations, not to replace planes or fix-wings, which are more efficient for the applications that do not require hovering. As for convertible VTOLS / fix-wings, they are cool but not so versatile, because their hovering endurance is very limited, only useful for VTOL take-off / launch. That makes it possible to take-off from smaller areas than planes, but do not have a performance comparable to a multirotor. Hope this clarifies some doubts mentioned on the thread.

Anyone know if it's a series or parallel hybrid? Looks like it uses electric motors out on the props like most drones which would imply series. If so interested to know the generator setup, usually thats heavy / inefficient vs mechanical drive from engine, but quad copter needs independent speed control for each prop to steer I thought.

There’s a few collective pitch quadrotors that use a single gas drivetrain to spin the props and servos for pitch control.

Example: Stingray 500 - https://youtu.be/TnGhEInTXYc?t=36

Agree with your observations. This is a big quad, 30” (fixed pitch) props and not a ton of payload...probably serial.

What advantage would a collective pitch quad have over a helicopter?

Dunno. I imagine it's use-case dependent, quads can go faster (rc quads can hit 200mph) and are more nimble (presumably due to lower moment of inertia).

I have zero clue how they would scale up though. All I know is that I'm not flying in a quad and helicopters seem to haul heavy shit pretty well.

It sounds like you have seen little of the speed and agility RC helicos can exhibit, for example: https://www.youtube.com/watch?v=PptMrBFAO-A

Yes, it is a series hybrid, the engine acts as a range-extender. The mechanics of the aircraft are much simpler this way and therefore more reliable. We are not sure about the efficiency, though. There are no helicopters under 25kg MTOW with our flight time right now.

I wouldn't be surprised if the cartels were not funding research and development of such machines. I am not saying this particular one, but having an autonomous drone flying over long distance and capable of some more serious cargo seems like a dream come true (for example 100 mile radius should be enough to cross the border). If they could pair it with autonomous submarines then this opens the world of possibilities when it comes to moving the product across the world.

Also see the Pipistrel Nuuva V300 UAV

https://www.pipistrel-aircraft.com/aircraft/nuuva-v300/

The Nuuva V300 long-range, large-capacity, autonomous UAV can take off and land vertically with battery power, without requiring a runway, and can carry loads up to 300kg (around 660 lb) for more than 300km (around 186 miles)

Any successful flying platform will start with a mission that includes payload capacity, range (distance), operating costs, and weather resilience.

The difference between a hobbyist and a professional is that the hobbyist builds a platform first and looks for a mission/customer after spending R&D dollars. The professional starts with a mission/customer before proceeding to R&D.

Question for an aeronautical engineer: Can you take the engine nacelle of an airplane and rotate it vertically?

So instead of being horizontal, can it be vertical, where the exhaust points down? Or does the engine need the compression and air velocity from the forward motion of the plane to compress and ignite the oxygen?

A jet engine that needs forward motion to compress air is called a "ram jet" which is only used in a few applications even though it is so simple.

Airplanes normally use either "turbo jets" or "turbo fans". These use the exhaust to spin a turbine at the back of the engine which in turn spins a compressor at the front (and also a larger "fan" in the case of a turbo fan). So the airplane can be completely stopped at the end of the runway and rev up the engine to full power to start the takeoff.

A normal plane only needs its engines to have enough thrust that is a fraction of the craft's weight to overcome drag enough to keep it flying at cruise speed. So pointing it down would not lift the plane off the ground. But there have been designs with powerful enough jet engines:

https://en.wikipedia.org/wiki/Ryan_X-13_Vertijet

An alternative is to rotate just the engine instead of the whole plane, and even more practical is to simply divert the exhaust of a horizontal engine downwards when needed:

https://en.wikipedia.org/wiki/Hawker_Siddeley_Harrier

Nice explanation for the layman. Thanks.

The X-13 would make for an excellent VTOL drone. As would the Harrier. And I assume the F-35B would be a good candidate for one as well.

Their page reminds me a lot of the feature drone sales pages you see over at banggood.com or aliexpress, ebay, etc. But I don't find it that impressive overall. If they want actual range, put wings on it. You'll see that all the delivery drones are doing such a thing.

Would it make sense as to build such a design where wings are integrated but Tilted at an upward angle, so when the drone is angled downward to improve forward thrust, the lift is generated by the wings and the motors are used mostly for propulsion, dramatically improving efficiency and getting the best of both worlds?

That's what Amazon did with theirs, correct? It must be difficult to control or have some other drawback, otherwise it feels like such an obvious win.

Maybe stability in windy conditions? or additional mobility issues at low speed.

There are a number of factors. Size, for one. Wings are big. They are also heavy. And during a vertical take off and landing, they aren't wings. They're sails.

That does make a lot of sense. I wonder, would a better design include making the arms attaching to the rotors have the same aerodynamic profile of a wing, made of carbon fibre to reduce weight. For propulsion the rotors can rotate do different angles depending on desired speed?

I've been thinking about the possibility of applying some computing power to recognizing or predicting thermals to use for greatly extending flight range. I'm sure this problem could be solved with today's technology, and it might provide some very large scale benefits.

There are already self thermalling RC gliders. But thermals are slow things, and everything these days has to be fast, right? Thermals would only allow for greater loitering. IF the thermal stays where you want to loiter. They move a lot.

That's impressive and really futuristic. I don't see the price tag, though.

Would it make sense to use hydrogen fuel to further decrease the weight?

AFAIK hydrogen is hard to store, so your storage tank might be pretty heavy. It also has lower energy density than gasoline/kerosine.

Cost-wise, no

There have certainly been cost effective hydrogen powered long distance drones. One potential benefit is that you can run fuel cells, which are silent and quite a bit more efficient than a two-stroke driving a generator. OTOH, getting similar energy density is challenging, as others have said. Although you can come quite close with liquid hydrogen, if you can live with a fuel that's not storable for long times at small quantities in the field.

Since hydrogen is very low density you'd pay through the nose in terms of an increase in drag and a decrease of max wind tolerance.

Doosan is currently marketing a hydrogen fuel cell powered UAS.

http://www.doosanmobility.com/en/

Equivalent hydrogen multirotors at this stage do not have the payload capacity of a hybrid fuel-electric drone. They might be a great solution in the future, but the technology is not there yet.

why not just use an airplane

There are probably additional correct answers (all depending on the use case/flight plan) but the takeoff/landing profile for a drone vs. an airplane is one answer to your question.

i'm sure someone out there as stuck ardupilot inside an R/C V-22 Osprey. Seems like that would be the best of both... or worst of both hah

Some people do use airplanes. Bush planes have been used for a long time to deliver things to remote places... ok, well, not oil rigs, but almost anywhere else. Some of them can take off and land in less than 100 feet. Risk of course is that a human is in it. A drone is less liability and less maintenance costs. Planes will still be used for heavier objects and human transport for some time.

What about using methanol? It has been cleared for use powering laptops. Cleaner burning and quieter than 2-stroke petrol?

https://www.zdnet.com/article/methanol-powered-laptops-clear...

Methanol has half the energy density of gasoline.

Do the advantages of clean and quiet burning, and perhaps a lighter and simpler engine, outweigh that?

Now if only the webpage could fly at 10 qps for 1 hour ...

Sorry about that! :(

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