Hybrid Drones Could Have Massively Extended Flight Times

Multirotor drones truly took off with the availability of lithium polymer batteries, brushless motors, and cheap IMUs. Their performance continues to improve, but their flight time remains relatively short due to the limits of battery technology. [Nicolai Valenti] aims to solve the problem by developing a hybrid generator for drones.

The basic concept consists of a small gasoline engine, connected to a brushless motor employed as a generator. The electricity generated is used to run the main flight motors of the multirotor drone. The high energy density of gasoline helps to offset the added weight of the generator set, and [Nicolai] is aiming to reach a goal of two hours of flight time.

There are many engineering problems to overcome. Engine starting, vibration and rectification are all significant challenges, but [Nicolai] is tackling them and has already commenced flight testing. Experiments are ongoing with 500 W, 1,000 W, and 2,000 W designs, and work is ongoing to optimise the engine and electronics package.

It’s a project that holds the potential to massively expand the range of operation for medium to large multirotors, and should unlock certain capabilities that have thus far been limited by short battery runtimes. Gasoline powered drones aren’t a new idea, but we’ve seen precious little in the hybrid space. We look forward to seeiing how this technology develops. Video after the break.

129 thoughts on “Hybrid Drones Could Have Massively Extended Flight Times

    1. You do know how bad lithium batteries are for the environment right? Not to mention how do you think most batteries are charges, heres a hint it’s not renewable energy all your doing is shifting the point of co2 generation back from the power plant to the drone itself

      1. Somewhere in China all the nature is stripped away to make room for a breathtakingly massive strip mine to obtain the materials that go into that battery. No doubt this is all done using fossil-fuel burning heavy equipment. We don’t want to know what is in the slag pool.

        Then it is taken, probably by a diesel burning train to a coastal city and loaded onto a ship.

        That ship switches it’s fuel over to the dirtiest, nastiest and cheapest fuel available as soon as it hits international waters and continues burning that for the majority of the trip.

        Once it reaches your shore it still has another train ride and a truck ride ahead of it, not to mention a stop at an assembly plant where it is turned into a battery by the operation of more energy using machinery.

        Finally, you plug it into a charger where electricity produced mostly by burning coal is used partially to charge the battery but also partially just dissipated as waste heat in your home. The waste heat ends up getting sent outside by your air-conditioner which uses even more coal-electricity.

        Finally, you take your battery and drive or ride to the park, either way most likely in a vehicle that burns more fossil fuels. There you put it in your toy, fly it around a bit and brag to your friends about how environmentally conscious you are for using an electric motor instead of a gas engine.

        1. Everyone knows that but it’s popular today to drive a car that takes you halfway to work where you expect to find a charging pole.

          And when you get to work a charging station costs you a fortune to enable you to get halfway home.

          1. That is complete nonsense, janostman.

            The average US driver drives 41 miles a day. The average commuting distance is less than that.

            The practical range of mass-market electrical vehicles is much more than that. Even the Chevy Volt, which as a range on gasoline + battery should be able to manage the average commute on battery alone.

            “Wow. Can I use this to shut up my environmentalist friends?”

            Only if you want to look like a reactionary fool.

        2. You left out the part where all the employees of the manufacturing plant drive their gas and diesel burning vehicles to and from work five days a week and maintain at least half their entire energy gobbling housholds just so they can go to work each day. Then their is the rest of their lives, the lives of all the city, county, state and national employees that support their existance for the sole benefit of all the working stiffs who make the batteries, package, ship, sell and ect. ad nauseam. Enjoy.

        3. “electricity produced mostly by burning coal”

          We dont do that in the UK any more.
          We burn wood pellets in converted coal power stations.
          The wood comes from places like the USA where it’s sent to port on diesel trains, loaded on to ships and I quote::

          “ship switches it’s fuel over to the dirtiest, nastiest and cheapest fuel available as soon as it hits international waters and continues burning that for the majority of the trip”

          It then arrives at a UK port and is back on the train again to teh ex-coal fired power station.

          Thus we are able to claim (with a straight face…) that we are burning “renewable fuel”

      2. The charging isn’t really the issue. I’ve done the math on CO2 from charging a Tesla Model S, even assuming it’s [i]exclusively[/i] run off coal-fired plants, and it’s still equivalent to driving a car that gets something like 300 MPG.

        (I don’t like coal-fired plants, but they’re better than burning gas straight in the car. You can put pretty big carbon-capture equipment on a static plant that you can’t carry around in a car/drone/whatever.)

        1. As much as 75% of the electricity produced by the coal/fossil fuel plant never makes it from there to where the rubber meets the road. Transmission line loss is huge, battery charger loss is significant, battery storage and release to cars electric motor losses are significant, and drive line loss is significant. Suddenly your 300% looks more like 25%. Ouch.

      3. Really?

        Electricity is much more fungible than fossil fuels. An electric motor can be powered from any source of electricity, and those sources are, increasingly, renewable.

        Fossil fuel power plants are point emitters, which means their emissions are easier to manage, and investments in energy efficiency are amortized across a much higher duty cycle.

        As for how bad lithium batteries are for the environment, this really needs to be looked at from a systems perspective. Are renewables + lithium ion batteries (and other forms of energy storage used to correct for supply/demand mismatches) worse for the environment than the alternative? Both involve disruption of landscapes for materials extraction. That’s not good, but climate change disrupts the entire landscape.

        None of which is to say that I think hybrid drones are necessarily a bad idea.

        1. Nope, they’re a great idea. Creates more industry and business which creates more jobs and holds the real promise of someday establishing a highway in the air infrastructure for every day people. They’re going to be huge fun and unbelievably convenient. Can’t wait.

    2. Seriously?

      Most of us are visiting this site using vastly over-powered computers that are supplied electricity from mostly coal-burning power plants. And you want to complain about someone playing with an engine so small that it fit’s in the palm of one’s hand? Besides being tiny, how many hours of operation does a toy like this typically see?

      Finding the smallest, least consequential sources of pollution and raising a huge fuss about them is NOT the way to help our planet. All it accomplishes is to reassure climate change deniers that they are correct and their opposition if full of shit.

      1. You got that right. Lot of the fuss, hype and over-reaction just makes Climate Change look silly. The Earth’s atmosphere is about 260 billion cubic miles, and it took 300 years to double the CO2, which still isn’t a whole lot, 0.04%. I don’t know much about carbon foot printing this tiny gas engine, but you got to be kidding, if you think it’s going to make a lot of difference. Besides, we still have a little over 10 years, before we reach the point of no return, the tipping point, where we all are going to burn in hell, for our carbon sins.

        Think we should quit trying to meddle with nature, it’s work these things much longer than we walked on our hind legs, everything is going to be just fine. Plants do incredibly well with 5 times the CO2 available. The better they grow, the more CO2 they suck out of the sky. And as an added bonus, provide food for every living thing on the planet.

        This is our first inter-glacial, so how does anyone really know what’s normal? A consensus of climatologist, who believe? That’s faith and religion, not science.

  1. I wonder if using the gas engine directly driving a central prop to provide a baseline level of lift would be more efficient – less weight for a smaller generator and fewer losses in the generation-to-motors power pathway. A small battery would buffer short-term power fluctuations to avoid the need for rapid accel/decel of the gas engine

    1. A larger, more blade-like central prop would also be more efficient at producing lift than the number of typically small props needed to produce the equivalent lift. IIRC some university did a study and made such a craft a couple of years ago. It was pure electric, not gas, but the concept was proven. It was (??) 15% more efficient than a same sized quad.

    2. Or you could use one engine and no electricity except for the imu. Each prop sync at the same speed and a collective pitch in the 4 corners. Not even sure using gas for a generator is more efficient than direct drive.

    3. Undoubtedly yes. Turning liquid fuel into combustion into mechanical energy into a magnetic field into an electric bus into chemical storage is dramatically less efficient than just using the mechanical energy to perform useful work…

    4. I’ve never seen a good argument for hybrids over just traditional single prop helicopter with a gas engine.

      The math just doesn’t add up. I could understand if traditional helicopter engines were designed to deal with massive peak loads at the detriment of continuous low power efficiency (like a car). Then a hybrid might make sense… but they’re not. It’s not like it’s stopped at a red light getting <1MPG, then accelerating at 5MPG, then on the highway at 30MPH.

      Hovering is like 50% maximum power.

      There's no significant difference in gas engine efficiency between hovering and max climb. Making it a hybrid system just appears to hurt the power/weight ratio and efficiency. Even if all the electronics are 100% efficient, the gas engine's power output needs to roughly match the craft's average power consumption. So even if the electric motors can pump out 10X more power to the props, it now has the additional weight of that secondary power system and it can only last as long as there is battery capacity.

      A large single prop is significantly more efficient than multirotor. Egg-beater style dual prop is the only exception.

    1. Probably weight advantages to this setup, and gas engines are slower to respond so can end up being less stable in flight when they don’t react fast enough to small and/or quick throttle adjustments.

      1. A electronically modulated CVT gearbox for each rotor.
        The gasoline is kept at a even rpm range in the band where it produces the most rotational energy compared to fuel consumption.
        Like some Toyota hybrids do when running off the gasoline engine instead of batteries.

  2. Does anybody wonder why the gas generator, and not a greener alternative? Think this project really illustrates the energy problem of Climate Change. There really is nothing with the same density for the weight, and the price, to replace fossil fuels. The alternate replacements are going to take up a lot more space, and deliver less energy, for a much higher price. A gas powered generator for a drone, and making good enough sense to work out the details, doesn’t really speak well, for converting the planet to non-carbon fuels.

          1. You guys are missing andrej’s point. It’s a lot more efficient to glide than it is to hover. When I first saw the title I thought it would be about a quadcopter that can take off and then fly around like a plane.

          2. Jack, Fonz, lets not get lost in technical myopia, the point is absolutely valid – using small propellers to provide all lift is about the most inefficient way to fly as is possible.

            Now there can be valid reasons why the method is a necessary evil, so I’m not criticizing this project at all. But while pointing out that all airfoils ultimately work the same way is valid, suggesting through omission and/or deliberately failing to acknowledge that there aren’t massive differences in efficiency is not.

          3. Yes. Assuming you already have free energy pushing you horizontally you can convert that into energy which pushes you vertically.

            Free horizontal energy. I wonder if that’s how unicorns fly?

          4. @Doc Oct – ” It’s a lot more efficient to glide than it is to hover.”

            In other words, you can achieve altitude for free by just first achieving a higher altitude. Um.. yah. I don’t see any problem with that logic. I think you should go sell it to the airline industry. Think of the fuel savings!

            Also, one might want to hover in place. You can’t glide in place, if you did you would be hovering. Gliding is the trading of downward velocity for forward momentum. What if you don’t WANT to go forward?

          5. @Palm

            You’re well named, because you’re making me facepalm over how badly you understand aircraft.

            Rotorcraft are insanely inefficient. It’s one of their biggest characteristics. I mean, the reason people ever dreamed of and built tiltrotors like the Osprey (which killed a bunch of people through development and early deployment) was that in fixed-wing mode the range is massively better. It flies more efficiently!

    1. I didnt wonder. I did however have a little chuckle to myself inside*. battery technology has came a long way but liquid fuels are still king in energy density for mobile applications.

      *I am pro-environment, but im also realistic, sometimes you have to use the best tool for the job, and for anyone crying about it, invent something better, and change the world.

          1. Paradigm thinking that’s caused desertification maybe along with a bunch of scattered neighborhoods that don’t take advantage of volume and materials resources when planning surface area production?

          2. Because there are still cheaper sources of hydrocarbons buried in the ground. By ‘cheaper’ I mean cost in money, it’s vastly more expensive long term, as we’re discovering.

          3. Mostly because one must construct infrastructure for algae farming. Oil industry is also a problem – they will fight with any and all competitors. There might also be legal problems. For example a few years back polish farmer started making algae diesel fuel for his car. When tax office found out, they forced him to pay huge penalty for making fuel. Turns out that in Poland one must open customs office on his farm, hire a customs officer and pay all taxes, which makes fuel more expensive than buying normal fuel. It’s the same for biodiesel made from soybeans or any other plant…

          4. With due respect to the infrastructure arguments drones use a minuscule amount of fuel. I would love to see a home-scale hydrogen cracker project specific to hybrid drones. I bet a single largish solar panel could crack enough hydrogen in a day to power your drone for several hours.

            I’d also love to see, as mentioned above, a hybrid blade/winged drone project because if the drone is moving at sufficient speed there is no reason to use propellers for lift if your goal is air time.

          5. The problem with hydrogen is storage as it’ll need to be pressurized/liquidity to be of any use. Having some carbon in it makes it less volatile and more convenient to use.
            Probably more practical to convert organic garbage to methane or other short chain molecules. That and grow worms for livestock feed as land fills are becoming a problem.

          6. @Moryc do you have any documentation on the farmer’s process? All I found on a quick search for “algae diesel fuel” was bacteria that can grow in water contaminated diesel fuel and “diesel fuel from algae” mostly scientists are working on it.

        1. Large or small, they will run on bio fuel.
          However, the vapor pressure of biodiesel is much higher than diesel, so it needs to be preheated so it can be ignited. (Most don’t know this) I ran my turbines on Methane, but they needed diesel to start, due to the low BTU value of the methane.

    2. What I get a chuckle from is the people that think fossil fuels are somehow never going to be replaced.

      Yes they have high energy density and have been in use for centuries now in some form or fashion. But because of that you have entire communities and cultures built around fossil fuels and people do not like change to a fault, especially when change might mean your multibillion dollar lifestyle may be at risk. therefore there is a huge and quite angry resistance to getting away from fossil fuels by those in that industry.

      Think about it… We didn’t always have little computers with a connection to the entire world in our pockets… That type of technology is a mere blip on the timescale compared to fossil fuels – but we went from entire room sized computers that could barely add two numbers together to the world in your pocket in the blink of an eye, really…

      Even with this huge resistance to changing our economy to run on things other than fossil fuels, things are improving every day, solar cells are getting more and more efficient, as are wind and tide turbines and all the other alternative combustibles – batteries are getting better too. It’s not going to happen over night, it isn’t going to be a single silver bullet but i can assure you it will change regardless. But oil will still be needed and used in some form or fashion, and eventually it will be replaced by things completely synthetic.

      So resistance is futile – what isn’t helping is all the cynicism…

      1. It’s not cynicism to be worried about the continuing detrimental impact of burning fossil fuels. I agree with you that given enough time, with an environment roughly as it is now, we’d be able to find our energy in myriad other places and store it in numerous novel ways. The environment is changing though, time is marching on. It may well be that our current civilisations will collapse before solving the technical problems, it may well be that we tip the environment over the edge before we can disseminate the technologies, especially if that dissemination must rely on private companies.

        1. The problem is and will ultimately always be overcrowding. There are too many people, we take up space and burn through resources quickly because we can’t live without creature comforts. It’s not a carbon emission problem at all. It’s a too many fleshy bag of bones problem.

          1. We’ve always been changing the climate to suit us though, my home area in England was covered in trees before humans arrived, but it was essentially barren by the bronze age. There certainly weren’t too many humans at that time.

            I don’t see ‘overpopulation’ being solved by technology unless we invent really implausibly cheap and fast space travel. Populations in the developed world seem to stabilise, presumably around the level of affordability, maybe we should make it excessively expensive to raise a child? Maybe we should do the one child limit thing like China did. If you lower birthrates you’re going to have to kill off some old people to balance your economy… it’s all very complicated.

    3. still waiting on a gas turbine based generator design. stands to be significantly more compact and pose less of a vibration issue. there are a lot of small jet engine designs out there but nothing specifically optimized for power generation.

      1. Joe Mama.. The actual turbine generator set is called “APU” for Auxiliary Power Unit.
        Used by the military worldwide. I worked with Dr. Marius Paul in the 1980s, and his company supplied simple cycle turbines for APU duty. My turbines were a bit larger, running gen sets producing upwards of 50 MW and selling the energy to So Cal Edison. Yore kilowatts will vary.

        1. APU’s are very cool. I worked at an off the grid research center. We had a trailer and what I considered to be big (30KW) diesel genset to power up our trailer. You use a *lot* of AC in a trailer in the desert, and even more so when the trailer is full of electronics. Cooling is a huge piece of the power budget. The folks a ways down from us, we had no idea what they were doing and they had no idea what we were doing but they had one of the of the jet turbine gensets. It was about the same size or perhaps a bit smaller than ours, and chatting with one of the guys in that group about it, about 10X more power. They had a much larger spread out there than we did. The other interesting thing about that project was the ritual of after opening the trailer up for the morning, going through it with a big stick and banging it around to turf up any rattlesnakes that decided to take up residence over night. Never caught one in our trailer but other folks out there had.

          1. Some of the APU design work I witnessed, used very small commercial turbos, modified with a combustion can. Lots of extras, scaled down to fit in the tight confines of a military device.
            Someone clever would grab a small motorcycle turbo and add the can. Bingo, free power.

        2. if its used as the primary power plant for a drone then its no longer auxiliary is it?

          im well aware of apus, but i am not aware of any small drone-sized units that can provide 100% of the power needed for the brushless motors on a drone and still get off the ground. id love to see one.

    4. The best-of-both-world solution would be to use renewable energy stored and transported as liquid fuel.

      That involves taking CO2 from the air and cramming it into water making it effectively carbon-neutral.

      Hilariously, if you want to make it carbon-negative you just pour the resulting gasoline/diesel into the ground “for the environment”.

      1. What do you mean by ‘cramming’ the CO2 into water? If you mix CO2 with water you get a solution of CO2 in water, which is not a fuel and will just lose CO2 over time. If you put a lot of energy in (more energy than you get out of turning the fuel into CO2 and water in the first place) you might be able to create something that has less oxygen, but where do you get that energy from?

    5. Greener today would be settling for a shorter run-time; but the stated goal of this project is a longer run time. Greener might also mean having a longer run time with a lighter payload and/or larger size, but that might not meet his requirements either.

      Solve one problem at a time. Get the hybrid solution flying, then look for alternatives to fossil fuels. Perhaps there’s a CNG solution that doesn’t emit nitrates – greener, but still emits CO2.

      And if you have the magic bullet that solves energy density without emitting greenhouse gases, there are billions of dollars waiting for you.

    6. There is NO BATTERY IN EXISTENCE that has the energy density of gasoline. Also, no government has control of the primary driver of climate, which is the sun. And you people had to start saying “Climate Change” when the world stopped warming, around 18 years ago. Nothing you do, and no amount of totalitarianism can prevent the world from getting colder, or warmer, depending on where we are in the cycles. Besides, who are YOU to say what the climate should be?

      To [Nicolai Valenti]: very nice copter build, and I salute your clever gasoline/electric solution.

  3. So just wondering, wouldn’t it be much better to use a gasoline engine with two big propellors turning counter to each other in the center, to do the heavy lifting. And 4 brushless motors in the corners to do the balancing and tilting part?

  4. Nuclear power & renewables –> electricity, hydrogen, & synthetic hydrocarbons for aircraft and remote power and transportation; just like we use now refined from oil wells.
    Recycle nuclear waste until it is depleted of energy and danger.
    Encourage or mandate non-recycling of synthetic hydrocarbon plastics as well as other carbon based garbage and after one use sequester that synthetic from the atmosphere carbon in large encapsulated blocks. Make the consumer economy lock the carbon back up, it could even be buried like coal and left for a post apocalypse societal reboot hopefully with some fossil artefacts encouraging to wean off of this synth-coal ASAP to avoid catastrophe again.

    1. No, don’t do that.
      No doubt other pollutants besides just CO2 will be created in the process of making that plastic.
      Reuse it.

      If you want to remove carbon from the air and sequester it then grow fields of fast-growing plants and bury those out in the desert.

  5. I wonder how much less efficient is this hybrid multi-copter approach compared to a same-weight gas helicopter.

    Electric helicopters are incredibly more efficient than same-weight (not same-size) electric drones to begin with. Both in theory and in my personal experience.
    And adding ‘gas vs hybrid’ into the mix certainly shifts the efficiency difference even more towards helis being more efficient.

    1. ive always wondered this myself. id like to see more tilt rotor designs with a good aerodynamic cruise profile but still be a vtol. there has got to be a better way than brute force hovering with poor aerodynamic optimization.

      1. I thought the whole push for quads and their ilk was to eliminate complicated, fussy linkages and swashplates. It’s what happens when an EE, vs an ME, designs a helicopter.

        Still the question of a more efficient flying vehicle, that can do VTOL, is a good and longstanding one. A hybrid of plane and quad/hex/many-copter might be something like DARPA’s Lightningstrike. The end result might resemble a plane or a helicopter, depending of how much flight time is to be spent in forward flight vs hovering.

        1. I agree with MacAttack. I have a design for a variable speed system for a gas powered quad in my head, but the fly in the ointment so to speak are the mechanical pieces. As Mac stated the beauty of the quad was getting rid of all of that. Still my idea used a mechanical variable speed transmission to drive the quad blades and a little pancake generator to power the electronics (keep a charge on the battery). This to me seems to be the most efficient approach. I suspect the mechanics are more efficient than a bigger generator and more motors. I suspect my system would also be much lighter. The downside is that if the motor runs out of gas or stalls, the gig us up. With a generator powered electric version, and some on board lion cells, you would still have power to bring it back down in a controller fashion should the motor stall or run out of gas.

        2. Completely agree. I have a helicopter and checking/repairing the whole mechanical system after a crash is a nightmare.

          Varying pitch multicopter brings worst from both world!
          1. Inability to glide and inefficiency of having multiple rotors from multicopters.
          2. Mechanical complexity from helicopters.

          1. For a concept try this. Imagine 2 permanent magnets, shaped as discs, placed concentric with the main rotor shaft, but above and below where the rotor blade connects the the shaft. A small lever arm is connected to the blade and can alter it’s AoA. You can guess the rest, a coil on the lever arm can be energized so as to force the coil to move up or down in the magnetic field. You now have an electromagnetic swash plate. Details of force and response time needed are … details. :)

            Or reverse it, put a magnet on the lever arm and coils around the main shaft. No need for brushes now.

          2. But Mac, AIUI…
            The helicopter main rotor can have the forward moving blade take a smaller “bite” (less angle of attack) while the rear moving blade can take a bigger “bite” thereby pushing the helicopter in the forward direction. So, a swashplate is not that simple, it has to adjust the AOA between blades separately.

      1. Re: the EM swashplate – I’m not sure why I couldn’t reply above (no Reply button) but yes I understand how a swashplate varies blade pitch cyclically. In my explanation above think of the coil like a voice coil in a speaker. The magnetic forces can vary over a cycle, assuming the rotation rate doesn’t exceed the frequency response of the coil system. A “minor” detail to be attended to. :)

  6. What about a co-axial helicopter blades powered by gas for doing the heavy lifting, surrounded by 4 brushless motors for the movement and motion? This would be best out of two worlds right?

    1. Skip the extra motors and controllers. Just go the way rc copters, co-ax and conventional, have always gone, direct servo control to a swashplate. Much more efficient.

  7. I had been testing this idea using an old nitro powered RC plane motor and brushless AC motor as the generator and also used the engine for vertical lift as a two fer. It was glorious while it flew

  8. Regarding that idea of sequestering plastics and other fossil fuel supported products?
    We’ve tried it. We called it “the city dump” or “sanitary landfill”
    The stories of preserved hot dogs and other stuff, are legendary for it.

  9. http://www.totem.energy/en/features/
    It uses a modified Fiat engine, the same used on Fiat 500 and Panda, coupled a generator, and it’s modified to run on methane or biogas.
    You chan buy in Italy and Holland a Fiat Panda running on CNG. Unfortunately the CNG (compressed natural gas) uses heavy tanks unsuitable for a drone. They are viable on cars.

    You could build cars running on renewables, the big problem is that if all cars are converted on using methane or biogas the renewable supply will be innsufficient.

  10. I like to see something like this in cars. They way we use combustion engine on cars is far from optimal but electric motors have way better efficiency. Optimizing small engine and store electricity on capacitors we get smaller carbon footprint while convenience of long ranges.

  11. Instead of a IC-engine, generator and fuel, could it carry lots of batteries and jettison them like drop-tanks as they deplete? I think this would effectively double the energy density of the additional batteries.

  12. Project is a bit light on info. What engine, motor and electrics? I was considering doing this a while ago but just bought a generator instead. Mine is much heavier and I’m not sure it is more efficient.

  13. Nobody ever brings up that power bus is under-engineered for cost even on a DJI unit.. You’re probably getting 1/3 the flight time with your DJI Mavic 2 as you would same battery and features but better power bus..

    Most Shenzhen grade drones barely even have power firmware and bus..

  14. Best Lithium-metal batteries have energy density of 1,8MJ/kg. Dry cow dung has 15,5MJ/kg. Biodesel – 42,2MJ/kg, diesel – 45,6MJ/kg, petrol – 46,4MJ/kg. And battery technology won’t get much better in terms of energy density than dry cow dung. So no, world won’t switch to electric vehicles, because they are too heavy, take too long to charge and ain’t environmentally-friendly.

    When fossil fuels will end, we will just make them. It’s very simple:
    1. Grow some algae using sunlight, water and CO2 from atmosphere and some free biomass.
    2. Remove most of the water, put the wet algae in pressure cooker and cook under high pressure and temperature.
    3. Get from it crude oil and some asphalt-like remains that can be used to feed more algae.
    4. Refine your oil.
    5. Profit.

  15. I wonder if anyone has made a drone design based on a hanglider? The launch would be on a cliff as per usual but then hot air currents (thermals) would be used to provide lift and controls would be in place to guide the craft to and from and whilst in the currents. Flights would be first to attain sufficient altitude using natural thermals and then to glide to the next thermals site and so on. Only using lipo power for propulsion when absolutely necessary. Flights should be essentially perpetual….

  16. Want max load and long flight time? Gas helicopter, single prop or dual prop intermesh.

    Want slightly better maneuverability at the expense of the above? Multicopter.

    Want significantly better maneuverability at the expense of flight time? Super light weight electric with high “C” LiPos that get drained in a couple minutes.

    Want an electric multicopter with worse maneuverability, range, flight time, load capacity and speed than a gas helicopter?

    Hybrid.

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