Manned Electric Helicopter With 7 Tail Rotors

One of the best things to come from the growing drone industry is the development of compact and powerful brushless motors. We’ve seen several multi-rotors capable of carrying a human, but electric helicopters are rare. [OskarRDA] decided to experiment with this, converting his single-seat ultralight helicopter to electric power and giving it seven tail rotors in the process. Flight footage after the break.

The helicopter in question started life as a Mosquito Air, a bare-bones kit helicopter originally powered by a two-stroke engine. The engine and gearbox were replaced with an EMRAX 228 109 kW brushless motor. Initially, he used the conventional drive-shaft powered tail rotor but wanted to experiment with multiple smaller rotors powered by separate motors, which has several advantages. He only really needed four of the 5008 or 5010 size motors with 18″ props to get comparable thrust, but he added more for redundancy. The new setup was also lighter, even with its independent batteries, at 7.5 kg compared to the 8.1 kg of the old tail rotor assembly.

One of the major advantages of a conventional helicopter over a multirotor is the ability to autorotate safely to the ground if the engine fails. A coupled tail rotor bleeds some energy from the main rotor while autorotating, but since the tail rotor has independent power in this case, it allows all the energy to be used by the main rotor, theoretically decreasing decent speed by 120 feet per second. [OskarRDA] did some engine failure and autorotation test flights, and the results were positive. He likes his new tail rotors enough that he doesn’t plan on going back to a single large rotor.

Power for the main motor is provided by a 7.8 kWh, 40 kg LiPo battery pack mounted beneath the seat. Theoretically, this would allow flight times of up to 27 minutes, but [OskarRDA] has kept most of his flights to 10 minutes or less. He didn’t add any electronic gyro for stabilization, but he did add some electronic coupling between the main motor and tail motors, to reduce the torque correction required by the pilot. Even so, it is clear from the flight footage that [OskarRDA] is a skilled helicopter pilot.

While being able to lift a human is cool, this would also make an excellent unmanned platform for a heavy lift applications. Besides manned multi-rotors, we’ve also seen electric powered paragliders, and of course [Peter Sripol]’s scratch built electric planes.

Thanks [smerrett79] for the tip!

56 thoughts on “Manned Electric Helicopter With 7 Tail Rotors

    1. Given the speeds and heights a helicopter can achieve such padded suit would only be only for the feel-good effect but wouldn’t really help you much in case of a catastrophic problem.

      Helo is not a motorcycle where the padding is not to protect you from the impact itself (you will still break bones if you hit hard enough!) but from scraping along the tarmac which could literally rip flesh off the bones. Which is not really a risk with a helicopter, even something like this.

      He is wearing a harness keeping him in the seat, so even in the case of a crash on landing he will be protected by the body of the machine. And if the crash is hard enough to crush the the helicopter or throw the pilot off, then bike leathers will only make more mess to pick up in the body bag …

      1. the CE 2 protectors inside my motorcycle suit are for impact protection and i wouldn’t drive without them.They would certainly help preventing or reducing injury on the specific bodyparts when falling from a certain hight (where “certain” is TBD ;)

          1. I’d wager you’ve never rode a motorcycle in your life or taken a nasty spill on one. If you had you’d understand the utility in wearing such gear as well as wearing a helmet.

        1. CE armour is designed for ‘fall from height’ protection: to protect against ground impact after a highside flips you into the air. It is not intended for impact protection against you sliding into an object at speed (let along just hitting one head-on, or vice versa). Its design and certification revolves around closed-course racing where obstacles are removed or energy-absorbing, not typical road riding conditions where you encounter other vehicles, walls and bollards, pedestrians, etc. The closest thing to dedicated road-racing protection is the most recent generation of wide-coverage body worn airbags (the ones that enclose the entire chest cavity and brace the neck and spine). Even those are unlikely to protect you from a helicopter crash, even if you could figure out a reliable method to trigger them just above ground level!

      2. Not to argue with you, because you could be fully right about the helicopter. But I want to clarify a thing that people don’t realise when they talk about a motorcycle crash.

        A motorcycle (well, at least a streetbike) weighs around 180 kilograms (almost 400 lb). If you go down with the motorcyle, it can literally THROW you into the ground with it’s weight. So, for instance, I weigh 62 kilogram (136 lb). But the impact will be as if I would have weighed 240 kg (500+ lb).

        High speeds have their risk as well. Because there is a chance that the motorbike will throw you 3 meter (10 feet) UP in the air, a high sider. The impact will be comparable to falling out of a second-floor window.

        In general, the lower your speed, the more chance the bike will smash you into the ground. Because at higher speeds, you are more likely to be thrown off the bike before it has the chance to smash you into the ground. Sadly I have experience with this, crashing at 20 km/h (12 mph), and smashing the elbow joint (ulnar head fracture)

        This is why there is impact protection in a motorbike’s suit. I also wear a special back protector at all times. Mainly because if I get thrown off the bike, I might be lucky enough to manouver myself such that I can land on my back (protector).

      1. There’s another factor: because it’s an ultralight heli, there is also a certain amount of risk that if you unstrap and get out too quickly, it could be light enough to lift off the ground as you stand up. Which I’m guessing would be bad.

    1. I think the motor is probably a per hour rating, but I’m not sure. I haven’t looked at motors in a long time.

      The battery is undoubtedly a 7.8kwh rating. Math it out and you probably get the 20 min flight time. The motor isn’t running full power all the time.

      1. No, the motor is for sure no “per hour” rating. As “kW/h” is nonsense. It uses (draws) up to 109kW, so on full power it drains a 8kWh battery quite fast. It can fly for 8/109 h on full power

    2. The current XE version of the Mosquito helicopter is powered by a 48kW 2-stroke, which means it’s generally using less power than that. I have my doubts that the airframe/mast/rotors could even handle 109kW.

      1. Would be nice if they could get their hands on one or more of those Rotor X modified Wankle engines being developed by Liquid Pistion. They are working with the U.S. Military on a rotary engine that has 3 combustion chambers, is still a 4 cycle and has only 2 moving pieces aside from the lube system and bearings. The only way you can get one as far as I know is to give the Co. $30k and the promise not to reverse engineer the engine for outside development or production.

  1. Tail rotors are not required for autorotation, since the torque needed to drive the rotor is being generated in the rotor itself, no counter torque is needed. this is why autogyro’s don’t have tail rotors.

    that being said, a tail vertical and horizontal surface is highly recommended, and this helicopter doesn’t seem to have that. if the props can provide thrust in both directions, which they can’t if he’s using conventional multirotor hardware, it’ll make yaw changes like Derick Zoolander though.

  2. There is definitely something to be said for having the main rotor blades higher off the ground than the tallest of people, or those people could lose something rather important. Maybe they are but it looks decidedly dodgy right at end wherr he appears to be about to stand up with the rotors still spinning down!

  3. I would shit my pants if I was that guy flying this contraption. I used to fly soaring planes and I have a feeling he does not quite have it under control. At 2:22 he nearly touched the ground with his tail. Before he seemed not to control the rotation around Z axis.

    1. Looks to be properly in control to me.
      Certainly that looks aggressive compared to typical taxi flying, but that isn’t what he’s doing.
      Keep in mind he’ll be adjusting his technique/skills, as the pedal inputs no longer rob/aid disc power.

    2. I’d say those “rotating while flying in a straight line” tricks are a pretty good indicator of his skill, as is the “stopping on a dime” move (no under- or over-shoot). The tail was about four feet off the ground.

  4. Damn, one should think of other people more when doing stuff like this. Why not stick with the simple single tail rotor, instead of 7 fiddly little ones, just think of the poor guy that’s going to have to try to chisel that in the engraving on your tombstone. ;-)

    1. First of all: if one of those 7 fiddly motors break, he still has 6 left. Quite a nice thing to have. :)

      But I think that managing the torque of each individual motors, could give the helicopter a bunch of extra stability and manouvrability.

      And also, normally there’s a drive shaft going from the main engine to the back, with a clutch assembly or such. But such a shaft is rotating mass, and in itself can negatively affect the stability again. Imagine spinning up the revs on that shaft: the helicopter will experience a torque in the opposite direction and would want to go on it’s side.

        1. NOTAR is garbage. There’s not many pilots you’ll find wanting to fly one since they feel mushy and unresponsive in comparison to a standard tail rotor design. Definitely safer to people on the ground, though.

  5. “One of the major advantages of a conventional helicopter over a multirotor is the ability to autorotate safely to the ground if the engine fails.”

    ….or at least that’s the idea! Luckily both electric helis and multi-rotors can add a fair amount of redundancies with a small weight penalty. What a heli has over a multi-rotor is better efficiency, but the rotor system is way more complicated.

    On a side tangent, I find it irritating that, in the US, an ultralight’s weight limit is 254lb dry, which with the 5 gallon limit means roughly 285lb wet. However, if your ultralight is electric, you’re limited to 254lb including batteries. An extra 31lbs allowance for batteries would make a huge difference in the capabilities of electric ultralights.

    1. The even bigger advantage of a heli is the variable collective pitch, which is what makes autorotation possible. Sink rate on fixed-pitch multirotors is not comfortable. (But it’s not the sink rate that kills you – it’s the excessive acceleration at the end.)

      1. Sure, a heli can allow for autorotation, but a multi-copter can have enough redundancies so that total power loss becomes unlikely. Of course, you can do something similar to a helicopter (multiple motors and power sources)

    1. Feather? Do you think these are variable pitch? They’re not. And “freewheeling” electrically-powered props doesn’t work so well due to motor cogging – you get drag, drag, drag, and then when the airspeed through them reaches a threshold they start spinning and you get a sudden reduction of drag. Not conducive to remaining in control.

      Also, electric motors are more efficient at lower power, since heating loss = I^2 * R. That is, loss increases as the square of the motor current. So for example, if each motor takes 10 A and has 1 ohm copper resistance, that would be 100 W of loss per motor, or 700 W total. Put 70 A through one motor, and you get 4900 W of loss. (This is assuming the same motor voltage and speed, because a suitably larger prop is used.) This has to be considered along with the weight of the system, where seven motors and props (and the associated structure) is probably greater than one larger motor and prop. It’s all that engineering stuff. But it also could have been an economic concern, where there is a sudden jump in price when you go above the largest motors in the “model” market.

    1. because 1 is less than 7. But as stated in the article, it’s for redundancy purposes.

      He’s not the only one doing multiple tail rotors, however. Bell Helicopters showed off an electric 4 tail rotor demonstrator last yet:

      When they use the word “revolutionary” in their press release, I assume they’re referring to the fact that the tail rotors revolve.

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