VOLOCOPTER: As a follow up to its Multicopter 1, European start-up e-volo is back with a revised "volocopter" design that adds two more rotors, a serial hybrid drive and long-term plans for going to 100-percent battery power.
Image: Courtesy of e-volo
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Inventor and physicist Thomas Senkel created an Internet sensation with the October 2011 video of his maiden—and only—test flight of a spidery proof-of-concept 16-rotor helicopter dubbed Multicopter 1. Now the maker of the experimental personal aviation craft, the European start-up e-volo, is back with a revised "volocopter" design that adds two more rotors, a serial hybrid drive and long-term plans for going to 100 percent battery power.
The new design calls for 1.8-meter, 0.5-kilogram carbon-fiber blades, each paired with a motor. They are arrayed around a hub in two concentric circles over a boxy one- or two-person cockpit.
After awarding the volocopter concept a Lindbergh Prize for Innovation in April, Yolanka Wulff, executive director of The Charles A. and Anne Morrow Lindbergh Foundation, admitted the idea of the multi-blade chopper at first seems "nutty." Looking beyond the novel appearance, however, she says, e-volo's concept excels in safety, energy efficiency and simplicity, which were the bases of the prize.
All three attributes arrive thanks largely to evolo’s removal of classic helicopter elements. First, the energy-robbing high-mass main rotor, transmission, tail boom and tail rotor are gone. The enormous blades over a normal chopper's cabin create lift, but their mass creates a high degree of stress and wear on the craft. And the small tail rotor, perched vertically out on a boom behind the cabin, keeps the helicopter's body from spinning in the opposite direction as the main blades, but it also eats up about 30 percent of a helicopter's power.
The volocopter's multiple rotor blades individually would not create the torque that a single large rotor produces, and they offer redundancy for safety. Hypothetically, the volocopter could fly with a few as 12 functioning rotors, as long as those rotors were not all clustered together on one side, says Senkel, the aircraft's co-inventor and e-volo's lead construction engineer.
Without the iconic two-prop configuration, the craft would be lighter, making it more fuel efficient and reducing the physical complexity of delivering power to the top and rear blades from a single engine. Nor would the volocopter need an energy-hungry transmission. In fact, "there will be no mechanical connection between the gas engine and the blades," Senkel says. That means fewer points of energy loss and more redundancy for safety.
E-volo's design eliminates the dependence on a single source of power to the blades. As a serial-hybrid vehicle, the volocopter would have a gas-fueled engine, in this case an engine capable of generating 50- to 75 kilowatts, typical of ultralight aircraft. Rather than mechanically drive the rotors, the engine would generate power for electric motors as well as charge onboard lithium batteries. Should it fail, the batteries are expected to provide enough backup power so the craft could make a controlled landing.
Whereas helicopters navigate by changing the pitch of the main and tail rotor blades, the volocopter's maneuverability will depend on changing the speed of individual rotors. Although more complex, it is more precise in principle to control a craft using three to six redundant microcontrollers (in case one or more fails) interpreting instructions from a pilot using a game console–like joystick—instead of rudder pedals, a control stick and a throttle.
Wulff's first impression about the volocopter's design is not uncommon. E-volo's computer-animated promotional videos of a gleaming white, carbon-fiber and fiberglass craft beneath a thatch of blades recall the many-winged would-be flying machines of the late 19th century. This point is not lost on Senkel.
"I understand these skeptical opinions," he says. "The design concept looks like a blender. But we really are making a safe flying machine."
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27 Comments
Add CommentInteresting design. However, wile it may eliminate the "energy-robbing high-mass main rotor, transmission, tail boom and tail rotor", the 15 tail rotor sized 'main rotors' require what appears to be a significant structural assembly housing a very complex drive mechanism.
Reply | Report Abuse | Link to thisAlso, as I understand helicopters are steered by tilting the main rotor using a complex steering mechanism. It wasn't explained in the article whether similarly complex steering mechanisms will be used to tilt each of the 15 'main rotors' in this design...
It doesn't seem that this design offers any reduction in complexity or weight over traditional helicopter designs, although there are certainly some benefits to reducing the spinning mass of one or two large rotors...
Regarding steering, the e-volo web site states
Reply | Report Abuse | Link to thishttp://www.e-volo.com/information/how-does-the-volocopter-work
that steering is accomplished by modifying the rotation speed of each rotor. However, that would seem to require either a very complex transmission-drive mechanism or separate electric motors for each rotor.
Judging from the apparent lack of maneuverability demonstrated in the test flight, I'm not sure the test mule had any steering capability at all!
JTDWYER,
Reply | Report Abuse | Link to thisThe steering and forward propulsion are controlled by varying the (electrical) power to the individual rotors. Increasing the power to the rotors in the rear will tilt the tail up and move the craft forward. It also looks to have a rear thrust (vertically mounted) blade for forward motion. Direction can be controlled by increasing the power to the blades that are rotating in one direction while decreasing the power to the other blades. The net effect would be the same total lift (no change in altitude, but a change in the axial torque on the craft).
As for the reduction in weight of the structure, the non-rotating carbon fiber structure for the individual rotors would be cheaper and easier to fabricate than a modern large blade. This weight would be offset by the elimination of the heavy metal transmission, tail boom and drive shaft. The small blades on this craft would be a fixed pitch, one piece unit, similar to an ultralight prop or an old fashioned fixed pitch airplane prop.
The big difference here is that it is much easier, lighter and cheaper to control electrical power than mechanical power. Same reason modern railroad engines are "diesel-electric" drive instead of a direct diesel drive, like an automobile. Diesel power drives a generator that drives motors on the wheel axles. This allows the bogies to move (for turns) and for slow, easy starts, and an easy reverse with no transmission. Imagine trying to slip the clutch on a diesel locomotive to get the train moving. To be honest, here are (or were) a few direct drive locomotives built, usually for light "yard work".
JT,
Reply | Report Abuse | Link to thisAlso, on the steering, this model looks like it has vertical steering vanes (rudders) on the rear. Not sure if these are for steering (like an airboat steering) or just stability.
As I understand it, the main engine just generates electricity to power the electric motors in each rotor. Transmission of power would be through cables, not mechanically. The real complexity would be in the individual control of so many rotors.
Reply | Report Abuse | Link to thisAnother option for controlling the "forward motion" is changing the CG. This could be done by "tilting" the passenger pod relative to the rotor structure. The direction could be controlled by turning the pod beneath the rotor structure to drive the craft in a different direction.
Reply | Report Abuse | Link to thisThanks for pointing out the small rear 'thruster' prop in the illustration - it makes me wonder how much forward thrust could be produced by this system. The rear prop doesn't seem to have sufficient clearance to produce a lot of airflow - but I'm just guessing...
Reply | Report Abuse | Link to thisAssuming that each of the 18 'main rotors' is directly coupled to an electric motor, the broad distribution of weight and high center of mass might also make maneuverability problematic. I think electric motors are still pretty heavy...
Reply | Report Abuse | Link to thisNot necessarily. With the cabin below the rotor frame it is highly unlikely that the CG is all that high. In fact for maneuverability you probably don't want CG to be too low either. One horsepower = about .75 KW, so lets see...
Reply | Report Abuse | Link to this16 rotors at total of say 76 KW = 4 KW/rotor = under 5 hp/motor. Your average industrial 3-phase induction motor in this power category does weigh in at say 90-100lbs, but those are cast-iron frame motors that are in no way shape or form designed for this kind of application. Imagine aluminum or composite construction, I'd be very surprised if it isn't possible to build a similar motor that weighs 30 lbs, but I'm no electric motor guy. Certainly doesn't seem like a HUGE problem, just an engineering detail.
Overall the whole concept seems pretty interesting. Given that all you need are some electronics to allow the pilot to translate control movements into motor speed the whole thing sounds VASTLY simpler than helicopters. There are many advantages in all likelihood. Helicopters have very tricky aerodynamics for instance. Things like ring vortex, which would almost certainly not be a problem here.
Of course any new design brings with it the possibility of new issues too. This whole thing might work, and it might not. It will be interesting to see...
Not buyin' the weight or cost savings potential. Electric motors, even theoretical aluminum framed ones, are by their nature, heavy. A lot of motors powerful enough to run that many rotors is not going to be cheap. Plus you need enough battery power for a controlled landing in an emergency, and batteries are, of course, heavy. And expensive. I imagine the superstructure could be composed of lightweight materials, but the lighter the material, the more expensive it's going to be. I guess the controls wouldn't weigh all that much compared to conventional design, but their complexity is going to cost more.
Reply | Report Abuse | Link to thisPlease read the article first...
Reply | Report Abuse | Link to this"Rather than mechanically drive the rotors, the engine would generate power for electric motors as well as charge onboard lithium batteries. Should it fail, the batteries are expected to provide enough backup power so the craft could make a controlled landing."
"Whereas helicopters navigate by changing the pitch of the main and tail rotor blades, the volocopter's maneuverability will depend on changing the speed of individual rotors. Although more complex, it is more precise in principle to control a craft using three to six redundant microcontrollers (in case one or more fails) interpreting instructions from a pilot using a game console–like joystick—instead of rudder pedals, a control stick and a throttle."
Look at the tables in Wikipedia's power-to-weight ratio page:
Reply | Report Abuse | Link to thishttp://en.wikipedia.org/wiki/Power-to-weight_ratio
You'll see that electric motors on the order required are between 1 and 10 kW/kg, while fueled aircraft engines, obviously designed for greatest power-to-weight, only get 0.5 kW/kg.
Also note that take-off requires the greatest thrust of any part of flight, while that is the time the fuel weight is the greatest. Thus, fuel-efficiency has a multiplier effect.
The only plausible argument against weight savings of a series hybrid system depends on the extra weight of batteries. Electric motors are *not* by nature heavier than alternatives.
Tharter: Take a look at the prototype linked at the beginning of the article. The motors are each about the size of your fist, I doubt they weigh much more than 1 lb a piece. They look like brushless motors used for RC vehicles.
Reply | Report Abuse | Link to thisI tell ya this right now: I'd much rather clamber into this prototype than even go near an Osprey while it's running...
Reply | Report Abuse | Link to thisThis looks to me like a brilliant design for commuter type VTOL aircraft, but it is a long way from replacing the sheer mass needed for safely handling heavy lift requirements.
Reply | Report Abuse | Link to thisI can envision a day when these types of air craft will become safe enough for computers to operate and pilots will become a hands off passenger with only navigation and emergency landing decisions their only function. This would hasten the day when VTOL's really become a practical alternative to the automobile for commuting while leaving the roads a bit more freed up for trucks and buses.
Yes, thanks. I also missed the statement:
Reply | Report Abuse | Link to this"The craft will also need to weigh no more than 450 kilograms to remain in the ultralight category, which is likewise subject to fewer government aviation regulations, according to Senkel."
I wasn't thinking along these lines at all, based on the apparent two seat configuration shown in the illustration. As stated by http://en.wikipedia.org/wiki/Ultralight_aviation
"The United States FAA's definition of an ultralight is significantly different from that in most other countries and can lead to some confusion when discussing the topic. The governing regulation in the United States is FAR 103 Ultralight Vehicles, which specifies a powered "ultralight" as a single seat vehicle of less than 5 US gallons (19 L) fuel capacity, empty weight of less than 254 pounds (115 kg), a top speed of 55 knots (102 km/h or 64 mph), and a maximum stall speed not exceeding 24 knots (45 km/h or 27.6 mph). Restrictions include flying only during daylight hours and over unpopulated areas."
Personally, while the benefit of unpowered rotor-float down is often cited as an advantage (ignoring potential driveline or rotor damage), I'm not at all sure that I wouldn't rather be in a fixed wing ultralight in the event of a wind gust or downdraft...
Helicopters have variable pitched rotor blades. Having fixed blades also should reduce complexity and weight.
Reply | Report Abuse | Link to thisThis gives pause to the idea of placing eletric motors/brake in the wheels of cars.By removing the drive train you reduce the weight,and bring down the cost of all wheel drive while increacing mileage and control.Hope to see some on the road soon.As for the chopter look for it in toy stores soon.
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Reply | Report Abuse | Link to thisI'm into these kind of things and this isn't something I'd buy if I had money.
As far as eff it's not as good as they say. Larger dia rotors are a lot more eff than small ones.
They are right about the standard helicopter but a twin rotor gives you the eff eliminating the tail rotor.
To say electric drive is more eff and lower weight than gearing just shows how off they are. And I design, build EV's and drive them every day.
The most simple and eff is twin counter-rotating overhead rotors that just need to be angled where you want to go. The lower loading of the rotors is more eff than those many little ones with little gearing weight and almost no structure, unlike the massive arms of the design shown.
The twin rotor is inherently stable with few parts, no cyclic, just plain rotors has many fewer failure points. Add a ballastic parachute and it's hard to beat safety wise.
Have a look around RC model aircraft shops to see the advances in e.g. brushless electric motor technology and also lithium battery technology. This probably bodes well for designs along the lines described in the article.
Reply | Report Abuse | Link to thisI fly a radio-controlled 41-inch diameter 8-blade "octocopter" with 14-inch props. The frame is 3mm thich carbon fiber. The single most expensive peice of equipment on the craft is the flight control computer. Its a 2-inch square circuit board, packed with electronics (gyros, accellerometers, barometric pressure sensor, a couple microcontrollers, etc) and costs about $550 USD. The eight motors run about $100 USD each. This type of craft doesn't require high-torque. These are very low-torque, medium-speed motors.
Reply | Report Abuse | Link to thisTo all the people that express doubt about this kind of craft, let me tell you from first-hand experience: They work. They are lighter than traditional helis, extremely maneuverable, super simple, and almost as cheap.
All the complexity is in the electronics. I dont run any redundant electronics because weight is an issue on my small RC model. But on a craft capable of carrying people you could toss in 2 or 3 redundant electronics cores and never miss the few ounces they take up.
This certainly is an interesting concept and may come to be a successful design.
Reply | Report Abuse | Link to thisHas anyone here seen film of the early designs of Helicopters at which we laugh but a very successful aircraft emerged from those funny (almost)flying things.
An electronic control for varying to pitch and yaw angles is conceivable .
I may not be here to see it, but I think this concept may well become a viable aircraft. Not sure of whether it is a fixed wing or rotating wing A/C.
They've been in toy stores for a while now. Just check out Parrot AR Drone - the most expensive part is the smartphone needed to control it.
Reply | Report Abuse | Link to thisNot much of aeronautics, but a lot about electronics and electricity, but the explanation given by the article, I realize that this device would be handled like any modern printer where the electric motors, which work precisely on time by instructions given through an electronic card. I'm sure you are on track.
Reply | Report Abuse | Link to thisThis could achieve better efficiency, because it could blow a larger mass of air than a helicopter. Now, it will never fly as fast. Helicopter blades change the angle of attack, such that the blade can work forwards as well as backwards. It needs to do this, because the direction of force is quite different to the direction of motion. The direction of motion is horizontal, whereas the direction of force, where it must blow the air, is nearly vertical.
Reply | Report Abuse | Link to thisYou need variable pitched blades to fly horizontally. While you fly horizontally, you still have to blow the air mostly downwards.
Reply | Report Abuse | Link to thisYou can easily use a computer software (with some hardware) to calculate and control the tilts of the volocopter. The thing that I would be worried is debris floating in the air as well as the numerous environment factors like rain, high (or multidirectional) winds. With small blades (and light framework) it would be easily affected by the environment.
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