A prototype hybrid quadcopter can fly several times farther than conventional battery-powered ones.
A new hybrid gas-electric aircraft could make drone delivery more practical. Developed by a startup called Top Flight Technologies, the six-rotor drone can fly for more than two-and-a-half hours—or 160 kilometers—carrying a payload weighing nine kilograms.
The aircraft’s range is many times that of any quadcopter on the market—the most popular type of drone for its maneuverability. Almost all quadcopters run on batteries, and can fly for only about 40 minutes between charges with a payload weighing just a couple of kilograms. The new drone can also fly more than twice as far as a radio-controlled, gasoline-powered helicopter of similar size.
Top Flight’s technology is distinct from what’s being developed by Google. The Google aircraft takes off vertically but then reorients itself and flies like an airplane. But the company isn’t saying much about how far the prototype drones can travel or how much they can carry. And demonstrations of the aircraft in Australia involved delivering relatively lightweight packages, such as dog treats, vaccines, and a first-aid kit.
The efficiency of Top Flight’s drone is made possible by using batteries to supplement the gasoline engine. Power can come from the batteries, from a gasoline generator, or from both at once. And because the gasoline engine doesn’t have to supply all of the power, it’s possible to use a much smaller and more efficient one. Unlike a hybrid car, however, Top Flight’s drone doesn’t capture energy from braking.
Top Flight isn’t the first to try hybrid technology with drones. The U.S. Army and Air Force, together with an Oregon-based company called Northwest UAV, have experimented with hybrid airplanes. A representative of Northwest UAV says the company is also working on a hybrid system for use with multi-rotor craft such as quadcopters.
Top Flight was founded and is advised by researchers from Draper Laboratories and MIT. It has selected a relatively simple type of hybrid engine, known as a series hybrid, in which there is no mechanical connection between the gasoline engine and the rotors. The engine serves only as a generator that charges the battery or supplies electricity to the electric motors. Long Phan, cofounder and CEO of Top Flight, says “future vehicles will fly well over three hours—we already have the new engine to do it.” The company is also developing object-avoidance technology and other safety features—which likely will be required for drones, at least in the United States (see “FAA’s Caution Not the Only Obstacle for Drone Delivery”). Phan says the company hopes to start selling its hybrid drones by the end of the year.
Full article here Hybrid power for drones
Comments
JB,
I am not arguing against the general application of hybrid technology, A Prius happliy sits on the ground and requires no power to just sit there.
Basically it requires power to accelerate and maintain speed across an extremely wide range, under these circumstances a relatively constant speed (optimized) engine and an electric hybrid system can happily provide the variable power needed more efficiently than a conventional mecahincal fuel only system.
That is pretty much the opposite of the requirements for a multicopter.
It requires a relatively constant speed / power with only slight change for every condition where it isn't turned off sitting on the ground.
Under those circumstances, the same nearly constant speed engine that is optimal for a ground hybrid system may also be nearly optimal for an airborne (multicopter) mechanical only system and the entire hybrid electric contrivance is entirely superfluous conversion loss and extra weight and volume.
A hybrid multicopter is by definition non-optimal.
The mechanical losses and power conversion and transmission inefficiencies in a fuel engine equipped variable pitch quadcopter would always be much less than those in an equivalent "hybrid" multicopter.
I honestly can't think of a case where a hybrid multicopter could provide any "advantage" over a variable pitch fuel multicopter, even with the most exotic brushless generator and ultra efficient and high power density batteries you could dream up.
Simply the straight fuel copter could always out last it.
Oh, wait, I just thought up the exception SNAP generator!
Probably still don't need hybrid though, just the SNAP generator itself.
And of course since you probably wouldn't want any extra weight, you'd probably have to lose the shielding which might cause trouble with radio communications to say nothing of irradiating everyone in the vicinity.
http://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_Power
Ok Rob
I did say typically and just below so it didn't cover everything. I did also mention that the Prius, as one of the very few vehicles on the road (I have two btw) has the ability to run on the Atkinson cycle, which can use delayed valve timing to reduce the volumetric capacity of the engine without running into knocking issues, effectively stating the opposite, that in fact a ICE can have a high BSFC even at lower revs. That is of course provided you give it a bit of flexibility by making it a hybrid.
I was however, trying to make the point that hybrids can and will work! ;-)
We just don't have electronic valve control on RC engines yet, so making a two stroke gaser run at +80% WOT was my only ICE option for that scale, and the only relevant example to make. In an aircraft weight results in an increase in drag, so making what weight you have in the ICE produce the most usable energy is also a factor to keep consumption down, even at times if it is above best BSFC. Having an engine that is only run at 50% WOT can also mean I'm carrying 50% ICE for nothing in a hybrid combination. Plus unlike in a car where torque is required for drive-ability, this is not so in a aircraft, and the ICE can be configured accordingly, as once again "typically" BSFC is worst at highest torque. Do you have any BSFC maps for small below 50cc ICE handy for me to examine? I haven't found many good sources yet to compare engines of that size. I suppose that will be one of the first things I'll be able to run on my RC hybrid setup...seeing it has a built in dyno!
On electric start for the UAVME 2016: 1.3.2 says: "Upon landing, the aircraft must automatically remove power from any propellers making it safe for Joe to approach"
The question here is how they define "remove power" and if a clutch will suffice so that one can keep the motor running. Either way a safety case will need to be made, and given that only the top 20 applicants will even make it to the event (last time it was open to as many would come) it would seem probable they will more likely dismiss those that present a greater risk first. So I'd say electric start is better than a clutch for a heli, but a small prop multi better than a heli, and a single prop foamie better than a multi etc. There's also points for safety that increase your chances of winning.
JB, you have to be careful with some of the blanket statements about ICE efficiency being highest at maximum power.
If efficiency is measured as Brake Specific Fuel Consumption (as it typically is) then it's just not true that in all cases, max efficiency is at full power. Many high performance engines require considerable excess fuel enrichment and spark advance reduction to avoid detonation, which results in much, much lower BSFC than at more moderate power settings.
Your statements may be correct in the case of low power/weight engines, with very low compression ratios, running very high octane fuels (ie: most airplane engines). But not for high power/weight ratio engines with high compression and low octane fuel compatibility.
You also made a statement about 2016 OBC requiring electric start. Are you sure? Others have read that it only requires the rotors to be stopped, not the motor.
Hey Gary buddy
I can agree to the sentiment, but what assumptions are you making on hybrid efficiency and performance, and ICE engine performance to come to that conclusion? Not all hybrid configurations are the same. Taken as a whole, in larger vehicles like a Prius, the hybrid efficiency of the drivetrain (not vehicle) is better than the ICE operating by itself with gears, due to the extent of optimization that improves the efficiency of the ICE thermodynamics under constant load. (ie input to output decoupling) Generally speaking most non-forced induction ICE engines have fuel to kinetic max efficiency power band at maximum power output and RPM, or just under. That means unless your driving the ICE "flat out" it's not as efficient as it could be in converting fuel into kinetic energy, so making it efficient means sacrificing the availability of peak power.
In the case of the Prius it uses electrically controlled variable valve timing to optimise ICE efficiency at lower RPM as well using the Atkinson cycle (not otto), but this is not possible on a RC scale yet, so operating the ICE at RPM Max is nearly the only option for RC. At that point you are left with no headroom for peak if you want to make the ICE as small and as efficient as possible. As you know weight also impacts flight efficiency, which is the whole reason for efficient propulsion that is made as light and small as possible. So the smaller and faster the ICE the better.
Also the torque curve on a ICE is not as flat as a electric, so a highly optimized, much smaller, high RPM engine would find it more difficult to cope with pitch change requests, and also require a high amount of gearing etc. Note that load variations even at constant RPM causes variations in fuel consumption/efficiency as well. (aka flooring it out of gear or uphill in too high a gear) The hybrid configuration I'm working on at the moment is less than a kg per kW, so there's lots of room/weight available for fuel, which is the increase in performance I'm looking for over lithium.
Another advantage of a hybrid drive-train is the ability to electrically start the ICE without a rotor clutch or extra starter motor, which for the 2016 Outback Challenge safety case is a must have especially when using a heli.
With the Prius type hybrid configuration it's possible to transfer all ICE power without converting it to electrical first, with no lag in introducing electric peak power. It's also possible with that system to start the ICE but have the rotors stopped, without needing a clutch to de-couple the drive train. Refuelling instead of recharging is also of benefit in some scenarios. As mentioned previously in some configurations a hybrid might just be more desirable for the task, especially for a VTOL, where the forward thrust power is significantly less than hover.
Super capacitors are an option to provide peak but are significantly harder to power manage than batteries and larger/more expensive per Wh too. Having a battery available to land on engine failure is also a bonus. I can agree that on a multi the range of performance required is more limited, provided the payload remains the same. In the case of Top Flight they are proposing freight deliveries which is a whole other level of absurdity IMHO. ;-)
The Wright brothers also wrought with the laws of physics - and won. Sometimes it just takes some perseverance and mind over matter! ;-)
Regards
JB
Hi JB,
Even in this argument it falls a bit flat, sure, you can probably make a fuel/generator/ hybrid multi that will fly further than a all electric multi, but if you simply made a fuel variable pitch multi, my original argument still stands, all things being equal, the fuel var pitch multi will still out fly and outlast the "hybrid" by a considerable margin.
The losses in the var pitch multi are tiny in comparison to the hybrid conversion losses and the same for the weight penalties.
Also as I said the batteries on that hybrid are next to useless, because you are almost always within 10 percent of your nominal thrust - power - lift requirements.
A Super capacitor for instant takeoff or a short burst would make more sense than a battery in this use.
The battery part of a hybrid only does you any good if you have at least 2 significantly different performance / power requirements, and on a multi, you really - don't!
As a true gas - electric - battery hybrid, there is simply no real benefit to the batteries in this application and they only represent extra weight (and extra conversion losses).
Somebody may make this thing actually fly, but physics make it a really hard way to go to get worthwhile performance out of it.
There are always a few people who think they have a great idea even though some one little bit of physics disagrees.
Physics - always wins
lol Gary
I can agree with the helicopter comparison, I made no such claim that a hybrid powered quad would in some way defeat the physics of running a larger rotor on a heli. The point here is however that they also claim to improve the range of quads by using a hybrid drivetrain. In this scenario the higher fuel energy density and claims of an increase or 2-3x the range seems justified, and in their configuration is technically the only way to add liquid fuel as a energy source, apart form variable pitch props etc.
Overall depending on the platform chosen I think hybridisation will help improve performance, especially when fuel can be used instead of lithium batteries, on some platforms more than others.
Regards
JB
The concept that a multirotor hybrid can have more efficiency, endurance or range than an equivalent fuel helicopter is absolute nonsense.
The Generator, batteries, fuel to mechanical to electric to motor conversion all represent loss's many of which are simply not there for a helicopter.
Also the efficiency of the helis large rotor will always exceed considerably the efficiency of a roughly equivalents multis much smaller props.
All those extra parts Batteries and generator also mean extra weight for the multi further reducing it's performance.
Even if you made the worlds worst heli, it would still be more efficient than this cludge.
Also, a full hybrid only really does you any good if you have at least 2 different performance requirements, multis simply don't, they require hover thrust and generally a small margin above and below that.
The batteries are practically useless in this scenario because you are never out of your median power requirement.
In a fixed wing you have a wide range of power requirements, from literally nothing for gliding, soaring or landing to high for takeoff and climb.
At least there a true hybrid might make some sense, but for this it is nonsense. Period!
A heli could literally fly circles around this thing until it ran out of gas and crashed and then the heli could still fly circles around it's wreckage.
A doctoral student in my lab finished his thesis on a hybrid power plant. In his case, it was used for long endurance airship. He build most of the airship (the balloon is huge, almost 25' long, you can see it in his thesis), but never got to fly it. His calculations showed many days of flight time.
Here is his thesis. He spend more that 100h on experimental tests on the power plant.
Doesn't seem they have a working device yet. Looks like they want to investigate the demand in such devices first or pick a big investor. Well... business.
Yeah, I agree. For a series hybrid, I can't see how could realistically do better than 80%? Because you need 90% for generation, and then the motor. Most motors are only 70-80% efficient in their actual operating range.
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