< PreviousKiwiFlyer Magazine Issue 72 10 Electric Mosquito New Zealand’s first electric helicopter ZK-IAB started its life as ZK-HNG. HNG was a conventional helicopter with a petrol engine, two-bladed main rotor and standard mechanically driven tail rotor. But that is where convention stopped. HNG was a bare bones, single seat kitset aircraft which was on occasion named the ‘strap-on’ helicopter. HNG was the first microlight ‘Mosquito’ helicopter registered in New Zealand, imported and assembled by myself in 2008. The helicopter itself was very well designed and manufactured; the weak point was the two-stroke engine powering it. Power to weight was excellent, though at the expense of reliability. HNG spent 60 hours in the air, but time spent maintaining the engine might have exceeded that. The idea develops About six years ago I started thinking of changing to something better, and the idea of an electric helicopter was hatched. It took four years of thinking, searching for a suitable motor and playing with numbers before I finally bit the bullet and ordered an EMRAX 228 motor from Slovenia and a PM100 drive from Cascadia Motion in the United States. The drive was a total overkill, able to deliver 100 kW continuous power but in hindsight was an excellent choice. It’s extremely well engineered and built, and has all the features (and much more) required for a helicopter application. My first impression when unpacking the motor was of disbelief. The thing is tiny (smaller than a dinner plate), weighs 12 kg and can deliver a peak power of 109 kW which will put a Rotax 915 iS to shame. Average continuous power is much lower, however the motor is just about the perfect choice for a single seat helicopter. Design and installation The original Mosquito helicopter has things running at three speeds. The engine and clutch run at 6000 rpm which is then brought down to 2500 rpm with a primary belt reduction. The one-way bearing, gearboxes, tail rotor driveshaft and tail rotor all run at 2500 rpm. Then there is a secondary belt reduction down to 540 rpm, being the speed at which the main rotor turns. The EMRAX electric motor is rated at 6000 rpm but is most efficient at around 2500 rpm. The obvious choice was to thus get rid of the primary reduction and run the motor at 2500 rpm. An added bonus is that the existing one-way bearing could be reused with minor machining - and only one new interface part had to be made between the motor and the one-way bearing. The motor and drive were installed and wired up, with a throttle assembly coming from an electric scooter. The drive communicates using a CAN bus, which is the standard communication system used in all cars, trucks, buses and even the new Rotax 91Xi engines. A microcontroller board was built to communicate with the drive and display relevant information on an LCD screen on the instrument panel. The drive can be configured to run either in torque control or speed control mode, and a governing system that feels similar to that of Robinson helicopters was implemented. If the motor speed is less than 60% the drive is in torque control mode with motor torque controlled by the throttle. When the speed exceeds 60% and the throttle is above 50% the drive switches to speed control mode which is basically a built-in governor. To disengage the governor the throttle needs to be closed below a set-point. For normal flight in governor mode the throttle is simply kept at maximum.11 2021 #1 Both motor and drive are liquid cooled. A very nice electric pump used by Porsche was installed and is controlled by the microcontroller board. The pump switches on when any temperature exceeds 30 degrees C, and the speed can even be varied to save energy. Initial tests showed that without liquid cooling it took 90 seconds for motor and drive temperatures to get to 60 degrees C. During development this was more than enough time to complete a test, so the full liquid cooling system only became operational quite late in the story. Thus in simple terms, the two-stroke engine plus all the fuel systems were removed, the electric motor and drive installed (thanks to lots of time during the COVID lockdown) and then it was time to start spinning things up to see if the idea could actually take off. Blades turning Initial tests were done with the helicopter tied down and power supplied by a dedicated DC power supply. The first step was to connect only the motor so that the no-load losses of the motor could be measured. Then the tail rotor was connected to measure the tail rotor power, and that was a real eye opener. Even with the tail rotor generating zero thrust it was consuming 1.4 kW of power. That quickly went up to over 3 kW when thrust was required. Whenever the tail rotor turns at rated speed it thus requires a minimum of 1.4 kW to keep spinning, even in an autorotation. More about that later. The next step was to connect the main rotor to see how much power it needed. Here again the power required just to keep the rotor spinning was more than expected, about 8 kW at zero thrust. To lift off, total power of about 22 kW was needed, and this was without any added weight to simulate batteries. (We’re still tethered to mains power at this point). The tail was using 3 kW, which means that the main rotor needed just under 20kW to hover. Extending the initial concept Take away the noise and vibration of the two-stroke engine and all of a sudden you hear and feel things that were previously impossible to hear and feel. What became really obvious was vibration originating from the tail rotor driveshaft. Two days were spent taking out the driveshaft and trying to straighten it as far as possible. This improved the vibration, but with everything else so smooth and quiet it was still annoying. It was time for a better solution. A quick physics calculation showed that the tail rotor thrust would need to be somewhere in the 10-15 kg range. A search for a suitable motor and prop combination to generate the required thrust proved futile; thinking outside the square might be required. Considering things that fly already, there was one obvious candidate to investigate more closely. Drones with a lifting capability of 15 kg were becoming readily available and the cost was dropping dramatically. Acquiring a drone that could lift 15 kg and mounting it vertically where the tail rotor used to be seemed like a very elegant solution. The question was, would it work in real life? Rather impulsively a six-arm 15 kg drone was ordered. While it was on its way the mechanical tail rotor was removed and I started pondering as to how the drone could be mounted in its place. The total diameter of the drone was much larger than the original tail KiwiFlyer Magazine Issue 72 12 rotor, and it quickly became clear that it couldn’t be located in the same place. There was no reason to maintain the drone’s rotor configuration however, so alternative ways to mount the motors were investigated, finally arriving at the configuration currently on the aircraft. Replacement 25 mm carbon fibre mounting tubes were custom made by Kilwell in Rotorua and brackets were fabricated to fasten everything to the existing tail boom. When the motors and props arrived everything was ready to be bolted on. There were two more issues that needed to be solved. Firstly where does the power come from and secondly, how do you control thrust? Being an electric helicopter all power on board has to at some point come from a battery. The tail drives run at 25V and the main battery is configured for a much higher voltage than this, so the easiest solution was to locate a separate dedicated tail rotor battery on the tail. My first impressions were that weight would be an issue, but when everything was weighed the mass of the electric tail rotor (including battery) ended up being less than that of the mechanical tail rotor parts that were removed. Win-win all the way! Tail rotor control Next came tail rotor control. The original tail rotor was controlled by a push/pull cable running from the foot pedals all the way to the tail rotor. The new tail rotor motors needed only one PWM (pulse width modulated) signal to control the speed which is basically radio-controlled aeroplane technology that has been around for years. The same signal controls all seven motors, which means only two wires are needed to be run from the front to the back. The signal has to be generated somewhere, and the logical solution was to use the same microcontroller that was talking to the main drive and also driving the display panel. That side was easy, but the microcontroller still needed an input from the pilot’s foot pedals to know what the pilot wanted. To do this a potentiometer was mounted on the airframe with linkages to the foot pedals, and the output fed directly into the microcontroller. As the foot pedals were moved the potentiometer would turn and the microcontroller could read their position. Tail rotor correlation Then came another lightbulb moment. Most helicopters have a throttle correlator which automatically increases throttle if collective pitch (on the main rotor blades for non-helicopter pilots, Ed.) is pulled, and decreases throttle if collective is lowered. This reduces pilot workload, the correlator doing most of the throttle work when the collective is moved. Wouldn’t it be great if we could make an equivalent tail thrust correlator? If main rotor torque is increased we know that tail rotor thrust will need to be increased and vice versa. The microcontroller already knows what the main rotor torque is because it constantly communicates with the motor drive, so a tail rotor correlator could be implemented easily with just a few lines of software code. This was quickly done, and works an absolute treat. Large foot pedal movement requirements due to main rotor power changes are eliminated. All the pilot has to do with this system is fine tuning. The correlator does have an interesting side effect though. During one tethered hover test the main drive tripped, which in helicopter terms is termed an engine failure in the hover. In a conventional helicopter the pilot will immediately know that LAST LOT LEFT SOLD SOLD SOLD SOLD SOLD SOLD SOLD Lot 4 is a 5500m2 site with direct access to the 839 metre runway. 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All maintenance enquiries are welcome, including for: Annual review of airworthiness Avionics inspections Import /export services C of A issue 2200 hr / 12 year overhaul of Robinson helicopters Modifications and Upgrades Field Maintenance Supply of new & part-life Robinson parts Helicopter Leasing Helicopter Sales Logistics Services Robinson Helicopter Acquisitions Roger: 027 498 2812 heli@helispecs.co.nz 13 Kittyhawk Way Tauranga Airport Mount Maunganui 3116 helispecs.co.nz Electric Mosquito13 2021 #1 It’s a serious test flying programme that has only just commenced, but already it’s starting to look like fun. Michael Norton imageKiwiFlyer Magazine Issue 72 14 The small black motor packs 109 kW of peak power. One of seven tail rotors from the donor drone. Green for go and an ex-scooter throttle.Half of a total 40 kg of batteries that power the main motor. Standard Mosquito helicopter rotorhead and controls with DragonWings blades. A skid foot - standard minimalist Mosquito hardware.Permission to fly was received on 8th December. A potentiometer measures pedal location for tail control.The microcontroller and power parameters display. Electric Mosquito09 489 9650 val@hoodbrokers.com www.hoodinsurance.co.nz Public Liability Insurance Business Protection Insurance General Insurance Offering the best possible solutions to protect you business and yourself. 15 2021 #1 the engine has stopped because of two things happening; firstly the noise stops, and secondly the helicopter yaws (due tail rotor thrust still countering the main rotor drive torque that is no longer there). In the circumstance of an engine failure the pilot of an electric helicopter is at an immediate disadvantage because when there is no engine noise in the first place, a sudden lack of noise cannot be used as an indicator of power loss. When the motor stopped there was also no yaw because the tail rotor correlator automatically reduced tail rotor thrust to zero when the main rotor torque disappeared. What did happen, however, is the helicopter rolled to the left because the tail rotor thrust had disappeared. This also happens in conventional helicopters, but is a small effect compared to the dominant yaw and is hardly worthwhile mentioning. So when the un-commanded roll came there was a very confused pilot sitting in the seat. It was a case of - there’s a problem, don’t know what, get this thing on the ground as quick as I can. Even back on the ground I wasn’t quite sure what had just happened. The tail rotor correlator was such a small software change that makes normal flying so much easier. There is the mentioned side effect on a traditional engine-out procedure, however once the pilot is aware that the helicopter no longer yaws if the engine fails, this behaviour simply becomes the new norm and is actually very nice to live with. Redundancy There are advantages in having seven tail motors, one being multiple redundancy. If one or even three motors fail it does not result in loss of tail rotor control, as full yaw control in the hover has been proven with only four motors operating. Two tail rotor batteries could be installed with three motors running off one battery and the other four motors running off the second battery, then ensuring redundancy in case of a battery failure. That might be a future improvement. There are also potential control system redundancies to consider in the future, but for now effort is going into confirming the basic design and behaviours of the aircraft. Getting ready to cut the tethers So far the extra weight of a main battery pack had been ignored. Calculations showed that for a 20 minute flight the battery would weigh about 40 kg. The next step was thus to tie on some containers with sand to simulate the extra battery weight. It was surprising how much the rotor blade noise increased with the extra weight. Without it there was minimal blade noise but with the extra weight the machine started to sound like a real helicopter. As expected, power requirements did increase. The main rotor alone was now consuming 21 kW while the new tail rotors consumed about 1.4 kW. The tests all showed that the electric tail would fly. The time had arrived to cut the tethers, and to do that legally would require a permit to fly, issued by our NZ CAA. To get the ball rolling CAA was duly informed of the intention to fly a first-in-the-world electric helicopter with electric tail rotor, and at the same time the main batteries were ordered. The batteries arrived and a suitable way to mount them had to be found. The placement of the batteries would be used to obtain the correct centre of gravity location which was done with a ‘hang’ test to factory specifications. Here a rookie mistake was uncovered; P: 06 879 8593 M: 022 636 6573 E: sammy@primaryavionics.co.nz Cresco Lane, Main North Road, Hawkes Bay Airport www.primaryavionics.co.nz Call Sammy today to discuss which option would be the best for you and your aircraft. GARMIN GTX 335 APPAREO STRATUS ESG L3 NGT-9000 Need ADS-b? With the New Southern Sky ADS-b mandate now underway, and the rebates being paid ($2500 for out +$500 for in), now is the perfect time to get your ADS-b sorted.Next course: New Plymouth 1-5 March. Course fee is $1850 +GST which includes a hard copy of the latest IATA DGR book. Contact Jim on 021 966254 or email: james@iceaviation.co.nz The full 5-day course is required for packers, shippers and acceptance personnel, and also covers all of the requirements for pilots and ground handlers. We are able to train your Acceptance Personnel as well as packers, shippers, pilots, loaders, etc. This training includes carriage of infectious substances. You must be qualified to do this if you intend to carry Covid Vaccines! Everyone involved in the carriage of DG by air needs to be trained and qualified by a CAA approved training provider. Approved Dangerous Goods Training Course KiwiFlyer Magazine Issue 72 16 About Oskar Stielau There are bound to be KiwiFlyer readers wondering who this person is who built himself an electric helicopter. So we asked. Oskar’s fascination with rotorcraft started as a kid at an air show when he first saw a helicopter come in to land. He was amazed that something could just hang in the air like that, and promised himself that one day he was going to fly and own one of these amazing machines. Little did he know back then where the fascination would one day lead to. After studying electrical engineering and working for a few years, he was finally in a position to get into the air. It started off by learning to fly trikes, and then getting into gyrocopters - at the time considered the poor man’s helicopter. Even then an obsession for trying to change (and hopefully improve) things was becoming apparent - his first gyro was an old Bensen from which he removed the McCulloch engine and bolted on a Rotax. Later he built a Gyrobee, a single seat ‘pocket rocket’ which provided lots of entertainment during annual NZ Autogyro Association meetings at Dannevirke. A few years later the dream of flying a helicopter become a reality, when he learned to fly a R22 at Tauranga and Ardmore. While busy with his PPL(H) Oskar ordered the first Mosquito kitset helicopter to be delivered to New Zealand. This was his first helicopter build, so there was now the pull between gyro and helicopter flying. In the end the helicopter won. And that Mosquito kitset helicopter became the predecessor of the all-electric ZK-IAB. Oskar’s involvement with electrical vehicles in fact precedes this by quite a while. He worked in Ashburton for a year on the Designline electric bus, and was also involved in the design of the first New Zealand built hybrid electric bus exported to Japan – all well before electric vehicles became mainstream. Being ahead of the innovation curve isn’t a new thing therefore, so it’s perhaps no surprise Oskar has now built an all– electric helicopter before anybody else. If you’d like to find out more, get in contact with Oskar on +64 21 215 8327 or by email to: oskar@hfpower.co.nz Oskar wearing a post-flight smile after another successful exercise from the test flight programme. Electric Mosquito17 2021 #1 when testing on a slope always measure the slope before starting out! I had assumed the slope to be about 3 degrees, and very quickly got used to what I thought was aircraft level. But the hang test showed that my perception of ‘level’ was actually 3 degrees tail heavy. Going back to the slope I found that it was between 5 and 6 degrees, so the main batteries had to be placed a bit more forward than first envisioned. In the meantime CAA had come back with a detailed list of requirements to get the aircraft to the point where it could be flown legally. The first step was aircraft registration, the helicopter becoming ZK-IAB. Since the helicopter had been previously registered and flown 60 hours in its former configuration, there was a debate as to whether this should be classified as a new aircraft or a modified one. In the end it did not matter - a temporary microlight flight permit would be issued and 40 hours of test flying would need to be logged. Thanks Colin One of the requirements for a flight permit to fly is an annual inspection. I started phoning around to see who would be prepared to do that, but for most inspectors the idea of inspecting a first-in-the-world electric helicopter with electric tail rotor proved to be a bit too much outside the square. My enquiries saw me climbing the RAANZ ladder until being passed on to Colin Alexander at Solo Wings. Colin was super enthusiastic when he heard what I was planning to do, and was of invaluable help in the paperwork process. CAA was coming up to Tauranga in December to inspect two other planes, and Colin suggested that I bring the helicopter down and have all the paperwork done in one go. There was still a bit of work to do on mounting and wiring up the main batteries, and all of a sudden the pressure was on! The contraption was loaded onto a trailer and driven down to Tauranga. The first day was spent with Colin doing the inspection and sorting out all the necessary paperwork for the CAA visit the next morning. The CAA visit resulted in a bit of to and fro-ing. Fortunately Colin was batting for the helicopter. This was completely understandable and I certainly wouldn’t like to be in CAA’s shoes when someone crazy comes along wanting to fly some odd new machine they had designed and built in a shed. We are indeed fortunate in New Zealand that CAA still accommodates Kiwi backyard endeavours such as mine. First flight After CAA handed over the temporary flight permit the helicopter was legal to fly. And of course then everybody wanted to see it fly! The batteries were not fully charged so the first flight would have to be a short one. IAB was moved outside, the batteries connected, and on a beautiful summer day the first un-tethered lift-off took place. This helicopter feels like a true magic carpet; traditional helicopters come close but they always have large amounts of noise and vibration as part of the package. The only sound in the electric helicopter is blade noise, which for a helicopter pilot is very therapeutic (you never want that noise to stop!). Just as nice is the absolute (and very un-helicopter like) lack of vibration. Flight testing begins Tests to date have included loss of main motor drive in the hover, loss of tail rotor in the hover and ‘quickstops’ to the point of splitting needles (when rotor rpm over-runs main drive rpm). The helicopter A screen shot from the data logging system showing current draw during a series of short flights and quickstops. Aviation Safety Supplies Limited P: 07 5430075 or 027 280 6549 E: lklee@aviationsafety.co.nz www.aviationsafety.co.nz Professional Survival Equipment for Serious AviatorsPerforming a quickstop. Several such manoeuvres can be seen on the chart showing current draw from the batteries during a short test flight. KiwiFlyer Magazine Issue 72 18 www.avcraft.co.nz Avcraft Engineering NZ Ltd. Feilding Aerodrome 06 212 0920 mat@avcraft.co.nz From a 50 hour inspection on a Cessna 150, to a KingAir Phase Inspection or a Pilatus PC-12 Annual, our experienced engineers have the skills, knowledge and tooling to assist you with all scheduled and unscheduled maintenance requirements. Plus: Aircraft recoveries, Insurance repairs, Rebuilds, Sheet metal work, Corrosion repairs, Paint refinishing, Fabric work, Maintenance Control, and Avionics. Electric Mosquitohas been flying beautifully with no unexpected characteristics so far. The tail rotor correlator works great, with only small pedal movements required even when there are large changes in main rotor drive torque. What has been found is that tail rotor power varies hugely for different manoeuvres. A moderate left pedal turn uses roughly four times the power of a moderate right pedal turn. This can be seen on the graph which shows tail rotor battery current during a test flight - during the three quickstops the tail power dropped to zero because the main rotor torque had dropped to zero (needles were split). Looking at the peaks it is also easy to see how conventional helicopter pilots can get into trouble during low rotor rpm conditions by undertaking a manoeuvre that requires high tail rotor power (which only serves to drag rpm down further). Having the electric tail completely independent of the main rotor has some interesting consequences when the helicopter is in autorotation. Recall that early tests with the conventional mechanical tail rotor showed the tail rotor consuming a surprisingly large amount of power, even when generating zero thrust. In an autorotation this power can only come from the main rotor, and the tail rotor thus acts as a brake on the main rotor. Not only does this reduce the autorotation performance of the helicopter, it also produces a negative torque on the airframe during autorotation. Last week the helicopter did its first autorotation and as the theory predicted it was a non-event. Winds were around 15 kts and in forward flight the aircraft is extremely yaw stable. Pedal workload is virtually zero, even when entering an auto. Partly this is the tail rotor thrust correlator doing its job, but it also feels as if the large surface area of the tail rotor array acts as a very good vertical stabiliser. To conclude When doing something that hasn’t been done before, one always goes through various stages of thought. It starts with a lightbulb moment when the idea is first hatched, followed by a few weeks or months of wondering if it could ever work. Then comes the number crunching, followed by looking around for whatever might be available to help implement the idea. The excitement builds up when everything works on paper and parts to build and test are ordered. Next comes the hard work stage, putting things together and testing. There are always some ‘what was I thinking, this won’t work’ moments which threaten to derail the whole project, but fortunately thus far an alternate solution has always been found. The doubt really creeps in when a machine like this is finally cleared to fly un-tethered. With ropes tying everything down to just above the ground there’s not much that can go wrong. Remove the ropes and all of a sudden the playing field changes completely. But by then it’s much too late not to commit - so much time and effort has been invested that backing out can’t be an option. So each flight is preceded by many days of thinking what to do, what could go wrong, and what to do if things do go wrong. Each actual flight has ended up being a huge buzz and an amazing learning experience. Imagine being Igor Sikorsky, Arthur Young or any of the other helicopter pioneers who started such a process from complete scratch without all the technology available today. I take my hat off to them all. Oskar Stielau 021 215 8327 or oskar@hfpower.co.nz YouTube channel: OskarRDA 19 2021 #1 F K Michael Norton imageNext >