Electric flight: bringing a spark to the British skies By Captain Robin Evans, Senior Log Contributor icture your local airfield in winter: everything hangared or tied down, caf shut, windsock restless. Today would be no different, but for the potential difference of EASAs first certified, production electric aircraft the Pipistrel Velis Electro. Ground zero for this quiet revolution is Damyns Hall Aerodrome, tucked just inside the M25 north of Dartford, home of Fly About Aviation, Pipistrels UK distributor. Such is the potential impact, Fly Abouts Deepak Mahajan is in discussion with the DfT today, instructor Claire Bartlett running through a condensed version of its differences course. Designed and built in Slovenia, the Velis Electro is intended as a PPL trainer, identical to its Rotax brethren. Pipistrel founder and CEO Ivo Boscarol is perhaps the Burt Rutan of lightweight, production aircraft and increasingly, their alternative power sources. He began when Slovenia was part of the former Yugoslavia and alternative (microlight) flying was illegal. When the military closed up for the day, homebuilts would appear in the evening, locals referring to them as bats, hence Pipistrel. One alternative became another, the firm having produced electrical aircraft since 2007. Walkaround Externally, the most obvious giveaway is the port air intake bearing a high voltage decal. This supplies cooling airflow to the radiator, keeping the liquid-cooled batteries within safe temperature range the warm air exhausted from an oval port beneath the rear fuselage. On cold mornings, warm air can be fed through the air intake to warm the batteries to 10oC while you make the walkaround. Extensive use of composites and other weight concessions (no cockpit heater, ballistic recovery parachute or navigation lights) mean an empty weight of 428kg and MTOW 600kg. It has full-span flaperons (integrated flaps and ailerons) and without speedbrakes its slippery. The prop turns freely with the tap of a finger, at the same time not to be pushed on as you might a conventional one. Immediately behind this is an axial-flux motor and the forward, desktop-computer sized battery. Behind removable seat panels sits the aft battery, arranging 1152 18-650 type cells (see box Battery type rating, below left) in what would be the baggage hold. Tested for crashworthiness and thermal runaway, the two battery units connect in parallel; if one fails, it is automatically disconnected; flight is still possible on the other. Two small pumps feed coolant hoses, which are checked preflight for no obvious coolant leakage or bubbles evident in a sight-glass. The cooling system and secure mounting for their 72kg cases are why they are charged in-situ only. They supply a nominal 345v network controlled by a Battery Management System (BMS) responsible for cell balancing or voltage protections. The prototype Velis Electro was tested with a propeller that enabled generation of power to recharge the batteries. Because of complexity and cost consideration, this was changed to a three-blade, fixed-pitch propellor for certification. Dont be idle The centre pedestal offers four pull and toggle switches. Turning the master switch on performs a self-test, briefly running the stick shaker, fed by an alpha sensor in the pitot tube the stall behaviour so benign. Avionics on introduces a new way to consider fuel state: State of Charge (% SoC) is what you think of on your phone, State of Health (% SoH) the longer-term measure of the batterys ability to deliver it. The carbon-weave panel has a large cutaway on each side for maps and light stowage. It includes a USB data logger socket and firmware update port, plus a dual USB for phone or iPad. A Kanardia multi-function display integrates several instruments into a single AI mounted in front of the left seat pilot, with analogue backups. Six-footers do fit, with visibility no issue from all-glazed, gullwing doors. Theres a multi-function upper nav display, with Ts & Ps appearing on an electrical powerplant system interface (EPSI) display that also offers centralised warnings. BATT EN (engage) and PWR EN start up the coolant pumps and make the prop live. If started with the power lever off the zero stop, a cutout prevents it engaging. At the slightest nudge above zero (idle an irrelevant term), the three blades spin up and were whirring over the grass. Run-up checks are that the batteries are at their minimum 10oC and a single cycle of the power lever, confirming >50kW available without cautions: no mags, mixture or carb heat. Recharging of the Pipistrel is via a beefy, suitcasesized charger box on castors People have said they can hear birds singing while you take off thats the biggest compliment you can pay Claire describes how to reconsider fuel in SoC consumption terms for phases of flight: taxi 1-2%, takeoff 3% and climb to 1000 7%. Pipistrels use an up/down flow between power and flaps; going up means flow up. The elbow-positioned flap handle goes to zero at 300, reduce to 48kW climb power and check airspeed accelerating to 75kts. We head south on a loop over the Dartford Crossing and then east along the Thames. The ancient Tilbury Fort slides past and we skirt around Thurrock for some general handling. The trimmer is electric, but seldom used the controls are light, pitch particularly staying where it is left. We dispense with the very precise digital RPM and fly by kW datums: just another form of expressing power. Ten minutes of 20kW, 82kt cruise consumes 15% SoC; at 25kW its 19%, in household terms about 10 kettles. The EPSI indicates instantaneous endurance, which needs a hefty pinch of salt on takeoff. The noise is also far less: music to ears, inside or out. To rejoin, Claire introduces a guide of 60% SoC to equate to a maximum six miles from the field, at 50% five miles. Before turning base, Pipistrels down flow is used: idle power, check airspeed below 81kts (VFE) and select flap 1. Unlike a piston engine, idle gives very little drag. Deepak later describes all Pipistrels as characteristically slippery, suggesting a one degree approach pitch reduction equates to a 5kt speed increase. Approaches are flown at 58-60kts with a flaps two limit of 65kts, taken rolling onto final. Its not an aircraft that favours a high and close circuit, especially without speedbrakes, the book actively reminding to sideslip if needed. The southerly at Damyns Hall also requires sidestepping around power lines at 300 and its not a calm day. Going around doesnt need full power, 40kW works fine. READ MORE Battery type rating Considerations A guide is that 2% SoC equals a minute of flight: absolute endurance is 50 minutes. In practice, 35 minutes aloft has used 60% SoC. Taxiing in after landing, a caution warns SoC 30%. Mindful of this situation arising for students in the circuit, Pipistrel publishes a series of error chain procedures, <30% SoC included. The procedure is not to make an anxious, tight circuit that would increase instability risk, but follow the standard pattern. If reaching 15% while airborne, the triggered caution introduces an entirely new situation to the pilot: no go-around available. Recharging is via a beefy, suitcase-sized charger box on castors. Recharge current is dictated by the local supply and must be three-phase. Here, the hardware specifically installed in the hangar permits the maximum 32A; higher currents recharge quicker, albeit at higher temperatures, important to consider in summer. The charger interacts with the BMS to optimise the charging cycle and run the coolant pumps. Charging cycles are logged (each flight counting twice: discharge and subsequent charge) by USB for Pipistrel. Batteries currently work on a 700h interval, although it is envisaged that once proven this might increase. The electric flight movement has physical, as well as figurative foundations at Damyns Hall: groundworks being installed for two additional hangars to add to the pair already full of Pipistrels. Deepak explains that several clients have already taken deliveries. SEMET Blackbushe Aviation also operates the type, the training market motivated by low, long-term running costs (quoted charging is 2.50/flight hour) for local sorties and circuit training. People have said they can hear birds singing while you take off thats the biggest compliment you can pay, says Deepak. He describes how this permits flight when pistons are discouraged for noise abatement, typically those still moments at the start and end of the day where the Pipistrel story began. Potential difference Electricity offers an efficient power, with less heat and noise wastage. Motors are tolerant of attitude, G-force, shock cooling and aspiration with altitude. With far fewer moving parts, maintenance is minimal and the CG remains fixed though the aircraft gets no lighter. While hydrogen has become the big target, it is understood that electric will suit small passenger aircraft, alongside becoming a significant part of wider public de-carbonisation. Intended for flight schools, the Velis is likely to become the aircraft that airline cadets will train on in some proportion before their prospective employers take delivery of their equivalents. Lessons learned and data returned will inform future design, pilot awareness, market confidence and regulation. Advances in energy density, lithium-air batteries most recently cited as the next threshold, and demand will be key to unlocking charging locations and speed. This is still true of electric cars, making their first practical appearance around 2010 and only now cementing their practicality and ubiquity. Stripping out the legacy tech of a combustion engine suddenly seems akin to replacing control cables with fly-by-wire, equally audacious once upon a time. That is the state of charge, and health, of electric flight as it, too, gets under way and in many ways, you would barely notice. Fly the Velis Electro with Fly About Aviation Damyns Hall Aerodrome, Upminster, RM14 2TQ 07540 899 690 What3words: leaned.give.nets www.flyaboutaviation.com READ MORE BATTERY TYPE RATING Industrial li-ion batteries are designated by diameter/ height: an 18-650 measuring 18 x 65.0mm (regardless of design, chemistry and voltage, in these terms, the humble AA would be a 14.5-505). Likely, you already use the ubiquitous 18-650 concealed in the modules of power tools, laptops and electric cars Argos is also selling them individually for the vaping market. ELECTRIC FLIGHT