Record-setters

Ed Hicks finds out more about the LAA members who helped Rolls-Royce create a world record-breaking electric-powered kitplane

Photography: Rolls-Royce, Electroflight and Ed Hicks

Plenty has been written about the Spirit of Innovation aircraft built by Electroflight under UK E-Conditions for Rolls-Royce, especially since the aircraft successfully set five world records at the end of 2021. What you may not have realised though, is that lots of the people involved in the project were also LAA members. Homebuilders, engineers and pilots, they all played various parts in the record-breaking programme success.

Electroflight grew from LAA Inspector Roger Targett’s idea to create an electric racing aircraft, which started to take shape around 2010. Having worked on Red Bull racer Steve Jones’ aircraft, Roger thought the idea of an electric-powered racer would be a natural evolution, given the very short flight times – around 90 seconds – of race aircraft around the course. Steve agreed, and before too long was an founding investor in Electroflight, along with Nick Sills. As funds allowed, the development of the P1E slowly progressed, and Electroflight quietly began making a name for itself in the emerging market of high-powered electric propulsion for aerospace.

When Rolls-Royce needed a partner for its ACCEL (Accelerating the Electrification of Flight), they turned to Electroflight. The plan? To create an electric-powered aircraft that could beat the existing 213mph electric record set in 2017 by Walter Extra’s Siemens powered Extra 330LE, and hopefully take it to beyond 300mph.

Stjohn Youngman had been working in automotive engineering for a number of years on start-ups mainly

Stressing the NXTe LAA member John Wighton kept

close eye on the stresses throughout the NXTe airframe

Way back when in 2010, Roger Targett asked for some support with his visionary project for a single-seat, electric, pylon racer. Some initial engineering work was completed early on and the P1E later emerged as a static prototype airframe, Roger having learned many lessons on the way.

Wind forward to 2018, and I had decided to reinvent my aerospace consulting business that I started in 1988. The 250 projects we had contributed to included everything from a new SSDR, through many LAA/GA types such as the Speedtwin Mk2, Centaur Seaplane plus many modifications. Excursions into larger aircraft projects also came and went.

The call came in from Electroflight’s Stjohn Youngman. He had seen our advert in LA, and wanted to speak about the Rolls-Royce ACCEL programme. It was clear from the start that this was a well-managed and properly funded project. The objectives were clear, milestones defined. What it needed matched Acroflight’s core competency –that being experience with lightweight composite structures, stress analysis and compliance validation. The NXT airframe needed modification to facilitate transport. The choices included a removable wing or a fuselage joint. After trade studies and risk assessments the split fuselage was chosen. Dr Bill Brooks undertook much of the analysis. Verification of the analysis-based design was achieved via tests conducted at TWI.

Right Stress analysis of the end plates of the motor stack.

Below right Analysis of the battery case under thrust, torque and gyroscopic loading. Contours show stress distribution, arrows show interface loads.

Below Mapping the aerodynamic pressures on the cowling.

Far left top Purchased from France, NXT kit 10 and the crashdamaged Big Frog around electric vehicles, but loved flying and did his PPL in a Pitts (yes, really!), and he’s been rebuilding a Laser Z200.

Top left Rob Martin working on the bottom wing skin. The team found inconsistencies in work already done, and had to check and rebuild the structure.

Far left bottom Jigging and bonding the horizontal stabiliser into position. The empennage was re-used from the Big Frog airframe after careful inspection and repair. The fin is the only piece of structure not to use carbon fibre.

Left Rob Martin working on the mounting of one of the new, lighter undercarriage legs which were made for the project.

Having moved to the area near Electroflight HQ, he called up Roger after looking at its website. “While they still weren’t ready to employ people, we kept in touch. Then one day I had an email mentioning they had got a meeting with Rolls-Royce. The P1E was designed to be a race aircraft, very small, very light, and consequently used a small power train, around 100 kilowatts. From Rolls-Royce’s perspective that was too small a step. I had some thoughts around electrifying different aircraft and the Nemesis NXT designed by legendary air racer Jon Sharp was one of those that I thought was ripe for conversion to electric. With it, I thought we could look at 400 kilowatts or even a little more.”

The NXT was optimised for high-speed flight, with a thin Natural Laminar Flow wing. The aircraft also used a single 340 litre fuel tank in the fuselage right over the main spar (and CofG), offering plenty of space for batteries.

Stjohn, who went on to manage the programme for Electroflight, adds, “We knew that the programme was tight, and soon realised that if we didn’t have an NXT airframe, there would be no programme. So for three months, we scoured the globe for the remaining kits, and found kit number 10, which was relatively untouched, in France. It came with the crash-damaged remains of another NXT which had raced with a diesel engine under the name Big Frog. We bought both before the programme was officially launched, which was a gamble that paid off.

“But, there was also only one set of paper drawings. We had begun to 3d scan the kit parts, when luckily we were offered help by Colin Boyd, who had bought the rights to the NXT and had all the design CAD files. Suddenly we had every single part in its initial truest form, as it was designed, and it transformed what we were able to do, especially as a huge element was packaging the powertrain to fit the airframe. It probably saved us a year of effort. It also helped reassure Rolls-Royce that the kit parts conformed to the original design. It also helped us undo some of the construction work that had been done to the aircraft, some of which had been modified.”

Roger continues, “We soon realised we needed more help with the construction, so I asked Andy Draper at LAA Engineering for some people I might contact to see if they’d help us and he suggested Rob Martin. Rob is highly experienced in composite manufacturing, and after I kept pestering him, he finally caved in and joined us.

Stjohn adds, “We still needed a build manual though. Rolls-Royce had asked us what documentation were we building the aircraft to – conformity was an important factor to them. There was a series of 14 or so DVDs, made by Jon Sharp where he’s effectively being filmed as he builds the first one, and sometimes you’d get to a point where he says, ‘Oh, by the way, such and such point on the last video wasn’t right, so you should do this instead’. From a conformity point, that made people a bit nervous! So Rob sat down and watched probably 100 hours of video from start to finish and used that to create a build manual for the aircraft.

“In the end, that helped us pick up some non-conformity in some key areas of construction done by builders of the airframe before we got our hands on it. We were looking at the lower wing half, and realised that the ribs had all been

A functional aspect of electric aircraft is the need to land at the take-off weight. The regulations often allow a max landing weight of 95% of the MAUW for IC-powered aircraft. The NXT main gear is retractable and tightly faired for low drag. We undertook a loads analysis using CS-23 requirements. As the NXT has a high-wing loading, the ground reaction load factor (ng) was high with a decent rate of 10 ft/sec. However, the 4130N steel main gear felt heavy, possibly over-designed. Some weight-saving measures were identified and a full FE-based analysis was conducted to identify how much material could come off.

This analysis was done based on the MAUW of 1,379kg. Around 12kg reduction was deemed acceptable, with the caveat that all landings should be wheeler-type (no 3-pointers). The irony of this work was that the MAUW was later raised to 1,450kg, requiring a further round of FE/ stress work using non-linear techniques to show compliance with Limit loads and to predict where failures might occur should those loads reach Ultimate levels.

Moving on (beyond the original remit), we next tackled the energy storage system (ESS). We had already looked at the electric motor mounting structure. The ESS is a structural box supporting a combined mass of around 750kg. It needed to be demountable to allow development and maintenance work on the ESS systems. Structurally, it penetrated the firewall taking up the space previously occupied by the fuel tank. A unique mounting design was imagined, simulated and optimised. This was done in conjunction with MGI Engineering, whose F1 and Formula-E experience proved invaluable.

The ESS is highly complex and proved tricky to manufacture, it is made from carbon fibre with embedded metallic hardpoints for the mountings and motor frame, etc. The tooling face is the inside – to ensure the battery cell modules, cooling, monitoring systems, etc have an accurately defined space. The manufacturing task was undertaken by ATLAS Composites who also had to cope with Covid-19 lockdowns.

The aerodynamic shape of the aircraft was changed at the front, the wide cheeks (for IC engine clearance) were gone. Paulo Iscold, the renowned expert credited with many ‘fast’ achievements provided input for the cowling cooling inlet, internal ducts and outlets. He conducted CFD work on the fuselage to determine if the static margin (yaw stability) had been affected and to generate surface pressure that we could use after mapping in our cowling FEM. Roger and the build team translated our designs into the beautiful shape of the NXTe.

The beauty of working on an E-Conditions project is the speed at which things can be achieved. We were unable (or willing) to forgo peer checks and oversight from our highly capable R-R counterparts.

The final stress and design reports went through the ‘ringer’, a critical review is an important element, especially when the Competent Person is, effectively, self-certifying the aircraft.

Proof of the theoretical performance capability manifested from the successful early flights to the record-breaking runs. A great achievement, one that the whole team should be proud of.

F lying the NXTe

LAA member Steve Jones takes us through a typical sortie…

One look at an NXT is likely to raise the eyebrows, if not the heart rate. When I first saw one in the flesh I remember thinking ‘crikey, is this a good idea?!’

A conventional walk around reveals a very serious piece of aeronautical artistry. All pretty standard until you get to the propeller. Grab hold of it and spin it to check for freedom and lack of play. No ignition system is present, so it cannot fire. This takes some getting used to. Cooling is critical so, while around the front, have a good look into the cooling ducts to the radiators.

Arriving back at the cockpit carefully strap on the parachute then throw a leg over the side, and with a bit of a hop you are standing on a bit of foam – the seat. Carefully shimmy down without connecting with any knobs, switches or the small side-stick. You are aiming for what I would call the ‘Lotus position’, sitting reclined on the floor, legs outstretched, with pedals touching the balls of your feet through your soft shoes. It’s very comfortable and sporty, but tight around the pilot, so make sure you have everything connected and stowed. The cockpit is another work of art, but more Star Trek than General Aviation. The systems are beautifully designed but quite complicated, so a checklist is essential. Turning things on in the wrong order will cause bad things to happen internally. Carefully working through the checklists ends with ‘Inverters 1,2 and 3 to Run’. Until now there has been complete silence, but these switches also control three cooling pumps which you will now hear. The ‘throttle’ (or torque lever or whatever you fancy calling it) is completely closed, so the propeller is stationary, but we are ready to taxi.

We call the Tower for taxi clearance. Normally, they reply with something like ‘how can you taxi when you haven’t started!’ We gently open the ‘throttle’ and the propeller starts to slowly rotate with a faint swishing noise, and we are off. Visibility from the cockpit it extremely poor with nothing available between the left side of the cowling and the right wing tip. The secret weapon is the view from the under fuselage camera which can be selected on the pilot’s instrument screen. Bizarrely, the safest way of taxying is to spend most of the time looking at the screen. This feels very unnatural. If you wish to stop, close the throttle and the propeller will stop rotating, allowing you to coast to a halt. ATC will normally ask if you have a problem because of the stationary prop!

The take-off needs some care. Hold the side-stick back to stop the tail lifting while setting about 10% torque. Check that all three powertrains are delivering the same torque, then smoothly increase to 30% to escalate speed. The power delivery is turbine-smooth. There is no forward view, so concentrate on keeping straight by sighting down the left side of the cowling. Once nicely straight increase torque to 70% and smoothly swap the pull on the stick to a moderate push. The tail will start to slowly rise and a forward view will appear. Now pause – do not be tempted to drag the aeroplane into the air. It has a very abrupt wing-drop at the stall and that would be a disaster near the ground. So relax and wait for 100-110kt of airspeed before positively rotating to convince the aircraft to fly. At a decent height select gear up. It probably will not retract completely, so be ready to do a hefty ‘bunt’ when passing 1,000ft to extinguish the green lights. bonded in the wrong place, plus the layups on the main spar web hadn’t been correctly carried out.”

The whole point of this project is to go as fast as possible so we won’t bother with any cruising! Once the gear and flaps are retracted increase torque to 100%. The aeroplane will continue to accelerate to about 300kt (345mph). Directional stability is poor so a continual effort is required to keep from side-slipping in either direction. It’s quite labour intensive to fly accurately but not unpleasant. Be careful not to stray too far from the runway because you will need to be landing in 8-15 minutes.

Because of the very poor view out the front, the approach is best flown from 1,500ft on a very tight left Base. Idle power early, to slow down to 130kt to select gear down. A firm yaw left and right quickly gets the two green lights to illuminate, then select full flap. The aeroplane is now extremely draggy, so all that excess height we had a few seconds ago can be used to fly a very steep approach at 130kt, in a moderate left-turn, aiming at the runway numbers. This all sounds like madness, but it is a marvellous way of improving the forward view. Still at idle power, raise the nose a tad to reduce speed to 120kt. As we pass about 200ft, adding 5% or so of torque reduces the rate of decent a bit, but is not essential. What is essential is to concentrate on running the main wheels gently on to the runway at between 100 and 110kt as the throttle is closed. The trailing link undercarriage is nicely soft and after touchdown the tail can be held up, with increasing forward stick, to allow an excellent view ahead. At about 60kt the tail will start to fall and with it the view. Now be careful, the only reference to maintain direction is the left side of the runway, so concentrate as we are still travelling pretty fast. Do not brake until at very low speed. Once the speed has reduced, select the taxi camera to help with the tricky return to parking.

Another key figure on the build was homebuilder Andy McKee says Roger. “Andy emailed us just at a time when we really need to push on, and with his beautiful Silence Twister build as his CV, he was definitely in. Andy worked throughout the airframe, but was particularly involved in all the canopy work which included a jettison system modification that Rolls-Royce asked to be created and installed. At the peak of construction efforts, there were four of us on the airframe – Dan Lamb, Nigel Lamb’s son, joined in too.”

Stjohn adds, “When it looked like we’d need stress work done, I had remembered seeing an advert in the LAA mag for John Wighton at Acroflight. John, was brilliant in that he was a light aircraft builder and flyer, but had also been a stress signatory for big aerospace manufacturers. There are very few people in the world whose experience covers such a huge range.”

While Big Frog wasn’t going to fly again, it did donate it’s aft fuselage to the NXTe. Stjohn continues, “Our new kit’s rear fuselage and fin had been assembled and modified. We talked to Colin Boyd about building new parts, but that was clearly going to take time. This was also when we were figuring out how to make the aircraft easy to transport by road – with such limited range and E-conditions restrictions to comply with, flying it was not an option! World-renowned aerodynamics professor Paulo Iscold suggested making the tail removable, and when we looked into the design, Jon Sharp had made provision for a transport joint in the fuselage mouldings. So we cut it in half and added a lap joint to connect the two parts. Once the old tail had been carefully stripped and repaired, we were able to screw it back onto the newer forward fuselage.”

Below Cowlings were modelled in CAD. Side seams use the same piano hinge method for the join, which is popular with homebuilders.

Below right Three stacked motors, inverters, a structural battery case and an integrated cooling system make up the powertrain. There’s half as much battery again inside the airframe that’s hidden from view.

Big Frog also donated all it’s control surfaces. Roger adds, “All the control surfaces were missing from kit 10, and all of Big Frog's had been lightly damaged. While we tried scanning them to verify the integrity of their internal structure and the security of the various control surface mounts, in the end we had to carefully take them apart, checked the structures, then rebuilt them.”

Roger confessed that when it came to fitting the custom carbon cowling for the NXTe, he was sceptical of Stjohn’s instructions. “The final powertrain was still far from being ready to be mounted, but we needed to get on and complete the cowlings. Stjohn just said to cut it to the CAD dimensions and it will be fine. Now, I’m a pencil and paper guy, and I thought there’s no way this will work once the powertrain is fitted, but to be fair, it really did.”

Above left Adding the lap joint structure to make the tail section removable.

Above Roger and Rob inside the fuselage during an epic 14-hour work session to fit the powertrain mount tubes and reinforce the firewall.

Below Carefully ‘cooking’ the completed airframe.

Above right The cockpit was originally designed for two, but for this project, it was built as a single-seater. Note the centre stick.

The powertrain is an astonishing combination of motors, inverters and batteries. The motors, three YASA 750 R units, were low-speed, high-torque units that could be ‘stacked’ one on top of the other. A single shaft slots through all three, and onto that fits an MT electricallycontrollable pitch propeller. The result is a maximum total output of 400kW or about 530hp.

To power the motors there’s Electroflight own battery system. It’s packed inside a case, the ‘energy storage system’, which is a structural element that is split into three individually sealed units. Each battery unit is about 700 volts, completely isolated, and connected to its own inverter, which in turn is connected to an individual motor. In total, over 6,000 individual cells connected together using Ultrasonic wire bonding, are used. Each is a little bigger than an AA battery, and are the sort of thing you’d find in high discharge, fast recharge device like a Dyson vacuum. Keeping everything cool, is nine individual cooling circuits that have full redundancy across the three powertrain systems. Custom radiators were fed air from two small NACA inlets on forward are of the lower cowl.

The biggest modification that was made to the airframe was to allow for this very large powertrain unit to attach into the airframe. Stjohn adds, “What used to be a standard firewall is now a complex piece of preg-preg composite, it looks like the same shape but with a big hole that allows the battery to pass through it. Four carbon tubes are laid up close into the sides of the airframe, at the end of which are large steel pins that the battery slides on to. The whole lot creates a stiff structure, that we think is superior to the original design. It was a massive task for Rob and Roger though, and it was completed in one very long 14-hour day as the all the elements had to be installed in one single, wet lamination.”

Once the composite fabrication was completed, the team built a box around the airframe while it sat in its construction jig, and then cooked the airframe overnight at a carefully controlled temperature to perfectly cure everything, ensuring optimum structural strength.

In the cockpit, you’ll find some pretty standard homebuilding kit, Garmin G3X Touch, Trig radio and transponder and an ASI and altimeter.

Roger adds, “Manuel Queiroz was a big help with configuring the Garmin systems after installation. The airspeed indicator was Steve Jones’ request – he just wanted a simple, single sweep unit that went from 0 to 500 miles per hour. The only one we could find was a from a WWII American fighter, a Thunderbolt I think it was. Ray Hillyer, who designed and built instrument calibration equipment for Smiths, calibrated our ASI and altimeter set up. In action, the pitot static system proved a little troublesome, and we eventually switched to using cockpit static as a number of the NXTe’s internal pressure sensors showed that internal static was very suitable to use. While I remember, another LAA’er that helped in the later stages was John Eagles, who was the programmes CAA licensed signing engineer."

Goals achieved, records set…

By the end of the programme the NXTe had flown 30 times, totalling just under seven hours flight time and covered 2,200km. In that time the systems proved to be amazingly reliable throughout, something that Stjohn credits to the motorsport influences that were strong throughout the development of the powertrain and its systems. Only the undercarriage proved challenging, refusing to fully retract on the first flight. Not a fault per se, just aerodynamic loads on the gear doors proving to be a challenge. The solution on later flights was just to work with it and ‘bunt’ to assist it into the up position. The first landing, which was made flapless and used the full length of Boscombe Down’s runway, used a complete set of disk and pads. Stjohn adds, “We picked Beringer units during the build as they were lighter and we knew they'd give us greater stopping power. We were glad we did, else we would have probably been off the end of the runway!”

Roger sums it up well. “For me, as an LAA Inspector, to have been involved with the ACCEL NXTe programme, has been very special. To develop and build probably one of the fastest kit planes this side of the Atlantic and an all electrically propelled one at that seems remarkable. The whole team has done an incredible job. The icing on the cake is to have come away with five world records.”

Those records included a top speed of 345.4mph over 3 kilometres, flown by Rolls-Royce test pilot Phill O’Dell, and in the hands of Steve Jones, 330mph over a 15 kilometre course, and also a time to climb to 3,000 metres of 202 seconds – that’s over 3,000ft per minute!

Goals achieved, the Spirit of Innovation has retired. It's heading to the Science Museum where it will share space with the Supermarine S6B. Another Rolls-Royce pioneering collaboration, it's not quite as fast as the NXTe, and used that old technology petrol stuff… ■