Zuri’s Technology Demonstrator 2.0 Engine, Built by EdgePerformance

Seven questions for Thomas Hauklien

Thomas Hauklien founded EdgePerformance in Notodden, Norway, in 2006. The company has sold about 1,600 engines and 3,500 fuel injection kits for Rotax-powered light aircraft, and its ThrustVik engines, rated at 185 to 210 hp, power uncrewed aircraft up to the 1,350 kg class. Hauklien is CEO and founder, and a test pilot with about 3,500 hours. Answers have been edited for length and clarity.

What is the hardest part of running a piston engine in a hybrid-electric aircraft?

Cooling. On a conventional aircraft engine the propeller blows air over the engine and keeps it cool. In a hybrid system there is no propeller, so that airflow has to come from somewhere else. That is the biggest obstacle with an engine in a hybrid system, and it will be for sure the biggest one here.

The engine drives a generator rather than a propeller. What does that change in how you tune and test it?

Not a great deal beyond the cooling. The load profile of a generator can differ from that of a propeller, but the ECU runs closed-loop control and can correct that. After the initial load test runs we extract the ECU data and make fine adjustments to the mapping.

What did EdgePerformance change from the standard Rotax 912 ULS?

We start with a 912 ULS that is new from the factory. We then tear the engine apart and replace the camshaft, pistons and cylinders. We convert the ignition to an ECU-controlled system with variable ignition timing and install our own fuel injection system. For this application the gearbox has been replaced by a direct-drive unit, because the generator needs a higher PTO speed than a propeller.

What fuels can it run on?

The engine is designed to run on MOGAS RON 98 and on ethanol-blended gasoline with any ethanol content from 1 to 100 percent. A flex-fuel sensor measures the resistance of the fuel, which tells the ECU the actual ethanol content, and the ECU changes the amount of fuel injected in real time.

In an uncrewed aircraft there is no pilot to notice a problem. How does that change engine monitoring?

It requires more sensors, more data gathering, and an ECU smart enough to monitor that data in real time and make its own decisions, based on sensor input and on sensor failures.

How was the engine tested before it went to Zuri?

Every engine we build runs for 60 to 90 minutes on our engine dyno. It has to complete a break-in procedure and deliver correct and consistent performance, which is logged in our database and compared to baseline values. Our dyno is a water brake, which we use for endurance testing and repeatable accuracy. It behaves much like a generator, so the test is very representative of generator operation. In this case the first runs changed nothing in the hardware or calibration, because the base engine is an already proven and well-tested platform. What was new for us was running this specific engine on ethanol.

Where does EdgePerformance’s work end and Zuri’s begin?

The engine supplied to Zuri is based on our proven design; the ethanol option and the direct-drive PTO were unique to this application. We have focused entirely on the propulsion system up to the PTO shaft. Everything after that is Zuri.

Inside the integration: the Zuri side of the shaft

Past the PTO shaft, the work is Zuri’s. Radim Laga, Electrical Systems Lead, and his team turn an engine into a hybrid-electric power unit.

Sensors and calibration. “We added more precise sensors on the engine and modified the wiring to the ECU,” Laga says. “For example, we replaced the head temperature sensors with more precise ones and did the ECU wiring and calibration for them. There is also a custom fuel level sensor for the tank, which we set and calibrated in the ECU.” The ECU itself earns praise: “It lets you customize the sensors, controls, logs and communication. We are happy EdgePerformance chose this particular ECU, because it is very user-friendly.”

Started by the generator. In TD 2.0 the engine has no starter motor. The generator spins the engine up, and the starter comes off to save weight. Zuri’s own genset control unit, developed in-house, manages the whole power unit: it commands the electronic throttle valve using operating parameters from the ECU, tells the motor controller how much electrical power the aircraft needs from the generator, and handles the electrical protections. “That is a very simple explanation,” Laga says, “but the genset control unit is basically the main control unit for the whole genset.”

The cooling question. At idle on the Prague rig, the engine confirmed three things: it runs correctly as delivered, the oil and water-cooling Zuri designed for it holds, and the sensors feeding its controller read correctly. Full power is the next question, and it is the one Hauklien names first. “We have prepared the engine for power and thermal tests at a dedicated engine facility,” Laga says. “The main goal is to find out how much air we will need to keep it in the operational temperature range.” The engine will run on E85, 85 percent ethanol and 15 percent gasoline. Zuri expects 20 to 30 percent less heat generation than with standard gasoline, a figure the tests will confirm or correct.

Finding the fuel was its own small project. In Europe, refineries sell E85 in minimum quantities of around 1,600 liters. Zuri found a supplier that sells to racing teams in 55-liter lots.

Once the thermal data is in, Zuri will modify the cooling system and the fuselage to deliver that airflow, and finish integrating the generator with the motor controller and the genset control unit, which is on hold until the thermal results are known.

Built for civil and defense missions

EdgePerformance’s engines are classed as dual-use items, so certain exports require a license. Zuri builds on a European, ITAR-free supply base and names its suppliers. This engine configuration contains no ITAR-controlled components.

The same qualities matter to both civil and defense missions. Fuel flexibility means an operator can run on premium automotive gasoline or ethanol blends of any strength, with AVGAS 100LL as an occasional fallback, whether at a regional airfield or a forward logistics site. Continuous sensor monitoring and autonomous fault handling by the ECU are what allow an aircraft with no pilot on board to be trusted with a load. And a proven base engine, tested against baseline on every unit, keeps risk out of the part of the aircraft that is not new.

“It requires more sensors, more data gathering, and an ECU smart enough to monitor that data in real time and make its own decisions.”

Thomas Hauklien

TD 2.0’s architecture carries directly into Zuri’s uncrewed cargo VTOL, which will carry 115 kg across a 679 km design range, 569 km with a full 30-minute reserve, taking off and landing vertically without a runway.

What comes next

The engine’s next public outing is Future Forces Exhibition and Forum in Prague, 21 to 23 October. After the show it goes to a dedicated test facility for power and thermal testing under load on E85. TD 2.0’s first flight is planned for Q2 2027, when ground test says it is ready.

“The main goal is to find out how much air we will need to keep it in the operational temperature range.”

Radim Laga, Electrical Systems Lead, Zuri

… notes from SP,

Here are additional questions we from AAM Nation asked  EdgePerformance and Zuri

Answers below in your order. Those on the engine itself are from EdgePerformance; those on integration and testing are from Zuri. Where a figure depends on the full-power thermal test, which has not yet run, we say so rather than estimate.

What specific mechanical and control-system changes were made to the Rotax 912 ULS for constant-speed generator duty, rather than its conventional aircraft-propulsion role?

EdgePerformance starts with a 912 ULS that is new from the factory, tears the engine apart, and replaces the camshaft, pistons and cylinders. The ignition is converted to an ECU-controlled system with variable ignition timing, and EdgePerformance installs its own fuel injection system. For this application the gearbox has been replaced by a direct-drive unit, because the generator needs a higher PTO speed than a propeller. Whether the load is a generator or a propeller, the engine load increases the same way: the MAP sensor registers the change and the ECU adjusts fueling and ignition timing to maintain power and air-fuel balance. Running the generator is very much like running the engine on a water-brake dyno. After the initial load test runs the ECU data is extracted and any fine adjustments made to the mapping.

In particular, please detail changes to operating RPM range, ECU/calibration, lubrication, valve train, crankshaft or gearbox arrangement, and expected overhaul interval.

• Operating range: rated 93.0 kW (124.7 hp) at 5,800 rpm. Rotax engines are designed to run at or below 5,500 rpm continuously, or at full takeoff power at 5,800 rpm limited to five minutes.
• ECU and calibration: closed-loop control with variable ignition timing. The engine does not know whether it is coupled to a dyno, a propeller or a generator; engine load is engine load.
• Lubrication: no changes on this engine model. XPS 5W-50 oil.
• Valve train: camshaft only.
• Crankshaft: stock.
• Gearbox: removed, replaced by a direct-drive PTO.
• Overhaul: TBO is 2,000 hours or 15 years, whichever comes first. Service intervals are 100 hours, or 50 hours when operated on AVGAS 100LL or on fuel containing 10 percent or more ethanol, to get rid of the ethanol and lead deposits in the oil

What continuous and peak electrical power can the engine-generator set deliver at the DC bus, and what are the corresponding fuel-consumption figures?

The engine’s shaft rating is 93.0 kW at 5,800 rpm. Continuous and peak power at the DC bus, and the corresponding fuel consumption, are outputs of the full-power thermal test on E85, which follows Future Forces Exhibition and Forum. What Zuri shares from those results, and when, will be decided once the data is in.

Please provide brake-specific fuel consumption or electrical-specific fuel consumption at representative load points, including take-off/climb-equivalent, cruise, and battery-charging operation.

These are measured in the same test, whose scenarios are based on typical and emergency flight-profile missions and which records fuel consumption alongside the thermal data. No figures are stated before they are measured.

How is the engine cooled during VTOL and low-airspeed operation, when there is limited or no conventional ram-air flow and no propeller wash?

There is no propeller on the engine, so the airflow has to come from somewhere else. Zuri has engineered the NACA duct and positioned the radiators in such a way that it is possible to cool the genset during the vertical takeoff phase as well as during horizontal flight. The ethanol-rich fuel also helps to get rid of excess heat from the engine. At idle on the Prague rig the oil and water cooling Zuri designed held; the full-power test measures how much air the engine needs at power, and the cooling system and fuselage will be modified to deliver that airflow.

What are the cooling-system architecture, fan or ducting requirements, coolant/oil temperature margins, and anticipated performance in hot-day, high-altitude, and hover conditions?

The cooling architecture is described in the previous answer. Ducting requirements, temperature margins and performance in hot-day, high-altitude and hover conditions are what the thermal test is designed to establish; Zuri will not state them in advance of the measurement.

What validation has been completed for E85 and E100 operation, and how does ethanol use affect engine durability, cold starting, fuel-system materials, lubrication, emissions, and power output?

• Validation: this engine has run on E10, E85 and E100 for 30 minutes on each blend to verify that the ECU makes the correct changes based on ethanol content. Durability is verified on EdgePerformance’s other engine models and projects without issues.
• Cold starting: with an ethanol concentration above 25 to 40 percent, cold starting below freezing temperature becomes increasingly difficult.
• Fuel-system materials: the only parts of the engine and fuel supply system needing modification to run on ethanol are the fuel hoses, which are PTFE-lined under stainless or nylon braiding.
• Lubrication: unchanged.
• Emissions: the engine runs lean and efficient. E100 virtually eliminates tailpipe particulate matter and drastically cuts net lifecycle greenhouse gases. Due to the high oxygen content and combustion dynamics, un-optimized or cold engines running E100 can see an increase in acetaldehyde and nitrogen oxide emissions.
• Power output: a normally aspirated engine typically makes about 3 to 7 percent more power on E100 than on regular gasoline, provided the engine is tuned to take advantage of ethanol’s higher octane rating, which allows more aggressive ignition timing. Ethanol also absorbs more heat as it vaporizes in the intake tract, which cools the air-fuel charge and increases air density inside the cylinder.

Is the system able to detect and automatically compensate for varying ethanol content or fuel quality in operational use?

Yes. The engine is designed to run on MOGAS RON 98 and on 0 to 100 percent ethanol blends. A flex-fuel sensor measures the fuel, which tells the ECU the actual ethanol content, and the ECU changes the amount of fuel injected in real time.

How is the generator electrically integrated with TD 2.0’s battery and distributed propulsion system?

The engine drives the generator, and the generator also starts the engine, so there is no starter motor. Zuri’s genset control unit, developed in-house, commands the electronic throttle valve using operating parameters from the ECU over CAN, tells the motor controller how much electrical power the aircraft needs from the generator, and handles the electrical protections. Power from the generator and the batteries is distributed via high-voltage power distribution units, which also guarantee a redundant power supply to each propulsion unit. The battery buffers the peaks of takeoff, transition and landing and recharges from the generator in cruise; if the generator stops, the battery’s reserve carries the landing.

Please explain the generator’s voltage and power-electronics architecture, fault isolation, redundancy, battery-buffering strategy, electromagnetic-compatibility approach, and the aircraft’s behavior following a generator, inverter, or propulsion-motor failure.

The architecture is as published: a series hybrid in which the battery buffers the peaks of takeoff, transition and landing and carries the landing if the generator stops, with redundant power distribution to each propulsion unit and redundant fly-by-wire keeping the aircraft controllable after the loss of a rotor. The detailed power-electronics design, including bus voltage, fault isolation and the EMC approach, is not something Zuri publishes.

What are the pass/fail criteria for the upcoming E85 loaded power and thermal tests, and when do you expect to publish measured results?

Several test scenarios are planned, based on typical and emergency flight-profile missions. This means not only the thermal parameters, temperatures and the airflow needed to cool the engine, but also the transient response and fuel consumption. What Zuri shares from the results, and when, will be decided once the data is in.