Hill Helicopters successfully ran its clean sheet GT50 engine to 55% N1, bringing the first new light turbine helicopter engine in four decades to life. Hill announced the achievement today during its live HX50 Update and AMA (ask me anything) event on its YouTube channel, where it also played the video of the first engine test.
The GT50 engine is specifically developed to power the Hill HX50 — a ground-up, five-seat light helicopter design — as well as future Hill-designed aircraft.
The test took place at 3:51 a.m. British Summer Time (BST) on July 20 at Hill’s Production Centre 1 facility in Stafford, England. The starter accelerated the company’s first GT50 prototype to 55% N1 (27,000 RPM), and the engine ignited on the first attempt. The engine maintained 55% N1 for five minutes and was briefly brought up to 33,000 RPM with no issues raised beyond a minor lubrication set up error that was quickly remedied. In a conscious conservative approach to the first operation, starter-driven cold-crank tests were performed prior to fuel introduction and ignition.
“Just getting a new engine design to start, fire up, and self-sustain can often be quite a difficult thing,” Jason Hill, the company’s founder and CEO, told Vertical Plus. “There’s a lot of uncertainty around fuel systems, combustion, the matching between the compressor and the turbine stages, and all of those things can often conspire against you for it to just not start or go at all. So, for ours to literally just fire up and work as it should on the first attempt was an amazing experience and a massive technical achievement.”
Compounding the level of achievement is the fact that the Hill Helicopters team designed and manufactured the engine’s 438 precision parts in-house, from tooling, forging, casting, milling, and finishing to testing and assembly. “Nothing but raw materials came in the front door of the factory,” Hill emphasized.
Next Steps
The initial GT50 prototype was instrumented to measure temperatures, pressures, rotational speeds, flow rates, and vibration. The resulting data revealed no surprises, Hill said, allowing the engineering team to now focus on expected tuning work to maximize power as it continues phased testing.
“The next stage now is to systematically work the engine through its entire speed range and through its entire power range, and do that at incremental steady-state speeds,” Hill told Vertical Plus. Acceleration and deceleration ramps will come after, he added, where data collected during this phase will be used to map the full-authority digital engine control (FADEC) and develop the engine’s automatic-start sequence.
The HX50 will then undergo a certification endurance test before being torn down, inspected, rebuilt, and connected to the power turbine. It will go through all the phases of testing again with the power turbine before progressing to the aircraft, Hill said.
Hill expects to install the GT50 engine in the HX50 airframe for full aircraft ground test in early 2027. If all goes as planned, he hopes to conduct the HX50’s first flight around April 2027.
A Cost-Competitive Design
Hill initially announced the company’s plans to build a ground up engine for its bespoke HX50 light helicopter design in November 2020.
“To make the Hill HX50 powerful, capable, and affordable, we needed a 500-horsepower turbine,” Hill told Vertical Plus earlier this year. “While there are some really good turbine engines in that class, they are appallingly expensive. Really, there is no good reason for them to be that expensive. It’s that there’s just no competition. If we wanted to make the HX50 at a price point that was going to really stimulate the general aviation market and open new opportunities for commercial operators, we had to make the price point more accessible.”
Hill’s solution was to design, manufacture, and build the aircraft’s engine, which “allows us to fully control the cost,” he said.
The Hill GT50’s design targets include 400 hp continuous power, 440 hp take-off power for five minutes at up to 10,000 feet and ISA +15°C, and 500 hp emergency power for 30 seconds. The engine has a target weight of 220 lbs. (100 kg), target fuel consumption of 35 US gallons per hour at maximum continuous power, and a published time before overhaul (TBO) target of 5,000 hours or 20,000 cycles, on condition. It will also feature a dual-channel Hill FADEC with manual reversion.
