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Honeywell’s investment in a hybrid electric version of its HTS900 turboshaft engine could eventually pay off for its conventional helicopter customers, too.
That’s according to Bryan Wood, senior director of Honeywell’s hybrid electric and electric propulsion programs. Wood spoke to Vertical in advance of HAI Heli-Expo 2019 in Atlanta, Georgia, where the company displayed a prototype HTS900 turbogenerator in early March.
The 1,000-shaft horsepower class HTS900 is an evolution of the LTS101 engine originally developed by Lycoming. It’s currently installed on the Eagle 407HP — a re-engined version of the Bell 407 — and the Kopter SH09 helicopter now undergoing certification flight testing in Switzerland.
Denver, Colorado-based XTI Aircraft Company also intends to use the HTS900 in its hybrid electric TriFan 600 vertical takeoff and landing (VTOL) aircraft. That’s the first confirmed hybrid electric application for the HTS900 turbogenerator, although “there are definitely more [companies] than that that we’re currently working with,” Wood said.
To adapt the engine for hybrid electric applications, Honeywell modified the engine control unit and gearbox and added two compact, 200-kilowatt generators. Now, the company is in the process of pairing the prototype with electric motors, motor controllers, and batteries for a more complete demonstration model.
These are the only modifications that Honeywell has made to the engine to date. However, Wood said the company is also evaluating potential modifications to the core that could alter some engine shutdown requirements.
Currently, HTS900 operators are required to perform a two-minute engine cool down at idle, followed by a 10-second post-shutdown “purge” that relies on the aircraft battery to power the starter motor. The procedure is a legacy of instances in which carbon build-up on oil jets led to distress of the number 2/3 bearing pack in LTS101 engines. Honeywell has retained the procedure despite intervening design changes to the rear bearing support housing.
When asked about this purge requirement in the context of hybrid electric operations, Wood said, “We’re looking at potential modifications to eliminate that.” Any such changes could “absolutely” flow back to conventional helicopter operators, he said, although he could not speculate on a timeframe for this.
Contemplating entry into the urban air mobility (UAM) space has also forced Honeywell to evaluate its manufacturing capabilities in ways that could eventually yield benefits for all HTS900 operators, he said. UAM proponents forecast an eventual need for tens of thousands of electric or hybrid electric VTOL aircraft to serve as air taxis in crowded cities.
As Wood pointed out, “We’re not used to dealing with manufacturing volumes of that size in the aerospace industry. So we are currently looking at changes in regards to how we source material, how we manufacture our engines, different design flow changes even to our shop floor, to really figure out how we’ll be able to handle the level of volume we’re talking about in this space.”
While many companies are pursuing fully electric VTOL aircraft for UAM applications, Wood said that Honeywell expects hybrid electric models to dominate for at least the next 15 to 20 years, based on current and projected battery technology and Federal Aviation Administration fuel reserve requirements (currently 20 minutes for helicopters operating under visual flight rules).
“Beyond that, even if you do have significant leaps in battery technology and there’s some lax that’s shown on behalf of regulatory bodies in regards to mission reserves, you can only most likely complete a 50- to 60-mile round trip without having to recharge,” he said. “We’ve talked to quite a few [aircraft developers] that are interested in doing . . . San Diego to L.A., or Silicon Valley to San Francisco for example, and that will be very difficult to do that with an all-electric vehicle. So I think there will always be a market for hybrid.”