With 3D printing, brushless dc motors, and high-speed digital controls, Domin is at the forefront of revolutionizing how the aerospace industry uses hydraulics.
Domin is working towards making aerospace more sustainable by decreasing the weight of onboard hydraulics. Image: Adobe Stock
Aerospace dramatically influenced hydraulics’ evolution in the last century. The move from manual to hydraulic actuation happened quickly in the 1950s and 1960s, yet fundamental hydraulic designs in aircraft have not changed as much since.
“If you look at some of the pumps on the 787, for example, they are probably identical to the ones that were on the 747 in terms of design — even though there were 40 years between them — for several reasons, not least of which is that they work and they’re good,” said Simon Jones, CTO of Domin.
Today, many aircraft have three central systems, each with multiple pumps and reservoirs. Power transfer units may be present if a pump fails to transfer pressure between different systems. Each actuator also has redundancies with separate hydraulic and electrical systems. Plus, all this equipment requires extensive piping that adds immense weight, complexity, and assembly time.
“What you end up with are planes lugging between one-and-a-half and two-and-a-half tons of hydraulic equipment around with them all the time and burning hundreds of kilos of fuel per flight just to lift these hydraulics,” said Jones. “They generally all have two-stage valves constantly taking a few kilowatts of quiescent loss the whole time you’re flying. For an eight-hour flight, that’s a huge number of kilowatt hours just to power the hydraulics to do nothing. So, you’re caught in this world where hydraulics are great, but having that hydraulic system on board is hugely costly in terms of infrastructure, size, weight, and power.”
Jones has an aerospace background and previously worked on gas turbines to reduce the weight of certain parts by tens of grams, even single-digit grams at times. He was hard-pressed to take every little piece of weight he could off the engine to get more out of the fuel. Every hundred grams of weight salvaged improved fuel burn by 0.1% and saved the company hundreds of thousands.
“The scale of waste in terms of the amount of energy needed to carry huge systems around on these aircraft is just baffling,” said Jones. “Hydraulics is great, but electrified systems are also great. The best solution, therefore, should be bringing those two together and using the best of hydraulics without the clunky central stuff, giving it full digital control, and putting it into an electrified system.”
Domin poses to decentralize hydraulic systems and move toward hybrid-electric aircraft to leverage the best of both worlds while shrinking components, reducing weight, and decreasing energy consumption. Jones stated that hydraulics persists because of its power-dense force transmission but doesn’t lend itself well to lightweight electrified architectures, where digital signal transmission enables asset monitoring and optimization.
Domin is validating its compact electro-hydraulic actuation technology to replace traditional, bulky hydraulic components in aircraft. Image: Domin
“The other nice thing is that you can manage redundancy by having multiple units or multiple redundant systems within a given actuator, for example. You can also locally manage energy storage, harvesting, and reuse,” he said.
However, capturing and reusing energy may not be feasible for all systems. For example, braking would be challenging due to its immense energy requirements, whereas flight controls have fully reversible cycles. Today, a big pump applies constant pressure through valves that are always on alert to lift and lower the flight control surfaces. This could be an opportunity to manage energy and eliminate losses so that no energy would be consumed.
“The reason it’s not done today is because it’s really hard to shrink hydraulics and get them to a point where they are efficient, small, compact, and lightweight. If you buy a pump, a valve, and an accumulator and bring all those together, you then have a big block. It just doesn’t work.” said Jones. “If you look at electrohydrostatic systems today, they look like a Frankenstein thing. There’s a few flying, but it hasn’t taken the industry by storm yet because it’s big, clunky, and generally prone to reliability issues.”
Since hydraulics don’t naturally shrink very well in this case, electromechanical actuators may seem like the sensible solution. However, for applications with high levels of shock, vibration, dirt, and temperature fluctuation, as is common for aircraft brakes, landing gear, and flight controls, such solutions can jam and compromise safety. They also must be sized according to the largest force they’d have to exert and hold, drawing power the entire time.
“There have been billions spent on electromechanical systems for aerospace, and there are almost none flying. And the ones that are aren’t competitive with traditional hydraulic solutions,” said Jones. “So, we’ve identified this niche in the market where everyone wants to use less energy and have less weight. Everyone wants these modern digital systems, but no one can shrink and integrate traditional hydraulic systems nicely. That is the sweet spot for us.”
Shown here is an exploded view of Domin’s S4 Pro, its smallest direct drive servo valve. Image: Domin
Domin’s core technology comprises ultra-compact, high-performance pumps and high-speed switching valves. The company uses enabling tools, including metal 3D printing, to develop hydraulic products that allow electricity to generate and modulate pressure in a very complex, high-bandwidth manner. Though large-scale commercial aircraft are on their radar, the team has progressed in validating its products on helicopters.
“We’ve done a lot of work on helicopter braking systems. Today, they’ve got a pump on the top deck and pipe all these things down to the cockpit. The pilots have some pedals, and they control some valves. Then, there are more pipes down to the brakes, and you have a separate parking brake with another pump and accumulator. All those things can come out, and we can drop in a really small — the size of an apple — little hydraulic system next to the brake. That’s all control over wire, effectively, and we’re talking tens of kilos of weight savings, which is significant on one of those aircraft,” said Jones.
But Jones and his team aren’t just looking to compete in the market — they want to make a positive impact on society while decreasing humanity’s footprint. He isn’t convinced that hydrogen and other solutions will be ready for a long time, so he’s thinking about what he can do right now to improve flying today.
“There’s obviously a trend of people who are motivated to look at the sustainability of things and the scarcity of resources,” he said. “But being sustainable doesn’t mean that people shouldn’t fly. It just means that we should make flying easier with a lower overall penalty to the environment.
“Engineers have the power to increase prosperity across the world. We have the power to deliver things that allow more people to do great things and give more people choices. We would love it if we made technology that meant there weren’t necessarily fewer flights, but more people would get on a flight and go and connect with people or see the world or travel — but while recognizing that the [resources] we have in the world … are scarce. Therefore, we should do our best to deliver things that let more people experience all that, but at a lower penalty than today. That’s where we’d love to get to.”
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