HopFlyt Hops to the Future

Maryland eVTOL Startup Combines 90-year-old Wing Design with Recent Tech Developments for an Innovative Flying Taxi.

By John M. Doyle

Vertiflite, Jan/Feb 2020

A Maryland startup has combined a 90-year-old aircraft design that was ahead of its time with the latest breakthroughs in composite materials, computational fluid dynamics (CFD) and an innovative tilt-wing configuration to develop an electric vertical takeoff and landing (eVTOL) flying taxi that could navigate high-rise urban landscapes.

HopFlyt, a team of current and former military pilots, engineers and scientists, has come up with a unique concept. The Venturi will be a four-seat, battery-powered, on-demand, piloted aircraft with less noise than a helicopter and low-to-zero exhaust emissions. HopFlyt developers say Venturi will be able to realize the longed-for goal of mobile urban aviation — the flying cars of Star Wars and The Jetsons — with independently variable incident channel wings and canards. Not only will its wings and canards tilt up or down, they can do it independent of each other, eliminating standard flight controls.

The initial goal, said HopFlyt President and CEO Rob Winston, is a sustainable eVTOL that can take passengers and their luggage directly to the airport or building-to-building, skipping traffic and cutting a one-hour car trip to a 10-minute trip by air. Venturi’s goal is to provide “the most efficient, safe, quiet design out there. In fact, that’s our tag line, ‘Giving back time with safe, reliable, point-to-point transportation,’” said Winston.

Located on the Western Shore of the Chesapeake Bay in Lusby, Maryland, the HopFlyt team can call upon years on experience in aviation, engineering and aerospace design. In addition to Winston, an engineer and retired Marine Corps pilot, the three co-founders include his wife, Lucille Winston, a former NASA test engineer; and Rory Feely, an active duty Marine Corps helicopter pilot, who is executive officer of the US Navy’s Test Pilot School at nearby Naval Air Station Patuxent River.

The Growing Demand

A collision of economic, environmental and cultural needs in recent years has driven a demand for urban air mobility (UAM). Increasingly, traffic jams around major metropolitan areas and the airports that serve them have sparked rising frustration among commuters, especially in an era when everything from food delivery to taxi service is acquired quickly through the exploding number of mobile phone applications.

Members of the HopFlyt team behind the full-size tooling
of the eVTOL’s fuselage at the company’s Lusby, Maryland,
hangar and workshop.

Americans spend an average of 276 hours every year commuting to and from work — 26% of them are trapped over two hours a day in traffic during their commute, according to data from the 2016 US Census Bureau, the American Community Survey and Maryland’s State Highway Administration. The economic cost is billions of dollars annually through lost productivity. As climate change rises as a national and international issue, concern about the millions of gallons of gasoline wasted and the noise and pollution created by traffic gridlock are also rising.

Since multinational ride-hailing company Uber announced at the VFS 3rd Annual eVTOL Workshop to create an urban air mobility ecosystem using electric VTOL aircraft, the rush to develop marketable and sustainable on-demand urban air mobility has been gaining steam (see “The Demand for On-Demand Mobility,” Vertiflite, Jan/Feb 2017). Big aerospace companies like Airbus, Boeing and Bell, as well as scores of startups are all designing, building or flying eVTOL aircraft, many of which can only carry one person.

HopFlyt is using a combination of small-scale models, CFD and computer simulation to prove its concepts and develop the software for the Venturi’s flight controls and distributed electrical propulsion system. Winston thinks his team has an array of talent, resourcefulness and a unique collection of old and new technologies that will make Venturi an eVTOL standout.

Autodesk’s CFD imagery of the Venturi at takeoff based on HopFlyt’s engineering computer models. The upper cowling ducts are retractable to reduce drag in forward flight. (Courtesy of HopFlyt)

At NASA, Lucille Winston, who serves as HopFlyt Vice President, developed space-rated hardware for satellites, the International Space Station and the Space Shuttle. She also worked aviation combat survivability systems for numerous US Army, Navy and Marine Corps projects.

Feely, HopFlyt’s Chief Financial Officer and Chief Test Pilot, is an active duty Marine Corps aviator and a military experimental test pilot. He logged over 300 combat hours in the AH-1W Super Cobra and AH-1Z Viper during four deployments to Iraq between 2003 and 2005. Feely also has masters’ degrees in aerospace engineering and technical program management, and has flown a wide variety of high-performance fixed- and rotary-wing aircraft from the F/A-18 Hornet fighter jet to the V-22 Osprey tiltrotor and CH-53 King Stallion heavy lifter.

Rob Winston has also flown a variety of aircraft in his 37 years as a pilot — 32 different types, both civil and military — including 22 years in the Marine Corps flying mostly KC-130 Hercules aerial refueling tankers. He was a test director and operational test pilot for the KC-130J, and also worked program management, advanced development and engineering for the Navy, as well as a former NASA test engineer. Additionally, Winston has designed a handful of experimental aircraft from scratch, including one of the world’s fastest seaplanes.

“In late 2015 to early 2016, I was trying to think through what worked and did not work with the channel wing, the advances in solid state gyros, electric motors and trying to simplify the overall design of a VTOL,” Winston said. The Winstons formed HopFlyt with Feely in December 2016. “With additional research, we were ready to build the first model and we put it together quickly in five months,” Winston said.

“That’s because of democratization in the aerospace industry,” Winston said. “We have the same computing power and programs as the big companies like Lockheed and Boeing. We’re able to do the same type of work and simulations that they can do, with global reach on parts manufacturing.” Thanks to a large 3D printer, HopFlyt is able to build high-end molds and parts very quickly on site. There’s been a huge change in the industry in the past four or five years, Winston said. “Because these computing tools were so expensive, they were out of reach for small companies. Now you can buy them by the month,” he noted.

“Something Old, Something New…”

A unique component of the HopFlyt Venturi design that led to rapid development is the Custer Channel Wing, a largely forgotten attempt to create extremely short takeoff and landing (STOL) airplanes nearly a century ago. Willard Custer came up with the idea of reversing the normal method of powered flight: instead of using the engines to push the aircraft through the air, he used the engine to suck the air across and through the wing, creating lift immediately when engine power was added.

Willard Custer stands beside his CCW-5, which came the closest to reaching production. (Courtesy of the Custer Research Foundation)

Custer got the idea for his creation in the 1920s when he took refuge in a barn during a severe storm. He was stunned and fascinated to see the storm suck the roof off the barn and carry it away. Interested in aviation but not a pilot, Custer began a series of experimental aircraft designs incorporating large channels in the wings, which has been likened to a half-barrel shape. He was awarded 27 patents for his discoveries between 1929 and 1974; he built three different twin-engine aircraft in the 1940s and 1950s with his trademark curved ducts to channel air around the rotating propellers.

He demonstrated how his design could draw enough air through the channel to lift the airplane off the ground with hardly any forward motion, but was unable to interest the military or major manufacturers. “Great design,” said Winston, but the hitch in Custer’s theory was the aircraft’s inability to fly very slow because it only had standard flight control surfaces. “You have to have airflow over your rudder and your ailerons, or you have no control. His plane could fly below 20 mph (40 km/h), but you couldn’t control it below 20 mph.”

The second, 1/5-scale model of the Venturi shown here in the HopFlyt hangar was tested in hover, transition and forward flight in January 2019. (Author photo)

HopFlyt built on Custer’s idea, adding tilting wings and canards with counter-rotating propellers. “One to push the air and when the air’s really moving it becomes much easier to push it even faster. And that’s where part of the efficiency comes from,” Feely explained.

Hopflyt President and CEO Rob Winston shows off a 3D-printed wing section for a sub-scale model of Venturi while standing in front of the tooling for the full-size wing channel. (Author photo)

“The channel itself is actually an airfoil section and when power is applied, air flows over it, creating lift with no forward motion.” With the help of CFD studies provided by software maker Autodesk, HopFlyt was able to measure and assess Venturi’s takeoff thrust. Because of the extra lift, Venturi’s wings don’t have to rotate up to 90 degrees like the V-22 Osprey. Eventually, when a full-size Venturi is completed, “the wings will just go up to 70 degrees for a vertical takeoff because the resultant vector is straight up. About 800 lb [363 kg] of additional lift from these wings will result just because of their shape.” Because the wings and canards rotate and the fuselage stays parallel to the ground, takeoffs and landings in the Venturi will be more like an elevator ride. The craft will also be able to quickly counter sudden gusts of wind because all the wings and canards are controlled independently.

“Something Borrowed, Something… Red”

Venturi propulsion will be provided by the pairs of counter-rotating propellers, mounted towards the rear of each of the two channels in each wing. The 16 specially designed, very thin, six bladed propellers are optimized for takeoff thrust, high-speed flight and reduced noise. Winston got the initial idea from an old NASA study that investigated ways to make commercial airliners more fuel efficient by modifying propellers — at the time, a long-overlooked part of aviation technology.

The Venturi in forward flight, with the rings representing the leading edge of the retracted upper ducts. (Courtesy of HopFlyt)

HopFlyt has two patent filings pending on the unique, channeled tilting wing. “Nobody’s ever done a canard, and a wing that change incident and are independent, left and right,” said Winston. “There are also no standard controls surfaces. There’s no ailerons. There’s no flaps. There’s no rudder, no vertical stabilizer, elevator — any of that,” he said, adding the absent control surfaces will also mean less drag on the aircraft. Autodesk is also partnering with HopFlyt to build a set of propellers for the ground test the company plans to perform in early 2020.

HopFlyt is making composite tooling using 3D printed parts to form 100% carbon graphite aircraft. In October, the company completed the full-size, bright red fuselage tooling, which will eventually be overlaid with composite material to make the actual fuselage, said Feely.

Venturi’s propulsion will be 100% electric for now, but space in the fuselage is being allotted to potentially house a hybrid system. “We are unsure of where battery technology will be in two years when we are ready to fly,” Winston explained, “so we have made provisions in the design for it to be a hybrid electric, with an internal combustion engine running a generator, in order to reduce weight and increase range.”

In contrast to the Custer Channel Wing, the Venturi closes the circle above the wing. This provides additional lift in low speed flight, but the upper shrouds retract radially into the wings to reduce drag for high-speed flight.

Winston explained that the retractable shrouds perform a number of important functions. The shrouds are in place over the props for takeoff, landing and any ground operations only. From a safety perspective, they enclose the props for ground operations. They are also designed to reduce the aerodynamic noise of the props both passively and actively. They increase the thrust of the props by around 20% at low speeds, according to Autodesk’s CFD models. They retract above 50 kt (93 km/h), which reduces the overall of the drag of the aircraft. “The retractable shrouds are a novel feature of our design that gets us an edge on the competition,” said Winston.

Startup Spirit

While HopFlyt faces a raft of competitors, many of them well-financed or backed by large corporations like Airbus and Boeing, Winston said being big or having a lot of money is no guarantee of success. Some of the well-financed eVTOL outfits “are already starting to fold,” he said, because they created big organizations, mirroring big aerospace companies, hiring lots of people and running up “tremendous bills to pay.”

“And of course, we’re doing it right here at a private airport, in a private hangar with virtually no overhead costs,” said Winston. He and his wife live in a fly-in community, where every house surrounding a small airstrip has a hangar. The Winstons’ hangar, in addition to housing at least two small airplanes, serves as HopFlyt’s office, conference room, workshop and test lab.

“We have a true startup mentality here,” Winston said. The team has lots of experience, “but we’re not specialized,” he noted. “Everybody works across the different disciplines in design and engineering and construction.” That team includes Clark Fuller, the mechanical design lead and HopFlyt’s only full-time employee. In addition to handling most of the 3D printing, Fuller created the engineering computer models used by Autodesk for CFD analysis. Other team members are Rei McCauley, a mechanical and materials design engineer; Daniel Perez, a flight controls and modeling intern from the University of Maryland; Scott Zupanic and Peter Allen, both senior research engineers; and research engineer Neil Winston.

“It’s pretty awesome going from ideas, to prototypes in 2-3 weeks here, getting stuff in the air really quickly,” said Fuller. Feely said the team 3D printed the very first prototype part for the 1/7-scale model of the Venturi in July 2017, “and then we flew in December, so it was five months from ‘Hey can we do this?’ to ‘Holy smokes we just did this.’ And then the next thing we said was ‘let’s improve upon the design’ and then we built another one.” The larger 1/5-scale model was tested in hover, transition and forward flight in January 2019. “We plan on flying the 1/4-model in June 2020,” Feely said.

About the Author

John M. Doyle spent 27 years as a writer and editor with the Associated Press and Aviation Week & Space Technology. As a freelance defense and aviation journalist, he writes frequently about the manned and unmanned vertical lift aircraft needs of the military, homeland security and private sector. His website is www.4gwar.wordpress.com/ and he can be reached at jmdoyle52@gmail.com.

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