Testing turbulence for a landing Cyclone

In a wind tunnel adjacent the Ottawa International Airport, a small team of researchers is measuring the impact of air wake on helicopter landings on the Royal Canadian Navy’s (RCN) interim auxiliary oiler replenishment (AOR) ship.

The National Research Council of Canada has constructed a 1:50 scale model of the Royal Canadian Navy's interim auxiliary oiler replenishment ship. NRC Photo
The National Research Council of Canada has constructed a 1:50 scale model of the Royal Canadian Navy’s interim auxiliary oiler replenishment ship. NRC Photo
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Next fall, Quebec shipbuilder Chantier Davie is expected to deliver an at-sea sustainment ship to the RCN to help bridge a gap between its recently retired Protecteur-class AORs and a new fleet of joint support ships.

Since every class of ship generates unique wind conditions above and to the sides of its flight deck, delivery of a new ship will mean a new operating environment for Royal Canadian Air Force pilots of the CH-148 Cyclone, the RCAF’s maritime helicopter currently undergoing operational test and evaluation as it prepares to enter service.

On a rotating pad in the centre of the nine-metre wide wind tunnel, researchers with the National Research Council of Canada (NRC) have constructed a 1:50 scale model of the 185-metre replenishment ship. Over the next two weeks they will conduct a series of tests to measure and better understand the air wake forces on an approaching helicopter.

“The flow field that develops around a ship when the wind is blowing or the ship is steaming [can create] an air dynamic environment that is very complex,” said Alanna Wall, a research council officer with the NRC, the government’s subject matter experts on ship wake research.

Researchers are employing a novel rotor measurement rig (see foreground) that holds a model of a CH-148 Cyclone above or to the side of the flight deck at varying heights. NRC Photo
Researchers are employing a novel rotor measurement rig (see foreground) that holds a model of a CH-148 Cyclone above or to the side of the flight deck at varying heights. NRC Photo

As wind flows over the ship, it creates a separation bubble behind the superstructure, known as a shear layer, where the wind flow slows and can even reverse, she explained. Transiting from fast air into the bubble, which is moving with the ship, is one of several factors that can complicate helicopter landings.

“The severity of that turbulence and the shape of that bubble changes with the ship design,” she said. “This [wind tunnel] layout allows us to measure the forces acting on the helicopter and then use that to really understand what effect the air wake of the ship is having on the helicopter.”

To capture data about helicopter performance in that turbulence, the researchers are employing a novel rotor measurement rig that holds a model of a Cyclone above or to the side of the flight deck at varying heights and can rotate its blades at 11,500 revolutions per minute, a high speed necessary to “mimic the wind behaviour profile that a pilot might encounter at sea,” said Sean McTavish, a research council officer.

The testing will also help the Navy and Air Force determine where best to place anemometers on the ship to improve the accuracy of the instrument’s wind speed readings.

“All ships have anemometers to sense the wind speed at sea,” said Wall. “Those anemometers are biased by the presence of the ship which distorts the flow. So we can sense those distortions and make the measurements at sea more accurate.”

The NRC’s findings will be provided to the navy planners and air force test pilots. The RCAF’s Helicopter Operational Test and Evaluation Facility (HOTEF) at 12 Wing Shearwater, N.S., is currently conducting operational trials with a CH-148 embarked on HMCS Montreal.

The scale model of the replenishment ship, which took about three months to build, was designed and manufactured by the NRC’s fabrication services based on specifications provided by Chantier Davie.

The scale model of the replenishment ship was designed and manufactured by the NRC's fabrication services based on specifications provided by Chantier Davie. NRC Photo
The scale model of the replenishment ship was designed and manufactured by the NRC’s fabrication services based on specifications provided by Chantier Davie. NRC Photo

Last November the federal government signed a contract with Project Resolve, a consortium comprised of Davie and three partner companies, to convert a commercial container ship, MV Asterix, into an AOR, complete with a rear helicopter deck and two hangers designed for the Sikorsky CH-148 Cyclone and able to accommodate the Boeing CH-147F Chinook.

The deal was struck after the RCN was forced to retire its two remaining Protecteur-class replenishment ships in September 2014 after one sustained serious damage in a fire earlier that year and the other showed levels of corrosion that had degraded its structural integrity. Though the navy is in the process of acquiring two joint support ships, known as the Queenston-class, to resume at-sea logistics support and sealift capabilities, the first is not expected to be delivered until 2020.

In the interim, arrangements have been made with the Chilean navy and Spanish navy to provide periodic at-sea support to Canadian Forces operations and training exercises on the west and east coasts, respectively, until the Asterix is delivered in late 2017.

Originally commissioned in 1970 to test short takeoff and landing aircraft–many de Havilland planes underwent early testing here–the NRC’s largest wind tunnel has since become an experimentation centre for custom ships, transport trucks and vehicles, as well as bridges, buildings and other infrastructure. And its unique approach to modeling conditions vital to end users such as RCAF test pilots has given it prominent standing among its North Atlantic Treaty Organization (NATO) and allied peers.

“A lot of other countries do this work computationally; we are the only country that is doing it experimentally,” said Wall, highlighting an approach that makes Canada an attractive partner for collaboration.

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