Set against military-style, charcoal-green paint, the most visually striking features of the CH-47D Chinooks from Rotak Helicopter Services are their neon tail decals and mid-body stripes.

But during wildfire season this summer, the most notable features may be their massive, expandable, hydraulically-powered FT11K underbelly tanks.

“It’s the first of its kind,” said Ely Woods, founder and general manager of the Anchorage, Alaska-based company. “And probably the biggest advantage to the tank is that it’s the lightest on the market — and the fastest to get off the aircraft. We can go from a flying tanked helicopter and then convert it back to a bucketed helicopter and put it back in the air in about 40 minutes.”

In early 2022, Rotak contracted Helitak Firefighting Equipment of Australia to develop an underbelly tank that closely resembles the tanks Helitak has designed for about 20 other light, medium and heavy-lift helicopter platforms.

The idea was to maximize the CH-47D’s carrying capacity by using a lightweight external tank, allowing Rotak to carry additional personnel, supplies, a Bambi water bucket, and even a land vehicle, in the aircraft’s formidable interior cargo hold.

“It just gives us more options,” Woods said. “And it’s a lot less modification to the aircraft, which was a big deal for us. The Helitak tank requires no structural modifications to install.”

At press time, final testing was underway on the 2,905 US gallon (11,000 liter) tank, and Federal Aviation Administration approval was said to be imminent.

Rotak is the FT11K launch customer and plans to use it on two CH-47D Chinook rotorcraft it acquired from Columbia Helicopters in July 2022. Design and manufacturing were carried out in Australia, with installations completed in Camarillo, California.

The two helicopters are now based in Mesa, Arizona. Rotak intends to deploy them on firefighting contracts in the U.S. this year before potentially expanding overseas.

“Right now, our focus is right here in the U.S.,” Woods said. “We’re going to employ these, test them out and refine it as best as we can.”

The FT-11K tank is said to be the first belly-mounted tank developed for the CH-47D Chinook, which has become a key platform in the firefighting capabilities of several U.S. operators.

When empty, the tank folds like an accordion and measures just 14 inches (36 centimeters) high. It expands hydraulically into a trapezium shape as it collects water with a snorkel and can reach its full 26,455-pound (12,000-kilogram) capacity in a mere 60 seconds.

Pilots use the Helitak Fire Tank Controller and Cyclic Control to release the water load, dropping it in as little as four seconds, or as many as 40 seconds.

Though designed as an external tank, it can also fit within the CH-47D interior cargo hold.

We ended up removing three inches from the design to make that happen,” said Jason Schellaars, CEO and chief engineer at Helitak.

This versatility may prove a difference-maker as Rotak competes for firefighting contracts, building on its previous efforts with water buckets on Kaman K-MAX aircraft.

The K-MAX is ideal for powerline construction and telecom tower installation and repair —Rotak’s core business, until recently. But the Chinook is a formidable new tool in its belt.

“There’s obviously going to be some competitive value there,” Woods said. “But really what the motive was for getting involved with fire with these [Chinook] aircraft is that it’s the biggest, fastest, best thing you can put on it. The [U.S.] Forest Service and other agencies have a liking for these larger aircraft that can move quickly.”

Helitak has designed similar expandable tanks for the Sikorsky S-92, UH-60 and S-70 Black Hawk, as well as the Airbus AS332 and H225 Super Puma, and the Boeing Vertol CH-46 Sea Knight.

Its small- and medium-lift tanks serve an array of platforms from Airbus, Bell and Leonardo, with capacities starting at 1,000 liters (264 US gallons). Their trapezium shapes create head pressure that allows for a high-volume, targeted drop pattern, the company said.

Helitak began designing expandable tanks to address the limitations of other tanks on the market, noting many firefighting helicopters were capable of carrying far greater payloads than existing tanks allowed.

They also quickly lost head pressure, meaning controlling the drop was a challenge, Helitak has said. Their expandable tanks are designed to solve both problems.

“Their design team is very innovative,” Woods said. “There’s a very creative thought process there, and it’s been a good collaboration.”

Rotak and Helitak featured the FT11K tank at the HAI Heli-Expo 2023 in March, and received positive reviews.

“We had a lot of people very excited to see the aircraft and come chat with us — a lot of old friends, new customers and existing customer — so it was great,” Woods said. “Everyone seemed really interested in the designs we put together, and seeing the aircraft up close … and we’re excited to help pioneer some new ideas.”