Sikorsky has chosen prudence over spectacle and delayed the first flight of its S-97 Raider prototype until 2015.

The company, which has invested more than $150 million of internal funding to develop the coaxial rigid-rotor vertical-lift platform, originally planned for it to fly before then end of 2014, but has yet to begin ground testing in preparation for the aircraft’s maiden flight.

Doug Shidler, who headed the Raider project before taking the helm of the company’s joint multi-role development effort, tells Flightglobal there is no particular issues holding the programme back.

“We are going through several lab ground tests right now and we are planning to get into aircraft ground run here in the next couple of weeks,” he says. “As with any development program and first-of-type, there are discoveries. We haven’t had too much discovery, nothing that is insurmountable. We’re making some really good progress in getting the aircraft set for doing its ground runs.”

Raider uses coaxial rotors for vertical lift and a tail propeller for forward thrust. The combination allows for flight characteristics that are physically impossible for existing rotorcraft designs. There is no programme of record within the US military for the aircraft, though the US Army has been monitoring the development effort as it looks to eventually replace its existing, and aging, helicopter fleet.

A transmission system testbed is being built in parallel with the Raider, of which there will be two flying prototypes. The first is designed specifically for the flight test phase. The second will be a demonstration aircraft that will travel and be flown for prospective customers.

The fuselage for Raider II is complete and the remaining parts have been manufactured and delivered. Construction of the second aircraft will begin in early 2015, he says.

Ground runs are scheduled to begin this month, he says. Data gathered while the aircraft remains tethered to the ground will be used to inform flight testing, which should begin in early 2015.

“We were targeting flying by the end of the year,” he says. “It is not any one particular thing or any issue. It’s the nature of development and pulling the first of type together. We’re not rushing it, we are making sure we do it in a very judicious fashion to make sure we are getting into the air safely.”

Army officials desire helicopters that can fly higher, faster and farther than current designs. The Raider is being billed as a potential armed aerial scout or for use by special operations forces.

It was designed to carry more than 4,990kg (11,000lb), or six troops plus crew. With external weapons mounted, Sikorsky says it will fly at least 220kt (407km/h). Unarmed it will fly at up to perhaps 270kt, but S-97 chief engineer Andy Bernhard will not specify how fast they intend to fly it during testing.

Raider was announced, designed and built in four years based on the company's experiences with the X2 concept demonstrator. Raider brings that aircraft's technology into a practical aircraft that can demonstrate real-world mission capabilities.

In partnership with Boeing, Sikorsky plans to scale up Raider’s compound, rigid coaxial rotor configuration into a platform that will satisfy the army’s requirement for the joint multirole technology demonstration (JMR-TD). That programme will validate technologies for the eventual future vertical lift (FVL) platform, which is seeking three classes of helicopter – medium, then light and heavy – to eventually replace all the service’s vertical lift aircraft. Sikorsky and Boeing have dubbed their JMR demonstrator the SB-1 Defiant.

Sikorsky has built fly-by-wire aircraft before and gained experience with coaxial rotors with the X2. Still, as a clean-sheet design with novel propulsion and lift configurations, the Raider has presented unique challenges, says Steve Engebretson, Sikorsky’s director of military programme marketing.

“The amount of data we have on this configuration is relatively limited,” he says. “To quote one of our test pilots, we’re going to learn something from the aircraft from the first time he picks it up off the ground. Every time we spin this rotor, we are probably going to learn something new about how it operates.”

When Raider does get airborne, the company plans to dive directly into substantive testing, Shidler says. First flight is planned to last about 1h, he says.

“We don’t want to just pick the wheels off the ground and get the glamour shot and put them back down again,” he says. “We’re all about making sure we have productive flight testing.”