FORT WORTH—Bell Helicopter’s FC-X mockup concept demonstrator is proving to be more than just a talking point.
The company’s innovations team in Fort Worth is preparing to demonstrate a full-scale Bell 407/429-class cross-flow fan anti-torque system and hopes to switch it on this summer.
A thrust-vectoring electric-driven fan embedded in the tail boom could someday replace traditional tail rotors on certain commercial and military helicopters, providing greater lateral and pitch control as well as improved safety and lower noise emissions.
Unveiled at Heli-Expo 2017 in Dallas, the FC-X full-scale mockup (designated FXC-001) is Bell’s call to the future, featuring main rotor blades with variable-sweep tips, high-energy-absorbing landing gear, a modular cabin and single-pilot augmented reality cockpit, as well as a hybrid-electric anti-torque system.
Scott Drennan, who heads Bell’s innovation team and helped bring FC-X to life, said during a media tour at the company’s headquarters here that while many FC-X features are still conceptual, the anti-torque system is already being tested.
The company has a 3/4-scale version that has run at 1,000 rpm. Bell is now “growing” that technology demonstrator to full size for testing up to 6,000 rpm. “This summer, we plan to run it at full scale and get thrust,” Drennan says.
The new anti-torque system is Bell’s answer to competing technology already on the market, such as MD Helicopter’s Notar anti-torque system, offered on the MD 902 Explorer. Notar uses an engine-driven variable-pitch fan to pressurize the tail boom to generate airflow, which is directed through slots in the tailboom to generate sideforce and a rotating nozzle at the rear for safer, quieter directional control without a tail rotor. If tests are successful, Bell says its anti-torque system may match or exceed its rivals.
Asked how close Bell was to commercializing this technology, Drennan said “pretty close.” It will be one of Bell’s first steps toward incorporating hybrid-electric propulsion into its rotorcraft. The aim is first to differentiate Bell’s products, but also open up collaborative research efforts with military and civil research laboratories to find other unique applications.
“This will change helicopter safety, performance and noise,” Drennan says. “We know we’re doing the right thing when our internal programs raise their hand or Darpa, NASA or the Defense Department raise their hands [to test the technology].”
Bell is not exactly sure how great the noise reduction will be, since noise perception varies depending on the direction of the emissions and the rpm of the electric motor. Bell has computer-generated thrust and noise data, but must prove it in live trials.
Drennan’s innovations team is also spending a lot of time on autonomous fly-by-wire flight control software. It is setting up a dedicated Systems Integration Laboratory (SIL) to test new control laws.
The SIL will take about six to 12 months to set up and should be ready by early 2018. Drennan says the SIL will probably be set up at Plant 2 on Bell’s main Fort Worth campus.
The company is further away from testing FC-X-style variable-sweep blade tips. The company has not decided whether the tips should be electrically or mechanically actuated, or how far along the blade the pivots should be positioned, given the strong centrifugal forces in play.
This technology would enable more efficient flight and help reduce noise caused by blade vortex interactions. The tips would be extended in hover to create a wider load-bearing rotor disk, and then swept back in forward flight to improve performance.
“We need to look at this in rotorcraft because it does offer some performance and noise benefits if you can get it to work,” Drennan says.
The FC-X concept is a slight departure from Bell’s tiltrotor-centric mindset, even though it is still heavily invested in the Bell-Boeing V-22 Osprey, Bell V-280 Valor and V-247 Vigilant aircraft.
The company is not backing away from commercial and military tiltrotor concepts, but says some missions still favor conventional-looking, single-disk helicopters. The company is also still studying tailsitter airplane concepts for certain applications.
“Tailsitters are an interesting area to look at too,” Drennan says. “They don’t have good hover performance, but for certain tactical situations, maybe there’s just a small launch-and-recovery area and you get on the wing and stay on the wing [for most of the flight]. You can do some tailsitter configurations that keep everybody [inside] level.”
The company has even begun talking about lifting-body helicopter designs. FC-X has a noticeable chine for aesthetic purposes, but Bell engineers have thought of sculpting future airframes to generate additional lift during forward flight.