Bell 525 Lab Simulator Allows Fly-by-wire Trials
The Bell 525 is flying off the coast of California en route to the main runway at Camp Pendleton. I beep the fingertip switch on the sidestick collective to slow for a smooth landing, thanks to the new helicopter’s coupled fly-by-wire (FBW) controls.
I’m not in the real helicopter–it won’t fly until next year–but rather in a cockpit simulator called the SIL (system integration lab) CAB at Bell headquarters in Fort Worth, Texas. Here in this oversized no-motion device, Bell engineers are tweaking the FBW control laws for the new super-medium twin. They’re about 80 percent done, according to Troy Caudill, Bell’s principal experimental test pilot. “We have some work cut out for us, but we are getting there,” he said.
Caudill is working with a bank of engineers, seated at mission control-style control consoles behind us, to finish the job, including all the engine data and the mechanical response characteristics. Some of those await component completion. Caudill cautioned that the SIL CAB does not quite fly like the real thing. “This is a development tool,” he said. “This is not the final cut.” Nevertheless, just sitting in it and manipulating the controls, you come away with a feeling of just how radically different this helicopter will be.
Start with the basic cockpit layout that Bell calls ARC (awareness, reactive, control) Horizon: a low-slung instrument panel with four Garmin G5000 12-inch screens (the production helicopter will have the G5000H, still under development), the futuristic sidesticks and the plunging cockpit side windows that provide excellent visibility. The middle of the panel still has quite a bit of room left for customer-specified equipment. The engines are Fadec-controlled, so there are no throttles, just a control panel with three-position knobs for each engine (crank, idle, fly).
Everything is triple-redundant, but simple. The battery is basically there to start the auxiliary power unit. Switch on, the MFD shows voltage and fuel, then the APU lights and everything comes up, including a simplified checklist. Under standard conditions, Caudill thinks the start-up and departure sequence will take less than five minutes–a big plus for search-and-rescue/medevac operations.
Offshore oil and gas is expected to be a big share of the 525’s market, and ARC Horizon is being designed to allow pilots to modify approaches to offshore structures while en route. “The FAA-approved approaches will be loaded into the system, but a lot of those [offshore] platforms float–the winds change and the platforms move, so the pilot has to have the ability to plug in the final approach course, altitudes and ranges,” Caudill said.
With the assistance of a “variable stability helicopter” (VSH), which is a flying Bell 412 test bed operated by the Canadian National Research Council, Bell has been developing FBW for many years. The VSH’s computers are connected to the flight controls and allow the helicopter to simulate the characteristics of various fixed- and rotary-wing aircraft. “We brought the VSH down here [Fort Worth] one summer and the non-pilots loved it–until we switched off the augmentation. But it was a good way of demonstrating what control laws can do for you,” Caudill said.
The principle of FBW in helicopters was first broached in a 1962 NATO study entitled, “The Model-Controlled Method for the Development of Variable-Stability Aircraft.” Four years later, Bell began flying the X-22 ducted-fan research aircraft with a variable stability system.
Caudill acknowledged that the initial FBW tuning for the 525 “was a little too responsive.” I find the controls in the SIL CAB to be extremely sensitive, so I can only imagine.
“I’m an old Cobra guy and I kind of like to think sporty,” Caudill admitted, “but this is a larger aircraft and [customers] probably don’t want it that sporty.”
Sportiness aside, for Caudill FBW is all about safety. “I don’t think you can overemphasize the safety aspect. There was a lot of [internal] debate on whether to do fly-by-wire or mechanical controls when we started this program. My argument has always been that you can’t put a price on safety. Yes, fly-by-wire costs more, but basic aircraft with mechanical controls always saturate at the worst possible time and pilots get in trouble when they task-saturate, especially in conditions they weren’t expecting, such as low visibility. That is when they crash. With fly-by-wire, if you don’t like what’s happening, let go. The aircraft will do what it’s commanded to do and then you’ll have the time to figure it out.” When you let go of the controls at forward speeds below 10 knots, the FBW system automatically pulls the 525 into a hover.
Caudill used a brownout landing as an example. “Say you are in a really dusty environment, kicking up all this dust, but clear to land. I know what is below me so I can just beep it down and land. I know the helicopter is going to maintain position. This is one of the major safety benefits of fly-by-wire.”
The beeping of the switch on the collective when in coupled mode takes a little getting used to. Past 10 knots, the nose dips a little as ground speed hold mode kicks in. To overcome the gradually increasing force when moving the controls away from the trim point, just hit the thumb button for the force trim release on either the cyclic or collective, pull back and climb. The coupled controls allow lateral inputs while maintaining airspeed and altitude and will return the helicopter to hover if it was displaced from hover. The ball stays centered without touching the pedals. In a turn, the coupled controls maintain the bank angle until the pilot turns or beeps out of the turn.
“You really don’t understand the capability that fly-by-wire has until you experience it,” said Larry Thimmesch, Bell vice president of commercial programs. “Yes, it is really nice to fly, but in situations when you have to autorotate, when you need to be looking out the window rather than at the gauges, those critical seconds in the man-machine interface, that is where it can really help the pilot.”
“Hopefully when we are done this is going to be an aircraft pilots love to fly. They will not want to get out of the cockpit,” Caudill said.
Heli-Expo attendees have a chance to test a 525 cockpit simulator at the Bell booth (No. N5612).