Dassault Adds More Smarts to Falcon Autothrottles

 - February 1, 2021, 8:00 AM

Dassault’s twin-engine Rafale fighter jet is equipped with what in retrospect seems an absurdly simple design feature: a single throttle lever to control both engines. Dassault engineers had long discussed a similar application for a business jet and now the French manufacturer has conducted extensive flight tests of a single-throttle lever integrated with the three-engine Falcon 7X’s fly-by-wire digital flight control system. In late October, I had the opportunity to test-fly its SmartThrottle in the 7X flight-test aircraft and experienced another new feature that Dassault has also been testing—a full recovery mode function that can help pilots recover from a loss-of-control situation.

The flight testing that Dassault conducted on the experimental 7X revealed significant safety and operational benefits. However, the company hasn’t yet decided on when the SmartThrottle might be integrated into a new airplane. The next Falcon model is the so-called “Falcon Next,” but Dassault has not yet officially launched this program and it isn’t known yet whether this aircraft might feature the SmartThrottle and the recovery mode features that are enabled by the SmartThrottle’s integration with the fly-by-wire digital flight control system (DFCS).

RCY
We flipped the Falcon 7X nearly upside down before pushing the recovery button.

According to Dassault, the 7X SmartThrottle test program got underway more than two years ago. To put it simply, the SmartThrottle is like an enhanced autothrottle, incorporating all the normal autothrottle capabilities but taking advantage of digital technology to add safety features such as upset recovery, more comprehensive emergency descent modes, and engine failure mitigation, along with single-power-lever operation.

For the purposes of flight testing, the 7X was modified with the single-lever SmartThrottle along with three manual “mini-throttles” that can operate each engine individually and during takeoff and landing. Ultimately, a certified version of the SmartThrottle would be usable from takeoff to touchdown, but during testing the SmartThrottle was usable only once airborne.

The flight test SmartThrottle has LED light strips
The flight test SmartThrottle has LED light strips on either side to highlight engine condition.

The 7X’s instrument panel was modified with the pilot’s primary flight display (PFD) replaced with a touchscreen display that mirrored all the functions of the normal 7X’s mode-control panel. Two smaller display screens were mounted on the outboard side of the panel, only for displaying flight-test-related information. The flight-test 7X was set up for single-pilot operation from the left seat so that another test pilot or pilots getting demonstrations of the system could fly from the right seat while not being required crewmembers.

Dassault test pilot Philippe Duchateau (l) briefs AIN’s Matt Thurber on the SmartThrottle.
Dassault test pilot Philippe Duchateau (l) briefs AIN’s Matt Thurber on the SmartThrottle.

Because the SmartThrottle is entirely digital, engineers can add all sorts of features to take advantage of the technology. Soft and hard stops can be programmed so the pilot feels a detent at the maximum climb power setting, for example, but the detent can be changed depending on conditions. The throttle’s friction is also adjustable, not by the pilot, but engineers can tweak friction settings electronically.

It’s the marriage of the SmartThrottle with the DFCS that adds even more capability, not just the ease of engine management and simpler handling of engine-inoperative situations but also further extending the DFCS’s capabilities. Now Dassault is moving that concept forward to take full advantage of the flight control infrastructure that it has been developing since the 1950s.

Dassault DFCS

In the 1950s, Dassault leadership decided to bring all flight control design and manufacturing in-house and set up the flight controls department in Argonay, France. This development stemmed from the crash of a Mystère IV B fighter jet, serial number one, during a demonstration flight flown by legendary test pilot Constantin Rozanoff at Dassault’s former Melun Villaroche flight-test center near Paris. The crash had to do with the flight controls, and Dassault decided that owning the flight control engineering and production would help improve safety and allow designers more control of aircraft handling characteristics.

Dassault’s first fly-by-wire (FBW) business jet, the 7X, owes much of its flight control design to Dassault’s military jet development, starting with the Mirage 2000 but especially the Rafale. The company's fighters and business jets such as the Falcon 7X, 8X, and upcoming 6X all share a key characteristic, a so-called “closed-loop” fly-by-wire design.

Open-loop FBW basically replicates the characteristics of conventional flight controls where a yoke is connected to cables, pushrods, and in some cases hydraulic boosters. In an open-loop FBW system, the pilot’s movement of a yoke or sidestick sends electronic signals that result in proportional movement of a control surface, just like with the mechanical controls, and the aircraft must be trimmed to maintain each different attitude. Any small perturbation such as turbulence moves the airplane away from the desired attitude, and the pilot has to constantly move the controls to return to the attitude, or trim when selecting a new attitude, and thus this is also known as a trim-stable FBW system.

Closed-loop FBW is path-stable, which means that the pilot uses the controls to select the desired flight path then lets go of the sidestick. Thus, the FBW maintains the flight path or trajectory without further input from the pilot. Dassault illustrates this by showing a video of two FBW jets in side-by-side windows, flying in the same trajectory, and the pilot flying the Falcon can be seen with no hand movement while the other jet’s pilot is constantly moving the controls to maintain the desired flight path. That is one of the reasons Dassault believes the flying qualities of its aircraft are superior.

The DFCS adds another dimension, however, and that is to use the optimal combination of control surfaces to respond to the pilot’s request, as transmitted through the sidestick, rudder pedals, and—with SmartThrottle—the engines in more than just a normal autothrottle sense.

Although the 6X won’t be fitted with the new SmartThrottle, Dassault has added new elements to its DFCS, which now includes all secondary control surfaces and nosewheel steering. A new control surface—a flaperon—on the 6X combines flaps and aileron functions. By incorporating every control, the 6X essentially wrings all the possible benefit out of FBW in terms of trajectory management.

Energy Management

The Rafale demonstrated that adding the engines with single-lever-power control to the DFCS brings the benefits of energy management into the FBW sphere. Dassault engineers naturally wondered what would the result be if the same were done for a Falcon, according to flight control system engineer Francois Dupre, and this was the genesis of the experimental 7X test program.

“What if we could broaden the flight control strategy to energy management with a single command to control the aircraft?” he asked. By including the engines, helping the pilot manage energy, it would help the pilot control speed with less workload, Dupre added.

Not only that, but the engine integration enables new functions to improve operational safety, he said. This can include helping the pilot in a low- or high-speed condition, which is already something that is done with autothrottle-equipped aircraft. But SmartThrottle adds the capability to manage the entire engine operating envelope, including engine failure, while allowing the pilot to keep flying the airplane the same way as normal (without an engine failure).

“The idea is to have the same [flying process] even in case of engine failure,” Dupre explained. “You’re still managing energy and will see it decrease, but you don’t have to take care of lateral control—that’s done automatically by the DFCS.”

Dassault has demonstrated some of this functionality in the twin-engine Rafale with its single power lever. Its DFCS, for example, uses the jet’s control surfaces to provide air-brake functionality. By managing the Rafale’s energy, the DFCS allows pilots, especially in the naval version that lands on aircraft carriers, to focus on flying the proper trajectory with no need to divert attention to speed or even angle-of-attack. “The workload is very high, especially in bad weather,” said Dupre, “so it’s very useful for navy pilots.”

Of course, adding these capabilities to the DFCS means that Dassault has to work closely with engine manufacturers to gain full access to every aspect of the engine’s operation. “We have to define the interface,” said Dupre. “Functions need to have vision of the performance of the engine. There must exist some exchange between systems and engines, just like we do with control surfaces. The system has to have a better understanding of the situation. The reactivity of the function has to take into account the dynamics of the engine.”

But even with an accurate computer model of the engine, pilots still must fly many actual flight tests to fine-tune the system in real conditions. And Dassault has developed techniques to do just that.

The concept of automation takes on new meaning when all the primary and secondary controls are managed by the DFCS. What this allows is still complete and full control authority by the pilot and improved performance but also the opportunity to assist the pilot in recovering the aircraft if something goes wrong.

“The DFCS enables us to take the benefit from full authority,” explained DFCS engineer Alain Boucher. “This is the same level of authority the pilot has with manual control. But we’re trying to increase the automation level as a way of getting quicker and more accurate reactions to hazardous situations.” As well, this could include adding functions like TAWS (terrain) and TCAS (traffic) and making them part of the automation and performance and safety improvements.

Such a system could easily help a pilot recover from an upset caused by a wake turbulence encounter. “There are all kinds of unusual attitudes where the pilot may be lost a little bit and doesn’t know what to do,” said Boucher. “This could bring many [opportunities] to the crew in these kinds of situations.”

Basic safety is already covered by certification requirements, but these new features aren’t addressed, yet. “My goal is to say all these subjects could be part of a certification program,” he said. “We’re going toward more safety and more protections for the aircraft and crew. It could become part of regulations in the future.”

Recovery Mode

Ultimately, the features that Dassault explored with the experimental 7X were integration of the SmartThrottle and using the DFCS capabilities to effect the recovery mode. The Rafale does have recovery mode, but it also has an added high-level mode called ground protection. This uses the fighter’s DFCS to constantly look at the current and projected trajectory, and if it determines that the trajectory is going to result in impact with the ground, it pulls up to maximum g to maneuver the Rafale back to safety. This is enormously helpful if the pilot succumbs to g-induced loss of consciousness. The Lockheed Martin F-16 has a similar system called Automatic Ground Collision Avoidance System, which has so far saved 10 pilots and nine F-16s. One Rafale has been saved by the system, making ground protection well worthwhile.

Philippe Duchateau, Matt Thurber
Dassault test pilot Philippe Duchateau showed AIN’s Thurber the Rafale’s single throttle. (Photo: Vadim Feldzer)

Dassault could add ground protection to the Falcon DFCS at some point, but that wasn’t part of the experimental 7X test program. The ground protection could be enabled by tapping the Falcon Eye head-up display’s high-performance camera system. “We can use all that stuff to contribute to safety,” said Patrick Parnis, Dassault's head of marketing.

To use the recovery mode, the pilot has to push a button to initiate the recovery, then the DFCS takes over and returns the airplane to a safe attitude. In the experimental Falcon 7X, recovery mode was programmed to stay within 1.5 g, which is more comfortable for passengers. “For civil aircraft, recovery mode will enhance safety to help pilot in difficult conditions,” said Jean-Louis Montel, a special advisor on technical and design issues for Dassault chairman and CEO Eric Trappier.

FalconEye and also the primary flight display could help show the pilot that the aircraft is approaching a loss-of-control situation, and if the pilot doesn’t correct the situation then the DFCS could engage recovery mode automatically. “The idea is to prevent an upset, but if the pilot doesn’t react, maybe he is focused on other things, automation will take the lead,” said Montel. All of this is still under consideration and will be informed by the experimental 7X tests.

However, the goal is always to keep the pilot in the loop as much as possible. “If we have a complex system and the pilot is not in the loop, the time to apply the right procedures is very long and not compatible with times taken into account in safety studies,” he added. “The idea is to have the pilot in the loop, and not have a discontinuity between the pilot and the automation.”

“Clearly this is a challenge when you go for more automation,” said Boucher. But the automation inherent in Dassault’s recovery system is designed to help pilots, who have shown that a frequent reaction to an unexpected unusual attitude is the wrong control input. “That means seconds that you lose [for recovery],” he said.

And, of course, for each option, Dassault will have to carefully consider the steps needed to obtain certification for the SmartThrottle and recovery modes, including backup modes. “We’re just at the beginning of the story,” said Montel.

Test Flying the 7X Recovery Mode

Before flying the flight-text 7X for the SmartThrottle and recovery mode demo, I spent some time in Dassault’s simulation lab at its St. Cloud, France headquarters, getting familiarized with the 7X flight deck and its flight characteristics. The lab simulator isn’t set up with the SmartThrottle/recovery system, however. But it was helpful to “fly” the simulator and practice some of the maneuvers we’d test in the real airplane the following day.

Matt Thurber, Philippe Duchateau, Tom Vallette
After the final flight of the SmartThrottle setup in the flight test Falcon 7X, AIN editor-in-chief Matt Thurber (l) with test pilots Philippe Duchateau (c) and Tom Vallette (r). (Photo: Vadim Feldzer)

The following day I was escorted into Dassault’s flight-test center at the Istres-Le Tubé Air Base, where all the company’s military and civil flight-test activities take place. This was to be the final flight of the SmartThrottle-equipped 7X, and the data recorded by the telemetry office would be used as part of the analysis.

Prior to my flight, Dassault test pilots logged 50 hours in the specially-outfitted 7X, collecting data during two test campaigns. Many of the flights introduced operational Dassault pilots to the SmartThrottle and recovery system.

The SmartThrottle in the test 7X, mounted in the center of the forward console between the seats, looks almost like an old-style automobile automatic transmission gear shifter. It is bracketed by strips of LED lights on either side that can highlight various conditions as a way of giving the pilot instant feedback on the status of the engines.

Because it’s digitally controlled, engineers can vary the SmartThrottle friction or set hard or soft stops for different requirements. For example, the pilot might feel a click when approaching a reduced-power takeoff setting or feel a hard stop preventing the application of more power if the airplane is nearing Vmo (maximum operating speed). The lights alongside the SmartThrottle could highlight problems such as showing the power setting the digital flight control system (DFCS) is using if the throttle itself were jammed.

Three lights on the aft side of the throttle quadrant illuminate green when the engines are connected to the SmartThrottle and red when the mini-throttles are engaged. For takeoff and landing, only the mini-throttles could be used during the test program, but a production version of this system would not include the mini-throttles.

With test pilots Philippe Duchateau in the left seat and Tom Valette in the jump seat, I flew from the right seat, but as this was a flight-test setup only one pilot was required. Thus, I was playing the role of an observer/demonstratee and not a required crewmember.

During the briefing before the flight, Duchateau explained Dassault’s philosophy behind the recovery system. “The aim of the recovery function is to help in case the crew gets a little bit lost in attitude,” he said. Newer-generation pilots tend to fly less hands-on and a recovery function can help get them out of trouble. “But also wake turbulence, if you’re getting flipped over, you don’t have to think about how to get back to a normal position; it will take you back to a nice flying position.”

Using the mini-throttles for takeoff felt a little strange, but then again, it reminded me to wonder why power levers have to be one of a fistful of throttles as in the typical jet design. An electronically controlled engine’s power settings could be manipulated by any old variable switch or knob, after all.

I took off from Istres-Le Tubé’s Runway 33 in good weather with calm winds and climbed to 5,000 feet while I refamiliarized myself with the DFCS. I’ve flown the Falcon 8X before, so the 7X felt comfortable, matching the 8X’s easy handling characteristics. Fly-by-wire certainly makes large airplanes more pleasant to fly.

We first programmed the RNAV 33 approach in the Honeywell-based EASy avionics, then pulled the power back on the left engine mini-throttle to simulate one-engine-out operation. With slats/flaps 3 set and hand flying, near minimums at about 300 feet, I clicked the go-around button once and pushed the SmartThrottle forward and watched the power come up on the two “good” engines. Meanwhile, the DFCS commanded the flight director to bank slightly to the right and kept the airplane on course, and then we climbed to 2,500 feet.

Having to move just one lever to command whatever power is available is far simpler and less taxing than trying to figure out which engine has failed and then dealing with three separate levers.

For the second and same approach, with all three engines operating and autopilot on, at 300 feet I pushed the go-around button once for the initial “soft” go-around, which provides a relatively gentle maneuver, then pushed the go-around button again to engage the more aggressive “high” go-around. This moved the nose to about 17 degrees, with full power, resulting in a 4,000 fpm climb.

Continuing the climb, Duchateau showed me some climb modes that were tested on this 7X—a “comfort” climb and “fast” climb. The comfort climb is optimized for passenger comfort, for example, avoiding a rapid pull-down while leveling off.

We leveled at FL400 for a demonstration of the emergency descent mode, which is designed either to happen fully automatically if the pilots are incapacitated or allows the pilot at the controls to manage the maneuver. The pilot can, for example, control direction while the DFCS continues the rapid descent, thus minimizing the pilot’s workload.

The descent mode turned us 90 degrees to the left and dropped the nose almost 20 degrees at maximum speed, with descent rate settling at 10,000 fpm, bringing the 7X rapidly down to FL200. Here we planned to fly the recovery maneuvers—the real meat of this demonstration.

Level at FL200 at 250 kias, Duchateau instructed me to fly a series of maneuvers where I would bank steeply then let the nose drop below the horizon. These varied between banks of 110 to 120 degrees with the nose dropping 7 to 15 degrees. We did these in clean configuration and at medium speeds, from 200 to 250 kias.

Each time I generated the upset maneuver, I would let go of the controls and Duchateau would press the recovery button on the instrument panel. And each time the DFCS smoothly and precisely returned the 7X to straight and level flight, pulling a maximum of 1.7 g, well below the limit of 2.5 g. Of course, the DFCS also ran the SmartThrottle as needed to manage the recovery properly.

The final maneuver was with slats/flaps 3 and landing gear down, where I slowed the 7X to 114 kias, Vref at that weight and configuration, then banked left 40 degrees and allowed the nose to drop 10 degrees. After I released the controls and Duchateau pressed the recovery button, the 7X righted itself, losing just 200 feet and pulling 1.4 g. This was a good demonstration of how the recovery mode could help resolve an upset in the airport environment.

What was interesting about these exercises was that I didn’t need to try to recall the upset recovery mantra that I’ve learned during a few upset prevention and recovery training courses I’ve attended. The DFCS operates much faster than a human, using any control needed to care for the airplane and its occupants.

Ultimately, the recovery process was safe and amazingly smooth. I admit that it was a lot of fun getting to flip the 7X nearly all the way over, watching the gorgeous Marseille coastline fill the windows, and feeling forces rarely felt in a business jet.