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Flight Controls

G500 Systems

When it comes to the flight control system of any airplane, I find it helpful to look at the things we have control over in the cockpit and analyze those in terms of What they do, Why they do that, and How they do that. I do that for normal operations, abnormal operations, and emergency operations. When I am done with that, I should have everything covered. If not, in my mind, it isn't worth knowing. But keep in mind this is the first airplane I've flown with a fly-by-wire system. If that is true for you too, perhaps we should start with a primer.



A Primer . . .


A GVII Fly-by-wire Primer

In an attempt to make this section more conversational and instructive, I will skip my usual practice of carefully quoting source material and sparingly offering my own comments. What follows is just the opposite: what I've learned about this system with links to the source material which follow in the sections of this page further down.

You have to get through the complexity to get to the simplicity.”

The fly-by-wire system on the Gulfstream GVII (G500) is my introduction to flight controls connected to the pilot via electrons. My history is more than just cables to electrons, but in all of the airplanes there was at least some kind of physical connection between stick and rudder and everything that makes the airplane bend to the pilots will.

Even if you have a background in this kind of thing, the GVII approach is unique in many ways. No matter your background, you will have some challenges in front of you when trying to learn the GVII flight control system. The current school house method gets the job done, but it takes a while to learn and doesn’t really give students a firm grasp of what causes what to happen. You typically start with the Flight Control Computers (FCCs), dive into the Flight Control Laws (CLAWS), and work your way outward to the Active Control Sidesticks (ACSs), and then on to control surfaces themselves. I think the flaw with this method is you are starting with the unknown bits you are unfamiliar with (the computers), and then going to the more familiar bits (the stick and the control surfaces). I think it might be easier to go from familiar to unfamiliar under normal circumstances, and then look at the cases where things become abnormal. So let’s do that.

The path I took to get here

My first jet was the Cessna T-37 which had two sticks (one for the student, one for the instructor) connected via cables to conventional ailerons, elevators, and a rudder. I imagine it wasn’t too much different than what you would find in a Piper Cub. Advantage: easy to understand and troubleshoot. Disadvantage: control loading becomes difficult with increasing size and speed range of aircraft.

My second jet was the Northrup T-38 which also had two sticks but the cables were connected to hydraulic actuators and the airplane had a flyable stabilizer. This allowed the airplane to be flown with great precision (it was used by the USAF Thunderbirds for a while) and great speed (Mach 1.2). Advantage: lighter control forces required to move larger controls. Disadvantage: the aircraft could not be landed with wind-milling hydraulics. A dual engine loss required the pilots to eject.

My third jet was a Boeing KC-135A tanker which was a 300,000 lb. aircraft with a huge speed and altitude range but only hydraulic “boost” provided to the rudder. The rest of the flight controls relied on balance tabs which, basically, gave pilots control of small tabs on each surface. The small tabs pushed the larger surface and a balance bay in front of the control created a vacuum to further move the surface. It was an idea Rube Goldberg would have been proud of. If you want to be amazed by what can be done by clever engineers, read about “leakage regulation” here: Balance Tabs. The rudder boost was hydraulic and the stabilizer was moved by an electric motor. Advantage: able to move large control surfaces without complicated hydraulics. Disadvantage: the controls tended to be a bit sloppy.

My fifth jet was the Boeing 747 which had all hydraulic controls. It was one of the best flying airplanes I’ve ever had my hands on, but there were no backups. Advantage: able to move large control surfaces very precisely with light control forces. Disadvantage: if the hydraulics quit, the airplane was close to unflyable. See Case Study: Japan Airlines 123.

My sixth jet was the Gulfstream III, a business jet with hydraulic controls backed up by cables. The stabilizer was mechanically linked to the flaps and was fairly reliable. Advantage: hydraulic “boost” with an always available backup. Disadvantage: the control forces remained fairly heavy and the backup system wasn’t really easy to fly.

The airplanes that followed were all variations or combinations of these first few jets. At first glance, going to fly-by-wire seems to be a quest to further reduce weight by eliminating all those cables and hydraulics. But adding multiple high-speed computers to the mix allows designers to increase speed, stability, and safety while reducing weight. Fly-by-wire has been around for a while and many of the current versions flying haven’t been as bullet proof as originally promised. Gulfstream came to this point with the GVI (G650) and have further fined tuned with the GVII. I think the best place to start learning about this version of fly-by-wire is to start with the basic inputs (stick and rudder pedals) and outputs (control surfaces). Only then will we be ready to dive into the electrons.

Hardware: The stick and rudder

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Photo: G500 Active Control Sidestick (ACS), left seat

Click photo for a larger image

There are a lot of aircraft out there with electronic sidesticks but, as far as I know, only one other provides feedback to the pilot as well as takes pilot inputs. The Lockheed Martin F-35 Joint Strike Fighter. But for now, just realize that you move this stick left and right for ailerons, fore and aft for elevator, and the rudder pedals for the rudder. It does this with Rotary Variable Differential Transducers (RVDTs) that turn sidestick, rudder pedal, speedbrake handle, and rudder trim knob movements into electrical signals. You will feel airloads and autopilot inputs in your hand, as well as any inputs the other pilot makes with the opposite stick. (It is a lot more complicated than that, but the stick and rudder in the GVII are analogous to that in the Piper Cub.)

Hardware: Pitch control

Primary pitch control on a small aircraft with a narrow weight and speed range, like our previously mentioned Piper Cub, is fairly straight forward: an elevator on the trailing edge of the horizontal stabilizer. The stick moves the elevator up or down which causes the tail to move in the opposite direction and therefore the nose in the same direction. Larger speed and weight ranges are often handled by adding a movable horizontal stabilizer. Most of the Gulfstreams that I’ve flown have the stabilizer move in reaction to flap position as a way of compensating for changes in speed. The problem with this solution is you are usually flying with the elevator in an unfaired position; it isn’t aligned with the stabilizer and will create added drag. Most of the larger aircraft that I’ve flown have the yoke (or stick) directly move the elevator while the pitch trim switch moves the stabilizer. You end up with a faired stabilizer to minimize drag, provided the pilot is doing a good job of trimming the aircraft. The GVII solution is an automatic version of this: the pilot moves the elevator with the stick, the stabilizer “auto offsets to offload any persistent elevator offset” and you end up with a faired elevator. Conventional trim switches are provided to retrim the airplane to a new speed, as well as a “Trim Speed Sync” (TSS) button to retrim to 1G flight.

Secondary pitch control is usually accomplished by leading and trailing edge devices that effectively change the camber of the wing, making it more suitable for low-speed flight. The Gulfstream solution has been to use only trailing edge flaps for this purpose. Earlier Guflstreams used hydraulic lines from the engines to the cockpit to flap motors in the wheel well. Starting with the GV the hydraulics to the cockpit were replaced with electronics, making the flap handle nothing more than an electronic switch. The GVII continues this practice.

Hardware: Roll control

Roll control on most aircraft consists of ailerons but many also use a series of spoilers to augment that roll. Moving the stick to the left, for example, will raise the left aileron and the left outboard and midboard spoilers while lowering the opposite aileron. This produces a roll to the left. The spoilers can also be used symmetrically to act as speed brakes in the air and ground spoilers on the ground. The GVII acts conventionally in this respect except the ailerons are also used as ground spoilers on the ground by both deflecting upwards.

Hardware: Yaw control

Yaw control on most aircraft is one or more rudders attached to the trailing edge of the vertical fin. The rudder is normally connected to rudder pedals, allowing the pilots to deflect the rudder to one side by pressing on the same side rudder pedal. Higher speed aircraft usually add a yaw damper to help coordinate turns and dampen any tendency for the aircraft to Dutch Roll. The GVII acts conventionally in this respect except the allowable rudder deflection is regulated by aircraft speed: the faster the airplane is traveling the less deflection is allowed.

Hardware: Connecting stick and rudder to the flight controls

In a Piper Cub the stick and rudder are connected to each control surface directly with cables, pulleys, and bell cranks. In a T-38, the cables end at hydraulic actuators which translate the mechanical motion of the cables into hydraulic pressures at the control surfaces. In a fly-by-wire aircraft, the stick and rudder are connected to electrical devices that translate their mechanical motions into electrical signals. These signals are usually analog, meaning they are varying voltages. A small voltage could, for example, mean a small deflection where a large voltage means a large deflection. At the other end of the wire, these analog signals are turned into mechanical motions for a hydraulic or mechanic actuator to actually deflect the control surface. Such a system can be subject to signal losses (voltages decrease over distance) and calibration issues (how much deflection is really wanted against “a little” voltage?). The GVII solution appears to be unique in many ways.

The Active Control Sidesticks (ACSs) are connected to Rotary Variable Differential Transducers (RVDTs) that correlate stick positions forward/aft and left/right into electrical voltages that are analog signals. Each ACS has an internal computer with two channels, one active and one standby. These computers turn the analog voltages into digital signals. A digital signal is far more useful than an analog voltage in that the signal does not degrade over distance, leaves no doubt as to the position of the stick, and can be used by other computers.

The rudder pedals are conventional in that they are mechanically linked from left seat to right seat, but unconventional in that they are connected to another RVDT that correlates rudder pedal position into an electrical voltage.

The digital pitch and roll output signals of the ACSs and yaw analog output signal of the rudder pedals are sent to two Flight Control Computers (FCCs). The FCCs take these inputs, as well as the inputs from the autopilots, and send those to 8 Remote Electronics Units (REUs). The REUs control actuators, two for every primary flight control surface, one for each midboard and outboard spoiler, one for both inboard spoilers. One of the REUs for the rudder also controls the horizontal stabilizer.

Each REU translates the digital signal from the FCCs and turns those into commands for what are sometimes called Electro-Hydraulic Servo Actuators (EHSAs) but are more commonly simply called Hydraulic Actuators (HAs). There is an HA for each aileron, each elevator, the rudder, and one for each inboard and midboard spoiler; for a total of 9 HAs. (The outboard spoilers use a different actuator type, more about that later.) The HAs have two possible modes: active and damped bypass. In active mode, the HAs drive their control surfaces using left or right hydraulic pressure. If the actuator fails due to a hydraulic loss, REU failure, or other reason, the actuator reverts to “damped bypass” mode where it uses trapped hydraulic fluid to reduce flutter.

Some of the REUs also work with Electrical Backup Hydraulic Actuators (EBHAs) which also work in an active mode, using left and right hydraulic system pressure. The EBHAs also have a damped bypass mode. The EBHAs additionally have an Electrical Backup (EB) mode which becomes active when hydraulic pressure is not available for a surface. In that case, the EBHA uses a electrical motor to drive a motor pump at the actuator to pressurize trapped hydraulic fluid.

Two of the REUs also translate digital signals from the FCCs for use of the Horizontal Stabilizer Motor Control Unit (HS MCE), which positions the Horizontal Stabilizer Trim Actuator (HSTA). The HSTA uses one of two motors (one active, one standby) in reaction to commands from the FCCs, the ACSs, or the pedestal trim switch. Pilots normally only trim the stabilizer on the ground and even then it is usually done by the FMS. The stabilizer automatically offsets any persistent elevator movement to keep the elevator in a “faired” position.

Hardware: Spoilers

There are three panels on each wing called the inboard, midboard, and outboard spoilers. They are controlled by the FCCs through REUs. The inboard and midboard spoilers are moved by HAs using left or right system hydraulic pressure and do not have an electrical backup. The outboard spoilers are moved by EBHAs which also use left and right hydraulic pressure but include an electrical pump that can use trapped hydraulic fluid in the event normal system pressure isn’t available. Note that these EBHAs are used in normal operations using left or right system hydraulic pressure. (More about abnormal operations below.)

The spoiler panels operate automatically to assist in roll control, as speed brakes during an automatic Emergency Descent, and as ground spoilers during a takeoff abort or landing. As ground spoilers they will automatically stow after the speed has decreased during rollout or if the throttles are advanced out of idle.

Hardware: Flaps

The flaps are electrically actuated by a cockpit handle that sends signals to a Flap Electronic Control Unit (FECU) which communicates with a Hydraulic Control Module (HCM). The HCM provides hydraulic pressure to a Power Drive Unit (PDU) which drives the flaps through torsion tubes. The elevator is automatically biased trailing edge up to compensate for any nose-down pitching moment.

Software: Making it all seem natural

As complex as all of this seems, you can fly the airplane without knowing any of the details “behind the curtain.” The ACSs, FCCs, the HSTA MCE, and the FECU make it all seem like that Piper Cub, but even simpler. It is only important to understand how it does this for times when something goes wrong.

The sidesticks move 10° forward, left, and right, as well as 15° aft. But the pressure needed to move outboard and forward are reduced to compensate for normal arm strength in those directions. In most conditions, each stick moves to match the other. In what is called “active mode,” the sticks move in reaction to dynamic forces on the control surfaces, the other pilot’s inputs, the autopilot, and roll trim. Opposite sidestick inputs are normally averaged.

You will hear about “Flight Control Laws” which may obfuscate what is really going on here. A flight control law is nothing more than lines of software code that tell the various computers what to do in various conditions. These laws can be thought of as modes of operations, as if they were labels on a switch. There are four:

  1. Normal Mode. In this control law, control deflections asked for you by the ACSs or autopilot are sent to the flight control surfaces in amounts inversely proportional to airspeed. The amount of control deflection decreases with increases in airspeed. This is called gain and in normal mode is varies from the slowest to fastest speeds. You are also given a number of protections (more on that below). Normal mode is the only mode you can dispatch in.

  2. Alternate Mode. You will degrade to alternate mode if you find yourself down to a single air data or inertial reference source, or if the FCCs lose communication with the REUs controlling the HS MCE. You have four air data sources and if you lose three, you will go to alternate mode. You have 3 IRUs and 1 Attitude Heading Reference System (AHRS), you need at least 2 IRUs or an IRU and the AHRS to stay in normal mode. In alternate control law, control deflections are based on one of two gains. High speed gain occurs when the flaps and gear are up and is based on 340 KCAS. So whatever speed you are flying you control deflections are based on the highest possible speed, so the airplane will be relatively sluggish. Low speed gain occurs when the flaps or gear are extended and is based on 250 KCAS. The slower you are, the more sluggish the airplane will be. Think of it this way, gain will be set to the highest available airspeed: VMO when clean, VFE for 10° flaps with gear or flaps extended. In this mode you do not have auto-retract speed brakes, you lose the autopilot, as well as most of the flight envelope protections. The sidesticks, however, remain linked. You can go from Alternate to Normal using an FCC reset switch.

  3. Direct Mode. While alternate mode seems to happen as a result of things outside the flight control system, direct mode happens as a result of things within it: if all 4 FCC channels become invalid. In this control law, your gain is set as it was in alternate mode but the sidesticks are degraded and you lose more of the automatic protection features. You cannot go from direct to alternate or normal modes.

  4. Backup Mode. Backup mode happens after you lose all normal hydraulic pressure, if all four FCC channels fail, or the Backup Flight Control Unit (BFCU) loses feedback from the REUs. The backup mode uses its own computers and the EBHAs. The EBHAs will use normal hydraulic pressure if it is available or its own motors to use trapped hydraulic fluid to drive control surfaces without normal hydraulic pressure. In this control law, you have no gain at all any movement of the ACS will be directly reflected in the control surfaces. You will not have inboard and midboard spoilers, yaw trim, and your only pitch trim will be from the pedestal switch. You cannot go from this mode to any other.

These modes are not sequential, you don’t step from normal to alternate to direct to backup. It just depends on what kind of failure you are dealing with.

Software: Adding layers of safety

The Flight Control Computers have multiple layers to guard against faults. Each FCC contains two channels (A and B) with three power sources. An Uninterruptable Power Supply battery powers channels 1A and 2B, half the REUs, and the Backup Flight Control Unit. The Emergency AC bus keeps the UPS battery charged. With that bus unpowered, the UPS battery is good for about 30 minutes. The Left ESS powers FCC Channel 1B and the Right ESS powers FCC Channel 2A.

Each FCC channel has two lanes: a command lane (to send position commands) and a monitor lane (to duplicate monitor lane computations and check the command lane). The FCCs offer several features under normal mode designed to protect the aircraft:

  1. AOA limiting. Pitch control is restricted to prevent exceeding stall AOA. It activates approaching 0.88 or 0.93 AOA depending the rate of deceleration. The flight control system will reduce AOA for you if you do not. Full aft stick can only get you to 0.95 AOA. The only way to exit this mode is to reduce your AOA. More about this: Low Speed Awareness / Auto-Throttle Speed Protection.

  2. Note there are no AOA vanes. The AOA is computed from varying air pressures sensed by the air data probes. There are four probes, the system normally throws out the high and the low and averages the remaining two. If you are down to three probes, it takes the middle. If you are down to two probes it averages both. If you are down to one probe you are no longer in "normal" mode of the flight control system.

  3. High speed protection. Pitch control is restricted to prevent overspeed by limiting nose down authority. The protections are faded out as bank angle exceeds 60°. More about this: Auto-Throttle Speed Protection / High-Speed Protection.

  4. Maneuver load alleviation. The ailerons will symmetrically deflect upwards to reduce loads when the pilot command more than 1.5Gs, to as much as 3° deflection at or above 2.5 Gs.

  5. Speedbrake auto-retract. The speed brakes will automatically retract at approximately 90% thrust lever angle.

  6. Dynamic rudder limiting. The system will act to reduce pilot inputs that will overstress the rudder, though pilots are still cautioned against rudder reversals.

When things go wrong: Sensors

The loss of air or inertial data can cause the flight control system to degrade from normal to alternate mode. You can retain normal mode with two IRUs or with one IRU and the AHRS. Likewise, you can retain normal mode with at least two air data sources.

When things go wrong: Computers

If all four FCC channels become invalid (their command and monitor lanes don’t agree), a different set of software is used to take over in alternate mode. In this mode, flying qualities are the same as alternate mode except the sidesticks will be degraded and more of your protective features will be unavailable.

A Backup Flight Control Unit (BFCU) is designed for “get home capability” if both FCCs fail. It is powered by the UPS bus and has its own set of RVDTs in the sidesticks and rudder pedals. It communicates directly with REUs that control EBHAs which remain in active mode (using left and right system hydraulic pressure) unless hydraulic pressure is not available. The BFCU sends commands but does not receive position information, so control sensors will be shown as black and neutral.

When things go wrong: Hydraulics

Losing the left hydraulic system pressure and fluid limits your top speed to 285 KCAS / 0.90 M, means your flaps will not work, means you cannot use the autothrottles for approach and landing with flaps 10° or less, and means your midboard spoilers will be inoperative. Other than that, your flight control system remains in normal mode.

Losing the right hydraulic system pressure and/or fluid limits your top speed to 285 KCAS / 0.90 M and means your inboard spoilers will be inoperative. Other than that, your flight control system remains in normal mode.

Losing the left system pressure only limits your top speed to 285 KCAS / 0.90 M and means your midboard spoilers will be inoperative. Other than that, your flight control system remains in normal mode.

Losing left and right hydraulic system pressure places your flight controls and outboard spoilers into EB mode and limits your top speed to 285 KCAS / 0.90 M. If the failure occurred within 2 hours of takeoff you are to land at the nearest suitable airport (because the fluid will still be hot after takeoff and could weaken a seal to the point of leaking), otherwise you are to land “as soon as practicable.”

Losing left and right hydraulic system pressure and fluid adds to your woes in that you won’t have flaps so you can’t use autothrottles and cannot accept any tailwind if the flaps are 10° or less.

When things go wrong: Electrical

A fly-by-wire system obviously needs electrons to flow through those wires and losing all electrical power generation from the two engine-driven generators and the APU generator would be bad news. The flight control system normally gets its power through an Uninteruptable Power System (UPS) battery and the backup through an Electrical Backup Hydraulic Actuator (EBHA) battery. Both are good for only 30 minutes if not charged, so there is a Ram Air Turbine (RAT) generator to keep them charged.

A few things out of the ordinary

Unlike previous Gulfstreams, there isn’t a way to manually unlink the control stick as some earlier aircraft allow the yokes to be unlinked. There isn’t a jam monitor or hard over protection system to remove jammed or uncommanded control movement. You may get control surface fail CAS messages and the checklist does offer corrective action.

Unlike previous Gulfstreams, uncommanded ground spoilers are no longer considered a threat, in fact there are no procedures for such an event.

So, is it any good?

At first blush this seems to be a very good fly-by-wire system and it appears they’ve “thought of everything.” Of course, you never know about the thing you don’t know. One of the more ridiculous things I’ve ever read in a manufacturer’s publication is this, found on page 6-18 of the PAS:

Degrade to Backup Mode, BFCU Active (U), “Probability of occurrence is < 1 in a billion per flight hour.”

It reminds me of a similar statement from NASA about the chance of a catastrophic loss of a space shuttle. But I don’t fault Gulfstream for their faulty statistics, it is probably to be expected. The have every right to be proud of this airplane and this fly-by-wire system. I think this will be the system to emulate for many years to come.


How it Works . . .


Normal Operations — The What

From a pilot's perspective, all the stick does is control the pitch and roll of the aircraft while adding a few buttons to provide pitch and roll trim, autopilot disconnect, trim speed synchronization, HUD/EVS control, and a push-to-talk switch. The rudder pedals, speed brake handle, and various trim switches all "appear" to be conventional interfaces between pilot and aircraft.

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Photo: G500 Active Control Sidestick (ACS), left seat

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Photo: Rudder Pedals, PAS, p. 6-30

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Normal Operations — The Why

Why? Because during the first decade of manned powered flight, there were various methods for controlling ailerons, elevators, and rudders with no real standardization. Lawrence Sperry, founder of the Sperry Gyroscope Company, needed to have control inputs brought to a central location in a way easily connected to his gyroscopes. He settled on a stick to control pitch and roll, rudder pedals to control yaw. And one hundred years later, your G500 uses the same convention.

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Photo: 1913 Curtis Biplane outfitted with Sperry autopilot

Click photo for a larger image

Normal Operations — The How

Under normal operations, you move the Active Control Sidestick just as you would in any conventional airplane with a stick and the end result is movement in the ailerons and elevators. Between your hand and those controls, however, there is a small mechanic interface to an analog electrical interface, to a digital interface, some software, more digital electrics, some hydraulics, and finally a mechanical interface. There is a lot going on that appears to be very simple.

The Active Control Sidesticks

The Active Control Sidesticks are connected to an electronic device that turns the position of the stick into voltages as an output. It sits on motors that position the stick to reflect inputs from the rest of the airplane (the other stick, the controls themselves, and the stick shaker).

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Photo: G500 Active Control Sidesticks, GVII-G500 MM, §27-05-01

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Photo: G500 ACS range of motion, PAS, p. 6-25

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You move the stick with your hand to send electronic signals to the Flight Control Computers (FCC).

[PAS, p. 6-25] Range of motion: 10° Fwd, 15° Aft, 10° Left and Right

The Rudder Pedals

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Photo: G500 Rudder pedals, GVII-G500 MM, §27-22-02, figure 2

Click photo for a larger image

[PAS, p. 6-29] There are position sensors attached to the rudder pedals that a read by the Flight Control Computers (FCCs). The FCCs send these signals to the rudder REUs which command their respective actuators to move the rudder. The maximum deflection is 25° at low speeds, 3.6° and high speeds.

The Flap Handle

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Photo: G500 Flap handle, PAS, p. 6-36

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[PAS, p. 6-36] The "flap control module" is located on the center pedestal aft of the throttle quadrant. It electrically controls the Flap Electronic Control Unit (FECU).

The Speedbrake Handle

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Photo: G500 Speed brake handle, PAS, p. 6-40

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[PAS, p. 6-40] The speed brakes are electrically controlled.

The Trim Switches

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Photo: Pitch and roll trim control, PAS, p. 6-26

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[PAS, p. 6-26, 6-31]

  • Pitch and Roll Trim
  • The primary switches are on the Active Control Sidestick (ACS). A secondary way is with the pedestal pitch trim switches. If you trim using the ACS switches for more than 3 seconds the trim stops. When between 100 knots and VMO/MMO, trim will go no lower than AOA Limiting. Mistrim → Can't trim below 187 kts; requires 0.5G of force to maintain level flight at 250 kts if trimmed for 187 kts.

    I think what this means is the if you try to trim the airplane to fly too slowly, the trim refuses and you will have to apply 0.5G back pressure to fly that slowly.

  • Yaw Trim
  • The yaw trim switch is on the center console. When turned, a signal is sent to the Flight Control Computer to move the entire rudder. Spring loaded to center position.

The "magic" that goes on inside the Flight Control Computer

Two magical things happen in the FCC millions of time every second that makes your life easy but also your understanding of the system quite difficult. First, it turns those analog voltages from the various input sources into digital ones and zeros so it can be used by the computers inside the FCC and everywhere in the airplane where this information is needed. But it manages that data according to its own rules of conduct. The convention is to call these rules of conduct: Flight Control Laws.

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Photo: G500 Flight Control Computer, PAS, p. 6-1

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These "laws" are nothing more than a set of software instructions that tell the Flight Control Computer how to behave under certain sets of circumstances. When everything is normal, these laws tell the FCC to relay your inputs to the rest of the airplane and for the rest of the airplane to give you the feedback in your hands that tells you everything is normal.

[PAS, p. 6-10] FCCs contain software called Control Laws or CLAWS developed by Gulfstream specifically for G500 / 600. These laws makes the aircraft fly like a Gulfstream. They dampens undesirable aircraft motions such as Dutch roll. Some of the features designed for aircraft protection: AOA Limiting, High Speed Protection, Maneuver Load Alleviation, Speedbrake Auto-Retract, Dynamic Rudder Limiting, Elevator Split Load Limiting.

The ACS "outputs" to you

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Photo: G500 ACS force plate and sensor, PAS, p. 6-25

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The Flight Control Computers (FCC) send signals to the motors in the Active Control Sidesticks to reflect movement from the opposite ACS as well as "feel" from the associated flight control.

[PAS, p. 6-25] In active and degraded active modes, forces applied above the force plate are recognized and motors move stick to match amount of force.

[PAS, p. 6-22] In active mode, feedback mode provides a layer of situational awareness for control surface loading. This gives an “electronic feel” as stick forces change to simulate dynamic forces on flight control surfaces. The other pilot's inputs are also sent to the opposite stick. An autopilot and roll trim backdrive provides feedback in the sticks.)

[PAS, p. 6-22] The FCCs average sidestick position inputs. Sidestick motion is synchronized by cross-cockpit coupling. Input on one stick produces the same motion on the opposite stick.

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Photo: G500 Flight Control Synoptic legend, PAS, p. 6-54

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[PAS, p. 6-51]

  • Actuator info not displayed unless a malfunction exists.
  • Pitch trim indicates stab trim setting against a green takeoff band when WOW in ground mode and Perf Init CG entered.
  • Pitch trim indicates tick marks for pitch trim from 100 knots to 340 knots (60 knots per tick) when WOW in air mode and above 10' AGL.

The electrons from your input to the flight controls

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Photo: G500 Fly-by-wire architecture, PAS, p. 6-3

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The position of the Active Control Sidesticks are converted into an analog electrical signal by Rotary Variable Differential Transducers (RVDTs) which output a voltage to the Flight Control Computers. The FCCs convert these analog signals into digital signals which are sent along wires to the data buses and then to Remote Electronic Units (REUs), which translates the digital signals into instructions to the control actuators.

[PAS, p. 6-2] The flight controls are electrically controlled and hydraulically actuated. Two Flight Control Computers (FCC’s), each with 2 channels, convert the flight control input from the pilot, copilot, or autopilot to electronic signals. These electronic signals are sent to Remote Electronic Units (REU’s) which then command their respective hydraulic actuators to move, which moves the flight control surfaces to the requested position. In addition, a Backup Flight Control Unit (BFCU) can control the FCS in the event all 4 FCC channels fail.

From electrical signal to mechanical movement

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Photo: G500 Elevator EHSA actuator, GVII-G500 MM, §27-33-01

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The Electro-Hydraulic Servo Actuators (EHSA) turn the digital electrical signals from the REUs into control position movement using hydraulic pressure from normal (left or right) sources.

[PAS, p. 6-5]

  • There are 9 Electro-Hydraulic Servo Actuators (EHSAs): left aileron, right aileron, left elevator, right elevator, rudder, left inboard spoiler panel, left midboard spoiler panel, right inboard spoiler panel, and right midboard spoiler panel.
  • Use left or right hydraulic system pressure.
  • Commanded by an REU.

Pitch, Roll, and Yaw Control

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Photo: G500 Pitch and roll, PAS, p. 6-21

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[PAS, p. 6-20] Pitch Control

  • Conventional left and right elevators
  • Installed in horizontal tail

[PAS, p. 6-21] Roll Control

  • Conventional left and right ailerons — Installed in left and right wings on outer trailing edge
  • Mid and outboard spoiler panels — Installed in top, trailing edge portion of wings inboard of ailerons, extend max of 55° to improve roll response

[PAS, p. 6-29] Yaw Control

  • Conventional rudder surface installed in aft portion of vertical stabilizer
  • Max rudder deflection is scheduled as a function o Mach number: 25° at low speed, 3.6° at high speed

Secondary Flight Controls

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Photo: G500 Horizontal Stabilizer Control, PAS, p. 6-33

Click photo for a larger image

[PAS, p. 6-33] Horizontal Stabilizer Trim System (HSTS)

  • Located on top of vertical stabilizer, fully trimmable
  • Horizontal Stabilizer Trim Actuator (HSTA) located in the vertical stabilizer, two motors (one active, one standby), moves a jack screw.
  • Trim accomplished via switches on either Active Control Sidestick or the pitch trim switch on the pedestal.
  • Under normal conditions the pilot only trims the stabilizer on the ground
  • The stabilizer automatically offset any persistent elevator offset. The stabilizer and elevators move simultaneously in opposite directions with a rate depending on airspeed. The stabilizer moves to a new trim position while the elevator moves to a "faired" position.
  • FCCs command stabilizer to 0° position after landing (approximately 20 seconds after ground spoiler retraction, 10 seconds after speed drops below 42 knots.
  • Takeoff pitch trim is automatically set if FMS PERF and Takeoff Init done prior to Initiating FCS test.
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Photo: G500 Flaps hydraulic control module, PAS, p. 6-37

Click photo for a larger image

[PAS, pp. 6-37, 6-38]

  • A Flap Electronic Control Unit (FECU) receives information from 2 Flap Handle RVDT and a rotary switch.
  • The FECU has control and monitor lanes which prevent flap movement in the event of a disagreement.
  • A Hydraulic Control Module (HCM) provides hydraulic system pressure to a Power Drive Unit (PDU) as commanded by the FECU.
  • The PDU turn flap actuators through torque tubes to position flaps.

Spoilers

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Photo: G500 Spoilers synoptic, PAS, p. 6-41

Click photo for a larger image

[PAS, p. 6-41] Ground Spoilers

  • During rejected takeoff or at touchdown, all spoiler panels deploy to 55°, ailerons fully deploy trailing edge up (full roll authority still available for crosswinds), increases drag, spoils lift which improves brake effectiveness
  • Triggers automatically when both throttles are at idle and one of the following criteria met: both main gear WOW = Ground, one main gear WOW = G and opposite wheel spin > 47 kts, or both main wheels spin and radar alt < 10’ and either flaps > 21° or GPWS Flap Inhibit selected
  • Auto stow when:
    • Airspeed and wheel speed < 42 kts for 10 secs, or
    • Either throttle not at idle, or if 2 of following 3 occur: both MLG WOW in air mode, wheel speed < 47 kts, or RA > 10'

Speed Brakes

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Photo: G500 Speed Brakes synoptic, PAS, p. 6-43

Click photo for a larger image

[PAS, p. 6-43] Speed Brakes

  • Manually operated with handle on center pedestal; to operate first move to left and then pull aft.
  • Proportional to lever displacement; max extension in flight is 30°, on ground 55° with flaps ≥ 10° (with radio altimeter < 10' and WOW from either main gear, or 30° with flaps < 10°.
  • Electrically controlled from RVDT in handle, sends signal to FCCs.
  • When handle moved aft, CAS: Speed Brakes Extended
  • If thrust lever angle > 26° CAS: Speed Brakes Extended
  • If thrust lever angle increased > 90° the spoiler panels auto retract (handle remains extended), CAS: Speed Brakes Auto Retract.

Roll Spoilers

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Photo: G500 Roll Spoilers synoptic, PAS, p. 6-44

Click photo for a larger image

[PAS, p. 6-44] Roll Spoilers

  • Midboard and outboard spoilers work in conjunction with ailerons to improve roll response
  • Fully automatic; sidestick roll signals from RVDTs are sent to FCCs which send commands to REUs that control the spoiler actuators
  • Spoiler extension varies based on sidestick inputs, 55° maximum

Synoptics Legend

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Photo: Synoptics Legend (Sheet 1), G500 AFM, §03-13-190, sheet 1

Click photo for a larger image

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Photo: Synoptics Legend (Sheet 2), G500 AFM, §03-13-190, sheet 2

Click photo for a larger image

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Photo: Synoptics Legend (Sheet 3), G500 AFM, §03-13-190, sheet 3

Click photo for a larger image


The Components in Greater Detail . . .


Active Control Sidesticks

The Active Control Sidesticks are designed to act like they are connected to pitch and roll control surfaces by cables and pulleys but produce a feel that changes throughout the flight envelope. You end up with an easier to fly airplane that protects you from you, or so they say. These sticks are unlike what you will find in an Airbus or Falcon; Gulfstream has learned from their mistakes.

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Photo: Active Control Sidesticks, PAS, p. 6-22

Click photo for a larger image

[PAS, pp. 6-22 to 6-24]

  • Located on left and right side of flight deck, each contains an internal computer with 2 channels, one active, one in standby.
  • Electronically controlled to provide feel, centering, and dampening.
  • FCC’s average sidestick position inputs.
  • When sidestick motion is synchronized by cross-cockpit coupling, sidesticks are linked to each other. Input on one stick → Same motion on opposite stick.
  • Operational modes
    • Active Mode: Provides feedback via an "electronic feel," stick forces change to simulate dynamic forces on flight control surfaces, as well as from autopilot, roll trim, and stick shaker. Stick moves in response to other pilot's inputs.
    • Degraded Active Mode: Caused by loss of data from both FCCs or a miscompare between sidesticks. Electronic feel is degraded (uses fixed versus variable gains), could result in less than optimal handling during high speed cruise or low speed approach and landing.
    • Passive Mode: A reversionary mode which can be caused by internal failures in sidesticks or loss of data from FCCs. It could happen to one stick and not the other. Can result in a loss of electronic feel, centering, damping, and less than optimal handling characteristics. If it happens in flight you can continue to destination, but on the ground you cannot dispatch.
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Photo: Cross cockpit coupling, PAS, p. 6-23

Click photo for a larger image

AP DISC / TSS button

That little red button appears to do three things in this airplane: disconnect the autopilot, stop runaway trim, and trim for 1G flight.

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Photo: AP DISC / TSS button, PAS, p. 6-27

Click photo for a larger image

[PAS, pp. 6-22 to 6-27]

  • AP DISC disengages the autopilot on the first press and silences the autopilot disengagement tone on the second.(Too much pressure on the sidestick also disengages the autopilot.
  • AP DISC also stops runaway trim on all three axis.
  • TSS (Trim Speed Sync) is available with the autopilot off: trims pitch for 1G at current speed. (Should not be used in a level turn.)

Backup Flight Control Unit (BFCU)

The Backup Flight Control Unit (BFCU) is more than just a backup Flight Control Computer, it includes backup Rotary Variable Differential Transducers (RVDTs), electrical power source, and actuators. You lose a number of capabilities, but you will still be flying.

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Photo: G500 Backup Flight Control Unit (BFCU), PAS, p. 6-9

Click photo for a larger image

[PAS, p. 6-9]

  • Designed for “get home capability” if both FCCs fail: Chance of that happening → 1 in 1 billion per flight hour
  • Powered by UPS bus
  • Has own set of RVDTs for sidesticks and rudder pedals
  • Outboard spoiler roll control is provided; Speedbrake and ground spoiler functions are inop
  • Once active
    • Communicates directly with REUs that control EBHAs
      • EBHAs not in electrical backup mode in this case; Unless normal hyd power not available
      • Utilizes separate, single-direction backup data buses, so REUs can’t communicate back to the cockpit
      • Actuators and surface positions unknown thus not displayed
      • Synoptic indications
        • Control surface positions black and neutral
        • Non-EBHA REUs amber
        • Inop spoilers and trim displayed with amber X
    • Active for duration of flight (can’t be reset to FCC ops)
    • EBHAs inop < 47 kts

Data Buses

So what is a data bus? It can be as simple as a wire or as complicated as a bank of networked computers. Many of the systems on the G500 are on a bus connected through Data Concentration Units. I don't think that is the case with the flight controls, but I am still in research mode.

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Photo:

Click photo for a larger image

Flap Electronic Control Unit (FECU)

You can think of the Flap Electronic Control Unit (FECU) as the Flight Control Computer for the flaps.

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Photo: G500 FECU AMM, §27-55-02, fig. 3

Click photo for a larger image

[PAS, p. 6-37]

  • 2 power sources for redundancy: Left and Right Ess DC
  • Receives info from 2 Flap Handle RVDT’s and a rotary switch (Provides redundant info to FECU to determine valid flap commands)
  • FECU has command and monitor lanes: Command lane sends info from FECU to Hydraulic Control Module (HCM). Monitor lane monitors commanded flap position, Flap position, flap speed, and the direction of movement.
  • Command and Monitor lanes must agree on commanded flap position before flaps are allowed to move.
  • Flap malfunctions (jam, asymmetry, runaway, etc.) will interrupts flap motion by stopping hydraulic pressure at the HCM.

Flaps

The flaps are controlled by a handle that is little more than a switch and an RVDT that sends electrons to a computer (FECU) which send signals to a hydraulic motor (PDU). Everything is monitored and there is no "backup" or "alternate" as found on the GIV and earlier.

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Photo: G500 Flaps hydraulic control module, PAS, p. 6-37

Click photo for a larger image

[PAS, pp. 6-36 to 6-38]

  • Fowler type flaps track rearward and downward, mounted in four flap tracks attached to rear wing spar.
  • A Flap Electronic Control Unit (FECU) receives information from 2 Flap Handle RVDT and a rotary switch.
  • The FECU has control and monitor lanes which prevent flap movement in the event of a disagreement.
  • A Hydraulic Control Module (HCM) provides hydraulic system pressure to a Power Drive Unit (PDU) as commanded by the FECU.
  • Hydraulically powered by left, PTU, or Aux systems.
  • The PDU turn flap actuators through torque tubes to position flaps.
  • The elevator is biased trailing edge up when flaps are extended to compensate for a nose-down pitching moment.
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Photo: G500 Flaps indications, PAS, p. 6-39

Click photo for a larger image

Flight Control Computers (FCCs)

The Flight Control Computers (FCCs) take in all the inputs (including what your hands and feet are doing, what the atmosphere is doing, and what the various flight control components are doing) and output instructions to those components and report back to you what is going on. Those magical Flight Control Laws are nothing more than a list of rules the FCC follows under various conditions. Each FCC includes a lot of redundancy and backup systems, and there are two of them. If they both fail, you also have a Backup Flight Control Unit (BFCU).

[PAS, p. 6-4]

  • FCC #1 located in the LEER
  • FCC #2 located in the REER
  • Backup Flight Control Unit (BFCU) located under cabin floor just aft of EERs
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Photo: G500 Flight Control Computers (FCCs), PAS, p. 6-7

Click photo for a larger image

Components

[PAS, p. 6-7]

  • Each FCC contains
    • 2 Channels (A and B)
    • Cooling fan between channels
  • Power Sources (3)
    • UPS → FCC 1A & FCC 2B
    • Left Ess → FCC 1B
    • Right Ess → FCC 2A
    • UPS → BFCU
  • FCC Channels (4)
    • Contain the Control Laws (CLAWS)
      • Programming for each flight control surface
      • Housed within each FCC channel
      • Normally one channel from each FCC sends inputs to REU; REU averages the 2 inputs then commands its actuator
      • If needed, any single channel can control all flight controls; Quadruple redundancy
    • Each channel contains 2 lanes
      • Command Lane; Sends position commands to:
        • Control surface actuators
        • Monitor Lane
      • Monitor Lane
        • Performs same computation as Command Lane
        • Compares calculations to Command Lanes
      • Each lane utilizes
        • Same type of hardware (A or B)
        • Different software; Act as self-checking pair for error detection
    • FCC 2/3 Synoptic indications
      • Green = Powered
      • Green and boxed Green = Active
      • Green and boxed Gray = Standby
      • White = Inactive

Flight Control Actuators

There are 9 actuators for normal operations called Electro-Hydraulic Servo Actuators (EHSAs) that take signals from an REU and fluid from either the left or right hydraulic systems and turn that into a physical movement of the associated aileron (2), elevator (2), rudder (1), and midboard and inboard spoilers (4).

There are also 7 backup actuators for abnormal operations called Electrical Backup Hydraulic Actuators (EBHAs) to drive the ailerons (2), elevator (2), rudder (1), and the outboard spoilers (2). The EBHAs can use left or right hydraulic system pressure, if available. If not available, the EBHA has a pump that uses trapped hydraulic fluid to provide its own pressure. The EBHA has its own REU that receives FCC commands but does not report back control surface position.

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Photo: G500 Left Elevator EHSA, IPC, §27-33-01, fig. 1

Click photo for a larger image

[PAS, pp. 6-5 to 6-6]

  • Two actuators for each primary flight control surface
    • Aileron (4)
    • Elevator (4)
    • Rudder (2)
  • One actuator for each spoiler panel (6), 2 Types
    • (9) Electro-Hydraulic Servo Actuators (EHSA’s)
      • One for each primary flight control surface (5)
      • One for each Inboard and Midboard spoiler panel (4)
      • Uses Left or Right Hydraulic System pressure
      • Commanded by an REU
    • (7) Electrical Backup Hydraulic Actuators (EBHA’s)
      • One for each primary flight control surface (5)
      • One for each outboard (multifunction) spoiler (2)
      • Normally uses left or right hydraulic system pressure
      • Normally commanded by an REU
      • If normal hydraulic pressure not available
        • Reverts to Electric Backup (EB) mode
        • Utilizes electric power to drive a pump at the actuator
          • Pressurizes trapped hydraulic fluid
          • Acts as a third hydraulic system
      • Each EBHA has a EBMCE with dual roles for that actuator
        • Powers the pump for trapped hyd fluid
        • Backup REU
          • Able to receive FCC commands
          • Unable to report back the control surface position
  • Normal operation of primary flight control surface actuators
    • EHSA & EBHA on each single surface
      • Active
      • Powered by their respective Left or Right hydraulic system
    • REU’s compare commanded to actual surface position; If error detected → New command sent to correct error
  • Actuators operate in one of the following modes or states
    • EHSA’s
      • Active
      • Damped Bypass
    • EBHA’s
      • Active
      • Damped Bypass
      • Electric Backup (EB)
  • Active Mode
    • Normal state of operation
    • Powered by Left or Right Hydraulic System pressure
  • Damped Bypass Mode
    • If actuator fails (hydraulic loss, REU fail, etc): Reverts to a damped condition; Hyd pressure trapped within actuator; Suppresses surface flutter in flight
    • For surfaces with dual actuators (primary flight controls): Damped actuator will passively follow the working actuator
  • EB Mode
    • EBHA’s only
    • When normal hydraulic pressure not available for that surface; Utilizes electric power to drive a motor pump at the actuator
      • Pressurizes trapped hydraulic fluid
      • Acts as a third hydraulic system

Flight Control System Batteries

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Photo: G500 FCS Batteries, PAS, p. 6-45 and 6-46

Click photo for a larger image

[PAS, p. 6-45]

  • Electric Battery Hydraulic Actuators (EBHA) battery powers Electric Backup Hydraulic Actuators' Motor Control Electronics (MCEs).
  • UPS Battery powers FCC Channels 1A and 2B, Backup Flight Control Unit (BFCU), and provides a secondary power source for Remote Electronic Units (REU’s).
  • Select ON in any order (Checks volts per Airplane Power-Up checklist, powers actuators before the computers, initiates a System Power-On Self-Test; takes about 45 seconds.

Horizontal Stabilizer Trim Actuator (HSTA)

The Horizontal Stabilizer Trim Actuator (HSTA) is a conventional jack screw connected to two motors which are controlled by Motor Control Electronics (MCE).

images

Photo: G500 Horizontal Stabilizer Control, PAS, p. 6-33

Click photo for a larger image

[PAS, p. 6-33] Horizontal Stabilizer Trim System (HSTS)

  • Horizontal Stabilizer Trim Actuator (HSTA) is located in the vertical stabilizer and has dual and identical electric motor-brake assemblies. One motor is capable of full HSTA performance. One motor is active while the other is in standby mode. The motor moves a jack screw → Moves the stab control surface.
  • Located on top of vertical stabilizer, fully trimmable
  • Horizontal Stabilizer Trim Actuator (HSTA) located in the vertical stabilizer, two motors (one active, one standby), moves a jack screw.
  • Trim accomplished via switches on either Active Control Sidestick or the pitch trim switch on the pedestal.
  • Under normal conditions the pilot only trims the stabilizer on the ground
  • The stabilizer automatically offset any persistent elevator offset. The stabilizer and elevators move simultaneously in opposite directions with a rate depending on airspeed. The stabilizer moves to a new trim position while the elevator moves to a "faired" position.
  • FCCs command stabilizer to 0° position after landing (approximately 20 seconds after ground spoiler retraction, 10 seconds after speed drops below 42 knots.
  • Takeoff pitch trim is automatically set if FMS PERF and Takeoff Init done prior to Initiating FCS test.
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Photo: G500 Horizontal Stabilizer Synoptics, PAS, p. 6-35

Click photo for a larger image

Primary Pitch Trim Switches

Pitch trim is automatic on two levels. If you simply push or pull the nose to where it needs to be, the stabilizer moves to center the elevator, relieving you of the need to apply pressure. But if you don't want to wait for that, pressing the AP DISC/TSS button the stabilizer trims for 1G at the current speed. But you can trim the old fashion way if you wish.

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Photo: Primary Pitch Trim Switches, PAS, p. 6-26

Click photo for a larger image

[PAS, p. 6-26]

  • Forward / Aft = NOSE DN / NOSE UP (split switch to prevent inadvertent activation)
  • Left / Right = LWD / RWD
  • Trims entire control surface (no trim tabs)
  • FCCs move stabilizer to "offload" elevator to keep it faired
  • Trim stops if switch activated for more than 3 seconds
  • Trim range: 100 knots to VMO / MMO
  • Will not trim to less than AOA limiting
  • If airspeed greater than 250 knots, will not trim to less than 187 knots (will require 0.5G back pressure to maintain level flight)

Remote Electronics Units (REUs)

There are seven Remote Electronics Units (REU) located between the FCC and the associated actuator, and an eighth REU between the FCC and the Horizontal Stabilizer Trim System (HSTS). Each REU translates FCC signals into control movement, monitors that movement and reports back to the FCC, and disables actuation channels if anomalies occur.

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Photo: Remote Electronic Units (REUs), GVII-G500 MM, §27-04-01, figure 6

Click photo for a larger image

[PAS, p. 6-3] 8 Remote Electronics Units (REUs)

  • Multichannel
  • Provide control and monitoring of Primary Flight Control Actuation System (PFCAS) and Horizontal Stabilizer Trim System (HSTS)
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Photo: Remote Electronic Units (REUs), PAS, p. 6-4

Click photo for a larger image

[PAS, p. 6-4]

  • Control actuators and HSTS based on FCC commands
  • Report control surface positions back to FCC’s
  • Located in multiple locations
    • Wings (4)
    • Tail (3)
    • Main gear well (1)
  • Each REU has 2 DC power sources for redundancy
  • Multi-channel (2) each with command and monitor lanes
    • Independently receive and process: FCC signals, Sensor data
    • Verifies proper actuator response: If anomalies occur, can disable actuation channels and data buses, reverts to a fail-safe state to prevent erroneous outputs
    • Each actuator has its own REU channel
  • Auto re-engagement of actuators in flight
    • With loss of and subsequent restoration of: REU electric power, Hydraulic pressure
    • FLT CTRL RESET Switch not required

Rotary Variable Differential Transducers (RVDTs)

When you get rid of pulleys, cables, and levers in a flight control system you end up needing a way to measure rotational movements, such as the angle of the power levers, position of the ailerons, etc. A Rotary Variable Differential Transducer (RVDT) is something like a very precise potentiometer. It takes an electrical input and varies the output according to the angle that is being measured. It makes for an inaccurate measurement if done purely using the analog output. But coupled to a computer and turned digital, it can be very precise.

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Photo: G500 Spoiler RVDT (Item C), MM, §27-64-01, fig. 2 sheet 2

Click photo for a larger image

This is just an example, from one of the spoiler panels. The RVDT is the round part of Item C in the drawing.

Rudder Pedals

The rudder pedals feel "normal" though there are only electrons between you and the rudder.

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Photo: G500 Rudder pedals, PAS, p. 6-30

Click photo for a larger image

[PAS, pp. 6-29 to 6-30]

  • Pilot and copilot rudder assemblies are mechanically connected.
  • The pedals will move +/- 3" from neutral.
  • There are position sensors attached to the rudder pedals that a read by the Flight Control Computers (FCCs). The FCCs send these signals to the rudder REUs which command their respective actuators to move the rudder. The maximum deflection is 25° at low speeds, 3.6° and high speeds.
  • Artificial feel is provided by damper and spring, rudder force is proportional to pedal displacement

Spoilers / Speed Brakes

There are 3 panels on each wing: inboard, midboard, and outboard. The inboards and outboards are powered by the right hydraulic system, the midboards by the left hydraulic system. Only the outboards have a non-hydraulic backup through Electronic Backup Hydraulic Actuators (EBHAs). The Byzantine valve system of earlier Gulfstreams is gone, all the protection now is from the Flight Control Computer.

Spoilers

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Photo: G500 Spoilers synoptic, PAS, p. 6-41

Click photo for a larger image

[PAS, p. 6-41] Ground Spoilers

  • During rejected takeoff or at touchdown, all spoiler panels deploy to 55°, ailerons fully deploy trailing edge up (full roll authority still available for crosswinds), increases drag, spoils lift which improves brake effectiveness
  • Triggers automatically when both throttles are at idle and one of the following criteria met: both main gear WOW = Ground, one main gear WOW = G and opposite wheel spin > 47 kts, or both main wheels spin and radar alt < 10’ and either flaps > 21° or GPWS Flap Inhibit selected
  • Auto stow when:
    • Airspeed and wheel speed < 42 kts for 10 secs, or
    • Either throttle not at idle, or if 2 of following 3 occur: both MLG WOW in air mode, wheel speed < 47 kts, or RA > 10'

Speed Brakes

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Photo: G500 Speed Brakes synoptic, PAS, p. 6-43

Click photo for a larger image

[PAS, p. 6-43] Speed Brakes

  • Manually operated with handle on center pedestal; to operate first move to left and then pull aft.
  • Proportional to lever displacement; max extension in flight is 30°, on ground 55° with flaps ≥ 10° (with radio altimeter < 10' and WOW from either main gear, or 30° with flaps < 10°.
  • Electrically controlled from RVDT in handle, sends signal to FCCs.
  • When handle moved aft, CAS: Speed Brakes Extended
  • If thrust lever angle > 26° CAS: Speed Brakes Extended
  • If thrust lever angle increased > 90° the spoiler panels auto retract (handle remains extended), CAS: Speed Brakes Auto Retract.

Roll Spoilers

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Photo: G500 Roll Spoilers synoptic, PAS, p. 6-44

Click photo for a larger image

[PAS, p. 6-44] Roll Spoilers

  • Midboard and outboard spoilers work in conjunction with ailerons to improve roll response
  • Fully automatic; sidestick roll signals from RVDTs are sent to FCCs which send commands to REUs that control the spoiler actuators
  • Spoiler extension varies based on sidestick inputs, 55° maximum

Yaw Trim

The Yaw Trim switch sends signals to the Flight Control Computer with instruction to trim the entire surface.

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Photo: Yaw trim controls, PAS, p. 6-31

Click photo for a larger image

[PAS, p. 6-31] The yaw trim switch is on the center console. When turned, a signal is sent to the Flight Control Computer to move the entire rudder. Spring loaded to center position.

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Photo: Yaw trim controls, PAS, p. 6-32

Click photo for a larger image


Limitations and Abnormal Procedures . . .


Limitations

[AFM, §01-27-10] Normal Control Laws

  • Continued flight at or below stick shaker activation speed is prohibited.

  • NOTE

    The AOA limiting / stall protection system is only available in the normal flight control mode. Stick shaker/stall warning is provided in Alternate mode at 0.85 AOA.

  • Speed brake extension with flaps 39 or with landing gear extended is prohibited.

[AFM, §01-27-20] Degraded Control Laws

  • Flight into known icing conditions is prohibited when operating in a flight control law mode other than normal (Alternate, Direct or Backup). If the flight control law mode degrades from normal while in icing conditions, exit icing conditions as soon as possible.

  • NOTE

    The AOA limiting / stall protection system is only available in the normal flight control mode. Stick shaker/stall warning is provided in Alternate mode at 0.85 AOA.

  • Intentional degradation from normal mode or disabling of any flight control system is prohibited.

References

Gulfstream GVII-G500 Airplane Flight Manual, Revision 1, August 31, 2018

Gulfstream GVII-G500 Aircraft Maintenance Manual, Revision 2, December 15/18

Gulfstream GVII-G500 Illustrated Parts Catalog, Revision 2, December 15/18

Gulfstream GVII-G500 Production Aircraft Systems, Revision 1, Oct 1, 2018

Revision: 20190524
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