AUTOPILOTS GPS SATELITE NAVIGATION

If you say 'Autopilot' most people think of airplanes. But boats also use autopilots. Indeed, boats can probably go one better. Airplanes usually only go between two waypoints: the takeoff location and the landing destination. In between an aircraft autopilot adjusts altitude and can even land a plane by itself to preset program parameters. This is especially useful in adverse weather conditions such as fog.

Autopilots are also used in boats, more correctly known as an Autohelm. Cars don't have auto-steering equipment. That's a long way off. But they do have GPS navigation aids such as TomTom and Garmin, which can plot a complicated route based on digital road maps. it might never be practical to build cars with auto steering/braking/accelerating, etc, but it is possible, and with sensors to detect other vehicles - who knows. But as we say, it's not practical or cost effective at the moment.

Most navigation aids these days use the satellite based Global Positioning System or GPS, to tell a captain where his boat or airplane is on the surface of the planet, or where a cyclist is, to include his speed, etc, calculated between satellite readings.

The most advanced marine autopilot conceptually is called: "Bruce." Once you've input the waypoints, 'Bruce' can literally sail around the world for you. Unfortunately, Bruce is a fictional autopilot that is operated by an advanced computer aboard the SolarNavigator in the John Storm adventure series.

Modern Autohelms are very advanced, but not as clever as the fictional Bruce. One day we will have Bruce for real; we're not that far off now. You communicate with Bruce by speaking to him. Bruce prefers to be thought of as male in gender but can be programmed to be female. Bruce has limited artificial intelligence capability, so that to the human operator he (or she) can have a conversation about headings, speed and a host of other variables, to include add-ons that close watertight hatches and trim the craft for bad weather.

You can't buy Bruce just yet, but you can buy some very good GPS based electronic, or mechanical self steering gear as seen on this page and via the links at the bottom of the page. As most market development is lead by consumer preferences, the more your purchases steer towards Bruce, the sooner a Bruce or Sheila will hit the market shelves.

Self-steering gear is equipment used on ships and boats to maintain a chosen course without constant human action. It is also known by several other terms, such as autopilot (borrowed from aircraft and considered incorrect by some) and autohelm (technically a Raymarine trademark, but often used generically). Several forms of self-steering gear exist, divided into two categories: electronic and mechanical.

Electronic self-steering is controlled by electronics operating according to one or more input sensors, invariably at least a magnetic compass and sometimes wind direction or GPS position versus a chosen waypoint. The electronics module calculates the required steering movement and a drive mechanism (usually electrical, though possibly hydraulic in larger systems) causes the rudder to move accordingly.

There are several possibilities for the interface between the drive mechanism and the conventional steering system. On yachts, the three most common systems are:

Direct drive, in which an actuator is attached to the steering quadrant, at the top of the rudder stock inside the boat. This is the least intrusive method of installation.

Wheel mounting, in which a motor is mounted near the steering wheel, and can be engaged with it when in use. This typically involves either a belt drive or a toothed gear-ring attached to the wheel itself, and is a common option for retro-fitted installations on yachts with a wheel.

Tiller-pilots are usually the only option on smaller vessels steered with a tiller. They consist of an electrically driven ram which is mounted between the tiller and a fitting on the side of the cockpit. Some are entirely self-contained, needing only a power supply, while others have the control unit separate from the actuator. These are quite popular, as they are maintenance-free and easy to install.

Workings of a marine tiller-pilot

Depending on the sophistication of the control unit (e.g. tiller pilot, steering wheel attached Chartplotter, ...), electronic self-steering gear can be programmed to hold a certain compass course, to maintain a certain angle to the wind (so that sailing boats need not change their sail trim), to steer towards a certain position, or any other function which can reasonably be defined. However, the amount of power required by electrical actuators, especially if constantly in action because of sea and weather conditions, is a serious consideration. Long-distance cruisers, which have no external source of electricity and often do not run their engines for propulsion, typically have relatively strict power budgets and do not use electrical steering for any length of time. As the electronic autopilot systems require electricity to operate, many vessels also make use of PV solar panels or small wind turbines on the boat. This eliminates extra pollution and cuts costs.

Mechanical or "wind vane" self-steering started out as a way to keep model sail boats on course. The first time that it was used to cross an ocean was on a motorboat. The most widespread form of self steering, the servo pendulum was introduced to cope with the power requried to operate a larger rudder and was a successor to the servo trim tab principle. (introduced by Herbert "Blondie" Hasler) Both methods use the power derived from the motion of the boat through the water to hold a constant angle to the wind with the use of the boat's main rudder. Despite the popularity of servo systems one manufacturer has successfully developed a system that uses an auxiliary rudder direct from the windvane; the picture of the windvane shown uses this principle with the previously used large fabric vane on a vertical axis.(the use of wind vanes with a horrizontal axis is now predominant used) Offshore, the wind direction is relatively stable, so over a number of hours this results in a reasonably constant compass course, and also means that the sails need not be adjusted. Mechanical self-steering can be complicated to set up, so it is typically used only for long-distance sailing where the same course is maintained for long periods. Many boats fitted with mechanical self-steering also carry an electrical autohelm for use over shorter periods where it is not worth setting up the wind vane.

Mechanical self-steering gear is made by a number of manufacturers, but most share the same principle. A narrow upright board, the wind vane, is mounted on a horrizontal axis carrier that is itself rotated so that with the boat traveling in the desired direction the vane is vertical and edge-on to the wind. The wind vane is held upright by a small weight below the pivot, but if the boat turns so that the board is no longer edge-on to the wind it will be blown over to one side as the extra surface area is revealed. This movement is transmitted by a series of linkages to a blade (or oar) in the water. In the simplest devices this blade acts directly as a secondary rudder, and steers the boat back onto the proper course however most designs of windvane self steering find that the force provided by the wind vane alone is not sufficient to make this system work and hence a so-called servo pendulum system is used.

As the blade described above turns, the pressure of water moving past it causes it to swing out sideways on the end of a pivoted rod. The length of this rod and the speed of the water means that a considerable force is available at the top end of it, sufficient to change the course of much larger boats. This is achieved either by a connection to the main wheel or tiller (typically involving a complex arrangement of lines and blocks rigged around the stern of the boat) or by fixing the main steering in place and equipping the self-steering gear with its own rudder. Once the boat has moved back to its correct course, the wind vane stands up again as it is no longer blown over by the wind.

To make wind vane self steering work well it is essential to have the vessel's sails balanced with little load on the rudder before any attempt is made to engage the self steering. With the sails are trimmed correctly wind vane self-steering is very effective. Some experimentation and judgement is usually needed, however, to determine the proper settings for a given vessel and steering mechanism. In addition, wind vanes perform poorly in very light winds, as the forces needed to operate them are much reduced. The same applies when travelling downwind, as the apparent wind speed is reduced by the speed of the boat.

As well as their requirement for power, many long-distance cruisers observe that electronic self-steering machinery is complex and unlikely to be repairable without spare parts in remote areas. By contrast, the often agricultural-looking mechanism of a wind vane gear offers at least the possibility of an improvised repair at sea, and can usually be rebuilt on land using non-specific parts (sometimes plumbing parts) by a local welder or machinist.

Another version of wind vane self steering on sail boats is known as the vertical axis vane and usually, because of the inferior power it has to its Servo Pendulum cousins it makes use of a trim tab hung off the rudder to control the course of the boat. The vane spins at right angles to the ground and can lock to the trim tab in any desired position, as the boat falls off the wind the vane will be turned by the wind and will take the trim tab with it which in turn causes the rudder to move in the opposite direction and thus corrects course. Generally self steering like this, with a trim tab can only be used on boats with transom (or aft hung double enders) rudders as the trim tab needs to be mounted directly to and aft of the rudder to produce the desired effect, and of course has to be controlled even as the rudder swings side to side. This is typically accomplished by use of a slotted bar in which the connection to the vane assembly can slide in as the rudder turns. These self steering systems are generally simpler and are thus easier to set and adjust course as they don't make use of lines controlling the rudder but control it more directly through solid linkages.

A related device has been used on some windmills, the fantail, a small windmill mounted at right angles to the main sails which automatically turns the heavy cap and main sails into the wind, (invented in England in 1745). (When the wind is already directly into the main vanes, the fantail remains essentially motionless.)

A popular source on contemporary windvane technology is The Windvane Self-Steering Handbook. One particularly valuable contribution of Morris's book is his coverage of the variety of alloys used in vane gear manufacturing. Morris admits to his practice of setting a kitchen timer for a half hour at a time and sleeping while the windvane steering device controls the helm, even in head winds of 25 to 35 knots. In a recent interview, he said he once narrowly missed being hit by a huge freighter while sleeping on his sail up the Red Sea. Morris points out, "An autopilot wouldn't have made any difference in this case. If I had been using an electronic autopilot, that freighter still would have been there. I made a choice to sail two-thirds of my circumnavigation single-handed, and I accepted the risks that came with that decision. I guess fate was on my side."

Developments

For quite a long time there was little development in the self steering systems that were available commercially. Most new developments came in the form of self-build systems. Crucial roles were played by Walt Murray, an American who published his designs on his website, and Dutchman Jan Alkema who developed a new windvane, the so called Up Side Down windvane (USD for short, commercially available from only one brand) and a new kind of servo pendulum system that could be fitted to boats with a transom hung rudder. For this last invention Jan Alkema was rewarded the John Hogg-Price from the AYRS ( Amateur Yacht Research Society) in 2005. Jan Alkema published a lot of his inventions on Walt Murray's website.

Famous self-steering boats

Some of the most famous self-steering boats include:
Maltese Falcon
Shin Aitoku Maru
Son of Town Hall, self-steering junk raft which made a transatlantic crossing in 1998

An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles. The autopilot of an aircraft is sometimes referred to as "George", after one of the key contributors to its development.

In the early days of aviation, aircraft required the continuous attention of a pilot in order to fly safely. As aircraft range increased allowing flights of many hours, the constant attention led to serious fatigue. An autopilot is designed to perform some of the tasks of the pilot.

The first aircraft autopilot was developed by Sperry Corporation in 1912. The autopilot connected a gyroscopic Heading indicator and attitude indicator to hydraulically operated elevators and rudder (ailerons were not connected as wing dihedral was counted upon to produce the necessary roll stability.) It permitted the aircraft to fly straight and level on a compass course without a pilot's attention, greatly reducing the pilot's workload.

Lawrence Sperry (the son of famous inventor Elmer Sperry) demonstrated it two years later in 1914 at an aviation safety contest held in Paris. At the contest, Sperry demonstrated the credibility of the invention by flying the aircraft with his hands away from the controls and visible to onlookers of the contest. This autopilot system was also capable of performing take-off and landing, and the French military command showed immediate interest in the autopilot system. Elmer Sperry Jr., the son of first gyro auto-pilot, Lawrence Sperry, and Capt Shiras continued work after the war on the auto-pilot developed by Elmer Sperry's father, and in 1930 test a more compact and reliable auto-pilot which kept a US Army Air Corps aircraft on a true heading and altitude for three hours, that was probably of the type used by Wiley Post to fly alone around the world in less than eight days in 1933.

In 1930 the Royal Aircraft Establishment in England developed an autopilot called a pilots' assister that used a gyroscope and compressed air to move the flight controls.

Further development of the autopilot were performed, such as improved control algorithms and hydraulic servomechanisms. Also, inclusion of additional instrumentation such as the radio-navigation aids made it possible to fly during night and in bad weather. In 1947 a US Air Force C-54 made a transatlantic flight, including takeoff and landing, completely under the control of an autopilot.

In the early 1920s, the Standard Oil tanker J.A. Moffet became the first ship to use an autopilot.

Modern autopilots

Not all of the passenger aircraft flying today have an autopilot system. Older and smaller general aviation aircraft especially are still hand-flown, and even small airliners with fewer than twenty seats may also be without an autopilot as they are used on short-duration flights with two pilots. The installation of autopilots in aircraft with more than twenty seats is generally made mandatory by international aviation regulations. There are three levels of control in autopilots for smaller aircraft. A single-axis autopilot controls an aircraft in the roll axis only; such autopilots are also known colloquially as "wing levellers," reflecting their limitations. A two-axis autopilot controls an aircraft in the pitch axis as well as roll, and may be little more than a "wing leveller" with limited pitch oscillation-correcting ability; or it may receive inputs from on-board radio navigation systems to provide true automatic flight guidance once the aircraft has taken off until shortly before landing; or its capabilities may lie somewhere between these two extremes. A three-axis autopilot adds control in the yaw axis and is not required in many small aircraft.

Autopilots in modern complex aircraft are three-axis and generally divide a flight into taxi, takeoff, ascent, cruise (level flight), descent, approach, and landing phases. Autopilots exist that automate all of these flight phases except the taxiing. An autopilot-controlled landing on a runway and controlling the aircraft on rollout (i.e. keeping it on the centre of the runway) is known as a CAT IIIb landing or Autoland, available on many major airports' runways today, especially at airports subject to adverse weather phenomena such as fog. Landing, rollout, and taxi control to the aircraft parking position is known as CAT IIIc. This is not used to date, but may be used in the future. An autopilot is often an integral component of a Flight Management System.

Modern autopilots use computer software to control the aircraft. The software reads the aircraft's current position, and then controls a Flight Control System to guide the aircraft. In such a system, besides classic flight controls, many autopilots incorporate thrust control capabilities that can control throttles to optimize the airspeed, and move fuel to different tanks to balance the aircraft in an optimal attitude in the air. Although autopilots handle new or dangerous situations inflexibly, they generally fly an aircraft with a lower fuel-consumption than a human pilot.

The autopilot in a modern large aircraft typically reads its position and the aircraft's attitude from an inertial guidance system. Inertial guidance systems accumulate errors over time. They will incorporate error reduction systems such as the carousel system that rotates once a minute so that any errors are dissipated in different directions and have an overall nulling effect. Error in gyroscopes is known as drift. This is due to physical properties within the system, be it mechanical or laser guided, that corrupt positional data. The disagreements between the two are resolved with digital signal processing, most often a six-dimensional Kalman filter. The six dimensions are usually roll, pitch, yaw, altitude, latitude, and longitude. Aircraft may fly routes that have a required performance factor, therefore the amount of error or actual performance factor must be monitored in order to fly those particular routes. The longer the flight, the more error accumulates within the system. Radio aids such as DME, DME updates, and GPS may be used to correct the aircraft position.

The hardware of an autopilot varies from implementation to implementation, but is generally designed with redundancy and reliability as foremost considerations. For example, the Rockwell Collins AFDS-770 Autopilot Flight Director System used on the Boeing 777, uses triplicated FCP-2002 microprocessors which have been formally verified and are fabricated in a radiation resistant process.

Software and hardware in an autopilot is tightly controlled, and extensive test procedures are put in place.

Some autopilots also use design diversity. In this safety feature, critical software processes will not only run on separate computers and possibly even using different architectures, but each computer will run software created by different engineering teams, often being programmed in different programming languages. It is generally considered unlikely that different engineering teams will make the same mistakes. As the software becomes more expensive and complex, design diversity is becoming less common because fewer engineering companies can afford it. The flight control computers on the Space Shuttle used this design: there were five computers, four of which redundantly ran identical software, and a fifth backup running software that was developed independently. The software on the fifth system provided only the basic functions needed to fly the Shuttle, further reducing any possible commonality with the software running on the four primary systems.

Categories

Instrument-aided landings are defined in categories by the International Civil Aviation Organization. These are dependent upon the required visibility level and the degree to which the landing can be conducted automatically without input by the pilot.

CAT I - This category permits pilots to land with a decision height of 200 ft (61 m) and a forward visibility or Runway Visual Range (RVR) of 550 m. Simplex autopilots are sufficient.

CAT II - This category permits pilots to land with a decision height between 200 ft and 100 ft (≈ 30 m) and a RVR of 300 m. Autopilots have a fail passive requirement.

CAT IIIa -This category permits pilots to land with a decision height as low as 50 ft (15 m) and a RVR of 200 m. It needs a fail-passive autopilot. There must be only a 10−6 probability of landing outside the prescribed area.

CAT IIIb - As IIIa but with the addition of automatic roll out after touchdown incorporated with the pilot taking control some distance along the runway. This category permits pilots to land with a decision height less than 50 feet or no decision height and a forward visibility of 250 ft (76 m, compare this to aircraft size, some of which are now over 70 m long) or 300 ft (91 m) in the United States. For a landing-without-decision aid, a fail-operational autopilot is needed. For this category some form of runway guidance system is needed: at least fail-passive but it needs to be fail-operational for landing without decision height or for RVR below 100 m.

CAT IIIc - As IIIb but without decision height or visibility minimums, also known as "zero-zero".
Fail-passive autopilot: in case of failure, the aircraft stays in a controllable position and the pilot can take control of it to go around or finish landing. It is usually a dual-channel system.

Fail-operational autopilot: in case of a failure below alert height, the approach, flare and landing can still be completed automatically. It is usually a triple-channel system or dual-dual system.

Radio-controlled models

In radio-controlled modelling, and especially RC aircraft and helicopters, an autopilot is usually a set of extra hardware and software that deals with pre-programming the model's flight.

Sailing with Autohelm - Youtube

Autohelm 3000 - Youtube

Comnav 1420 - Youtube

Simrad AP24 & AP28 - Youtube

Simrad Autopilot - Youtube

Raymarine Autopilot - Youtube

This passage planning and online navigation program offers you the MAX C-Map cartography providing accuracy, detail, world wide coverage, as well as all the Neptune course calculations and tidal data. The C-Map charts can be installed directly onto your PC.

The program performs course to steer, course over ground and optimised departure calculations, displaying tidal streams, and reference port tides, also the program interface to GPS and AIS.

After a calculation the results are readily available on screen and takes into account the effects of tides using the inbuilt tidal data.

If you are interested in the effects of wind weather reports and forecasts on to your PC. The weather forecasts interfaces the wind details to Neptune C-Map Plotter Planner with the option of using the forecast and Neptune tidal data to produce Course Calculations.

The routes can be edited on screen and will show your the no sail areas. For those interested in boat performance then Polar Plots and boat speed estimation routines for the wind conditions are built into the software. The program's output is easily copied to the clipboard for pasting into a passage plan for SOLAS purposes.

Connected to a GPS the program will act as a plotter and at the same time allow you some very flexible waypoint management between PC and GPS. If you do not connect a GPS to the PC you can plot in manual mode. Waypoint files can be created either by typing in the co-ordinates and names or by simply pointing and clicking with your mouse, you can keep and edit many waypoint files on your PC and call them up at the click of a mouse. Once a leg has been set-up you can use the tide roll function to see the effects of different departure times on the course to steer and the effects of course over ground.

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Neptune C-Map Planner is an easy to use programs, full of great features, calculations and a pleasure to use.

Auto helms.. tillerpilots. any advice out there?

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