Finding Your Way Home

Once you have had your fill of the scenery, or if the tank fill level (Equipment | Fuel and Payload) starts to drop towards the 50 percent mark, it's time to turn the plane southeast. What now follows is the procedure which is sometimes jokingly referred to as "Chasing the needle": If the vertical needle in the VOR instrument points to the right, then steer the plane past the 130 degree angle on the compass on the right. If it points to the left, then you steer to the left (Figure 11).

Figure 11: If the vertical VOR needle is to the left of the center, then you fly slightly to the left of the 130 degree course you actually planned (pink). If it deflects to the right, turn in the same direction (blue). If the needle is in the middle, simply follow the planned course (white).

You may want to watch the autopilot first to see how it does this. A Cessna 172P from 1982 only comes with a simple version that cannot be programmed with a route consisting of waypoints. But the KAP-140 autopilot by Bendix [5] can fly along the radial of the active VOR. In the Cessna model, the autopilot cannot be activated using the FlightGear autopilot menu, but only by clicking on its control buttons in the cockpit.

If you switch it on by selecting AP, then it first holds the course and pitch of the aircraft. Click on UP or DN until the number on the right in the autopilot reads 0000 – this stands for a climb rate of zero feet per minute. In other words, the aircraft will maintain its current altitude. Then, using the left-hand dial (marked red in Figure  11), turn the heading indicator to the 130 degree radial of the home course determined before takeoff, and click on the HDG (heading) autopilot button.

The Cessna now turns to 130 degrees, but does not yet compensate for the probable lateral shift in the course (vertical pointer in the VOR, also visible on the chart display). This only happens when you click NAV on the autopilot. Now the autopilot will take you back to the starting airport, but will stubbornly maintain altitude. You have to initiate the descent yourself, at the right time, by pressing the UP and DN buttons.

You also have to manually keep the speed at around 100 knots with the throttle stick. At a ground speed of 120 knots, the aircraft will travel two nautical miles per minute. You can read this off on the DME unit as long as you follow the radial. The mile is the unit commonly used in aviation, which is why the DME also measures in this unit.

If you are flying at 7,000 feet, it will take you 10 minutes to descend to roughly 1,000 feet at a sink rate of 600 feet per minute. This is equivalent to a flight distance of 20 miles. The distance to the VOR is shown by the DME. In our case, you still have to compensate for the 12 miles that the VOR is located behind our home airfield. In other words, you need to start descending 32 miles before the VOR by setting a sink rate of -600 feet on the autopilot with the UP and DN buttons.

As soon as you see the runway (on the map in the browser or on the map display in the FlightGear window), you need to approach manually at about 60 knots. As you will now see, a successful manual landing requires some practice.

Jet Power

Once you have mastered the art of manual flying, the good old Cessna may seem too boring for you. Why not fly a real airliner like the Boeing 777-300, another quality FlightGear model? Its wiki page [6] explains how to launch the triple-seven if you do not want to use the shortcut via the Autostart menu entry. Aircraft-specific operating details can also always be accessed in FlightGear using the Shift+? shortcut.

It is clear that such a large aircraft's response to the controls is a little slower than that of the small Cessna. On the whole though, it's not a massive difference when using a three-axis joystick. The fact that flying the 777 still feels completely different is more due to the screen-based instruments and the digital flight management computer that can automatically fly the aircraft along the entire route – if necessary, up to a few meters before touchdown.

You have already seen the cockpit of the Boeing 777 in Figure 6. The left screen combines airspeed indicator (left), altimeter (right), and compass (below). In the middle is the artificial horizon, which shows the horizontal and vertical position of the airplane even without a view to the outside. The navigation screen to the right with the flight management computer display (Autopilot | Route Manager) shows the planned course.

If the Boeing 777 with a top speed of 513 knots (950km/h) is not fast enough for you, try a Mach 2 fighter. The McDonnell Douglas F-15C "Eagle" (Figure 12) is recommended in FlightGear. The jet, designed as an air superiority fighter, will knock you clean out of your gaming chair even without G-force simulation.

Figure 12: The F-15C "Eagle" – shown with full afterburner here – is an agile fighter that can make you dizzy even in the simulator.

Technical Problems

However, the first test with the F-15C was followed by disillusionment. This had nothing to do with the virtual aircraft, but with the technology of the PC on which the simulation was running: The game only managed disappointingly low frame rates of around 16 frames per second, and the rate also fluctuated strongly. This made it impossible to play FlightGear meaningfully.

Troubleshooting revealed that the load on the graphics card, like with other flight models, hardly exceeded 50 percent. However, one of the four CPU cores was running almost permanently at 100 percent load. Even switching off CPU-intensive simulation elements like the Advanced Weather system or AI Traffic hardly improved the situation. Was it really impossible to play FlightGear on a powerful AMD Ryzen 1800X CPU without any restrictions?

The solution was to add the sparsely documented and experimental startup option:

--prop:/sim/rendering/multithreading-mode=DrawThreadPerContext

It distributed the load over all four cores, keeping them well away from a full load scenario that would slow down the simulation. The simulation then ran smoothly at frame rates of around 50 fps. Only the head-up display of the F-15C did not move as fast as the aircraft itself.