Flight Simulator

version 0.26
Anton Norup Sørensen

Latest edition of this document: April, 2002
This document is distributed in HTML format as "ver_docs.htm" and in plain text as "vertigo.txt"


Hardware requirements
Controls: Linear / exponential controls
Controls: Noise filter
Graphics resolution
Graphics: Viewing geometry
Graphics: Set landscape drawing distance
Keyboard commands
Head Up Display
Navigation mode
Air to ground mode
Air to air mode
Flight Model
Propeller engines
Jet engines
Rocket engines
Selectable aircraft
Grumman F-14A Tomcat
British Aerospace Sea Harrier
Lockheed F-104 Starfighter
Lockheed U-2
Vought F4U-1 Corsair
Saab MFI-17 Supporter
Dihedral demo
North American X-15A-2
Grumman Lunar Module 5
Carrier Landings
Catapult launches
Other things to try
Flight data logging
Tips for beginners
Version history
Latest changes: April 2002, version 0.26
Known bugs
Other "home-built" flight sims
About the author
Why is the simulator called "Vertigo"?
How can YOU help making Vertigo better?


I have wanted to write my own flight simulator since I got my first computer, a VIC-20 back in 1982, or so. The commercially available flight simulators often offered great game-play, but had frustratingly crude flight models. In the winter 1993/94, I enjoyed Eyal Lebedinsky's public domain simulator, "FLY8". It convinced me that it was possible to write a fairly realistic and fast simulator, running on a IBM-compatible PC, as a hobby project. In the summer of 1994, I bought my first PC, and started writing Vertigo in the autumn. It was my first piece of C-code longer than ten lines.
Mean while, the quality of simulators for the PC has risen considerably, and some have quite nice flight models. Still, programming on your own is worthwhile, as a means to understanding the physics of flight and plainly having fun.


In short:
Vertigo is a flight simulator that focuses on realism of the flight model. Several types of aircraft are selectable. Scenario is a mountain-landscape with an airfield, surrounded by a sea on which an aircraft carrier sails. Also a Lunar scenario is available. Day or night illumination can be selected.


You are using this software at your own risk. I am not responsible for any damage to your soft- or hardware caused by the included software.

This program is a computer game. It is not suitable for flight training or aircraft design. Failure to understand this may lead to a life-threatening situation.

If this program crashes, interrupts may be left in a way that will crash the entire computer, requiring a reboot. So do not run any other programs operating on important files etc., while running Vertigo.



Vertigo is not plug-and-play. It will take a little effort to get it
running properly.
Please take your time to go through the steps described in INSTALL.TXT

Hardware requirements

The simulator will in principle run on a 386 PC with math co-processor, but to get proper performance, you will at least need a 486DX2/66. A 100MHz Pentium or faster is recommended. For low-end PCs, read the section on "Configure calculations" carefully. For controls, an analog joystick is strongly recommended, but a mouse can also be used. Rudder pedals and throttle are supported. There are problems with some modern joystics. The old-fashioned analog ones using the gameport usually work well. For sound, only Sound Blaster compatible cards are supported. For proper setup under DOS, define the BLASTER environment variable, e.g. SET BLASTER=A220 I5 D1 H1 T4


Access the Main Menu by pressing [ESC] in Vertigo. The nice MGUI (Morello Graphical User Interface) is used. The menu is intended to be mouse operated, but it is also possible to use keyboard: Arrow keys changes focus between items. TAB skips between sections. ENTER activates an item. F10 activates the upper menu bar. I like to think the menues are very easy to use. Nevertheless, here are a few explanations for some of the more obscure options:

Controls menu: Linear / Exponential controls:

Exponential mode has 50% lower sensitivity at small deflection, but at larger deflection the sensitivity increases rapidly. The full stroke is the same in both modes. Exponential controls are recommended.

Controls menu: Noise filter:

The joystick can be read 1, 3, or 5 times for each frame. The median of the readings is used as control input. For a noisy joystick setup, use a large number of readings.

Graphics: Graphics resolution:

The three resolutions can only be selected at program start-up, not in-flight. The monitor frequency will also be changed, but this will only be effective when the program is re-started. There is no guarantee that the resolutions listed in the menu actually works on your hardware.

Graphics menu: Viewing geometry:

In order to percieve the correct perspective of the 3D graphics, you must enter correct values here. If you do not have an extremely large monitor, or almost touch the screen with your nose, you will get a rather limited field of view, unfortunately. You can get a bigger FOV by altering the values, but this will introduce geometrical distortions, too. The default setting is for an unnaturally large field of view, typical of what is encountered in most simulators.

Graphics menu: Set landscape drawing distance:

This parameter sets to what distance to draw the fractal landscape out to, between 4 and 10 kilometers, with 8 kilometers as defult. There is a difference in frame rate of up to 50% between the two extreme settings, so adjusting this parameter may help you to achieve a proper frame rate.

Configure calculations:

Here you state how many iterations of the flight model that is performed for each screen update. Calculations are done for a real-time model. The more iterations per second, the more precise the model will get. If the intervals between calculations becomes comparable to the dynamic time-scale for the aircraft, errors will be significant, leading to oscillations, eventually making the plane unflyable. The onset of oscillations depends on the selected aircraft, but generally becomes a problem at high velocities,if the calculation rate goes much below 20 Hertz. On the ground the friction forces on the wheels will require more than 50 calculations per second to avoid oscillations. As the Harrier is the most sensitive aircraft to this problem, you should use this aircraft stationary on the ground when adjusting the rate. Another symptom of a too low calculation rate is violent oscillations when locked onto the catapult. Of course, you will also want to see what is going on, so the calculation rate will be a compromise between precision and frame-rate. For 486's, around 5 calculations per update will give a calculation rate close to 70 Hz, and 10-15 frames/sec. This should be perfectly OK for both precision and vision. On 586's, you will have no trouble with precision or frame-rate if you use more than 3 calculations per update. The calculation/frame rate is also strongly depending on the selection of graphics detail. For the highest frame rate, use "flat ground" instead of "fractal landscape". Only high-end machines are expected to perform properly using the fractal ground. Personally, I prefer flat ground for flying on a 486DX2/66. The frame-rate and calculation-rate is displayed when you exit Vertigo. As the rate displayed is the average for the entire run, you will have to exit, reenter and then exit again, for a reliable number, if you change the configuration.


If you are having too many difficulties with controlling the aircraft, you may want to change the realism settings. Here are listed the settings for maximum realism: Realistic propeller engine Active / button in Realistic jet engine Active / button in Wind Active / button in Manual rudder control Active / button in

Keyboard commands

Please refer to the menu page, accessible by pressing [ESC]. The keys are described in the seperate file KEYS.TXT for easy access. Do not use the "Pause" button! This will confuse the timing of the flight model. Use "P" instead.

Head Up Display

The default color of the HUD is monochrome green. If you want a multi-color HUD or to turn the HUD off, cycle between these modes by pressing "ALT h". The HUD is similar to what is seen in other simulators: The small cross at the centre is where the nose is pointing, and is also the neutral point for the control deflection markers: red cross for the stick, and red vertical bar for the rudder. If your calibration seems OK, you can switch the control markers off (and on again) by pressing [j]. If you have entered correct values in the Graphics configuration menu, the scale of the pitch ladder and the heading strip should correspond to the actual angle. I have taken the liberty to extend the pitch ladder to the entire screen, which is probably what we will see with large HUDs or helmet mounted displays in the future. In the top right corner, angle of attack is displayed in degrees. The altitude ladder at the right side is displayed in feet. Negative altitude is red. 005 reads 50 feet. Below the altitude is printed in numbers: 0004 reads 4 feet. Note that the altitude is measured from sea-level, and is not indicating your height above the ground. Below that is the vertical velocity in feet per second. Vertical velocity is also displayed by a vertical bar to the left of the altitude ladder. Blue for positive, and red for negative. The bar reaches the end of the scale at 100 fps, marked by a white border. If the altitude Above Ground Level is 3000ft or less, the altitude AGL is displayed to the lower right. If this gets below 300 feet, the color will be red. If a ground collission is predicted within a few seconds, a "PULL UP" message will flash in the center of the HUD. As the prediction is very simple, based only on the ground directly below, it should be interpreted with caution. Lowering the undercarriage disables the warning. The Indicated airspeed ladder is at the left, displaying knots. 05 reads 50 kts. Below, true airspeed is printed by digits, and immediately below that, the Mach number is shown. At the upper left is a g-load meter. A marker move around: The flight path marker is drawn as a simple aircraft seen from behind, with body, wings and vertical stabilizer. This shows the direction of your velocity vector, i.e. where you are going. You may find this to be your most important instrument, especially during landing.

Navigation mode

Above center, a compass tape is displayed. A 'V' arrow marks the direction to the selected waypoint. To the lower right a text array provides further information: Uppermost to the left is the waypoint number, and to the right the waypoint type. Below to the left is the distance in nautical miles and to the right the direction to it. At the bottom the estimated time to reach the waypoint is shown, assuming current speed and course. If this is 100 minutes or more, "--:--" is displayed. At the very bottom, so low that it will be behind the analog instruments if they are displayed, you will find a bank indicator. There are tick marks for 0, 10, 20, 30, 45 and 60 degrees of bank. If the bank exceeds 60 degrees, the needle will be flashing.

Air to ground mode

Two gun sight modes are available, depending on air-to-ground or air-to-air mode, as shown to the lower left along with the number of remaining gun rounds. The CCIP (Continuous Calculated Impact Point) gun sight is a larger circle with a dot in the center, shown in A-G mode. This predicts where a bullet fired at this moment will hit the ground. It only shows up if the flight time of the bullet from shot to impact is less than 10 seconds. The calculation is rather precise, probably more than is possible in real life.

Air to air mode

In A-A mode, a "snake" is shown, indicating the path that projectiles fired within about the last three seconds would follow. If a target is selected, it will be surrounded by a box, and if it is within the distance corresponding to the furthest point of the snake, a Lead Computing Optical Sight (LCOS) marker will be displayed. Placing this circle on a moving target and firing is not a guarantee for a hit, as the display lags one bullet time of flight behind. So think ahead! Inside the LCOS circle, a target range clock is shown. Each quarter of a circle represents a distance of 1000 feet. At the perimeter of the target box, two markers are shown: The line is the target heading reltive to yours, projected onto the horizontal plane. If you are on the same heading, the line will be above the box, and below if you are on opposite headings. The target aspect angle is displayed by a "V". Aspect angle is angle between the target heading and the line of sight between the target and you. If the V is at the bottom, the target will be seen from behind. If it is horizontal, you are looking at the side if the target. Extending from the center axis marker, a line is pointing towards the selected target, also if it is outside the screen. Target range (in nm) , closure speed (in knots) and aspect angle is written to the lower right.


Instruments normally not shown in a HUD is at the lower section of the screen. Throttle is displayed in the leftmost box. For the simple jet and propelle engine model, the red bar is the actual percentage RPM, while the broad green bar is the requested value. A yellow "A" is displayed in the middle of the throttle bar when auto-throttle is active (F-14 and Lunar Module only). For the detailed jet and propeller engine model, a black vertically sliding lever is the throttle. If the jet engine has afterburner, a number in the middle of the throttle slider indicates the number of afterburner stages set to burn. To the right of it there is a lever with a narrow blue handle for propeller RPM setting. Further right is the flap setting indicator. Red again showing the actual position, and broad green the desired. A number of "G"'s indicates the status of the gear. Their positions are corresponding to the location on the airframe. Gray for retracted. Red for moving. Yellow for down. Bright green for contact with ground. When wheel brakes are activated, the symbol changes to a "W". Below, aircraft with air brakes will have the status of the brake shown by a "B" in different colors like for the gear, but with yellow indicating fully extended. Similarly, an "H" shows the status of the arresting hook. For the Harrier, a nozzle angle diagram is shown. Angle ticks have 15 degrees intervals. Green line for desired angle, red for actual. When DLC is activated in the F-14, spoiler deflection is indicated by a yellow marker between green middle and limit markers at the bottom of the screen. Also for the F-14, sweep mode and angle is displayed to the lower right by an arrow-like symbol, with "A" or "M" inside to indicate automatic or manual sweep mode, and the sweep angle is in degrees below. In the right corner, trim settings are displayed, using red marks on a grey cross resembling an aircraft. The tick on the vertical line displays elevator trim, on the long upper horizontal line, aileron trim, and on the lower short horizontal line, rudder trim is shown. Flying simpler aircraft like the Corsair and Supporter feels more realistic with the HUD off, which is the default mode for these aircraft. You can cycle between the HUD off mode and different color modes by pressing [ALT h] . At the bottom of the screen, a few "real" analog instruments are shown. The lay-out is in most cases inspired by the Supporter cockpit instruments. All aircraft: Artificial horizon: Displays pitch and roll. Shortcomings: Makes a unrealistic "flip" at zenith/nadir, and the numbers look weird. Cannot be tilted by nasty maneuvers. Airspeed: This displays indicated airspeed in knots. Vertical Velocity Indicator: Behaves ideally, i.e. no lag or altitude influence. Unit: Thousands of feet per minute. ILS needles: Works like those on the HUD. A red flag is visible when the ILS is inactive. Compass: Looks like a magnetic compass, but has no of the effects implemented that makes magnetic compasses tricky. Accellerometer: Displays G's pulled. Narrow needles indicate max/min load during the flight. Altimeter: Has a needle that turns once per 1000 feet and a digital display showing hundreds of feet. Altitude based on air density is shown, *not* height over ground! Air pressure is always 1013 HPa at sea level in this simulation, so the altimeter does not need adjustment. Turn and slip: Consists of a ball, ideally supposed to show yaw, but in reality showing the ratio of acceleration in the aircraft's horizontal axis to the acceleration in the vertical axis. This means, that change in g-load and changes in rudder input, for instance, will also affect the position of the ball. The needle above shows the angular speed around the vertical axis, in arbitrary units. Fuel level: This twin dial shows the fraction of internal fuel left. Gear position indicator: The coloured of a letter for each wheel indicates the position: Dark for up, yellow for moving and green for down. Also airbrake and hook position are shown. For the VVI, IAS and ALT indictors, a delay in response time is modelled. Propeller engine only: RPM dial: Units are 100's of Rounds Per Minute. Manifold pressure: I'll have to work a little on this still to display proper values, especially at low RPM. Units are inches of Hg. Fuel flow: Units are gallons per hour. Jet engine only: These instruments are made to resemble the lay-out in the F14 as much as possible, with some modification to make them useable for single engine aircraft also. RPM percentage: A vertical strip shows the RPM, in units tens of percent of the military throttle RPM. The scale is in two segments in order to give more precise readings above idle RPM. Exhaust Gas Temperature (EGT): This two-scale vertical strip instrument shows the EGT in units of tens of degrees Celcius. Fuel flow: This two-scale vertical strip instrument shows the fuel flow to the combustion chamber in units of thousands of pounds per hour. The fuel flow to afterburners is not shown. Map: The only head-down instrument is a map, continuously updated to be centered on your position and rotated to your heading. View by pressing "m" and zoom in/out by pressing "+" and "-" on the keypad. Zooming out to draw a large portion of the map will make the computer extremely busy, which will mean less time to perform flight model calculations. This may lead to unstable aircraft behaviour while you are looking at the map, so be careful!


Although the graphics is very simple, most of the time is spent on drawing. To allow for precise flight model calculations, graphics has to be kept at a minimum. Two scenarios are available: Earth and Moon landscapes. Two types of landscape can be selected from the Configure graphics => Landscape type menu. Flat: The ground is simply a green flat surface, with a blue sky above. The ground within 10 kilometers of the viewer is marked by a grid of brown lines. The side of a square is 1 km. Within 1 km of the viewer, another gray grid marks the ground. The side of a gray square is 100 m. Fractal: This generates a random fractal mountain-landscape, with water at sea-level. The surface is drawn using triangles, whose shortest lines are 1 km. You will have to judge, if you can accept the decrease in frame-rate compared to the flat landscape. See the "Set landscape drawing distance" section to optimize this mode. The runway orientation is 00-18, and is 1500m long, 40m wide. In the sea, an aircraft carrier moves about. See the description further down. The Moon landscape is all grey, with hills and plains. There will always be at least a 1km square flat area at the intended landing site. The most important difference is of course the atmospheric pressure of zero and the weak gravitational pull on the Moon. Illumination changes with the time of day. From the menu, day, night, dawn or dusk can be selected. During dawn and dusk, the lighting will change between day and night condition during half an hour. As the time since program start is added to the time selected in the menu, delecting dawn or dusk after a long flight may result in instant day or night. During nighttime, the runway and carrier will be marked by artificial lights. Almost all stars visible to the unaided eye will be displayed in the night sky. The orientation of the sky can be set by specifying the local latitude and the sidereal time in the menu.

Flight model

The aircraft is modelled as a combination of objects. For each object, the forces acting on it are calculated, and from the object's position relative to the centre of gravity of the entire set, resulting force and torque is calculated. By measuring the real time elapsed, the forces are translated to new vector and angular velocities for the airframe. For each object the velocity and angle of the incoming air is calculated from the attitude and speed of the aircraft, also taking into account the angular velocity of the airframe. For instance, the airspeed of the outer wing is influenced by yaw rate, and the AOA is influenced by roll rate. The group of objects, on which aerodynamic forces (lift, profile- and induced drag) are calculated typically consist of body, port/stb. inner wing, port/stb. outer wing, horizontal and vertical stabilizer, totalling 7 objects. The properties (chamber, geometric AOA, area) of the relevant objects are changed according to control input. E.g. the properties of the two outer wing sections are modified by aileron input. The forces are calculated from the empiric equations in basic aerodynamics textbooks. The density of the atmosphere decreases exponentially with altitude, and the temperature decreases linearly up to the tropospause, and is constant above that. On objects representing undercarriage, the only aerodynamic force calculated is profile drag. Forces on the wheels when on the ground distinguish between static and dynamic drag, and include rolling friction. ABS-type brakes are implemented, so skidding along the rolling direction will only occur if you also skid sideways. Forces are calculated parallel and perpendicular to each wheel, making steering possible, as the angle of one of the wheels is connected to the rudder input. The spring forces in the upward direction are damped. In addition, hard-points are at nose- tail- and wing-tips. These only provide friction-drag and spring forces from the ground. There are certainly still some shortcomings in the calculation of ground- friction forces. While of limited precision during fairly normal attitudes, they are completely wrong if you are inverted (You are also doing something completely wrong, if you encounter that situation!) If you go for a drive in the fractal landscape, you will find that the wheel forces are not calculated correctly on non-horizontal surfaces. For aircraft having hydraulic actuators for the control surfaces, the rate of movement has an upper limit to emulate the response time. Fuel tanks are located in wings and body, affecting aircraft weight and inertia. Typically, the wing tanks are emptied before the body tanks are used. All objects, except hard-points are affected by gravitational forces. Auto-coordination can be activated, controlling rudder position to minimize yaw. As this only can correct for yaw appearing, not anticipate it, a small amount of yaw will still be present. Also, the rudder has limited effectiveness, so you can enter a situation where a large amount of yaw still occurs. The aircraft are all conventionally stable: Any pitch and yaw will tend to be eliminated without any control input from the pilot. The stability combined with inadequate damping of the motion around the equilibrium position appears as a "nose bounce" for some aircraft. You can minimize the bounce by applying smooth stich movements and keep the aircraft in trim. Propeller and jet engines comes in two types: Simple force generators and more detailed models described below.

Propeller engines

In the detailed version of the propeller engine, ehe engine is a torque generator acting on the propeller. The amount of torque depends on the throttle setting, RPM and air desity. Torque will typically try to increase the RPM of the propeller, but at high RPM and low throttle, the engine will act as a brake. The propeller has mass and rotates rapidly. Torque on the propeller from the engine will inflict the opposite torque on the airframe and the rotating mass will act as a huge gyroscope, turning the airframe in a direction perpendicular to the direction that the airframe tries to rotate the propeller. The propeller is a rotating wing. The angle of attack of the propeller depends on the blade pitch, RPM, position angle and radius on the propeller disc, airspeed, airframe pitch and yaw and the inflow and vortex airspeed. This results in pretty complex behaviour of the resulting lift and drag vectors. These can be split in directions along the propeller axis and perpendicular to it, resulting in thrust and drag acting as torque. In addition propeller thrust and torque also depends on air density. The actual lift and drag coefficients are derived from wind tunnel data for the NACA0012 profile. Because of airframe pitch and yaw, the thrust is changing over the propeller disc, causing asymmetric thrust, known as P-factor. The propeller thrust accelerates air backwards and the drag/torque creates a vortex. The flow is partially absorbed by the body and wing root, but some of it hits the tail surfaces. This increases control efficiency at low speed, but the vortex hits at an angle, causing a yaw moment that must be countered by rudder input. As the effective angle of attack and depends on airspeed, the propeller thrust efficiency is strongly depending on airspeed too. To expand the range with good thrust and efficiency, the propeller pitch can be changed. The pitch is adjusted by a servo mechanism to result in a fixed RPM. The desired RPM can be set by the pilot. The Corsair engine has a two speed auxiliary blower in addition to the constant speed supercharger. The blower operates in idle at low altitude and at two speeds at higher altitude, controlled automatically. Also, a 2:1 reduction gear between engine and propeller is implemented.

Jet engines

In the detailed version of the jet engine model, the throttle position sets the desired RPM percentage, with a maximum RPM of 100%. The thrust depends on RPM, altitude and airspeed. There is a slight decrease in thrust at moderate airspeeds as the exhaust speed is nearly constant while the intake airspeed increases. At higher airspeeds, ram-effect helps the compressor, and thrust increases with the square of the speed. At very high speeds, thrust may be limited by variable air intake ramps, as for the F-14. The RPM response speed degrades with altitude. Fuel consumption vary with RPM setting and decreases with altitude. Afterburners can be lit gradually, e.g. the F-14 has five burner stages. The fuel consumption at full afterburner is about five times higher than at conventional thrust, and giving only about a two-fold increase in thrust. Note that the fuel flow to the afterburner will not be shown on the FF instrument, but it will be seen after a short while on the fuel level gauge. The afterburner throttle is indicated by a number in the middle of the throttle handle slider. A compressor stall may be started by poor intake airflow or a too high combustion chamber pressure. The symptoms will be a sudden drop in thrust, very high exhaust gas temperature, and dropping RPM. Provoking a compressor stall may be done by a combination of high AoA or yaw, low indicated airspeed, high throttle setting or advancing the throttle too fast. The cure is to reduce throttle to idle and reduce AoA. Flame outs also show the symptoms of a drop in thrust and RPM, but is distinguished by a drop in EGT too. Flame outs may be started by flying at very high altitudes or reducing the throttle too fast at high altitudes. Also recovery from a compressor stall may lead to flame out. Engine air restarts are initiated py pressing "e". For a succesfull restart, go to moderate or low altitude and pick up speed to windmill RPM to a useful range. Do not apply throttle too abruptly, or you will stall the engine during the restart.

Rocket engines

The rocket engine is, at least in principle, the simplest of the three modelled types of engines. Thrust is proportional to the amount of fuel and oxidizer pumped into the combustion chamber, regulated by the throttle. The engines modeled for the X-15 and Lunar Module both have a considerable thrust even at idle throttle. To toggle fuel flow and ignition, press "e".


It was with mixed feelings that I started to implement weapons on aircraft in Vertigo. Violence is being glorified by a huge part of the entertainment industry, and I believe this is contributing to increasing violence among people. Please, never forget the cruelty of war, whatever enjoyment you may have from strafing the targets. So far only cannons are implemented, as these are my idea of the weapon of a classic ace. Each gun has a limited amount of ammunition and a specific rate of fire. The trajectory of projectiles are influenced by: Initial velocity: The sum of aircraft velocity and muzzle velocity. (You will then have a slightly larger gun range when flying fast.) Gravity. Drag: Depending on speed and altitude. Mass: A heavy projectile will be less influenced by drag. Gun pointing, not necessarily parallel to the axis of the aircraft. Barrel imprecision: A small random angle to the pointing is added. With all these factors, you will be happy to have the CCIP/LCOS gun sights described in the HUD section. In turn, your aircraft feels the recoil from the guns. You may even utilize this for maneuvering on the ground! Bullet impact is only checked for the ground and the practice targets. Up to 500 individual trajectories are calculated at one time - if you fire very long salvos, you may have to let go of the trigger to allow some bullets to impact before you can shoot again. Note, that long salvos may also reduce frame rate on other than high-end computers. Only one bullet per gun can be fired for each calculation iteration. If, for instance, your calculation frequency is less than 100 Hz, you will not be able to utilize the full fire power of the 100 rounds/second gatling in the Starfighter. A fraction of the projectiles are displayed as tracers, about one in three for fast firing guns, and a higher ratio for slower guns. The tracers cease to burn after five seconds, but the flight path of all projectiles is calculated for 15 seconds, after which they are ignored.


You can hone your gunnery skills at a target range close to the airfield, with a suitably named waypoint. The targets are red and white diamonds that will withstand 10 direct hits before they burst. With a diameter of about 4 meters, they are quite difficult to hit. One target is placed on the ground. Beware that you can see it through a hill, but you can't fly through the hill. Four targets circle at random altitudes, speeds and g-loads. To lock on to the next target, press "SHIFT t". To get external and internal padlock views, press "/" and "*".

Selectable aircraft

From Main Menu, under Select aircraft, you find six aircraft: F-14A Tomcat, F-104 Starfighter, U-2, F4U Corsair, Harrier and MFI-17 Supporter. Do not be fooled by the precise naming of these models. The models only have a very vague resemblance to the real aircraft. For most of the aircraft, I have just entered crude overall sizes, weight etc. from the one-page descriptions that can be found everywhere. I have only little specific data to allow for a precise simulation of any aircraft. - I would be grateful to be provided with them though! Comparisons of the performance of the models with the real thing are very welcome. Among the reasons for choosing an aircraft to model are: Unique aerodynamic properties (goes for the Harrier, U-2, F-14 and F-104), engine properites: Corsair and sentimental reasons: Supporter. A fair chance of proper modelling - You will not find dynamically unstable fly-by-wire aircraft and other complicating matters - at least not yet...

Grumman F-14A Tomcat:

The Tomcat has in several ways a unique design, caused by the requirements for a fleet defence aircraft: High speed, long patrol time, high payload, low landing speed and good maneuverability. This is accomplished by using variable geometry wings and other features, which are elaborated on below: Variable sweep wings: Sweep is controlled as a function of the Mach number. At low speed, sweep is at a minimum of 20 degrees to minimize induced drag. From about Mach 0.7 to 1.2, sweep is gradually increased to 68 degrees to minimize supersonic drag. Increasing sweep moves the center of lift backwards, which decreases maneuverability. Sweep can also be controlled manually by using keys F9 to F12. Key "s" toggles between manual and automatic mode. Mode and sweep angle is displayed to the lower right by an arrow-like symbol, with "A" or "M" inside to indicate sweep mode, and the sweep angle in degrees below. At sweep angles larger than 55 degrees, flaps and spoilers will be retracted. Glove vanes: Above Mach 1, the center of pressure moves backward, although this is not yet implemented in the flight model. This means a larger down-force on the elevator is required, creating more trim drag. To counter this, glove vanes are extended at Mach 1.4. This moves the center of lift forward, which in turn means less drag. Tailerons and differential spoilers: As ailerons work badly in combination with variable sweep, the aileron function is moved to the tail. At sweep less than 55 degrees, differential spoilers on the upper side of the wings assist roll control. On the wing going down, the spoiler is extended, while it remains flush on the other wing. This method has the advantage of counteracting adverse yaw. Landing: The Tomcat can be landed as any carrier-based aircraft, by fiddling with throttle and stick. Airspeed will be in the range of 115 to 145 knots depending on fuel load, but the optimum AoA is always 10.8 deg. However, another way to land is to use the following two features: Auto-throttle: Toggle auto-throttle by pressing "t" while the throttle is about halfway forward. Now the engines are controlled by a servo mechanism reacting on the aircraft angle of attack. If AoA is less than 10.8 deg, you are going too fast and throttle is reduced, and vice versa. Auto-throttle can be disengaged by moving the throttle handle to idle or full power. A yellow "A" is displayed in the middle of the throttle bar when auto-throttle is active. Unfortunately, I find the auto-throttle very hard to use. Maybe I will manage to tweak it to behave nicer. Direct Lift Control: With constant airspeed and AoA, the way to control your position on the glideslope is to change the amount of lift by controlling the spoiler deflection. When gear is selected down and brakes out, DLC is activated. The spoilers deflect to a middle position of 7 degrees, and deflection is adjusted by pressing "q" for more lift and "a" for less lift. As the tomcat in this version is near minimum weight, you will need a quite large spoiler deflection to stay on the glide slope. Also when landing by stick and throttle only, it will be a good idea to set the DLC to an appropriate value. When DLC is active, spoiler deflection is indicated at the bottom of ths screen. Retracting the air brake will disengage DLC. At touchdown, the spoilers will move to a maximum deflection of 55 degrees in order to avoid bouncing off the deck. Again, retracting air brakes will retract the spoilers. Dual engines: The A-model Tomcat is generally considered under-powered. As this model is not loaded with external stores, that will not be a big problem. A single engine failure makes for an interesting flight due to the strong yaw produced by the remaining working engine. If you are not careful, you will end up in the notorious flat spin. An engine failure may be initiated by pressing "F", or by tormenting the engines. Especially, a yaw will make the engine in the turbulence from the nose prone to a compressor stall. Armament: One 20mm M-61 gatling cannon with 675 rounds. There are a lot of books about the Tomcat - the one I like the most is: Aviation fact file: Modern fighting aircraft: F-14 By Mike Spick Salamander books, 1985 ISBN 0 86101 194 5

British Aerospace Sea Harrier:

Weight allows for VTOL. Features vectored thrust and jet-supported attitude controls. A ground cushion effect kludge is added. This increases vertical thrust gradually to 120% at 1 meter altitude. New versions of the Harrier has gyro-stabilization to make hovering easier. In this simulation, you do not have that luxury. It will probably take some practice to make this thing do what you actually planned to, when hovering. Carrier landing configuration: You have no tail hook and will be ignored by the LSO. Use thrust vectoring for landing. Armament: Two 30mm Aden cannons, with 130 rounds per gun.

Lockheed F-104 Starfighter:

Weight is as with tanks almost empty. Stay fast! Paint scheme inspired by USAF F-104N used for astronaut training. Carrier landing configuration: Yep, I know a real F-104 would never survive this. Fly the glide slope at +9.0 deg AoA. Armament: One 20mm M-61 gatling cannon with 725 rounds. Fires 6000 rounds/minute.

Lockheed U-2:

The single main gear is located well in front of the centre of gravity, so when the tail-wheel rises, you are in a very unstable situation. I suggest you keep the tail wheel on the ground as long as the main wheel is touching ground too. I recommend reading the section by Tony LeVier at the end of chapter 6 in Ben R. Rich and Leo Janos' "Skunk Works" about landing the U-2. No drop-off wheel struts at the wing tips during take-off, so be careful! The real aircraft is extremely fragile, so this this will be really interesting to fly if I ever get to implement stress limits. The engine is very powerful. Implementing altitude dependent engine effectiveness would be interesting, as it only delivers 7% of the power at sea-level when at 70000ft. Carrier landing configuration: +3.3 deg AoA.

Vought F4U-1 Corsair:

The 2000 HP R-2800-8 propeller engine provides tremendous power, but also torque, asymmetric thrust, gyroscopic forces and slipstream vortex, making this a very challenging aircraft. If you select the realistic engine model, rudder pedals are strongly recommended. If you don't have pedals, enable auto-coordination. Be careful not to nose-over when using the wheel brakes. The supercharger has an auxiliary blower that is operated automatically at three speeds, depending on altitude: Neutral: 0 - 8000 ft Low : 8000 - 13000 ft High : 13000 - ft The blower setting is indicated by a letter on the throttle slider. Carrier landing configuration: +6.0 deg AoA. The long nose will make it difficult to see the carrier during approach, but you can cheat by selection not to display the airframe from the cockpit. Armament: Six 0.50 in machine guns with 400 RPG (inboard four) and 375 RPG (outboard two). Convergence is set to 300 meters.

SAAB MFI-17 Supporter:

A small propeller aircraft used for basic training, reconnaissance and logistics by the Danish and Norwegian air forces, and even as a light attack aircraft by the Zambian and Pakistani Air Force. This is the easiest aircraft to fly of those included, so if you are new to Vertigo, you should start with this one. Carrier landing configuration: +5.5 deg AoA. You have no tail hook, so step on the brakes when landed. Armament: Although it has six weapons stations, no weapons are provided in this simulation.

Dihedral demo:

This model is based on the SAAB MFI-17, but is altered to test upgrades of the flight model. The graphics is unchanged, but the flight model is quite different. As a new feature, wing dihedral can be specified, and this model has a positive dihedral of 15 degrees. This creates a rather strong roll stability. Ailerons and flaps are disabled, but roll can easily be controlled by the rudder due to the roll-yaw coupling that results from dihedral. The vertical tail fin is made too small, making yaw stability much smaller than roll stability. This makes it possible to demonstrate the "Dutch roll" by kicking the rudder briefly. The wing lift coefficient is as for a NACA0012 profile.

North American X-15A-2:

The X-15 was a hypersonic and high altitude research aircraft, that flew from 1959 to 68. It provided essential information that made building the Space Shuttle possible. The second of three X-15s built, was modified to the X-15A-2, capable of carrying external jettisonable fuel tanks, which are not modelled in this simulation. Dropped from about 50.000ft from a B-52, the flight profile may be relatively flat, aiming for high speed, or steep if high altitude is desired. Without external tanks, the highest speed reached was 3565 knots TAS and the highest Mach number 6.06. The highest altitude attained was 314.750 feet, well above the boundary defined as space. You may easily beat the altitude record in the simulation, but that would likely mean a steeper re-entry that what was used, possibly over-stressing the airframe. The steepest re-entry flown was -38 degrees, with an angle of attack up to 26 degrees. At extreme altitudes, the airflow will be too weak to provide adequate attitude control. Pressing "r" will toggle the activation of a Reaction Control System that will enable you to control the aircraft outside the atmosphere. When you leave the B-52, your airfield will be 175nm ahead of you. After flying your research profile, you will have to glide back to a landing there. This is also a tribute to the guys from Argonaut Software that made Birds Of Prey back in 1992, including an X-15 simulation that I enjoyed a lot.

Grumman Lunar Module-5 "Eagle":

The Lunar Module was used in the Apollo missions for the first manned landings on the Moon. In this simulation, you can pilot the LM down from the "Low Gate" point to touchdown. Low Gate is at a height of 500ft above the surface. The velocity of the LM should at this point be 21 m/s forward and 5 m/s down. The amount of useable fuel aboard has been reduced by the de-orbit maneuver from the original 8164kg to 522kg, so there is not much left for loitering around. Using throttle and attitude thrusters, guide the LM to a soft landing. An auto-throttle function can be toggled by pressing "t". This will aim at a descent rate of -1 m/s. During the descent, you will hear actual radio transmissions from the "Eagle" landing on 20 July 1969 at the appropriate heights. At a height of 2 meters, you will get the "Contact lights" report, and you may choose to turn off the engine by pressing "e", or continue down under power. Thanks to H. Frik for making the beautiful graphics for the LM descent stage. It is by far the most detailed object in the entire program. He also provided lots of data and sound files for the LM simulation.

Carrier landings

Maybe the greatest challenge in modern aviation is to land safely aboard an aircraft carrier. Here you get to practice clear weather day or night time landings. The Carrier: On startup, a Nimitz class carrier is placed somewhere in the sea. The deck will pitch, roll and heave proportionally to the strength of the wind. You can select several locations relative to the carrier at startup: On deck: You will be placed ready for take-off, but you will have to do it without the catapult. On final: You will be placed in landing configuration on the glide slope a few miles out. Approach: You will be placed behind the carrier several miles out and you will have to put yourself on the glide slope. You can of course also start from the runway and find the carrier, which will be at the appropriate waypoint. LSO: If you are approximately on the glide slope, the Landing Safety Officer will establish contact when you are 3/4 nautical mile away from the deck. At this point, the LSO will expect you to have gone dirty, i.e. lowered gear, hook and flaps. You answer by telling aircraft type, that you have the ball in sight and the amount fuel left in thousands of pounds. You will then be guided by voice until you are safely down, or "waved off" if the approach is unsafe. Meatball: At a distance of about two miles, the Optical Landing System will become visible, located mid-ship on the port side. The arrangement looks like this: R Y R R Y R G G G G G R Y R G G G G G R Y R R The R, G, Y letters marks lamps of red, green and yellow color, respectively. The yellow and red lights in the central column are made using a Fresnel lens system so that each light emits an approximately 0.5 degree wide cone in the vertical range and much broader horizontally. These lights make up the "meatball". Each lens is tilted so that if you are above the glide slope, you will see one of the upper lamps and if below, the lower lamps. The lowest lamp is red to warn of this dangerous situation. If you are within 0.15 degrees of the glide slope, the lamp aligned with the green "datum line" will be visible - you are on the correct -3.5 degree glide slope. If you are deviating 1 degree or more vertically, no meatball will be visible - you will have to eyeball what is wrong, use the ILS or listen to the LSO. At large distance, the position of the ball can be hard to see as the entire arrangement just takes up a handfull of pixels. I have made the vertical offset of the meatball larger than in reality to compensate for this. If you keep the ball centered, you will touch down with the hook hitting the deck between the second and third wire, thereby catching the third wire. As the vertical separation between the hook and your eyes is different for the different aircraft, the height of the meatball has to be adjusted accordingly. This is being done by rolling the lights a few degrees - as you are sideways offset to the lights when in the groove, this will look like a vertical displacement of the lights - beware that if you are not lined up, the meatball will give wrong information, e.g. place you too low if you are port of the centerline. The entire OLS arrangement is gyroscopically stabilized, to avoid ship movement affecting the glide slope indication. The stabilization can not eliminate the vertical motion, though, so a pilot with a steady hand may be able to notice a slightly oscillating meatball. The two vertical rows of red lights are used for signalling "wave off". Lining up: To line up visually, examine the center line painted on the deck and continued vertically down at the rear. When lined up, the two line segments must both appear vertical. Note that due to crosswind, you cannot just place the HUD flight path marker on the center line. Approach indexer: Each aircraft has a specific angle of attack to maintain when on the glide slope, providing high lift safely below the stall AoA. The airspeed is closely linked to the AoA: If you are fast but following the glide slope, the AoA will be too low and vice versa. The optimum airspeed changes with aircraft weight, while the best AoA remains the same, so if you keep the prescribed AoA and stay in the groove, you (almost) don't have to think about the airspeed. The AoA to be used is listed in the aircraft descriptions above. The indexer is located in the mid-left part of the HUD, and will be visible when HUD is on and gear down. If the AoA is too large, the upper red downward pointing arrow will illuminate. If AoA is too small, the lower green upward pointing arrow will light up. Correct AoA will be marked by a yellow ring in between the arrows. ILS: The Instrument Landing System displays a horizontal and a vertical needle, at the center of the HUD, measuring line-up and glide-slope error, respectively. At full stroke, the needles show you are 3 degrees off. The type of ILS modelled here is a part of the modern Automated Carrier Landing System, which eliminates ship roll and pitch from the signal, as well as parallax angle to the antennas. The ILS is not intended for daytime clear weather use, so when you get confident, try landing without it by switching to navigation mode (press "n") instead of ILS mode (press "i"). Landing grades: Each landing attempt is graded by three values: The wire number caught, a classification and a score. The LSO will evaluate the score on your flying from the moment he asks you to call the ball and until you catch a wire or are waved off. Wire number: Catching the number three wire is the ideal, while number two and four are acceptable. Catching the #1 wire may be a symptom of a dangerous situation where you were too close to the ramp. Classification Score Description _OK_ 4 points Perfect! OK 4 points Small deviations corrected by pilot. (OK) / Fair 3 points Deviations usually corrected without LSO calls. No grade 2 points Large deviations requiring LSO help. Cut pass 1 or 0 points Unsafe pass - may have resulted in damage or injury without LSO help. Wave off 0 points Landing aborted by LSO because of pilot error. Bolter 0 points All wires missed. In addition, out of the context of carrier operations, some statistics on the the individual types of deviations are given, in the form of Root-Mean-Square error. Also, a floating point "overall score" is given. A bonus is given for switching off ILS and/or HUD before calling the ball. For each of the realism options that are set for max. realism, a bonus is also given. The maximum possible score is 10.0. I will keep a "Sierra Hotel" table of the best landings on the Vertigo homepage. To submit a landing score, mail me your name, the score, aircraft type, HUD and ILS on/off status, realism menu options and the four letter validation code printed below the score. Press "p" for a pause to study the landing debriefing. Landing pattern: Selecting "Carrier: On final" sets you up for a straight-in landing, but in day-time and clear weather, a landing pattern is the correct method. A pattern is flown by passing the carrier at 800 feet in the upwind direction, where you will be ignored by the LSO, turning left and starting a slow decelleration and descent, turning downwind and going dirty, turning base leg behind the carrier and turning to arrive on final at 350 feet altitude, 3/4 of a mile beind the carrier and on approach speed, to be asked to "call the ball" as you come out of the turn. Due to the limited sense of spatial awareness possible in this simulator, flying a pattern will be quite difficult. The waypoint padlock will probably be helpful. Wind: The carrier will be heading into the wind at a speed resulting in 25 kts of wind down the deck. If the natural wind is more than 25 kts, this will not be possible, and you will have stronger wind, regardless of what you are told on the radio! The landing strip is angled 9.2 degrees relative to the deck, so you will have a slight crosswind from starboard. The carrier will maneuver to avoid ground, so the wind relative to the deck may change. If you want to create more difficult landings, go to the menu and switch wind off and on again - the wind will now be of a different strength and direction. Trapping: The wire force is set for each aircraft. The Corsair and U-2 will be decellerated at 1G, the F-14 at 2G, and the F-104 at 3.5G, which would probably rip it apart in the real world. When you come to a standstill, you can raise the hook and take off under your own engine power only, or if you are in the F-14, you can proceed to the catapults. Credits: The carrier landing simulation would never have been possible without the generous and competent advice from: Cole Pierce (gun one), Mike Yukish, Chuck Kilogre, Bill Horne, Pete B. D., Tom M. Olivier, Jim Muse, John Simon and those I forgot in the hurry. Thank you! Information for making the simulation more precise is always welcome.

Catapult launches

The four catapults on the aircraft carrier can be selected as starting position in the menu - you will be assigned a random one, or you can taxi onto a catapult from the deck. Taxiing will have to be done extremely precisely and slowly, if you are to be attached to the catapult. Normally, a "yellow shirt" would guide you, but here you are on your own. Behind you, the jet blast deflector will rise. To launch, apply full throttle and go into afterburner. If you are using keyboard for throttle control, first press on F4 will take you to full military throttle, and subsequent presses will light the burner stages. After a few seconds, the cat will fire. You will be pushed forward with an acceleration of approx. 2G. Only aircraft properly equipped can be launched, which means the F-14 Tomcat only. If you experience oscillations when locked to the catapult, increase the calculation rate in the graphics menu.

Other things to try

As you probably have found out by now, there are no missions. So how come that I still do not find it completely uninteresting to fly this thing after a couple of carrier traps and some targets destroyed? Below are listed a few things, that I find funny to try:
  • Test piloting:
    Take the aircraft and the flight model to the limits and find out how it behaves. Compare with the performance of the real aircraft, if you have the data, find out where the realism of the flight model fails. I'll be happy to hear about your results.
  • Radio-controlled flight:
    Viewing from the tower, you can fly in a manner similar to R/C flight. Be sure to select a fairly slow aircraft with a small turning radius. You will easily get confused interpreting the attitude of the aircraft, but this is also experienced in real life in difficult lighting situations.
  • Aerobatics:
    You can perform a wide range of aerobatic maneuvers, including some that involve stalling.
  • Spins

    A stall may develop into a spin, especially if aileron and rudder input is given to provoke it. The tendency to spin varies greatly between the aircraft. Mainly because of their relatively short wings, the Starfighter and Harrier tumbles rather than spins. The U-2 takes a lot of work to spin, but when it gets going, it will be even harder to stop. The F-14 can be spun, if strongly provoked, but shutting down one engine causes a high risk of entering a flat spin. The T-17 spins easily and recovery is effortless. The Corsair is very prone to enter a spin that may easily become flat and tough to get out of.
    Recovery from a spin depends on a lot of factors, but roughly goes as this:
    Flaps: Up
    Throttle: Idle
    Stick: Center, or a little forward
    Rudder: Opposite rotation until it stops
    Pull gently out of dive when airspeed is sufficient.
  • Landing:
    The skills of a pilot is often judged in the smoothness of the landing. When you routinely can bring the Starfighter to a stop before the end of the runway, you are getting the hang of it.
  • Hovering:
    A very difficult exercise is to practise vertical take-off and landings in the Harrier. I believe the simulation is more difficult to handle than the real Harrier, due to less stability and poorer awareness of your attitude.
  • Taxiing:
    Aircraft are often quite clumsy on the ground, so high-speed taxiing can be a challenge.
  • Strafing the tower:
    Check your aim by switching to tower view immediately after firing.

  • Flight data logging

    For a detailed analysis of your flight, you can record many data parameters. Logging is toggled by the key "SHIFT l". The data are recorded in a file named fdata###.log, with a number increasing for each log created. Data are stored as plain text, and may be loaded into spreadsheets etc. The logging frequency is 1Hz. A line is entered with the following data seperated in columns:
    Time (s)
    Aircraft x, y and z coordiantes (m)
    Angular speed around x, y and z axis of aircraft (rad/s)
    Vertical velocity (m/s)
    TAS, IAS (kts)
    Mach number
    Angle of attack and yaw angle (rad)
    Acceleration along x, y and z axis of aircraft (m/s/s)

    Tips for beginners

    There is really no need to make it too difficult for yourself in the beginning. These are the suggested options for a gentle start:

    Aircraft: MFI-17 Supporter.
    Realism: Wind and realistic propeller engine: Off.
    Graphics: Landscape type: Flat.
    Press "ALT h" to get the head-up display.
    Make sure that you have a quite large field of view, e.g. set the viewing distance to about half of the real value in the graphics menu.

    Version history

    August 1995: Version 0.10

  • First release.

    December 1995: Version 0.11

  • Fractal landscape added.
  • More details around the airfield.
  • Ground forces on wheels calculated in more detail.
  • Profile drag dependence on flap deflection included.
  • Some trimming on aircraft models, especially the Harrier.
  • SVGA graphics drivers removed because of poor performance.

    March 1996: Version 0.12

  • More detailed rendering, with hidden surface removal.
  • Air brakes for the jet aircraft.
  • Quick joystick centering for those of us with a cheap game card.
  • Vought F4U Crusader, with more graphic detail than previous models.
  • Machine guns on aircraft.
  • CCIP gun-sight.
  • Pause mode.
  • Position lights on some aircraft.
  • Status line in external view.

    May 1996: Version 0.13

  • More detailed rendering of the Harrier and the U-2

    July 1996: Version 0.14

  • Filled polygons with light source shading for aircraft and landscape.
  • All aircraft are now drawn using polygons.
  • SAAB MFI-17 Supporter added.
  • The generic aircraft models removed.
  • Display of HUD [h] and controls position [j] can be toggled.
  • Clean exit from floating point errors - reboot is still recommended, though.

    September 1996: Version 0.15

  • Video page flipping flicker eliminated.
  • Less time spent on objects and terrain outside the field of view or far away.
  • Undercarriage less hysterical about low calculation frequencies.

    November 1996: Version 0.16

  • First release compiled using djgpp:
  • 256 color SVGA graphics.
  • Haze colouring of distant scenery.
  • Gyroscopic precession forces from propeller included.
  • Wind of random direction and strength added.
  • Waypoints with HUD navigation info.
  • Scrolling, zoom-able map.
  • Messages from tower.
  • Ground collision detection improved.
  • Setup files for Thrustmaster FLCS and TQS included.
  • Dots on ground to improve depth perception.
  • Selectable landscape drawing distance.

    February 1997. Version 0.17

  • Nimitz class aircraft carrier:
    Sails into wind, trying to keep 25kts of wind over deck.
    Rolls, pitches and heaves depending on wind strength.
    Maneuvers to avoid land.
    Detailed arresting wire forces.
    ILS beacon.
    "Meatball" with adjustable tilt.
    Approach indexer
    Landing Safety Officer is guiding you down by voice.
    View from LSO station. Select by pressing "Home"
    Landing grades/score given.
  • Sound support for Sound Blaster compatible cards:
    Aircraft sounds have doppler frequency change and
    volume depending on distance.
    Sampled speech (LSO etc.)
  • Controls:
    Analog throttle supported.
    Adjustable null zone.
    Adjustable noise filter.
    Nicer menu structure.
    Control surface deflection decreased to more realistic values.
  • Starting location menu.
  • Wheel rotational momentum added.
  • HUD-modes:
    Air-air Select by "Enter"
    Air-ground "Backspace"
    Navigation "n"
    ILS "i"
    HUD on/off Changed to "ALT h"
  • Bugfixes:
    Scaling factor in gravitational torque corrected.
    Flaps now updated when swapping planes in mid-flight.
    FLCS un-pause works without delay.

    June 1997. Version 0.18

  • Propeller engine:
    Engine torque depending on power, RPM and air density.
    Propeller treated as a rotating wing, causing:
    Efficiency depending on RPM, flight speed,
    propeller pitch and air density.
    Propeller slipstream / vortex affecting tail surfaces.
    Torque from drag and inertia.
    Constant speed propeller, with pitch depending on RPM.
    Blade lift and drag calculated from wind tunnel data.
    RPM setting handle:
    CTRL F1: low RPM CTRL F4: high RPM
    CTRL F2: decrease RPM CTRL F3: increase RPM
    RPM display.
  • Flight model:
    Angular momentum coupling between axes.
    Induced drag calculations more detailed. Adverse yaw stronger.
    Side-slipping forces stronger.
    F-104: Landing speed lowered to 180 kts, AoA 7.4 deg.
    F4U: "Toe-out" on gear for better ground handling.
    F4U: Approach AoA lowered to 5.0 deg.
    Anti-bounce kludge: Toggleable from Realism menu, this will make control easier when turned on. But it has no real-world equivalent.
  • Control surfaces:
    Limited actuator speed.
    Rudder auto-coordination option.
    Rudder trim: left: ( right: )
    Aileron trim: left: { right: }
  • Graphics:
    Animated graphics of:
    Control surfaces, flaps, brakes, landing gear and propeller.
    Analog instruments:
    Turn & slip indicator.
    RPM dial.
    "nose-pointer" added.
    AoA display added.
    Trim position indicators.
    Vector graphics mode removed.
  • Sound:
    Slight changes to LSO comms.
    Stall horn added.
    Menu for setting speech, engine and miscellaneous sound volume.
    "-nosound" option for people with incompatible hardware.
  • Misc:
    More reasonable wind directions when using RWY 00.
    LSO wave-off limit and landing grades tweaked.
    Documentation in HTML format.
    Anti-flicker delay no longer needed.
  • Bugfixes:
    Angular inertia of right size - it was too small before.
    Polygons filling the entire screen are now (mostly) drawn.
    LSO altitude instructions corrected.
  • September 1997. Version 0.19

  • Sound:
    Speech samples of higher quality contributed by [anonymous contributor] (LSO voice) and Mac McAuley (pilot voice).
  • Flight model:
    F-14A Tomcat added, with:
    Variable geometry wings and glove vanes, sweep set from Mach number.
    Auto-throttle, toggle by pressing "t".
    "Direct Lift Control" spoiler manipulation. Increase lift by pressing "q", decrease by "a".
    Roll control using taileron and differential spoilers.
    Undercarriage cannot be lowered while on ground.
    Gear-up landings improved.
    Engine failures possible. Press "F" to get one within the next minute.
    Wing C_p location depends on flap deflection.
    Air temperature depends on altitude.
    Location of center of pressure and gravity adjusted for less pitch and yaw stability, decreasing "nose bounce".
    Control surface gain adjusted.
    Approach speed and AoA adjusted.
    Anti-bounce kludge removed.
  • Graphics:
    Mach number display added.
    Auto-throttle and DLC indicators (F-14 only).
  • Controls:
    Linear and exponential controls now have same total stroke.
  • January 1998. Version 0.20

  • Flight model:
    Decreased induced drag.
    Glove vane servo improved.
    Flaps retract at sweep above 55 deg.
    Manual sweep mode:
    Toggle auto/manual by "s" key.
    [F9]: Minimum sweep, 20 deg.
    [F10]: Decrease sweep by 5 deg.
    [F11]: Increase sweep by 5 deg.
    [F12]: Maximum sweep, 68deg.
  • Propeller engine:
    F-4U engine has two-speed auxiliary blower, operated automatically.
    F-4U engine has 2:1 reduction gear.
    Manifold pressure display.
  • Graphics:
    Night / dusk / day / dawn selection, with dynamically changing light intensity.
    Carrier and runway lights.
    1630 stars displayed from the Yale Bright Star Catalogue. Sky orientation can be set for any time and location.
    Wing sweep angle and mode indicator (F-14 only).
    Monochrome option. Toggle by "ALT h".
    Altitude above ground level and "PULL UP" warning are displayed.
    Analog instruments:
    Artificial horizon
    Indicated Airspeed
    Vertical Velocity Indicator
    ILS needles
    Magnetic compass
    Manifold pressure
  • User interface:
    The graphical user interface, MGUI by Vincenzo Morello, is used. Among the improvements to the menu system are the possibility of selecting aircraft type before flight, and graphical joystick calibration.
    Mouse support re-established. It causes some screen flickering when used.
  • Bug fix:
    Sticky behaviour at 0/180 heading removed.
    Auto-throttle now works with HUD off.
    Vertical velocity on HUD now of correct size: Ft/sec.
  • June 1998. Version 0.21

  • Flight model:
    New aircraft, called "X-17" for demonstrating work in progress. Introduces wing dihedral for roll stability and undersized tail fin, making aircraft prone to "Dutch roll". Has no ailerons or flaps, but is easily steered using rudder.
    Stall angle increased when slats are extended. Makes handling of the F-14 better at high AoA.
    Control sensitivity adjusted for each aircraft.
  • Catapults:
    The four catapults can be selected as starting locations, or can be taxied onto from the deck. Properly equipped aircraft (F-14 only) can then be launched.
  • Graphics:
    Wind-bag at airfield, turning and inflating according to wind.
    Moving jet blast deflectors behind catapults.
    Instrument panel display can be toggled by key "SHIFT i".
    Padlock view of target or waypoint from cockpit by key "*".
    Padlock view of target or waypoint in external view by key "/".
    In air-to-air mode, a gun "snake" is displayed, and a Lead Computing Optical Sight pipper for the selected target.
    Inside LCOS is a range clock.
    Selected target has a box around it, with relative heading and aspect markers.
    To the lower right, target range, closure speed and aspect angle are displayed.
    Number of remaining gun rounds is written at lower left.
    Analog instruments:
    Delayed response for instruments sensing air pressure: VVI, ALT and IAS indicators.
  • Guns:
    Only a fraction of the rounds are tracers.
    Tracers extinguish after 5 seconds, but all bullets flies for 15 seconds.
    Recoil made less prominent.
  • Targets:
    Gunnery practice range at waypoint "TARGETS".
    Four circling targets at random speeds, g-loads and altitudes.
    One stationary target on surface.
    Next target can be selected by key "SHIFT t".
  • Sound:
    Warning message when crash is likely.
    Rumble from wheels when rolling.
    Catapult launch sound.
    Tweaked stall horn.
    Sound when hitting or destroying a target.
  • Source code:
    The source code for defining the graphic objects is now available for downloading. You can design your own objects and load them into the simulator.
  • November 1998. Version 0.22

  • Flight model:
    Fuel tanks, with selectable starting quantity.
    Fuel consumption by jet and propeller engines.
    Detailed jet engine model as option:
    Thrust depending on Mach number and altitude.
    Multi stage afterburners.
    Compressor stalls.
    Wind-milling and air-restarts, key "e".
    Trans- and super-sonic drag.
    Maximum control surface deflection decreases with increasing airspeed.
    F-14 auto-throttle is now governed by AoA, but works poorly.
    Restored efficiency of Harrier attitude controls.
  • Graphics:
    Cockpit walls and canopy frames in internal view, although very crude. Toggle by key "d". Caution: Panning while showing cockpit triggers a bug in the graphics engine.
    Display of aircraft in internal view can be toggled by key "SHIFT d".
    Internal cockpit panning.
    Smooth / instant panning option.
    Analog instruments:
    Dual fuel quantity display.
    Fuel flow, jet and prop version.
    RPM, now also jet version.
    Exhaust gas temperature, jet only.
    Undercarriage position.
    Bank indicator.
  • Sound:
    Ball calls include fuel state.
    Sounds for afterburner.
  • Misc:
    Now only judges airspeed from AoA.
    Less eager to wave-off and more generous with grades.
    More options saved in config file.
  • August 2000. Version 0.23

  • Flight model:
    North American X-15A-2 added:
    Rocket engine w. fuel consumption
    Reaction Control System, toggle activation by key "r".
    High altitude drop option added.
    Dynamic centre-of-gravity calculations corrected.
    High altitude atmosphere model more detailed.
  • Graphics:
    Sky darkens with altitude, and stars appear.
    Menu-system debugged and tweaked.
    AoA chevron colours swapped to correct order.
  • Sound:
    Rocket engine sound added.
  • Misc:
    Larger fraction of source code released.
    Black screen startup pause on some systems is removed.
    Jet fuel flow indicator now shows zero when out of fuel.
    Auto-throttle debug info removed.
  • September 2001. Version 0.24

  • Flight model:
    Grumman Lunar Module added:
    Highly detailed descent module graphics made by H. Frik.
    More detailed rocket engine model:
    General orientation.
    Non-zero idle thrust.
    Fuel flow toggle by key "e".
    Auto throttle (key "T") for Lunar Module.
  • Scenario:
    Moon scenario added:
    Grey landscape with mountains and "seas".
    No atmosphere and reduced gravity.
    "On surface" and "Low Gate" starting locations.
  • Graphics:
    Solar position on the sky depends on time and geographic latitude.
    Contrast of illumination depends on atmospheric pressure.
    A few custom colours for aircraft, in stead of the fixed pallette.
  • Sound:
    Radio communications for the Apollo 11 mission added.
  • Misc:
    Complete source code released.
    Engineering mode, key "E" for more panning and zooming freedom.
  • September 2001. Version 0.24.1

    Maintenance release
  • Graphics:
    Page flipping works again when using the mouse.
  • Misc:
    Source made compatible with LibGRX 2.4.3.
  • March 2002. Version 0.25

    Flight data logging to text file can be toggled by key "SHIFT-l"
    Vertical keypad panning reversed when in cockpit
    Keypad 5 restores forward view
    Source made compatible with Allegro 4.0

    Latest version: April 2002. Version 0.26

    First functional release for the Linux environment.
    Runs in window under X11 or full screen in console
    Joystick input is missing, though.
    Using Allegro for graphics and input. LibGRX is abandoned.
    Using CGUI for menues. MGUI is abandoned.
    Easier program installation in DOS/Windows.
    Trim keys moved.
    Use SHIFT plus arrow keys for elevator and aileron trim.
    Use ALT plus left/right arrow keys for rudder trim.
    Corrected throttle position when swapping planes and starting.
    No more flameout when swapping from prop to jet plane.
    And more...

    Known bugs

    Some of these are:
    * The joystick calibration routine messes up timing - better to exit the program after calibrating. * Panning inside cockpit while displaying internal cockpit graphics triggers a bug in the graphics engine. This especially happens if smooth panning is enabled and the "viewing distance" in the graphics menu is large.
    * Some parts of the HUD does not scale correctly to the screen dimension data you enter.
    * Occasional overflow or divide by zero halts, especially when you are stationary on the ground.
    * Objects that are supposed to be hidden behind a hill are often drawn.

    Many more bugs are suspected. De-bugging is slow and pain-staking, partly due to my messy programming. Also, adding new features (and bugs!) is much more fun, so expect many bugs to appear. Bug reports are always welcome. Make them as detailed as possible.


    The most recent version can be fetched via WWW at

    Deadline for next update:
    I have no idea. Don't hold your breath for it!

    When you upgrade, you may just as well delete the entire old vertigo directory, to avoid unused files and a conflict with the old configuration file.


    The Vertigo binaries are distributed as freeware.
    This means that the program is distributed free of charge. It may not be sold in any form. Vertigo may only be distributed as the original zipped archive containing the files listed in the installation section.

    The source code for Vertigo is available for downloading. These sources are distributed under the GNU General Public License for free software. Read the license file included in the source package for further details.


    If Vertigo halts because of an error before you are able to go to the main menu, you can force Vertigo to re-configure by deleting the VER_CNF.GCC file manually.
    Further instructions are found in INSTALL.TXT

    Home-built flight simulators

    Please visit my on-line listing of these.

    About the author

    I have been hooked on flight as long as I can remember, and spent a significant part of my childhood tossing paper planes and the like.

    In 1986, I entered the Royal Danish Air Force in an attempt to become a fighter pilot. After ten months of training, including 18 hours in the Saab T-17 Supporter, the instructors and I agreed, that I did not have the "magic touch".

    Afterwards I started studying physics and computer science, specializing in astronomy, and have now got my MSc degree at the University of Aarhus, Denmark.

    Currently, I am at the Copenhagen University Observatory, working on instrumentation for astronomical telescopes.

    I have crashed a couple radio-controlled model aircraft beyond worthwhile repair, and still have a semi-scale model of the Saab Supporter, that flies all too rare. Now I am mostly playing with electrically powered flying wings, which are great fun.

    In the spring of 1997, I have joined a soaring club, the Flyvestation Værløse Svæveflyveklub. If you think, the Vertigo releases are occurring less frequently now, you got the reason here. The real thing is more fun than tampering with a simulation.

    Why is the simulator called "Vertigo"?

    Several companies use the name "Vertigo" for a product, so why don't I choose a more original name that fits the simulator better?

    Well, I like the name for two reasons:
    The spatial disorientation experienced by pilots under IFR conditions is even more pronounced in simulators, due to the extremely limited field of view and lack of feed-back from e.g. accelerations.
    The name also is a good description of the confusion that characterizes the creation of the simulator. I have just put in what ever I felt like doing, and there is no real theme.

    How can YOU help making Vertigo better?

    Making a complete flight simulator is a big job, and I am happy to get any help you can offer. As of version 0.24, all of the source code has been released, making it possible for you to make modifications and extensions to the program. Download the source code and read the accompanying documentation for more details. Here are some suggestions for areas where you can help:
    You could:
  • Design some nice graphic objects to be included in the simulator, by adding to the distributed source code. For instance, you could make aircraft, ships, buildings, cars,...
  • Make an object designer program that is easier to use than putting the numbers directly into the source code.
  • Make a converter from your favourite 3D editor format to my format.
  • Provide sound samples replacing the current ones, as some of these may be violating copyrights. Or provide nice samples for future extensions of the sound.
  • Provide documentation on aircraft performance, aerodynamics, engines, carrier operations, and other details that could help make the simulator more accurate.
  • Please note, that whatever you contribute, I have no obligation to include it in the official release of the simulator.


  • The joystick reading routine has been copied and modified from Eyal Lebedinsky's FLY8 simulator.
  • From version 0.16, the DJGPP compiler is used. DJGPP is a MS-DOS port of the GNU gcc compiler. The port is done by DJ Delorie and friends. It is distributed from
  • Shawn Hargreaves' "Allegro" library is used for graphics, sound, key/mouse input and timing. Allegro has great cross-platform support. It is distributed from
  • In version 0.26, the graphical user interface "CGUI" by Christer Sandberg is used. It can be found at
  • MGUI by Vincenzo Morello, was used from version 0.20 to 0.25. The code is still present in Vertigo, but it is not updated for later versions. Get it at
  • Some lift and drag coefficients are derived from wind tunnel data provided by L. Lazauskas.
  • I got a lot of neat data on the F4U from Jerry "Zman" Zollman and Greg O'Sullivan. "Zeno" also have put some goodies on his page:
  • LSO samples are made by [anonymous contributor] with assistance from Mac McAuley.
  • Thanks to Jouni Raitamaki for providing jet engine data.
  • Thanks to H. Frik for making the beautiful graphics for the Lunar Module descent stage. He also provided lots of data and sound files for the LM simulation.
  • Thanks to A. Lamprou for bug reports.


    Comments on Vertigo are appreciated. Send them to:

    Anton Norup Sørensen
    e-mail: a_norup at post dot tele dot dk