Flight simulation

A simulation video game provides an excellent extended environment that enables players to do things they do not usually do or are unable to do in real life. Knowledge of physics and other sciences is very helpful for understanding how an aircraft should be designed and flown in specific ways, and followed by aviation procedures. Real-world pilots are required to spend time in a level D simulator, but the cost of official training can be extremely high. If they want more practice time at a lower cost, they can train and maintain their proficiency using a home setup simulator.

Flight simulation makes great use of classical mechanics to replicate the behavior of an aircraft, but it is less accurate and realistic in simulating crash effects, as it does not account for material properties like chemical bonding and molecular interaction. Imagine you are conducting an experiment in which you were able to repeat the falling of a cup made of glass with absolute precision under the same conditions such as height, release point, ground touch point, touchdown velocity, rotational orientation (yaw, pitch, roll), pressure, temperature, and surrounding air flow billions of times, could you possibly find at least two instances where the cup cracks in exactly the same pattern? This is a typical question that distinguishes the physics of large-body object motion from the physics that deals with randomness of particle at atomic level.

An aviation enthusiast does not necessarily become a pilot to learn how to fly an aircraft. There are a plenty of resources provided by FAA that help you enrich your aviation knowledge along with a flight simulation such as FAA-H-8083-25C, FAA-H-8083-3C, and FAA-H-8083-15C. An intuitive understanding of how a flight simulation works would be great for calibrating user expectations on software advancements and shortcomings. This post may not be the best but I find that it carries out many notable insights into the design of 2 immersive flight simulations with high-fidelity aircraft, both of them are great in their own ways.

The evolution of flight simulation

Taking a look at the evolution of Microsoft Flight Simulator (MSFS), I was surprised at how dramatically computer advancement has transformed virtual worlds. What began in 1982-1984 as a basic simulator with simplistic visual frames as in The Legend of Kage has transformed into a fascinating digital representation of global geography. Early versions presented players with minimal geometric landscapes that less defined the realism of simulation. Over decades, with the incremental advances of computer graphics and data processing, the simulator gradually incorporated more sophisticated mapping techniques that led to the remarkable change of scenery construction and world modeling.

I have never tried MSFS. However, from my experience with X-Plane and resources regrading MSFS, the developer might leverage satellite imagery, topographic data, and advanced ML rendering algorithms in the development, allowing modern versions to recreate entire continents with extreme precision. The terrain is visually accurate—it captures subtle geographical landscapes such as mountain ranges, vegetation, city buildings, and even dynamic weather patterns like wind as reflected in grass and tree or atmospheric phenomenon haze. This is not just about visual improvements but also about how computational power has enabled more complex modeling and turned the simulator into an environment for exploring and understanding flight systems, aerodynamics, and environmental interactions.

The realism reaches the level that I thought I could even live in the simulation. For many moments, the line between simulation and reality vanished and left me fully drawn into the world of flying. I do not have any long cinematic videos generated from replays, but I found that these videos serve as good references for the experience I have been through.

As born a decade later, X-Plane just can not be compared with MSFS when it comes to its history. Its render engine already leverages new technologies and is pretty decent so players may not experience any significant changes between different versions. However, in terms of physics simulation and system in depth, X-Plane is potentially superior, giving it an advantage over MSFS especially for training purposes.

This is me flying with the popular GA Cessna 172 when trying to visit the Royal Observatory, located in Greenwich, London, where the Prime Meridian Line (0° longitude) crosses. There is a red ball named the Greenwich Time Ball on top of the Flamsteed House. At 12:55 each day, the ball rises halfway up its mast before rising to the top at 12:58, and falls at 13:00 exactly. This has been the signal of time to the citizens along the River Thames for a long history. I was first introduced to this place in a geography lesson about global time zones in my school years and later revisited it in astronomy courses. Ever since, it has become a place of great interest to me.

Missing physical effects in simulation

Physical effects such as g-force cannot be experienced in simulation but during real flights. The same thing happens when going upstairs or downstairs in an elevator, body weight slightly changes and the brain informs me when the change is sudden during acceleration and deceleration. This is because the lift force pushes the body and causes it a bit more and less weight than usual. Some people might be more sensitive to g-force than others. And this signal can be used as a method to detect vertical speed (VS) changes in a real flight.

Why does altimeter measure pressure?

The reason why it measures air pressure to calculate altitude, not relative to the sea level, is due to lift-coefficient as aircraft relies on air pressure to maintain lift. For example, aircraft are required to maintain a vertical distance of at least 1000 feet, so if 2 aircraft enter the same geographical location, they will translate their altitude relatively to avoid collision. Or when an aircraft is flying close to the upper limit of its maximum altitude relative to the sea level and trying to maintain that altitude, the engine may struggle to produce thrust if the aircraft enters a region with lower air density intake. In the worst case, this may lead to a system corruption and place the aircraft in a very dangerous situation.

Flight procedures reflect the aircraft capabilities

What should pilot do when the cabin pressurization suddenly drops and does not appear to be fixed? What altitude should pilot maintain his aircraft? It is 8000 feet. Human biological system can operate normally with little to no side effects even without oxygen suppliers at this altitude, and the airframe can survive structural stress by not experiencing high pressure of cabin. Another reason is the cabin pressurization requires energy, leading to pressurizing to sea level costs more and eventually increasing the cost of travel. So, instead of designing the airframe to resist the pressure at sea level, the pressure of cabin is adjusted to that of 8000 feet at high altitude.

Does flight level affect bank angle?

What influences bank angle is as above also, pressure or air density decreases at high altitude, the aircraft produces less thrust but still achieves high speed for travel efficiency, high bank angle may put the aircraft in a more dangerous situation, flying closer to stall speed. For a commercial aircraft like B737, and probably A320, the bank angle at 10000ft (FL100) is 30 degree and should be set to 10 degree once it passes 30000ft (FL300). This can be found in the procedure checklist. But aircraft is designed to fly beyond the normal conditions to deal with unexpected situations and request from ATC, so bank angle can be higher than usual. If pilot tries to let their aircraft fly exceeding threshold numbers, there will be visual and sound warnings showing up. Some modern aircraft like A320 family are equipped with fly-by-wire system to help maintain stable flight, pilot will not be able to turn with a steep bank angle under Normal Law. Of course, there are more factors related to pressure or air density and they coexist in mathematical formulas, by looking at how one changes we can predict and understand the others.

Fluid dynamics

Fluid dynamics is simulated and directly affects on the body of aircraft. Take a single engine general aviation (GA) Cirrus SR22 when taking off for example, the propeller rotation generating thrust pushing the aircraft forward will also create a spiral air flow affecting on the vertical stabilizer, causing the aircraft heading slightly point off the course. This effect varies on different single engine GAs and requires different adjustments from pilot. Another example is when an aircraft is flying, vortex, the air flow circulating a centerline is formed at the wingtip. Pilot is aware of this to maintain a safe distance from any aircraft flying ahead to avoid unstable flight. In aviation, this phenomenon is known as wake turbulence and there are procedures in place for this specific type of turbulence, especially during take off and landing in a busy traffic.

Aircraft and Ancient marine reptiles

Aircraft design is influenced by birds and may also be inspired by ancient marine reptiles. Both the sky and ocean are fluid environments that share similar properties such as pressure and flow. Just as many other phenomena in physics, they have a tendency to travel from high to lower pressure region in order to maintain balance. As their molecules have mass, they are still subjective to gravity and under the influence of gravitational force.

Ocean has been the environment for many organisms including ancient marine reptiles. Some creatures like Plesiosaurs underwent the evolution of aquatic adaptations to shape their bodies for drag reduction and lift generation to enhance travel efficiency.

Airbus Beluga and Boeing Dreamlifter

The Airbus Beluga is a freighter aircraft designed primarily for transporting large aircraft components. From its interior, I can see the cockpit of the ST is very similar to that of an A300 while the XL is like an A330. Boeing has a comparable aircraft, the Dreamlifter, whose exterior looks a bit weird as it is a modified version of the B747-400. It is always very exciting to learn to fly a modern aircraft as there are many advanced technologies emulated in a nearly real-world flight simulation.

B737 and A320 cockpit

Footage

Traveling in the Earth’s atmosphere is much easier compared to traveling in deep space. For travel within cities, we are going to use lighter aircraft, which are more efficient for short distances and low altitudes.

Boeing 777F Crosswind landing practice in VVNB (Noi Bai International Airport)

Landing under crosswind conditions is experienced in day-to-day flights. Like an ideal condition approach, the pilot has to plan landing performance including information such as ICAO code, runway number, navigation assistance, temperature, wind velocity and direction, gross weight, and so on. Several inputs are manually entered by the pilot while some others are automatically retrieved and calculated by the computer.

Newton’s first law on inertia best describes this situation. The aircraft needs to meet certain conditions on approach & landing velocity and runway length with the current gross weight. To achieve the desired velocity, the aircraft has its flaps extended to generate more lift while allow it to fly at a lower velocity. The flap setting was 25 or 30 degrees on landing in my flight as I remember. All B777 variants have 6 flap levels ranging from 1 to 30 and the video also shows that the flap angle is high.

The landing was a bit challenging because of crosswind and a wind component is added to calculate the final vector. In navigation, this vector has the direction known as course and this course is aligned with the runway centerline. The other vector is heading, where the nose of the aircraft is pointing and has the magnitude of thrust provided by the engine.

TBM900 VFR flying practice in VHHX - (Kai Tak Airport - Hong Kong)

Kai Tak IGS RWY 13 is one of the most challenging approaches in aviation history. Pilots had to make a steep bank angle turn at low altitude right over the city buildings just the moment before landing. For some reasons, the runway is favored by many B747 aircraft. The aircraft is big in size and two of them were modified as Space Shuttle carriers. Today, we can only experience the breathtaking nature of that approach through flight simulators.

MD-11 ILS Landing practice in LFPG (Charles de Gaulle Airport)

Charles de Gaulle Airport is one of the largest and busiest airports in the world and serves as a major hub in Europe and many countries from different continents. Known for its size, design, and high volume of international traffic, it is also a historic place for Airbus aircraft debuts. Despite entering the industry later than some of the big names like Boeing, Airbus has become a major aircraft manufacturer and symbol of innovation in aviation.

TBM900 ATC (Air Traffic Control) practice in KJFK (John F. Kennedy International Airport - New York)

TBM900 IFR & ATC practice in KSFO (San Francisco International Airport)

A321CEO CFM Go-around practice in WSSS (Changi Airport)

In aviation, safety is highly prioritized and go-around procedure is an example of this principle. A go-around occurs when an aircraft decides to abort a landing usually due to unsafe conditions like low visibility, unstable approach, adverse weather, runway obstructions, or even request from ATC. Instead of making a touchdown or after having already touched down, the aircraft applies full thrust, climbs up, enters holding pattern, and waits for further clearance. The holding pattern can be programmed on MCDU.

Baron 58 Twin-engined aircraft VFR Flying practice in Great Britain Central

Mesh scenery and model from satellite imagery

To improve the flight simulation experience, having photorealistic mesh scenery installed is highly recommended. It is especially ideal when you are flying at the altitude of 3000 feet or higher. However, as you descend closer to the airport, you might want to select tiles with higher zoom level to maintain visual quality. As you move farther from the airport and gain altitude, lower zoom level is a way to go to save disk space and memory while the environment still looks impressive.

The scenery creation process needs to go through several stages including selecting satellite imagery service like Google or Bing, mesh regions and their corresponding zoom levels, and a set of 3D models used to fill on top of the terrain. After the final stage, you will have a quite good looking of buildings, bridges, and trees at where they should be, but not very close to the real world as extra manual works for specific buildings and arrangements are required. Fortunately, many of these works can be easily found and downloaded from the community forum.

Example of output

2023-05-28 21:06:02.267 python [28903:8574801] [CATransaction synchronize] called within transaction
2023-05-28 21:06:02.365 python [28903:8574801] [CATransaction synchronize] called within transaction
7-Zip [64] 17.05 : Copyright (c) 1999-2021 Igor Pavlov : 2017-08-28 p7zip Version 17.05 (locale=utf8, Utf16=on, HugeFiles=on, 64 bits, 8 CPUS LE)
Scanning the drive for archives:
1 file,
6029724 bytes (5889 KiB)
Extracting archive: ./tmp/+10+106.dsf.7z
Path = ./tmp/+10+106.dsf.7Z
Type = 7z
Physical Size = 6029724
Headers Size = 124
Method = LZMA: 12m
Solid = -
Blocks = 1
Everything is ok
Size: 12323438
Compressed: 6029724

Very accurate 3D models of Shanghai, manually built by the community, sits on top of the mesh scenery. They look so realistic.

Airport & Flight

SWISS Aircraft

Aerial Views of Our Airbus A220

Avro RJ100 - an aircraft legend leaves the SWISS fleet