The Sad Demise of Propulsion Controlled Aircraft

Sioux City Crash

In July 1989, a DC-10 chartered by United Airlines, Flight 232, crash-landed in Sioux City after a disastrous loss of all hydraulics rendering the plane uncontrollable. One-hundred and twelve souls lost their lives in that accident considered one of the worst air disasters in US history. The hydraulic fluid, which actuates the flight controls based on pilot input, leaked out after an uncontained failure of the tail engine severing the lines.

The hopeless last moments of United Airlines Flight 232

One off-duty training captain, joined the cockpit after hearing the explosion from the back. Through experimentation, he discovered that by manipulating the throttle controls, he could control the plane slightly and attempt a safe landing. While everything seemed under control, at the last seconds before impact at Sioux Gateway Airport, the plane banked hard and flipped over and burst into flames.

The terrifying final moments of JAL123 recorded on CVR.

Japan Airlines 123 Disaster

Four years before, in August 1985, Japan Airlines 123, was the subject of the world’s worst single aircraft disaster in aviation. An improper repair of the rear bulkhead caused it to rupture after several cabin pressurization cycles over hundreds of flights and slowly tore the rear tailfin. All the hydraulic pipes ran through the tail and their breakage caused again, all the hydraulic fluid to leak leading to the subsequent loss of all flight controls.

Again, the pilots followed the technique of the Sioux City flight. They wanted to fly back to Haneda airport but despite all the heroic efforts to control the plane for an incredible 30 minutes, fate was against them and they crashed into the mountains near Mount Fuji. As the single worst aircraft crash in history, 505 people lost their lives.

DHL Takedown

It seemed at this point that the aviation industry still didn’t learn their lessons after two similar crashes. Years later, in 2003, a DHL Airbus A300 cargo took off from Baghdad, Iraq towards Bahrain and shortly got hit from by a man-portable surface-to-air missile from Fedayeen terrorist group. It struck the left wing causing damage to it and subsequent fuel leak. The hydraulic lines ran through the damaged wing and all three leaked and failed. Again, the pilots lost all flight controls.

Captain Éric Gennote was forced to improvise again using the same technique as in the previous incidents. He managed to turn back to the airport but had to make two approaches because the first final was too close. As an incredible feat of flying, they managed to land the plane safely with a damaged wing, leaking fuel and no flight controls though they went off the runway. It was the first instance of a plane crippled by lost hydraulics managing to land safely at an airport without injury.

Other Incidents of Flight Control Failure

Many more incidents occurred over aviation history counting over a dozen. Wikipedia lists a comprehensive compilation of these types of incidents.

Throttle Only Control

All the pilots in the flights above learned that by controlling the throttles they could slightly control the plane with throttle commands alone. To climb, more power would be needed to increase the speed of the plane thus increasing lift. To descend, the opposite would be done dropping lift. Turning was done through asymmetric adjustment of the throttles while the engine with more power would cause the plane to lift from that side to turn in that direction.

However, despite the effectiveness of said technique, the flight paths tended to be erratic with constant pitching movements would cause a phugoid cycle. The plane would climb until it lost enough speed and pitch down and lose altitude. During the descent, the plane would gather up speed until it started climbing again. This rollercoaster ride made it hard to stabilize the aircraft and be the cause of quite the terrifying maneuvers.  

An amazing demonstration of a flight control-free landing in a simulator.

PSX Simulation

The developer of Aerowinx PSX, a Boeing 747 flight simulator, has created an excellent demo where they manage to control an aircraft with only throttle commands. As seen in the video on the side, we can see the first landing attempt to be aborted (go-around) only to return back for another approach and make a successful landing. While this is only a simulation, it shows that it is possible to control an aircraft without flight surfaces and only throttle control instead.

PCA Tests

Little did these pilots know, there was already software in development that would save the plane in cases like these. In 1993, NASA with the cooperation of McDonnell-Douglas, managed to create a system that would control and land the aircraft safely without any flight controls. It was dubbed Propulsion Controlled Aircraft (or PCA). The principle was similar to what the pilots in the mentioned incidents above attempted to do (by moving the throttles up and down) but done so systematically and automatically. However, since the system was run by software, it could be more precise and generate a more stable flight.

It was first implemented on an F-15 tested in the Dryden Facility and was demonstrated to safely land the plane that looked exactly like a normal landing. The increased stability was dramatic and the increase in control would be impossible to replicate by even the most skilled of pilots. They also tested the system on a passenger MD-11 aircraft with similar results. The MD-11 has its third tail engine set at idle to mimic the more common two-engine configuration found on most aircraft.

NASA’s demonstration of PCA

The system works through the autopilot with the pilots setting the heading, altitude and vertical speed that they desire and instead of manipulating the trim and flight controls, it would send the commands to the engines. No new sensors would need to be installed simply relying on the already existing ones.

PCA had an excellent success rate and landings were not only survivable but looked a lot like a normal landing. In fact, with PCA, I believe that none of the above accidents would have ever happened ending up being but a short NTSB report.

FAA Rejection

To me, the system seemed like a really trivial installation and with the software already developed, not very costly. However, the future of the technology was looking bleak. From Bill Burcham’s rough sketch to a prototype fully developed along with engineer Tom Wolf at NASA, lead to a system that seemed integral to future aircraft. However, that did not happen.

The FAA which oversaw the project concluded that it wasn’t financially worthwhile to implement such system. Their reasoning was that complete hydraulic loss was so rare, 1 in 100 million, that it wasn’t worth installing PCA onto the aircraft of the future. Enthusiasts of the technology such as Dave Hayes, from the Airline Pilots Association, and Dennis Fitch, one of the captains who survived the Sioux City crash, were thoroughly disappointed when this technology was thrown out.

Conclusion

No matter how rare that such incident apparently is, it’s happened so many times in aviation history. We can’t say it’s unlikely anymore. The 632 people who died from said failures certainly agree. Aviation is known to be the pinnacle of safety but recent times have shown that manufacturers have chosen a culture of profits and the consequences might cause even more incidents. Isn’t it enough that I mention the MCAS on the Boeing 737 MAX that resulted in the destruction of two aircraft and hundreds of deaths?

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The above flights have been dramatized by the excellent Mayday documentary series:

• Japan Air Flight 123

• United Airlines Flight 232

• DHL Takedown Incident

NES Musical Masterpieces

This article requires some knowledge of oscillation for producing sound. I’ll also confess that determining what chiptune sounds good requires an appreciation for them.

In my opinion, the Nintendo Entertainment System is the first video game console to feature games that have gameplay that still holds up to today. People still play NES for their playbility rather than solely their nostalgia factor. Older consoles like the Atari 2600 featured very simplistic games that gamers only play today for nostalgic reasons. Those who didn’t grow up with the Atari console don’t find any meaning in them.

I’m not sure if I mentioned this before on my blog, but I have an incredibly soft spot for chiptunes. There’s a charm to pushing these chips that can only make simple sounds to their limits to create a beautiful piece of music. I enjoy melodic music and what other than video games have solid and consistent melodies? There are some composers that I consider magicians because they make songs so deep that you’d put it in a club.

The NES APU, the sound chip in the NES, is what generates the simple tones to create music and sound through the console. Quality was lukewarm with the original Famicom and NES that outputed sound and video through a single coaxial cable. Eventually, a composite output was added providing a purer sound, though it was mono only despite many artists writing stereophonic music. Certain enthusiasts build mods to extract both channels.

There was five channels on the APU. Two pulse-wave (square) channels with four pulse-width settings in addition to a triangle channel. A random noise generator. Finally, a PCM for playing samples, although low-quality due to memory limitations.

I’ll give a basic explanation of how most games used these channels though some artists were more creative with their use. The two pulse channels supported the main melody, one was the main one and the other supported it (say with a slightly different pitch). The triangle channel was used to add bass. Finally, the noise channel was used for percussion.

Additional sound chips were used in cartridges that added extra channels or FM synthesis. I will talk about a few of these later but won’t cover all of them since there’s quite a few. I’ll go through some games that use them. Unfortunately, the sound chips could only be used on the Japanese Famicom since the NES didn’t have the sound passthrough through the cartridge slot. American ports of these games had to make shift with use of the available 5 channels and often the game sounded more muddled in comparison to their Japanese counterparts.

I want to take a dive into a few a games that have music that I consider ‘masterpieces’. There’s no real criteria other than my subjective tastes. Many won’t agree with me but I’m sure it will be appreciated by those who love ‘old things’. I hope you enjoy a few tunes and the order is set by my preference.

Super Mario Bros.

The overworld theme in Super Mario Brothers isn’t something I would consider a masterpiece. However, it’s such a classic that I felt that I had to include it here. There’s not much to comment about, it uses channels in the same way that most games do. Virtually everyone has heard some version of this song and I would consider it the prime example of chiptune.

Some noticed that parts of the music would be interrupted while jumping. It’s because all five channels were used for the music and nothing was left for sound. The sound effect would take place of one of the square wave channels so that it could play.

Mega Man 2

I would best describe Mega Man 2’s music as the ‘traditional’ sound of the NES. No special techniques are used for production, no intense melodies; just music that perfectly fits the atmosphere and theme of the level or the situation.

The boss of the stage, Quick Man, uses electricity as his weapon therefore the music has an electric sound to it. The music also plays at a faster tempo because of Quick Man was quicker than other bosses in the battle.

Mega Man 2 is an excellent example that simple music can still sound pleasant without the input of a master who knows every limitation of the chip and instead used it traditionally. Mega Man 2 uses the typical channel setup that was mentioned above for producing melody and beat.

One interesting fact about the composer’s goal was to create very simple melodies only composed of a few notes. The idea was to make catchy songs that were almost as simple as a pop song with a similar structure.

Silver Surfer

Tim Follin is probably the composer with the worst luck. He pushed soundchips to their limits making some amazing pieces except there was one caveat, the games he was contracted for were absolutely terrible.

Silver Surfer was torn apart more than a decade ago by The Angry Video Game Nerd. It sent him into a fit of endless cursing and swearing. However, he oddly didn’t comment on the amazing music in the game. Maybe he was too distracted by the awful gameplay.

The insanely fast paced music almost sounded something that would come out of the SID Chip on the Commodore 64. It was demoscene quality to be honest. He even managed to produce a convincing electric guitar sound.

The kick sound isn’t created with the usual DPCM sample like done in most games. Instead the triangle channel is with a pitch change is used to create a quick thump. He uses the same channel for the kick but what really showed that Tim Follin was a master at his art is that the two never played at the same time. It required quite a bit of creative production to never have them clash.

I really want to highlight how bad his luck is. Imagine being the composer for a Pictionary game, I’m sure you’d write something atmospheric and melow. Instead, Follin decided to compose something that would fit an Action-Adventure game where you’d be saving the galaxy from mutant aliens.

This is unusually intense for a board game but perhaps this was to make up for the boring nature of the game. I wonder what kind of music we’d end up with if he was composing for Chess Master.

Admittedly, Tim Follin confesses that he often didn’t compose music to follow the theme of the game but rather see what he could do with the limitations of the sound chip. That might explain the situation with Pictionary.

Journey to Silius

If any game completely broke the rules on the traditional method of using channels, it’s Journey to Silius. The artists did an amazing job of creating something that sounded so much fuller than the average NES game. The bass was stronger, the melodies more engaging and a beat that sounded completely different.

The two pulse channels were still used for the melody but instead of using the noise channel for the drums only, they combined the noise and triangle channels to create a very realistic sounding drum. This was because attack was done with the noise channel and decay using the triangle channel. However, the stroke of genius was using the traditionally unused DPCM sample channel for the bass. The samples used for the bass are pretty high quality and provide for that deep sound we crave when listening to music.

Castlevania 3

The music between the American and Japanese Castlevania sound completely different. This is due to the use of a chip VRC6 which adds two square wave channels (pulse) and one sawtooth channel. It’s not secret that having additional channels creates for a deeper sound and this is definitely the case for Akumajou Densetsu. There’s not much to comment other than to listen.

It’s quite obvious that the American version sounds much more dull. The artists didn’t really use any creative techniques to make up for the missing VRC6 chip. Instead, they used the typical arrangement using channels to generate beat and melody. It’s a bit disappointing.

Lagrange Point

Lagrange Point doesn’t sound like any NES game in existence. Rather than primitive sounds, we hear a pleasant and smooth track being played. This is due to the use of a special chip, the VRC7, which adds 6 channels of FM Synthesis. The sound produced ends up reaching 16-bit territory.

I won’t go into detail of what FM Synthesis is because I’m leaving that for another blog post. However, it can be noted that the VRC7 is used exclusively for the music while all other sounds effects are still done with the NES APU. The contrast between the two sounds is a bit jarring in my opinion and generates a disjumbled mess of 8-bit and 16-bit sound. I have to admit it’s quite strange to see 8-bit graphics with 16-bit sound, it doesn’t feel right.

Gimmick!

This company is playing its magic tricks again. If anyone could make the 8-bit NES sound and look 16-bit, it would be Sunsoft. Wikipedia lists some of the amazing techniques to generate such beautiful graphics using mostly graphics tiling optimizations.

My favourite track is an unused one, Strange Memories of Death. It has all the elements of a good song, catchiness, good production, a rich sound and oddly a dark undertone which flows really smoothly.

Gimmick was the only game to use the Sunsoft FME-7 chip which contained the Sunsoft 5B. It contained extra channels which the game used mostly to produce more bass (similar to Journey to Silius). Interestingly, the game didn’t make use of all the channels of the chip neither were all the features such as noise. It’s also the only game that uses the chip.

I put Gimmick! last on this list because it’s my favourite soundtrack on the NES. It spans multiple genres and sounds like a mix of different video game music styles. Apparently, this is what the artist intended. It has a rich deep sound unparalleled by any other NES game and I bet the bass would sound nice on a decent set of speakers or headphones.

Conclusion

This was just a small sampler of some of the good music that is on the NES. I haven’t played that many NES games and had to find other ways to discover interesting music. There’s a lot to listen to on grad1u52’s YouTube channel though unfortunately they add a reverb effect to the music which puts it further away from the original.

Chiptunes are an acquired taste for most people who are used to pop but I consider those to be simple music as well. I have shared with peers these songs and they have found them interesting but it didn’t light them up. It was just something that sounded different to them.

My next writing adventure will be about FM Synthesis which is my favourite way of generating sound. Most focus will be on the Yamaha YM2612 in the Sega Genesis and perhaps the OPL2 from the AdLib PC sound card.

If you have your favourites on the console, feel free to share them. Other kinds of chiptunes are welcome in the comments section below.

Automatic Transmission Simulation in Games

I know automotive enthusiasts will hate me for saying this, but automatic transmissions are an incredibly fascinating technology. Manual transmissions these days are reserved for the track, while most of the developing world is moving to a fleet majoritarily composed of automatics.

These days, even enthusiasts will admit that automatics are more efficient, shift faster and easier to drive than a stick shift. However, no one will disagree that a standard is much more fun and engaging.

How Automatics Work

To over-simplify things a little, transmissions exist due to the limitations in a combustion engine. It has a several narrow RPM ranges where it either produces the most power, the most torque or is the most efficient. The different gears in a transmission allow the engine to operate at the speed ideal for the driving condition while staying within those narrow RPM ranges. For a more complete and accurate explanation, please see this section on Wikipedia.

The part that I always found the most interesting about automatic transmissions was the shifting schedule. In other words, at what car speed to shift the gear up or down. The algorithm didn't seem simply arbitrary or simple and before I could drive, I did not have a way to experiment in computer games to figure out this logic.

Most driving games don't actually implement a true automatic. Rather, cars are all equipped with a manual transmission and the 'automatic' mode is actually a driver assist. The logic behind is simple, when the engine is near redline, it shifts up. When slowing down, downshifts occur at the maximum possible engine speed without exceeding the redline on the previous gear. However, this logic does not resemble at all what happens in a true automatic in real life.

After getting my license, I was excited to finally experience this shifting logic for myself. I was very surprised at how intelligently designed the system was, and how it adapted to driving conditions.

How Automatics Behave

The main concept of an automatic revolves around this: the harder you press the throttle, the later it shifts up. When driving slowly in a city for example, you need little power from the engine to accelerate. Therefore, it does not make sense to use the engine's entire RPM range in the first few gears to get up to speed, as running an engine faster is less fuel efficient. Rather, shifting early in the RPM range will maximize efficiency.

Automatic cars attempt to run at the highest gear to allow the engine to run in the most efficient range. However, higher gears provide poor acceleration when in a low RPM.

If the throttle is fully depressed, the car will shift in a way to make use of the entire RPM range of the engine up to the redline, this is the maximize performance and prevent lugging that would occur in a higher gear. 

The other component is kickdown when depressing the throttle. At first, the car is at cruising certain speed and a higher gear will be engaged for fuel economy. However, if the throttle is depressed harder, the transmission will command a down shift, or several, to hit an RPM range suited for better performance.

Current automatics have become very advanced and take a multitude of factors into consideration to decide when to shift. Grade shift logic for example will adjust gear selection based on hill grade to help with acceleration on a steep incline or provide engine braking when going downhill.

Each manufacturer implements their own unique algorithms and systems though the above concepts generally remain the same.

Automatics in Games

I had great difficulty finding games that simulated automatics correctly. In fact, out of the hundreds of driving games I've tried, only three simulated them in road cars. 

Admittedly, this is not an important aspect in racing, as most track cars use manual transmissions for better control. However, many of these games include road cars available to the general public and I found it odd that this kind of detail was missing.

I will analyse each game and demonstrate how it handles and simulates this kind of transmission. We'll be comparing them to the most common type of automatic transmission, the torque converter-based one. 

The Test

A test was devised that will demonstrate each game's capability at simulating the behaviour of an automatic transmission. It only aims to show the basic behaviours of the shifting schedule of an automatic. 

- First, the car will be driven slowly at city driving speeds. We expect the transmission to perform early shifts for fuel economy. 
- Once reaching 70 km/h, the throttle will be fully depressed. This should initiate a kickdown, where the transmission selects the lowest possible gear for maximum acceleration.
- While accelerating, the car should only upshift at maximum RPM to maximize acceleration
- At 120km/h, the throttle will be fully released. At this point, the car will upshift to the highest possible gear for fuel economy. This is the cruising stage.

Other behaviours will be noted which are typical of torque converter-based automatic transmissions:

• Slipping on acceleration due to torque converter and resulting torque multiplication.

• Creeping forward when in drive with brake released.

• Smooth and sluggish shifting between gears with no jerking movements between shifts.

Each test will be shown in a short video demonstrating the capabilities of each games.

Live for Speed

Live for Speed is racing simulation with physics accuracy that can be most admired by a perfectionist. Car handling feels so right and the feel for reaching the car's limit of grip is spectacular. Despite showing it's age now, few racing simulations come close to having the accurate driving feel of Live for Speed.

As a sim for purist racing fans, Live for Speed does not simulate automatic transmissions at all. Rather, the 'automatic' mode is a driving aid, that shifts for you in a way ideal for maximum performance rather than fuel efficiency. I'm including this game to show what a failing test would look like. 

Let's cruise along with the Hatchback XF GTI on the track and drive it through our test:

Notice how shifting only occurs upon reaching the redline. While slowing down, downshifts happen as soon as possible to make use of engine braking. This kind of shifting is great for racing as it is very predictable but not for saving fuel in a city car.

An LFS forum user by the pseudonym 'tigerboyz' created a mod that simulates the shifting schedule of an automatic though it still feels like a driving aid. The slushy feeling of a torque converter or forward creeping are not simulated. Instead, this mod simply uses the manual transmission and shifts at points where an automatic would.

Enthusia

Enthusia is likely to be the first game of it's kind to simulate automatic transmissions correctly. I noted this while skimming a Wikipedia article about the game describing this kind of accurate modeling.

I eventually got my hands on the game through emulation. The game was a commercial failure, likely in part due to it's difficulty stemming from it's accurate driving dynamics and competition from the much more popular counterpart, Gran Turismo 4. Therefore, securing a physical copy is prohibitively expensive.

Let's take a look at how Enthusia portrays an automatic transmission.

As seen in the video, Enthusia pretty much nails automatic transmission shifting behaviour. However, the shifts do appear like they come for a torque converter, albeit an aggressive one. 

The shifts don't happen that early and gears are held for a bit too long. It is almost as if the game is simulates a 'Sport' or 'Second Range' mode which is seen in some cars for sportier driving. This kind of mode shifts at higher RPMs for more responsive throttle feel and allows more use of engine braking for peppier driving.

Interestingly, when slowing down, the transmission down shifts in a way that favours performance driving. In other words, as the car slows down, downshifts occur to make use of engine braking to help the car slow down. In the average car, this does not happen, rather, shifting down only happens when the car has slowed down considerably or during kickdown.

However, one big part is missing: the characteristic creep when releasing the brake. The car stays immobile even with the handbrake released.

The game further emphases the stock transmission normally equipped with the car when selecting 'manual' or 'automatic' before a race. In cars with an automatic transmission, the choices are 'automatic' or 'semi-automatic' emphasizing that the car does not actually include a true manual with clutch and gear selector. For manual cars, 'gear assist' and 'manual' are displayed which indicates that the car won't be equipped with an automatic, rather an AI will assist the driver in shifting.

The selections for a Toyota Corolla, a car normally equipped with a torque converter-based automatic.

The selections for a Honda Accord Type-R, a car normally equipped with a clutch-based manual.

The game also simulate CVTs which shows just show niche-focused this game really is.

One last thing I'd like to mention about this game is how quirky it is. The presentation is really artistic for a racing game with a very cinematic intro and lively menu music. The car selection is really something to talk about with not only the stereotypical selection of road and racing cars, but also minivans, hybrids and SUVs. Enthusia really lets even the most niche of enthusiasts drive their favourites. Here's a few of them:

City Car Driving

Russian-based Forward Development seemed to have a very different take on a driving game: one that actually portrays everyday driving. Instead of testing the limits of your cars in a tight racing track, you'll be stuck in traffic in rain, merging on highways while checking your blind spot and of course, wearing your seat belt.

While the driving dynamics are not the most accurate or engaging, they're suitable for the leisurely pace known to most city drivers. Oversteer might not feel convincing, but the traffic patterns seem to mimic reality with impatient drivers, those who change lanes without signals and so on.

Let's get behind the wheel of an average car equipped with an automatic. We got rid of the traffic so we could speed at our leisure.

Clearly, the simulation of the automatic transmission is very impressive. The slushy shifts, the shifting schedule and the lurch of torque multiplication are all there. Everything feels right. There's even the characteristic automatic transmission creep when releasing the brake when in drive.

This game doesn't have much quirks, it's just a good education tool to get new drivers acquainted with the feel of driving, or perhaps those who enjoy driving so much they want to do it at home.

BeamNG.drive

Renowned for it's incredibly realistic crash physics, BeamNG.drive shows how well driving dynamics can be simulated even without any pre-canned behaviours. In BeamNG.drive, cars behave based on the sum of their parts such as drivetrain, tires, aerodynamics and so on. While not the most accurate driving simulator, the mechanics are incredibly convincing.

BeamNG.drive vehicle roaster focuses on daily road cars rather than performance vehicles. As a result, stock vehicles can be equipped with torque converter automatics, CVTs and of course manual transmissions.

Out of all the games tested so far, BeamNG.drive is a clear winner in terms of simulating torque converter-based automatics. From the sluggish acceleration due to torque multiplication to the smooth shifting and accurate shifting schedule, the game provides the most realistic feeling automatic driving experience.

Let's get straight to the test with this game.

What's obvious is how much it feels like you're driving a normal car in the city. The initial lunge from the torque converter to the sluggish shifts. Even the delayed kickdown is portrayed after flooring the accelerator. It's very impressive. Of course, it creeps forward as soon as you put it into drive.

The amount of options simulating different kind of transmissions is staggering:
- High stall torque converters
- CVTs
- Transbrakes
- Dual-Clutch Automatic Transmissions
- Sport Mode Selection
- Manual Mode in an Automatic Transmission

Each one of the features above is simulated in a very convincing way. If you're interested in tinkering with car behaviour, I highly recommend this game.

Final Thoughts

This kind of endavour was more of satisfying an obsession than anything else. This is probably one of the most niche things I've ever written about. Most racing fans simply floor the accelerator when the count down reaches zero, however I like to test the limits of games and see how much attention to detail they really put in. Even when it's not intended, games tend to become a sandbox for me.

Attention to detail is something I really appreciate. Few games go the extra mile to mimic intricate details of reality and it's really admirable. Now, for noticing that a game simulates automatic transmission logic, that is a personal problem of obsessiveness that I may have! 

It's hard for me to believe that the games above are the only ones in existence that simulate such concept of the automotive world. If you know any other games that simulate this behaviour, let me know by submitting a comment.