At the time of writing, I've covered most of the basics of material mechanics.
I believe I've repeatedly emphasized the importance of mechanics of materials in my previous explanations.
Having covered the fundamentals of material mechanics, which are essential for mechanical design, I would like to introduce the extremely important topic of engineering ethics, drawing lessons from major mistakes of the past.
The reason I didn't introduce engineering ethics at the beginning of the mechanical design course is that by first acquiring knowledge of materials mechanics, students can truly understand the seriousness of past failures and how to think about countermeasures.
The world's three biggest failures + major accidents in Japan and the fundamentals of engineering ethics.
Famous for machineryThis article will explain the three major disasters in the world: the Comet jet crash, the Liberty shipwreck, and the collapse of the Tacoma Bridge..
The world's first jet passenger plane, the Comet, crashed in succession.
Liberty ships sank in succession
The collapsed Tacoma Bridge
I'd also like to introduce a recall cover-up case involving a certain automobile company that is more familiar to Japanese people (I don't know if there was any need to hide the company, but I thought I'd mention it anyway).
In all of these casesPeople have died (fortunately, no lives were lost on the Tacoma Bridge).Yes, you can enjoy Okesa Persimmons in the form ofIn mechanical design, if you make a mistake in your analysis (especially in the analysis of material mechanics), it can actually result in someone's death.
I think many people will probably agree with my opinion,No one shall harm, steal, or threaten the life or property of another person.I think
Furthermore, I believe that tools should fundamentally be useful to people, contribute to their happiness in any way possible, and should never cause harm to people.
HoweverEven actions taken with good intentions and without malicious intent can sometimes cause harm to others.worst,While assets can be returned, a life cannot be brought back.
It could potentially lead to the loss of that life.One of the major issues to consider is the insufficient examination of material mechanics.
The incident I'm going to discuss today involves a tragic accident in which many customers, who were told that the service was "safe thanks to the latest technology," paid for it and lost their lives.
Let's start with the Comet plane crash, which is arguably the worst of the three accidents.
To deepen understanding, I will explain the historical and technological background (8% of this is the author's personal interest).
First, let's explain the technical brilliance of the four-engine jet passenger aircraft, the Comet, which began commercial flight in 1952.
The Comet is one of my favorite airplanes because of its wing-mounted jet engines.
Performance of aircraft engines around the world in 1940
As a former engine designer and a fan of airplanes and the military, I might be a bit long-winded, but I hope you'll bear with me.
This alone is enough material to fill about three books, but I'll try to keep it as concise as possible.
The mainstream and challenges of aircraft engines at the time
First of all, the aircraft engines of that time were gasoline reciprocating engines, just like many modern cars (although diesel engines also existed).
A reciprocating engine is a mechanism that converts reciprocating motion into rotational motion, and is essentially an engine that uses a piston-crank mechanism.
A tube and a lid are attached to this reciprocating part.Fuel and air are placed in a closed space and burned.
The force (pressure) of the expanding air from the burning fuel is used to move (descend) a component (piston).
After burning, the parts are moved (upward) by the piston-crank mechanism due to inertia.
And so onThe goal is to extract continuous rotational energy.
Because it is necessary to supply air and fuel and exhaust at set times, there is a fuel supply device (carburetor, mechanical injection, etc.), and the engine cover has intake and exhaust pipes, each with a valve.
Furthermore, it has an ignition device (spark plug) to ignite the mixture of fuel and air. A spark plug is like a giant lighter.
Let's look at each process while keeping the above equipment in mind.
Continuation
As shown in the diagram, it repeats four processes: intake, combustion, expansion, and exhaust (actually, intake, compression, combustion, expansion, and exhaust), so it is called a four-stroke engine.
While there are other types such as 2-stroke and diesel engines, the mainstream is this gasoline-4-stroke reciprocating engine.
However, aircraft engines of that era were far larger and more powerful than the engines in modern passenger cars (but their fuel efficiency was considerably worse).
The size and power output of a reciprocating engine are, quite roughly speaking, proportional to its displacement, which is the amount (volume) of air the engine can take in.
While the average modern passenger car has an engine displacement of approximately 1000-2000cc, the aircraft engines of that era were around 15000-35000cc, roughly 10-16 times larger.
Engines at that time were large and quite complex.
The important thing here isThe technical difficulty of an engine isn't determined by its size; complex engines, whether large or small, are difficult to develop and manufacture in their own way.
Even back in 1940, only Japan, the US, Germany, and the UK were capable of producing decent reciprocating engines for aircraft (the number might be even smaller now).
Even in the 21st century, very few countries are capable of developing and mass-producing competitive passenger car engines (even in rapidly developing China, it's still difficult).
Such massive reciprocating engines had already reached their performance limits for aircraft at that time (around 1938-1940).
The limitations of aircraft reciprocating engines in the 1930s
As you can see from the diagram of the reciprocating engine above, in a reciprocating engine, the amount of fuel supplied can be controlled to some extent, but the amount of air is basically supplied by the negative pressure created when the piston moves downward.
The problem then becomes the groundIn a spherical atmosphere, the air thins as altitude increases, reducing the amount of air available for combustion and drastically decreasing engine power.
Therefore, simply put, at an altitude of around 8000m, the engine's output drops by more than 60% compared to ground level.
Therefore, the specifications for the reciprocating engines of World War II aircraft list the power output at takeoff (altitude 0m) and the power output at different altitudes.You can think of the power of a reciprocating engine as being proportional to the amount of intake air (actually, it's proportional to the amount of air and fuel).
In other words, ReciprocatingEhEngine performance largely depends on the altitude at which the aircraft can fly.
In wartime, the primary purpose of an airplane is, of course, combat, so speed, maneuverability, armament, and altitude performance are all extremely important.
- If you can gain a higher altitude than the enemy, they won't be able to approach, allowing you to secure a safe and advantageous position.
Maintaining a high altitude is also advantageous because it allows you to use potential energy to achieve higher speeds when fighting at a lower altitude (as in Void's energy maneuver warfare theory).
When flying at high altitudes, the air is thinner, which naturally reduces air resistance. This means that less force is needed to achieve high speeds, and because there is less resistance, fuel efficiency improves, increasing the range of movement.
Simply put, the advantage of being able to achieve high altitude is that you can launch unilateral attacks from a position where the enemy cannot reach you.
Simply being able to fly higher than your enemy gives you a significant advantage.
On the other hand, as mentioned earlier, the performance of a reciprocating engine decreases as the altitude increases due to the thinner air. A simple reciprocating engine could only reach an altitude of about 5000m.
The engineers at the time racked their brains and came up with the idea of "installing a mechanism to forcibly take in air."
The emergence, widespread adoption, and evolution of mechanical superchargers (around 1940)
A mechanism that forcibly takes in airIn the early stages of World War II, mechanical superchargers were the dominant type of engine.
To put it simply, without fear of misunderstandingIt borrows some of the rotational force from the engine to spin something like a windmill, compress the air, and supply it to the engine.
By the way, a windmill is called an impeller.
In reality, it looks like the picture below.
This allowed for significantly higher altitudes, but because war is an extremely brutal competition for performance, this mechanical supercharger also evolved at a frightening speed.
Initially, they simply attached a shaft to the engine to drive a supercharger, and rotated the windmill at roughly the same speed as the engine.
The engineers quickly decided to make the wind turbines spin faster to draw more air into the engine.
Soon after, mechanical superchargers appeared that attached a gearbox to the wind turbine shaft to increase the speed in two or three stages (counted as 2nd gear, 3rd gear, etc.) in order to supply more air.
Furthermore, they even added two mechanical superchargers (which for some reason are counted as stage 1 and stage 2) to try and take in as much air as possible.
As you can see from the diagram, it would be a very complex and difficult device. Naturally, the increased number of devices would make the aircraft larger and heavier, which must have been quite a challenge for the engineers.
However, this mechanical supercharger also quickly reaches its limits.
The biggest hurdle was that at the time, wind turbines were basically increased in speed by changing the gear ratio with gears. The operating speed of aircraft engines at the time was approximately 1500 rpm (1500 revolutions per minute), so transmitting driving force at a similar rotational speed was not difficult, butIf the load doubles, triples, quadruples... and then increases to ten times, the gears and windmill bearings will seize up and simply cannot withstand the load.
Even in the 21st century, the highest rotational speed of gears and bearings I've encountered in mass production is around 20000 rpm. Considering the technology and military applications of the time, I think the limit was probably around 5000 rpm.
AnywaysLubrication of gears and bearings is a very complex and difficult process.
Use of fluid couplings (fluid couplings)
Amidst this, Germany, a nation of mechanical geniuses, took a step ahead by using fluid-based Flucan couplings to transmit power to superchargers, essentially saying, "If it's too difficult, just don't use gears."
While "Furcan" might seem like an abbreviation for "fluid coupling," it's actually called a Furcan joint because it was developed at the Furcan Shipyard (although there are various theories).
The Furkan Shipyard was a shipyard with a long tradition, established in 1805, and reached its peak in the 1980s, but unfortunately went bankrupt in the 1990s due to management failures.
The mechanism is simple: place two fans facing each other, and when you turn on one fan, the other one will also turn on; the driving force is transmitted by a fluid.
If you turn off the fan and focus on the direction of the airflow, it will look like the diagram below.
Another example is when you blow on a windmill; it spins. It might be easier to understand if you imagine generating wind with another windmill instead of blowing on it.
Focusing on the shape of the wings, the mechanism is as shown in the diagram below.
In reality, the wing shape is a bit more complex, and oil is used instead of air to improve transmission efficiency.
Below, I've included a layout that closely resembles the actual mechanism used, for reference. Note that the input and output vanes are in the opposite positions to those described above, and the input rotates as a whole case.
In reality, it looks like the picture below.
By now, you should understand how driving force is transmitted using fluid.
However, in order to actually use a mechanical supercharger efficiently, it is necessary to increase the speed.
The basic mechanism for increasing speed involves increasing the number of blades on the driven side relative to the number of blades on the driving side (the blade shape is also modified). Although unlikely, if we assume a transmission efficiency of 100%, then 10 blades on the driving side and 20 blades on the driven side would double the speed (in reality, considering fluid losses, it's probably around 1.3 to 1.5 times).
Germany used this mechanism to overcome the limitations of gears and utilize mechanical superchargers (with a ratio of around 2 and twice the engine speed).
This mechanism has even more advantages: by changing the amount of oil used as the working fluid, the transmission efficiency can be altered. By cleverly utilizing the changes in transmission efficiency, the speed increase ratio can be changed.
While gears can only change the speed increase ratio in steps, the Fullcan system allows adjustment by changing the amount of oil, enabling the mechanical supercharger to operate at the optimal rotational speed for each specific application, making it an extremely efficient mechanism (theoretically, stepless).
In reality, it wasn't continuously variable but used with several predetermined settings, though there were more settings than a mechanical system with only two speeds (there are various theories and it's unclear).
I could understand if they made just one or two prototypes, but I'm astonished that the Germans, as expected, mass-produced them during wartime. In fact, aircraft equipped with this Furkan joint had overwhelming combat power, albeit for a short period (there were many other factors as well).
The engine that actually featured a Furcan coupling was the Daimler-Benz (now Mercedes-Benz) DB601, and the most representative model was the Messerschmitt Bf109.
The rotating part on the far right of the engine is the mechanical supercharger, and the turbocharger coupling is located behind it (unfortunately, I don't have a good photo).
The Bf109 was an extremely powerful aircraft until the Battle of Britain.
However, this doesn't mean that the problems with mechanical superchargers have been solved. Even with a full-can coupling, there's a limit to the speed increase ratio (at best, it's about twice as high).
If space were unlimited, you could increase speed by using multiple stages of Flucan couplings (4 stages, 6 stages, etc.), but compactness was paramount for wartime aircraft, so that wasn't possible.
So the geniuses of that time thought about it. And the new method they came up with wasThey decided to use the exhaust fumes that they had previously been discarding to power wind turbines.
The emergence of superchargers that utilize exhaust gases (around 1942)
This is what is commonly known as a turbocharger, or exhaust gas supercharger, which many people are probably familiar with.
This eliminates the need to install complex and troublesome machinery such as transmissions and full-clutch couplings.排It can be made by attaching a drive turbine to a pipe through which gas passes, and then attaching another wind turbine for air compression on the same shaft.The mechanism is very simple.
A compressor that actually uses exhaust gas looks like the one in the picture below.
The key feature of this mechanism is that, unlike a mechanical supercharger, it doesn't require a shaft or gears from the engine to rotate the wind turbine. It's clearly simpler and more compact than a full-sized turbocharger.
These exhaust gases have a tremendous amount of energy, and depending on the distance from the engine, if you are close to the engine...With pressures of several MPa (over 10 atmospheres) and temperatures of around 900°C, wind turbines rotate at very high speeds.Even during World War II, it exceeded 10000 rpm (about twice that of a mechanical engine).
Moreover, while mechanical superchargers borrowed some of the engine's output to operate, exhaust gas superchargers utilize the energy of exhaust gases that would otherwise be wasted.The mechanical efficiency is completely different.
This was an incredible device that compressed air intensely, increasing engine power and allowing for higher altitudes. Incidentally, this exhaust gas-powered supercharger is called a turbocharger (sometimes simply called a turbine).
The exhaust gas-powered supercharger is simple, highly efficient, and appears to have no drawbacks, but its realization involved numerous extremely difficult technical challenges.
Let's briefly list some typical challenges.
Developing and manufacturing heat-resistant materials (such as Inconel) that can withstand high-temperature exhaust gases is extremely difficult.
• Large quantities of rare metals (mainly nickel) are needed to create heat-resistant materials.
• Development and manufacturing of bearings capable of withstanding tens of thousands of rpm. This requires advanced materials and high precision manufacturing.
The structure and mechanism are simple,It requires advanced materials technology and resources, and can only be realized in a wealthy country with advanced technology and abundant resources.
At the time, almost only the United States was able to overcome these technical challenges and mass-produce the weapon for military use.
However, even this exhaust gas-powered supercharger, which seemed to be perfect, soon reached its limits.
The next limit is that compressing the air too much causes the intake air temperature to rise, leading to abnormal combustion and engine failure.
moreoverAir expands as its temperature rises, so once it's compressed to a certain point, its density can't increase any further. Therefore, the amount of air an engine can draw in won't increase beyond a certain point (no matter how much boost is applied).
To solve this problem, geniuses think and devise countermeasures.
Next time, I'll talk about countermeasures and the crucial development of propellers.
Appendix: The aftermath of the Furukan joint
During World War II, the Flucan coupling was used to drive mechanical superchargers in aircraft engines, but it was eventually superseded by exhaust gas superchargers and disappeared from the market. However, it continued to develop and become widespread in industry.
Most people today use an advanced version of the Fulcan coupling. The drive transmission mechanism in an automatic transmission car is an advanced version of the Fulcan, called a torque converter.
It's a common misconception, but while a full-size torque converter is an advanced version, it's a different thing altogether. The key difference is that a torque converter has an added torque amplification function.
The explanation of torque converters is not the main topic of this article, and there are many good explanatory videos available, so I encourage you to look them up.
It's interesting how the torque converter joint, which was defeated in the world of aircraft, has now become the dominant force in the automotive world, where torque converters are found in almost all automatic transmission vehicles.
In Japan, 99% of cars are automatic transmissions (AT), and I think about 90% of those ATs use torque converters. So, there are hardly any people who have never used a torque converter. If you consider people who have ridden in an AT car, even if they don't drive themselves, then 99.9% of Japanese people have used one.
To those who found this article helpful in understanding design:
Since we're on the subject, I'd like to recommend a book that's essential for mechanical design.
To be honest, the content is extremely unhelpful, but it can be used like a dictionary when you forget the details. If you read this article, you should be able to understand the content and use it effectively. It also includes commonly used standards, making it quite useful.
If you don't already own one, I highly recommend getting one, even though it's a bit pricey. However, new ones are expensive, so if you're considering buying a used one, I strongly recommend checking that the surface roughness conforms to the new JIS standard.
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