Cars

Sublime Curiosity in the Real World

Well, not exactly. It’s actually Roadkill, which is, as far as I’m concerned, the only car show anybody needs. I want to be on Freiburger and Finnegan’s side if the world goes all Mad Max. They’ve built all sorts of amazing shit. A rear-engine 1950 Ford dump truck. A Datsun with a turbocharged V6. A street-legal stock car. A 1000-horsepower ’81 Camaro. They’re seriously worth checking out if you’re even slightly interested in cars.

But I would like to draw your attention, in particular, to this episode, in which Frieburger and Finnegan supercharge a Monza Spyder. That seems like the kind of thing ordinary car guys would do. Except that they don’t do the obvious and slap a proper supercharger on it. Instead, they boost the horsepower by sticking five leaf-blowers in the trunk and pumping the air through PVC piping and into the engine. Because Roadkill.

 

I wanted to draw y’all’s attention to it, not only because Roadkill is awesome, but also because I feel like this is an instance of Sublime Curiosity leaking into the real world (or maybe the real world leaking into Sublime Curiosity, but that doesn’t sound very likely, does it?) A ridiculous idea made flesh. That’s what I’m all about here, and if I had some sort of weird Sublime Curiosity trophy, Roadkill would get it.

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Cars, physics, thought experiment

A City on Wheels

Writing this blog, I find myself talking a lot about my weird little obsessions. I have a lot of them. If they were of a more practical bent, maybe I could’ve been a great composer or an architect, or the guy who invented Cards Against Humanity. But no, I end up wondering more abstract stuff, like how tall a mountain can get, or what it would take to centrifuge someone to death. While I was doing research for my post about hooking a cargo-ship diesel to my car, another old obsession came bubbling up: the idea of a town on wheels.

I’ve already done a few back-of-the-envelope numbers for this post, and the results are less than encouraging. But hey, even if it’s not actually doable, I get to talk about gigantic engines and huge wheels, and show you pictures of cool-looking mining equipment. Because I am, in my soul, still a ten-year-old playing with Tonka trucks in a mud puddle.

The Wheels

Here’s a picture of one of the world’s largest dump trucks:

liebherr_t282_1

That is a Liebherr T 282B. (Have you noticed that all the really cool machines have really boring names?) Anyway, the Liebherr is among the largest trucks in the world. It can carry 360 metric tons. It was only recently outdone by the BelAZ 75710 (see what I mean about the names?), which can carry 450 metric tons. Although it doesn’t look as immediately impressive and imposing as the BelAZ or the Caterpillar 797F, it’s got one really cool thing going for it: it’s kind of the Prius of mining trucks. That is to say, it’s almost a hybrid.

I say almost because it doesn’t (as far as I know) have regenerative braking or a big battery bank for storing power. But those gigantic wheels in the back? They’re not driven by a big beefy mechanical drivetrain like you find in an ordinary car or in a Caterpillar 797F. They’re driven by electric motors so big you could put a blanket in one and call it a Japanese hotel room. The power to drive them comes from a 3,600-horsepower Detroit Diesel, which runs an oversized alternator. (For the record, the BelAZ 75710 uses the same setup.)

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Cars

The 1964 Chrysler Turbine Car

Not even a week after writing a post in which I considered putting a turboshaft engine in an ordinary car, I discovered that it’s actually been done. More than once. Most of the attempts are by hobbyists, but a few big car companies actually tried it out.

One of these was the 1964 Chrysler Turbine Car. It was powered by a 130-horsepower turboshaft engine. I’m no car expert, but from what I’ve read, it looks like it was an amazing machine. High take-off torque. Simpler cooling requirements. No need for oil changes. Longer lifespan. Fast start-ups even in cold weather. Could run on diesel, unleaded gasoline, kerosene, aviation kerosene, vegetable oil, and, reportedly, tequila.

Unfortunately, the project fell through. Only 50 Chrysler Turbines were ever produced, and only 9 are known to have survived, and only a few of those still have working engines.

Somebody really needs to bring the turboshaft back. You wanna sell more cars? Do something cool like putting a turbine in a production car.

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Cars, physics, thought experiment

Supersonic Toyota? (Cars, Part 2)

A while ago, I wrote a post that examined, in much greater and (slightly) more accurate detail what speeds my 2007 Toyota Yaris, with its stock drivetrain, could manage under different conditions. This post is all about Earth at sea level, which has gotta be the most boring place for a space enthusiast. Earth at sea level is what rockets are built to get away from, right? But I can make things interesting again by getting rid of the whole “sensible stock drivetrain” thing.

But first, since it’s been quite a while, a refresher: My Yaris looks like this:

2007_toyota_yaris_9100

Its stock four-cylinder engine produces about 100 horsepower and about 100 foot-pounds of torque. My drivetrain has the following gear ratios: 1st: 2.874, 2nd: 1.552, 3rd: 1.000, 4th: 0.700, torque converter: 1.950, differential: 4.237. The drag coefficient is 0.29 and the cross-sectional area is 1.96 square meters. The wheel radius is 14 inches. I’m totally writing all this down for your information, and not so I can be lazy and not have to refer back to the previous post to get the numbers later.

Anyway…let’s start dropping different engines into my car. In some cases, I’m going to leave the drivetrain the same. In other cases, either out of curiosity or for practical reasons (a rarity around here), I’ll consider a different drivetrain. As you guys know by now, if I’m gonna do something, I’m gonna overdo it. But for a change, I’m going to shoot low to start with. I’m going to consider a motor that’s actually less powerful than my actual one.

An Electric Go-Kart Motor

There are people out there who do really high-quality gas-to-electric conversions. I don’t remember where I saw it, but there was one blog-type site that actually detailed converting a similar Toyota to mine to electric power. That conversion involved a large number of batteries and a lot of careful engineering. Me? I’m just slapping this random go-kart motor into it and sticking a couple car batteries in the trunk.

The motor in question produces up to 4 newton-meters (2.95 foot-pounds). That’s not a lot. That’s equivalent to resting the lightest dumbbell they sell at Walmart on the end of a ruler. That is to say, if you glued one end of a ruler to the shaft of this motor and the other end to a table, the motor might not be able to break the ruler.

But I’m feeling optimistic, so let’s do the math anyway. In 4th gear (which gives maximum wheel speed), that 4 newton-meters of torque becomes 4 * 1.950 * 4.237 * 0.700 = 21 Newton-meters. Divide that by the 14-inch radius of my wheels, and the force applied at maximum wheel-speed is 59.060 Newtons. Plug that into the reverse drag equation from the previous post, and you get 12.76 m/s (28.55 mph, 45.95 km/h). That’s actually not too shabby, considering my car probably weighs a good ten times as much as a go-kart and has at least twice the cross-sectional area.

For the electrically-inclined, if I was using ordinary 12 volt batteries, I’d need to assemble them in series strings of 5, to meet the 48 volts required by the motor and overcome losses and varying battery voltages. One of these strings could supply the necessary current of 36 amps to drive the motor at maximum speed and maximum torque. Ordinary car batteries would provide between one and two hours’ drive-time per 5-battery string. That’s actually not too bad. I couldn’t ever take my go-kart Yaris on the highway, but as a runabout, it might work.

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A Toyota on Mars (Cars, Part 1)

I’ve said this before: I drive a 2007 Toyota Yaris. It’s a tiny economy car that looks like this:

2007_toyota_yaris_9100

(Image from RageGarage.net)

The 2007 Yaris has a standard Toyota 4-cylinder engine that can produce about 100 horsepower (74.570 kW) and 100 foot-pounds of torque (135.6 newton-metres). A little leprechaun told me that my particular Yaris can reach 110 mph (177 km/h) for short periods, although the leprechaun was shitting his pants the entire time.

A long time ago, [I computed how fast my Yaris could theoretically go]. But that was before I discovered Motor Trend’s awesome Roadkill YouTube series. Binge-watching that show led to a brief obsession with cars, engines, and drivetrains. There’s something very compelling about watching two men with the skills of veteran mechanics but maturity somewhere around the six-year-old level (they’re half a notch above me). And because of that brief obsession, I learned enough to re-do some of the calculations from my previous post, and say with more authority just how fast my Yaris can go.

Let’s start out with the boring case of an ordinary Yaris with an ordinary Yaris engine driving on an ordinary road in an ordinary Earth atmosphere. As I said, the Yaris can produce 100 HP and 100 ft-lbs of torque. But that’s not what reaches the wheels. What reaches the wheels depends on the drivetrain.

I spent an unholy amount of time trying to figure out just what was in a Yaris drivetrain. I saw some diagrams that made me whimper. But here’s the basics: the Yaris, like most front-wheel drive automatic-transmission cars, transmits power from the engine to the transaxle, which is a weird and complicated hybrid of transmission, differential, and axle. Being a four-speed, my transmission has the following four gear ratios: 1st = 2.847, 2nd = 1.552, 3rd = 1.000, 4th = 0.700. (If you don’t know: a gear ratio is [radius of the gear receiving the power] / [radius of the gear sending the power]. Gear ratio determines how fast the driven gear (that is, gear 2, the one being pushed around) turns relative to the drive gear. It also determines how much torque the driven gear can exert, for a given torque exerted by the drive gear. It sounds more complicated than it is. For simplicity’s sake: If a gear train has a gear ratio greater than 1, its output speed will be lower than its input speed, and its output torque will be higher than its input torque. For a gear ratio of 1, they remain unchanged. For a gear ratio less than one, its output speed will be higher than its input speed, but its output torque will be lower than its input torque.)

But as it turns out, there’s a scarily large number of gears in a modern drivetrain. And there’s other weird shit in there, too. On its way to the wheels, the engine’s power also has to pass through a torque converter. The torque converter transmits power from the engine to the transmission and also allows the transmission to change gears without physically disconnecting from the engine (which is how shifting works in a manual transmission). A torque converter is a bizarre-looking piece of machinery. It’s sort of an oil turbine with a clutch attached, and its operating principles confuse and frighten me. Here’s what it looks like:

torque_convertor_ford_cutaway1

(Image from dieselperformance.com)

Because of principles I don’t understand (It has something to do with the design of that impeller in the middle), a torque converter also has what amounts to a gear ratio. In my engine, the ratio is 1.950.

But there’s one last complication: the differential. A differential (for people who don’t know, like my two-months-ago self) takes power from one input shaft and sends it to two output shafts. It’s a beautifully elegant device, and probably one of the coolest mechanical devices ever invented. You see, most cars send power to their wheels via a single driveshaft. Trouble is, there are two wheels. You could just set up a few simple gears to make the driveshaft turn the wheels directly, but there’s a problem with that: cars need to turn once in a while. If they don’t, they rapidly stop being cars and start being scrap metal. But when a car turns, the inside wheel is closer to the center of the turning circle than the outside one. Because of how circular motion works, that means the outside wheel has to spin faster than the inside one to move around the circle. Without a differential, they have to spin at the same speed, meaning turning is going to be hard and you’re going to wear out your tires and your gears in a hurry. A differential allows the inside wheel to slow down and the outside wheel to spin up, all while transmitting the same amount of power. It’s really cool. And it looks cool, too:

cutaway20axle20differential20diff-1

(Image from topgear.uk.net)

(Am I the only one who finds metal gears really satisfying to look at?)

Anyway, differentials usually have a gear ratio different than 1.000. In the case of my Yaris, the ratio is 4.237.

So let’s say I’m in first gear. The engine produces 100 ft-lbs of torque. Passing through the torque converter converts that (so that’s why they call it that) into 195 ft-lbs, simultaneously reducing the rotation speed by a factor of 1.950. For reference, 195 ft-lbs of torque is what a bolt would feel if Clancy Brown was sitting on the end of a horizontal wrench 1 foot (30 cm) long. There’s an image for you. Passing through the transmissions first gear multiplies that torque by 2.847, for 555 ft-lbs of torque. (Equivalent to Clancy Brown, Keith David, and a small child all standing on the end of a foot-long wrench.) The differential multiplies the torque by 4.237 (and further reduces the rotation speed), for a final torque at the wheel-hubs of 2,352 ft-lbs (equivalent to hanging two of my car from the end of that one-foot wrench, or sitting Clancy Brown and Peter Dinklage at the end of a 10-foot wrench. This is a weird party…)

By this point, you’d be well within your rights to say “Why the hell are you babbling about gear ratios?” Believe it or not, there’s a reason. I need to know how much torque reaches the wheels to know how much drag force my car can resist when it’s in its highest gear (4th). That tells you, to much higher certainty, how fast my car can go.

In 4th gear, my car produces (100 * 1.950 * 0.700 * 4.237), or 578 ft-lbs of torque. I know from previous research that my car has a drag coefficient of about 0.29 and a cross-sectional area of 1.96 square meters. My wheels have a radius of 14 inches (36 cm), so, from the torque equation (which is beautifully simple), the force they exert on the road in 4th gear is: 495 pounds, or 2,204 Newtons. Now, unfortunately, I have to do some algebra with the drag-force equation:

2,204 Newtons = (1/2) * [density of air] * [speed]^2 * [drag coefficient] * [cross-sectional area]

Which gives my car’s maximum speed (at sea level on Earth) as 174 mph (281 km/h). As I made sure to point out in the previous post, my tires are only rated for 115 mph, so it would be unwise to test this.

I live in Charlotte, North Carolina, United States. Charlotte’s pretty close to sea level. What if I lived in Denver, Colorado, the famous mile-high city? The lower density of air at that altitude would allow me to reach 197 mph (317 km/h). Of course, the thinner air would also mean my engine would produce less power and less torque, but I’m ignoring those extra complications for the moment.

And what about on Mars? The atmosphere there is fifty times less dense than Earth’s (although it varies a lot). On Mars, I could break Mach 1 (well, I could break the speed equivalent to Mach 1 at sea level on Earth; sorry, people will yell at me if I don’t specify that). I could theoretically reach 1,393 mph (2,242 km/h). That’s almost Mach 2. I made sure to specify theoretically, because at that speed, I’m pretty sure my tires would fling themselves apart, the oil in my transmission and differential would flash-boil, and the gears would chew themselves into a very fine metal paste. And I would die.

Now, we’ve already established that a submarine car, while possible, isn’t terribly useful for most applications. But it’s Sublime Curiosity tradition now, so how fast could I drive on the seafloor? Well, if we provide compressed air for my engine, oxygen tanks for me, dive weights to keep the car from floating, reinforcement to keep the car from imploding, and paddle-wheel tires to let the car bite into the silty bottom, I could reach a whole 6.22 mph (10.01 km/h). On land, I can run faster than that, even as out-of-shape as I am. So I guess the submarine car is still dead.

But wait! What if I wasn’t cursed with this low-power (and pleasantly fuel-efficient) economy engine? How fast could I go then? For that, tune in to Part 2. That’s where the fun begins, and where I start slapping crazy shit like V12 Bugatti engines into my hatchback.

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Return of the submarine-car!

About a month ago, I tried to figure out how fast my 2007 Toyota Yaris would be able to drive underwater. I came up with 15 MPH (23 km/h, 6.52 m/s), which is respectable for a submerged economy car, but not that impressive for an underwater vehicle. Plus, as commenter Azure James correctly pointed out, propelling a car underwater isn’t as simple as having the horsepower to overcome drag: you have to make sure your drivetrain, from engine to gearbox to wheels, can generate enough torque to overcome the drag force.

As usual, I took this as an opportunity to imagine something ridiculous and draw a stupid picture. I present to you, the Hobo Sullivan Cruiser, the world’s most impractical underwater vehicle!

Underwater Car

It would be about the size of a large van or a small delivery truck, and that’s mostly because it has to accommodate a spherical pressure hull. Because if I’m going to make an underwater car, I’m for damn sure going to make it able to drive into the Challenger Deep! A lot of the other stuff is self-explanatory. The outer hull has a half-torpedo shape (Or if you prefer, half-cigar shape. Or, if you’re really picky, half a Sears-Haack body.) That’s to minimize drag. I chose to power it with a fuel cell and electric motors because those allow a greater range of rotation speeds (which, as my commenter correctly pointed out, would limit my speed on Mars, since a normal gearbox can’t get the wheel speeds up high enough to propel an ordinary car at 300+ MPH). Plus, with electric motors, exhaust isn’t as serious a problem.

The power for the electric motors is provided by a methanol-oxygen fuel cell. I chose methanol for one reason: space. Hydrogen, even compressed and cooled to cryogenic temperatures, takes up a lot of room. If you look at the hydrogen-burning stages of the Saturn V, the tanks are mostly hydrogen with a little spheroid at the end for the oxygen. Methanol fuel cells don’t provide as much power, but methanol’s a hell of a lot easier to transport. I’d still have to do something about the exhaust from the fuel cell, but for now, let’s assume I run the fuel cell hot enough that the pressure pushes it out a one-way valve.

You know, the more I look at it, the more “screw wheels” makes it look like I’ve got some weird grudge against wheels. In reality, those funny-looking objects are screw-drive wheels, which are so good at all-terrain they make tanks drive home to their hangars and weep transmission fluid into their berths.

That glorious contraption is the 1929 Fordson snow machine. It’s got huge pontoon-shaped wheels that turn on an axis parallel to the direction of travel, rather than perpendicular, with the force provided by many small segments of the helical screw pushing against the snow as the wheels turn. Because the pontoon wheels have such a large footprint, they don’t sink even in deep snow. And there is, of course, the cool factor, which is almost off the scale here. And now, let me send it careening completely off the scale by showing you the Russian incarnation of the screw-drive all-terrain vehicle:

When they say this is an all-terrain vehicle, they mean all terrain. Including the surface of a fucking lake. It’s hard not to be impressed.

Okay. So screw-wheels are cool. Is that reason enough to complicate the design of my submarine car to throw four of them on there? Well, yes. The seafloor is unpredictable. Without vegetation to anchor it or ordinary algae and fungi to bind it, the seafloor can have a wide variety of textures, and almost all of them would be a nightmare for a wheeled vehicle: silt six feet deep, loose sand, gravel rocks, weird clay, mud, sulfide sludge spewed from seafloor volcanoes… A wheel is very likely to sink into a morass like that. I could make the wheels larger, but a pneumatic wheel will deflate at seafloor pressures. I could make the wheels non-pneumatic, but they’re still big and bulky and taking up a lot of room, and they’re going to increase drag, which I’m already spending all my energy fighting. Tracks might work, but they contain an awful lot of joints and moving parts, and would probably get silted up.

Of course, screws as small as the one in the illustration probably wouldn’t fare too well in soft silt, either, so I’d have to make them larger, but nonetheless, I’d say screw wheels are the optimal solution. And besides that, they’re fucking awesome!

Of course, all this is really moot. There’s a very good physics reason we don’t turn all cars into planes (And plenty of other reasons, if you see how people drive on the ground.): it’s hard to generate lift in air. For a long time, many believed heavier-than-air flying machines were impossible, and they only became really successful a century ago. Air isn’t all that dense. An average 80-kilogram (172-pound) human could comfortably stand in a box 2 meters on an edge. That box would be seriously oversized, but the air in it would still only weigh 10 kilograms.

A box of water 2 meters on an edge, though, would weigh 8,000 kilograms, or about the same amount as an African elephant. Water is dense. Denser fluids resist being pushed around, and therefore more readily generate force. In my earlier article, I figured out that my car would theoretically be able to go 135 miles an hour in air, but only 15 miles an hour in water. But when it comes to flying, that resistive force comes in handy, because you don’t need very big wings to turn your submarine car into a submarine…submarine. Here’s a picture to illustrate how much better wings work in water than they do in air:

Hydrofoil_old

(Source.)

That is a boat. Being lifted almost completely out of the water by wings that look to me to be smaller than the wings on a Cessna.

And there’s another thing that makes an underwater vehicle confined to a surface kind of silly: buoyancy. Like I said, air’s not very dense, and for a bag full of gas to lift anything, it has to be less dense than the surrounding medium. There aren’t many gases less dense than air. There are hydrogen and helium, of course, but both are made of such small atoms that they leak out of containers no matter what you do, and hydrogen is flammable. There’s hot air, but that’s a lot denser than hydrogen or helium, and after a certain altitude, it gets hard to heat it up enough to provide useful lift.

Now here are some things that are less dense than water: Myself. Wood. Warmer water. Air. Compressed air. Methanol. Ethanol. Propanol. Butanol. Low-density polyethylene. In other words, around half the matter (by volume) in a submarine is less dense than water. Submarines actually have to take on extra water to sink. I had to stick depleted uranium ballast weights in my ocean car just to make sure it wouldn’t float.

But really, why shouldn’t it float? It’s not like I couldn’t stick landing skids or water-filled pontoons on a regular submarine and then have a submarine that can go to the bottom. And with a little creativity and plenty of power (provided by a wide variety of sources), you can adjust your buoyancy on-the-fly.

So forget the submarine car. I just want a submarine.

Actually, that’s a lie. I want a submarine car with screw-wheels. But I’m going to use it on land. Because, holy shit, look at those motherfuckers in the videos up above!

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Forget flying cars. I want a submarine car!

The metal container powered by the explosion of million-year-old liquefied algae which transports me over long distances (My car. Yes, I know I’m a smart-ass.) is a 2007 Toyota Yaris hatchback. It’s a decent enough car, I suppose. It looks about like this:

Image

(Many thanks to the nice person on the Wikimedia Commons who put the photo in the public domain, since I lost the only good photo of my car before it got all scruffy.) According to its specifications, its engine can produce 106 horsepower (79 kilowatts), it weighs 2,326 pounds (meaning it masses 1,055 kilograms), and has a drag coefficient of 0.29 and a projected area of 1.96 square meters (I love the Internet). Those are all the numbers I need to calculate my car’s maximum theoretical speed. I’ll be doing this by equating the drag power on the car (from the formula (1/2) * (density air) * (velocity)^3 * (projected area) * (drag coefficient)) with the engine’s power. I will be slightly naughty by neglecting rolling resistance, which for my car, is usually negligible.

1. Maximum speed on Earth, at sea level: 135 MPH (217 km/h or 60.19 m/s). I may or may not have gotten it up to 105 MPH once, so this estimate seems about right. Worryingly, according to the spec sheet for my tires, they’re only rated up to 112 MPH…

2. Maximum speed on Mars: (Assuming I carry my own oxygen, both for me and for the engine.) 538 MPH (866 km/h, 240.50 m/s). I would break the speed record for a wheel-driven land vehicle (Donald Campbell in the BlueBird CN7) by over 100 MPH. And probably die in a rapid and spectacular fashion. But that’d be all right: I always wanted to be buried on Mars.

3. Maximum speed on Venus: (Assuming I avoid dying in burning, screaming, supercritical-carbon-dioxide-and-sulfuric-acid agony.) 36 MPH (58 km/h, 16.23 m/s). Unfortunately, the short-sighted manufacturers didn’t say whether my tires are resistant to quasi-liquid CO2 at 90 atmospheres. The bastards.

4. Maximum speed underwater: This is the one we’re all here for! Water is dense shit and puts up a lot of resistance, as anyone who ever tried running in a swimming pool can attest. Maximum speed: 15 MPH (23 km/h, 6.52 m/s). Wolfram Alpha tells me I’d only be driving half as fast as Usain Bolt can run. I shall withhold judgment until we clock Mr. Bolt’s hundred-meter seafloor sprint.

5. Maximum speed in an ocean of liquid mercury: (Assuming we filled my car with gold bricks to keep it from floating to the surface. Also, why is there an ocean of liquid mercury? That’s horrible.) Maximum speed: 6 MPH (10 km/h, 2.74 m/s). I can bicycle faster than that (although not in a sea of mercury, admittedly). Of course, mercury is so heavy that, even if our sea was only 5 meters deep, the pressure at the seafloor would be high enough to make my tires implode. Which would, of course, be the least of my problems.

6. And finally, just for fun, my maximum speed in neutronium. Neutronium is what you get when a star collapses and the pressures rise so high that all its atoms’ nuclei get shoved together into one gigantic pile of protons and neutrons. It’s just about the densest stuff you can get without forming a black hole, and my car could push me through it at a whole 0.1 microns per second, which is only fifty times slower than the swimming speed of an average bacterium.

I’ve now spent far too long imagining myself being crushed by horrible pressures. I need to go lie down and imagine myself being vaporized, to balance it out.

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