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This was an idea generated by my sister that I thought was very interesting. I intended to make it work by strapping rollerblades on a person's legs and utilize a compressed gas/steam-powered pumping device that would be worn on the back of the character. A gas pumper would push the character forward at high speed (kind of like a rocket backpack) while the rollerblades could be used for directional control. These two are connected to each other with wires and are worn like a suit. There should be something balancing weight (or do you have suggestions?) to keep the character balanced while moving.

Is it possible? If not then how can I improve it? Are there any similar alternatives?

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    $\begingroup$ sounds like a steampunk device if i ever heard one. $\endgroup$ Aug 13, 2019 at 9:11
  • $\begingroup$ developed? Without a doubt. Useful? Doubtfully as steam producing machinery would defy it's jet power with it's own weight (so machine, water, burner). There are few questions with answers that have mathematical answer to "steam powered" things. $\endgroup$ Aug 13, 2019 at 9:20
  • $\begingroup$ 18th century (American revolution, 1765-1783), or 19th century (Stockton and Darlington Railway, 1825)? $\endgroup$
    – AlexP
    Aug 13, 2019 at 18:17

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Many issues here, all going against this:

  • Producing steam requires a lot of heavy machinery: you need to carry water, coal and the boiler. Are you sure you want all that weight in a backpack? How are you going to fuel the boiler on your back?
  • Rollerblade can be used when you have a smooth pavement to roll on. Already a cobbled road would be a nightmare, and most of the roads in 18th century were not even that fancy, with just loose ground, dusty when dry, muddy when wet, with deep carved trenches were the chariot wheels were passing. Nothing suitable for a rollerblade.
  • Steering: if you are going at high velocity and you want to steer, you will put a high load on your wheels unless you take a very large curving radius: I doubt that rollerblades will survive the challenge.

I think you can't go any better than Stephenson's Rocket.

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  • $\begingroup$ I will just note that there is an IRL segment of society mad/awesome enough that they build giant off-road rollerblades and use kite-surfing-kites and proceed to fling themselves along beaches and grassy fields at ridiculous speeds. They are called 'kite-skates' or (more aptly) 'doomwheels.' Anyway, so rollerblades on non-tarmac surfaces aren't a complete non-starter - at least for some people $\endgroup$
    – sdfgeoff
    Nov 19, 2023 at 9:39
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First, you need bigger wheels. The reason carriages (17th-20th century) have such large wheels is that larger wheels "soften" bumps and irregularities in the road surface by allowing a longer travel distance to climb over the height change.

Then you need to use small, powerful steam engines on the skates to drive the wheels; this gets you many times the propulsion effect over the same amount of steam used as a jet or rocket, even with air entrainment or a ducted airscrew.

In order to make small steam engines powerful, you need to run your steam at high pressure, which means high temperature.

Now we have the basic building blocks -- a high temperature, high pressure boiler system, with spring-assisted articulated leg struts to carry the weight of the boiler and fuel tank (it'll have to be petroleum, like kerosene; that's the only high energy density, fast/clean burning, easy stoking fuel that can operate this kind of boiler), and wheels at least as large as those on a 1900 vintage road bicycle (not a penny farthing, but the kind the Wright Brothers built before they switched to airplanes).

In the end, it's going to look at lot more like a badly drawn horseless carriage -- but small enough to (more or less) wear instead of sitting in.

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Perhaps the water runs through the wheels and uses the vibration and friction to generate the heat needed for a small amount of steam pressure.

Put that in with some kind of wind sail and perhaps some skis and a hill and u got urself something to start the propulsion.

Conclusion

in the end for the day steam isn't going to propel a human on a device that can be carried by a person but perhaps help the wheels spin for longer to decrease the need to propel as often

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No chance

The engines did get more efficient over the course of the 18th Century, but they tended to remain two man operations, one to drive and one to shovel coal, and mostly they got bigger and heavier. We're not counting the weight of coal and water here. Engines of the period aren't condensers, you need to keep pouring water in at one end to allow for the steam coming out at the other.

So if you're happy for your roller skater to have a 4 ton engine operated by two men and a trailer load of coal following along behind him then go for it, but it doesn't feel like that's in the spirit of your problem.

It's not until the 19th century that you get the relatively compact and mobile traction engines that are more practical on the open roads but they still weigh in the region of 4.5 tons. Stephenson's Rocket was actually a nice lightweight engine at a mere 4 tons.

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    $\begingroup$ 1829 is in the 19th century. $\endgroup$
    – AlexP
    Aug 13, 2019 at 12:58
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The OP has not been back in the last 4 years, so here is a short answer that can be expanded if ever of interest.

All the existing answers are wrong.

This is entirely doable. Issues are mass & range, speed, temperature & safety,
In about that order. Perhaps :-). A flash-boiler, alcohol or kerosne fired, and a burner plus a water supply will generate steam, able to generate powers in the fractional to few horsepower range, either with tiny lightweight reciprocating motors, or by steam rocket.

Wheels are an issue- but sensible engineering can create wheels able to handle surfaces of the day. I'll levae that to others to fill out.

A "flash boiler" will convert thermal energy to steam at low to medium pressure at acceptable mass and energy levels in this context.
Hydrocarbon fuels have acceptable mass and volume energy densities. A litre of ethanol or kerosine have energy content of very roughly 10 kWh / litre or kilogram (higher for kerosene) and delivered energy as steam in the say 1-3 kWh /litre range.

A "Flash Boiler" (FB) consists of a coil of pipe (usually copper) heated by an external source - here a burner, with pressurised water introduced appropriately

Even at 1 kWh/litre say 5 litres of fuel will provide 5 kWh - say 1 kW for 5 hours or 5 kW for 1 hour or ... .

The main limitation once safe (if not sane) operation is achieved is liable to be water capacity. Steam generation requires about a gram of water per 2 kW seconds of steam generated. So a kg of water produces about 2000 kg-seconds of steam. If a rocket is is used (see below) assuming delivered "vehicle power" in the say 1% - 20% range or 20 to 400 kg seconds per kg of water.

While small model reciprocating engines are well known (see below) powers in the HP + range are able to be delivered directly by direct steam rockets. Achieving this does not require rocket science in practice, only in theory :-).

A steam rocket need be neither extremely large or heavy. Being strong enough to deal with peak pressure out of the flash boiler "is a really good idea".


Flash steam to reciprocating engines for models delivering powers in the HP range are well known:

How to build flash steam generatos and related steam enines here

  • Includes page 23-53 full detail for building a model aircraft engine weighing 3/4 ounce and delivering 1/4 HP to a propellor. 60 psi operating at 3500 RPM :-) . Steam generator weight not stated but probably well underone pound. That's about 200 Watt delivered, or about the power of a very low end ebike. Propellor optimisation would allow low velocity vehicle operation.

  • Page 34 - Hydroplane. 1 HP+ delivered to prop. 30 mph max speed. Top models achieve 120 mph+

Flash steam based model hydroplanes - 120 mph. 20cc steam engine ! here

Wikipedia - steam rocket

A HTP (Hydrogen Peroxide) rocket can deliver about 300 kg-seconds per kg of HTP using silver-catalyst screens and 85% HT P (the upper limit for silver due to screen melting). The early HTP rocket packs delivers 17 seconds of flight. A say 10 kg propellant load would deliver say 300 seconds at 10mkg thrust. Hydroghen Peroxide would have been able to be synthesisedsd and concentrated "back then". First produced 1818 - Wikipedia. 100% HTP delivers 440 kg-seconds pere kg.

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As L. Dutch said, steam engines are bulky. But they already had air compression in the 18th century. Just one step forward to put the compressed air in bottles. You could use it to drive your wheels.

Take care to select the right size of wheels as L.Dutch mentioned. Your whole equipment is gonna be bulky, but you might be able to carry it. You won't be able to go fast and go far, and if you fall and the valve breaks, it's gonna rip down your legs/arms/head choose your target.

In general, I would not do it.

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Aluminum powered ramjet backpack.

Because we are talking about fiction,and we want physics to be firmly in the service of awesome.

Consider first Project Pluto: the nuclear powered ramjet. https://en.wikipedia.org/wiki/Project_Pluto

The working fluid of this rocket is air. Like any other ramjet it pulls air in thru the front and shoots it out the back to provide thrust. Jet engines generate the heat by burning fuel. The nuclear ramjet generated heat with a fission reaction.

Having a fission reaction strapped to your back poses some difficulties. Burning aluminum is much safer! The mechanism is the same except the core of the backpack is aluminum metal. It is started with a thermite fuse and once going, air is used as the oxidant. The oxygen is consumed to produce alumimum oxide but the nitrogen is heated up greatly and vented out the rocket nozzle in back to provide thrust.

You would need to get up to speed to get air flowing past the aluminum, which you could do with a hill or by skating hard. Once flowing you could adjust thrust with a choke for the air intake. The air flowing by also keeps the backpack coolish.

Really this is just a jetpack full of burning near-molten metal and you are wearing rollerblades. As one does.

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