For Questions That Don't Merit Their Own Thread

[magnemoe]

10 hours ago, kerbiloid said:

The creosote, they are dark from, is cancerogenic.

Unless they use an eco-friendly green creosote.

That is for wood sleepers who was replaced couple of decades ago here in Norway, sold to public and usually ending up as retaining walls and similar in gardens. 

[farmerben]

Wooden sleepers are being replaced with concrete here too.  Adding fresh ballast sometimes makes sense.  About half the network of railroads in the US is abandoned.  A few major lines are profitable for long distance bulk transport.  

We have excellent and very cheap passenger service between St Louis and Chicago (100 mph in several sections).  But, I'm told it is not profitable.  Only the service between Washington DC and Boston turns a profit.

[monophonic]

Wooden railway sleepers is the only remaining allowed use for creosote in the EU. It is in general forbidden due to the carsinogenicity, but no-one has been able to devise a treatment that makes wood survive even half as long buried in ground, thus creosote is still allowed in sleepers. Wood and concrete sleepers have somewhat different properties making replacement of one with the other not a straightforward process, unless you can accept a severe downgrade in allowable travel speeds.

The crushed stone ballast used with concrete sleepers breaks down over time, as passing trains causes movements that grinds the individual rocks against each other. Natural erosion processes also occur, even cracking stones in halves. Thus the ballast needs to be renewed or replaced periodically. Renewing includes filtering out undersize stones and adding fresh ballast to balance the lost amount. Some filtering machines use rubber beaters rotating at high speeds. Sufficiently large stones get thrown a small distance by the beaters while too small, lighter stones fly farther and are discarded beside the railbed. They should be caught and funneled down though, as big-ish rocks flying at high speeds in open areas are a safety risk.

[darthgently]

4 hours ago, monophonic said:

but no-one has been able to devise a treatment that makes wood survive even half as long buried in ground

They should look into farming Black Locust trees for sleepers then.  That wood will last over a century buried in wet ground with no additives and has about the same strength properties as oak (iirc)

[farmerben]

1 hour ago, darthgently said:

They should look into farming Black Locust trees for sleepers then.  That wood will last over a century buried in wet ground with no additives and has about the same strength properties as oak (iirc)

I've got lots of Black Locust on my property.  I love it.  It is undoubtedly the best untreated wood for this purpose in North America.  That said it does get crummy with age.  I'm not sure it lasts longer than creosote soaked wood.

However I  doubt is steel reinforced concrete sleepers will last 100 years either.  They tear up and rebuild automobile roads much more frequently than that.  Fiberglass reinforcement might be better than steel from a longevity perspective.

 

[StrandedonEarth]

Rebar made of spun basalt is a thing…

[K^2]

5 hours ago, farmerben said:

Fiberglass reinforcement might be better than steel from a longevity perspective.

2 hours ago, StrandedonEarth said:

Rebar made of spun basalt is a thing…

While these are a thing, and I don't know the details of all the magic that goes into selecting rebar for concrete, the problem is matching thermal expansion coefficients. Typical value for concrete used in construction is about 10E-6 cm/cm/°C. Steel is usually a touch higher, but very close, and the two can be tuned relatively easily, so you can match rebar to concrete almost perfectly for pretty much every practical need.

Glass fibers tend to be closer to 5E-6 cm/cm/°C. There are, apparently, ways to bring down the thermal expansion coefficient of concrete closer to this value, but it's on a threshold and limits the kind of mixes you can use. I'm sure there are use cases where the ability of the rebar to withstand corrosion are drastically more important than being picky with the concrete mix, but it's still important to keep in mind that it is a significant limitation. I have no idea if this is relevant to the railroad ties (sleepers), but if you're asking a question about, "Why are they not using fiberglass for X?" this is often the cause. Cost is the other factor, of course, but less so when you're going for longevity builds, as you normally wouldn't use the cheapest steel rebar for these projects anyways.

We are probably going to be seeing a shift away from steel for reinforcement as the time goes on, and we might abandon it entirely at some point in the future, but we're definitely not there yet.

[farmerben]

The problem with steel rebar is that once oxygen or moisture gets in, it's game over.  Rust expands and damages the rest.

Ferrocement boats use the best cement available.  But these boats don't last forever.

Edited July 25 by farmerben

[kerbiloid]

https://en.wikipedia.org/wiki/Malleable_iron

The cast iron doesn't get rusted.

[monophonic]

20 hours ago, darthgently said:

They should look into farming Black Locust trees for sleepers then.  That wood will last over a century buried in wet ground with no additives and has about the same strength properties as oak (iirc)

Fully buried in constantly wet terrain is no problem. The multitude of swamp mummies discovered attests to the ability of matter to stay together in a low oxygen environment. For railroad sleepers the problem is that they are by necessity exposed to air from above, and thus get wet and dry out repeatedly as weather, well, weathers. If that wood can handle that for a century, I'm amazed! Regular creosoted wood ties last about thirty years, I think.

Future is  in concrete or new materials though. As amazing as wood is, modern management methods make the consistent predictability of those a very valuable property. Trees are always individuals and sleepers made from any wood have much higher variability on durability and dynamic behaviour under load.

[kerbiloid]

Venice stands on underwater wood.

A normal practice of all times. No contact with air rules.

Have an island, then place underwater wooden cells filled with ground and stones to reinforce and to align it. Build on top.

[darthgently]

1 hour ago, monophonic said:

Fully buried in constantly wet terrain is no problem.

I meant like a fence post, buried at one end

[farmerben]

I wonder what the limiting factors are for battery powered train engines.  The most powerful engines existing are powered by overhead pantograph.  We will not see mass electric trains in the US because building the overhead lines would be too disruptive to existing infrastructure.  Unless, we do an interrupted pantograph.  Where the battery can be recharged at stations, or along convenient stretches of rural land.  Charge while moving by overhead pantograph, then go battery only through towns, etc.  It would create demand for the worlds best AC-> DC rectifier.

[Terwin]

14 minutes ago, farmerben said:

I wonder what the limiting factors are for battery powered train engines.  The most powerful engines existing are powered by overhead pantograph.  We will not see mass electric trains in the US because building the overhead lines would be too disruptive to existing infrastructure.  Unless, we do an interrupted pantograph.  Where the battery can be recharged at stations, or along convenient stretches of rural land.  Charge while moving by overhead pantograph, then go battery only through towns, etc.  It would create demand for the worlds best AC-> DC rectifier.

The faster the train travels, the more wear on both the pantograph and the lines themselves, also the less power that can be transferred.  This makes charging while traveling across rural areas a bad idea as either it is ineffective, or your train travels very slow when it could be moving very fast.

Station charging may be less of an issue, depending on how long the engine spends at each station.

Have you looked at how much power is required for the different classes of train? 

I could see it being viable for light commuter trains, but heavy industrial trains seem likely to need too much power between stops.

[farmerben]

18 minutes ago, Terwin said:

 

Have you looked at how much power is required for the different classes of train? 

 

Power is not a problem.  We have diesel electric hybrids now.  The issue is batteries have 40 times less energy/kg than diesel fuel.  

[K^2]

6 hours ago, Terwin said:

The faster the train travels, the more wear on both the pantograph and the lines themselves

I do wonder how much work it would be to have the maglev pantograph that doesn't experience wear in the same way...

But realistically, unless there are amazing breakthrough in batteries, I suspect the future for the trains is hydrogen. Diesel turbines can be converted into hydrogen turbines relatively readily. Alternatively, hydrogen fuel cells are an option. In either case, the biggest problem is the size and weight of the fuel tanks, and adding an extra car just for hydrogen isn't going to affect the performance of the train all that much. I'm sure there will be safety concerns, but hydrogen EVs in the recent years have demonstrated that this can be done reasonably safely.

[kerbiloid]

8 hours ago, farmerben said:

I wonder what the limiting factors are for battery powered train engines. 

Train surfers. They need room to stand.

[ARS]

So... This has been bugging me for a while. While helicopter comes in many configurations of their rotors, what makes me curious is that, we have classic one rotor configuration, two rotors (tiltrotor, tandem and coaxial), four rotors (quadcopters) and multi rotors (above that), there's very little to no design for helicopter with tri-rotor configuration. As far as I know, the only design of tri-rotor helicopter that's actually built is Cierva W.11 Air Horse (largest of it's time, has three rotors, driven by single engine), which has it's development being terminated after the crash of the first prototype, killing three of it's crew. Why there's a lack of interest? I mean, the design is workable for a drone. What's the advantage and disadvantage of trirotor design?

[kerbiloid]

Spoiler

A project, to deliver lightweight ICBM to taiga.

 

Spoiler

A test craft

 

 

[farmerben]

8 hours ago, K^2 said:

I do wonder how much work it would be to have the maglev pantograph that doesn't experience wear in the same way...

But realistically, unless there are amazing breakthrough in batteries, I suspect the future for the trains is hydrogen. Diesel turbines can be converted into hydrogen turbines relatively readily. Alternatively, hydrogen fuel cells are an option. In either case, the biggest problem is the size and weight of the fuel tanks, and adding an extra car just for hydrogen isn't going to affect the performance of the train all that much. I'm sure there will be safety concerns, but hydrogen EVs in the recent years have demonstrated that this can be done reasonably safely.

What do you mean by "maglev pantograph" ?  Does this mean magnets under the track and induction coils on the engines?

I searched that the typical diesel-electric locomotive carries about 16 tons of fuel.  I'm not sure how many miles/hours that will last.  But it's equivalent to over 600 tons of batteries.  You can put over 100 tons of freight per car ( around 200 tons max total car weight).  So you have to swap batteries often, or recharge them.  It is possible, though probably impractical, to have 6 cars full of batteries just to match the range of diesel.

Edited July 27 by farmerben

[ARS]

5 hours ago, kerbiloid said:

  Hide contents

A project, to deliver lightweight ICBM to taiga.

 

  Hide contents

A test craft

 

 

For helis that has three rotors where one is a pusher, I know about that. What I mean is the one that looks like in the first video, where all the rotors is facing upwards

[KSK]

16 hours ago, Terwin said:

The faster the train travels, the more wear on both the pantograph and the lines themselves, also the less power that can be transferred.  This makes charging while traveling across rural areas a bad idea as either it is ineffective, or your train travels very slow when it could be moving very fast.

Station charging may be less of an issue, depending on how long the engine spends at each station.

Have you looked at how much power is required for the different classes of train? 

I could see it being viable for light commuter trains, but heavy industrial trains seem likely to need too much power between stops.

How fast are we talking about here?  Speed limit on the TGV is 200 mph and they use pantographs.  Assuming Wikipedia is a reliable source, there were a bit over 2,700 miles of high speed track as of June 2021, with another four sections planned, so presumably maintenance isn't insurmountable especially as the TGV system seems to be profitable.

Admittedly, distance might be more of an obstacle in the US - I don't know whether 200 mph for a high speed train would be fast enough to make it competitive.

[darthgently]

How about over passes that hot swap batteries as the train passes underneath at 200mph?  J/K

[DDE]

1 hour ago, ARS said:

For helis that has three rotors where one is a pusher, I know about that. What I mean is the one that looks like in the first video, where all the rotors is facing upwards

I think the big question is "why". There are persuasive use cases for specifically two rotors, and in small craft for four rotors. Hexcopters and octocopters just seem to be an attempt to scale uo the quadcopter tech beyond a point where four engines would be sufficient, but without fundamentally changing it (say, using ICEs).

There's no situation outside of compound helis that requires three rotors.

[AckSed]

For battery-powered trains: how much can regenerative braking and rail electrification reduce the amount of batteries? The classic diesel-electric train generally shunts the regen power to a resistor, which seems like a waste.

Edited July 27 by AckSed