For Questions That Don't Merit Their Own Thread

[magnemoe]

6 hours ago, darthgently said:

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

This, its an initiative for high speed rails to have batteries so they can use them on tunnels and bridges to reduce construction cost. 
Relevant for high speed rail as its the one who is expanding and normal rails has to be compatible with old stock. 
Second way of hybrid is to have diesel engines and a pantographs then the line is electric. 

[kerbiloid]

Windmill generators. The faster it runs, the more it provides.

[darthgently]

I can't remember if it is real, or a concept, but I recall something about diesel-electric trains being able to transfer power to one another via the rails in some cases.  So one going down a mountain in regen mode would provide some power to another train behind it coming up the other side of the mountain.  Or maybe it was just multiple engines on the same train pooling regen and use.  Ring any bells?  Sorry so vague

[K^2]

12 hours ago, farmerben said:

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

Nah, I mean pantograph rides on the wire via maglev. Probably using induced eddies in the wires to create a "cushion" so that there is no direct mechanical contact. I'm sure it would introduce additional constraints on how the overhead wires are constructed, like the material, tension, etc. But maybe that's still viable for high speed trains?

Maglev track for the train doesn't, unfortunately, solve the main issue. While moving induction coils to the track would make the train itself almost entirely passive, it would make the track construction way more expensive. Prohibitively so, almost certainly. By the way, in this setup, both the train and the tracks can still have permanent magnets taking up most of the weight, with the induction coils only used for stability adjustments and propulsion. And the track itself can simply be providing a constant AC to the coils, with train's logic adjusting phase differences between on-board coils as well as tapping into them to power lights, electronics, etc on board. Other than, "Each segment of the track now needs a sizable coil of low-resistance wire," this is very workable. Unfortunately, the coils are still pretty expensive and when you start looking at thousands of miles of track,  it's a non-starter without something drastically changing in metal prices.

12 hours ago, farmerben said:

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.

Yeah, that's why I suggested hydrogen. You'd be able to cut it down to just a few tons of hydrogen, which should just about fit in a larger tanker car.

 

4 hours ago, AckSed said:

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.

Not that much, unfortunately. Average freighter is about 4,000 tons. It would take about 100kg of DT at 30% efficiency to get it to 60mph. Going with the above quote of 16T of DT on a locomotive, it'd take you 16 starts and stops just to get to 10% saving. And I'm sure the schedules for freighters are already optimized around having them have to stop as infrequently as possible specifically to save on the fuel.

Inclines might be a bigger factor, but here you can't get away with just partial storage. If most of your fuel was used to go uphill, you do need to store all of it back into the batteries on the way down. That's an amazing fuel saving, of course, but it doesn't help you any with reducing the total weight of the necessary batteries.

Honestly, a battery-free diesel hybrid that can tap into the grid is probably the best we can do right now. Using the grid as source or storage for both regenerative breaking and going up/down hills where available, and managing on diesel everywhere else. This lets you place wires more strategically, drastically reducing the fuel use, as well as allowing the train to travel slower in these areas - again such as going up or down an incline, while maintaining a higher speed in areas where overhead wires are not available.

[AckSed]

Thank you for answering but it's braking. Gah, sometimes it quite annoys me that spellcheck can't tell the difference.

[kerbiloid]

6 hours ago, AckSed said:

braking

Sometimes...

Spoiler

 

Hi-tech is good, but

Spoiler

Lithium

 

Hydrogen

 

Diesel fuel

 

***

 

 

Edited July 28 by kerbiloid

[darthgently]

Battery quality really matters

 

[Nuke]

^ouch. and it waited for it to be carried into the least escapeable location to go boom. its this kind of thing that almost makes me want to throw away all my bare unprotected 18650 cells. almost.

On 7/26/2024 at 1:54 AM, kerbiloid said:

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.

my town likes to eat houses. most are built on piles, since the ground is spongey and is not suited to foundations without pre-compresssion. every year you see boat houses get eaten by the sea, and most of the inland houses are not level.

big construction project for this year is a new hospital, and they had gravel trucks running back and fourth for several months just to pre-compress the ground. they also encountered large boulders that needed to be blasted away. do we really need a new hospital, probably not. its going to have the same problem as the existing one, not enough staff and will ship you to another town for anything more severe than stitches. our state would rather dump money into one big, oppulent, expensive, centralized facility in anchorage than do normal construction in regional locations, then eat a boatload of travel expenses on an airline that gouges.

Edited July 29 by Nuke

[GDJ]

20 hours ago, darthgently said:

Battery quality really matters

 

This is why NiMH batteries are still around. I love Lithiums for the energy density, but when you see this happening........

[monophonic]

On 7/26/2024 at 10:06 PM, 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.

I feel the issue of adding catenary has been exaggerated there. Many lines in the New England area used to have one as well. What exact infrastructure are you thinking of? This side of the pond the railbed is often lowered by a couple of feet to get the needed extra height in a tunnel or under a bridge. Through trusses can be a little more difficult, we have a few where the top cross members have been replaced with upward arcing parts to make room. A bigger issue I see is the extremely tall pantographs needed to reach a catenary that fits US style double stackers and autoracks underneath.

The rectifier thing is a non-issue. Most currently in production electric locomotives use a DC intermediate circuit anyway, thus have such a rectifier circuit. It is an off the shelf part. Also battery-electric trains are now available from multiple manufacturers (Siemens, Alstom at least) and starting to enter service in Germany. They are mostly replacing diesel units on unelectrified rural lines though, charging in the cities where catenary power is available.

On 7/27/2024 at 7:03 AM, ARS said:

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?

Torque balancing with an odd number of rotors is a complex issue even in a drone. You need the ability to tilt at least one rotor, extra anti-torque rotor like on a single rotor helicopter, or very precise tilt and RPM equalization like on the Cierva. Meanwhile even number of rotors makes it trivial, as you can rotate equal numbers of rotors in opposite directions and adjust with minor changes to RPMs. I see no advantages in having three rotors over four.

On 7/27/2024 at 10:25 PM, magnemoe said:

This, its an initiative for high speed rails to have batteries so they can use them on tunnels and bridges to reduce construction cost. 
Relevant for high speed rail as its the one who is expanding and normal rails has to be compatible with old stock. 
Second way of hybrid is to have diesel engines and a pantographs then the line is electric. 

The driving force on tunnel sizes in high speed rail is the impact from the pressure spike caused by the train entering the tunnel at high speed. Removing the catenary will not allow reducing the size of the tunnels. Only limiting speed in tunnels would, but that would negate the advantages of building high speed rail in the first place.

On 7/28/2024 at 2:13 AM, K^2 said:

Nah, I mean pantograph rides on the wire via maglev. Probably using induced eddies in the wires to create a "cushion" so that there is no direct mechanical contact. I'm sure it would introduce additional constraints on how the overhead wires are constructed, like the material, tension, etc. But maybe that's still viable for high speed trains?

The arc caused by the air gap would eat at the wire and pantograph like no tomorrow. This is already an issue with traditional wire and carbon brush panto in freezing conditions. Newest locomotives here have an option to have the forward pantograph disconnected but up just to brush ice off the wire so the connected rear pantograph can make better contact with the wire. The need to prematurely replace wire due to pitting from arcing is just that expensive. The electric company won't provide the power lost in the arc for free, either.

I once traveled in the first car behind an earlier generation electric locomotive in a cold winter night. The light from arcing lit up the terrain by the track well enough you could have read a book there, and it was an almost constant light. There was a lot of energy lost as light that night.

[RKunze]

On 7/28/2024 at 1:13 AM, K^2 said:

Nah, I mean pantograph rides on the wire via maglev. Probably using induced eddies in the wires to create a "cushion" so that there is no direct mechanical contact.

Hmm. How do you get the power from the wire to the pantograph in this case?

At the voltages involved, I'm pretty sure an electric arc will work technically (or rather, will be pretty much unavoidable), but I’m equally sure having a constant arc with enough current to drive a train will be quite hard on both the wire and the pantograph. Probably harder than having the pantograph scrape along the wire...

[kerbiloid]

Many-many iPhone chargers along the train would turn it into remotely charged iTrain.

[darthgently]

Marine cargo ships have a Plimsoll line painted along the hull that indicates that the ship is overloaded if the line submerges.

When launching a rocket do the engineers rely on bookkeeping of known part masses, amounts of fuel loaded, and known payload mass to track gross weight, or are load cells used that actually measure the gross mass in real time on the pad?  I can imagine either is more than adequate, but am curious what methods may be used with what frequency 

[kerbiloid]

I guess, before launching the rocket, the submarine must be balanced.

So, on flooding the shaft the compensating ballast tank gets filled until the balance gets restored.

Then both shaft and compensating tank get blown dry, while the main ballast tank receives equal amount of water to restore buoyancy.

But I may be wrong.

Also, the fins are used to hold the submarine at the very launch moment, and thus the submarine must have 5 kn (?) speed for launching.

Edited July 31 by kerbiloid

[darthgently]

1 hour ago, kerbiloid said:

I guess, before launching the rocket, the submarine must be balanced.

So, on flooding the shaft the compensating ballast tank gets filled until the balance gets restored.

Then both shaft and compensating tank get blown dry, while the main ballast tank receives equal amount of water to restore buoyancy.

But I may be wrong.

Also, the fins are used to hold the submarine at the very launch moment, and thus the submarine must have 5 kn (?) speed for launching.

That is very interesting but I meant for land launches.  Do any of the current launch vehicles incorporate load cells in the pad to monitor gross weight or do they just rely on adding up known dry mass, payload mass, and fuel mass via bookkeeping?

[magnemoe]

3 hours ago, darthgently said:

That is very interesting but I meant for land launches.  Do any of the current launch vehicles incorporate load cells in the pad to monitor gross weight or do they just rely on adding up known dry mass, payload mass, and fuel mass via bookkeeping?

They might have load cells but I guess they just use fuel mass added, probably having some level sensors in tanks to account for boil off including in the piping from storage tanks to rocket. 
This would be very accurate if you know the level and temperature of fuel and oxidizer. 

Launching an rocket from an submarine, after the missile is launched the tube will fill with water instead of mostly rockets seconds after launch. Water should be lighter. 

[farmerben]

If the actual mass differed from the predicted mass, somebody screwed up badly in a way that would likely cost the mission.

 

[darthgently]

7 hours ago, farmerben said:

If the actual mass differed from the predicted mass, somebody screwed up badly in a way that would likely cost the mission.

 

That is the point of my question.  What if a tech installed a small access plate ajar such that a Florida rainstorm ended up leaving 50 kilos of water pooled on board across various niches?  I'm just curious how much this is a deal.  Or not a deal.  For cargo ships, especially for their insurers, it is a very big deal, thus the requirement of the painted Plimsoll line.   

Anyway, I figured since 50 kilos of rain in the payload fairing could make or break an abort to orbit in case of a fuel leak or something it seems like a valid question whether anyone is using load cells rather than bookkeeping 

Edited August 1 by darthgently

[magnemoe]

3 hours ago, farmerben said:

If the actual mass differed from the predicted mass, somebody screwed up badly in a way that would likely cost the mission.

 

Yes but you don't need load cells for this not sure how accurate they would be with an tall rocket with wind anyway. 

[darthgently]

4 minutes ago, magnemoe said:

Yes but you don't need load cells for this not sure how accurate they would be with an tall rocket with wind anyway. 

Just average the readings.  The leeward side will read high, the windward low.  

[farmerben]

When it comes to laser driven light sails where is it best to put the lasers?  Earth's surface is not ideal from the atmosphere and rotation standpoint, but the cost is lower than putting them in space.

 

 

[kerbiloid]

At the Low Solar Orbit, 0.1 AU.

This is also used in the KSPI-E mod + Photon Sail addition.

[AckSed]

Other possibilities:

Luna's surface gives you a big rock to push off and abundant solar during its day.

Earth-Luna L5 can use a solar sail itself to reset its position after a hard day of beaming.

[kerbiloid]

The Moon phases make the power production highly volatile.

And the lunar night lasts for two week.

So, the industrial consumers should unstoppably vary their production by orders of magnitude through the month.
Big industrial plants rarely like this, they need established production rate.

[StrandedonEarth]

Deep space is the only real option for constant LOS and power production, Presumably around an L-point