Fractional drives

[spank]

A small chart I worked up for intermediate sized drives, with an eye toward smaller ships.
The design charts are a little granular at the low end.
To use simply select the column that match the drive performance you want, go down the chart until you get to the tonnage of your ship. That's the size of the drive required. If your hull is between two number use the larger number.

 

[Spinward Flow]

This is why you want a FORMULA ... not a TABLE ... for this kind of endeavor.
It's why LBB5.80 is a superior method, since it is formula based rather than table based, when it comes to starship construction paradigms.

The design charts are a little granular at the low end.

Too granular.
I keep wanting to try building 300 and 500 ton starships using LBB2 and then ... oh ... yeah ... you "can't" using the RAW (without gimping yourself).

 

[infojunky]

This is why you want a FORMULA ... not a TABLE ... for this kind of endeavor.
It's why LBB5.80 is a superior method, since it is formula based rather than table based, when it comes to starship construction paradigms.

Too granular.
I keep wanting to try building 300 and 500 ton starships using LBB2 and then ... oh ... yeah ... you "can't" using the RAW (without gimping yourself).

Well with a little effort at deconstructing mathematically the tables you have useful formula for drives. Further more using the RAW you can use the standard drives derated to the performance that you wish for the design. In that the major fraction of drive volume exists within the fuel and that volume is controlled by hull size grossly.

 

[mike wightman]

A look up table is often more use than a formula since you don't need to remember he formula and you don't need to plug in the numbers.
Look up tables are all over engineering...

Nice work.

 

[Spinward Flow]

Further more using the RAW you can use the standard drives derated to the performance that you wish for the design.

Except then the "standard" drives are no longer STANDARD ...

 

[Dragoner]

Look up tables are all over engineering...

Indeed, I have shelves of books with them; tabular data is practice vs formulas being theory.

 

[Grav_Moped]

Well with a little effort at deconstructing mathematically the tables you have useful formula for drives. Further more using the RAW you can use the standard drives derated to the performance that you wish for the design. In that the major fraction of drive volume exists within the fuel and that volume is controlled by hull size grossly.

Well, yeah.
In LBB2, Jump-1 (unless using drop tanks) requires 12.5% of tonnage plus 5 tons, of which 10% of tonnage is the jump fuel and 2.5% of tonnage plus 5 tons are the actual drives.

It's worth noting that the underlying formula for maneuver drives breaks down below 2G*100 tons ("Size A"), producing nonsensical results for drives smaller than that.

 

[whartung]

This is why you want a FORMULA ... not a TABLE ... for this kind of endeavor.

Yea, but, still, the "formula" isn't reality in anyway, shape, or form.

There are other factors in powerplant design that makes having an "infinitely scalable" design not workable. There are simply engineering breakpoints that kick in to place.

I can't speak to large freighters, but most powerplants here on Terra Firma are not scalable. The vessel is built around the available plants, and if it's not enough, they gang them up.

This concept is similar to adding cylinders to the motor (2-4-6-8), or rotors in a Rotary motor.

But even still, while there are V-12, even V-16 motors, they're more a novelty.

It's a lot of trouble to engineer these things, and there's only real economy in scaling the operations.

 

[infojunky]

It's worth noting that the underlying formula for maneuver drives breaks down below 2G*100 tons ("Size A"), producing nonsensical results for drives smaller than that.

It fits in a Set function, but I generally clean it up to match the gross formula.

 

[infojunky]

Yea, but, still, the "formula" isn't reality in anyway, shape, or form.

There are other factors in powerplant design that makes having an "infinitely scalable" design not workable. There are simply engineering breakpoints that kick in to place.

Honestly if we know the Output of a Standard Power plant then add multiples shouldn't be a problem.

I can't speak to large freighters, but most powerplants here on Terra Firma are not scalable. The vessel is built around the available plants, and if it's not enough, they gang them up.

They are and they aren't, derated engines can provide more power than they are rated for with the proviso that the supporting hardware is up to snuff. It's not uncommon for a engine to be beefier than one would expect for it's rated power band, with looks towards durability or ease of manufacture and similar factors.

This concept is similar to adding cylinders to the motor (2-4-6-8), or rotors in a Rotary motor.

Note said nothing about adding, there several engines I have seen or heard of where one or more cylinders don't fire. Essentially the extra cylinder is just a balancing weight on the cam.

But even still, while there are V-12, even V-16 motors, they're more a novelty.

Also note there are multiple cylinder straight engines as well, Note these are normally found in thing like Tractors and Ships.

 

[Grav_Moped]

It fits in a Set function, but I generally clean it up to match the gross formula.

Here's the graph showing the problem:



The drive performance table deviates from the expected values at rating=1 and 1000Td, and at several points for drive sizes W-Z.

Honestly if we know the Output of a Standard Power plant then add multiples shouldn't be a problem.

It really only matters if you're keeping the LBB2&3 tech paradigm of "bigger is always better, and only higher tech lets you build bigger". The point of it is to force tradeoffs between performance and size at lower tech levels.

On the other hand, if using multiples of drives with a fixed-tonnage plus proportional-tonnage formula (LBB2), stacking smaller drives to get around the size limits provides efficiencies at higher tech levels (or rather, adds inefficiencies at lower tech levels). Example: Jump-6 in 200Td as one Size-F drive (TL-10) is 35Td, but as two Size C drives (TL-9) it requires 40Td. Amusingly, the price is the same either way.

 

[Spinward Flow]

Here's the graph showing the problem:

Gets even more fun when you realize that in LBB2 the standard-A drives were just dropped into small craft and uprated proportionately.

A-drive in 200 tons = Code: 1

50 ton Cutter = 200/50 = 4G and Power Plant-4
40 ton Pinnace = 200/40 = 5G and Power Plant-5
30 ton Ship's Boat = 200/30 = 7G 6G and Power Plant-7 6

And then they threw the 10Pn fuel formula out the window for LBB2 small craft, otherwise they would all require way too much fuel and have no useful cargo fraction potential.

 

[Grav_Moped]

Gets even more fun when you realize that in LBB2 the standard-A drives were just dropped into small craft and uprated proportionately.

A-drive in 200 tons = Code: 1

50 ton Cutter = 200/50 = 4G and Power Plant-4
40 ton Pinnace = 200/40 = 5G and Power Plant-5
30 ton Ship's Boat = 200/30 = 7G 6G and Power Plant-7 6

And then they threw the 10Pn fuel formula out the window for LBB2 small craft, otherwise they would all require way too much fuel and have no useful cargo fraction potential.

Oh, it's funnier than that. Starships had the (non-proportional-to-size) maneuver fuel burn rate of small craft in the '77 rules. The 10Pn formula provided for two days continuous max acceleration -- that is, more than you'd ever use, so you didn't have to track it.

 

[Grav_Moped]

Oh, it's funnier than that. Starships had the (non-proportional-to-size) maneuver fuel burn rate of small craft in the '77 rules. The 10Pn formula provided for two days continuous max acceleration -- that is, more than you'd ever use, so you didn't have to track it.

Which is to say, they didn't just stuff Size A Drives into small craft, they used starship fuel burn rates too!

They simply allowed small craft to have smaller fuel reserves.

 

[spank]

It fits in a Set function, but I generally clean it up to match the gross formula.

It is a set function, I just think it's a little dinked, From LBB 2, The J-drive and Power plant are (drive size number) * (number)+(number)
Jump drives are (5*drive size number) + 5, so {10,15,20,35....} etc.
Power plants are (3*drive size number) +1 so {1,4,7,10,13...} etc
Maneuver drives are (2*(drive size number -1)) +1 so {1,3,5,7...} etc

You see the problem, I think it should be (2*drive size number)+1 so {3,5,7,9,11....} this progression would fit more with the other two drive types.
It would also adjusting the whole drive size chart.

Here's the graph showing the problem:
View attachment 3090


The drive performance table deviates from the expected values at rating=1 and 1000Td, and at several points for drive sizes W-Z.


It really only matters if you're keeping the LBB2&3 tech paradigm of "bigger is always better, and only higher tech lets you build bigger". The point of it is to force tradeoffs between performance and size at lower tech levels.

On the other hand, if using multiples of drives with a fixed-tonnage plus proportional-tonnage formula (LBB2), stacking smaller drives to get around the size limits provides efficiencies at higher tech levels (or rather, adds inefficiencies at lower tech levels). Example: Jump-6 in 200Td as one Size-F drive (TL-10) is 35Td, but as two Size C drives (TL-9) it requires 40Td. Amusingly, the price is the same either way.

I worked around this quirk by adjusting the size of the size "a" drive up one ton. IMHO all the M-drives should be 2 tons heavier. but this was more expedient, I was already making a chart anyway, and this really only effected the ships I was making the chart for.

 

[spank]

The drive performance table deviates from the expected values at rating=1 and 1000Td, and at several points for drive sizes W-Z.

I can get the same numbers as the LBB 2 drive potential table for anything under 4000 tons and type V drives.

 

[aramis]

This is why you want a FORMULA ... not a TABLE ... for this kind of endeavor.
It's why LBB5.80 is a superior method, since it is formula based rather than table based, when it comes to starship construction paradigms.

Too granular.
I keep wanting to try building 300 and 500 ton starships using LBB2 and then ... oh ... yeah ... you "can't" using the RAW (without gimping yourself).

can't copyright the output of a formula. Can copyright a table that's inconsistent.

 

[Spinward Flow]

can't copyright the output of a formula. Can copyright a table that's inconsistent.

Where's the facepalm emote? There's got to be one around here somewhere ...

 

[Spartan159]

Where's the facepalm emote? There's got to be one around here somewhere ...

We need this.

 

[Grav_Moped]

It is a set function, I just think it's a little dinked, From LBB 2, The J-drive and Power plant are (drive size number) * (number)+(number)
Jump drives are (5*drive size number) + 5, so {10,15,20,35....} etc.
Power plants are (3*drive size number) +1 so {1,4,7,10,13...} etc
Maneuver drives are (2*(drive size number -1)) +1 so {1,3,5,7...} etc

You see the problem, I think it should be (2*drive size number)+1 so {3,5,7,9,11....} this progression would fit more with the other two drive types.
It would also adjusting the whole drive size chart.

I worked around this quirk by adjusting the size of the size "a" drive up one ton. IMHO all the M-drives should be 2 tons heavier. but this was more expedient, I was already making a chart anyway, and this really only effected the ships I was making the chart for.

It is a bit "dinked".
I'm looking at it from the front end, and see it as (per the rules) constraining the domain of the function rather than the range; the effect is the same, though. The key issue is that (maneuver drive Gs * tons) must be greater than 200. After that, the letter drive sizes are just specific outputs of the formula that manifest when the function's domain is set to elements of the set {100, 200, 400, 600...}.

And some of this goes back to LBB2 '77 which did not require Pn=Jn (which is where the broken-design XBoat comes from) so that the only thing you needed the power plant for was the maneuver drive. Note that the constant components of their respective drive tonnage formulae cancel each other out, so the tonnage committed to maneuver (aside from fuel, but that formula was just bonkers anyhow) was actually linearly proportional to acceleration!