Effects of Scale on Maneuverability and Acceleration

[CRMcNeill]

In my line of work as a truck driver, I deal with differences in scale on a nearly constant basis. A fully loaded semi can weigh as much as 40 times more than a common automobile, is easily five times longer, takes four times as long to accelerate and decelerate, and requires much more room to perform simple maneuvers such as making a 90 degree turn. In game terms, I would definitely say that a semi-truck is Walker-scale compared to the Speeder-scale cars around it. In fact, based on my experiences in traffic, I almost wonder if speeder bikes should be considered Character-Scale, not Speeder.

This has gotten me thinking about another loophole in the WEG rules; scale modifiers are applied to rolls to resist damage (larger scale) or rolls to avoid being hit (smaller scale), but there is no mention of the other effects of scale that I alluded to above; larger scale vehicles tend to take longer to accelerate and decelerate than smaller vehicles, and they tend to be less maneuverable and require more room to make normal maneuvers than smaller vehicles.

I've already addressed part of this with one house rule; I apply scale modifiers as penalties when larger scale ships attempt to match maneuvers with smaller scale ships, with penalties reduced if the larger scale ship spreads the move over several rounds. For example, if a Star Destroyer is chasing the Millennium Falcon (6D scale difference), and the Falcon makes a 90 degree turn, the Destroyer is at -6D to match the Falcon's turn. However, for every round the Destroyer delays making the turn, the penalty reduces by 1D, so the Destroyer could wait 6 rounds and turn normally, or could take the middle path and try to turn at increased difficulty (but less than the full -6D) before the full 6 rounds are up (Cinematically, the destroyer isn't actually waiting 6 rounds to make the turn; they are simply turning more gradually, and will not actually complete the turn until the round where they make the Piloting roll to make the turn).

What I'm currently considering is also applying some form of scale modifier to acceleration and deceleration rates, as well. To me, it seems logical that, while larger vessels may eventually be able to match speeds with smaller vessels, they would need a longer time to run up to that speed. So what would be equitable multipliers to apply to acceleration rates when dealing with vehicles / vessels of differing scale classes?
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"No set of rules can cover every situation. It's expected that you will make up new rules to suit the needs of your game." - The Star Wars Roleplaying Game, 2R&E, pg. 69, WEG, 1996.

The CRMcNeill Stat/Rule Index

[atgxtg]

I ran into this while playing around with vehicle design rules.

Basically, acceleration starts off as the thrust/mass ratio or a vehicle, but it drops off in an atmosphere as thrust is needed to maintain a given speed based on how aerodynamic the vehicle is. A larger vehicle with a high thrust to mass ratio can indeed accurate as fast or even faster than a lighter vehicle.

I don't think scale would help here, in fact I think it would hurt and cause problems. For example a typical real world fighter jet has better acceleration than a a typical real world car or motorcycle. So scale would hurt there. In game a X-Wing can certainly accelerate faster than a speeder bike.

What might make more sense would be to give vehicles a rating that shows how much they can change their speed band in one round (or, for slpw vehicles how many rounds it takes to change their speed band). That is kinda already in the game with characters being able to shift two speed bands at once.

Most vehicles should keep the 1/1 change, but you could have some sluggish vehicles take 2 rounds per increase or even more.

I wouldn't advise using that for space vechiles though. the SPACE values in the RPG actually correspond fairly well with the relative acceleration ratings given by Luscafilm.

[vanir]

I agree with atgxtg for what it's worth, a mate owned his own full size prime mover and rented the trailer. Point being he ran around with no trailer a bit and leapfrogging unnecessary gears it was fast, I mean we dragged off 351 clevelands from the lights fast. Something to do with no trailer and 900hp I guess, come off the clutch into a high gear and you're doing 30mph in a few bouncy seconds, rinse and repeat to 100 if you want, they do sort of hit a brick wall much faster than that but as atgxtg outlined it's to do with exponential wind resistance (a typical 1975 passenger sedan requires 200hp to punch much past 135mph irrespective of gearing, a 1985 Mercedes needs only 150hp, that's drag coefficient for you and this is where fuel economy is a big factor).

Acceleration with groundcars has to do with torque transmission to overcome inertia. As you go faster drag is a factor in atmosphere (which uses liquid dynamics) so horsepower then becomes important which is a product of engine speed so reciprocal inertia that was working against your torque transmission starts working for your momentum against wind resistance. Ultimately the math all starts at specific thrust of a chemical fuel and machinery and all the other factors bleeds it (compensated by pouring more fuel in).

A Nimitz class aircraft carrier displaces around the same as a SuperMax container ship but is many, many times more manoeuvrable and handy with incomparable acceleration. Many very heavy military ships will easily outdo domestic vessels a fraction of their displacement/size. It's a power and design thing. Even characteristics about an engine of the same power output can affect acceleration differently because it can be so conditional.

Modern, high performance jet engines involve varying gas speeds more than thrust volume for given thrust ratings to provide different rates of acceleration at different air densities and under different flight conditions. Fighters with bigger diameter engines and exhaust cones as a rule perform better at higher altitudes than smaller diameter ones, which in turn tend to have faster initial rates at lower altitudes and this is completely apart from thrust ratings (which are all at sea level anyway so don't account for conditional tuning). A very high thrust rating just means you can lift a big carry weight off a short runway really, many aircraft with lower comparable thrust ratings have higher max speed ratings.

Varying gas speeds at common flow rates is also involved in conditional four stroke performance tuning (ultramodern engines use variable length intake runners to work with this). You can tune entirely different performance characteristics at common outputs.

As for a House Rule, we were already using 2E and have only been integrating 2R&E changes on a case by case basis only if it improved the existing system. We only added the 1/1 acceleration/deceleration rate for vehicles and not characters, which I maintain can bound to maximum speed within just over a second since I can, ergo anyone can.

I could see good justification for specialised, high speed craft in SWU like speederbikes (especially swoops which have a thrust booster) to accelerate at more like 2/1. I'd treat it as a case by case basis for the craft, and include jury rigged "hotrod spaceships" designed for high sublight performance.

Starfighters are funny, they don't really act anything like real jet fighters and I use a long list of House rules to change that. But I haven't dealt with the power settings issue.
In jets the minimum possible power output to keep the engine burning fuel and making thrust is 60% of the military rating (max dry). That's the idle speed. The whole thing about jets is that they're fast and pilots don't mean in terms of top speed when they say that, they mean landing speeds are really scary fast and your cruise speed is 0.7 Mach, to go much slower you have to idle the engines and then you're a glider. Maintaining landing speed on approach is a case of very careful power management, power on you climb, power off you drop, you actually use that instead of the stick to land the thing because it doesn't go that slow under constant power. You control your speed with the stick just like a glider on the approach because you are one at low speeds.

So that's a weird thing about jet fighters that doesn't translate to starfighters very well. Cruise speed isn't much slower than military (although initial rates and trim is much different and better for combat), and afterburners or all out speed is really just to punch it out supersonic. Cruise speed for a modern jet fighter under warload might be 0.7 Mach with all out top speed of 1.5 Mach (advertised speed ratings are fanciful to say the least, an F-15 for example is nominally speed restricted to 1.78 Mach all out, not the 2.5+ Mach you read in high school library books).

If you ran starfighters like that they'd have speed settings limited to 2 moves/rd (cruise), 3 moves/rd (military) and 4 moves/rd (all out) and that's it, otherwise it's power off. This would make them more realistic to fly as dangerously fast craft that require high piloting skill to negotiate. Not necessarily faster than everything else at maximum speed, but they're fast and scary because that type of craft simply doesn't know how to fly slowly...ever.

That's the only real major departure I can see for the WEG system, but it would best apply to starfighters operating in atmosphere, or atmospheric craft that don't use repulsorlifts. Thing about repulsorlifts is they're anti-gravity engines, they defy some rules about conventional aerodynamics.

[DougRed4]

Without even reading what the two responses are yet, I'll throw out my 2 credits.

I completely agree with the house rule you've made regarding turning and maneuverability.

I'm not so convinced that acceleration/deceleration should have that factored in, though, at least in space. The normal laws of physics don't really apply the same way in the vacuum of space that they would on the highways here. For ground vehicles, it totally makes sense. But I don't think it should work the same way in space.

BTW, I completely agree that speeder bikes should be character scale.

[CRMcNeill]

[CRMcNeill]

[Naaman]

This is a tough one. I came up with some chase rules that actually work quite well for racing, chases and combat, but so far they have always occurred when all vehicles involved have matching scales.

I guess the simplest thing would be to treat an evading vehicle as "dodging" a pursuing vehicle. Instead of rolling attack/defense, your "to hit" roll is a piloting check and the dodge roll is an opposed piloting check. Whoever benefits from the difference in scale gets to add the scale bonus. If the pursuer fails the roll, the pursuee gets away or at least creates a larger gap or whatever your rules are for braking pursuit.

[jmanski]

I'm in with crmcneill on this one. I just can't see a Star Destroyer making the same turn as a freighter due to simple size and weight. I also can't see a Star Destroyer accelerating or decelerating as well as a freighter.

How about we use a closer scale analogy? What about a speeder to a starfighter? If an airspeeder is making a turn through a busy city and a starfighter is chasing, isn't it inherently more difficult for the starfighter to match that turn?
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Blasted rules. Why can't they just be perfect?

[garhkal]

Depends.. some fighters by virtue of design, may be MORE maneuverable than the airspeeder.
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Confucious sayeth, don't wash cat while drunk!

[vanir]

Not to mention a guided missile frigate will out accelerate a lot of cars.

I tried to create a physics frame to work with but it didn't take. I'll try it some simpler way.
Pushing water as an analogue to accelerate the object pushing the water. Atmospheres use fluid dynamics and act exactly like water, according to GR there is some argument that to a mild and largely unobserved extent, space acts like this too.

So hold your hand up like you're saying "talk to the hand" and push water. You can feel the amount of force which would accelerate an object.
Put your hand level and knifelike and push in water. Much less resistance.
Same engine, same object, same thrust, more water-force one way less water-force the other.

In this way a gigantic mass like a star destroyer with engines the size of a star destroyers engines may very well easily out accelerate a light freighter with an engine barely adequate to haul its tiny loads.

It's not a scale thing. It's a power and design thing. Manoeuvrability is something else and already handled in scale classes.

Crmcneill my issue is that when the same vehicle you called walker scale isn't heavily loaded as a cargo hauler, under scaling it would remain walker scale if you ruled vehicles that size were walker scale and adjusted acceleration between scales. It's not to do with scales.

As a suggestion, you're looking for something like encumberance rules for vehicles. Not to do with scale, but encumberance.

[CRMcNeill]

Part of the problem is that the point can get missed if it is made with an essay instead of a paragraph.

How would you handle encumbrance rules, then? It can't just be cargo capacity, as an ISD or MC80 would be dragged down by a relatively small amount of cargo (compared to the capacity of dedicated transport ships).
_________________
"No set of rules can cover every situation. It's expected that you will make up new rules to suit the needs of your game." - The Star Wars Roleplaying Game, 2R&E, pg. 69, WEG, 1996.

The CRMcNeill Stat/Rule Index

[vanir]

Sometimes it takes a bit of a process to strip down and articulate, it's not meant as a lecture but just unwravel my own thoughts.

You've already thought more about this than me so I can only abstract off the top of my head, I may miss obvious counterpoints here.

Bulk cargo haulers (as opposed to ubiquitous domestic freighters) I would suggest are already heavily encumbered as listed, due to design parameters to haul such loads their performance doesn't actually increase when unloaded without modification.

However domestic, utility and military craft I would say can definitely benefit from encumberance rules. But there is a volume issue regarding cargo mass density, you would need to carry very dense materials like minerals to benefit from overloading for encumberance. Or modify the ship to carry external cargo pods for extra cargo volume (weight aside).

Say you had encumberance rules along the lines of restricting speed to 2 moves, acceleration/deceleration to 1 move per 2rds, and 0D manoeuvrability adjustment, this could be workable for 200% listed cargo capacity because most craft will still perform better than a similarly sized bulk hauler and their basic structure, power distribution and inherent design just isn't meant for heavy cargo hauling anyway.
edit. or maybe 300%, since I think I recall seeing some external pods for the YT-1300 somewhere as a modification to increase cargo to 200% at the cost of 1 move and -1D manoeuvrability (min 0D), or something like that. Dunno, what do you think?

[CRMcNeill]

It makes sense. A Move penalty would be easier to apply, and would just as realistically degrade the acceleration rate. Should that rule be applied only to commercial ships, and just assume that military vessels always have sufficient power to run normally?

On a related note, how should gravity wells affect Acceleration and Maneuverability? Increased acceleration on approach to a planet, and decreased on departure? Bonus to Maneuverability when making a turn in the direction of the gravity well? Varying bonuses based on the size of the gravity well? I know the concept of using gravity slingshot maneuvers has been used in the EU, and I have my ideas for it, but I would appreciate some input.
_________________
"No set of rules can cover every situation. It's expected that you will make up new rules to suit the needs of your game." - The Star Wars Roleplaying Game, 2R&E, pg. 69, WEG, 1996.

The CRMcNeill Stat/Rule Index

[atgxtg]

Well, what I was working on was calculating the SPACE score for ships using the Thrust/Mass Ratio. It handled things like light/partial/ full loads very well, as a ships TMR (thrust-t0-mass ratio) would change as the ship's mass increased.

I was reverse engineering masses based on the fighter's thrust rating in KTU ans acceleration (in Gs). Most ships were working out at around 1 SPACE per 400Gs, or about 1 MGLT per 40Gs. I think the actual number was something like 1 per 390 or 410, but I'd have to check my notes. This worked for most ships and the ones that didn't usually had a reason.

If we assume 1 KTU = 1 kilo-ton unit of thrust we can get a mass of about 8.1 tons for an X-Wing.





But, we could simplify a lot of that for your purposes. A good rule of thumb for freighters is to assume that about 25% of the mass of a freighter is cargo. So as SPACE= acceleration, and Acceleration = Thrust/Mass, then if thrust is a constant, the change in acceleration is inversely porportail to the change in mass (in plain English that means that less cargo means a faster ship, and more cargo means a slower ship).



There are (at least) three ways to go from here: [This is where it gets simpler, really]


1) If we assume that the listed SPACE speed is for a ship with a full cargo hold, then a ship with an empty hold would move 33% faster (SPACE 3 would go up to SPACE 4).


2) If we assume that SPACE speed assumes an empty hold then a ship with a full hold would move 25% slower (that is MOve 4 would slow to move 3).


3) If we assume that the listed SPACE is for s for a partially full hold then you can assume a change of about 20% in either direction depending on how much cargo is being carried.



#3 is probably the best, easiest assumption to go with, and translates into about a +1/-1 variation in the SPACE score of most freighters for a light/average/full load cargo carried.

Note that this wouldn't apply to fighters, and they don't carry much cargo as a percentage of their total mass.


You can work up some values for other types of vessels with a little thought. Most capital ships probably don't change much more than a freighter, although tanker ships probably would, as would carriers and troopships. .

[vanir]

okay now that system atgxtg posted I'm very liking.

for starships other than starfighters no cargo +1 space unit to movement rates, full cargo -1 space unit to movement.

Combine with earlier conversation, overload by 200% listed cargo (external pods may have to be used for physical volume), -1 movement action possible at all out speed (maximum declared moves is 3 moves all out speed not 4) and -1D manoeuvrability. Overload by 300% and maximum movement speed is half maximum speed or maximum of 2 move declarations top speed, and manoeuvrability reduced to 0D, plus acceleration/deceleration is capped at 1 move per 2rds.

Personally I think that doesn't sound bad. Just needs adjustment to work on a common, simpler system. Maybe use the +1/-1 rule, then apply to overloading listed cargo to the limits of thrust/mass ratio.

So a medium freighter with a move of space: 5...
empty moves and accelerates working at space:6
half cargo loaded space:5
full cargo space: 4
overloaded 150% space: 3
overloaded 200% space: 2 and -1D manoeuvrability
overloaded 300% space: 1 and 0D manoeuvrability

that I like...thinking on the run here...