GURPS Vehicles by 1337JiveTurkey

maths

posted by 1337JiveTurkey Original SA post

OK. Since my book was falling apart anyhow, I just grabbed a PDF copy of...

GURPS Vehicles


The concept behind GURPS Vehicles is pretty simple: If there's a vehicle that you can imagine, odds are that you can create at least a reasonable approximation of it so long as you've got OCD. There are two things that any vehicle designer needs to think about first:

1 -- Basic Vehicle Concept

There's a lot more options than just cars, boats or airplanes. For starters, it's possible to just jam all three together. Sure, it's gonna be hard to get a boat going fast enough to take off without resorting to rockets, but there's nothing preventing it.

I'm going to start off with a fairly simple starting example: A single-seater autogyro.

2 -- Tech Level

Tech Level is used throughout GURPS to tell how advanced some civilization or its technology is. TL0 is Stone Age while TL16 is ludicrous tech. In GURPS 3rd edition, the current Tech Level is TL7, while TL6 would be WWII and TL8 would be near future. TL10 is a pretty standard level for GURPS Space, while (IMO) TL12 is about the limit before things start getting silly. In GURPS 4th edition, they decided to make things a bit more fine grained in the 19th and 20th centuries and we are now TL8, with the near future being TL9. This is an important concept because it's pervasive throughout the book.

For this autogyro, I'm going to go with TL8.

Subassemblies

All vehicles are made of subassemblies, such as the body, wings, wheels, turrets, etc. Less common options include hydrofoils, hovercraft skirts and the like. Pods and superstructures can hold components that we don't want in the body itself, like jet engines. For what it's worth, if you don't think that the next few sections are complicated enough, you're free to apply them differently to every single subassembly within limits. Making only half a vehicle stealthy misses the point completely.

Autogyros require at the very least an autogyro rotor and landing gear of some sort. In this case, we'll say it has three small retractable wheels . In addition since we might want to strap some ordnance on this puppy, we'll say it's got a pair of stub wings . They provide almost no lift, but give space for fuel and weapon hardpoints. Finally, we'll need a pod to hold our propulsion.

Body Features

The body of a vehicle can be special in various ways. For instance it's possible to streamline a body or give it a hull that can float or submerse. It's also possible to add slope to the body of a vehicle as well as superstructures and turrets. Slope reduces the usable interior volume in exchange for thicker effective armor.

Also important is the frame strength and materials. It's possible to make a frame that's anywhere from super-flimsy to a literal tank with different materials depending on the need. A super-light frame made of advanced materials (satellite) weighs about 1% of an extra-heavy frame made of very cheap materials (tank). A modern jet fighter would have an extra-heavy advanced frame. To add even more to the cost of a frame, it's possible to get an adaptive frame that changes shapes or a robotic frame to let a computer control it directly. If you've got wings or a rotor, then bend over and get ready to financially take it up the ass since everything literally gets 10 times as expensive.

Our autogyro is going to have good streamlining . The frame is going to be heavy and made of very expensive materials. Compared to a jet fighter, this is about half the HP at a 5th of the price. We'll need to calculate how much this is going to cost us later on based on the size of the vehicle based on its surface area in square feet. We can calculate the basic modifiers right now:

TL8 Structure – 4 pounds, $50 per square foot
Heavy – 1.5 times as heavy, 2 times as expensive
Very Expensive – .5 times as heavy, 5 times as expensive
Good Streamlining – 1.5 times as expensive
Has Wings or Rotors (or both) – 10 times as expensive
Structure – 3 pounds, $7,500 per square foot

Surface Features

The most obvious surface feature is armor, although there's also solar cells, a convertible top, flight decks, and other stuff. Armor can be made of wood, metal, composites, ablative plastics, textiles or laminated ceramics. It's also possible to get this at varying levels of expense just like the frame. Armor is measured in DR allowing for very fine-grained choice of thickness. A rule of thumb is that DR 70 is about the same as an inch thick steel plate angled at 90 degrees. If that's not enough to drive you nuts, it's possible to give differing levels of armor to every single face of every single subassembly and then add extra armor to individual components.

Still not happy with all the options? You can layer different types to boot. Nonrigid armor is far lighter than the alternatives although it provides only a tiny amount of protection from collisions.

Our autogyro is going to have advanced composite armor since we've already blown the bank on the structure. We're going to go with only DR 10. This is only going to provide DR 5 in collisions, but we're in bigger trouble if that happens on an autogyro. Since we don't have any slope, this is PD 3. PD makes it harder to hit something, while DR reduces the damage directly.

TL8 Advanced Composite Armor – .1 pounds, $50 per DR per square foot
DR 10 – 1 pound, $500 per square foot

Motive Power

Obviously any vehicle needs some sort of motive power, even if it's just pulled by some random guy holding a rope. Motive power for any source is rated in kW, and a source's weight and volume depends on how much power it's designed to use. A ducted fan seems like a reasonable choice to power this. At TL8, a ducted fan provides 4 pounds of thrust per kW. It weighs 4 pounds per kW for small ones less than 5kW in power. For larger ones, it's 18 pounds plus .4 pounds per kW. The volume is 1/100th of the weight, and the price is $40 per pound. I'm going to make this 150 kW.

TL8 Ducted Fan – 600 pounds thrust, 150 kW power needed, 78 pounds, .78 cf, $3,120

Instruments and Electronics

Every vehicle after TL5 will likely have some sort of electronics, even if it's just an AM radio and some headlights. For our autogyro, we'll go with a forward-facing AESA with a 10 mile range, as well as a PESA with a 5 mile range. The AESA is a combination RADAR/LADAR with shorter range imaging modes to boot. The PESA is a camera capable of viewing from far infrared to ultraviolet as well as acting as a low light TV. It's capable of 5x magnification due to the range. The PESA can also act as a camera in any of its modes as well.

Being TL8, we're going to want a computer of some sort. I'm picking a high capacity small computer which can run up to three programs of complexity 2. It'll have a terminal for use by the pilot.

I'm not going to itemize the miscellaneous bullshit but suffice it to say we've got a couple of communications radios, a milspec GPS, a black box, high precision navigational equipment, IFF, autopilot, advanced radar/laser detector and HUD. This is about what you'd find in a modern fighter but scaled down a bit.

TL8 AESA (10 mile range) – +17 scan, 2.5 kW power needed, 30 pounds, .6 cf, $50,000
TL8 PESA (5 mile range) – negligible power needed, 20 pounds, .4 cf, $80,000
High Capacity Small Computer – up to 3 complexity 2 programs at once, 2 pounds, .04 cf, $1,500
Terminal – 40 pounds, 2 cf, $1000
Other stuff – .02 kW power needed, 69 pounds, 1.98 cf, $9,750

Other Equipment

There needs to be a place for the pilot obviously as well as controls. Since I have a computer with terminal, I can use the computerized controls . I'm going to pick a roomy crew station . Additionally there's going to be a compact fire suppression system to stop fires as soon as they start.

Roomy Crew Station – 40 pounds, 40 cf, $100
Computerized Controls – $1,000
Compact Fire Suppression System – 50 pounds, 1 cf, $500

Power Sources

Vehicles that use power need some sort of source, ranging from the mundane to the exotic. I'm going to pick a high performance gas turbine with 160 kW to cover motive power and any other possible requirements. Everything in this section I'm stuffing in the pod with the ducted fan.

TL8 HP Gas Turbine – 4.8 gallons per hour jet fuel, 90 pounds, 1.8 cf, $7,200
Light self-sealing Gas Tank – 24 gallon capacity, 12 pounds, 3.6 cf, $480
Jet Fuel – 124 pounds, $72

Weapons

For various reasons, I'm not going to put any weapons directly on this. Hardpoint-mounted weapons are also possible, but I usually calculate everything else first so I can see what's reasonable and keeps the math the least painful.

Component Volume and Surface Area

So now we're at the point where we add everything up and see how much this thing weighs. We calculate the volume of the body first, and then we calculate the size of the other subassemblies based on that. If the engine was in the body, I'd need to include extra access space for it. The wheels are going to be .05 times the body size in volume. Each wing is at least .02 times the body size in volume, and the rotor is .02 times the body size. Surface area is the cube root of the volume squared and multiplied by 6, or multiplied by 18 for the rotors. We calculate the surface area of each separately and add them all together. At about this point I'm starting to round numbers like crazy because who gives a fuck about random ounces?

Body – 46 cf base, 1.2x for Good streamlining, 1.075x for Retractable wheels = 60 cf (rounded up), 100 sf, 300 HP
Pod – 6.2 cf, 1.2x for Good streamlining = 7.5 cf, 21 sf, 126 HP
Wheels – 3.6 cf, 15 sf, 30 HP per wheel (3 wheels)
Rotor – 1.5 cf, 24 sf, 144 HP
Wings – 2 cf each, 10 sf each, 60 HP per wing
Total – 180 square feet

Hardpoints

Each wing can support up to 1200 pounds of hardpoint-mounted weaponry. The body can support up to 6000 pounds if I really wanted to. At this point I'm actually sneaking ahead to see what I can carry without making this unable to fly at all. After a small amount of number juggling, I'm picking 4 hardpoints capable of carrying 200 pounds of stuff each. These are tapped, so they can carry fuel tanks and electronics pods using the extra power available.

4x 200 pound hardpoints – 40 pounds, $80

Costs and Weight

Now we calculate the cost and weight of the structure and armor:
$1,440,000 structural cost
720 pounds structural weight
+
$160,000 everything else
481 pounds everything else
199 pounds pilot

$1.6 million
1400 pounds without hardpoints loaded, 2200 with.

Performance

FINALLY.

I'm skipping some calculations because I want to get some sleep. Round all speeds to nearest 5 mph.

To find ground speed normally, take 1/4 the thrust from the ducted fan divided by the weight in tons. Take the square root of that and multiply by the speed factor, which for TL6+ wheels is 16. Then add 10% if it's over 50 mph and the vehicle has good streamlining (it should in our case). This gives 260 mph unloaded, 205 mph loaded.

Ground acceleration is top speed divided by the speed factor, then multiplied by .8. That's 13 mph/s unloaded, 10.25 mph/s loaded. Ground deceleration is 10 mph/s due to the wheels. Ground maneuverability is 1.25 G. Ground stability is 2. Ground pressure is moderate.

Stall speed is loaded weight divided by lifting area then multiplied by a factor for streamlining and then by 2 mph. This gives a stall speed of 55 unloaded, and 85 fully loaded. Unloaded it can take off in 60 yards. Loaded it can take off in 175 yards.

Aerial speed is the square root of 7,500 times aerial thrust then divided by aerial drag. Aerial thrust is 600. Unloaded aerial drag is 51.6, giving 295 mph. Loaded aerial drag is 71.6, giving 250 mph. Aerial acceleration is 8.5 mph/s unloaded, 5.5 mph/s loaded. The aerial maneuver rating is 50 G unloaded (holy shit), and 30 fully loaded. These are far beyond what a human being can survive although I think it may be due to the small size compared to the HP of the lifting devices. Aerial stability is 3.

Any questions?

design maths

posted by 1337JiveTurkey Original SA post

Since I never really got into depth with GURPS Vehicles, I figured that I should try and do it more justice or die trying.

GURPS Vehicles: Design

Every vehicle ultimately starts with a concept, ranging from dinosaur-drawn sledge to steampunk ornithopter to 22nd century FTL research vessel. There are very few concepts which are completely impossible to put into GURPS Vehicles terms, but sometimes it's easier to use different rules. In particular space opera designs give a much better feel when handled as terrestrial equivalents. So an Imperial Star Destroyer and TIE Fighter are going to feel a lot more "right" as a reskinned ship and airplane than using the space ship rules.

Subassemblies

Any vehicle consists of a body and normally one or more subassemblies. For getting around on the ground there are several options ranging from the trivial to the absurd:

• Skids—Like the ones on a helicopter or Santa's sleigh. These can optionally be made to retract. Generally these don't get much use except on snow once anybody's developed something better. The most obvious something being...
  
• Wheels—Hopefully what these are goes without saying. Subdivided into several flavors such as:
  
  • Standard—Round thingy.
    
  • Small—Small round thingy with bad off-road capability. These also come in a retractable flavor.
    
  • Heavy—Used on trucks and other vehicles requiring a heavy load capacity.
    
  • Railway—Heavy wheels only useable on railroad tracks but have extremely good performance.
    
  • Off-Road—Heavy wheels meant for use in rough terrain.
    
• Tracks—Clunky non-round thingies used on bulldozers and tanks. There are two optional types of tracks called the halftrack and the skitrack which are the equivalent of half tracks and half wheels/skids.
  
• Legs—The choice of giant mechas and battlesuit pilots everywhere. More practical legged vehicles are allowed to have four or more legs.
  
• Flexibody—Technically this isn't a subassembly since it involves making the vehicle body snakelike, but I'm including it with them since it logically fits here. This is the only form of ground locomotion more impractical than legs.
  

There's also subassemblies that are useful for getting around in the air:

• Wings—The defining characteristic of an airplane or an ornithopter.
  
  • Standard—Flat aerodynamic thingies.
    
  • Biplane—Twice as many flat aerodynamic thingies.
    
  • Triplane—More biplane than biplane wings.
    
  • STOL—Optimized for allowing short takeoffs and landings at the cost of top speed.
    
  • High Agility—Optimized for acrobatics.
    
  • Flarecraft—Optimized for flying all of ten feet off the ground.
    
  • Stub—Optimized for being really stubby. Also tend to get a lot of high explosives strapped to them.
    
• Rotors—The defining characteristic of a helicopter.
  
  • Top-and-Tail—The configuration that most people think of when they think of a helicopter.
    
  • Multiple Main—The configuration used by big utility helicopters, providing additional lifting power at the cost of agility. This is also the rotor type used for tilt rotor assemblies.
    
  • Coaxial—Multiple main rotors stacked on top of each other. Higher agility but heavier.
    
  • Autogyro—It's like a helicopter with no engine attached to the rotor. This makes it effectively a big lightweight wing.
    
• Hovercraft Skirts—The defining characteristic of a hovercraft. You can make a hovercraft without one, but it's far less efficient than if a skirt is used.
  
• Hydrofoils—I'd classify this as quite firmly nautical but the book figures they're flight-related in a way.
  
• Gas Envelopes—The defining characteristic of a doomed Presidential campaign. Can be filled with hot air, helium or hydrogen and can be built with or without an internal structure.
  

Finally there's other subassemblies that show up on various vessels:

• Open Mounts—These are effectively places where certain pieces of equipment are strapped to the outside of a vehicle. This provides effectively no armor, but allows the equipment to cover a wide arc or full circle rather than one direction. The radar on a ship, a machine gun on a tank or anything outside of the vehicle would count as an open mount.
  
• Superstructures—This covers things like the deckhouse on a ship. If there's something that's sticking off your vehicle that you can't really classify as anything else, odds are it's a superstructure or a pod.
  
• Pod—This is normally used to house extra equipment outside of the body of a vehicle like engines on an airplane. It's also possible to use these as outriggers on a boat or external fuel tanks. Detachable equipment pods are also ultimately pods.
  
• Masts—Tall wooden or metal poles used to either hang sails from or to attach open mounts for sensors. There can be up to six masts on a single vehicle, and there are rigging options ranging from sailboat or viking longboat to ship of the line.
  
• Turrets—Rotating superstructures that give the directional flexibility of open mounts while still protecting the mounted equipment. Most commonly seen with guns although a radome is sort of like a turret for a radar. These can also be made to pop up for unpleasant surprises and aerodynamic advantages. Finally, this is normally used to model the head of a giant robot.
  
• Arms—Limbs used to manipulate things.
  

Body Features

Vehicles can also have various features which aren't reflected in any single component or subassembly.

• Flotation Hull—Anything that's going to float in water is obviously going to at least need a flotation hull. This doesn't make the vehicle particularly fast in the water or even assure that it's buoyant enough to float. Those issues are dealt with separately to allow for full fidelity to the source material of Magic Schoolbus campaigns.
  
• Submersible Hull—This allows a vehicle to both dive and surface. Doesn't allow the occupants to breathe, but the boat's gonna be just fine.
  
• Hydrodynamic Lines—Like aerodynamics for water. This is what you want if you're in need of an actual boat. Hydrodynamic features are measured in fineness. How fine the lines are determines how easily a hull slices through the water, with supertankers being somewhat on the opposite end of the scale from racing yachts. These don't help as much underwater but still they're better than nothing.
  
• Submarine Lines—These are specialized hydrodynamic features for optimal underwater performance at the cost of surface performance.
  
• Catamaran/Trimaran Hull—Double/Triple-hulled boat designs giving great stability.
  
• Streamlining—Like hydrodynamics for air. This comes in various levels that are restricted by particularly non-aerodynamic features such as masts, tracks or motorcycle seating.
  
• Lifting Body—Literally anything will fly if you strap a big enough engine to it. This feature is for vehicles which are specifically designed to get extra lift from their bodies like the space shuttle.
  
• Slope—This is messy enough to warrant its own piece.
  

Slope

In order to provide better protection from attacks in a certain direction, armor can be sloped away from the vertical in that direction. If you've ever wondered how in World of Tanks high tier Soviet tanks will bounce just about anything, it's because they've got crazy slope. This is determined separately for each of the four directions of the vehicle (front, back, left, right) and can be either 0, 30 or 60 degrees. Online supplements allowed any angle at all, although 75 degrees and beyond were pretty implausible. More slope means a higher chance of bouncing stuff at the cost of more space wasted.

That's bad enough, but it's possible to have different slopes for different surfaces of every single turret and superstructure. And while we're calculating all those slopes separately, it's possible to have different armor thicknesses for every single face of every single subassembly! Still not enough? You can layer different types of armor so you end up with some armor resisting armor piercing damage, some armor being ablative and some armor being nonrigid because why the fuck not!? However that's for a future section.





5 pages down, 195 to go.

edit: Didn't finish a sentence in there, whoops!

design texts

posted by 1337JiveTurkey Original SA post

GURPS Vehicles: Design (cont'd)

Components

Components are the internals of the body and subassemblies and help with details such as moving, seeing things, shooting things and figuring out where you are. Basically if you want a vehicle to do just about anything, you need a component to help it along. The statistics of interest for every component are their weight, volume, cost and power requirements. They're all pretty self-explanatory.

Every component needs to be located in some part of the vehicle. For most vehicles this doesn't really matter, but giant robots may care. After that, the book goes into the various types of components available for a vehicle in general like propulsion, lift, weaponry, instruments and the like.

Space (and not the outer kind)

The next part deals with calculating how much space everything takes up. For starters that includes the components the vehicle has plus minutiae like a rocket's fuel tanks or a blimp's gas envelope. After that comes a whole lot of extra space calculations. To get a better feel for phonebook-like nature of this section, feel free to listen to listen to this while reading along.

Access Space

Some components need more space than they take up by themselves. All propulsion systems and power plants need to have additional access space in addition to the space that they take up. This works out to the same amount of space that the component itself actually takes up. For vehicles that are intended to be used for a long period of time, the minimum access space doubles. It's sort of hard to drop the engine on a freighter to fix a malfunctioning oil pump. Access space isn't required in a few cases: If the vehicle's unmanned or is a battlesuit, harness or cycle, then no space is needed. Also if the component's in a pod like a jet engine on an airliner, it doesn't need any space.

Some subassemblies require extra space in whatever they're attached to. A turret or open mount needs space to house the mechanisms for its rotation. Pop-up turrets, retractable wheels and the like also need space to store themselves. Retractable wheels determine their volume based on the size of the body so the book saves some time and sanity by making them take up a flat percentage of the body volume.

Body Features and Space

Body features also take up effective space because they prevent everything from being laid out in the most compact way possible. A hypersonic jet is going to be long and narrow for instance. Slope also takes up effective space depending on how much was used. Just making the front of a turret 30 degrees would add 10% to the effective volume of the turret. Making every side sloped at 60 degrees multiplies the effective volume by five since it's now a giant armored pancake.

Space for the Sake of Space

Just about every vehicle is going to have some space set aside for cargo as well as some space which is simply empty. Beyond their in-game uses, cargo space and empty space are both great for rounding out numbers nicely. If a vehicle's 97.3 cubic feet, then just add 2.7 cubic feet of empty space and call it a day. Cargo space also gives weight flexibility since you can just say the trunk is 22.8 cubic feet and allows 373 pounds of junk to be stored in it.



Next up: GURPS Geometry Homework

design docs

posted by 1337JiveTurkey Original SA post

GURPS Vehicles: Design (further cont'd)

At this point we've got an idea of the basic structure, components and size of the vehicle-to-be. (Yeah, I haven't gotten to what said components are but I'm staying mostly faithful to the book's sequence)

Surface Area

The surface area is calculated on a per-subassembly basis and then we add it together for the rest of the calculations in the chapter. There's a table given for the smaller volumes, but the general formula is just the cube root of the volume squared and then multiplied by 6. Additional modifiers are provided for some subassembly types such as wings or rotors, but not for everything that would affect the surface area of the vessel.

This is actually a pretty odd way of doing things because there are a lot of things that affect the surface area more than they affect usable volume. Stuff like sloped armor, aerodynamic streamlining and most of what we did last update would obviously qualify but it doesn't. By putting it with volume modifiers, a streamlined car would (if sealed up) float better than a non-streamlined car. In fact the hydrodynamic lines modifiers also modify the buoyancy of a ship in terms of pounds per cubic foot of displaced water because of that effect.

The results if we just make a vehicle consisting of nothing but a (presumably arbitrarily shaped) 1 cubic foot water tank:

• 1 cubic foot water tank—Takes up 1 cubic foot of space, displaces 1 cubic foot of water.
  
• 1 cubic foot water tank in a wing—Takes up 1 cubic foot of space, displaces 1 cubic foot of water, has 10 times the surface area as the first.
  
• 1 cubic foot water tank, radical aerodynamic streamlining—Takes up 1.4 cubic feet of space, displaces 1.4 cubic feet of water. This can be made to float when completely filled with water.
  
• 1 cubic foot water tank, very fine hydrodynamic lines—Takes up 1.3 cubic feet of space, displaces .94 cubic feet of water by mass. Unlike the previous, this one will sink.
  
• 1 cubic foot water tank, 60 degrees slope on 4 sides—Takes up 5 cubic feet, displaces 5 cubic feet of water. A human being could stand on top of this thing and it would still keep floating even when filled with water.
  

Structure

Every vehicle needs some sort of structure to hold it together and we're finally getting around to adding that.

Structures range from super-light to extra-heavy. Something like a realistic spaceship is going to have a super-light structure, while a tank is extra-heavy. On a different axis, it's possible to pick how high quality the materials that make up the structure are. These range from very cheap to advanced to allow for options like concrete boats or ultra-lightweight satellites.

These multipliers help determine how heavy the structure is per square foot of vehicle surface area as well as how expensive it is. This has the same problem as I mentioned in the previous section since structural weight is more based on the volume of a vehicle more than the surface area. The overall structural price is also affected by certain factors like the vehicle having streamlining or wings. This allows for regular cars to be fairly cheap while jet fighters are still ludicrously expensive.

If that's not complicated enough, you're allowed to have different structural options for different subcomponents to allow for a very strong passenger compartment and the rest of the vehicle being made out of chipboard.

Then come the options related to structures:

• Robotic—This allows a computer to control the functions of the vehicle directly. For something like a UAV or a car that can drive itself, this is necessary.
  
• Responsive—This is for a body that changes its structural shape in response to loads, making it more maneuverable.
  
• Biomechanical—A combination of organic and mechanical components capable of healing damage slowly. This can take years to actually heal anything completely.
  
• Living Metal—A much higher tech version of biomechanical structures. This is pretty much what happens if you built a car out of the T1000. It doesn't have to bother with details like doors since the nanobots that make up the structure can just move out of the way directly.
  
• Compartmentalization—This allows the interior of a vehicle to be broken into several self-contained compartments like as seen on a battleship, tank, submarine or the like.
  
• Improved Suspension—Makes a vehicle more maneuverable and faster. Based on the size of the wheels or tracks instead of the body structure. There's also Improved Brakes, All-Wheel Steering and Smartwheels which I'm just tossing in here to keep the list somewhat manageable but also allow the vehicle to drive better.
  
• Folding Wings—Allow the wings or rotors to be folded up for compact stowage on aircraft carriers and the like.
  
• Variable Sweep Wings—Vital for the proper modeling of Tyrannosaurs in F14s.
  
• Controlled Instability—The easiest way to make an airplane go in any direction fast is to make it want to go in every direction at once, then use a computer to keep it from falling out of the sky. Common on state-of-the art fighter jets; faces potentially insurmountable regulatory hurdles in passenger aircraft.
  

armor/surface features

posted by 1337JiveTurkey Original SA post

GURPS Vehicles: Armor and Surface Features

Finally, we need to figure out what covers the outside of our vehicle. This can range from a couple of layers of furs for a Flintstones-tech tank to well over a foot of nano-constructed unobtanium for a starship. All armor in GURPS is measured by its DR and PD. PD is passive defense and increases the attacker's target number to hit. DR is damage resistance and subtracts damage from successful hits.

As a rule of thumb for people modeling real world vehicles, 1 inch of unhardened flat steel plate is 70 DR. Since damage is done using d6s, this is about enough to stop 20d6 half the time. This isn't mentioned directly in the rules, but it's useful to know in order to get a good sense of scale. Of course not everything is going to be covered in inches of steel, so obviously being GURPS Vehicles, we've got options .

• Wood—The cheapest and most available armor material. This ranges in quality from cheap pine to expensive teak or hickory, but all are flammable and you don't see much technological improvement. However once TL10 rolls around, advanced wood armor made from trees genetically engineered to be as strong as steel becomes available. I don't think anyone's ever actually used it, but it's still there.
  
• Metal—This represents increasingly advanced alloys from the bronze age to the far future, but doesn't really become practical until TL5, the industrial revolution. Metal is the standard armor and doesn't have any particularly special rules about it.
  
• Composite—This material includes all the types of high-tech reinforced composites seen in aircraft and high-end cars today. Composite armor is much stronger by weight than metal, but it's far more expensive. Additionally composite armor protects about half as well against collision damage as metal.
  
• Ablative—Ablative armor ablates or gets blown away to protect the vehicle from an attack. This makes it much lighter per DR of protection, but sustained attack will eat through the armor eventually. Ablative armor is also flammable but can be coated with a thin ceramic layer to prevent that.
  
• Nonrigid—Nonrigid armor is some sort of cloth stretched over the vehicle's structure. Depending on the tech level it can be leather, canvas, kevlar or some advanced mono crystalline fiber weave (monocrys). Obviously nonrigid armor is absolutely crappy protecting against collisions. It's also got all of the same limitations as chain armor from the other GURPS rulesets: Explosions and crushing attacks allow 1 hit to get through on any 5-6 damage die rolled and DR against impaling attacks is 1. So why deal with all that crap? It's lighter per point of DR than even ablative armor.
  
• Reflex—A type of nonrigid armor from GURPS Ultratech which can turn itself rigid in anticipation of an attack. This makes it ludicrously expensive but against slow attacks like giant robots punching, collisions and the like it protects like very lightweight metal armor. Against guns it works most of the time, rail guns a bit less, and lasers are just hopeless.
  
• Laminate—The sort of stuff used on modern main battle tanks, engineered to provide twice the protection against HEAT attacks. Since HEAT cuts any armor's protection by 90%, this is obviously a big deal. On a protection-to-weight ratio, laminate is equal to composite and it doesn't have the penalty to collision damage. Only problem is that it costs up to $100 a pound and tanks can carry thousands of pounds of armor.
  

Making it More Complicated

So if you remember previously where we included a separate armor slope for every face of every subassembly? 30 degree slopes increase the effective DR of a location by 50% while 60 degrees doubles the DR. However you're also allowed to just put a different amount of armor on every single face of the vehicle. This can save tremendous amounts of weight on something like a tank which doesn't need as much armor on the bottom as on the sides. The downside (or upside depending on your mindset) is that you've got to calculate a separate armor value for up to a dozen different spots on the vehicle.

Still not enough? You're also allowed to layer armor of different types. For instance since nonrigid armor lets damage through a lot of the time, adding a backing of some cheap rigid armor as a backstop is often a good idea. Medieval warfare used soaked hides on top of wooden siege equipment extensively. Another option might be putting a layer of armor on top of ablative armor to soak small amounts of damage and let the ablative take the big hits. One difficulty is that if the ablative armor gets totally eaten away, any layers on top of it are also destroyed.

Want even more? You can also have gun shields and armored skirts to provide partial armor for certain otherwise unarmored locations. Open frame armor turns the armor on a location into a roll cage-type structure. Boats, submarines, spacecraft and the like aren't able to use this for various reasons. To top it all off, you're also allowed to just armor the crap out of individual components to protect them against critical hits and I guess you could apply all the rules we've covered previously to that armor.

Vision

There are optional rules for how easy it is to see out of the vehicle. The visibility is determined at this point since it's usually related to the amount of armor provided. For instance tanks have terrible vision compared to cars, but there's not a big windshield to put a shell through. Not using windshields is presumably some of the advanced technology lost between now and 3025 in the Mechwarrior universe.

Surface Features

After the armor comes the various surface features of the vehicle. This includes waterproofing, sealing and a variety of component-like options we'll cover later.

Statistics

At this point the vehicle is complete and it's time to calculate all of the relevant statistics. For all the crazy complexity, many of the stats are exactly the same as for individuals. The structure determines the HP of the vehicle by location and the HT score is based on the HP per ton. The size modifier is the same as used in creature combat. There's also stuff like loaded and submerged weights plus an entire chapter of performance statistics, but for now we're done.



AND THAT'S IT FOR CHAPTER 1!

propulsion/lift systems

posted by 1337JiveTurkey Original SA post

GURPS Vehicles: Propulsion and Lift Systems

Naturally a vehicle in order to count as such requires some sort of motive power rather than the party just standing behind it and pushing. Or not if you decide to use harnesses . Being GURPS Vehicles, standing in front of it and pulling is not only supported but there are increasingly technologically sophisticated options. For those who aren't so much interested in purely technological solutions, the book helpfully points out that zombies, golems and robots are also possible alternatives to your standard draft animal.

Rope Harness—It's a rope tied to whoever or whatever is pulling the vehicle. Multiply the animals' combined strength scores by .0075 to get the effective motive powers, so an army of 50 peasants with standard 10 ST each will produce about 3.75 kW of barge-hauling power.
Yoke-and-Pole Harness—It's a pole attached to a rigid collar, rather than what's effectively a leash. Multiply the animals' combined strength scores by .01 to get the effective motive power.
Shaft-and-Collar Harness—Same as before, but now it actually distributes the load across the draft animal's shoulders rather than across its neck. This has a .015 multiplier.
Whiffletree Harness—Strictly speaking it's a lever for dividing the load evenly between two draft animals, but I won't complain about the .02 multiplier.

These have their limitations. Naturally they can't be used in deep water without teams of draft dolphins, so alternatives like oars are required. Oars are more efficient than even the best dolphin teams and get a efficiency boost at higher tech levels due to improved biomechanics. On the downside, collision damage to the side of a vessel with oars disables an oar for every 10 points of damage the vehicle takes and deals 2d6 damage to the rower. For designers not wanting to deal with feeding and housing hundreds of rowers, sails are a popular alternative.

Square Rig—This is your standard big rectangular sail seen on galleys and longboats, both notable in that they carried lots of rowers because the sails suck unless the wind is blowing perfectly.
Fore-and-Aft Rig—The type of sail seen on sailboats, dhows and xebecs. The last one is mainly worth remembering for Scrabble.
Full Rig—A multi-mast configuration with multiple square sails hanging from yardarms and triangular jibs for control. This isn't quite as maneuverable as a fore-and-aft rig in theory but the sheer amount of sail area makes up for it.

Sails are rated by the number of square feet that they cover which is proportional to the square of the average mast height, with the maximum mast height being some function of the volume of the vehicle. If those options aren't enough, it's also possible to have aerial sails for flying ships and synthetic sails or bioplas (ultra lightweight, regenerating material) sails for high tech ships. Not included in GURPS Vehicles but found in some of the supplements are rigid sails and powered sails.

Powered aquatic propulsion comes later in the chapter, but since I'm already covering sails and oars, might as well get it out of the way as well.

Paddle Wheel —I guess this is in here for completeness or GURPS Mark Twain.
Screw Propeller —Bog-standard propeller like you'd see on any modern ship.
Ducted Propeller —Propeller with a shroud to increase its efficiency and make it more silent.
Hydrojet or MHD Tunnel —Like seen on jetskis and other vessels which operate in very shallow water. MHD Tunnels are silent but only operate in saltwater.

Now on to ground drivetrains, or at least dedicated ground drivetrains. Nothing really says that you can't have a wheeled vehicle with an Orion engine other than those jackbooted thugs at the EPA.

Wheeled —Either plain or all-wheel drive , these are pretty much what they sound like.
Tracked —For tanks, halftracks and skitracks. Heavier, less power efficient but much better on uneven terrain.
Legs —For giant robots, small robots and other impractical designs. On the plus side this does really well with uneven terrain.
Flexibody —Let's face it, sometimes legs are just too practical. Giant snake robots are there for when you want something that will never get off the drawing board in a million years.
Magnetic Levitation —AKA maglev is a technology used to cause trains to hover inches off of a track using magnetism and enormous amounts of cash. The game estimates maglev track at something like $4 million/mile while in practice it's closer to $40 million/mile.

Aerial propulsion is similar in that it's got a variety of options.

Aerial Propeller —Your bog standard airplane propeller. Occasionally used by archaeologists for killing Nazis.
Ducted Fan —Used on blimps, hovercraft and the Brooklands EA7 Optica due to improved efficiency at lower speeds. These can also be used with hoverskirts to improve their efficiency when pointed downwards as part of a hovercraft.
Turbojet —Relatively lightweight but fuel inefficient jet engines used in many older aircraft.
Turbofan —Fuel efficient but heavier jet engines that have pretty much replaced turbojets.
Ramjet —Jet engines without any form of turbine that produce lots of thrust at extremely high speeds but not at speeds below 400 mph.
Turbo-Ramjet —A turbojet that can transform into a ramjet in flight. Turbofans still leave this in the dust as far as efficiency goes, but this makes hypersonic flight feasible if not practical.
Hyperfan —In spite of the name, it's just a turbofan that runs on hydrogen. Efficiently mind you, but I wouldn't just go throwing around such nomenclature willy-nilly.
Fusion Air-Ram —A fusion-powered jet engine that heats the atmosphere passing through it with a fusion reactor embedded in the engine. Able to run for years nonstop in any atmosphere, if there's a jet engine worthy of the name hyperfan, it's this.

Sometimes you don't just want aerial propulsion but also want some lift as well. All of the following provide lift and most also provide with some forward thrust.

TTR Rotor —A helicopter rotor on top of the vehicle along with a rotor on the tail in order to keep the vehicle from spinning out of control.
CAR Rotor —A pair of contrarotating coaxial helicopter rotors together keeping the vehicle from spinning. Mainly used in old Soviet designs.
MMR Rotor —Two or more helicopter rotors not mounted coaxially like on transport helicopters. With a bunch of other requirements, this can also serve as the core of a tiltrotor system.
Ornithopter —Flapping wings for designs looking for a touch of the impractical. Not actually all that bad at higher tech levels with very small designs. If the lift is high enough an ornithopter can hover, but even if they can't ornithopters can fly very slowly due to the reduced weight in their stall speed calculations.
Lighter-than-air Gas —Helium, hydrogen, hot air or whatever in a big bag.
Levitation and Contragrav Generators —A variety of options for just saying screw it, this thing flies. These include magic enchantments, antigravity pastes, UFO propulsion, lifting gasses with negative density and the like.

Finally, space travel stuff.

Solid Rockets —Big steel tubes full of stuff which is borderline explosive.
Liquid Rockets —Rocket engines of the sort you'd expect to see on a modern spaceship. This uses a generic rocket fuel but there are supplemental rules for every bizarre combination of propellants that you can dream up. Hydrogen and RFNA? Why the fuck not?
MOX Rockets —Rocket engines using liquid oxygen plus some metal powder. Not particularly efficient but it's possible to mine the fuel in space.
Ion Drives —Extremely fuel efficient but low thrust designs that take months or years to get any appreciable amount of speed going. They also require something around 650 kW per pound of thrust.
Fission Rockets —Rockets using a built in fission reactor to heat water into (mildly radioactive) steam. The bigger impediment to using these rockets everywhere is their comparative lack of thrust.
Fusion Rockets —Fission rockets but without the radiation, much better fuel efficiency and low enough weight that they can be used as substitutes for conventional rockets.
Optimized Fusion Rockets —Instead of using water, these heat up much smaller amounts of hydrogen. This is the equivalent of an ion engine but even more efficient and without the power requirement.
Antimatter Thermal Rockets —Dumps tiny amounts of antimatter along with lots of matter into the combustion chamber, heating up the matter that doesn't get annihilated and pushing it out the back. Available surprisingly early although the costs of getting the antimatter and containing it are a different matter entirely.
Antimatter Pion Rocket —A more sophisticated drive that produces ion engine level thrust but at extremely high efficiencies approaching theoretical limits.
Reactionless Thrusters —You know those theoretical limits? Well screw 'em. Reactionless thrusters just sacrifice kilowatts to the gods of Go Fast and suddenly your spaceship is moving in the direction you want.

There's also a couple of options which are destined to remain science fiction. Orion Engines use a big armored plate strapped to a shock absorber on the back of the vehicle. Once a second or so the vehicle launches a nuclear bomb behind itself and sets it off, pushing the vehicle forward. Yes, someone thought that this was a Good Idea, enough to fund it for a short while in the 1960s.

Lightsails are completely different from normal sails and used for space ships, using the pressure produced by the solar wind to push the vehicle along. Seeing as that the thrust is measured in pounds per square mile of sail area, this won't get you anywhere very fast. At higher tech levels, it's possible to have up to 360,000 square miles of light sail which is still painfully slow, (especially as you get further and further from a star) but it's viable in a very academic sense. At least moreso than ion engines.

There's also options for faster than light travel, although not all of the options are going to be available in any campaign. Which are available depends more on the feel that the GM wants to convey than anything else.

Hyperdrives are an option for moving faster than the speed of light by jumping to hyperspace where it's possible to travel multiple parsecs per day. While in this space, the vehicle isn't capable of interacting with the rest of the universe. It takes a huge amount of energy to make the initial jump but staying in hyperspace is relatively cheap. Warp Drives are effectively engines that allow the vehicle to travel faster than the speed of light while remaining in interaction with the rest of the universe. They don't require any energy to make an initial jump to hyperspace, but they do use much more power to operate over a sustained period of time. Jump Drives allow jumps between two ends of a wormhole effectively instantaneously but require a massive amount of energy to operate and only work in specific locations. Teleporters are jump drives without any of the pesky limitations. Parachronic Conveyors are plot devices for jumping between alternate dimensions.