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Thrust Vector and Movement Systems

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Tue, 2011-03-29 10:44

Yerameyahu Yerameyahu's picture

Thrust Vector and Movement Systems

I have a question about Thrust Vector, and movement systems in general: in what environments do they work? I didn't want to make a whole thread, but the Gatecrashing Errata thread is more dropbox than discussion. :) The core book describes this as vectored air-breathing jet/fan engines (like a Harrier), right? It also says they're used with wings for actual flight. Ignoring questions like 'jesus, how loud, hot, and oxygen-eating are these things?', I'm wondering about the Kite morph in Gatecrashing. Its description says this: "In vacuum, it can drive itself with thrust-vector nozzles." Huh? (Interestingly, this *doesn't* contradict the letter of the core rules; though many other systems explicitly say 'Doesn't work in vacuum', Thrust Vector doesn't.) In Sunward, the Sundiver also has Thrust Vector, though it mentions a "powerful electromagnetic propulsion system that allows them to skate along solar magnetic lines of force"; I assume it uses that in space, and it's more plot device than mod. A follow up question is, 'does any kind of morph flight work in vacuum?' I'm just curious. All I've seen is the Gas Jet System in Sunward, which is not a movement system. Another question, set aside above, is the relative noise/light/heat emissions of movement systems, and their consumption needs (oxygen, mostly). I know that some can specifically borrow 'internal' reserves, but we're talking about a whole lot, right?

Tue, 2011-03-29 15:15

nezumi.hebereke nezumi.hebereke's picture

Re: Thrust Vector and Movement Systems

I assume the thrust vector can also use something like compressed or expanding gases to provide thrust, in which case it would work in a vacuum. The only place it wouldn't work is high-gravity locations, where the thrust required to counteract gravity is too high (however, winged crafts may still work in this situation since, while the gravity is higher, the air density is also higher).

Tue, 2011-03-29 16:29

Yerameyahu Yerameyahu's picture

Re: Thrust Vector and Movement Systems

So, the core book is wrong, then? Fine with me. :) Is fuel storage just something that this level of tech should handwave (air-breathing or vacuum, low-g or high-g)? I'm still concerned that there are so many different situations, which I feel like call for incompatible version of Thrust Vector.

Tue, 2011-03-29 16:56

nezumi.hebereke nezumi.hebereke's picture

Re: Thrust Vector and Movement Systems

I don't know that it's wrong, just not descriptive (I only glanced at the description though, and I didn't see a 'compressed gas jet system'). Turbofans or turbojets to create atmospheric lift with a set of wings, it says. Turbofans obviously require an atmosphere, but turbojets may not, depending on how they operate. And since 'vacuum' normally also means 'microgravity', jets are all you need. There are different styles of vector thrust which will be better or worse for different applications. You can break it out if you want. It depends on how often you want to throw equipment malfunctions at your players.

Tue, 2011-03-29 17:09

Yerameyahu Yerameyahu's picture

Re: Thrust Vector and Movement Systems

I think the language is pretty clear about requiring atmosphere (and wings, for that matter, beyond hovering), but I'm happy to bend the words for that. :) Why do you mention a 'compressed gas jet system'? There is such a system for free-fall maneuvering thrusters, but it's not related.

Tue, 2011-03-29 19:54

nezumi.hebereke nezumi.hebereke's picture

Re: Thrust Vector and Movement Systems

The description says to me that it functions in an atmosphere by doing X, Y, Z. That doesn't preclude it from functioning outside of an atmosphere. For instance, the space shuttle has wings that require an atmosphere to work, but it also works in a vacuum. I bring up a compressed gas jet system because the description of vector thrust specifies either fans or jets. Compressed gas jets are jets, and unlike other jet engines we see on aircraft, they can operate in a vacuum. Compressed gas jets are one of the cheapest and most efficient methods for small craft to operate in a vacuum, so it should absolutely be included as a maneuvering system. However, since I didn't see it listed under Movement Systems, I assume it's wrapped under Vector Thrust (since, strictly speaking, that's what it is). So, ipso facto, vector thrust would seem to logically include gas jet systems and can operate in a vacuum. (Also, excepting Wings, Vector Thrust is the only flying mobility system which does not specifically say it does not operate in a vaccuum.)

Tue, 2011-03-29 20:36

OneTrikPony OneTrikPony's picture

Re: Thrust Vector and Movement Systems

I think they throw "Thrust Vector" around way too loosely. I believe that when they write 'Vectored Thrust' or 'Thrust Vector' they're trying to give some sense of the manuverability the device has. When you see that word in an EP book it helps if you first ignore your own questions about fuel/propellant/energy source and understand that what ever the application of Newtonian and Thermodynamic laws the point is that you've got the ability to direct thrust in multiple directions from a single device. So when you see 'Vectored Thrust' or 'thrust vector' you should think of a mobility system that has almost but not quite the maneuverability that a Helicopter would have in a thick atmosphere and much more maneuverability than a fixed or flapping wing would have. From a Role Play perspective when you see 'Vectored Thrust' you can assume that propulsion is supplied by *some type* of Newtonian device that provides thrust by pushing mass VERY FAST in the direction opposite the desired vector of travel. So, You can assume that any vectored thrust craft is noisy in atmosphere, bright in space and Hot pretty much everywhere. It is usually not the Stealthy option compaired to other EP tech. From a GM perspective Vectored Thrust is the most efficient form of small craft propulsion in 0G vacuum but the least efficient propulsion system in Atmosphere. So you can tell your VT flying players that they run out of Gas; (propellant/fuel/energy) faster than Winged fliers. In atmosphere, wings and lifting bodies can abate this issue. As to the actual means of producing thrust; in atmosphere Combustion and that funky electromagnetic thing would work. Out of atmosphere you'll need some type of rocket. At least that's the way I play it.

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Tue, 2011-03-29 23:13

Yerameyahu Yerameyahu's picture

Re: Thrust Vector and Movement Systems

nezumi, I can see your argument that just because Thrust Vector clearly says it's 'turbojet/fan + wings +atmosphere', doesn't mean it's *not* a totally unrelated gas thruster system -wings -atmosphere. ;) I just think that's a huge stretch of an argument. I think that if they wanted 'Thrust Vector' to include any and all systems that might fit the definition of 'vector' and 'thrust', they shouldn't have specified something like Harrier jet. I do agree that it makes more *sense* to have it mean 'basically any system of thrusters/whatever'. I still am concerned that a system for vacuum isn't compatible with one for atmo, null-g vs. 1-g, etc. The question was, 'is this an error/gaping hole?', and I thank you guys for answering, 'yes'. :D Ditto for the question, 'where is the vacuum thruster movement system?' ('missing', except for the +Freefall system).

Thu, 2011-03-31 22:13

mickykitsune mickykitsune's picture

Re: Thrust Vector and Movement Systems

By its very definition, 'vectored thrust' merely describes a system of propulsion where the thrust of an engine or jet can be adjusted along different vectors. eg. a rocket exhaust where the nozzle / cone of the thrust can be redirected along any vector in a 90-degree arc. Thats all it means. Its not describing a means of propulsion - more a means of controlling propulsion :)

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Thu, 2011-03-31 22:43

#10

Yerameyahu Yerameyahu's picture

Re: Thrust Vector and Movement Systems

Sure. Now read what the book says about 'Thrust Vector'. … Yeah. That's the point. :)

Thu, 2011-03-31 23:02

#11

mickykitsune mickykitsune's picture

Re: Thrust Vector and Movement Systems

Yerameyahu wrote:
Sure. Now read what the book says about 'Thrust Vector'. … Yeah. That's the point. :)

Yeah... they're using the words Thrust Vector to describe the movement of a modern conventional aircraft - many of which have vectored thrust capabilities. Not the best choice of names.

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Thu, 2011-03-31 23:09

#12

Yerameyahu Yerameyahu's picture

Re: Thrust Vector and Movement Systems

Nope, sure isn't. I guess the solution is either ignore the details, or break 'Thrust Vector' down into a variety of systems appropriate for specific conditions: atmo, vacuum, micro-g, 1g+, close quarters, etc. Each specific variant can cost Moderate separately. It depends on whether your game is details-light or details-heavy… and if you ever need vacuum movement systems. :)

Sun, 2011-04-24 03:07

#13

Smokeskin

Re: Thrust Vector and Movement Systems

The way to understand this is that environments have two important properties, atmospheric pressure and gravity. Propulsion systems have two other properties, lift and thrust, which might depend on atmospheric pressure. A gas jet would provide the same level of thrust in any atmospheric pressure, while a fan's thrust depends on pressure. A vehicle without lift needs more thrust than there is gravity to fly. A sports racing motorcycle can deliver about 1g of acceleration, so you need lots of power to fly without lift in normal gravity, you're not getting that from gas nozzles. Lift counters gravity, and is a function of atmosphere, and for wings also airspeed. A blimp with very low thrust can move around fine in proper atmosphere, but drop pressure even a little and it'll be grounded, while a more powerful winged plane might just have to stay above a higher stall speed. Thinking about it like this makes it a lot easier to deal with. A 0.1g gas jet that is atmosphere independant, you know what it can do. A jet fighter with 2g of thrust and lift per atmosphere, or a blimp with 1.2g of lift and 0.05 thrust per atmosphere, likewise (I have no idea if the linear relationship is true, but it works). It doesn't take much work to describe the existing systems like this. The only thing left to consider is air friction at high speed in atmosphere.