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 Post subject: Fuel/Total Mass?
PostPosted: Sat Dec 02, 2006 12:35 am 
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What is the average fuel mass ratio for ships in AVT? What about ISP?


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PostPosted: Sat Dec 02, 2006 3:58 am 
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The average fuel mass ratio is 1.16. Overall the ratio goes up with ship's mass, but there is wide variation. Mass ratios for gunboats sit around 1.09, and the highest mass ratio is the Rafik Mk. 2 with 1.23.

I know Ken has stated Isp before, but I can't for the life of me remember it myself.

Delta-V = Ve * LN[R], so we can derive it - let's go with the Wasp:

Mass Ratio: 1.114
Transit Delta-V: 105 km/s (105,000 m/s)

Solve for Ve and we get: 972,608 m/s (972.6 km/s) (or about 0.003c)

Isp = Ve / 9.8066 = 99,178s for specific impulse while in Transit Mode.

Hope this helps.

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PostPosted: Sat Dec 02, 2006 10:37 am 
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Matt, the Science Behind The Rules note in the rulebook on Rockets gives the Isp.
[quote]
THE NUMBERS BEHIND THE RULES: ROCKETS
One AV:T fuel unit is 156.25 m/s of combat velocity change, or 1G for 16 seconds. A first generation drive is defined as providing one fuel unit for 0.5% of hull mass as fuel; for a 200 hullspace frigate, this is 1 hullspace per fuel unit. Higher generation drives multiply the number of fuel units by the generation of the drive; drive generations are incremented in “10thsâ€

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 Post subject:
PostPosted: Sat Dec 02, 2006 3:31 pm 
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Ok, yeah, when I said ISP I was actually looking for Ve. I once drew up a design for a ship that weighed about 2500 tons empty with a 2500 ton fuel load and got eight G's of thrust with a Ve of 50kps, or 1 G with 500kps. I kinda wanted to see how AVT ships compare...


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PostPosted: Sat Dec 02, 2006 3:50 pm 
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Jonathan Brase wrote:
Ok, yeah, when I said ISP I was actually looking for Ve. I once drew up a design for a ship that weighed about 2500 tons empty with a 2500 ton fuel load and got eight G's of thrust with a Ve of 50kps, or 1 G with 500kps. I kinda wanted to see how AVT ships compare...


Thrust is a function of m-dot, or, basically, how dense/massive your reaction mass is on a molecular level. In general, your hard constraint is how much power you can put into the engine without it melting off the end of your ship; the lighter the molecular weight of the propellant, the hotter/faster it'll go out the rear of the ship....so a given amount of energy will use less fuel (and thus increase fuel economy) to get the same amount of delta v - it'll just do it at a much lower acceleration rate as a function of time.

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 Post subject:
PostPosted: Sat Dec 02, 2006 7:21 pm 
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Ken Burnside wrote:
so a given amount of energy will use less fuel (and thus increase fuel economy) to get the same amount of delta v - it'll just do it at a much lower acceleration rate as a function of time.

I believe you mean power, not energy ;)


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PostPosted: Sun Dec 03, 2006 3:16 am 
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Anthony Jackson wrote:
Ken Burnside wrote:
so a given amount of energy will use less fuel (and thus increase fuel economy) to get the same amount of delta v - it'll just do it at a much lower acceleration rate as a function of time.

I believe you mean power, not energy ;)

Actually, if I understand the physics correctly, I think it would be energy. Power is just how fast the energy is delivered. We actually should be saying propellant or reaction mass instead of fuel, but I was the one that started using "fuel." Do the drives in AVT use their fusion exhaust for reaction mass, or do they heat a seperate propellant?


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PostPosted: Sun Dec 03, 2006 10:32 am 
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Jonathan Brase wrote:
Anthony Jackson wrote:
Ken Burnside wrote:
so a given amount of energy will use less fuel (and thus increase fuel economy) to get the same amount of delta v - it'll just do it at a much lower acceleration rate as a function of time.

I believe you mean power, not energy ;)

Actually, if I understand the physics correctly, I think it would be energy. Power is just how fast the energy is delivered. We actually should be saying propellant or reaction mass instead of fuel, but I was the one that started using "fuel." Do the drives in AVT use their fusion exhaust for reaction mass, or do they heat a seperate propellant?


In cruise mode, it's fusion byproducts jacketed with some propellant.

In combat mode it's fusion byproducts (and more of them) jacketed with a much higher mix of propellant.

We do not define what the propellant is, the fusion reaction is assumed to be neutronic enough to force long spindly masts and plates of lead doped concrete at the base plate of the engine.

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 Post subject:
PostPosted: Sun Dec 03, 2006 3:24 pm 
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Ken Burnside wrote:

We do not define what the propellant is


I've heard unobtainium works pretty well... Have you tried that? :-D


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 Post subject:
PostPosted: Sun Dec 03, 2006 6:31 pm 
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Jonathan Brase wrote:
Actually, if I understand the physics correctly, I think it would be energy.

Then you probably don't correctly understand the physics. Minimum power requirement for a drive is 0.5 * thrust * exhaust velocity, so a higher ISp drive requires more power to give the same thrust, or more energy to give the same delta-V.


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 Post subject:
PostPosted: Sun Dec 03, 2006 8:27 pm 
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Anthony Jackson wrote:
Jonathan Brase wrote:
Actually, if I understand the physics correctly, I think it would be energy.

Then you probably don't correctly understand the physics. Minimum power requirement for a drive is 0.5 * thrust * exhaust velocity, so a higher ISp drive requires more power to give the same thrust, or more energy to give the same delta-V.

Oh... wait a minute... he was talking about the molecular weight of the propellant...
Oops...[/i]


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