04-29-2018, 12:16 PM | #1 |
Join Date: Nov 2004
Location: Niagara, Canada
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[Vehicles] Low-grav, high-pressure aircraft
I'm toying with a setting resembling John Varley's "Gaea": a weirdly-living wheel-type space station, 1300 km in diameter and 250 km wide. ( http://ammonra.org/gaea/ has some nice pictures.) On the interior "surface", the centripetal acceleration is close enough to 0.2 gravities, and the pressure close enough to 2 atmospheres to just use those numbers.
Vehicles Expansion 2 gives a formula for stall speed in different gravities and pressures, and I'm guessing that in most Vehicles formulas, Loaded Weight refers to "GURPS Vehicles Weight" multiplied by the local gravity... but I'm not quite sure how I should adjust drag for pressure. Anyone know what math is involved? (I plan to use a Hard Science/no-superscience lens, and a biotech-oriented untransistorized steampunk approach wherever feasible. Eg, making anything made of metal more expensive - probably a blanket x10 cost, without going into details of monopolies and imports. Similarly, hydrogen is going to be a lot cheaper than helium as a lifting gas; and if anyone does put together a combustion engine, alcohol's going to be a cheaper fuel than petro-products, given how easy it is to distill on demand. My first goal once I have the right formulas is to try to put together stats for an ornithopter for a SizeMod -1, ST 10 pilot, made of wood, using a muscle engine; and to try and get it as light as possible.)
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Thank you for your time, -- DataPacRat "Then again, maybe I'm wrong." |
04-29-2018, 12:40 PM | #2 |
Join Date: Aug 2007
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Re: [Vehicles] Low-grav, high-pressure aircraft
Double pressure equals double drag. You're pushing twice as many air molecules out of your way.
Halve 1/2D of all physical weapons too.
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Fred Brackin |
04-29-2018, 01:05 PM | #3 | ||
Join Date: Nov 2004
Location: Niagara, Canada
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Re: [Vehicles] Low-grav, high-pressure aircraft
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And I also get to figure out whether a double-pressure (but still generally human-breathable) atmosphere counts as Dense or Very Dense; and whether I should come up with some quickie system for people used to planetary gravity trying to compensate for the station's Coriolis effects and vice versa; and where on the station the cosmic rays will have the least blockage; and so on. Anyone who's got any thoughts on anything of the sort, feel free to weigh in.
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Thank you for your time, -- DataPacRat "Then again, maybe I'm wrong." |
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04-29-2018, 03:21 PM | #4 | ||
Join Date: Apr 2005
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Re: [Vehicles] Low-grav, high-pressure aircraft
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04-29-2018, 06:28 PM | #5 | ||
Join Date: Nov 2004
Location: Niagara, Canada
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Re: [Vehicles] Low-grav, high-pressure aircraft
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... Mind you, I've now just realized that I don't even know where to begin looking up how any of the stats of combustion engines (alcohol-burning or otherwise) would change in such a setting. Anyone able to chip in?
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Thank you for your time, -- DataPacRat "Then again, maybe I'm wrong." |
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04-29-2018, 07:42 PM | #6 | |
Join Date: Apr 2005
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Re: [Vehicles] Low-grav, high-pressure aircraft
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Mind, I'm not entirely certain how accurate -1 HT due to high pressure is, but given that you have to move twice the mass of air, it sounds reasonable to me. Species that evolved there would do fine, but ones that developed in 1-atmosphere environments would probably find it at least somewhat unpleasant without a pressure suit. (No clue about your other questions, though) |
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04-30-2018, 02:36 AM | #7 |
Join Date: Nov 2004
Location: Niagara, Canada
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Re: [Vehicles] Low-grav, high-pressure aircraft
I've just finished cobbling together a first draft of a muscle-powered ornithopter that actually gets off the ground. It still needs some tweaking - depending on how drag works, the max airspeed is so close to the stall speed that climbing is ridiculously slow - but I'm about to fall asleep, so I'll post what I have so far in hopes of eliciting some feedback.
-----8<----- ** Gaean Flyer * Muscle-powered ornithopter. TL6ish. Metal items x10 normal cost. * Air pressure twice normal, local gravity one fifth normal. * Pilot and personal gear: ST 10, 100 lbs. ** Wings, Standard: * TL7 ornithopter drivetrain, 0.2 kW: thrust 0.4 lbs, lift 0.8 lbs, 1.2 lbs, 0.008 cf total (0.004 cf left wing, 0.004 cf right wing), $40 * Access Space: 0.008 cf total (0.004 left wing, 0.004 right wing) * Left Wing Volume: 0.008 cf * Left Wing Surface Area: 0.75 sf * Right Wing Volume: 0.008 cf * Right Wing Surface Area: 0.75 sf ** Body: * TL6 bicycle-style Muscle Engine, for ST 10: 0.2 kW, 5 lbs, 0.25 cf, $5 * Access Space: 0.25 cf * Exposed Cramped Crew Station: 20 lbs, 10 cf, $100 * Pilot & gear: 100 lbs * Body Volume: (10.5 cf, *1.25 for streamlining, *1.025 for retractable wheels) 13.45 cf * Body Surface Area: 40 sf ** Wheels: Retractable (into body), 3 * Wheels Volume: 0.05 * BodyVol = 0.05 * 13.45 = 0.6725 cf * Wheels Surface Area: 5 sf ** Structure: * Total Area: 46.5 sf * Streamlining: Very Good * Lifting Body * Frame: TL6, Super-Light, Very Cheap (wood), Wings, Very Good Streamlining, Lifting Body: Wt 46.5 * 8 * 0.1 * 2 = 74.4 lbs, 46.5 * $10 * 0.1 * 0.2 * 10 * 2 * 1.2 = $223.20 * Folding Wings: 0.05 * 1.5 / 46.5 * 74.4 = 0.12 lbs, $3 * Armor: DR 1 nonrigid: 0.06 lbs * 46.5 = 2.79 lbs, $13.95 ** Stats: * Empty Weight: 1.2 + 5 + 20 + 74.4 + 0.12 + 2.79 = 103.51 lbs * Loaded Weight: 203.51 lbs * Loaded Weight in Gaea: 40.702 lbs * Price: 40 + 5 + 100 + 223.20 + 3 + 13.95 = $385.15 * Hit Points: Body: 41.5 * 1.5 / 10 = 6 hp. Each wing hp: 0.75 * 1.5 / 10 = 1 * Health: (200 * 6 / 203.51) + 5 = 10.9, maxed to 6 * Lift Area: 0.75 + 0.75 + (46.5*.3) = 15.45 sf * Stall Speed in Gaea (from VEx2): StreamlineFactor * (LoadedWeight/LiftArea)^0.5 * 0.6324555 mph = 7.7 * (40.702 / 14.45)^.5 * 0.6324555 = 8.17 mph * aThrust: 0.4 lbs * aDrag: (46.5 / 5) + 10 = 19.3 * aDrag if double pressure doubles drag: 38.6 * aSpeed: (7500 * 0.4 / 19.3)^.5 = 12.47 mph * aSpeed if double pressure doubles drag: (7500 * 0.4 / 38.6)^.5 = 8.82 mph * aAccel: (0.4 / 203.51) * 20 = 0.04 mph/s * aMR: (2 / 203.51) * 6 * 30 = 1.77 rounded to 2 gravities * aSR: 1 * aDecel: 2*4 = 8 mph/s * gSpeed: ((0.4/4) / (203.51/2000))^.5 * 16 = 15.86 rounded to 16 mph * gAccel: 16 mph / 16 * .8 = 0.8 mph/s * gDecel: 10 mph/s * gSR: 2 * gMR: 1.25 (0.5 when wings unfolded) * gContactArea: WheelArea/50 = 5/50 = 0.1 * groundPressure: 40.702 / 0.1 = 407.02, Very Low IV, off-road speed 1/2 = 7.83 rounded to 8 mph * Takeoff Run: (8.17 * 8.17) / (4 * 0.8) = 20.85 yards * Landing Run: (8.17 * 8.17) / (4 * 10) = 1.67 yards (Grassy areas use off-road speed, which is slightly below stall speed. However, going down a slope can increase speed above max ground speed; as long as the flyer is going down a slope of at least a couple of degrees, it can take off from grassy areas.) (Given that gAccel is higher than aAccel, it's probably better to adjust the flaps to stay on the ground until max airspeed is reached.) (Climb rate: ... very low. Whole design probably needs tweaking.) ----->8-----
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Thank you for your time, -- DataPacRat "Then again, maybe I'm wrong." |
04-30-2018, 03:20 AM | #8 |
Join Date: Mar 2008
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Re: [Vehicles] Low-grav, high-pressure aircraft
If people have lived there long enough (1000 years is more then long enough here in Earth) they would have adapted physiologically somewhat to the pressure and O2 levels. We have at least three separate high altitude, four low temperature and one diving adapted populations here on Earth.
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04-30-2018, 06:01 AM | #9 | |
Join Date: Jun 2017
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Re: [Vehicles] Low-grav, high-pressure aircraft
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A far as the effect on humans, I doubt there is much research of the long term health effects of living in a high pressure atmosphere. I would be interested to know what the effect of living at 2 atmospheres for decades would be. Is is possible to have some for of acclimation to high pressures like our bodies do for low pressures? |
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04-30-2018, 09:43 AM | #10 | |
Join Date: Sep 2007
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Re: [Vehicles] Low-grav, high-pressure aircraft
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In short, more air pressure and a higher oxygen partial pressure means more fuel you can burn with that air in the same displacement of engine. The power increase will be linear with the increased amount of air, as will the fuel consumption. The weight of the engine itself stays the same, so you've got a better power-to-weight ratio. Or you design for the same power output, but then need a smaller and lighter engine to do that job. Or look at it this way -- the whole point of a turbocharger or supercharger is to compress the air going into the engine, so there's more in the cylinders. A higher pressure atmosphere means everyone has a free supercharger installed. (You've also got higher pressure resisting your attempt to push out the exhaust, so more restriction than would be Earth-normal. So you might derate the power increase a little bit to account for that.) |
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gravity, ornithopter, pressure, vehicles |
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