03-10-2021, 09:16 PM | #11 |
Join Date: Aug 2007
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Re: Air performance
All numbers about real world aircraft performance are simplifications in one way or other. For example check out Operation Sageburner at the link below.
The Navy was setting records and putting its' thumb in the USAF's eye while they were the only ones with the brand new F-4 Phantom. One of those digital thrusts was setting a new low altitude speed record. That was just over 900 miles per hour at ana ltiude of no more than 125 ft above sea level. I've heard they went as low as 50 ft. The usual number given for an F-4's top speed is as high as 1600 mph depending on altitude and many other factors. Check the World Records section. https://airandspace.si.edu/collectio...m_A19690213000 ....and if some of those numbers are surprisingly higher than what you find for an F/A-18 the F/A-18 wasn't designed for supersonic sprinting. It's a seldom used capability in combat aircraft and the amount of experience between the design periods for the F-4 and the F/A-18 have shown that.. Speed, engine power and other things depend heavily on many factors. That 2500 is probably a reasonable number for a hypothetical mature TL8 follow on to the TL7 SR-71 that would be using turbo-ramjets or scramjets as the first part of an orbital flight plan.
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Fred Brackin |
03-10-2021, 09:36 PM | #13 |
Join Date: Aug 2007
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Re: Air performance
Doing a truly accurate formula for winged aircraft with airbreathing engines is too complex for anything except a highly capable supercomputer program using far, far more data than any game system would supply..
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Fred Brackin |
03-10-2021, 10:40 PM | #14 | |
Join Date: Jul 2008
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Re: Air performance
Quote:
Where exciting streamlining comes in is mostly for very fast air-breathing craft with aerodynamic control surfaces. (A rocket stack could be considered pretty streamlined too, but it's a kind of boring streamlining since it doesn't really want to interact with the air at all.)
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident. |
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03-10-2021, 10:56 PM | #15 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: Air performance
Doing even a modestly accurate one is well into "don't try this without a computer" range.
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03-10-2021, 11:46 PM | #16 |
Join Date: Jul 2008
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Re: Air performance
And even if you could get an accurate max speed, it would become grossly inaccurate once you plugged it into a stat line, since in reality that maximum occurs under particular flying conditions (altitude/air pressure especially) whereas in GURPS it's treated as one number to fit all situations.
(An even slightly accurate aerodynamic flight simulator is another thing that isn't practical without a computer.)
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident. |
03-11-2021, 12:04 AM | #17 | |
Join Date: Aug 2004
Location: Binghamton, NY, USA. Near the river Styx in the 5th Circle.
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Re: Air performance
Quote:
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Eric B. Smith GURPS Data File Coordinator GURPSLand I shall pull the pin from this healing grenade and... Kaboom-baya. |
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03-11-2021, 01:06 AM | #18 | |
Join Date: Feb 2008
Location: UK
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Re: Air performance
Quote:
Of course. I'm certainly not expecting any great accuracy. But a different set of numbers in the air speed table wouldn't be any more complex. I'm just a bit surprised that a generic design available at any TL (7+) and any size performs so much better than most specialised real examples.
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Paul Blackwell Last edited by pgb; 03-11-2021 at 01:07 AM. Reason: Typo |
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03-11-2021, 03:15 AM | #19 | |
Join Date: Aug 2004
Location: Wellington, NZ
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Re: Air performance
Quote:
The jet engines in Spaceships have about four times the thrust they should, and about (at TL8) fifteen times the fuel efficiency. Mind you, Spaceships doesn't say whether it's making any allowances for the fuel savings from not flying at 100% power constantly. As for the top speeds, the given airspeeds in Spaceships might not be unreasonable for a non-airbreathing craft with hypersonic streamlining. Modern supersonic jet fighters are neither of these.
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Rupert Boleyn "A pessimist is an optimist with a sense of history." Last edited by Rupert; 03-11-2021 at 03:19 AM. |
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03-11-2021, 07:28 AM | #20 |
Hero of Democracy
Join Date: Mar 2012
Location: far from the ocean
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Re: Air performance
Last year I did an in-depth "down shifting" of the stats for aircraft using spaceships on my blog, trying to get stats that more closely match TL8 reality. The tweaks I made that you are interested in are as follows:
Streamlining: There is a lot more to streamlining that simply streamlined and unstreamlined. I use the following numbers as the "base speed" in the equation for airspeed spaceships gives on page 35.
Turbofan Engines: The thrust for Turbofan Jet Engines are twice as high as they should be: individual turbofan jet engines have thrust to weight ratio's of about 5, not 10 (to be honest, even that is a high number, 4 is more typical). The thrust for down shifted turbofan jets are half of their listed values. The numbers you get aren't perfect, but they are much closer.
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