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#11
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"root" wrote in message
... And also that the same glider on Mars has to fly 10 times faster in order to obtain the same lift, balancing the same weight. But due to the lower gravity on Mars, its weight would be lower, so the normal (best L/D) speed on Mars would be less than 10 times this speed on the earth. This speed can further be reduced by reducing the wing loading, which provides some benefits on the earth that are no more valuable on Mars, like speed, which is rather to high, and penetration, which makes little sense. So it is not unbelievable that soaring may happen on Mars at speeds between mach 0.5 and 0.7. Most of that sounds ok -- except your guess at mach speeds. Where do you come up with 0.5 to 0.7 mach? Remember that as air density decreases, so does the indicated airspeed at which we reach 1.0 mach. From memory (of many hours staring at airspeed/mach indicators), on Earth: 340 knots ias = 0.8 mach at approx. 28,000 ft., while at 39,000 ft., the ias drops to 260 knots while maintaining 0.8 mach. On Mars, with an air density of less than 1% of Earth's, it appears clear to me that because mach 1.0 will be reached at a very low indicated airspeed, a conventional glider (the original post referenced a PW-5) wouldn't have a chance. On a lighter note: what a view of Mars! I live in Manhattan, and even with a clear sky, we rarely can see more than the moon. But Mars is there for anyone who chooses to look up! While crossing the North Atlantic, Mars is so bright, you almost need to wear sunglasses as it comes over the eastern horizon! Some flight attendants refused to believe me that it was Mars, they thought it was another airplane! -Chris |
#12
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"C.Fleming" wrote:
"root" wrote in message ... And also that the same glider on Mars has to fly 10 times faster in order to obtain the same lift, balancing the same weight. But due to the lower gravity on Mars, its weight would be lower, so the normal (best L/D) speed on Mars would be less than 10 times this speed on the earth. This speed can further be reduced by reducing the wing loading, which provides some benefits on the earth that are no more valuable on Mars, like speed, which is rather to high, and penetration, which makes little sense. So it is not unbelievable that soaring may happen on Mars at speeds between mach 0.5 and 0.7. Most of that sounds ok -- except your guess at mach speeds. Where do you come up with 0.5 to 0.7 mach? Remember that as air density decreases, so does the indicated airspeed at which we reach 1.0 mach. From memory (of many hours staring at airspeed/mach indicators), on Earth: 340 knots ias = 0.8 mach at approx. 28,000 ft., while at 39,000 ft., the ias drops to 260 knots while maintaining 0.8 mach. On Mars, with an air density of less than 1% of Earth's, it appears clear to me that because mach 1.0 will be reached at a very low indicated airspeed, a conventional glider (the original post referenced a PW-5) wouldn't have a chance. Sorry, your calculations with weird units don't have an obvious meaning to my metric educated mind. I never thought of indicated airspeed, only tried to evaluate the ratio of true airspeeds on Mars and the earth to ensure similar (e.g. best L/D) flight conditions. My idea was that the speed of sound, while affected by the change in conditions, should not be affected by a very important factor. The factors involved are absolute temperature, molecular weight of the gas(es) and gamma (Cp/Cv). Gamma depends only on the atomicity. While I don't know exactly what are the components of the martian atmosphere, I guess it is not methane or CO2, but rather diatomic gases with molecular weigth near O2 and N2 as found on the earth. As all this is under a square root, changes must be huge to become significative, same thing for temperature. Halving the temperature on earth only decreases the speed of sound by a factor 0.7, and this is pretty cold. So 10 times the gliding speed on the earth is about the speed of sound on the earth, if the reduction of gravity and wing loading gives a factor that overrides the change in the speed of sound, subsonic soaring may be possible on Mars. |
#13
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Mach, Knots Indicated Airspeed (kias), and Feet: weird aeronautical units?
Last I checked, those were standard on both sides of the ocean, unless you're in Russia. Indicated airspeed and mach ratios are the two most important factors to consider! The glider needs to reach a specific Indicated Airspeed in order to produce adequate lift, which in the extremely thin Martian air would be an extremely fast True Airspeed. The minimum Indicated Airspeed needed is open for debate, but it certainly is significantly faster than 40 kias, due to slow-speed-buffet limits in the extremely thin air. We are also limited by the Mach Ratio, which for a conventional high-aspect ratio glider is quite low, nowhere close to 0.85 Mach-limited swept-wing subsonic jets. So, without asking a Boeing-McDonnell-Douglas Engineer to help me with the math, I think it's pretty safe to say that the minimum speed required of our PW-5 would be significantly faster than the maximum allowable speed; Hence, our glider no worky-worky. -Chris "Robert Ehrlich" wrote in message ... Sorry, your calculations with weird units don't have an obvious meaning to my metric educated mind. I never thought of indicated airspeed, only tried to evaluate the ratio of true airspeeds on Mars and the earth to ensure similar (e.g. best L/D) flight conditions. My idea was that the speed of sound, while affected by the change in conditions, should not be affected by a very important factor. The factors involved are absolute temperature, molecular weight of the gas(es) and gamma (Cp/Cv). Gamma depends only on the atomicity. While I don't know exactly what are the components of the martian atmosphere, I guess it is not methane or CO2, but rather diatomic gases with molecular weigth near O2 and N2 as found on the earth. As all this is under a square root, changes must be huge to become significative, same thing for temperature. Halving the temperature on earth only decreases the speed of sound by a factor 0.7, and this is pretty cold. So 10 times the gliding speed on the earth is about the speed of sound on the earth, if the reduction of gravity and wing loading gives a factor that overrides the change in the speed of sound, subsonic soaring may be possible on Mars. |
#14
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I'm sure all these problems would be solved by going to a flying wing
design. Any minute now a post will appear saying the Marske Pioneer has been tested on Mars and it would not spin and got 100:1 L/D and the proof will be up on the website as soon as the Martians give back the video camera... "C.Fleming" wrote in message ... Mach, Knots Indicated Airspeed (kias), and Feet: weird aeronautical units? Last I checked, those were standard on both sides of the ocean, unless you're in Russia. Indicated airspeed and mach ratios are the two most important factors to consider! The glider needs to reach a specific Indicated Airspeed in order to produce adequate lift, which in the extremely thin Martian air would be an extremely fast True Airspeed. The minimum Indicated Airspeed needed is open for debate, but it certainly is significantly faster than 40 kias, due to slow-speed-buffet limits in the extremely thin air. We are also limited by the Mach Ratio, which for a conventional high-aspect ratio glider is quite low, nowhere close to 0.85 Mach-limited swept-wing subsonic jets. So, without asking a Boeing-McDonnell-Douglas Engineer to help me with the math, I think it's pretty safe to say that the minimum speed required of our PW-5 would be significantly faster than the maximum allowable speed; Hence, our glider no worky-worky. -Chris |
#15
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#16
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On Thu, 28 Aug 2003 17:05:10 +0000, Robert Ehrlich
wrote: . My idea was that the speed of sound, while affected by the change in conditions, should not be affected by a very important factor. The factors involved are absolute temperature, molecular weight of the gas(es) and gamma (Cp/Cv). Gamma depends only on the atomicity. While I don't know exactly what are the components of the martian atmosphere, I guess it is not methane or CO2, but rather diatomic gases with molecular weigth near O2 and N2 as found on the earth. As all this is under a square root, changes must be huge to become significative, same thing for temperature. Halving the temperature on earth only decreases the speed of sound by a factor 0.7, and this is pretty cold. So 10 times the gliding speed on the earth is about the speed of sound on the earth, if the reduction of gravity and wing loading gives a factor that overrides the change in the speed of sound, subsonic soaring may be possible on Mars. The Martian atmosphere is mostly CO2. Anyone have a number for the speed of sound in CO2 at say 220 degrees K ? Then we can do the real numbers. Mike Borgelt |
#17
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Before we get too excited about soaring on mars, does anyone know if
the planet has significant thermal convection? |
#18
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It has the largest mountain ridge in the solar system!
"Liam Finley" wrote in message om... Before we get too excited about soaring on mars, does anyone know if the planet has significant thermal convection? |
#19
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Mike Borgelt wrote in message . ..
: Now apply that to a neutron star. The Cheela disagree with you. So do the inhabitants of "The Integral Trees". Mssrs. Skilling and Richardson seem to agree with me, at least that's where I got my info, not pulled out of my ass. Take it up with them. They're only professional astrophysicists, if they're still alive. Your qualifications? ps. BS degree in electronics doesn't cut it. |
#20
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