Echo38 Posted September 18, 2012 Posted September 18, 2012 About the O2 supply chart on pages 45 and 46 of the DCS: P-51D manual--why are supply times highest at 40,000 feet? I would expect supply times to lower as your altitude increases, as there is less atmospheric oxygen up there. No?
Nate--IRL-- Posted October 3, 2012 Posted October 3, 2012 I have wondered about that myself. It is the same chart in the real P-51 manual IIRC. Nate Ka-50 AutoPilot/stabilisation system description and operation by IvanK- Essential Reading
159th_Falcon Posted October 3, 2012 Posted October 3, 2012 Because of the pressure difference between the oxygen bottle and outside are being greatest there? Or in case of a chemical burning cartridge (or however there called) Because there is less oxygen at altitude it burns slower? [sIGPIC][/sIGPIC] The keeper of all mathematical knowledge and the oracle of flight modeling.:)
Echo38 Posted October 3, 2012 Author Posted October 3, 2012 (edited) I have wondered about that myself. It is the same chart in the real P-51 manual IIRC. Another funny thing about a different chart in the manual: takeoff and low-blower military power both have the same MP, RPM, blower, and mixture control settings, but the horsepower ratings and fuel flows differ. What causes the increase in fuel flow and horsepower between takeoff and military power at low blower? Since everything's set the same, the only differences I can think of are increased engine temperature and reduced fuel quantity. Oh, and maybe fuel volume decreases due to ambient temperature decreasing with altitude? But I can't think of how any of those could increase fuel flow. Unless perhaps it has something to do with the left wing tank and the vapor/fuel return line? I don't really understand the latter ... Because of the pressure difference between the oxygen bottle and outside are being greatest there? Or in case of a chemical burning cartridge (or however there called) Because there is less oxygen at altitude it burns slower? But a human's oxygen need remains constant with altitude, right? And the ambient oxygen amount decreases with altitude, so I would expect the internal oxygen demand to increase with altitude. I also don't understand why pressure differential would make any difference with this. Edited October 3, 2012 by Echo38
MTFDarkEagle Posted October 3, 2012 Posted October 3, 2012 hmmm very interesting.. As echo I'm unsure if the pressure differential has anything to do with this, because if I recall correctly, the P-51's cockpit is not pressurized.. Lukas - "TIN TIN" - 9th Shrek Air Strike Squadron TIN TIN's Cockpit thread
159th_Falcon Posted October 3, 2012 Posted October 3, 2012 Ok let me explain a wee bit further. Here down low on terra firma we have a pressure of 1000 units. (just random arbitrary value) So the bottle can flow oxygen to the mask until the pressure inside the bottle is also 1000 units. No pressure difference is no flow. Up high at 40 000 feet, pressure is lower, say 600 units. So now the bottle can provide an oxygen flow for longer, down to 600 units inside the bottle. Well, in theory ofcourse. [sIGPIC][/sIGPIC] The keeper of all mathematical knowledge and the oracle of flight modeling.:)
KLR Rico Posted October 4, 2012 Posted October 4, 2012 I think falcon is on the right track, but in a different way... It's not the pressure inside the bottle that's making the difference, but inside the mask. It would take 1000 units to fill the mask at sea level pressure, but only 600 units to fill the mask at altitude. The volume of air is unchanged, but the density is decreased. The opposite of this happens when scuba diving. On the surface, your air is supplied at 1 atmosphere (it has to match the surrounding pressure), but for every 33ft, pressure is increased by one atmosphere. At 66 ft, you're breathing air supplied at 3 atmospheres pressure, and you'll get 1/3 of the breaths from the tank than you would have had at the surface. i5-4670K@4.5GHz / 16 GB RAM / SSD / GTX1080 Rift CV1 / G-seat / modded FFB HOTAS
159th_Falcon Posted October 4, 2012 Posted October 4, 2012 Thanx, looks like were heading towards an answer. :thumbup: [sIGPIC][/sIGPIC] The keeper of all mathematical knowledge and the oracle of flight modeling.:)
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