Blackbird From , joined Dec 1969, posts, RR: Posted (7 years 4 months 3 weeks 5 days 7 hours ago) and read 7940 times:
Most jet-engines, especially older ones seem to run on a fixed fuel-to-air ratio regardless of altitude, and as a result fuel consumption seems to fall off significantly as you fly higher and higher, as does thrust.
My question has to do with the fact that as Mach-number increases, so does ram-air pressure, which in turn increases thrust: Does fuel consumption increase as ram-compression increases (as air pressure in the duct goes up as well)?
Tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 80
Reply 3, posted (7 years 4 months 3 weeks 3 days 1 hour ago) and read 7757 times:
Quoting Blackbird (Reply 2): I wasn't just talking about airspeeds, I was also talking about mach numbers too, technically at a high enough altitude I could be doing Mach 25 and read only 7 kts (upper edge of atmosphere)...
You need to be a little careful when you get out in the outer edges of the atmosphere...when the air gets thin enough for rarified gas dynamics to start applying (i.e. the individual atoms have almost no impact on each other) most of your fluid equations (which assume a continuum) go out the window.