David Megginson wrote: > Andy Ross writes: > > The way the code works is that it matches some performance curves I > > got out of McFarland for a 707 engine. The turbofans on the 747 > > actually won't be too terribly far off in their thrust performance, > > I'd think. > > This is probably a dumb question, but are you sure that your 707 > numbers were for a turbofan engine and not a turbojet engine? I think > that many of the 707 models shipped with turbojets.
The 707 did indeed have turbojets. But in the flight regime of a jetliner, there's not a whole lot of difference in thrust performance between a jet and a fan. The numbers (fuel consumption, N1/N2 speeds, etc...) will be different, of course, but their qualitative behavior is basically the same. There is provision in the configuration files for scaling the output numbers to a range appropriate for a given engine. Jets have higher TSFC and EPR values than fans, so they get bigger numbers in their configuration files. Where jets and fans differ most is in the transsonic regime. The higher exhaust pressure of a jet leads to higher exhaust velocities, and thus less thrust dropoff at speed. YASim tries to model this (I don't know how successfully) with an exhaust-speed tunable. [At supersonic speeds, lots of stuff is happening that won't be modelled well by the current code at all. The F-15C that I did for Gene, for example, was reading 130% N1 RPM at mach 2 or so. :)] In keeping with the YASim philosophy, the point is not to mimic any single engine perfectly (by the use of giant lookup tables, for instance), but to come up with a model that works well qualitatively for any engine. Andy -- Andrew J. Ross NextBus Information Systems Senior Software Engineer Emeryville, CA [EMAIL PROTECTED] http://www.nextbus.com "Men go crazy in conflagrations. They only get better one by one." - Sting (misquoted) _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
