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Guest Ron Freimuth

NASA EngineSim

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>Probably most of you already know it, but here is an>interesting Jet Engine Simulator designed by a NASA engineer>(requires Java):>>http://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.html>Marco One can also DL the java simulations and run them off line. I just noted 'turbo.java' contains the Enginesim source code. The Sun java development kit would be required to recompile it. I checked the Enginesim GE CF6 again, noting that "air flow" hit a limit before the throttle and thrust hit 100%. Normalized "Air Flow" is set in TBL 1507 of the AIR file. It also tends to saturate at higher CN1 values. Enginesim shows that thrust goes to zero around '55% throttle'. In fact, it should go negative. Ram drag subtracts from Gross Thrust, so when the former is equal to the later, thrust would be zero. FS thrust can go negative at higher FL's when the throttle is pulled back. Formulas for Air Flow, etc. are displayed in my Aired.ini Info. But, not enough detail unless one understands a bit more. Note EngineSim shows how TSFC varies with altitude and Mach. FS only lets one set a constant SFC: TSFC = 2*fuel_flow_factor. Since turbines such as the CF6, RB211, etc. run about 0.58 in cruise, I set fuel_flow_scalar to 1.16 in my B747-400 aircraft.cfg. Other turbines run higher; the old JT8D runs about 0.82 in cruise, so fuel_flow_scalar should be near 1.64. Any Jet aircraft.cfg file that uses the default fuel_flow_scalar = 1.00 is clearly modeled poorly. At the default low TSFC of 0.50, drags have to be set higher than real to get approximate fuel flow. Not surprising the MS jets all use the default, showing again that they are poorly modeled. RAF

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