![]() Then as you move right to Mach 0.5, the thrust falls as the turbine can’t deliver much ‘oomph’ due to the rapid inflow of air… like trying to climb a rope ladder while the rope is falling, trying to get thrust from an airstream always coming at you is simply an uphill battle that does not work too well. On the left, at Mach 0, you see the static thrust for each altitude. So, if you open the F-4 Phantom in Plane-Maker, go to the engines window, and then the Jet Curves tab on the right, you will be able to SEE EVERYTHING that I just talked about. Xflt nrm_shock_press_rat= xpow((gamma_p1 * sqr(M_use) ) / (gamma_m1 *sqr(M_use) + 2.0 ), gamma /gamma_m1) // //* xpow((gamma_p1 ) / (2.0 * gamma * sqr(M_use) - gamma_m1 ), 1.0 /gamma_m1) // normal shock total pressure ratio Here’s the equation for the losses across the normal shock, by the way: const xflt gamma =1.4 We simulate this with a normal shock, and the inlet efficiency gradually moves from ideal (total pressure recovery) to the worst possible (normal shock) as the inlet moves to and then past it’s maximum allowable Mach number. At some point, the aircraft speed overwhelms the inlets’ ability to accept the shockwaves, and losses occur. Planes like the F-4 Phantom, for example, take about FIVE MINUTES to get from Mach 1 to Mach 2 (a long time because the thrust only builds as the speed builds) but darn they hit Mach 2 and are still slowly accelerating! So, the faster you go, the more thrust you get! This is one reason that supersonic jet airplanes just keep speeding up, and up, and up, and up! Here is where this gets interesting: The faster you go, the higher the Mach number of air incoming to the inlet, and the more energy is available from the airstream to turn into THRUST! OK this gets good: As we move through Mach 1, we transition from the subsonic curve fit for subsonic engines to the pressure-recovery of the total energy of the airstream. So that is for subsonic inlets being dragged above their critical Mach number. the last thing you want coming into the front of your engine. No arbitrary losses above your critical Mach number, the normal shock, only a few atoms thick, slows all air that hits it across the space of a few atoms, dumping a huge amount of the incoming streams valuable kinetic energy and turning it instead into HEAT. This is pretty easy and boring and I have been doing this for years.īut here is where it starts to get good: As the inlet is dragged by an over-speeding airplane above it’s critical Mach number, normal shocks will now form across the inlet, DECIMATING the efficiency of the engine and robbing you of thrust. ![]() ![]() Here is how it works: For SUBSONIC dynamics, I curve fit maximum engine thrust ratio to static max thrust as a function of density altitude, Mach number, and engine bypass ratio. OK I overhauled and upgraded the jet engine model as well. Posted in Aircraft & Modeling, Development The LIFT from the propeller blade is referred to as THRUST. The DRAG on the propeller blade is what opposes rotation and makes them so darn hard to TURN. Well, as it turns out, there is a pretty darn cool way to do it, which is going into X-Plane 11 Beta-4: A spinning prop is just a spinning pair or trio or quartet of wings (as X-Plane has long understood) and those wings have LIFT and DRAG. ![]() X-Plane has historically done an excellent job of estimating the THRUST of propellers, typically to within just a few percent… but what about the SPIRALING SLIPSTREAM? This has been an area where X-Plane has been much weaker… I just don’t see any good solid references for determining the spiraling slipstream angles for propellers…Īnd it’s a real shame because the spiraling slip-stream hitting the vertical stab is so responsible for the left-turning tendency in single-engine props.īUT, can we do better? How would we estimate the slipstream angle, exactly? OK the new engine modeling for X-Plane 11 is great, but what good is an engine to us pilots without a propeller?
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