Andy Ross wrote > > Vivian Meazza wrote: > > With these values > > > > eng-power="1140" eng-rpm="2850" > > cruise-power="2850" cruise-rpm="1359" > > takeoff-power="1100" takeoff-rpm="1359" > > > > YASim appears go into a loop and provides no output. > > These settings don't make much sense in combination. > > The "eng" setting is a maximum power (at standard sea level) > for the engine without supercharging. In this case, the > normally aspirated engine develops 1140 HP at max RPM. > > The "cruise" numbers are used to fix the propeller's maximum > efficiency peak. The propeller you are using wants to sink > 2850 HP (more than double max sea level power) at less than > half (!) of the engine's max RPM. Even with 4x supercharging > (which sounds kinda high to me, but I'm not an expert), > that's just not going to work. Are you working from POH > numbers for this engine that might be typoed or misinterpreted? > > The "takeoff" values correspond to the power and RPM > developed by the aircraft at max throttle and zero airspeed. > It's there because propellers have funny, non-linear behavior > in the very low pitch regime (when the blades are partially > stalled). The default model produces strange results here, > so the FDM allows you specify a clamp to match real-world > behavior. It's not important to the solver, or for in-flight > performance. > > I'll look into the apparent infinite loop behavior. > > Andy >
The numbers are correct, it's how I've interpreted them and where I've put them that is the problem :-) The "eng" setting: the documentation that I am using (readme YASim) indicates that it is the "brake horsepower at cruise" I presumed that this was A. The supercharged output. The un-supercharged output is un-measured and would only be a rough guess. B. At the cruise altitude. The power output at any other altitude is somewhat different. Does the model understand variations of power with altitude? Now that I know that it is the un-supercharged number, I think I can adjust the number empirically to give a reasonable value. The "cruise" numbers - typo here I'm afraid: 1140 HP would be the right number. I've changed these so many times ..... 4x was just grabbed out of the air, but since the Boost Control Valve is open in the real aircraft up to 25000 ft or so, this didn't seem to matter. I was going to adjust this number in due course to try to model the proper boost curve. The "takeoff" values. Are these the power absorbed by the propeller at propeller rpm, or the engine output at engine rpm, super- or un-supercharged? Finally, I've had some difficulty understanding the concept of using absolute pressure for the Boost Control Valve (BCV). In the real world a BCV comprises, in principle, a plate exposed to manifold pressure on one side and to the local atmospheric pressure on the other and held closed by a spring which opens at the designed boost pressure (in this case 9 psi adjustable by the pilot to allow 12.5 psi for up to 5 mins), and is thus corrected for altitude. I've been scratching through the code, and can't confirm that YASim models this behaviour. Perhaps I don't need to bother? And I haven't even tackled the constant speed propeller! I suppose that we should update the documentation to reflect these misinterpretations. Thanks for your help. We'll have a Spitfire with a Merlin engine yet! Vivian Meazza _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
