Jon Berndt > > > Thanks, > > My question could be a question to Jon, Dave, and any JSB specialist. > > I just wonder, about, the opportunity to get profit of your work for > > developments on the JSB branch. The properties should be the same on > > the global FG level. > > Both FDM ->YASim ->JSBSim with a different "philosophic" approach should > > give the same end results. > > > > > -- > > Gerard > > See the FGPiston.h file in JSBSim. See the constructor in FGPiston.cpp for > exact specification in the new XML format (documentation pending). Here is > some data on what can be specified: > > Models Dave Luff's Turbo/Supercharged Piston engine model. > Additional elements are required for a supercharged engine. These can > be > left off a non-supercharged engine, ie. the changes are all backward > compatible at present. > > - NUMBOOSTSPEEDS - zero (or not present) for a naturally-aspirated > engine, > either 1, 2 or 3 for a boosted engine. This corresponds to the > number of > supercharger speeds. Merlin XII had 1 speed, Merlin 61 had 2, a > late > Griffon engine apparently had 3. No known engine more than 3, > although > some German engines apparently had a continuously variable-speed > supercharger. > > - BOOSTOVERRIDE - whether the boost pressure control system (either a > boost > control valve for superchargers or wastegate for turbochargers) can > be > overriden by the pilot. During wartime this was commonly possible, > and > known as "War Emergency Power" by the Brits. 1 or 0 in the config > file. > This isn't implemented in the model yet though, there would need to > be > some way of getting the boost control cutout lever position (on or > off) > from FlightGear first. > > - The next items are all appended with either 1, 2 or 3 depending on > which > boost speed they refer to, eg RATEDBOOST1. The rated values seems > to have > been a common convention at the time to express the maximum > continuously > available power, and the conditions to attain that power. > > - RATEDBOOST[123] - the absolute rated boost above sea level ambient > for a > given boost speed, in psi. Eg the Merlin XII had a rated boost of > 9psi, > giving approximately 42inHg manifold pressure up to the rated > altitude. > > - RATEDALTITUDE[123] - The altitude up to which rated boost can be > maintained. Up to this altitude the boost is maintained constant > for a > given throttle position by the BCV or wastegate. Beyond this > altitude the > manifold pressure must drop, since the supercharger is now at > maximum > unregulated output. The actual pressure multiplier of the > supercharger > system is calculated at initialisation from this value. > > - RATEDPOWER[123] - The power developed at rated boost at rated > altitude at > rated rpm. > > - RATEDRPM[123] - The rpm at which rated power is developed. > > - TAKEOFFBOOST - Takeoff boost in psi above ambient. Many aircraft > had an > extra boost setting beyond rated boost, but not totally uncontrolled > as in > the already mentioned boost-control-cutout, typically attained by > pushing > the throttle past a mechanical 'gate' preventing its inadvertant > use. This > was typically used for takeoff, and emergency situations, generally > for > not more than five minutes. This is a change in the boost control > setting, not the actual supercharger speed, and so would only give > extra > power below the rated altitude. When TAKEOFFBOOST is specified in > the > config file (and is above RATEDBOOST1), then the throttle position > is > interpreted as: > > - 0 to 0.95 : idle manifold pressure to rated boost (where attainable) > - 0.96, 0.97, 0.98 : rated boost (where attainable). > - 0.99, 1.0 : takeoff boost (where attainable). > > A typical takeoff boost for an earlyish Merlin was about 12psi, > compared > with a rated boost of 9psi. > > It is quite possible that other boost control settings could have been > used > on some aircraft, or that takeoff/extra boost could have activated by > other > means than pushing the throttle full forward through a gate, but this > will > suffice for now. > > Note that MAXMP is still the non-boosted max manifold pressure even > for > boosted engines - effectively this is simply a measure of the pressure > drop > through the fully open throttle. >
That all looks very good. Does your implementation of the Boost Control just control the pressure, or does it act on the throttle as I understand was the way it worked in the Merlin? In simulation terms the outcome is probably the same. V. _______________________________________________ Flightgear-devel mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
