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JSBSim Engines: Difference between revisions
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== FGPiston == | == FGPiston == | ||
Piston engine model. You enter values based on commonly available data and this model creates reasonable output values. | Piston engine model. You enter values based on commonly available data and this model creates reasonable output values. | ||
=== Configuration File Format === | |||
<piston_engine name="{string}"> | <piston_engine name="{string}"> | ||
<minmp unit="{INHG | PA | ATM}"> {number} </minmp> | <minmp unit="{INHG | PA | ATM}"> {number} </minmp> | ||
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<cooling-factor> {number} </cooling-factor> | <cooling-factor> {number} </cooling-factor> | ||
</piston_engine> | </piston_engine> | ||
=== Notes === | |||
* Intake & Throttle | * Intake & Throttle | ||
** The intake is modeled by <ram-air-factor>,<minmp>, <maxmp>, and <air-intake-impedance-factor>. | ** The intake is modeled by <ram-air-factor>,<minmp>, <maxmp>, and <air-intake-impedance-factor>. | ||
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** <air-intake-impedance-factor> is the fixed impedance in the air intake system. It is determined by <maxmp> if not supplied. This value is exposed on the property tree so it may be altered at runtime to simulate intake icing, alternate air, etc. | ** <air-intake-impedance-factor> is the fixed impedance in the air intake system. It is determined by <maxmp> if not supplied. This value is exposed on the property tree so it may be altered at runtime to simulate intake icing, alternate air, etc. | ||
* Boost | * Boost | ||
** <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> IGNORED | |||
** <boostmanual> whether a multispeed supercharger will manually or automatically shift boost speeds. On manual shifting the boost speeds is accomplished by controling propulsion/engine/boostspeed | |||
** <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 0.98 : idle manifold pressure to 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. | |||
** <ratedboost[123]> - the absolute rated boost above sea level ambient (14.7 PSI, 29.92 inHg) for a given boost speed, in psi. Eg the Merlin XII had a rated boost of 9psi, giving approximately 39inHg manifold pressure up to the rated altitude. | |||
*** 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. | |||
** <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. | |||
* Power production | * Power production | ||
** <sparkfaildrop> is the amount of power you get for single magneto operation, try a value of 0.8 or so. | ** <sparkfaildrop> is the amount of power you get for single magneto operation, try a value of 0.8 or so. | ||