> On Wednesday, May 29, 2002, at 04:06 am, Alex Perry wrote: > > >>> Just something to file away ... big jets should have a climb mode in > >>> which the power is regulated to max climb by the autothrottles and > >>> speed > >>> is held with the pitch control. > > Is this the mode activated by the CLB / CON switch (on the virtual > Boeing's I've flown....)?
Hi, I fly real Boeings (757/767) for a living, so maybe I can give some information on how autothrottle and autopilot work. This should be almost identical for all Boeing Jets and very similar for Airbuses, although Airbus uses different names for the modes. The CLB and CON (max. continuous thrust) you mentioned above (and the other two modes CRZ and TO/GA) are just limits. This means, that they set an upper limit on how much thrust will be provided by the autothrottle system. The autothrottle will decide on how much thrust is actually needed and the autothrottle will give that thrust up to the selected limit. The autothrottle has four basic modes, EPR, SPD, THR HLD and IDLE (and some others, which usually apply only to certain phases of flight) * SPD maintains the selected speed * THR HLD releases the throttle, so that the pilot can make adjustments. * EPR advances the throttles to the selected thrust limit (TO/GA, CLB, CRZ, CON, see above). Once the desired thrust limit is reached, autothrottle will go to THR HOLD mode. * IDLE retards the throttles to idle power. Once Idle thrust is reached, the autothrottle will go into THR HOLD mode. SPD and EPR can be manually selected by the pilot on the MCP (Mode Control Panel). The other modes are selected either by the autopilot or autothrottle system. The autopilot has three basic vertical modes (the fourth, VNAV (Vertical Navigation), can only be used together with FMC) They are FLCH (Flight Level Change), V/S (Vertical Speed) and ALT HOLD (Altitude Hold) * ALT HOLD will maintain the current altitude by adjusting the pitch. The autothrottle will go to SPD mode. * V/S Mode will cause the autopilot to adjust the pitch to maintain the given rate of climb/descent. The autothrottle will also go into SPD mode. * FLCH is the most common Mode for climb/descents. In this mode the autopilot orders the autothrottle to go to EPR mode for climbs or IDLE mode for descents, and maintains speed by adjusting pitch. Since the autothrottle will go to THR HOLD once the desired thrust is reached, the pilot can adjust the rate of climb/descent by adjusting the thrust with the throttles. For example, on a descent the pilot adds thrust, the aircraft will get faster and the autopilot increases pitch to keep the selected airspeed, thereby reducing the rate of the descent. Please note, that FLCH is mutually exclusive with the SPD and EPR autothrottle modes. Only one of the three modes can be selected. Hope this description hels. Thomas > > I'm assuming that one of the factors Alex alludes too is the FMC > restriction speeds / altitudes and the EPR settings selected, otherwise > it seems this mode wouldn't be terribly useful.. > > James > _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
