Boeing vs. Airbus – Part 3 Phoenix Simulation Software Airbus A320 Page 7

By SimHQ on May 4, 2005 in _air4, hide

The PSS flight model breaks down a bit at this point. The PSS flight model goes a bit wacky once the Alpha Floor warnings are ignored and continued back pressure on the stick will result in a stall. As airspeed dips into the red zone (Alpha max) the airplane drops like a rock from the sky with vertical speed going from a positive climb rate to -20,000 FPM or more in seconds. Here I’ve already been well into Alpha max and the VSI is indicating 28,900′ FPM down. Pitching the nose down slightly and increasing airspeed above Alpha max seems to bring the aircraft out of this mode and a gradual pull up to level flight can be accomplished. At those excessive rates of descent though there is little time to fix a problem.

This behavior is strictly an artifact of the PSS flight model, the real Airbus would never (well, never say never) allow you to get into this predicament (it would require a loss of Normal and Alternate Law) and even if it did stall it would probably be a more benign descent rate with more rapid and traditional recovery options. All of that said I don’t consider this a ding against the PSS flight model. It is my understanding that simulating fly-by-wire aircraft performance within the constraints of FS2004 is pretty difficult. Up to the very extreme limits of the Airbus fly-by-wire design the PSS model does a very good job. There does seem to be some “bobbing” in the pitch regime when pitch is first set, but smooth control inputs tend to reduce these and it could very well be a result of my controller setup. There is also the odd fact that trim still works even though the Airbus auto-trims.

Completing the flight regime test I extended the gear, put out full flaps and speedbrakes and pitched the nose down to the limit of 15 degrees as advertised. Once again PSS modeled the correct limits.

With the “air work” done I climb back up to FL240 and resume the route as planned. Utility services will have quite a job cleaning up the puke in the rear cabin upon arrival at London City! Checking the F-PLAN page of the MCDU shows our flight progress with estimates for each waypoint and a summary at the bottom indicating our ETA at London City, distance to go and estimated fuel onboard upon arrival. I take this opportunity to enter the VNAV data into the flight plan as well, setting the crossing restriction altitudes and speeds for the arrival.

The PSS virtual cockpit is nice, with clearly legible instruments and a clean layout. The avionics and switches are not interactive however so all of that must be done from the 2D panels. I spend about .000001% of my time in the VCs, so a non-clickable 3D pit isn’t a drawback for me personally.

Back in level flight I run the airspeed selector up to a value above redline to see if the aircraft will accelerate into Vmax range but the blue triangle stops at the bottom of the Vmax range. Foiled once again by the engineers at Airbus!

Eschewing the recommended economy throttle setting I keep the airspeed bug on the maximum for the rest of the flight, after our aerobatics routine back there we need to make up some time!

Cruising over central France I take some time to pan around the stunning PSS 3D model.