Porpoising - close to a solution

[AC103010]

Some weeks ago I asked for a solution to the problem of the vast majority of my aircraft porpoising but after many, many replies the problem is as bad as ever. Until this morning, that is. In mid cruise, at 31,000 ft in a B747 the amplitude was around 700 ft above and below the assigned flight level. Then I noticed that it was flying at around M0.76 when the Autothrottle was set at M0.84. N1 would not go above 90%.

As I install my aircraft I change the autopilot setting for autothrottle max from 90% to 100% but I hadn't done so with this one. So I changed this and the aircraft accelerated to M0.84.

The interesting thing was, though, that when I disconnected the autothrottle, to initially manually set the airspeed at M0.84 the porpoising stopped almost completely.

So it seems the problem is not with the flight dynamics themselves but with the autothrottle.

Now I could probably work out a rational explanation for this, ie greater speed, greater lift, slower speed, less lift, but in the meantime could someone suggest what is happening to the autothrottle and, more importantly, what needs to be changed.


Many thanks,


Allan

[mimi]

Have you tryed this?
Change or ad this to the aircraft in question in the aircraft.cfg

[pitot_static]
vertical_speed_time_constant=1

then change the number to 99 like this

[pitot_static]
vertical_speed_time_constant=99

scotty

[AC103010]

Hi Scotty,


Yes, tried that, and many more things in the config file.


Thanks for the reply, anyway.



Allan

[wsieffert]

Have you by any chance been using FS2002 Aircraft Editor (FSEdit.exe)? If so, some of the instability could be cause by the editor adding eight additional aerodynamic records to the *.air file. If you have been using the editor, I recommend you download AirEd152 from http://members.dsl-only.net/~eagle/ or http://perso.wanadoo.fr/hsors/FS_Soft/index.html plus get the latest aired.ini from the latter site.

Open your airfile with AirEd and arrow down to the bottom and delete records 1539 to the end. Right click each entry, then select remove. Once removed, save the file. Caution, if you open the file again in MS FS2002 Aircraft Editor, make a modification, it will reinstall these records.

You can use MS FS2002 Aircraft Editor but just remember to remove the extra records with AirEd each time.

W. Sieffert

[AC103010]

No, I haven't used this, at least not recently. But maybe this problem stems from the last time I used it.

It's worth looking at but it'll have to wait for a while because I'min the office at the moment.

Thanks for the tip


Allan