Lee Elliott <[EMAIL PROTECTED]> said: > Hello Jim, > > Sorry, I missed this post at first. The porpoising is certainly related to > the elev_adj_factor - the lower it is the worse the problem. It's hardly > apparent with the c-172 or 747 but more so with the a4.
Try increasing then. Generally the elev_adj_factor relates to the aircrafts speed conditions. It needs to be higher for faster, more powerful aircraft. The integral-component is used to augment the control output in situations where the elev_adj_factor is so low that the aircraft has difficulty zeroing in on the target altitude (like it hangs just below or above). If you see that then increase the integral-component in small steps. The 747 is as it is on my system is configured to behave reasonably well at normal operating speeds. You will see porpoising if you are cruising 400kts at 3000 ft. That said the controls are such that you may see some very subtle porpoising effect for a minute or so once the aircraft reaches altitude. This should go away. The A-4 has not been working well and needs to be reconfigured. > With the YF-23 it's > very obvious. Auto-throttle isn't the cause of the problem - it never used > to be a problem and it happens with static throttle settings anyway. I will look at the YF-23 and see if I can help it. > Reducing the elev_adj_factor doesn't fix the problem but just seems to reduce > the frequency of the oscillation - have another look at the C-172 but fly it > for several minutes in still air after you've reached the target alt - it'll > still dive and climb around the target alt, albeit very slowly. I will look at this again. It seemed fine to me, but maybe I didn't fly it long enough. > If I used > the same elev_adj_factor for the YF-23 as for the C-172 I think I'd probably > get the same period of oscillation but the amplitude would be greater - as it > is now, it's diving and climbing about 200ft either side of the target alt, > with a period of about 2-3 seconds. Used to be flat and steady. This is probably a side effect of a bug I fixed. This bug doesn't really affect most of the aircraft that much, it just smooths things out. But if the target-climb-rate is extremely high, it could create a problem. I'll see what I can do to improve it. > I'll be honest and admit that I don't know what the integral-contribution > does, so I don't mess with it. As I mentioned above. Worry about this only if you find the aircraft hanging slightly below or above target. Basically what happens is that every frame iteration, the A/P adds up the amount of the difference between where you are at and where you should be. This can end up being a very large number. The integral factor is the weight that this very large number is given in augmenting the amount of elevator commanded. So you see if the aircraft is hanging just below target altitude, eventually that number will get large enough to push the elevator control enough to correct the error. In effect the integral value affects how quickly this augmentation occurs. Generally it should be 0.001 ~ 0.01. > I think I've got to say that the bottom line is that this has not been a > problem until now and as far as I could tell from a quick test, the terrain > follow fucntion still seems to be as it was before. > > Apart from my ignorance, I'd not dispute the inclusion of new or improved > features but they've got to be implemented in such a way that they don't > break existing things. This is CVS. We try our best. :-) Like I said, other than the bug fix, there really isn't anything different with the altitude hold code. > How difficult would it be to have both a 'current' autopilot and a > development/experimental version, selectable via an option or, more > preferably, through the property tree, so that it could be changed in flight? > This isn't a rewrite, or overhaul. It's just some minor adjustments. Best, Jim _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
