L35A Pitchs Up at 29000ft

[ark 1,290]

I had overall smooth transitions from SPD to MACH during beta, however the aggressive pitchup occured one or two times (out of 20-30 flights). I was unable to determine the cause of them, so it's not related to the OS or installation, it must be something within the sim.

 

Matthias,

 

I had the aggressive pitch up happen to me yesterday for only about the 4th time since flying with ver 2.6 (which I fly regularly). I use FSX on a 4GHz system that runs smoothly most of the time. Here's one possibility for the randomness at which these pitch ups seem to happen.

 

In looking at the code it seems 5 ft altitude ranges are used to turn SPD hold on and off at 29000ft. If  the a/c is in the altitude range 29001 to 29005, SPD mode is turned off. If the a/c is in the range 29006 to 29010, OR in the range 28995 to 29000, SPD mode is turned on. The 29006-29010 range is for climbs, the 28995-29000 range is for descents. As explained above,  it is when SPD mode is turned on after being off that the reference IAS and Mach# are ‘updated’.

 

So, for example, assume we turn SPD mode on at say 1500ft and start climbing to 32000. The IAS at 1500 is now the reference speed value. When we reach the 29001-29005 range SPD mode is turned off, and then turned on again when we hit the 29006 to 29010 range at which time the reference Mach# is updated for the rest of the climb. On a descent, assume the SPD mode is turned on at 32000 and stays on until we hit the 29005 -29001 range at which time SPD mode is turned off. It then is turned on again in the 29000-28955 range and the reference IAS for the rest of the descent is captured. Very clever, but I wonder if these 5 ft altitude ranges may account for the random behavior some see at 29000ft. 

 

If the a/c VS is say 2000ft/min at 29000ft, it is only in one of these 5ft altitude ranges for 5ft x 60sec/2000ft = 0.15 seconds or 150 millisecs. If the VS is 3000ft/min, then the a/c is only in a 5 ft range for 0.1 sec or 100millisecs. As I understand it, the XML code is typically run 18 times/sec or every 55.5 milliseconds. So it seems that if the sim happens to be 'busy' when the a/c is in one of the 5ft ranges, there is a chance the SPD mode won’t be turned off in the 29001 to 29005 range, or maybe not turned on again in one of the ‘on’ ranges, and thus the Mach# or IAS, depending on which way you are going, won’t get updated.

 

I think this could certainly show up as a random problem, and the randomness of it makes it very difficult to test. One experimental idea to try to reduce how often these pitch ups happen would be to increase the size of the SPD hold 'on/ off' windows to say 10ft, although I don't know if there would be unintentional consequences to that. Since for some reason my friend seems to experience the pitch ups quite often (to the extent he prefers not to use ver 2.6),  I will ask him if he will try the larger SPD hold on/off windows to see if it helps or not.

 

Best,

Al

[MatzeH84 81]

Yay, that sounds reasonable! I am running at 4.3GHz and with the Lear it's usually very smooth. On slower PC's that problem may occur more often.. I will try to make some tests tomorrow with a light airplane and different rates of climb. I think you have a really good point here!

[Flysimware 647]

Try this update....http://www.flysimware.com/website/help/Learjet_35A_CAB_FILE.zip

[ark 1,290]

Try this update....http://www.flysimware.com/website/help/Learjet_35A_CAB_FILE.zip

 

I tried a few climbs and descents and it seems to work great so far.  And you can easily see the SPD Hold light go off,  and then on again as the a/c goes through the 100ft windows which is a nice way to confirm that nothing has been 'missed' by a busy sim. If the random pitch ups still happen but the lights go off and on as expected, then we know something else is going on.

 

Thanks very much!

 

Al

[MatzeH84 81]

What rates did you fly? I just tried with deliberate high power setting resulting in around 3000fpm and got the pitch up.

[ark 1,290]

What rates did you fly? I just tried with deliberate high power setting resulting in around 3000fpm and got the pitch up.

Well that's interesting. I just tried it again 3 times with at VS in the 3500ft/min range with no problems. I could see the IAS/Mach lights cycle on and off as expected.

I assume you saw the lights cycle as expected as well. If so, I'm thinking there is something in the feedback system that is not getting initialized or reset correctly after the Mach# is updated at 29000ft. Maybe another timing issue.

 

Al

[MatzeH84 81]

It switched directly from IAS to MACH without obviously being off for a noticable time. I will do further testing when I find the time.

[ark 1,290]

As I recall, the target Mach# (or IAS) is maintained by adjusting the VS, and when these aggressive pitch ups happen, it is as if the a/c is trying to maintain a new and very high VS. So I wonder if 'sometimes' the updated VS is not getting set correctly for some reason.  I will see if I can use any of the logging capabilities in FSUIPC to see what the target VS value is at any time.

It switched directly from IAS to MACH without obviously being off for a noticable time. I will do further testing when I find the time.

I think you should see a definite 'lights off' time.  Did you restart the sim or reload the a/c after loading the new Cab file into the panel.MAIN and/or panel.GNS folder?

Al

[Flysimware 647]

cab file was updated again....

 

http://www.flysimware.com/website/help/Learjet_35A_CAB_FILE.zip

[Flysimware 647]

Is the latest update working better?

[Flysimware 647]

I have been dealing with health issues and finally got a chance to test the new SPD HLD cab file made by a customer and i agree this is well written and i am re leasing a new version of the lear soon. Thanks!

[Cool 27]

Great  

I 'll install it today.

Thank you so much  :smile:

Pascal

[Cool 27]

I have tested tonight a climb up to FL310 in IAS mode = no problem anymore passing FL290.

The IAS mode switch to Mach mode at FL290 but the climb remain smooth as it should.

 

Thanks  :smile:

Pascal