Maintaining runway centreline in manual approach

[kevinh 409]

As matter of interest have you cross checked the inbound course selected by the 777 with that of the A320 and compared that with the localiser course of the ILS?

 

Is N1 exactly the same on both 777 engines?

 

It could be a control calibration issue that the Airbus model is zeroing out by maintaining wings level but the 777 is not.

[tcas_climb 45]

For the record guys,.......that was not me!

 

Afraid you might be seen as a troublemaker? Lol j/k

It could be a control calibration issue that the Airbus model is zeroing out by maintaining wings level but the 777 is not.

This could be the reason. Have you tried this with another aircraft that isn't fbw?

 

The part that sparked my interest is you said the drift disappeared when you switched off the PFC.

[LecLightning56 33]

I have tried the Level D 767 (non-FBW) by setting up the approach with FSiPanel and ensuring the weather is completely cleared to zero wind.

 

Lo and behold, if I disengage the autopilot at about 400-500 feet and fly manually, this simulation has the tendency to drift port or starboard slightly in the absence of aileron inputs. Personally I find this behaviour annoying in a sim, particularly having to make corrections at such low altitude, and suggests that something is not quite right somewhere. I have checked yoke calibration and I would have thought that setting null zones would eliminate issues with poor centralisation laterally of the controller, where the ailerons are concerned and similarly with the rudder pedals.

 

I have heard stories of very large aircraft handling 'straight down the bowling alley' in the real world and it seems strange that my only experience with this in FSX is with the baby Airbus.

 

I have also had an abortive attempt with the PMDG 747 and again the drift is present (how can you correct with rudder if no wind is present?).

 

I shall continue to investigate and see if I can improve on the current situation by some means.

 

 

Paul Hermon

[vololiberista 205]

I have tried the Level D 767 (non-FBW) by setting up the approach with FSiPanel and ensuring the weather is completely cleared to zero wind.

 

Lo and behold, if I disengage the autopilot at about 400-500 feet and fly manually, this simulation has the tendency to drift port or starboard slightly in the absence of aileron inputs. Personally I find this behaviour annoying in a sim, particularly having to make corrections at such low altitude, and suggests that something is not quite right somewhere. I have checked yoke calibration and I would have thought that setting null zones would eliminate issues with poor centralisation laterally of the controller, where the ailerons are concerned and similarly with the rudder pedals.

 

I have heard stories of very large aircraft handling 'straight down the bowling alley' in the real world and it seems strange that my only experience with this in FSX is with the baby Airbus.

 

I have also had an abortive attempt with the PMDG 747 and again the drift is present (how can you correct with rudder if no wind is present?).

 

I shall continue to investigate and see if I can improve on the current situation by some means.

 

 

Paul Hermon

Have you established the amount of fuel in each wing? If one wing is heavier then the a/c will always want to go in that direction!

[tcas_climb 45]

Try disconnecting your joystick and rudder and see what happens, if it still drifts then it's probably fsx crappy environment simulation.

[kevinh 409]

Try disconnecting your joystick and rudder and see what happens, if it still drifts then it's probably fsx crappy environment simulation.

Maybe, but the one thing you'd expect FSX to simulate well would be zero wind!

 

Any tiny asymmetry in the model can cause this kind of deviation. Slightly different thrust, a fraction of a unit or trim, a few pounds of fuel, etc. It's quite likely that the normal situation is some divergence and that the Airbus FBW is actively maintaining wings level. I don't think 777 FBW maintains wings level.

[Mike777 163]

Did you ever try this without using FSiPanel?  You never mentioned whether you did or not.  That would be the first thing to eliminate.  Kyle said in one of the first few posts that it does interact with weather.

 

Mike

[LecLightning56 33]

At last some progress. It would appear that the problem all along has been the setting of null zones for the controller axes. In particular, it would appear that the setting of a null zone for the aileron axis is the main culprit. My yoke centralizes accurately in the roll axis, so upon removal of the null zone for the aileron axis I am now getting acceptable results in my 'test' conditions whereby the 'drift' is minimised to an acceptable level (with minimal control inputs and no aileron inputs whatsoever, the PMDG 777 now touches down approximately 5 feet to the left of the centreline, which is very much better). So, just to recap, this appears to have been a controller calibration problem associated with the setting of a null zone in the aileron axis which is largely to blame. There is no further need to disconnect the primary flight computers as previously reported. I shall now go away and experiment with non-FBW aircraft (outside the scope of this thread).

 

I wish that there was a more authoritative guide to best practice with controllers where the use of null zones and sensitivity is concerned with application to FBW and non-FBW aircraft, but perhaps it is left to the individual to determine for himself to adjust accordingly to achieve the best results.

 

I think that I can discount FSiPanel in terms of the weather settings since these have always been set in FSX after FSiPanel has positioned the aircraft for the landing.

 

Thank you all for your contributions and if anyone has anything further to add then please send in your comments as you see fit.

 

 

Paul Hermon

[777simmer 117]

That is why when you wrote:

 

quote

The question to yourselves in the community is this: should one expect an aircraft of the proportions of the 777 to suffer such drift under nil wind if the controllers are effectively untouched

unquote

 

I replied in post 13 with:

quote

I disagree......the real question is......do other users see this as well!?

 

So far nobody reported that.

unquote

 

 

It is not that I dont make the wrong diagnosis myself here and there......but before you state things as fact (this is wrong and this is why) I think it would be better to wait untill at least a few other users confirm your observation.

 

But thx for clearing things up.

[LecLightning56 33]

Thanks 777simmer for pointing out the error of my ways!

[777simmer 117]

Thanks 777simmer for pointing out the error of my ways!

You are welcome.......glad I could help :-)

[downscc 1,327]

I wish that there was a more authoritative guide to best practice with controllers where the use of null zones and sensitivity is concerned with application to FBW and non-FBW aircraft, but perhaps it is left to the individual to determine for himself to adjust accordingly to achieve the best results.

 

Your experience reminded me of my first flight in a Mooney years ago. It was a show-off night flight with a date overflying Kansas City (before TCA's or Class-B and the air was still but my left wing kept dropping... I realized that it was just the weight of my thumb on the yoke horn. The Mooney doesn't use control cables, everything is solid rods and cranks with no hysterisis. Effectively, eliminating any null zone. By the way, it was a great flight.

[scandinavian13 5,192]

 

 

By the way, it was a great flight.

 

Glad it worked for you.  I all but banned flight dates...at least until I get to know them a little better.  Went on a first-date flight without thinking that, if it ended up that I wasn't into the girl, I'd be stuck in a very confined place, with no good options for escape.  That was a bit miserable.  Luckily, when my hand was grabbed to be held, I got out of it with "aww...hate to do this to you, but I was always taught to keep one hand on the throttle at all times..."

 

On the other hand, the last one I went on (knew her for a while) was actually pretty good.

 

...and now everyone knows more about me than they ever wanted to know - haha.

[Jude Bradley 659]

I can just picture you doing a roll,and leaving the door open for the poor girl.

Parachutes anyone? :huh: 
 

[scandinavian13 5,192]

I can just picture you doing a roll,and leaving the door open for the poor girl.

Parachutes anyone? :huh: 

 

 

haha - I know I come across as soulless, but I'm not that mean.  She was nice...just a little too...aggressive.

(Yes, I'm aware of the apparent irony in that last statement.)