FS 9 Autopilot

[dwhitley]

I have posted this topic in other FS forums, but thought the subject might draw a better answer here in Perter’s forum.

The following issue “may / could” be caused by an affect of FSUIPC, but worth discussing here to rule out the possibility.

Apparently, PMDG knows something about Autopilots that the other AC designers do not know. It may be that PMDG bypasses, or uses, some of the FSUIPC parameters to accomplish their better autopilot control over other AC designers.

The issue is the autopilot effectiveness. Specifically Roll in and out of headings, nav capture, and nav tracking. In my case, the PMDG 737 series behaves just like the real aircraft autopilot. It will promptly roll to and from a "Bugged" heading without lag, and capture the localizer (or any nav course) precisely at just about any intercept angle.

The approach to the correct design on the PMDG is apparently in the heading control. For example, compare a PMDG to just about any other FS aircraft. The PMDG will perform a precise 180 degree turn in 2 minutes. It does this by promptly rolling to the turn, and promptly rolling out of the turn. Other aircraft will slowly roll into the turn, continue the turn at a 3 degree per second rate, and then slowly roll out of the turn, thus taking about 2 minutes and 30 seconds to complete. This slow roll in and roll out process is what causes a lag in nav intercept, and thus causes hunting down the pathway (localizer, nav, etc).

The PMDG design apparently has accomplished the correct autopilot operation in areas other than the AC config file. I have compared the PMDG config file with other AC config files, and the flight tuning and autopilot code is virtually the same. Many replies in my other posts have suggested changing various numbers in the aileron_effectiveness, nav_proportional_control, and nav_integrator_control. These changes are basically cheating the system. It does create a little better capture rate, but affects the way the aircraft handles under manual pilot control.

If anyone wants to better understand the problem, fly a test with an FS factory aircraft and then a PMDG aircraft. Simply launch and level off somewhere at 3000 feet. Engage the AP on a heading, and then command a few turns. The problem will immediately become evident. Notice specifically how quickly the PMDG will roll into the turn, and how quickly it will roll out of the turn. Then, notice with other FS AC, how slowly the AC rolls in, and very slowly it rolls out. Timing the turns makes the problem even more evident. Time a 180 or 360 degree turn. Notice that the PMDG will make a 180 deg turn in 1 minute, and a 360 deg turn in 2 minutes. Pretty much standard for a real AC. Then, notice how long it takes the average FS AC to make the same turns. You will notice the longer time evolving from the very slow roll outs.

So, it is very evident that PMDG AC are designed differently in how the AP works. As mentioned earlier, I do not see any differences in the config files, so they are accomplishing the task through other methods.

There are several parameter within FSUIP that affect flight characteristics. Damping / spiking control, etc. As mentioned earlier, it may be some of these parameters that are causing the above issue with other MSFS aircraft. Or conversely, allowing PMDG to perform better flight characteristics with their autopilot. It may be that PMDG bypasses or uses some of the FSUIPC parameters to accomplish their autopilot’s better control.

It appears that MSFS is not the problem (as many have claimed) if one vendor can accomplish the correct procedure. I have tested various configurations within the AC CFG files and within FSUIPC without success, unless I am missing something.

That said, PMDG may have proprietary coding in the autopilot area. However, if not, they are accomplishing the tasks in other areas (other than the AC CFG file) of their package. So, if anyone knows where the fix may lie, or how PMDG accomplishes the correct autopilot operation, it would create better experience for those of us who fly in the real world.

This may all seem a bit picky, but I use MSFS to assist my real world flight students in instrument flight instruction. The error within the autopilot is very annoying and causes some confusion. PMDG had raised the standard of MSFS by being more of a real simulation experience vs a game. Thus, if anyone knows of a resolution to the above issue, then we are accomplishing a better environment for the RW pilots.

Thanks Dennis

[Pete Dowson]

So, it is very evident that PMDG AC are designed differently in how the AP works. As mentioned earlier, I do not see any differences in the config files, so they are accomplishing the task through other methods.

They don't use the FS autopilot. Full stop. They do their own control of the aircraft to accomplish the correct behaviour. There are others that do this too -- Level D with their 767, and Project Magenta on the seveal aircraft they support, though in the latter case they use a small part of the FS autopilot activity still.

It appears that MSFS is not the problem

Quite honestly, I don't see that you have stated any "problem" as such, yet. All you have done is asserted that PMDG's autopilot is better than the default one. No one will disagree with you there. It is 100% purpose designed for its specific model of aircraft. FS's autopilot is a generic one which tries to cope with every type of aircraft thrown at it. It is a wonder it does as well as it does!

That said, PMDG may have proprietary coding in the autopilot area.

Of course they have! It has cost them many thousands of man hours to get it so good!

The error within the autopilot is very annoying and causes some confusion.

And what "error" is this? You've spent a lot of words without once being specific about what it is you are complaining. If it is the general inaccuracy or lack of versatility of the default A/P in FS, then that is very well known. That A/P is derived from the original, designed for Cessna trainers, and adapted rather hopefully to all and sundry, from lesser aircraft right up to the 747. There is no way any one A/P setup can really do justice to all those differences. As I said, it is a small wonder it copes at all. Every more sophisticated add-on which does better does so because its authors don't have to cope with such a wide range of factors. They work on dedicated code specific to that aircraft, and that's what you pay for!

Regards

Pete

[dwhitley]

I agree about the man hours put in from various vendors. The auto pilot is quite a complex feature. My point is, MS and some other vendors did not approach the issue well as PMDG and others have. Thus, the following problem exist. I specifically outlined a test in my original post, but I will repeat it again.

Simply put, most FS aircraft, and a few add on aircraft, will not initially capture and track a nav signal. (Localizer etc) They will initially over shoot, but "eventually" will capture and track.

For example, when capturing a localizer, at a 30 deg intercept, the AP starts a turn to capture. As it captures, it starts a roll out. But due to the slow roll out of the autopilot, the AC will over shoot the localizer. Then, the AP ties to correct the opposite with a turn. Again, a slow roll out causes another overshoot in the opposite direction. This continuse until it eventually dampens and the localizer centers.

The problem that I see that causes the issue is,,,The slow rate of "roll in" and "roll out" of AP heading control. FS autopilots, once established in the turns, will continue to turn at at standard rate of 3 degrees per second. HOWEVER, getting in to the turn, and out of the turn is slow. It rolls into the turn at approximately 2 deg per second. Then, the roll out happens at even a slower rate of less than 1 deg per second. Once the turn has been established, the AC will turn and a standard 3 deg per second.

This is from the original post: I specifically outlined a test...

"

""If anyone wants to better understand the problem, fly a test with an FS factory aircraft and then a PMDG aircraft. Simply launch and level off somewhere at 3000 feet. Engage the AP on a heading, and then command a few turns. The problem will immediately become evident. Notice specifically how quickly the PMDG will roll into the turn, and how quickly it will roll out of the turn. Then, notice with other FS AC, how slowly the AC rolls in, and very slowly it rolls out.

Timing the turns makes the problem even more evident. Time a 180 or 360 degree turn. Notice that the PMDG will make a 180 deg turn in 1 minute, and a 360 deg turn in 2 minutes. Pretty much standard for a real AC. Then, notice how long it takes the average FS AC to make the same turns. You will notice the longer time evolving from the very slow roll outs.

So, it is very evident that PMDG AC are designed differently in how the AP works. As mentioned earlier, I do not see any differences in the config files, so they are accomplishing the task through other methods. "

The questions still is, is there anything that can be done to adjust for the FS autopilot's deficency?

Good day

Dennis

[Pete Dowson]

I agree about the man hours put in from various vendors. The auto pilot is quite a complex feature. My point is, MS and some other vendors did not approach the issue well as PMDG and others have.

Because, as I said, Microsoft have to provide a basic option which covers all manner of aircraft, whereas the vendors concentrate on the one aircraft at a time.

Microsoft Flight Simulator has always been so, a good basis for others to improve upon.

So, it is very evident that PMDG AC are designed differently in how the AP works. As mentioned earlier, I do not see any differences in the config files, so they are accomplishing the task through other methods. "

Yes, of course they are!!! As I said. A lot of code and hard work in designing it!

is there anything that can be done to adjust for the FS autopilot's deficency?

Yes, do as PMDG have done and write your own autopilot! The facilities are there. You can control throttle, elevator, aileron and trim. You can measure the accelerations and velocities in all directions, and the weight and balance of the aircraft. That is what the PMDG code is doing. it is reading the situation and controlling it. If you have the skills and hours to spend you can most certainly do the same. Go ahead! What specific aircraft are you thinking of tackling? You must choose, as it is not a case of "one fits all"!

Regards

Pete

[dwhitley]

The specific aircraft that I want to behave correctly is a third party AC (Cessna Citation CJ-1 from Eagle Soft.) Apparently, they use the internal FS Autopilot and did not build their own AP. I have written them about the issue, but have not received a response.

I have tried several modifications to CJ-1 config file, but realized that the changes were only cheating the system to obtain a particular result. I now realize that vendors like PMDG went beyond modifications, and built their own AP to address the deficiency of the FS AP. Obviously, there is an FS AP issue, and others have worked around the problem. Thus, there is a fix!

Since you profess to be an expert on the subject, seems like the great Peter Dowson could have designed a fix for the AP into the FSUIPC. i.e.

“FIX_AP” (Aircraft Specific)

“Adjust Roll rate by XX”

“Adjust Pitch Rate by xx”

Ect.

It seems to me that a FSUIPC fix would be something useful for customers that really understand the flight characteristics of aircraft, and know about the FS AP issue. Maybe your next version will address the issue.

I don’t pretend to be an AC designer. I am a flight Instructor /ATP. I drive them, I don’t fix them! I am only trying to understand the problem so that I may find a fix, (If there is a fix) to achieve a more pleasant experience with the SIM.

In closing, (and this is just future public relations suggestion,) The next time I need a little help with my car, or take it to the dealer for some work because it doesn’t shift properly, I truly hope they don’t tell me to go build a new transmission myself.

Good Day

Dennis

[pschlute]

Dennis

i think you are being a bit unfair here.

Pete has explained why the default FS autopilot is not as accurate as the one from a PMDG plane or a real aircraft. It is clear that to make it work perfectly for any specific aircraft would require many hours of work to create a completely new addon such as PMDG do.

If your issue is with the FS autopilot you should address your concerns to Microsoft, who will no doubt reply "what do you expect from a computer sim that costs $50". At the end of the day we get the sim we are prepared to pay for.

[Pete Dowson]

The specific aircraft that I want to behave correctly is a third party AC (Cessna Citation CJ-1 from Eagle Soft.) Apparently, they use the internal FS Autopilot and did not build their own AP.

Okay, that is of course true of most add=on aircraft. The PMDG and Level D examples, where the autopilot is pretty much completely replaced, are in the minority.

Since you profess to be an expert on the subject

No, I most certainly do not profess any such thing! All my developments for FS, over all these years, have been to enable others, who DO know what they are doing, to develop such capabilities. I have only ever provided the access into FS, the wherewithall to link solution to simulation. And in FSX, with Simconnect taking over thsat role, I don't even do that except for backward compatibility.

You obviously severely misunderstand the part my programs play in the FS world!

In closing, (and this is just future public relations suggestion,) The next time I need a little help with my car, or take it to the dealer for some work because it doesn’t shift properly, I truly hope they don’t tell me to go build a new transmission myself.

I think your attitude is extremely poor. You misunderstand things and blame others. If you read this thread again you can see that I've only tried to explain why you see what you see. I've not told you to build anything, as you appear to be telling me! In fact I specifically said "IF" in the only place where I was pointing out that it isn't easy:

"If you have the skills and hours to spend you can most certainly do the same.

Evidently you haven't, and neither have I, but you should not be venting your frustration about that here. It is not appropriate.

Pete

[dwhitley]

My attitude is enthusiasm and curiosity. I am a customer / consumer. Not a designer / programmer. I simply posted a topic for discussion, trying to learn if there was a fix to a particular issue. I sited examples of a properly working device vs a defective device. No blame, or praise,,, just example.

What I got in return was, an egotistical reply of “Build your own box” and often times in these, and other forums, “RTFM”

For a product that is revenue producing, I find it quite unacceptable for the owner of the product to address a paying customer in such a manner. A “helpful” suggestive conversation would have been more appropriate and productive. And then, to engage in further argumentative discussion with a “Paying Customer” is totally unacceptable.

This conversation is over

Good Day.

[Pete Dowson]

What I got in return was, an egotistical reply of “Build your own box” and often times in these, and other forums, “RTFM”

There was never any such reply! You are twisting the whole thread ridiculously. All you said was that the default autopilot wasn't so good and that, with the PMDG example, it could be better. And i agreed, it can be. As I explained, it just takes skill and timeand money therefore. I have neither the skill nor the time. Neither have you by the sound of it. You need to pursue your vendetta elsewhere.

This conversation is over

Good. I don't really want to hear from you again in any case. You either don't read or severely misread replies in any case, so it is a waste of effort. This has developed into a most unpleasant experience.