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jspringe

Autopilot is crazy

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Each time I think I understand how this autopilot works, it surprises me with something new.

This time, trying to descend from 8,500 to 3,000 to pickup an ILS glide slope. Autopilot is in Nav and Alt hold at 8,500. I am a bit late in descending, so I need to get to about 1,200 fpm. I use the rocker center of the two steering wheels and the aircraft starts to descend, but not enough. So I click the rocker several more times, but it still wont increase the descent angle any more than the current approx. 800fpm. The autopilot is controlling the trim and I can see that the trim wheel is just slightly negative (there is still plenty of negative trim available).

So, I disengage the autopilot and manually trim for 1,200fpm. Then I re-engage the autopilot thinking that it will resume Nav and hold the pitch that I have established. But instead of holding pitch, it levels off (actually noses up and goes positive pitch at first). Alt is not engaged. IAS is not engaged. What would possess the autopilot to override the pitch that was established? It seems like it has some memory of the prior pitch before it was previously disengaged. I tried this several more times with the same result. Each time the autopilot overrides the current trimmed pitch, bobbing and sometimes with about a 500 fpm descent after settling out.

Then, after all of that I hit the APPR button. GS goes green. But the autopilot decides to hold the current altitude and never follows the glide slope down.

Lateral modes seem fine, but vertical modes seem to be a great mystery.

Jason

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Each time I think I understand how this autopilot works, it surprises me with something new.

This time, trying to descend from 8,500 to 3,000 to pickup an ILS glide slope. Autopilot is in Nav and Alt hold at 8,500. I am a bit late in descending, so I need to get to about 1,200 fpm. I use the rocker center of the two steering wheels and the aircraft starts to descend, but not enough. So I click the rocker several more times, but it still wont increase the descent angle any more than the current approx. 800fpm. The autopilot is controlling the trim and I can see that the trim wheel is just slightly negative (there is still plenty of negative trim available).

So, I disengage the autopilot and manually trim for 1,200fpm. Then I re-engage the autopilot thinking that it will resume Nav and hold the pitch that I have established. But instead of holding pitch, it levels off (actually noses up and goes positive pitch at first). Alt is not engaged. IAS is not engaged. What would possess the autopilot to override the pitch that was established? It seems like it has some memory of the prior pitch before it was previously disengaged. I tried this several more times with the same result. Each time the autopilot overrides the current trimmed pitch, bobbing and sometimes with about a 500 fpm descent after settling out.

Then, after all of that I hit the APPR button. GS goes green. But the autopilot decides to hold the current altitude and never follows the glide slope down.

Lateral modes seem fine, but vertical modes seem to be a great mystery.

Jason

I've had the exact same things happen and for me I had to make sure my loadout was being calculated properly. I knew this because when I had it dial in right, I would disengage the Alt hold or the AP, I would get a very nearly level flight. I know they have to address the IAS issue, but for me the rocker function is working quite well. Before I begin any descent I dial in new altitude, press alt alert, reduce power and switch off alt hold. Then I start hitting the rocker and if my CG is right, I can get plenty, but if tail heavy it will not want to go beyond 500 fpm. I'm for sure not telling you how to fly, this has just been my experience so far. But other than a few sound issues and the IAS issues, this thing is fantastic in my opinion. As far as the APPR, I've never had an issue with this following the GS and long as I entered at the proper GS elevation.

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This is just an observation, but quite a few comments on the forum seem to relate to automation issues. Sure, use alt hold of you really are flying that far, but to me at least, this is supposed to be flown, not for some computer to fly it for me. Looking out the window and actually flying is far more rewarding.....to me at least.

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I agree completely Paul, its just that little immersion factor to know that the automated system has the ability to work if so desired. But hand flying this aircraft is fantastic. When all things are said and done with this software, it could easily be my all time favorite, it just matches the type of flying that I really enjoy.

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I am not complaining. I am a systems person and I expect the systems to work within some degree of what is realistic, documented, and possible within the limitations of FSX. When I set an intercept altitude and set the flight director Alt Alert, I expect it to capture (IAS mode has blown through and ignored the set altitude a couple of times... both on climb and descent - could be something I did wrong). And on localizer when the G/S CAPT is activated and has a green indicator, I don't expect the aircraft to continue merrily on a held altitude while the needle descends but the aircraft does not. Pitch hold is not allowing AP-off / AP-on reset adjustments and seems to remember the prior pitch (after turning AP off and re-establishing a new trim/pitch), and I have not been able to reliably dial in a constant pitch via the bank control (keeps settling back down to about +/- 800fpm).

Weight & balance could also have been a factor in some of my trial flights as LeadingEdge suggested. I did have a third-party loader that was errantly putting some fuel into the L&R MAIN tanks that do not exist in this model.

I'm sure some of this is pilot error or misunderstanding exact nuances of the autopilot system, but I also think there are possibly system issues. This isn't my first addon ;) But admittedly, this autopilot has some uniqueness.

I have faith that the developers will fix issues where they may exist, but I think it is important to report suspected issues so they can be accounted and looked into. Saying "look out the window and fly" is not reasonable advice :)

Jason

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Saying "look out the window and fly" is not reasonable advice :)

Jason

Sorry, I agree that was a bit flippant.

I'm going for an automated flight before bed to see what I can find.

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I think we need to try a few flights using the same loads to try and replicate some of these issues and maybe post in this thread each specific issue. I've just spent an hour flying around using the AP, including a descent using CWS, NAV, ALT and APPR with glideslope capture and followed down to 200ft with no issue on disengaging and even IAS mode followed by increased power to climb................and dozed off until 10,000ft only to find it quite happily climbing still at 140kts.

The only thing I didn't like was using IAS mode for descent as I found it hard to get a stable VS and speed. That said, I really don't know if this is expecting too much of the AP, it felt like I was trying to get it to do airliner AP things and I just can't imagine anyone flying a Twotter would do anything to reduce alt apart from power off and AP off.

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When I set an intercept altitude and set the flight director Alt Alert, I expect it to capture (IAS mode has blown through and ignored the set altitude a couple of times... both on climb and descent - could be something I did wrong).

:)

Jason

I'm pretty certain this is an example of expecting too much. The AP ALT mode will only hold the altitude when selected; it doesn't do capture.

If I'm wrong, could someone correct me please.....it's late and I'm tired and I'm still using the Twotter final beta and don't have the release manuals to hand.

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I'm pretty certain this is an example of expecting too much. The AP ALT mode will only hold the altitude when selected; it doesn't do capture.

If I'm wrong, could someone correct me please.....it's late and I'm tired and I'm still using the Twotter final beta and don't have the release manuals to hand.

Yes Paul your wrong. Dial in your altitude then select your AP on, then select Alt Alert and trim with your rocker. the Alt alert function will capture and hold your pre selected Altitude. Also, I meant the wrong part respectfully. God knows how much you've contributed to others in this hobby all these long years now..

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LeadingEdge is correct. There is both the Autopilot and the Flight Director. The FD can level off if you select the "Alt Alert" button above the artificial horizon.

It is possible that I have been inadvertently disengaging the "Alt Alert" while messing around with other autopilot modes (switching between IAS on/off and temporarily disengaging the autopilot to change the pitch). I will pay more attention to see if that has been the intermittent issue.

What I still struggle with is the pitch. If I engage the autopilot shortly after takeoff (say currently climbing at 500fpm) and I then want to change pitch to 1500fpm, I can not get the rocker switch center yokes to pitch up more than about 800fpm. So, I disengage the autopilot and manually trim for 1500fpm. But when I re-engage the autopilot to "hold the new pitch/trim" it immediately drops the nose back down close to where it was in the original pitch. Same kind of behavior with descents - can't seem to command a new pitch angle.

Also with pitch, once I have a pitch set, changing the torque pressure seems to affect the pitch. I thought the point of pitch mode versus IAS mode is that increasing or decreasing power would not affect pitch in pitch mode (I am well above stall speed).

IAS mode, as stated by others, has very large pitch swings. On a test descent, it porpoised from -2 to +1 over and over.

Jason

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The only thing I can offer to that is, if the aircraft has an improper loadout CG it will behave poorly. I load my aircraft by hand with the default MS and have gotten it down to a fine art by quite a bit of trial and error. Should it be this sensitive. Not sure. But I will say this, when you have a good CG and you disconnect from Alt Hold Or The AP, the nose will move ever so slightly in an up or down fashion. You have all the time in the world to begin your Rocker selections. I can easily obtain a 2000 fpm rate with three or four rolls of the mouse wheel over the Rocker. But the IAS must be fixed, I've done all weight ranges just to make sure it was a loadout issue in my particular case, as to the VS issues. Note, even though I made mention of 2000 FPM use with the AP, there would and should never be a reason to ever use that rate in either a climb or a descent. My opinion of coarse.

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I would like to add, for those who are experiencing extreme pitching either up or down when disconnecting from the AP or ALT HOLD feature. While your in level AP controlled flight at cruise speed, check your elevator trim wheel by mousing over it and make sure your in the -6 to +6 range max. When you increase these numbers in either direction you will see issues. This will show whether or not you have a good CG with your loadouts.

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Nail hit on the head. This aircraft is all about TRIM

Well TRIM and BALANCE

Well, TRIM and BALANCE and FLYING IT RIGHT

or to put it another way...

The autopilot is there to aid the pilot, not bandaid a bad pilot.

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Ok, so the autopilot is not "crazy".

There is one issue where buttons get pressed and they stay depressed in transition even though I have already released the mouse button. I'm not sure in that case if the button is still activated or not. I have learned in this case to click the button again to get it back to a normal state.

As for the altitude intercept, ... my fault. While experimenting with pitch angles, I was inadvertently switching off/on the AP in some cases which disengages the Flight Director Alt Alert mode.

Still have some doubts about the AP pitch mode. If I trim and hold a pitch and then engage the AP (with no other mode selected) it still seems to settle down to a lower pitch. And when I decrease power it noses down and increase power it noses up -- almost as if it were in IAS mode (it is not). On climb-out it seems to seek about 95kts and nearly maintains that.

The pitch control issue could be that I am near weight capacity in most of my flights. It certainly won't let me stall with the AP engaged.

Jason

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Still have some doubts about the AP pitch mode. If I trim and hold a pitch and then engage the AP (with no other mode selected) it still seems to settle down to a lower pitch. And when I decrease power it noses down and increase power it noses up -- almost as if it were in IAS mode (it is not). On climb-out it seems to seek about 95kts and nearly maintains that.

I believe what's happening in your case is something like this: you have the pitch control rocket in neutral (not touched since take off), you are in a climb with a positive pitch and perfectly trimmed, then you engage the AP. From now on the aircraft should follow the current pitch trim indication given by the rocket but, as it is in neutral, will make a nose down to capture that position and, as you are in a climb with power, it is reasonable that the climb will continue in a lower rate at least for a while.

I've made a light inspect of the gauge code so far, will have more clues probably tonight when going deeper on the scripts.

Tom

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Now that's the million dollar question. Does this AP have a built in correction system that does not allow too steep of a VS, either in manual rocker use or the IAS. That would be a question for someone who has a history with this unit. If it is fashioned and coded correctly, that would explain the trim assist lights coming on even in manual rocker mode. Never used this type of AP in the real world.

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Just rechecked the code and found the pitch rocket doesn't work as I believed; instead when "manual" vertical mode is engaged, it is translating the last captured pitch to the elevator control with a custom formula.

I'll try using a direct FSX control mode and see what happens.

Tom

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Ahhhh. That's explains plenty. So basically its been setup to not allow for over corrections, ie, bad piloting inputs. In other words easy mode.

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Using a direct FSX control works ok, as expected. Also increasing the gauge's update frequency to the standard rate helps to solve the bumpy ride we are getting so far.

Tom

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Now that's the million dollar question. Does this AP have a built in correction system that does not allow too steep of a VS, either in manual rocker use or the IAS. That would be a question for someone who has a history with this unit. If it is fashioned and coded correctly, that would explain the trim assist lights coming on even in manual rocker mode. Never used this type of AP in the real world.

As best I can tell, the rocker switch will adjust Pitch in increments of one degree to a maximum of +10 or minimum of -10 degrees.

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My experiences with the autopilot are that when I have my aircraft properly trimmed to levelflight and engage the autopilot without a vertical mode it pitches till it climbs with aproximately 1000 fpm. I can adjust this with the rocker switch but I would like to have it centered.

I'm pretty certain this is an example of expecting too much. The AP ALT mode will only hold the altitude when selected; it doesn't do capture.

If I'm wrong, could someone correct me please.....it's late and I'm tired and I'm still using the Twotter final beta and don't have the release manuals to hand.

Sadly the alt hold is not holding the current altitude everytime. I have a Goflight GF-46 and can set altitude and climb rate. When I have a look at the altitude set there it is often 0 ft. When being higher and engaging alt hold it sets a negative climb rate and descents. It seems to me like the alt hold mode is sometimes not able to set the desired altitude to the current one.

Ah, setting a climb rate and capturing an altitude works pretty good by only setting it via the Goflight module when in Alt Hold. I dont know if there is a way to turn this off. I have the feeling that this is the reason for some issues with Alt Hold mode.

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If your loadout CG was poor

My experiences with the autopilot are that when I have my aircraft properly trimmed to levelflight and engage the autopilot without a vertical mode it pitches till it climbs with aproximately 1000 fpm. I can adjust this with the rocker switch but I would like to have it centered.

Sadly the alt hold is not holding the current altitude everytime. I have a Goflight GF-46 and can set altitude and climb rate. When I have a look at the altitude set there it is often 0 ft. When being higher and engaging alt hold it sets a negative climb rate and descents. It seems to me like the alt hold mode is sometimes not able to set the desired altitude to the current one.

Ah, setting a climb rate and capturing an altitude works pretty good by only setting it via the Goflight module when in Alt Hold. I dont know if there is a way to turn this off. I have the feeling that this is the reason for some issues with Alt Hold mode.

If your loadout CG was poor to begin with, it won't matter how well you trim your aircraft manually before engaging the AP. The AP is not God like and does not have the logic to completely correct that, oh it will try, but the results are either a rapid nose up or down depending on the CG. I've Personally had loadouts that I could trim the aircraft manually and actually fly, but the automated system would not tolerate it. There is no doubt there are somethings that need to be looked at with the coding of this AP, but whatever corrections are implemented, you will always need to load the aircraft correctly. If in level flight with Alt hold in effect and your at cruise speed, look down and mouse over the Elevator trim wheel, if you have numbers greater than -6 or +6 you have not loaded correctly. I personally have not had any issues with Alt Hold. But then again, I use it only when I want to stop a climb or a descent for whatever reason. Opting to always utilize my Alt alert function to capture altitudes, which is far more precise.

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