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Autopilot Pitch Modes


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The autopilot in the MU-2 doesn't seem to behave like other position based autopilots I've seen.  Typically, you'll turn on the autopilot and set the horizontal and vertical mode you want and then use the autopilot pitch wheel to adjust the vertical mode you have selected.  This usually works by setting your desired altitude and then selecting "altitude capture" and then either "VS" or "IAS" mode during initial climb.  The autopilot will capture whatever vertical speed or indicated airspeed the airplane had at that moment.  Say you selected IAS mode during an initial climb at 120 kias.  The plane will hold 120 kias in the climb.  But, that's too slow, so you then spin the autopilot pitch wheel forward (down) until you reach your desired climb speed - something like 150 kias.  You can also use the pitch wheel to increase or decrease rate of climb in VS mode.  But this doesn't work in the MU-2.  Spinning the pitch wheel does nothing.  Same thing when starting a descent.  Say you're cruising at 20,000 feet.  To begin a descent, you would typically select your new desired altitude in the altitude preselect window - let's say 5000 feet.  Then click "alt select", then select VS mode.  Then you would roll the pitch wheel down until achieving your desired rate of descent.  A few clicks to get 1000 fpm down.  Then you can adjust rate of descent up or down throughout the descent by clicking the pitch wheel up or down.  Again, this does nothing in the MU-2.  New altitude selected, "alt set" turned on, VS mode selected, roll the pitch wheel forward and...nothing happens.  To get a descent going, I have to turn the autopilot off, push the yoke forward to pitch down, quickly turn the autopilot back on, select VS mode and then accept whatever vertical speed results.  No adjustments can be made to vertical speed - the autopilot pitch wheel does nothing.  I haven't set any of my hardware to control the autopilot pitch wheel.  I'm simply manipulating it with my mouse.  The animation shows the pitch wheel moving, but it has no effect on the actual pitch of the aircraft in any of the autopilot vertical modes.  I didn't see anything in the manual pertaining to the autopilot that might shed some light on this issue.

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34 minutes ago, Anthony Clark said:

To get a descent going, I have to turn the autopilot off, push the yoke forward to pitch down, quickly turn the autopilot back on, select VS mode and then accept whatever vertical speed results.  No adjustments can be made to vertical speed - the autopilot pitch wheel does nothing.  I haven't set any of my hardware to control the autopilot pitch wheel.  I'm simply manipulating it with my mouse.  The animation shows the pitch wheel moving, but it has no effect on the actual pitch of the aircraft in any of the autopilot vertical modes.

This is correct behavior for the autopilot in the MU-2.

As explained in the manual:

ALT (Altitude hold) Mode Select

Maintains indicated altitude at the time this mode is selected.

VS (vertical speed) mode select

This mode will hold the vertical speed at the time this mode is initiated. Vertical speed is NOT selectable by other means.

AS (indicated air speed) mode select

This mode will hold the indicated air speed at the time this mode is initiated by adjusting the pitch of the aircraft.

 

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Posted (edited)

Wow.  That severely limits the usefulness of the autopilot and the aircraft in general, particularly on a high performance, high altitude hotrod like the MU-2.  Even the autopilot in the 172 that I rent is more advanced - you can adjust the rate of climb or descent without turning the autopilot off.  Just push the up or down buttons to adjust the vertical speed.  It's simply inconceivable to me that you would have to turn the autopilot off, manually adjust the pitch, and turn the autopilot back on in order to change your rate of climb or descent.  I've never seen an autopilot like that on a real or simulated aircraft - with the exception of very simple units that only have altitude hold - no VS or IAS modes.  So, what does the autopilot pitch wheel actually do if it doesn't adjust the selected vertical mode?  Why is it even there if it doesn't do anything?  And what is the correct procedure for initiating a descent in the MU-2?

Edited by Anthony Clark
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2 hours ago, Anthony Clark said:

It's simply inconceivable to me that you would have to turn the autopilot off, manually adjust the pitch, and turn the autopilot back on in order to change your rate of climb or descent.

This is essentially how it is, though. Most MU-2 pilots would place the AP in STBY mode rather than totally disengage (this basically soft disengages the autopilot by keeping it "on", but not flying the aircraft), re-adjust, then re-engage any mode necessary.

It's not uncommon for an old autopilot, and yes, many 172's and other GA aircraft have better AP's these days. Technology has evolved a lot since the ~1980's and even 90's. This is definitely not unique to the MU-2 though.

The best practiced method would be to use the pitch trim wheel to assist in your VS mode. Once you dial in the VS trim to your liking, engage VS. The same would be said for descent.

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There are plenty of xplane aircraft whos aps, works exactly the same. I have a few. Just means the pilot, thats you actually has to fly the plane, After all isnt that what pilots train to do. Still remember a few years ago, Boeing retraining pilots because tech has caused them to forget how to fly, Its getting worse,

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12 hours ago, Anthony Clark said:

 It's simply inconceivable to me that you would have to turn the autopilot off, manually adjust the pitch, and turn the autopilot back on in order to change your rate of climb or descent

Me too...which is why you don't do it this way.  With the AP engaged and presumably in ALT mode, simply hit SBY ...or deselect the ALT mode.....or hit ALTSEL (all 3 cancel the ALT hold mode) and then use the pitch wheel to dial in the VVI you desire....WHILE the AP is still engaged.  When you achieve the rate of climb/descent you desire via the pitch wheel, then simply hit the VS mode button to hold that value.  Easy peasy....sure, not quite as easy as modern copilots for sure, but neither terribly bothersome either. 

TK

Edited by tkyler
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Alright.  Thanks.  I'll try it.  I searched the entire manual for that kind of description as to how it's done and didn't find any.  I actually didn't see anything at all about the autopilot in the manual.  I really did try to resolve the issue on my own before posting in the support forum.  I am a real world pilot, so I know how most of this stuff works.  I've never encountered an autopilot like the one in your MU-2 before.  They either have a simple altitude hold where you hand fly the aircraft to altitude and then engage the autopilot...or they have vertical speed modes and altitude preselect where you select your altitude and adjust your climb rate with a wheel or up/down buttons.  Never seen one with a vertical speed mode that isn't adjustable.  I'm looking forward to a more detailed manual that explains specific procedures for flying this plane or some tutorial videos.  Thanks again for your excellent work.

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5 minutes ago, Anthony Clark said:

I searched the entire manual for that kind of description as to how it's done and didn't find any.

There's a search function on the manual you can use. The word 'autopilot' would have yielded an immediate result: http://togasim.com/mu2docs/supplements/spz500.html#sperry-spz-500-autoflight-system

If all else fails, be sure to use that search function in the future. It's a quick way to get around. :)

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14 hours ago, mjrhealth said:

There are plenty of xplane aircraft whos aps, works exactly the same. I have a few. Just means the pilot, thats you actually has to fly the plane, After all isnt that what pilots train to do. Still remember a few years ago, Boeing retraining pilots because tech has caused them to forget how to fly, Its getting worse,

Sorry, this is the first one I've encountered that has a vertical speed mode that is not adjustable.  Typically autopilots have just a simple altitude hold or they have altitude preselect with an adjustable vertical speed mode.  Like the KAP140 in the 172 I fly in the real world.  Most other X-Plane aircraft have an S-TEC 55 or Garmin GFC500/600/700 that operates that same way.  The only other old school twin turboprop I have is Carenado's Cheyenne II.  It has an autopilot that looks very similar to the one in the MU-2, but its pitch wheel adjusts VS and IAS modes.

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Also, I just want to say thanks for the professional and patient responses.  No terse comments or belittling like I've encountered on another well-known X-Plane forum.  That one seems to be run by an immature school yard bully who loves putting others down and censoring those who post things he doesn't like.  I don't see any of that here.  Just kind professionalism.

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13 hours ago, zpkarol said:

The autopilot supplement definitively deserves an entry in the left-side documentation navigation menu BTW

its actually been on my todo list for some time....just end of summer stuffs (family) and this XP12 transition business is taking my time atm.  I fully intend to do a comprehensive AP supplement along with some tutorials as soon as possible.

-TK

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On 8/24/2022 at 8:27 PM, Anthony Clark said:

Sorry, this is the first one I've encountered that has a vertical speed mode that is not adjustable.  Typically autopilots have just a simple altitude hold or they have altitude preselect with an adjustable vertical speed mode.  Like the KAP140 in the 172 I fly in the real world.  Most other X-Plane aircraft have an S-TEC 55 or Garmin GFC500/600/700 that operates that same way.  The only other old school twin turboprop I have is Carenado's Cheyenne II.  It has an autopilot that looks very similar to the one in the MU-2, but its pitch wheel adjusts VS and IAS modes.

The Mu-2 does have support for the RealsimGear G500 software so if you've got that you can use it to control the VS speed as you'd expect.

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On 8/24/2022 at 2:20 PM, Anthony Clark said:

I searched the entire manual for that kind of description as to how it's done and didn't find any

So official "full manuals" of an autopilot system as old as the SPZ-500 aren't exactly floating around freely on the internet....BUT...*wink wink.....I may or may not have miraculously gained clarity on a lot of how this system operates....AND...I may or may not...ok MAY....be updating the docs to include a comprehensive SPZ-500 supplement on how the system works with answers to all your (and even my) questions.  Get ready for a few "HUHs?" (see quote below) ...can't say the AOM was as clear as....um..."my enlightenment".  

image.png

Turns out there are 8 other ways to disconnect the AP servos.   

-TK

Edited by tkyler
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On 8/24/2022 at 2:20 PM, Anthony Clark said:

or they have vertical speed modes and altitude preselect where you select your altitude and adjust your climb rate with a wheel or up/down buttons

So turns out that these are "options" as part of the Sperry SPZ-500 system...and being an older system, not a lot of the inputs were integrated into small form factor interfaces.... and subsequently,  not all of these options were adopted by the manufacturers.  Who knows what drove the decisions...weight...panel space, etc.  Below is the 'controller' that would allow you to dial in the IAS or VS for the SPZ-500 system....but this option was not installed by Mitsubishi.  Because you can simply adjust the pitch wheel to dial in VS or IAS and then "lock that in" via the mode buttons may have been considered enough.   Who knows.

-TK

 

s-l500.jpg

Edited by tkyler
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  • 4 weeks later...

As is also the case with the AFL King Air, the position of the AP on/off panel is down at the end of the pedestal which makes it’s extremely difficult for sim pilots to use safely. Unlike real life where your hand can quickly find the controls without looking, in the sim you have to look down and hunt with the mouse. In those long seconds when you are looking down, you can easily lose situational awareness. A very uncomfortable few moments which makes adjusting VS very difficult IMO.

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On 9/23/2022 at 8:15 AM, shootersteve77 said:

A very uncomfortable few moments which makes adjusting VS very difficult IMO.

The solution here the Marquise employed is the TCS mode (Touch Control Steering).  This is documented for the 2.0.3 update which should go out soon...its in X-Aviation's hands, but they're also working through multiple product transitions to V12, so it should hit soon enough.

The TCS is an effective way to alter IAS and VS values without having to look down or change/disable AP modes...and once you get used to it, dare I say somewhat preferred (by me anyhow) over a knob based solution...you can keep your eye on the instruments at all times while holding down the TCS button and changing the VS or IAS values.

-TK

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