[NO BUG] Autopilot Pitch Attitude Hold switch ONLY engages Roll Attitude Hold

[danny875]

As title suggests: Pitch Attitude Hold switch engages Roll Attitude Hold.

This can be verified by selecting a Roll attitude and engaging Pitch Attitude Hold then after a few seconds pull the paddle in for another few seconds and watching the Roll Hold release.

After release of paddle the previous Roll attitude is resumed.

 

Thanks and I’ll try and get a track file tomorrow.

[Deano87]

I believe this is correct?

 

When selecting ATT HOLD on the pitch AP autopilot switch it enables both the pitch and roll control for the autopilot. If the roll switch is in the ATT HOLD position it should also come on at this time. So I fail to see what the problem is?

[danny875]

OK well if that is true then why is my pitch not being held? As you can see from the track (and from my experience of this issue) the pitch is not held in this mode just the roll attitude.

 

Edit: You are correct that the roll should be engaged when a pitch mode is selected.... didn't mean to sound s***8y but my pitch attitude hold isn't working... :)

 

Track attached. (asymmetric load to quickly show my issue)

 

 

 

Thanks.

 

 

Dan.

AP Roll Test.trk

Edited October 7, 2019 by danny875

[Deano87]

I can’t watch your track right now but Pitch hold works ok for me. But it only holds nose position not flight path. So if you climb your flight path may well change as you slow down but the nose should be held in roughly the same position compared to the horizon.

 

As to whether this is the correct implementation of ATT hold. I don’t know.

[danny875]

Here's another track with no payload, engage Pitch Attitude hold with or without a bank and the aircraft falls from the sky even under full mil power or AB eventually...

AP Roll Test 2.trk

[imacken]

This thread is an echo of https://forums.eagle.ru/showthread.php?t=251411

[danny875]

It’s a bug report based on my findings on that thread, it wasn’t clear to me if it was just me who couldn’t get Pitch attitude hold to work or not. How did you get on with it?

[imacken]

I find this whole thing confusing like the rest of you.

On the one hand, I can see that the Pitch ATT HOLD holds the nose pitch constant, but what use is that if the plane just keeps slowing down, AOA increases and ultimately starts losing height?

Is this correct behaviour? If so, what is the point of it?

Regarding the Roll ATT HOLD. I can't work out what is going on there. Bank angle seems to be held no matter what. Is that because the Roll ATT HOLD is selecetd and the other 2 Roll options don't work yet?

Still very confused by this AP.

[danny875]

Agreed that is confusing.

In my mind (not a pilot but have used MSFS since 2000) Roll attitude obviously does just that but the pitch attitude is used in any situation where workload is high and you want to engage autopilot, Hold a set attitude to either climb or descend either straight ahead OR whilst in a turn / Hold.

Like i said this is just me and what I have come to expect from an autopilot.

 

Having said that good speed management is vital so that the AOA doesn’t increase.

Granted in a fighter jet this mode may not be used much / if at all and it would be good to get some real life examples of which modes are used in different flight regimes.

[bbrz]

On the one hand, I can see that the Pitch ATT HOLD holds the nose pitch constant, but what use is that if the plane just keeps slowing down, AOA increases and ultimately starts losing height?

Is this correct behaviour? If so, what is the point of it?

ATT HLD is the most basic function of most AP systems. If you engage the AP without any other mode, it usually maintains pitch and roll attitude, even when being disturbed by turbulence/gusts.

 

If speed decreases you will of course loose height, otherwise the AP mode would be ALT hold, not ATT hold.

[Bouli306]

Be aware the F-16 is a fighter and does not have a Flight management system 787 style :-).

 

These are the functions:

 

Pitch switch: Attitude hold: jet will maintain set attitude up to the point were there is no energy left... than it will start to descend

 

Altitude hold: Jet will try to hold the altitude at witch the switch is engaged..this is also depending on energy off course

 

Roll switch: Attitude hold (see pitch switch but not for pitch but for roll attitude)

 

Heading select: Autopilot will follow the heading bug on the EHSI

 

STRNG SEL: steer towards the selected steerpoint in DED

 

With the Paddle switch on the joystick you will interrupt the AP but releasing the paddle switch the AP will try to continue as set before pressing the paddle switch. Because the AP has no indication of being on sometimes a pilot will fight the Autopilot.

 

Attitude hols is sometimes set when pilot wants some time to sort out problems/communicate etc. I have seen it being used during flights in a CAS wheel for example. Set a pitch and roll attitude hold and pilot can write down a nine line....

[Arbil]

A quick Google search should net you an actual f16c\d manual that answers all these questions in depth. One thing I gleaned from it that isn't right in our simulation is that in autopilot modes the stick trim should not be functional.

[danny875]

Be aware the F-16 is a fighter and does not have a Flight management system 787 style :-).

 

These are the functions:

 

Pitch switch: Attitude hold: jet will maintain set attitude up to the point were there is no energy left... than it will start to descend

 

Altitude hold: Jet will try to hold the altitude at witch the switch is engaged..this is also depending on energy off course

 

Roll switch: Attitude hold (see pitch switch but not for pitch but for roll attitude)

 

Heading select: Autopilot will follow the heading bug on the EHSI

 

STRNG SEL: steer towards the selected steerpoint in DED

 

With the Paddle switch on the joystick you will interrupt the AP but releasing the paddle switch the AP will try to continue as set before pressing the paddle switch. Because the AP has no indication of being on sometimes a pilot will fight the Autopilot.

 

Attitude hols is sometimes set when pilot wants some time to sort out problems/communicate etc. I have seen it being used during flights in a CAS wheel for example. Set a pitch and roll attitude hold and pilot can write down a nine line....

 

 

Appreciate the reply, thanks. Can I ask what is your take on the current implementation of the Pitch ATT Hold? If it is correct I'll forget about it and enjoy.

 

 

Cheers

[danny875]

A quick Google search should net you an actual f16c\d manual that answers all these questions in depth. One thing I gleaned from it that isn't right in our simulation is that in autopilot modes the stick trim should not be functional.

 

 

Yes I have now done this thanks, I didn't find the answer to my original post though :)

 

 

The suggested limits that I may have seen are not what I experience...

[Arbil]

Yes I have now done this thanks, I didn't find the answer to my original post though :)

 

 

The suggested limits that I may have seen are not what I experience...

 

If I'm going off exactly what your title says, "Autopilot Pitch Attitude Hold switch engages Roll Attitude Hold", then that is how it should work. There is no off position for the Roll autopilot, it's either in steerpoint, heading select, or attitude hold. The autopilot on/off switch is the pitch hold, either Altitude or Attitude. Turning the autopilot on is always going to engage one form of roll autopilot no matter what. The only one working right now is the basic attitude hold, the middle position on the roll switch. I haven't had any problems with it working correctly so far. Now if the aircraft is out of trim it can feel like the roll attitude isn't really working but that is how its supposed to work.

 

None of the autopilot modes engage if pitch/roll exceeds/is exceeding 60 degrees, but the switches stay in their on position making it seem like maybe they should have engaged ... perhaps you are seeing this sometimes?

Edited October 8, 2019 by Arbil
I was breaking rules?

[danny875]

Yep I gues my oringinal post title was probably incorrect I should have called it Autopilot Pitch Attitude Hold switch ONLY engages Roll Attitude Hold.

The fact remains for me that the pitch element is not respected (ie, no pitch hold that I can rely on), I was initially unsure of how the AP worked on the F16, now that I have read and been told how it is supposed to work I am convinced it isn't right.

Yes the paddle is a nice easy way to adjust the system.

BTW we can not post anything out of manuals on here, do yourself a favour and delete that part...

I have not engaged the AP whilst exceeding limits.

 

 

Cheers

[Frederf]

I do not share this experience. I set AP pitch to attitude, put gun cross on say the 5 degree pitch ladder and I can change speed all I like and gun cross remains on 5 degree pitch ladder. All I have not to do is exceed 15 AOA.

[imacken]

AFAICS, the AP pitch ATT HOLD holds the pitch angle ok if there is sufficient energy. What it doesn’t do is hold the flight path angle by altering the throttle input, so inevitably, your plane will increase AOA and start losing altitude if held in pitch ATT HOLD long enough.

I think probably some people were/are expecting the pitch ATT HOLD to be a flight path hold.

[danny875]

Hi, is there any update on the checking part yet?

I know there’s a lot going on right now and I’m sure this isn’t a priority but will the pitch hold be fixed or is it correct as is?

Thanks

[bbrz]

The problem is that it's apparently working for most of us, but not for you. Difficult to check/troubleshoot...

[danny875]

Yeah I get what you mean, could you please try something for me?

Fly at 5k feet AGL pitch up so your FPM is say 3 degrees with plenty of energy (low AOA) then put it into a roll attitude of just 20 degrees. Engage pitch attitude hold and tell what happens after 30 seconds or so?

Thanks

[imacken]

Hi, is there any update on the checking part yet?

I know there’s a lot going on right now and I’m sure this isn’t a priority but will the pitch hold be fixed or is it correct as is?

Thanks

What is it that you're still not sure of? We've established that the pitch angle hold, i.e. to the boresight, is working OK. It's is not holding the flight path angle, and hence height, when energy starts dropping. I think it's working correctly in that respect.

[danny875]

Thanks for your input but I’m not talking about losing speed at all, quite the opposite because in the experience with any Roll angle and increasing speed the pitch attitude will decrease (along with FPM I know).

Could you also try this out just so that I can know if it is an issue with my install or a bug, either way I’ll be a happy camper...

Cheers

[imacken]

I didn't say anything about speed!

 

However, I tried what you said, and with a speed of around 400, an AOA of about 3 degress, a flight path of around 3 degrees and the gun cross (boresight) therefore on about 6, a roll angle of 20 degrees at 5,000 feet, it maintained the 6 degrees pitch and the 20 degrees of roll after about 2 minutes.

 

Seems fine to me.

[danny875]

I lost my last post so let’s just say it’s my issue and not ED’s and thanks for trying out the issue for me.

The speed thing was me trying to explain the issue because for me any bank angle always resulted in a dive.

Cheers, now I can get on with it...