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OnCourse

AutoPilot altitude setting causes plane to lunge up and stall...

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Turning on the autopilot altitude setting does not seem to work as intended, and in fact causes the plane to crash. The NAV functionality seems to work fine though. What is going on?

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Hi,

 

Could you exactly describe the steps you are doing? As the ALT function works for most of the pilots here, there must be something wrong with your approach to use it. So please provide more details (also SIM and version).

 

Rgds
Reinhard

 

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Hi,

 

Maybe these lines in the documentation provided will help you to use it correctly:

 

The following vertical modes can be selected on the AP-106 autopilot panel:

 

ALT: Will hold the altitude present when the ALT button was pressed.

 

IAS: Uses pitch to hold the indicated airspeed present when the IAS button was pressed: Increasing power will initiate or increase rate of climb. Decreasing power will initiate or increase rate of descent. IAS mode may therefore be used for both climb and descent.

 

ALT ALRT: Will automatically level out the aircraft once it has reached the set altitude when the AP is in either "Manual" or IAS mode

 

Rgds

Reinhard

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Hi,

 

It's a long time ago, when I flew a plane with the default autopilot, but as far as I remember, the ALT mode behaves different in the Twin Otter compared to the standard AP. isn't it? The default AP climbs or descends to the selected altitude and you can modify the VS to reach that altitude. The Twin Otter ALT button just holds the current altitude, as soon as you push it.

 

From the P3D manual:

5 - Altitude hold mode selector button

The altitude hold mode selector button engages the autopilot's altitude hold mode. When engaged, the aircraft climbs/descends to the altitude set in the altitude selector at the rate set in the vertical speed selector (see below).

 

 

Rgds

Reinhard

 

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At the time when I was flying the Twotter I kept some add. notes (most of them where provided by Finn, one of the devs):

 

Altitude Hold

Pushing the ALT button on the autopilot will make the aircraft level out and hold the altitude present when the button was pushed.

For automatical holding a preset altitude do as follows:

Set Your required altitude in the altitude alerter window - let´s say 7000 ft.

Press the ALT ALRT Button to the left of the altitude alerter.

Climb in either autopilot manual mode (Autopilot engaged, but with no vertical mode selected). Pitch attitude is set via the thumb knob/switch assambly in the center of the Yoke.

Use the mousewheel while hovering the cursor over the thumbwheel/switch assembly to set a desired upward pitch.

Or use IAS mode to climb at a desired speed. I.e set desired engine power, set elevator trim to an attitude that will keep a steady airspeed of let´s say 100 knots, push the IAS button on the autopilot and engage the autopilot.

The autopilot will now adjust pitch in order to hold the airspeed present when the IAS button was pushed.

Shortly before reaching the desired altitude, set in the altitude alerter window, the autopilot will automatically change from IAS hold to ALT hold.

In IAS mode You can adhust Your vertical speed by adding or reducing engine power.

If engine power becomes low, then the aircraft will descend instead of climb in order to keep the desired speed.

This way You can also descend from higher altitude and automatically level out at an desired altitude.

Just always remember to set the desired altitude on the altitude alerter and engaged ALT ALRT.

 

Climb and Descent

if ALT Mode engaged while using autopilot, first cancel ALT. Now you can use the rocker switch (in the middle of the yoke, next to where the "Yaw" button is) to pitch your aircraft up or down.

If any HDG or NAV is engaged, you can leave that on, and aircraft will fly up or down according to pitch setting. Use the ALT Alert button to Level out when selected altitude is reached.

Or:

You can also engage IAS mode.

Imagine this situation:

  • Your flying level in ALT mode wither power set to ~75%
  • Now engage IAS mode.
  • Increasing power will make You climb inorder to keep the airspeed present when You engaged IAS mode.
  • ower will make You descend inorder to keep the airspeed present when IAS mode was engaged

 

IAS Hold

First ensure that the aircraft is properly trimmed. Don´t start reducing power before engaging IAS.When flying level with a certain power setting, first engage IAS mode, then reduce power.

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1 hour ago, mopperle said:

At the time when I was flying the Twotter I kept some add. notes

 

As luck would have it, I made a recent video about this, including a couple of innovations you can easily add with some Lua code.

 

 

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On 6/11/2019 at 8:43 AM, mopperle said:

Pitch attitude is set via the thumb knob/switch assembly in the center of the Yoke.

 

This is where I am having my issue. If I try and use the pitch controls to correct the autopilot's sudden climb or descent, it automatically disengages the ALT mode. I usually bring the plane up manually to within 100ft of the assigned altitude, then engage AP (if it wasn't already on before), followed by ALT. Sometimes it will just lunge upwards or downwards by more than 1000ft even though I brought it within 100ft of its destination altitude.

 

I just tried it again and cannot seem to replicate the problem I was having before. Will record a video of it next time it is happening.

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4 hours ago, OnCourse said:

I just tried it again and cannot seem to replicate the problem I was having before. Will record a video of it next time it is happening.

 

The only way I can think of reproducing this behaviour is to disengage the A/P while ALT is still selected, fly to a different altitude and then re-engage the A/P. In this case it will try to re-acquire the altitude it was holding before.

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Because we believe this topic has been answered we have closed it. If you have any more questions feel free to open a new topic.

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