When I try to lower the altitude using the autopilot, the Twin Otter will nose down extremely, going to -4 or beyond that, on the VSI

[Abrams Tank 2]

Hi.  I am using the Twin Otter from the MSFS marketplace. So when I try to lower the altitude on the Twin Otter via the autopilot, the Twin Otter will nose down extremely, sometimes reaching -4 on the VSI, or even beyond -4 on the VSI.

 

The key thing I noticed is that the autopilot is on the entire time, when I try to lower the altitude. So here is what you can do to recreate this issue:

 

1. Takeoff from an airport.
2. “SET ALTITUDE” is set to 4000, the autopilot is set to on, and I have pushed the up arrow Vertical Speed button to raise the vertical speed to +500 feet per minute so I can reach 4000 feet faster.
3. The Twin Otter will reach the altitude of 4000 feet and stay there. I have not touched anything else in the mean time.
4. Now I am getting close to my destination. So I turn the blue altitude knob on the “SET ALTITUDE” to 1500 feet.
5. When I click the up arrow Vertical Speed button this time, the Twin Otter will nose down severely, jumping to as much -4 on the VSI, or even beyond -4 on the VSI.

The only thing that seems to prevent this is to turn off the autopilot, and turn it back on again. If I do this, the Twin Otter won’t nose down that severely (ie. it won’t go to -4, or -5 on the VSI), and the nose down is much more normal. This issue with the Twin Otter seems like some weird issue when I try to lower the altitude while keeping the autopilot on. This behavior for the Twin Otter is very different than how the G1000 autopilot works for the Cessna 172, I can keep the autopilot on at all times, when I want to lower the altitude of the Cessna 172 G1000, and the Cessna 172 G1000 will get to the lower altitude with a much more milder nose down and much more milder negative vertical speed (there is no need for me to turn the autopilot off and turn it on again, for the Cessna 172 G1000 when I want to go to a lower altitude).

 

Why does the Twin Otter nose down that severely, reaching -4 on the VSI, when I try to lower the altitude using the autopilot? Do I need to turn the autopilot off and on again, to properly lower the altitude with the Twin Otter without the VSI hitting -4? Is this how it works in real life too?

[MarkHurst 173]

39 minutes ago, Abrams Tank said:

1. Now I am getting close to my destination. So I turn the blue altitude knob on the “SET ALTITUDE” to 1500 feet.
2. When I click the up arrow Vertical Speed button this time, the Twin Otter will nose down severely, jumping to as much -4 on the VSI, or even beyond -4 on the VSI.

 

I'm not 100% sure what you are seeing here, but those two steps suggest you are expecting the wrong behaviour. (I assume you mean the DOWN arrow button in step 5, by the way.) If you are on ALT mode, the up/down buttons don't set vertical speed, they nudge the altitude up or down in small increments. Well that's what they're supposed to do, but they don't work according to the manual. I don't think that's a factor here. What you should do is to preselect the new altitude (your step 4), then press ALT to flip from ALT mode to VS mode, then press the down button a few times to set your VS.

 

That said, I have found the VS mode a bit buggy. I did some bits of SPAD.neXt programming to make it work better. I have made a video about this, which you can find on my YT channel by clicking the link in my signature. (I posted a link here before but it was removed.) Maybe that will help.

[Abrams Tank 2]

On 8/2/2022 at 12:42 AM, MarkHurst said:

 

I'm not 100% sure what you are seeing here, but those two steps suggest you are expecting the wrong behaviour. (I assume you mean the DOWN arrow button in step 5, by the way.) If you are on ALT mode, the up/down buttons don't set vertical speed, they nudge the altitude up or down in small increments. Well that's what they're supposed to do, but they don't work according to the manual. I don't think that's a factor here. What you should do is to preselect the new altitude (your step 4), then press ALT to flip from ALT mode to VS mode, then press the down button a few times to set your VS.

 

That said, I have found the VS mode a bit buggy. I did some bits of SPAD.neXt programming to make it work better. I have made a video about this, which you can find on my YT channel by clicking the link in my signature. (I posted a link here before but it was removed.) Maybe that will help.

 

Hi.  Thanks for your help! I tried it your way, by pushing ALT and changing it to VS speed mode, before hitting the vertical speed down arrow, in Step 5.  When I did this, the first time I clicked on the vertical speed down arrow, the vertical speed dropped very mildly (to -100 feet per minute or about -0.1 on the VSI) and the the Twin Otter nosed down ever so lightly, which was the behavior I expected.  This is much better than the behavior than before, when the Twin Otter nosed down severely, hitting -4 on the VSI! 

 

Thanks for your help!

[MarkHurst 173]

2 hours ago, Abrams Tank said:

 

Hi.  Thanks for your help! I tried it your way, by pushing ALT and changing it to VS speed mode, before hitting the vertical speed down arrow, in Step 5.  When I did this, the first time I clicked on the vertical speed down arrow, the vertical speed dropped very mildly (to -100 feet per minute or about -0.1 on the VSI) and the the Twin Otter nosed down ever so lightly, which was the behavior I expected.  This is much better than the behavior than before, when the Twin Otter nosed down severely, hitting -4 on the VSI! 

 

 

Yes, that sounds right. It will dial in 100-fpm increments with each button press!