Pitch going up and down with AP on

[Randy]

With my MCP unit on from CPflight at times when I change flight levels, lets say to climb, the plane starts to climb, pitching up on vert speed needle, but then, the plane will pitch downward, then come back upwards and so on and so on.   Anyone know why this happens.   

 Also, at times when I am descending, and I set speed reduction in AT, because I am desending, the idle goes only to 40% N1 and speed starts to increase a lot instead of coming down to the set lower AT speed.   Anyone know how to adjust it so idle goes to like 20% N1 like when just on start up? 

I use P3d v4, Spadnext, Project Magenta, and CPflight MCP unit. 

[Bob Scott]

What airplane?

20% N1 at idle on pretty much any jet engine operating at altitude is very low.  If you're accelerating in a descent, it's probably because you have too high a descent rate set.  Think of it like a sled going downhill--the steeper the hill, the faster you go.

[Randy]

Hi Bob,

I am using Project Magenta's 737-800 model.   During MCP AT I can only get 40% N1.   On start up I do get around 20%.   Because the plane speeds up during decent with AT, I usually try just 800 fpm with VS.  Do you know how I can get the PM MCP AT to give me 20% during flight if needed?

Randy 

Edited January 9, 2024 by Randy

[jcomm]

Ground idle is usually lower than FLIGHT IDLE. 

I have not the exact values present but FLIGHT IDLE in a 737 in approach configuration depends on N2 flight idle but could be around 32% N1...

Edited January 11, 2024 by jcomm

[OH-LXD]

Hi,  I have Project Magenta and Airbus full setup. I used to have same kind of up and down pitch behavior during climb.  Past years I have noticed that the model you use and some parameters will affect autopilot.  There is manual but quite limited info about what values and how they affect considering ini of cfg files.  Also support is pretty random as far as I have experienced.

Do you use exactly recommended aircraft model and FMC type file from PM update page?  Newest builds? 

In P3d you have aircraft folder that includes your preferred 737 aircraft.  There is aircraft.cfg file. What do you have in those lines : aileron and elevator effectiveness?  What about pitch stability setting?  What is you Thrust scalar value? 

I know nothing about PM737 software, but Airbus has possibility to use either FCU autopilot parameters to control pitch and bank or special PmFBW (fly-by-wire) software.  I use FBW because it has more sophisticated control options over autopilot.

Yours, Markus