Rainier Lamers
Well Known Member
This may be of relevance to Dynon and MGL autopilots (if the built in AP is used in case of the MGL).
During tests we discovered an interesting effect related to static pressure. This tends to affect only a few aircraft and is directly related to the static system and where and how static pressure is measured.
The new AP systems tend to be extremely good in resolving static pressure to very fine resolution. This can be a problem. Depending on type and placement of the static port, even very small changes in pitch attitude can lead to noticable changes in measured static pressure. This may be because the port is located in an area that is affected by turbulence caused by appendages or very sensitive to actual AOA. The changes in pressure are very small and do not really show on VSI or altimeter (not in a way that you would be bothered) - but the AP does see this and will initiate a correction (that it should not). This can be the start of an endless series of attempts by the AP to exactly capture the desired altitude - but it never manages, the static pressure keeps running away...
If you have issues like this that you cannot calibrate out by the AP's sensitivity settings, try the folowing:
For a test, vent the static directly to the cabin (static in the cabin does not seem to be influenced greatly by small attitude changes).
If this fixes or improves it. Time to find a better place for your static port...
Rainier
CEO MGL Avionics
During tests we discovered an interesting effect related to static pressure. This tends to affect only a few aircraft and is directly related to the static system and where and how static pressure is measured.
The new AP systems tend to be extremely good in resolving static pressure to very fine resolution. This can be a problem. Depending on type and placement of the static port, even very small changes in pitch attitude can lead to noticable changes in measured static pressure. This may be because the port is located in an area that is affected by turbulence caused by appendages or very sensitive to actual AOA. The changes in pressure are very small and do not really show on VSI or altimeter (not in a way that you would be bothered) - but the AP does see this and will initiate a correction (that it should not). This can be the start of an endless series of attempts by the AP to exactly capture the desired altitude - but it never manages, the static pressure keeps running away...
If you have issues like this that you cannot calibrate out by the AP's sensitivity settings, try the folowing:
For a test, vent the static directly to the cabin (static in the cabin does not seem to be influenced greatly by small attitude changes).
If this fixes or improves it. Time to find a better place for your static port...
Rainier
CEO MGL Avionics