For those of you with TT, Trio, or other autopilots...
Can you engage them while in unusual attitudes? If you can engage them, what do they do?
For example, if you are nose high and in a steep bank, how does the autopilot behave if you (try to) engage it? Does it continue to fly on in the unusual attitude or does it roll wings level and capture your heading?
Good question.
In case of ours - it depends and I don't have a straight answer (no pun intended). The answer I am giving is for a typical 2 axis system where one axis is typically connected to the ailerons and the other to the elevator. I am qualifying this as you can connect up to 6 servos to our system and thus can theoretically have a full authority system that will even drop your gear before touchdown (autoland if you have a radar altimeter). But let's stay with a normal 2 axis system as this is what most of our customers will be using (at least I think so).
If you do not have a current navigation solution (i.e. not an active GPS "goto", route, ILS, GLS, VOR, etc, etc), the autopilot will engage and do whatever it takes to hold the heading as well as the altitude at time of engagement (i.e. it automatically sets and switches to the altimeter and heading bug). The autopilot will cause the servos to engage at their current position and will then control them to achieve straight and level, subject to low and high airspeed limit restrictions.
If you have an active navigation solution prepared, as you engage the autopilot will then latch onto the heading (and altitude as required) from the navigation source correcting any unusual attitudes as required.
As interesting point, should you engage while you are upside down, it will attempt to level in upside down attitude first, before rolling you the right side up, all the while being aware of both lower and upper airspeed limits.
Obviously, some aircraft can do this better than others so this may be a little academic (you can tell I'm having fun with this thing
). The exact reaction also depends highly on the type of servos fitted (mainly servo speed) and how the autopilot system is characterised (and this is decided by our users).
As a footnote, our autopilot has not yet been released so final operation may differ slightly (but not much) and, as usual will likely develop with time due to user input and special requests - so no telling what it will do one day.
To be fair, autopilots that form part of EFIS systems tend to be able to do much more compared to stand-alone autopilots. The reason for this is that only the EFIS "knows" everything - actual attitude, rate of turn around all axis, magnetic heading, GPS track and heading, airspeed, vertical speed, climb or descent angle, G-forces, even terrain proximity. If you think about it - it's really the only place for an autopilot to be.
Many stand-alone autopilots simply do not have the luxury of all this data. Nevertheless, for simple flight stabilization and keeping track they can be just fine. Many are based on just a simple, single gyro mounted such that it will detect both roll and turn (but actually cannot distinguish between these). Needless to say, these types would not know if they are upside down.
Rainier
CEO MGL Avionics
P.S. Off to the airfield in a few minutes to do some more testing on our autopilot system. I'm having LOT's of fun...
