You and some others are not saying why though. You need to explain why, and in the light of products like the i-Gyro and Eagle tree Guardian using heading hold you need to explain why you are still fundamentally against it.

Alex, would be very interested to hear from you or Ali about why HH was not liked.

Andrew B, would also like to hear what it was that you didn't like about the feel of HH on elevator.

I have been using the Eagle Tree Guardian in prop models, in HH and rate modes. HH mode works well except that whatever you apply on the Guardian works to all 3 axes, and HH on rudder is bad as it makes the model sideslip in every turn. It isn't a fault, it's just that the control logic is optimised for 3D aeros rather than normal flight and HH on rudder would be good for things like Harrier rolls. However HH on the aileron and elevator works very well. Initially I feared that HH on the elevator would lead to unexpected stalls but it doesn’t. The thing is that you need a certain amount of back stick, usually a lot, to provoke a stall. The gain you set is in effect a max travel that the gyro can cause and if that is less than the elevator required to stall, the gyro in HH can’t stall the model because it simply can’t pull the stick back far enough. You only need a little gain to maintain attitude in normal flight speeds, any more and it starts hunting, and that low level of gain just won’t cause a stall.

I tried flight testing a trainer model in HH with a good amount of gain. What happens when you slow down? I put the model into a climb about 30 degrees and throttled to idle. Instead of immediately lowering the nose and maintaining speed, it stayed in that attitude as the gyro applied more and more elevator. Then still with some speed left the gyro reached its max gain/travel and the nose started to come down, until the model was descending still with the up elevator applied by the gyro. So the nose drops before the stall is reached as long as the gyro gain is less than required for the stall. I added power gently and the model just lifted its nose a bit, I added more power and so on and it just kept lifting the nose until it got back to the 30 degree nose up where it started.

I tried the same thing in level flight, throttle to idle, the gyro kept the fuselage level as the model slowed and started losing height, it ended in a level attitude descent at low speed but safely above the stall.

I then flew the model in level flight right to the point of the stall and released the stick. Since the gyro gain could not pull the elevator as much as I could, it promptly reduced elevator! The model nosed down a bit and descended but now well clear of the stall. I slowly applied power and it lifted the nose as I kept slowly applying more power, until it got the model into the same nose high attitude where I had let go of the stick but of course it now had more power and speed and was climbing. As I applied more power it just kept that same nose up attitude but accelerated up the climb.

You can get some unexpected effects when pulling higher angles of attack. For example if the gain means the gyro can pull about ¼ up elevator and you have it in slowish flight where the gyro is applying all of that, you start to pull back on the stick yourself which immediately cancels HH mode but you may have pulled back 1/8 stick, the gyro was applying ¼ stick so though you have pulled back the elevator has reduced not increased and the nose goes down in response to you pulling back a little. I also found that I lost some of the feedback about angles and speeds that pulling back on the stick gives me in slow flight.

For normal flying around I found that HH on elevator worked very well, but that at higher angles of attack/slower speeds it can give some odd effects and remove some of the information the pilot gets from the stick position about how the model is performing.