combat trim tries to adjust elevators to the effect of; if you let go of the stick, it will neither nose up or nose down. The faster you go, the more combat trim will lower the elevator tabs.
In the 38 this creates a problem when entering compression. You want to pull up, and combat trim is working aginst you by trimming elevators down. Also in real life as in AH, compression recovery could be achieved by trimming the elevators up, and eventually the trim catches enough air to change AoA enough for the wings to gain positive pressure underneath.
Something to keep in mind about elevator trim is that its effect on the wings AoA is cumulative with actual elevator operation. I will pick an abitray number of degree to explain my point. Lets say your plane will lose controled flight if your wings are pitched up 18degrees in relation to its direction of travel. It does not matter whether you are causing that pitch with elevators, trim, or a combination of the two. That threshhold of 18deg is still the same. In other words you can turn just as tight with neutral trim and max elevator angle, as you can with max trim and minimal elevator angle. The lift or stall happens at the wing, the elevator is just a tool to change the AoA of the wing.
Now add combat trim to the equation. The harder you turn, the more air you displace, the more drag produced, you lose speed. Now say you pull a tight turn at the edge of controled flight, and hold your elevators at a constant angle. The turn will slow you down, which causes the combat trim to tab up. So even though you kept a constant elevator angle with the stick, combat trim has in effect added more angle. If you were riding the edge it may have just pushed you over the edge.
The same applies to vertical stall maneuvers. You zoom to stall speed, and combat trim is trimming way up to adjust to your speed. After the stall over, combat trim is applying so much angle, that there is very little you can do with the stick. If you had manual trim neutral in that situation, you have more lattitude to apply elevator input at an earlier time.
Dont get me wrong, I have nothing aginst combat trim. In the 38, it is something I toggle on and off quickly to retrim my plane neutral relative to speed. In BnZ situations in any plane I may keep it on to give myself a stable shooting platform. Because of the reasons outlined above it is something I use on the basis of the situation, and not full time.
