Let me clarify what combat trim does, and when you should and should not use it.
Combat trim, as I understand it, is basically a table of trim conditions that map to various airspeeds, but it's not a large table, so most of the time it doesn't trim you exactly right. These trim conditions are for a clean airframe well within the normal flight envelope. What I mean by that is, it seems that combat trim doesn't have trim settings for very slow or very fast speeds, only the more middle range. For example in the P-38, I would say to disable CT and use manual trim under 200MPH or over 400MPH. Luckily, the second you hit the manual trim key, the CT is disengaged, and you can re-engage it again by using any of the three auto trim modes. You can have the best of both worlds.
The P38 is probably the plane that will use CT the least, since it's "normal flight envelope" is pretty small between high speed for it and when you start deploying combat flaps. Other planes like the Jug have a much wider range where you want to use CT... I use CT from about 180 to almost 500 in the Jug. In most planes, in most situations, you can just leave CT on all the time and be competitive, but the Fork Tailed Devil seems to be more sensitive than most.
CT is useful for BnZ type fighting where you are rapidly changing speeds within your normal flight envelope with a clean airframe. If you have drop tanks, it won't trim you properly. If you use flaps, it won't trim you properly. If you are flying too slowly, it won't trim you properly. Etc. So what I would do is as I get to the top of a loop as I engage and my speed is dropping below 200, I would pop a notch of flap and dial in a bit of nose-up trim to compensate. That disables my CT and I manual trim for the rest of the fight, or unless I'm in a situation where I use my auto-trim modes.
Now, the question was, how do you figure out how much to trim at a given speed, altitude, and flap position? The best way is to use the auto trim modes to do it for you!
Take a look at this article I wrote a while back. It has not been updated for combat trim, but the basics still apply for using the auto trim modes and manual trim settings:
http://users.andara.com/~sconrad/trim.htm The bottom line is that you will have to learn your aircraft so that you have a rough idea how much manual trim you need to dial in as you slow to low speed, and deploy varying degrees of flap. The only way to do this is to test. What you do is pick an altitude and fuel state, and get yourself there in your plane. Now decide on a speed... say 150 IAS if that is your sustained turning speed. Now you figure in a turn fight you'll have 3 notches of flap out at this speed... deploy that. Next type in ".speed 150" into the radio. Engage your auto-trim for speed mode (the one you use to climb) and let the plane stabilize... it is now perfectly trimmed for that altitude, speed, weight, and flap condition. Next you disengage the auto-trim mode and pull in your flaps, but try to keep the plane at the same speed by climbing a bit and/or cutting throttle. Once you have stabilized, use your manual trim to trim the plane out to fly at that speed... record how much trim you had to use. So if you were clean at 150 and dropped the same amount of flaps, you would need to put in that amount of trim in the opposite direction to compensate. Next let the plane speed up to your normal cruising speed, say 250. You'll have to hold it level, because as you speed up your trim state will get out of whack. Once you are at your cruise speed, trim the plane for level flight again manually, and again record how much trim you had to dial in. You now know roughly how much trim you have to use as you change from 150 to 250 MPH at that altitude, flap condition... etc. When you are doing this, don't worry about anything but elevator trim at first, and don't get too exact... just get close. You can also judge it by looking at your trim indicators instead of counting keystrokes if you like.
The point of all of that is not to know EXACTLY how many keystrokes of trim you need for every situation, but just to learn roughly how much you are going to need to adjust when using manual trim when you change speeds or deploy flaps. A key point is knowing which direction to trim when you deploy flaps, and roughly how much. Each plane is going to work a bit differently, so the best way to figure this out is to test it in your favourite ride.
Personally, I just leave CT on all the time, and disable it by using manual trim when I am extremely slow and using flaps, or when I am diving to INSANE SPEED (TM). Actually I'll normally use auto-trim angle or auto-trim for speed to get perfectly trimmed INSANE SPEED (TM) dives.
Does that make sense? Questions?
[ 11-01-2001: Message edited by: Lephturn ]
