Combat Trim - To Use or Not To Use, That is the Question

[TailLights]

I don't use CT most of the time, I flip it on/off, when I need a quick trim(then manual trim to set plane for my style)...

When CT sets my plane, it tends to climb. But I feel comportable a little descending while neutral. Maybe this is because pulling stick is easier than push stick, in my desk. ... I don't know :> Anyway I don't like that 'trimed point' of the CT. That's why I don't use CT as main use of Trim. It changes the 'feel' of the plane.

After reading this post, I'm feeling that maybe we are flying over-modeled-trim planes... Maybe trim should not affect the 'feeling' of flying.

what do you think? I've never flown any real plane, so I don't know. Can you please tell me that, a trim really affects the feeling/handling of Flying? or is trim just a mere physical 'force on stick' problem?  

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anyway, in AH, trimming does effects feeling of flying. and CT hurts my feeling, so I can't really use it. Maybe user-adjustable CT would solve? too complex? :>

[Toad]

 

Originally posted by Daff:
Full aileron deflection takes two hands and you'll very quickly get very large thigh muscles from the rudder.

Daff

What? Why didn't you just keep one hand on the stick and one on the aileron trim???

   

[Sorrow[S=A]]

Probably irrelevant here but: I have also read many times in recollections of pilots using trim. However: I think we may be misunderstanding something here. The pilots were usually using large trim adjustment wheels to move elevator trim etc etc. This wheel on most WWII fighters is RIGHT BESIDE THE THROTTLE. (sorry for caps). Thus if my understanding is right for the most part the trimming consisted of pulling your guts out on the stick then slapping the wheel forward or back in preperation for the next manuever. IE: in a pony if you were going into a loop you wouldn't touch the trim on the way up .. but on the way down you would roll that wheel back to let your self pull harder when you needed to pull out.

This AFAIK from the description was almost an unconcious thing- you knew you were going to need leverage in some manuevers and the cockpit was usually made so this was easy to do. It wasn't like they were "thinking" they were trimming- most seem to feel it was a natural thing to do. Also- this sems to be 90% related to elevator trim as this was AFAIK the only trim wheel right beside the throttle and pitch controls on almost every WWII fighter I have ever seen the cockpit pictures of.

If what I am saying makes sense Andy and Toad are right- it wasn't needed but rather in planes that had HIGH stick forces needed to manuever pilots would operate those wheels without thinking- rather like when driving a car we don't think about everything we do after a point- we just do it.

[Andy Bush]

Sorrow

Good post...and you mentioned a couple of things that can be added to.

First, let's look at a typical trim control layout...in this case, a P-51:

 

You make a good point about the size and location of the elevator trim wheel. As the picture shows, it is fairly large. It is mounted vertically to allow easier actuation. The pilot uses his left hand to rotate the trim wheel forward (clockwise) to trim nose down, and back for nose up. He can do this several ways.

Small adjustments are easy...just turn the wheel. For larger adjustments, many pilots found that they could make the input quicker by rotating the wheel with their palm...by placing their palm on the top of the wheel and then pushing or pulling to move the wheel through a larger rotation.

As you said, most trim inputs in a typical flight were made to the elevator. Rudder and aileron trim changes were less frequent. Because of this, these trim controls were twist knobs and were smaller and less easy to move in large increments.

While I seldom comment upon technique, I would note that arbitrarily adding 'nose up' trim on the back side of a loop would probably be unneccessary as long as the pilot intended on flying more or less of a symmetrical maneuver. If so, the exit speed would be about what the entry speed had been. Since the aircraft had been trimmed for the entry speed to begin with, the pilot would not notice any undue stick forces as he finished the maneuver. In fact, if he were to notice any out-of-trim forces during the maneuver, it would be at the top of the loop when the aircraft is at its slowest speed. If the pilot did not trim (nose up) in the pull up, the stick would get increasingly 'heavy' as his speed bled off...but then the feel would return towards 'neutral' as his speed increased coming back down.

With regard to A2A maneuvering, most trim changes comes as a result of airspeed changes brought about by maneuvers in the vertical or airspeed loss due to G-induced drag.

There are two factors in trimming during A2A maneuvering that should be considered. One is the magnitude of the trim change needed to keep the controls 'neutral' or 'hands off' as many pilots refer to it. In A2A combat, speed changes can be quite large, and the resultant trim change to maintain 'hands off' is also quite large.

Second is the time it takes the pilot to manipulate the trim control to make the needed change versus the time that elapses while he is in the maneuver. While the elevator trim wheel was designed to assist the pilot in making inputs quickly, often the speed changes occurred faster than the pilot could keep up with them. Often, the maneuver would be complete before the pilot would have the time to trim out the stick.

Because of this, many pilots elected to leave the trim alone during an engagement where speeds were changing rapidly. In prolonged conditions, such as a diving extension where the speed was expected to increase and then stay there, the pilot would probably trim off the stick pressure.

Finally, from a practical perspective, I found in my experience in A2A maneuvering that trim was way down my list of priorities. Not that trim wasn't important...it's just that other things had more of my attention. Things such as lift vector control, rates of closure, weapon envelopes, switchology, radio calls, SA on matter such as fuel state, fight location, and position of other bandits. These things kept me quite busy...trim was something I might adjust if I had nothing else more pressing...and this was seldom the case!

Andy

[Rickenbacker]

Right, what Andy said. This how I fight in AH, think about maneuvering, what's around me, my fuel state... anything but trim, becase I've already set a somewhat neutral trim that won't require huge stick movements to overcome, and don't have to worry about it.

Incidentally, this is how I fly in real life too, not that I've ever flown a combat aircraft, I fly gliders. And those trim wheels look overmodelled Andy, we usually only have a little teensy weensy lever for elevator trim. Of course, who needs aileron trim when you don't have a big noisy engine ruining all your maneuvers  .

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        Rickenbacker (Ricken)

                -ISAF-
the Independent Swedish Air Force

[Andy Bush]

Rickenbacker

>>And those trim wheels look overmodelled Andy, we usually only have a little teensy weensy lever for elevator trim<<

That is a real world picture from the USAF P-51 flight manual, not the sim.

Andy

[54Ed]

 

IE: in a pony if you were going into a loop you wouldn't touch the trim on the way up .. but on the way down you would roll that wheel back to let your self pull harder when you needed to pull out.

No need to trim at any point during a loop, mate.  Before you enter the maneuver, you trim the plane for level flight at fast cruise with power and prop at maneuver setting.

In a low power acro trainer, you will need to dive a bit to get entry speed, then level off briefly.  You will need forward stick pressure to keep it level at entry speed, because it is trimmed for a slightly slower speed.

The pullup is a 3.5G pull ... easy to do, just pull til you feel it in the seat of your pants.  No big deal, no trim required.

As you pass thru vertical and airspeed decays, you will need to pull the stick back further because control effectiveness decreases. Stick forces reduce as you slow down.

As you float over the top, you ease off on the stick to keep the loop round.  You are going slow at this point, and there is very little stick force required.  

As you come down the backside, you increase pressure again.  On the final pullup, you pull 3.5Gs again.  No trim is required for this, because it takes the exact same stick force that the pullup did.  You finish at the same airspeed and altitude that you started at.  

A few further comments on trim in combat.  Stick forces increase with airspeed.  After all, what is stick force but the air pushing back at you, right?  So you would NOT need to trim for momentary slow-speed conditions, because the physical forces involved are lighter.

So, logically, the only time you would really need to trim to reduce stick forces would be if you were going much faster than your trimmed-for speed, like in a fast dive like Andy says.  A few quick turns of the wheel in a sustained high speed dive is reasonable.  But you reduce the need for this sort of thing if you trim for a nice fast combat speed before you enter the fight.  Then you can just leave it alone, and keep HOTAS.

As for aileron trim, I can't think of a situation when you would EVER need to fiddle with it during a fight. After all, you would constantly be rolling in different directions.  Aileron trim is strictly to make life easy during level cruise.

Likewise for rudder.  The only situation I can think of where you MIGHT need to jockey the rudder trim would be if you trimmed for a slow speed and low torque, and then you dove really fast at full power, and the yaw was so large that you couldn't keep your nose on target to fire.  Tweaking the trim might be a better option than kicking the rudder hard, to reduce oscillations that would interfere with shooting.  

Man, I love hangar flying.  

[54Ed]

 

Andy does Fighter Ace have a more realistic FM then?

No, not by a long shot.  

I'm not a flight model snob either.  I played FA regularly for almost 3 years, and I like it.  But for realism, it doesn't hold a candle to AH.  Evidence: the "full realism" settings room of FA is empty because all the players left to come to AH.

FA's merit is in the gameplay.  The bases are close together and the pilots are packed in like sardines, so the dogfights come fast and furious.  It's a great place to learn the basics of ACM geometry without worrying about pesky little details like having to fly the plane.  

[humble]

I've got 1 point/question/clarification to add to this thread...

The FM here is/has evolved as variables are added/tweaked. If I remember correctly Andy helped me (and other trainers) sort out trim issues related to ACM. At that time the overall feeling was that applying some elevator trim did tighten turns in knife fighting. I believe it was shown that instead of trim functioning as a secondary control surface it actually extended the range of the primary control surface at the extremes. At that time trimming a plane did effect the FM envelope and allow for expanding the edge of the envelope. I do believe that this was one of the major FM issues addressed in 1.04.

Since the inclusion of cobat trim I've noticed it's ability to lock up planes at very high speeds as the near point of compression. I do know that in a high speed dive I'll often need to use max elv trim to recover...and often watched con trailing auger in.

Obviously Andy,Toad and 54ed have the real life stick time to explain how it really works...I'm not sure who has the clarity on how the AH FM trim works. I do feel manually trimming is a plus here still.

[Andy Bush]

Humble

>>I do know that in a high speed dive I'll often need to use max elv trim to recover...and often watched con trailing auger in.<<

LOL! That con was probably me!

I do agree. CT seems to accentuate the onset of 'compressibility' or whatever passes for it in this sim. In many WW2 fighters, control stiffening was not a function of compressibility so much as it was a matter of high speed airloads that the pilot was unable to deal with.

As you correctly point out, pilots are well advised to be alert in dives of any length...and to be ready to use trim to help their pull outs...otherwise, they won't make it!

At this point, I'm tending to side with the folks that de-emphasize CT...and go with a manual trim set up for a typical 'begin engagement' speed...say 250-300mph. Then I leave the trim alone unless needed for a pull out. This is particularly applicable for BnZ'ers who may find themselves in vertical slashing attacks.

Someone also made a suggestion to trim slightly nose heavy for better control 'feel'. I agree on this technique also.

Let's hear from some more of you experienced guys...what are your trim techniques?

Andy

[Sorrow[S=A]]

One other point here: Those of you comparing a WWII fighter to an acro plane- please stop that. It's not correct and you should know better. Any acro plane flown now is an evolution from designs and lessons learned from planes in the forties and WWII fighters behaved nowhere near as politely as those planes will.

 You also should consider in regards to trim that there were defined limits you could pull on the stick in WWII fighters- for example in a 109 it was physically impossible to pull harder than 40 lbs PSI of pressure on that stick. In lower speeds this meant nothing but when the plane went faster even before lockup you could be reefing on a stick that allready had 20-30 lbs of pressure forcing it away. In a case like this the pilot would undoubtedy learn quickly to anticipate trim changes and "palm" the wheel like andy mentioned so he could exert more force.

Aside from that CT to me has some oddities. For starters:
When pulling tight turns I have found CT makes all planes in the game snaproll to the left at or around 180mph despite it's normal stall speed. This includes the P-38 and happens even if your feeding a gentle right hand aileron in. Using rudder makes the departure occur quicker. Backing off stick travel slows the turn and allows the plane to travel closer to stall speed before snaprolling.
When turning I found that CT would accentuate slight rolls- A good example is that in films when someone is flying 90% of the time when the line up a tracking shot that passes under their nose they will fire to the right of the target. This is because as they lined up the target and pulled through the CT rolled them incremently right which meant as they passed under the nose the bullets missed and the shooter doesn't see.
Also- I have seen the CT use odd amounts of trim to compensate rudder on the P-38. Often you will see CT slide the trim to the left on the lightning for no apparent reason.

[humble]

I always trim for combat using auto trim as i begin merege...as plane comes into icon range i'll trim nose down a bit...starts the nose down part of merge I tend to favor...as I move to my lead turn I'll start to dial in up trim on elv as I slow down. i leave the rest alone mostly...little bit of right trim on the airleons maybe...I'll use my pedals to center the ball and leave rudder trim alone....now if we totally down on deck...less in 1.04...I'll fool more...seems like it still widens envelope...even though it shouldn't.

[54Ed]

Sorrow:

 

Those of you comparing a WWII fighter to an acro plane- please stop that. It's not correct and you should know better.

I assume you mean me.

I never state that a WWII fighter flies exactly like an acro plane.  But the laws of aerodynamics and physics have not changed in 60 years.  Some posts show no understanding of the physics of flight, so I am trying to be helpful.  Want an example?  Here's one:

 

IE: in a pony if you were going into a loop you wouldn't touch the trim on the way up .. but on the way down you would roll that wheel back to let your self pull harder when you needed to pull out.

On a correctly flown loop IN ANY AIRPLANE you do not have to "pull harder" on the pullout than on the initial pullup.  The airspeed, G force, and stick force are the same.

Look, you're as free as anyone else to post whatever you like.  But don't try and tell me to keep my opinions to myself.  This is an interesting topic, and I'll continue to post as I see fit.

[Toad]

 

Originally posted by humble:
I believe it was shown that instead of trim functioning as a secondary control surface it actually extended the range of the primary control surface at the extremes. At that time trimming a plane did effect the FM envelope and allow for expanding the edge of the envelope... I do feel manually trimming is a plus here still.

Humble, I think it  may still extend the range of travel. This laptop won't run the game for some reason but try this:

Offline use the external view from the rear on the runway. With elevator trim neutral, pull the stick full aft. Note elevator position. Now trim full nose up while watching the elevator. Does it move further?

Let me know what you find.

I agree with you though. I find manual trimming is still more precise and "user friendly". CT sometimes moves the trim in directions I'm not expecting...I don't care for that; I'd rather put it in myself so I know what's going on.

Just my .02.

[Minotaur]

I certainly don't know how some get the idea they can perform better without CT engaged.  I suspect that it is a more of a personal preference.   The pre 103 FM did allow increased turn rate by the use of elevator trim, 104 FM does not allow that from what I can notice.

From what I have observed, all CT has done is reduce pilot workload.  I don't seem to be trimming any less often, but when I do trim I don't have to trim as much.  

IE: I am on the trim controls almost as frequently, but the trim input has much less duration.  The use of CT keeps the trim closer to perfect.

For instance, in AH I trim from habit.  If I notice any A/C movement with the stick centered or a stick force required to maintain my desired flight aspect, I trim.  

Very simple...

I will also comment that I also instinctively hit "AutoTrim" at almost every opportunity, particularly AutoLevel, for a few seconds.  This quickly trims my plane perfectly for the speed that I am at and re-engages CT.


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Mino
The Wrecking Crew

"Hind tit suckin whiners. Begone with yah!"
Hangtime