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InCiSiOn89
10-27-2005, 07:04 AM
I know rudder trim helps keep u from drifting left or right but what do i need airlerion trim and elevator trim for and how would i use them for combat?

Tully__
10-27-2005, 07:54 AM
Elevator trim: Aircraft fly level with no control input at only one speed and power setting. If you increase power, you will either climb or need to hold the controls forward to increase speed and stay level. If you decrease power you will either descend or have to hold the stick back to maintain altitude but lose speed. Elevator trim allows you to change the speed/power setting at which the aircraft flys level, or adjust for a constant climb or descent without having to hold the stick back or forward.

Aileron trim: In order to turn the propellor the engine generates torque. In the result is the engine also tries to turn the entire aircraft in the opposite direction. Aicraft designers compensate for this by designing the wings with slightly different angles of attack, but the compensation only works for one speed/power setting. At higher settings the pilot will need to apply aileron to prevent the aircraft rolling opposite to propellor direction. At lower power settings the pilot will need to apply control input to prevent the aircraft rolling with the direction of the propellor.
Some aicraft have automatic compensators built in to the ailerons, but in other aircraft this situation is dealt with by manual aileron trim (and in some the pilot just has to deal with it http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif)

DmdSeeker
10-27-2005, 08:05 AM
You need trim for this:

Imagine you're flying at 80% throttle straight and level at 250 mph. Straight and level means the power of lift generated by the wings equals the power of gravity sucking you down.

Accept that the power of lift generated by the wings is a function of the speed of the air flowing around the wings.

Now you push the throttle to 100%. What do you expect to happen? Do you expect to go faster?

Well you don't; because as speed increases; so does lift; so instead of just going faster; you also begin to climb.

Now; you can of course counter this effect by pushing the stick forward a bit to hold it straight and level; and then your speed will indeed increase; but holding the stick forward all the time is tiring in a real plane and annoying in a game. So you use elevator trim to "tweak" the elevator so that the plane remains level; relieving you of having to hold the stick forward.

By the same theory; if you pull the throttle back to 60%; do you expect to slow down? Well; you don't; you begin to descend instead at the same airspeed. Again; you could hold the nose up with the stick; and then you will indeed slow down; but again; this is tireing/annoying; so you use elevator trim to "tweak" the elevator into holding the plane in level flight.

Aerliron trim is used to correct rolling tendancies in the same way; and the rolling tendancies come because every plane has a "perfect" speed where every thing is in balance. If your not at that "perfect" speed; then due to torque; the assymetric airflow over the two wingss and any inbuilt washout in the wings you'll slowly roll to one side. Again; you use aerliron trim to "tweak" the aerlirons into holding the plane level instead of holding level with the stick.

It's important to understand you don't "need" trim; and infact few planes have trim on all three axis; it's there to make your life easier; it's not a primary flight control (or shouldn't be); and has no real combat use except in very few high speed descent situations; where elevator trim can help you pull out from a dive so fast that the elevators don't have enough control on thier own.

InCiSiOn89
10-27-2005, 08:41 AM
What is difference between aerliron trim and rudder trim?


the trim will keep the plane leavel at a certain speed? so for example ur chasing some one at 100% and u set it so its level u will stay level during the chase making it easier to shoot enemy down but if u decrease speed u will be thrown off then u have to teak elevator trim with it ?

DmdSeeker
10-27-2005, 09:40 AM
You're getting the idea.

The difference between elevator trim and aerliron trim is that elevator trim moves the nose up and down; while aerliron trim rolls the plane left and right.

Try this:

Take a P38 (because it has trim on all axis; trims well and needs hardly any rudder or aerliron trim) and try to get it to fly "hands off" at 70% throttle.

It'll take a bit of fiddling at first; but you should be able to trim the plane to fly straight and level with no stick input - "hands off"; as it's called.

Once you managed that; push the throttle up to 95%; and see what happens (try to keep your hands off the stick). You should find that the plane starts to climb. Let it get stable in the climb; which will take a bit of time.

Once it's climbing in a steady state; trim it back to level flight.

Once it's level; cut throttle to 60% and see what happens. It should start to descend.

The key is (and this is a bit hard to understand at first); is that you trim for a given speed. Once the plane is trimmed, and flying in a steady state; adding power adds lift; and you climb; decreasing power decreases lift; and you descend.

It's a similar case when you land: You use the stick to control your speed (nose down you get faster; nose up you slow down); and the throttle to control your rate of descent (more power = slow descent; less power = faster descent).

I know that sounds wrong; because you probably think the stick is to make you go up and down; and the throttle is to make you go faster; but honestly; that's the way real pilots land and that's the way you should be trying to do it in the game :-)

Tully__
10-27-2005, 09:44 AM
Use rudder trim to trim out unwanted yaw, use aileron to trim out unwanted roll. Always correct rudder trim first because yaw will cause roll and you don't know if you need aileron trim until the rudder is correctly trimmed.


so for example ur chasing some one at 100% and u set it so its level u will stay level during the chase making it easier to shoot enemy down but if u decrease speed u will be thrown off then u have to teak elevator trim with it ? That's about it, though most will not mess too much with trim while in combat. It's rare (against human pilots) that combat turns into a straight line chase but if you're sure that you're going to get a shot while still travelling max power straight & level, by all means trim for those conditions.

InCiSiOn89
10-27-2005, 09:55 AM
wow i think i finally understand it..... but how does elevator trim effect the tightness of ur turn? because that still keeps me wondering why when i am chasing someone and they pull up to try to shake me and i follow them they end up right on my tail but i was following them the whole time...

DmdSeeker
10-27-2005, 10:10 AM
You're getting the idea; but don't over estimate the importance of trim in combat; after all few planes have it on all three axis; and some don't have any trim at all; yet they were effective.

In real life; the faster you go; the heavier the controls become.

In the game; this effect is modelled by the stick needing more movement at higher speeds in an attempt to mimic the fact that in a full power dive you'd need to pull back on the stick with both hands with all your strength. This is obviously not the case with your gaming joystick.

So instead; at very high speed your computer joystick is less effective; you have to move it more. Trim can help with this; especialy if you have trim mapped to a joy stick axis instead of to a keyboard button.

But it's an over rated phenomenen that's achieved a bit of a myth status.

Really; if you're dogfighting by using trim; you're doing something wrong; and while it can in some situations; in some planes to help tighten a turn; it does so by being deliberately "out of trim" and that costs you speed; plus there's always the risk you'll pull your own wings off.

Trim is really a fine adjustment designed to make the pilot's life easier; it's not a primary control surface.

Have a look here:

http://www.simhq.com/_air/air_003a.html

It's a very good article by a real pilot on how to use trim properly in games. It's not written especialy for IL-2; but every thing it says pretty much is true for pretty much any flight sim that's any good.

SithSpeeder
10-27-2005, 10:19 AM
Dmd--


if you're dogfighting by using trim; you're doing something wrong; and while it can in some situations; in some planes to help tighten a turn; it does so by being deliberately "out of trim" and that costs you speed; plus there's always the risk you'll pull your own wings off. Do you even use it on a slider in combat? If so, that is your opinion to which I respecfully disagree. If not, don't knock it until you try it. Various posts have shown that even Mr. Chuck Yeager used (Edit:--&gthttp://forums.ubi.com/groupee_common/emoticons/icon_wink.gif ELEVATOR TRIM in combat to turn better.

Also, I find that using (Edit:--&gthttp://forums.ubi.com/groupee_common/emoticons/icon_wink.gifELEVATOR trim to control my plane in pulling out of dives and such bleeds less Energy and reduces the chance that I rip my wings off. But that's just _my_ opinion (and I fly the P-51D...the king of wing-ripper-offing).

YMMV.

* _54th_Speeder *

DmdSeeker
10-27-2005, 10:39 AM
Originally posted by SithSpeeder:
Do you even use it on a slider in combat? If so, that is your opinion to which I respecfully disagree. If not, don't knock it until you try it. Various posts have shown that even Mr. Chuck Yeager used it in combat to turn better.

Also, I find that using trim to control my plane in pulling out of dives and such bleeds less Energy and reduces the chance that I rip my wings off. But that's just _my_ opinion (and I fly the P-51D...the king of wing-ripper-offing).

YMMV.

* _54th_Speeder *

Oh yes; I do indeed. But then do we agree we're talking only of elevator trim here? I'd be most surprised to hear your rudder trim is on a slider and that you use it in that way in combat even though many dive bombers "pre trimmed" the rudder at the start of the dive to help keep the ball centred at drop speed; was it that you were refering to?


However; now that you've raised the subject of how trim can be used in combat (and I'll admit I was avoiding it; I get the impression we're explaing what trim is to a releative newcomer); give the full nine yards...

How do you set up trim on a slider; which trim axis do you use and how do you use it?

InCiSiOn89
10-27-2005, 11:00 AM
Someone posted this


you have to remember, the faster you go, the more lift your wings produce. so, the nose will pitch up at higher speeds and down at lower speeds. to counter this, use the elevator trim(crt up/down). when you reach alt, keep the plane level at a given speed and trim up or down untill you dont have to even touch the stick. i dont even really worry about trim in combat for obvious reasons. your changing speed and alt and twisting and turning that it is piontless to trim for level flight. i WILL however do many "rough trims", just to make it easier to keep my guns on target.



what does he mean by rought trim cause that along with elevator trim might help keep my guns on my sight and turn quicker with my opponent

Tully__
10-27-2005, 11:13 AM
By rough trim he means trimming for a speed somewhere in the speed range you're using in combat. For a slow, low altitude turn fight you might trim for 350km/h, but if you're boom & zooming your speeds will be ranging from 350-650km/h and trimming for 500km/h would make more sense.

Tully__
10-27-2005, 11:20 AM
Originally posted by InCiSiOn89:
wow i think i finally understand it..... but how does elevator trim effect the tightness of ur turn? because that still keeps me wondering why when i am chasing someone and they pull up to try to shake me and i follow them they end up right on my tail but i was following them the whole time...

As aircraft travel faster, the pilot needs to exert more force to move the controls. This is because the wind is trying to force the controls to the neutral position and at higher speeds the wind exerts more force.

Trim uses aerodynamic force to offset the centre position of the controls instead of pilot strength. This means that at speeds so high that the pilot isn't able to achieve full control deflection, trim can provide some assistance.

While this does help in high speed turns, the effects on accuracy are severe and it's not likely to help you win a fight. What is more likely happening in the situation you describe is that the pilot of the other aircraft is flying his aircraft at speeds and in a manner where it outperforms yours, or they're using techniques like the high yo-yo or low yo-yo to improve relative turn performance of their aircraft relative to yours.

InCiSiOn89
10-27-2005, 05:29 PM
wait so tully u mean i am at like 350km/h then i would want to set elevator trim so it levels there?

Tully__
10-27-2005, 06:23 PM
Originally posted by InCiSiOn89:
wait so tully u mean i am at like 350km/h then i would want to set elevator trim so it levels there? Yes.

neural_dream
10-27-2005, 06:35 PM
Usually it's something like that:
For a given altitude, there is a critical throttle value, say 45%, over which the plane rotates usually left and tends to pitch up, and under which it rotates right and tends to pitch down. By trimming, you more or less change the critical value (i just invented the term; don't go around using it, http://forums.ubi.com/groupee_common/emoticons/icon_razz.gif) to the desired throttle setting. Always for a given altitude.