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View Full Version : Why rudder trim changes so much....



LEBillfish
06-16-2005, 01:45 PM
Hi All;

This may be elementary and "you just got that?" to some....Thought I'd post this for those slow learners like me.

3.04 and before we all know you set the elevator based on speed, the rudder you would pretty much set and leave alone.

In 4.01 however, you'll note whatever you do, all the trim constanly changes....

Pitch/Elevator seems more sensitive yet as before, you must constantly adjust for your speed.....

Roll/Ailerons on just a select few planes can you adjust that trim (pity...but if that is how it was kewl by me)...This though I've not tested it I'm guessing would be much like for rudder below.

Yaw/Rudder...As said, before it was a set and forget...Now however, anything you do changes it, or does it really? What I discovered is as follows...

Rudder used to center the bubble. Most planes with the bubble have a "bank needle" which to some degree shows both your amount of roll+climb (so how much turned to the side you are and how hard you're turning)....At this point still learning it so lets ignore it.

So I noticed that now...anything you do seems to move the bubble....Until you stabilize at a smooth cruising speed. Dives, climbs, throttle, prop pitch...any speed change really. I also noticed on planes that to center the bubble, you could sometimes simply adjust the throttle or prop pitch.

It then struck me, if you in planes now go from say 20% throttle to 95%, you sense/see/feel a strong lurch of the plane, and if you look you can see how "torque" actually twists the plane back and forth about it's axis.

So I just realized, any change in torque "now" is what is causing the bubble to move as it requires more rudder to hold the plane level and not slip. So it is really the torque your engine is producing of which a change in throttle, prop pitch, speed from a climb or dive working on that engine speed that generates the change.

Essentially.....expect it to change constantly unless in a steady smooth level cruise.

Anyone who knows better please correct any of that or fill us in more.

-HH-Quazi
06-16-2005, 02:23 PM
You are correct in your assumptions. And from what I have read, this is moddled correctly, or as close to correctly as can be given the limitations of a PC game to simulate real world physics. It sure does make one really pay more attention to flying. Used to just get up and make a long boring flight to the target area. Now that I have to pay more attention to rudder, elevator and aileron trim, time passes more quickly. I can see a real need for Pro Pedals now. The rocker on the X-45, when flying an ac like the Sturmovik that has no rudder trim, is hard to keep compressed to the point of keeping the bubble centered and reaching the other trim settings at the same time. Not to mention working the throttle for power.

SeaFireLIV
06-16-2005, 03:30 PM
Yep. And of course you find yourself having to trim the most just as you get on the six of a twisting, turning bogey. Takes skill to down a fighter now.

I have my trim now set to the hatswitch because of this and I`m looking into getting some rudder pedals.

sunflower1
06-16-2005, 04:31 PM
Essentially.....expect it to change constantly unless in a steady smooth level cruise.


This made me grin from ear to ear when I loaded the patch. A great leap forward, or something.

LEXX_Luthor
06-16-2005, 05:55 PM
The New FM's need for trimming is why Oleg increased the trim response back to usable levels, probably near how it was back in original IL~2 (I wasn't there then). This FM for BoB looks like its going to be quite advanced.

ClnlSandersLite
06-16-2005, 10:37 PM
Basic explanation.
Throttle/pitch: When you adjust these, the engine puts out more or less torque. You must rudder to account for it.

When you roll onto a side: The center of gravity and airlow shifts and causes the need to apply a slight correction on the turns.

Speed: The faster you're going, the more effective the verticle stabilizer/rudder is. Therefore, less rudder input is needed to correct. Conversly the slower your going, the less effective it is. So you'll need more correcting rudder at slow speeds.

triggerhappyfin
06-17-2005, 05:41 AM
Originally posted by sunflower1:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Essentially.....expect it to change constantly unless in a steady smooth level cruise.


This made me grin from ear to ear when I loaded the patch. A great leap forward, or something. </div></BLOCKQUOTE>

Me too, now I really get use for my little "trimbox" http://forums.ubi.com/images/smilies/59.gif

womenfly
06-17-2005, 06:19 AM
As a RL pilot I find the FM very close the RL aircraft in the trim. Adjust power €¦ re-trim, adjust speed ... re-trim, adjust altitude ... re-trim, you get the idea.

That is how you fly. Try a sideslip when landing ... full ailerons with opposite rudder and nose down, warning watch your airspeed on this one.

Something you could not do before!

I like it! ..... http://forums.ubi.com/images/smilies/25.gif

Chadburn
06-17-2005, 08:40 AM
Originally posted by womenfly:
As a RL pilot I find the FM very close the RL aircraft in the trim. Adjust power €¦ re-trim, adjust speed ... re-trim, adjust altitude ... re-trim, you get the idea.

That is how you fly. Try a sideslip when landing ... full ailerons with opposite rudder and nose down, warning watch your airspeed on this one.

Something you could not do before!

I like it! ..... http://forums.ubi.com/images/smilies/25.gif

Except that many WWII didn't have in-cockpit trim for the ailerons and the rudder, but the game offers no option to preset these before takeoff. For example, the 109 flies with constant sideslip which is not very realistic at all.

Zyzbot
06-17-2005, 08:51 AM
Originally posted by Chadburn:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by womenfly:
As a RL pilot I find the FM very close the RL aircraft in the trim. Adjust power €¦ re-trim, adjust speed ... re-trim, adjust altitude ... re-trim, you get the idea.

That is how you fly. Try a sideslip when landing ... full ailerons with opposite rudder and nose down, warning watch your airspeed on this one.

Something you could not do before!

I like it! ..... http://forums.ubi.com/images/smilies/25.gif

Except that many WWII didn't have in-cockpit trim for the ailerons and the rudder, but the game offers no option to preset these before takeoff. For example, the 109 flies with constant sideslip which is not very realistic at all. </div></BLOCKQUOTE>


Perhaps realistic...perhaps not. Comments from evaluation of a me-109E by RAF:

Lateral Trim

There is no procounced change of lateral trim with speed of throttle setting provided that care is taken to fly with no sideslip.

Directional Trim

Absence of rudder trimmer is a bad feature, although at low speeds the practical consequences are not so alarming as the curves might suggest, since the rudder is fairly light on the climb. At high speeds, however, the pilot is seriously inconvenienced, as above 300 mph about 2 1/2 degrees of port (left) rudder are needed for flight with no sideslip and a very heavy foot load is needed to keep this on. In consequence the pilot's left foot becomes tired, and this affects his ability to put on left rudder in order to assist a turn to port (left). Hence at high speeds the Bf 109E turns far more readily to the right than to the left.

Longitudinal Trim

Five three-quarter turns of a 11.7 in diameter wheel on the pilot's left are needed to move the adjustable tailplane through its full 12-degrees range. The wheel rotation is in the natural sense. Tailplane and elevator angles to trim were measured at various speeds in various condition; the elevator angles were corrected to constant tail setting. The airplane is statically stable both stick fixed and stick free.



I always figured that the 109 aileron and rudder were set on the ground to give good trim at normal cruise speed. I have only tried the 109K with the new FM but it seemed to be better at high speeds.

LEBillfish
06-17-2005, 09:10 AM
Lets think about what some have said regarding "non-adjustable trim being set on the ground"......

This I would agree is very true, however you must consider this. If what I stated about the new FM/Trimming above is true, and true for real life aircraft then that would mean the following.

On the ground trim would be set, and reset upon subsequent flights to tune in the trim for Rudder and Aileron.......At a particular speed and torque. Meaning, sure they might set it, but based on above it would only be good I would assume for a particular "cruise" condition.

All other contitions and the further from that optimum cruise you get.....The trim would be off more and more. So essentially 1 out of 10,000+ variable conditions will it be right....

Meaning, 99.999% of the time....It feels wrong.

All assumption, yet would seem logical based on what all of you just said.

SKULLS Virga
06-17-2005, 09:24 AM
Originally posted by Chadburn:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by womenfly:
As a RL pilot I find the FM very close the RL aircraft in the trim. Adjust power €¦ re-trim, adjust speed ... re-trim, adjust altitude ... re-trim, you get the idea.

That is how you fly. Try a sideslip when landing ... full ailerons with opposite rudder and nose down, warning watch your airspeed on this one.

Something you could not do before!

I like it! ..... http://forums.ubi.com/images/smilies/25.gif

Except that many WWII didn't have in-cockpit trim for the ailerons and the rudder, but the game offers no option to preset these before takeoff. For example, the 109 flies with constant sideslip which is not very realistic at all. </div></BLOCKQUOTE>

I think it is very realistic. It was the pilots job to make up the difference and keep the ball centered. On planes with no rudder trim, they developed very strong right legs. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

Chadburn
06-17-2005, 12:06 PM
The 109 did have rudder trim. It was adjusted on the ground as described by Billfish above.

And I agree Billfish. Pre-set trim means it is set for only a certain speed and a certain rpm. In the G6 this was around 420kph IAS and 2000-2100rpm (according to Finnish G6 manual) According to Mark Hanna, who flew a Spanish version of the 109, he needed right rudder input through the climb to off-set side slip, but once cruise speed was reached (for his was set for 240mph iirc)he said no more rudder input was required. Of course, that would change if he throttled up or down, dove or climbed.

I'm still experimenting, but I can only get the ball centred on the 109 at around 2000-2100rpm and a very slow cruise speed of 330kph - 340kph. Players who fly planes with in-cockpit trim get to input the level of trim they want. What's slightly unrealistic for planes like the 109, is that I get NO trim input at all, just some preset trim that's built into the game.