Rudder trim
Today I was flying in some light rain in my Arrow. I noticed the rain was streaming across my windshield on an angle indicating the nose was left of center. I adjusted the rudder trim until the rain tracked parallel to the windshield center post on both sides, i.e., adding more right rudder. After the adjustment the ball was displaced from center by about half the ball's diameter.
I am sure the TC is not that far off from level. In fact the ball is centered when sitting on the ground. My question is what else could be going on that could affect the yaw trim?
Thank you.
I am sure the TC is not that far off from level. In fact the ball is centered when sitting on the ground. My question is what else could be going on that could affect the yaw trim?
Thank you.
Comments
I must admit, I've never heard of trimming by this method.
Have hunted around for a "Takeoff Setting" for the rudder trim on my Arrow. Narrowed it down to turning the trim knob full right then applying 6-7 twists left. That seems to set it up nicely for a Vy initial climb. A few more left twists are added when transitioning to cruise climb.
Anybody else using a similar, or dissimilar, method?
From other comments - I did not take into account the affect of the prop wash on the air flow over the windshield. I will level the TC as suggested by Aviation Law.
Thanks for the comments. They were all useful.
Jim
> 78TARROW: On my Arrow, I leave the trim setting
> where it was after cruise flight and landing.
I can't think of a better place to leave it on a single.
> I suppose that each pilot has their own way to
> adjust the rudder trim but what seems to work for
> me is to trim for level flight after reaching
> cruise altitude and with the AP off adjust the
> rudder trim till the plane flys both straight and
> level with no tendency to turn with no hands or
> feet on any controls. As the fuel burns off from
> one tank there will be a need to re-adjust the
> rudder trim. Having this trimmmed right does seem
> to add some speed. BTW, in trimming it I do use
> my feet to apply the needed rudder pressure to
> maintain straight flight and then adjust the trim
> till all pressure is gone from my rudder pedals
> for this setting.
This technique is wrong. Rudder trim should not be used to level the wings or to remove any turn "tendency".
Using rudder trim to compensate for a miss-rigged airplane or poor fuel management is improper technique.
The ONLY thing rudder trim should be used for is to center the ball.
PilotKris
As the fuel burns off from one tank there will be a need to re-adjust the rudder trim
Its bad technique to use rudder trim to counteract fuel imbalances (even in Canada).
The only time it should be necessary to adjust rudder trim is with power and/or airspeed changes.
eldartford Wrote:
While flying under autopilot control you may note that you are holding a heading with the heading bug biased off, left or right. I adjust the rudder trim so as to eliminate the bias. A bias means that the AP is holding an aileron deflection to counteract the rudder. I find that this method gets me a few mph.
A "biased" AP heading bug (in heading mode) means your autopilot needs adjusting.
The ONLY thing you do with rudder trim is center the ball. If the plane still wants to turn, either:
1. Fuel imbalance
2. Aileron/Flap rigging is out.
3. The plane is bent.
PilotKris
With a Century or King autopilot, flying with the ball not centered will cause the heading bug to be "biased" one way and the AI to be "biased" the other. That would not be the case with an S-Tec autopilot. This also does not work in NAV/LOC or GPSS modes. Solution?
CENTER THE BALL!
It works 100% of the time with 100% of the autopilots, in 100% of the modes, no autopilot or even no electricity. It is also faster, more accurate, idiot proof and mirrors how you should be flying the aircraft (i.e.; "step on the ball").
PilotKris
This is lazy technique. Burning fuel causes a wing to be heavy. The answer is to switch tanks, not adjust the rudder trim. The adjustment is on the longitudinal axis, not the vertical axis. Plus it is much easier to flick the fuel selector than to put in trim adjustment, center the pedals, fine tune the trim adjustment and then verify the adjustment with the ball and make sure your heading doesn't change in level flight, only to readjust when the fuel burns down some more.
That all being said, I've seen more Turn Coordinators that are NOT installed level than are. Start with a level instrument as above.
Now, here's the bad news. Even though "check rudder trim" was on my pre-landing checklist, I overlooked it. So, I was surprised, when landing in a fairly stiff cross-wind, that I kept drifting unexpectedly to the right even though I thought I was applying the correct amount of aileron and rudder correction. Lesson learned: if you use rudder trim during cruise, be sure it's properly set for landing.
In other news... The "correct" amount of x-wind controls results in the long axis on & pointing down the centerline. It has absolutely nothing to do with rudder trim. If it is set for straight & level cruise, it will be extremely close to straight for landing. Let me be perfectly clear... You DO NOT put in rudder trim to correct for a X-Wind or any other landing. It is all in your feet and hands.
Rob: Why is rudder trim stupid if it contributes to a more comfortable flight and eases the workload a little?
> Leigh: I'm a relatively new pilot, and a new
> Cherokee 180C owner, so I don't claim expert
> status. It seems my usage during cruise, as
> described above, is exactly what the rudder trim
> is for. Please enlighten me if I'm wrong.
I really don't think that the slight amount of rudder trim applied to maintain coordinated flight in cruise will contribute to "drifting unexpectedly to the right during final approach."
My guess is you needed to apply more left wing down to stop your drift off the final approach course from the onset if you slip that far out.
> Rudder trim on a single is stupid anyway.
Rudder trim on a twin is stupid unless you have one caged. Then it's your best friend. Otherwise its not enough of a issue. I normally rest my feet on the rudders and it seems with just a little minute pressure I can keep it fairly centered. What's a 1/4 of a ball deflection going to do anyways? Slow me down a knot or two? No worries people drop thousands on speed mods to gain what 5-7 knots. Holy cow you saved like 5 mins on a really long flight.
> Rudder trim on a single is stupid anyway.
Spoken by man who's obviously never flown a high performance single....
>
> Rudder trim on a twin is stupid unless you have
> one caged.
Not so quick there Tony, Fly a twin with non-counterotating engines (like my Aztec) and you'll change your mind. While not needing as much rudder input as a high performance single, it's still subject to all the same asymmetric thrust issues (P-factor, torque) with spiral slipstream not as much an issue.
> ... Spoken by a man who owns a high performance
> single.
You sold the M20C and stepped up to a PA32?
> Fly a PC12 report back to me. The rudder imo isn't even that
> much of a concern.
(Been there, done that)
It isn't a concern because the PC12 has a YawDamper with automatic trim...