Rudder Trim

[Superpilot]

I'm sure I'm not the only mid-hour PPL (110) that has never used the rudder trim before. 3 different clubs/schools and a variety of instructors have never even touched on the subject. Of course I know what it roughly does but anyhow would appreciate a quick outline of when and what the rudder trim is used for, and any tips associated with it's use.

Thanks

[S-Works]

In a single where you have a very powerfull engine (like my Reims Rocket) the prop torque gives the need for a massive amount of right boot (in my case) on take off and climb. The rudder trim evens this out and takes the strain off your poor old leg in a sustained climb. If I am climbing into an airway at say FL100 that is a 10min climb and the rudder trim is worth its weight in gold. Power off it goes the other way (to a lesser degree) and so I use left rudder trim.

In a twin it is generally used to counter the effect of a failed engine, dead leg dead engine. I have spent a lot of time in the last month flying around on one engine in a twin and the rudder trim is a godsend then as well!

[smarthawke]

Reims Rocket = 'very powerful' ...?!!

[EGBKFLYER]

A trim is a trim is a trim. Use the main controls (Elevator, rudder etc) to select the attitude you require and ensure you fly in balance (balls in the middle!). Sense the force (e.g. forward/ aft stick or left/ right rudder). Move the trim to cancel the force.

Which to use first? Trim worst first - i.e. if your leg is going wobbly because of the rudder force it's holding, trim rudder first then elevator.

When to use it? Whenever you like! Use it when you have to cancel out a sustained input on the rudder pedals so you can fly in balance 'feet off'. Remember power changes affect balance, to moving the throttle significanly will mean retrimming.

Why don't instructors teach the use of rudder trim? I don't know (but I teach it personally). It might be because:

A lot of aircraft don't have one (PA28 is the only 'common' type I'm aware of that has one).

The wheel is down near the floor and moving it means most students will forget to look out/ move the elevator as the lean forward to find the wheel.

The rudder forces are not generally high enough for long enough to spend lots of time learning to trim them out (unlike the elevator).

It keeps student workload down

As Bose X says though - you will definitely be needing it in a twin, where rudder forces can be considerable.:eek:

Lastly, well done for asking the question and get your instructor to teach you how to use it next time you fly (or play with it yourself, if you know what I mean :ok: )

[S-Works]

what ar you driving then Smarthawke?

[smarthawke]

A gash old homebuild with the same power as a Rocket but weighing about 700lbs less.

All said in the best possible taste, please don't take it to heart!

Didn't mean to hijack the thread, it's good to see people asking questions and futhering their knowledge but sad Superpilot hasn't had the tuition he deserves.

[nouseforaname]

You want to be careful though. Sometimes when you come into land you will want to make sure that it is centered. This may require you to increase left rudder on final's but it will make everything proportionate in the flare.

I had a go in a single engine turbo prop the other day and the pilot said that it's one of his last checks is that the rudder is centered not selected for slight left rudder. Especially important if a go around was necessary.

[FlyingForFun]

Superpilot hasn't had the tuition he deservesNot sure that's fair on Superpilot's instructors. I never taught rudder trim in a C152 or C172, because they don't have one. You can only teach the student to use the facilities available in the aircraft you use.

I think EGBKFLYER's reply answers the question pretty completely.

FFF
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[mad_jock]

I disagree that they don't have one FFF.

Most do have one its just you can't change it in the air. Same with the wings.

I agree you don't teach the use of it apart from "see that bit of metal it's meant to be bent, please leave it alone"

From memory they are ment to be adjusted so that at cruise power at 2.5A the plane should be able to be flown with hands off and feet off the pedals. The ball should be in the middle and wings should remain level.

To adjust them if you grip them between your hands with the muscle bit at the base of your thumb and then ease them over in the opersite direction to what you require in the way of trim. It works just like a servo tab its just fixed. And it is worth doing and spending a few trial lessons getting them set up right. Makes it alot easier for the students doing nav to have a stable and in trim aircraft in all directions. Set the rudder first then the roll.

It has been known for students who have not been told about not fiddling with them to think that they have been bashed and really the plane would look much nicer with them striaght. Next trial lesson this cause's the instructor to exit the aircraft slightly grumpy and with a sore leg from having to sit with half a foot of rudder in for the last hour.

How to use it though if its fitted, its exactly the same as the pitch trim. You apply the control force required to do what you want and then adjust the trim until you require zero force. Thats in theory but most people after a while on SEP's fly it on the trim and without puting the force in with their feet they just screw the rudder trim until the ball is in the center. Its pretty much redundant on training aircraft and if say you were to see one on a school C172 I would ask first before using it. The tank selector and the rudder trim tend to be unused and have been known to break with there first use in 5 years. Not so bad with the rudder trim its just a sore leg but the tank selector could give you problems.

MJ

[IO540]

The OP doesn't mention the type but the only spamcan I know of that has it is the PA28.

On that one, it is in a barely accessible position, so doesn't get used unless you have arms like an ape (or there is a nice gurl in a short skirt in the P2 seat - but in that case you really want her in the P1 seat and regularly lean over to change over the fuel tank; one of the well kept secrets of ATPL hour builders).

Properly used, a rudder trim is a super feature. Set it to the "takeoff" position for takeoff, then as the plane is trimmed forward to speed up, you take a bit off it at a time, to keep the ball centred the whole time.

Doing it properly gives you up to a few kt of extra speed especially in climb.

I have never seen it used in the PA28 though. In a proper plane one uses it all the time - until perfectly trimmed for cruise.

[stiknruda]

I think (:cool: ) that the venerable C182 might just have one!

Half right deflection pre take-off and fine-tune later.

Stik

[n5296s]

I think (:cool: ) that the venerable C182 might just have one!

Indeed it does. Jolly handy too. Takes quite a lot of welly otherwise which during a climb up to FL200 (in a turbo) would be pretty tiring.

n5296s (which is a TR182)

[Kiltie]

Bose-x I agree the Reims Rocket is most worthy of rudder trim -these are very powerful engines developing much torque through big props on what was an airframe designed initially for a four-pot wheezing engine.

IO540 even on low powered PA-28s I have always used full right rudder trim for take-off, purely for the comfort of relaxing the right foot during high power low speed climb-outs. It's sensible to return the trim to the centre position after flight to avoid the spring being loaded over long periods spent on the ground.