rudder trim lesson?

[MarkW 1,490]

Just wondering if rudder trim is discussed in detail in any of the lessons, particularly during various phases of flight.  I am currently part way through lesson #8 and so far there has only been a very quick mention of it in lesson 3 or 4.

 

I am trying to figure out if the trim is something that is set on the ground before takeoff or just by feel in the air.

[Biggles205 0]

Yes some info on this would be welcome.  I seem to have heard somewhere that right rudder trim, about +3, should be set for take off.

[Airline2Sim 489]

Had a word with Josh about this as I wondered about it myself.

 

Essentially rudder trim in the real one is a lot more unforgiving than in the MJC Q400. A slight notch of right trim is set before takeoff to counter the yaw from the props and constant changes will be needed to the rudder trim when power changes are made to keep it in trim. Josh tells me it becomes quite instinctive in the end to adjust the power and then move your hand backwards to the trim nob. 

 

In FSX, it will fly a bit out of trim with everything left alone but it never gets badly out of shape. If you never did anything with the rudder trim (we didn't in the Cadet flights) then nothing particularly bad will happen, but it's not the best airmanship.

 

We've got a tutorial on the way which essentially mimics a 'sim session', where we will learn about the kind of things that happen in a sim session on the real one. A lot of this will cover things like looking at the pitch attitudes for takeoff and landing, power settings, yaw on takeoff, rudder trims and the like - stuff which probably happened too fast in the circuit flight to show you properly. We wanted on the Cadet training to get you quickly up to speed with the basics - now we'll be looking to refine it further. 

 

It's coming guys, I'll put a note in to cover rudder (and aileron) trims. 

[MarkW 1,490]

Thanks for the info.

[frostycab 0]

From a design perspective, I'm surprised that they didn't opt to put a rudder trim control on the control yoke so that trim and power could be adjusted together. Having to set power and release the throttles THEN move your hand back to the trim knob seems a bit odd. Did anyone at Bombardier actually talk to a pilot when they were designing this bird?

[Lindbergh 0]

Hi frostycab,

 

I think the trims are not meant for steering the A/C but only to eliminate the need to constantly apply pressure / input to the the flight controls. Therefore the pilot should compensate the bank / yaw by using the rudder pedals (in some situations you have to be very quick so that using the trims would be much too slow anyway) in the first place and only after having established a coordinated flight situation use the rudder trim to slowly compensate the rudder input. So in this case there is no need to operate the P/Ls and the rudder trim control at the same time.

 

Maybe this is the reason why the rudder pedals are still active in the DHD8 even after AP is engaged? But as I am not a real world pilot I am not sure if this is how it really works or if it is just a little bug in the simulation.

 

Cheers

Peter

[Q400 Operator 0]

Just to point out a few things......

 

Lindbergh - the rudder pedals remain active because the autopilot is only two axis (roll/pitch i.e. ailerons/elevators) and is only able to trim the elevators. To that end in the real aeroplane, even with autopilot engaged, the rudder pedals are still useable.

 

Biggles - Base position for the rudder trim before take off is 'a bit right'. Quite how much depends on the mass of the aircraft, the flap setting for departure and the fact that, in all honesty, each airframe will vary slightly. Experience slowly teaches you but essentially as long as it's somewhere between centre and a little right of centre that'll do just fine, once the aircraft's airborne simply use your feet on this pedals to keep it flying in balance.

 

In terms of its use in the air, Ben's quite right when he says the rudder (and therefore by association the rudder trim) input required to keep everything pointing exactly forward will change with every speed and power alteration (More power and same speed or less speed = right rudder. Less power or same power and more speed = left rudder).

 

Conventionally as someone states above the idea with trim is to make the control input, hold the aeroplane where you want it with the controls and then use the trimmers to relieve the control loads. Now this holds entirely true on the dash, however the rudder on the Q4 is a fairly big, powerful thing with the potential to wag the tail like an excited Labrador if you use it generously. It's also hydraulically powered. (As a matter of interest you'll find it's travel is restricted with Flap Zero, once Flap 5 or greater is selected note the increased rudder pedal travel available). This means that, at higher speeds, only very small inputs are required to accommodate the trim alterations required by power changes.

It's perfectly possibly to, for example, initiate a descent from FL200 at 250kts and, as you pull the power back, balance the trim change with the rudder pedals and then, once established in the descent, trim the rudder out using the switch. However, the pedal movement required will be quite literally only a half inch at most, quite possibly less; if you're less than perfectly controlled with your feet movement then you'll generate a fairly obvious and uncomfortable yaw movement. To eliminate this possibility a lot of guys simply do the power reduction in stages and, in-between each stage, add a little rudder trim. This is the process that generates this continual movement of your hand from power lever to rudder trim to power lever to rudder trim and so on. Technically, it's not the 'correct' way to fly the aeroplane but it works