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Dragonmount

How to properly set up trim on an aircraft?

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I realize that all aircraft are different, but is there general advice out there? I've never really bothered with it in flight simming because it seemed a bit complicated and I could get by without it. I'd like to learn now, so that's my question. Is there a general rule of thumb for setting up trim on an aircraft?

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Very very simply:

 

A lot of aircraft have a trim wheel or gauge. Often a default or neutral trim and a take off trim is shown, usually with an arrow or other mark on the wheel or gauge.

 

Zero or the default trim is often associated with cruise flight at typical power settings at a clean configuration (no flaps, spoilers etc)

 

Usually you trim nose up for take off, which is again based on a typical take off profile and power settings.

 

The trim's purpose is to take load off the controls so you don't have to keep pressure to keep the yoke or joystick where it is. In video games it's slightly different because it feels like you can release the yoke or joystick back to center. In reality it's about the pressure you exert in keeping the yoke or joystick in a specific spot.

 

In essence it's to help you maintain the attitude of the aircraft.

 

For most aircraft, you hand fly then trim to neutral pressure. Whether you are climbing, flying straight and level or descending.

 

The only exception is take off, where you trim the aircraft first to help with the initial climb.

 

The above refers to elevator trim, which is the most used. You may also have rudder and aileron trim, which again is for helping you maintain attitude.

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Easiest way to do it:

 

Set trim to takeoff trim when indicated on trim wheel, or otherwise specified in checklist when not, on light aircrafts before takeoff. Make sure the trim is in green band indicated on trim wheel on heavier aircrafts.

 

Use stick to point to where you want to go, then trim to neutralize stick input.

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I've noticed that pretty much all of the aircraft pull to the left a bit on take off do most aircraft have a rudder trim or something? (Sorry I don't know the terminology)

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That would be P-factor. Counter it with rudder input. I think on some warbirds you do pre-trim your rudder on the ground to counter the large amount of yaw generated by the powerful 1000+hp engine, but details vary per make and model, but on everything else you counter with rudder input only.

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The torque from said piston engine also causes a roll to the left (or right depending upon which way the propeller rotates).

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I've noticed that pretty much all of the aircraft pull to the left a bit on take off do most aircraft have a rudder trim or something? (Sorry I don't know the terminology)

Don't use rudder trim to counteract yawing forces of take off. Use rudder itself. The rudder required varies with torque and speed so trimming is not going to really stop it. You need to vary the rudder trim til the airplane gets up to speed and into a consistent climb. Best to do that manually.

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Don't use rudder trim to counteract yawing forces of take off. Use rudder itself. The rudder required varies with torque and speed so trimming is not going to really stop it. You need to vary the rudder trim til the airplane gets up to speed and into a consistent climb. Best to do that manually.

Yes you will need to be fleet of foot on the pedals to maintain directional control on takeoff, but you can certainly preset a certain amount of rudder trim against the turning tendencies to lighten the forces that you will have to work against. Look at any manual for high horsepowered single engined pistons like WWII warbirds and you will see manufacturers recommending settings for rudder trim for takeoff.

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That would be P-factor.

 

Strictly speaking, the left turning tendency in the takeoff roll is mainly due to the effect of torque and slipstream; asymmetric blade effect (P-factor) is an effect primarily caused by high AoA, so whilst there's a little of that in the initial climb, it's not the case during the ground roll.

 

As mentioned above, generally you will need to coordinate right rudder pressure with the application of power to keep the aircraft in balance (and conversely a reduction in power may require left rudder pressure). Trim is there to relieve control forces, so you select the attitude you require, hold it with the stick and then trim as required to neutralise the stick forces. In FS, select the attitude, run in some trim and gently release the pressure on the controls. See where the nose goes; if it wanders from the attitude you desire, reselect the attitude with control pressure, trim some more and repeat until the aircraft will maintain the attitude you wish with no control input.

 

Your average SEP is likely not equipped with rudder trim; however the C172 rudder, for instance, is set so that at normal cruising speeds little or no rudder pressure will be required to maintain balance. Some high-performance singles may have rudder trim, but it's mainly a multi-engine preserve (as you require a lot of it when flying asymmetric!).

 

Remember: P-A-T (Power-Attitude-Trim) is the sequence for establishing level flight from a descent, initiating a climb or descent or maintaining straught and level; A-P-T (Attitude-Power-Trim) for levelling off from a climb (as you would lose speed if you led with power in this situation).

 

Trimming properly will make hand-flying infinitely more enjoyable; the lack of force feedback is not necessarily an issue (typical airliners in real life, whilst having artificial feel units, essentially fly like MSFS; the control column will be centred when the aircraft is in trim if they are equipped with a trimmable horizontal stabiliser, unlike a light aircraft equipped with trim tabs where the stick neutral position will move as trim is applied).

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Adding to the above. Use rudder pressure to stay on the runway center line (right rudder for props turning clockwise from the cockpit view). Keep this rudder pressure as plane lifts off the runway, to stay on a center line direction of the runway.  As airspeed & altitude increases, the required pressure will become less.  As  been stated,  fixed rudder trim tabs (Cessna 172), cockpit adjustable tabs (if the plane has them) in addition to offset vertical stabilizers & offset engine mounts, which different aircraft may have,  will keep the plane from yawing at cruise speeds.

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In the real world, you will find your self constantly trimming during changes. I fly jets and I find that you have to trim about every 3 to 5 kts of speed change. Some one mentioned the old triangle, speed, pitch and power. Anytime you change any of these, you will have to trim.

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