Simviation Forum - lateral trim to compensate for asymetric loading?

May 17^th, 2010 at 9:07am

snippyfsxer Offline
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When flying tiny little planes in the sim, I normally put two passengers up front to avoid the asymetric loads. However, that is sort of cheating if you are flying alone.

So a plane like the Cherokee (at least in the sim, perhaps incorrectly), with only a pilot, wants to roll to the left. I think this plane only has rudder trim. So I can trim it out, for wings level, but then I'm flying at a slight crab angle.

Putting aside the issue of engine out situations in multi-engine planes, what is the proper use of Rudder, and or Aileron trim? Should I simply be trying to level the wings, or should I be trying to center the ball too? I never can manage to do both it seems. I'm sort of embarrassed to ask because I've been simming for so damned long, it sounds like such a basic issue to not know...

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Reply #1 - May 17^th, 2010 at 9:40am

olderndirt Offline
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You want the plane to fly straight so ball in the center. Burn fuel off your side first. Experience has shown that, in a wing low situation, it's mostly an aileron thing so bring wings level and apply whatever rudder, foot or trim, you need to keep it straight - usually not much.

THIS IS NOT A PANAM CLIPPER

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Reply #2 - May 17^th, 2010 at 1:32pm

-Crossfire- Offline
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I think you are talking about P-Factor.... where the downgoing blade (in a right-hand turning engine) produces more thrust than the upgoing blade. This causes a slight yaw to the left. Don't trim it out, just correct it with rudder.

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Reply #3 - May 17^th, 2010 at 9:13pm

snippyfsxer Offline
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-Crossfire- wrote on May 17^th, 2010 at 1:32pm:

I think you are talking about P-Factor.... where the downgoing blade (in a right-hand turning engine) produces more thrust than the upgoing blade. This causes a slight yaw to the left. Don't trim it out, just correct it with rudder.

No...that wasn't what I was talking about at all. I was referring to the moment arm around the roll axis resulting from pilot on the left, no passengers on the right, and both tanks full.

Someone correct me if I'm wrong: The Cherokee has no aileron trim, only a rudder trim on the right side of the throttle. (although you can use aileron trim in the sim with the keyboard, it isn't really there, so its not fair to use it). So basically, to address this condition, you are supposed to hold the wings level manually, with aileron, and then if necessary, use rudder trim to eliminate any side forces, if they are present? That seems tiring!
In real life, wouldn't it be more practical to just fly at a slight crab that results from right rudder trim, so that the pilot doesn't have to constantly hold the yoke to the right?

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Reply #4 - May 18^th, 2010 at 7:07am

Brett_Henderson Offline
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Quote:

Someone correct me if I'm wrong: The Cherokee has no aileron trim, only a rudder trim on the right side of the throttle. (although you can use aileron trim in the sim with the keyboard, it isn't really there, so its not fair to use it). So basically, to address this condition, you are supposed to hold the wings level manually, with aileron, and then if necessary, use rudder trim to eliminate any side forces, if they are present? That seems tiring!
In real life, wouldn't it be more practical to just fly at a slight crab that results from right rudder trim, so that the pilot doesn't have to constantly hold the yoke to the right?

You are correct..

Obviously, the ideal would be to fuel for the load,.. like, if I was flying a long leg by myself, I'd put more fuel in the right wing. I've never done the math, but my 220 lbs about 18" off center, can be be balanced by 40lbs of fuel some 5 feet from center... but that's not always practical.

The best you can do, is to time your tank switching to at least partially counter the imbalance. In reality, once in flight, unless you REALLY let things get out of whack, it's no big deal. A bit of rudder trim will do the trick for hands-off flight.

The old Warrior that I flew the most, had a heading-hold, autopilot (via ailerons).. so I could fly 400 miles touching only the tank-valve and elevator trim.. occasionally tweaking rudder trim Cool

Edit: Funny side-note.. When I was training.. we flew a pretty long leg in an old Tomahawk, and I neglected to keep the fuel balanced (instructor kept his mouth shut). While landing.. "Where the heck did this crosswind come from ?" Roll Eyes

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Reply #5 - May 18^th, 2010 at 7:22am

beaky Offline
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snippyfsxer wrote on May 17^th, 2010 at 9:13pm:

-Crossfire- wrote on May 17^th, 2010 at 1:32pm:

I think you are talking about P-Factor.... where the downgoing blade (in a right-hand turning engine) produces more thrust than the upgoing blade. This causes a slight yaw to the left. Don't trim it out, just correct it with rudder.

No...that wasn't what I was talking about at all. I was referring to the moment arm around the roll axis resulting from pilot on the left, no passengers on the right, and both tanks full.

Someone correct me if I'm wrong: The Cherokee has no aileron trim, only a rudder trim on the right side of the throttle. (although you can use aileron trim in the sim with the keyboard, it isn't really there, so its not fair to use it). So basically, to address this condition, you are supposed to hold the wings level manually, with aileron, and then if necessary, use rudder trim to eliminate any side forces, if they are present? That seems tiring!
In real life, wouldn't it be more practical to just fly at a slight crab that results from right rudder trim, so that the pilot doesn't have to constantly hold the yoke to the right?

I haven't encountered this in RL, except for a Cessna 150 I used to fly that had a tendency to yaw and roll a bit to the left when the right seat was unoccupied, but only because some idiot(s) kept bending the fixed rudder trim tab the wrong way during their preflight (and I kept forgetting about it, LOL)!!

Since the 150 does not have left/right fuel selection available, to compensate I would just hold a touch of rudder and hold the yoke in such a way as to hold in some aileron input. Worked well enough, and was not tiring.

Not so easy using a joystick in a simulator, but if you have rudder pedals, you might try at least the rudder thing. Due to dihedral, rudder input will actually cause the airplane to bank slightly.
Or just add some "pretend" aileron trim and "pretend" you are using some manual correction. Grin

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