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Auto Pilot Question (Read 320 times)

Feb 7^th, 2005 at 1:12pm

BenMK Ex Member

Hey I was wondering something last nite. When you make a turn with the AP, do you have to use rudder?

Thanks
-Ben

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Reply #1 - Feb 7^th, 2005 at 1:15pm

C Offline
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Having never used an autopilot (You don't need an autopilot boy! You sould be able to do at least 54 things at once!!! - but I have been employed as one myself on several types), I'd imagine the answer is no - on modern types the flight control computers would deal with any control inputs required, and on older types I imagine there would have been some kind of mechanical mixing if it was needed....

Charlie

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Reply #2 - Feb 7^th, 2005 at 5:31pm

beaky Offline
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Depends on the plane. I've only used the AP in FS9 on the C172, just for altitude hold (maybe it's me, but she doesn't trim out as well as the real thing), and it seems it's got a built-in wing leveler..., even without "HDG" enabled, it doesn't want to turn with the AP on. Trying to change heading with rudder only doesn't work too well, so I usually turn the AP off to turn, then turn it back on. Of course, there's no reason why you can't keep the HDG function enabled and change course by changing your DG bug, OBS, or GPS waypoint (depending on what you're using)...
I've never bothered with autopilots in my RL flights in Cessnas; I've always been VFR and eager to hone my heading and altitude-holding skills on every flight so as not to lose my touch.

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Reply #3 - Feb 7^th, 2005 at 5:51pm

Nexus Offline
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if the AP is one axis; Yes use the rudder since it's an entirely different axis (heading = longitudinal/roll axis, rudder = yaw axis)

But in a modern airliner, nope.

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Reply #4 - Feb 7^th, 2005 at 8:36pm

beaky Offline
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True about the airliners, but kicking rudder with a wing-leveller on is a sloppy way to turn in a light plane also. It'll roll a bit as one wing swings forward and catches a little more lift, and the nose will want to slew back the other way as you release rudder pressure. Probably not good for the AP servos, either. Two or three degress might be worth it, but for a major course change, either turn it offand turn manually or just reset the heading with whatever device you've got the AP slaved to.
Of course, if the AP itself is making the turn, it will be working that rudder for you. Or am I wrong...?

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Reply #5 - Feb 7^th, 2005 at 9:05pm

Saratoga Offline
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Most GA autopilots are two-axis, Pitch and Roll. They can climb, descend, and turn. They can also hold headings altitudes and what not. They do not however, coordinate the turns. Usually, the A/P will bank so smoothly and slowly you won't notice, but sometimes it is obvious and annoying. It's possible, if tricky, to coordinate it yourself, but if you are going to put that much effort into it, why not just take the A/P off? Airliner autopilots coordinate it all to make a sweet perfect turn while maintaining altitude and airspeed at the same time.

Pilot for a major US airline certified in the: EMB-120, CRJ, 727, 737, 757, 767, and A-320 and military, T-38, C-130, C-141, and C-5 along with misc. other small airplanes. Any questions, I'm here for you.

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