Adding an autopilot to an M5

[andy]

Autopilots are very helpful in single-pilot IFR if they keep you on-course and on-altitude while you're busy doing something else. That's even more true in IMC. The ones that connect to your GPS and fly an entire course, hold and approach are truly awesome. Like anything on an aircraft there's a price to pay besides the cost of purchase and installation. There's a bit of weight involved with the servos and linkages. Like any complex component the installation of an autopilots increases potential points of failure, probability of failure, maintenance complexity and maintenance cost.

I've flown several Cessnas with autopilots that demanded more attention than they were worth. In one case you had to be within 15 degrees of the GPS course before the autopilot would take over. In another case the autopilot aileron servo started chewing up the metal gear and bogging down manual aileron control. In another case the autopilot disconnected randomly on its own without a message.

My preference is to have no autopilot. I tend to too trust it too much and find myself focusing on other things without checking the autopilot's operation enough. It's a bit more fatiguing to manually maintain heading and altitude and fly approaches but you can train yourself to maintain heading and altitude without a lot of conscious thought. Instrument approaches demand your full attention whether you have an autopilot or not. I need the practice manually flying instrument approaches to stay proficient. I'm afraid that I might get rusty if I let an autopilot fly them and then have to fly one for real if the autopilot fails.

[Andy Young]

Good points, Andy, especially on maintaining proficiency with hand-flown approaches. That said, a GOOD autopilot can help reduce fatigue, leaving you sharper for those approaches, or for the last section of them after you turn the autopilot off.

I worked a job last winter that involved very long days flying between a big airport and a tricky off-field landing in a short, unimproved area. The enroute portion was 1.5 hours long, and completely straight and level over relatively featureless sea ice. I did over and over, several times each day. Using the autopilot on the enroute phase undeniably helped with the burn-out.

An autopilot can also improve safety and make for a better ride when your hands are full with other things. In my normal job, I have to do a trend analysis on the engine once each day. This involves filling out a form that records the current readings on several engine and flight gauges while holding an exact pressure altitude and power setting, all while continuing to scan for traffic (this is in VMC, at relatively low altitude) and doing all the other things we are supposed to stay on top of as pilots. It’s much safer (and smoother for the passengers) to use the autopilot during this phase.

Since we have autopilots, we are required to be proficient in coupled approaches, and demonstrate this on our annual checkride. In practice, I do tend to revert to hand-flying earlier than technically required, as the autopilot tends to hunt a bit as it gets closer to the airport. I’ll also fly some approaches without the autopilot at all, to maintain my proficiency.

[Mog]

The auto level feature on some units could be a life saver. And if the pilot is incapacitated the autopilot gives the passenger some time to make since of their situation assuming the autopilot is active or they know to hit the auto level button.

That’s a huge selling point for me for sure. Though I’m nowhere near a foot in the grave, you never know what could happen tomorrow. I’d feel much better if my passenger could either fly or at least have the ability to hit auto level and ask for help.

And I do agree I would be inclined to make longer x-country flights if I had autopilot. Largely because my Maule has a moderate left hand roll tendency that I have had difficulty getting rid of so I can’t take my hands off the yoke for very long.

[psehorne]

.. my Maule has a moderate left hand roll tendency that I have had difficulty getting rid of so I can’t take my hands off the yoke for very long.

I assume you know this, but just in case.... Maules are designed with a small amount of left roll with the ability to neutralize it with the right rudder trim control on the panel. Does the right rudder trim control on the panel eleviate any of this tendency? I don't know what model you have, perhaps earlier models did not have the right rudder trim control.

[Kirk]

If your airplane rolls left in cruise, pull the rudder trim out a bit at a time until it no longer rolls left. Should be about 2 units (the marks on the rudder trim shaft).

If it takes much more than that or the ball is significantly out of center, your plane is out of rig. I personally would live with 1/2 ball or less.

That’s assuming 65-75% cruise power somewhere near optimum altitude. Faster cruise or much below optimum takes less right rudder trim, slower cruise or much above optimum altitude requires more right rudder trim.

Kirk

[Mog]

I have my rudder trimmed for a centered ball in ideal conditions. I would probably see half ball or so to keep it from rolling. I’ve just always shot for dead center and never adjust it really. Maybe I should adjust it more aggressively.

[DavZeeMXT]

Duh, and here I am flying all these years pushing on the right pedal....

[Kirk]

Mog, I noticed mine was rolling a bit more left after being parked outside in some high winds. Had control locks clamped between flaps and ailerons. I suspect one of the flaps is twisted a bit, doesn’t quite line up when ailerons are neutral. Will check it all out in annual next month.

I flew quite a while in cruise dealing with the roll left before I started playing with the rudder trim more to get it straight. Seeing the ball out just messes with my sense of perfection.

Kirk

[Mog]

I replaced my flap hinge bushings and thought that cleaned up the problem. But it “came back”. Not sure it really came back, just that it was different and maybe the rudder was adjusted differently. I dunno.

[Andy Young]

Don’t forget about the influence of the tail wheel. It can cause problems of this sort in two different ways:

1. If the chains are rigged unevenly, such that the tailwheel doesn’t line up with the rudder when centered, it’ll catch the wind and push the tail sideways, even when the rudder itself is centered. You need the tailwheel off the ground to check this.

2. If the rudder pivot is too tight, or sticky from lack of servicing or internal damage/issues, it can hang up at an angle after takeoff. This is particularly prevalent after departing from a rough surface. This one is easy to diagnose: If, after takeoff, you are needing a fair bit of rudder input to stay straight, try giving the rudder pedal a sudden, forceful push. Usually, this will re-center the tailwheel. You might need to do it a few times, one side then the other, with successively gentler taps, to get it perfectly centered.

On many of the newer, made-by-ABI Scott-type tailwheels, the dowel pin that locates the lower thrust washer is too short, and is pressed down into the housing too far. This leaves too little protruding to properly prevent the thrust washer from rotating. Rotate it does, then gets hung up on top of the pin, creating a tight spot, and leading to the problem in #2. The solution is to remove the pin and place a very tiny washer under it to make it sit at the correct height. Too high will also lead to problems. The top of the pin must sit JUST below the top of the thrust washer.

[Kirk]

Good stuff Andy, thanks.

Have also found aircraft that have loose control cable tensions may be flying wing low or ball out of center. A bump on the controls, usually rudder may get it flying more straight.

That’s always been my cue to have the tensions checked. Seems that some IA view that part of the annual as optional.

Kirk

[Njacko]

I'll rock the boat and say "it's a bush plane, why does it need an autopilot?"

My Maule came with an S-TEC 60-2. I added GPSS so it just follows whatever route is in the GTN 650.

I think it’s a safety feature for single-pilot IMC and for the kind of long flights a Maule’s fuel capacity allows. After 6 or 7 hours from Scotland to the French Alps, for instance, I feel no worse than if I’d driven a couple of hours in a car - regardless of flight conditions.

[drak130]

I roll right. Hoping Maule Flight can correct during next months annual. No autopilot. Trying to use the gatoraid bottle on a 4 hr flight after two cups of coffee almost ended in a mess.

[Njacko]

I roll right. Hoping Maule Flight can correct during next months annual. No autopilot. Trying to use the gatoraid bottle on a 4 hr flight after two cups of coffee almost ended in a mess.

Spare a thought for glider pilots (we call them, perhaps unkindly, “the cyclists of the air”). No a/p, not even an engine, hugging some turbulent thermal or mountain wave for hours on end... Nuts!