After each flight, I look at the vertical profile in SkyDemon (my plane doesn’t have an autopilot). It’s often an embarrassing picture (rarely big deviations) but a still bumpy line. It doesn’t look like the variation is over +-100 feet, but it’s hard to tell because the line describing flight path is so thick.
I notice a deterioration in quality when I am flying tired or have not flown in a while. Morning quality is highest. Thermals and rough terrain make it worse. Flights over water tend to be pretty.
How smooth is your line sans pilote automatique?
I did 8 hours in one day twice – each day two times 4 hours with one hour break. On one of these flights I had 2 hours of solid IMC and it was very tiring. In general, holding altitude and heading was easy but keeping the track wasn’t due to changing crosswinds. I fly one hour legs manually very often because I love hand-flying and I’m able to maintain the altitude oscillation below 50 ft. If I really focus, l can make it spot on all the time.
That depends entirely on the weather. In stable conditions, I would say altitude typically varies only a few tens of feet. In strong thermals I have to concentrate to keep within the 100 feet expected by an IR pilot.
I think that it’s easy enough if you trim properly and focus your attention on it.
However, I think it’s a really bad idea to have to focus so much attention on a trivial task. It stops you seeing the bigger picture. How can you be checking and rechecking weather, fuel, aircraft serviceability and everything if most of your attention is on the AI?
For IFR (I would say for all route flying) the autopilot is a huge safety benefit.
Wise advice from the New Zealand CAA:
“For Part 91 Single Pilot IFR operations there is no such requirement. It is not considered prudent to fly Single Pilot IFR operations without similar equipment levels as required by Part 125 and Part 135 operations. This is a matter of managing cockpit workload, and being aware of the manner in which it can be reduced.” Full document here
This article by AOPA – although a little dated – gives sensible advice.
I would not fly Single Pilot/Singe Engine IFR without an autopilot.
Timothy wrote:
However, I think it’s a really bad idea to have to focus so much attention on a trivial task. It stops you seeing the bigger picture. How can you be checking and rechecking weather, fuel, aircraft serviceability and everything if most of your attention is on the AI?
Take that one step further, and you end up in the back of a B737. The best way to fly IFR for sure (fastest, safest, most comfortable, cheapest, you have lounges at each end with as much food and drinks you want, and flight attendants bringing you snack and drinks in the air) 
The point is to hand fly obviously. If it’s real bumpy, it’s futile to fight it IMO, sometimes even dangerous when flying in the mountains, since the winds are more powerful than a SEP. It’s better to keep the speed fairly constant and let alt be alt, it will average itself out in any case. When in smother air, then it’s back to “alt mode”, but I still see no reason to fight it, it’s the average that counts and +-100 feet is OK. In still air, keeping it spot on is no problem.
LeSving wrote:
The point is to hand fly obviously.
It’s far from obvious to me.
The heading title makes it kind of obvious to me
For the record, my flying is VFR. I would long ago have installed an autopilot in the plane if there were a viable EASA option, but there isn’t. So all my flying is “honest.” I agree with Timothy though that it is wasting a lot of effort on a trivial task. Deviations happen when I start working on other tasks (briefing the appropriate entry into a pattern; avoiding CAS, etc).
But assuming you have to do it, how smooth can you keep that line? Obviously depends on external factors, but also on the plane no doubt. The Rallye has to be flown. You can’t just set it up and leave it alone, like a well rigged 182.
I bet many people are probably worse than they suspect.
LeSving wrote:
The heading title makes it kind of obvious to me
Well, not really.
The question might be “I am trying to persuade my co-owners to invest in an autopilot because I am concerned about how good we are at holding altitude and heading over long distances without autopilot; what are your views?” for example.
