In 90hp puddlejumpers you tend to ride the thermals and accelerate through sinking air, generally less stressful on passengers and airframe.
WhiskeyPapa wrote:
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.
Bearing in mind during summer you’re likely to be facing some sort of convective activity with rising air, at least at lower altitudes, why are you so concerned about any altitude deviation? I flew recently an old Cessna 172 without autopilot and slavishly following an altitude was just a waste of time in bumpy air – in the end, I sat back and enjoyed the flight, keeping more or less at my selected altitude. However as there were no consequences of climbing or descending 100 feet or more, that was the main reason I didn’t bother chasing the altimeter….
Actually for me maintaining altitude and heading in most conditions is a measure of quality. Ideally you feel a deviation and correct before you notice it consciously (VMC not IMC). My point is I don’t do it as well as I’d like. Easy enough when that’s all you’re doing, but throw in some distraction like peeing into a bottle or briefing an approach, and quality goes down hill. I’m not talking about moderate or above turbulence of course.
I do see the value of an autopilot, but I think a good one might cause some skills to deteriorate.
WhiskeyPapa wrote:
Thermals and rough terrain make it worse
If you’re VFR, don’t try to fight it – just ride the thermals up and down (of course paying attention to any overlying controlled airspace). It’s less efficient to try and hold altitude in air that has vertical movement. You’re also less likely to run into someone else (or be run over by someone else) who’s fastidiously trying to maintain a specific level :-)
“You’re also less likely to run into someone else (or be run over by someone else) who’s fastidiously trying to maintain a specific level :-)”
Ha, ha, ha!
Maoraigh wrote:
The Jodel DR1050 I cannot trim hands-off after over 1500 hours.
I fly a cranked wing Robin and Id say that on the average summers day over France below 3000ft you “approximately trim” and expect your altitude to vary +/-100ft or more due to strong thermal activity and will absolutely need to manually fly the aeroplane all the time to keep that accuracy. In smooth air I can trim to hands off, but this is rare unless at altitude or early in the morning when a stratus layer has blocked the sun.
Flew LA to Kansas last year without autopilot. Got a little flak from the LA controllers for not keeping the altitudes tight enough in the beginning, but once up in cruise and all trimmed out over the desert it wasn’t that bad. It gets a little exhausting to fly like that, but once in awhile is sufferable. Dropped plane off in Tulsa on way back and got the antique autopilot fixed, so now all is good again.
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
Unlike you, all my flying is VFR, and I never use an autopilot. But I do have a different perspective.
I must prefer to strive to make the breadcrumbs look like there were flown on an autopilot. There are a few reason for this.
1. It makes you focus outside. Try this and most people’s first reaction will be to stare at the instruments pre-empting the tiniest movement. But if you do this, your breadcrumbs will look like continuous little waves. To make them look as straight as an autopilot, you’ll need to look outside and track something in the distance, with just occasional glances at the instruments. So it actually encourages looking outside. It’s the same as the difference between driving on a motorway staring 5 meters in front of your car, or looking into the distance. The first will involve lots of big corrections to stay between the lines on the road, but the second doesn’t.
2. It doesn’t take a lot of practice before this becomes a ‘motor skill’, or something that you do subconsciously. At that point, you have the luxury of being able to very accurately maintain heading and altitude while your conscious mind is working on a different problem. In my experience, five or six hours flying over 2-3 days, determined to make the breadcrumbs look like they were flown on autopilot, is all that’s required to make it a sub-conscious skill. But low currency afterwards takes that skill away. So for those of us who fly little during the winter, it’s good to get into the habit with some condensed early season flying, then hopefully it will stay with you all season long.
alioth wrote:
You’re also less likely to run into someone else (or be run over by someone else) who’s fastidiously trying to maintain a specific level :-)
Also you are burning more fuel when “you try to fix it”: flying constant angle of attack on constant trim (with changing ALT & ASI) during phugoid oscillations will give you a nice mpg figure 
To answer the original Q (I have been away, with just a phone):
It depends on
On a long flight in the TB20, in smooth air, 50ft is readily achievable. Due to autopilot failure(s), I have flown most of the way to Santorini and back by hand, and I doubt I deviated by more than 100ft. But I had a passenger who could hold wings level, and anyway you can do that with the rudder.
In rough air, no chance. Today, climbing from LFRQ to FL100, climbing in PIT mode at about +500fpm normally, the VS varied from 0 to +1500fpm according to the build-ups. If you were hand-flying in that, you would be struggling to hold say 200ft. On top, 8500ft, it was very smooth.
During the FAA IR in 2006 I was flying a PA28-161 in Arizona thermals and had to hold 100ft (the FAA IR checkride requirement), but flying twice a day for 2 weeks, mostly partial panel, everybody is a great pilot I am sure you could solo an F16 after solid practice like that. I had to sleep for an hour at lunchtime… but I was just a kid then (under 50 ).
One thing I learnt for IR renewals: even though the autopilot is allowed for enroute, disconnect it at least 10 mins before hand flying any approaches, otherwise they will be really crap. It takes a while to get the brain engaged…
And of course it depends on the plane. Some are much more stable than others.
Also a CS prop gives you a much more stable altitude. A fixed pitch prop, when pitched down, revs up the engine, which greatly increases the thrust, which makes it dive even more. A CS prop just keeps absorbing constant power the whole time, regardless of pitch excursions.
