Most IFR tourers tend to be stable (indeed heavy) in roll while light in pitch.
The TB20 is no exception but is great to hand fly. I once had an autopilot failure climbing out of Corfu and had to hand fly all the way to Santorini, and then back to the UK. It was VMC all the way though, and I had a co-pilot (Justine 
) who could keep the wings level. It makes it hard to do stuff like taking photos and taking a pee
I suspect a lot of planes are rigged out of trim, or have poorly lubricated control linkages which produce stiction and need constant attention.
Well, a lot of airplanes out there, certified or not, are just not pleasant to hand fly. Some reasons, as pointed by Peter above, others like just poor design.
As a matter of fact, some aircraft are so unpleasant to hand fly, that you need an AP… to « fly » ‘em 
There is simply no way to trim it properly. Somehow it needs to constantly worked on.
I find that for planes with side-by-side seating, long thin fuel tanks in the wings and no aileron trim this is often true. Depending on loading and fuel state there is very often some roll imbalance even when an effort is made to balance with fuel in flight. It would be nice for the pilot if some form of aileron trim were fitted, but it is not always the case.
Silvaire wrote:
Depending on loading and fuel state there is very often some roll imbalance even when an effort is made to balance with fuel in flight.
Interestingly on the TB-20 I was able to balance the roll axis well, using the little tabs at the end of the ailerons.
However the pitch axis remained problematic. I am not saying its not possible and the TB-20 is a great plane to fly, but her nose is a bit unstable.
I find it harder to set a stable descent rate vs. the Diamonds or a Cessna. It could be easily my poor piloting skills :D
Important thing is to balance the tanks, taking into account where the weight is (e.g. flying solo, or one huge person in the LHS and a small person in the RHS, etc, and how much is in the TKS tank) and start off with neutral aileron trim tabs.
Whenever I see heavily bent aileron trim tabs, there is something wrong. The flaps for example need to be firmly UP against the wing, both during flight and on the ground. They sometimes get bent down by people stepping on them and bending the 1970 Citroen windscreen wiper motor mechanism. A 1mm imbalance between the flaps will need a lot of aileron trim, and the whole plane will fly a bit weird.
Switch tanks according to where the ailerons sit. If one sits higher than the other, that means the other wing is heavy, so you need to draw fuel from the other wing. Time to switch to the right wing:
However I can’t think of what would make it excessively unstable in pitch.
And Peter, when you set a descent rate, let’s say 500 fpm, you set the power, pitch, trim it and then hands off the TB is keeping the 500 ft/m or there is an oscillation?
No oscillation after initial phugoid has dampened out. That is what is supposed to happen.
On descent when trimmed my TB20 was going like on rails – stable both on pitch and roll.
It is now a very long time since I flew the TB20, but I remember it as a stable and easily managed IFR platform. I only have fond memories…
TB20 is hugely stable, but when I let people fly in the RHS they always have trouble holding altitude.
I think this is for two reasons. Firstly the roll control is really quite heavy in cruise, yet pitch is relatively light. It isn’t what I would call harmonised.
Secondly, despite having pushrod controls, the ends of the pushrods are just flattened with a bolt through them. They don’t have a rose joint on the end of them, so you get some tolerance stackup and the result is some play or dead zone in the controls which can take some getting used to. Also probably more friction than if rose joints were used.
Its a lot more solid in the air than eg. A pa28 but probably takes some more getting used to.
