Peter wrote:
Which GA planes have a THS like airliners have?
Mooney M20. They actually take that concept a step further by moving the whole tail.
Here is a pic of the hinge and the trim connection above it. That is all that connects the tail to the airplane. Yet none of them have come off ever in flight. They can be changed on the ground quite well if need be, as can the whole wing.
If you remember the incident where a british Mooney lost it’s baggage door which in turn wrapped itself around the elevator, this may have well been in the mind of the pilot and why he put it down really fast.
alioth wrote:
Exactly. And on planes with a spring trim, it might not work at all.It won’t work at all, if it just spring biases the elevator (unless the controls have come disconnected at the stick, and the trimmer attaches elsewhere).
I don’t believe that a spring bias system would be allowed in place of a trim tab, or all moving horizontal stabilizer. It would not meet the requirement:
Sec. 23.677
Trim systems.
…………..
(b) Trimming devices must be designed so that, when any one connecting or transmitting element in the primary flight control system fails, normal trimming operation may be continued with-(1) For single-engine airplanes, the longitudinal trimming devices; or……………-Quote
If it were to be a spring bias on the elevator system, and the elevator system suffered a disconnect, the spring bias system would not longer work either. Spring bias is used on rudder systems though…
You find it a lot in gliders and powered gliders, Canards and some ULM.
A320 does have THS, but is also auto-trimmed by a computer, and will keep its attitude unless to do so by the mini stick. That’s one of the big difference of the fbw. So pilots do have conscience of that, but somehow may loose tha ability to trim if they are not flying trimmable airplane.
I think they may have to trim it again once they have lost their 3 IRS and switch to so-called direct-law.
I would imagine airliners have a whole load of special procedures for loss of control functionality. One Airbus pilot explained to me the various fallbacks, all the way to flying the plane with just a manual (hydraulic) override on the elevator and the rudder. The ailerons would be lost totally with the loss of computers. That FI I mentioned was a GA FI, btw.
But that isn’t “GA” 
Has anyone here had this in GA?
If a Mooney has de facto got a THS, what are the different ways to deal with failures?
I have had an interesting one. Loss of AHRS. You get frozen compass arcs on the EHSIs, and you get no heading data to the autopilot. An autopilot is always flying a heading (even when tracking GPS, LOC, VOR) as the primary objective, so the only lateral mode you get is ROL (wings level). The ALT hold mode still works because that doesn’t need heading. You can steer the plane with the rudder trim, by yawing it. I once did that for ~400nm. This is why understanding the exact autopilot modes is important. The foregoing is for a King AP; others may give up completely; see e.g. this (others have similar issues) and ask yourself whether the AP will still work when the PFD has packed up because one of the inputs has gone.
If a Mooney has de facto got a THS, what are the different ways to deal with failures?
Same as the TriPacer and the Cessna 185.
Failure of the elevator pushrod – control the airplane with trim wheel. Trim in the direction you want to point the nose.
Failure in the trim drive train (chain drive, trim screw stripped / jammed) – control the airplane with the elevator.
Maoraigh wrote:
On a post-maintenance flight, I’ve had insufficient elevator authority due to new seat cushions.
I certainly don’t want to second-guess you, but wasn’t that noticeable at the “controls full and correct check” before take-off?
Airborne_Again wrote:
but wasn’t that noticeable at the “controls full and correct check” before take-off?
It can be missed.
You move the stick all the way back, it hits what feels like the stop as you expect, but an inch or so less than normal – not enough you’ll necessarily realise it’s not hitting the actual control stop – it feels like it went all the way back. You find this out in the flare when you can’t quite three-point it normally because the aerodynamics don’t lie.
To catch things like this (upholstery changes in pilot seats) it needs to be on the maintenance worksheet, and someone needs to actually check the controls are hitting the stops, while on the ground, when you can stick inspection mirrors/heads in places you can’t do when the engine’s running.
Does anyone know of any accidents where the elevator control linkage failed?
The elevator control linkage no but there are plenty horror stories about the Cessna 185 and its design issue with the trim wheel where if a certain pin breaks the whole stab will run away under aerodynamic loads.
