This has been a very interesting thread to monitor. FT threads lack the vitriol found in many other fora, especially those of my compatriots it would seem.
I agree that the real point that the nstructor was attempting to state should ascertained by the neophyte and passed on to this place if possible, however if not then there are a cuople of comments that I would like to make.
If the point being made was that the additional camber effect of a down turned trim tab would provide additional lift to assist with the raising of the tail when in an aft CofG, then this is not the way to convey that information, because ,whilst true, it neglects the differing configurations of trimming methods (trimming stabilizer etc) in which this procedure will most definately result in an adverse effect.
If the instructor intended that the trim be used correctly - ie trim for nose down when configured aft CofG then this would seem to be stating the bleeding obvious and a little redundant.
If however the instructor was making the point that "if you find yourself in a situation where for some uncontrollable/unpredictable reason the Cof G has become (extreme) aft, then this might help..." he should have made that point quite specifically and added that this will only assist on certain types. - this would be an illustration of transfer of 'tribal' knowledge.
For part 23 the trimmablity of the vehicle is required to be demonstrated for a range of CofG, power/flap/gear combinations, and this along with the demonstrations of longitudinal control (not stability) and to a lesser extent the control forces for control during landing determine several major aspects of the CofG envelope. To provide any encouragement to a student they can operate outside the envelope by using 'tricks' is completely enethical and potentially lethal. Ther are some parts of the compliant envelope where it is acceptable to apply temporary two handed control wheel forces of 75 lb, single handed of 50 lbs and sustained forces of 10 lbs, so adding additional forces by adverse setting of a moveable tab and and aft CofG outside demonstrated limits, may well exceed the pilot's available strength.
I am not aware of the term 'trim stall' relating to any particular part 23 demonstration for the purpose of compliance, but clearly see the trim motor overload case as bing a suitable definition.
I think that the information contined in the above posts would indicate that a more appropriate comment from the instructor would have related to the careful and minimal application of flap for landing when an inadvertant aft CofG had been identified. application of extreme adverse positional trim seems to be poor advise. If hawever the advice was to set the trim in this position PRIOR to flight when an Aft CofG case has been identyified PRIOR to flight, then this is just utter stupidity.
For the FT I have been involved in thses cases are approached very carefully with the CofG moved to the aft position whilst in flight at a safe speed and height and with the additional added precautions of emergency egress available. accurate data logging and control force application is vital to establish the safe operating limits as well as repeatable limits for the demonstration fo compliance. You don't just load the 172 to the gunwhales, wedge the aft locker full of suitcases and tie down kits then squeeze the doors shut, applt full nose up trim start engines and attemt to depart on a scenic tour as the results will not be pretty.
HD