Flettner Trim Tab Acceptable Play

[SomethingScrewy]

I have a 1940 BC-65 with the uncommon Flettner trim tab. The aircraft is undergoing its annual inspection and the A&P/IA is asking how much up and down free play is acceptable in the trim tab. There is kind of a “dead zone” of slop if you move the tab up and down with your hand on its trailing edge (which has always been there, but I have never measured it). The cables to the tab appear tensioned fine, so not sure where in the mechanism the slop comes from. Before the mechanic tries to take it apart, he is looking for more information on how much play is acceptable. Any ideas?

[3Dreaming]

I assume you are talking about the trim flipper. It is a pretty simple system. A bell crank with a handle at the front, going to a bell crank in the back with cables in between. At the back the bell crank is attached to the shaft with a roll pin, it is possible the holes are worn. The shaft goes though two steel bushings in the fuselage, there could be some play there. The flippers are attached to the shaft with three screws each side, and there could be some play there. I would grab each side and see if there is any movement between sides. If there is tighten the screws that attach the flippers to the shaft. Next have someone hold the handle in front and move both flippers at the same time to check for movement between the shaft and bell crank.

[SomethingScrewy]

Thanks for the tips - I relayed the information and my A&P found a solution. This is about the flipper, and the play was in the rotational direction (motion driven by the bellcrank). The other directions were solid. The mechanic spotted two cotter pins by looking through an inspection port in the area, one of which was accessible. I did not see it myself, so I am not certain what part of the assembly the cotter pins hold together. He replaced one of the cotter pins with the next larger size pin, and that reduced the play considerably.

[3Dreaming]

From memory it should be a roll pin.