Hi all, I’m new to Mooneys and to this forum. I have an elevator trim observation and thoughts to contribute to this thread. I have recently purchased my dream personal plane, a 2005 Bravo GX. As great as she is, she has one aerodynamic idiosyncracy: in level cruise, over a wide range of power settings and weight loadings, she exhibits a distinct elevator up condition (see picture 1 below with elevator horns in an unfared position below the horizontal stab). Paint loss on the leading edge of the horn betrays the longstanding nature of this condition. Simultaneously, the STEC 55X autopilot establishes a strong nose down empennage trim condition with the net aerodynamic result for pitch being neutral. Turning off the autopilot confirms a neutral net pitch trim state.
This condition is undesirable for 3 reasons. (1) increased induced and parasite drag (2) capacity for horn icing leading to elevator lock - note paint loss (3) operating near the limits of nose-down empennage trim in case of out-of-range aft C of G condition, icing, unusual attitude recovery, etc.
I believe the extended elevator of the long bodies is the key to understanding this quirky condition. I gather that the long-bodies were provided extra elevator authority by extending the elevator with a ~1 inch chord full-span sheet aluminum tab along the trailing edge of the previous elevator design. Looking around at similar Mooneys, I see that most of these elevator extensions are deflected slightly downward compared to the chord of the parent elevator. This deflection is at least in part caused by the mounts for the static dissipators which remain attached to the “old” trailing edge and must run across the upper surface of the elevator extension.
This elevator extension design creates, in effect, an elevator tab down condition, leading aerodynamically to an elevator up condition that must be neutralized with opposite empennage nose down trim. As many of you know, elevator tabs are used as the prime elevator control surface in most large aircraft; their position at the trailing edge well behind the elevator hinge axis gives them tremendous leverage such that modest tab deflections give large opposite elevator deflections. This explains how a small error in the angle of incidence of the elevator extension in a long-body Mooney can have a relatively large effect on elevator position. The question is, what’s the best fix? Bending the elevator extension incrementally upward until neutral elevator position is established? Does anyone have experience with this? I know a bit about aerodynamics, but I’m no mechanic.
Chris Buller Mooney Bravo C-FDRX
