Horizontal Stabilizer Structural Analysis

Purpose

Evaluate structural strength of horizontal stabilizer and mounting to fuselage

Methodology

Evaluated shear loading of horizontal structure. Then performed an initial one-dimension calculation to evaluate straight static pull on mounting points with the total horizontal load. Revised to test the load with a moment about the quarter chord under various conditions. Depending on if the elevator is locked or not, the moment will shift fore and aft.

Results

Initial structural evaluation of the horizontal stabilizer itself resulted in significant margin (FOS >~40) for failure in shear on the combined front and rear spars. The one-dimensional load on the mounting points similarly resulted in low stress on all six tabs when loaded equitably (1.3ksi). The two-dimensional loading was evaluated with the moment at various fore/aft locations. Under normal flight conditions with the elevator free and +/-30% on the left/right (respectively) to represent roll, and the moment around the mean aerodynamic chord, the highest stress seen is 42ksi in compression on the forward left (+30%) and 12ksi in tension on the rear left (+30%); both are well under the 63ksi yield strenght of the steel. The other primary condition of locking the elevator actually slightly increase the compression (46ksi) but decreased the tension (7.6ksi) due to the locked elevator increasing the mean aerodynamic chord and moving the moment aft and outboard.

Conclusion

As failure from a tensile failure (bolt rip out) is seen as more catastrophic than from buckling, the low tensile loads prove advantageous, although neither failure mode will be seen within normal flight parameters (limit 3.8 g’s, below 158 knots, below 12,500 feet). Also, giving the taper of the leading edge and unique near-semi-circle shaped elevator, a locked elevator effectively counteracts the moment of the horizontal.