To Small-Tail Lancair Flyers,

Stability issues relative to the small-tail LNC2 have been debated for years.  My small- tail LNC2 exhibits an unstable flying mode that I have not seen discussed.  The purpose for submitting this informtation to lml is two fold (1) solicit input from other small-tail LNC2 flyers whether similar instability has been experienced and (2) provide a heads-up to small-tail LNC2 flyers that this potential for instability exists.

 

Instability Description:  In the right cross-wind landing configuration (right wing down, left rudder), the nose begins to oscillate up and down.  The oscillations increase in magnitude with or without pilot control input.  In 3 or 4 cycles the oscillations become  uncomfortable during flight tests at altitude and the uncontrolable oscillations are a serious hazard during an actual landing approach.  The problem does not exist in a left cross-wind configuration.

 

The problem appears to be caused by a loss of horizontal stabilzer effectiveness as the air flow corkscrews around the fuselage.  When the horizontal stabilizer becomes ineffective, the nose drops.  When the nose drops, the airflow to the horizontal stabilizer becomes more effective and the nose rises.  The oscillations stop when the right wing down and opposite rudder control inputs are neutralized.   In the right cross-wind configuration, elevator control inputs have no effected on the oscillations.   

 

The pilot can work around this stablilty problem once he knows that it exists by (1) avoiding the right cross wind, (2) using the crab landing technique. If the pilot is not aware of this problem, the natural response is to assume that the oscillations are pilot induced and attempt to dampen them prior to touch down.  This pilot response will likely test the ultimate structural integrity of the landing gear.

 

I am sure small-tail LNC2 flyers have attempted many right cross-wind landings and I have not seen problems with oscillations discussed.  Perhaps the problem is the result of some quirk in my construction.  Although the oscillations are so predictable and so pronounced, it is hard to imagine that my airplane is so different from everyone elses.  The following is a description of some characteristics of my small-tail Lancair 360.:

*  Kit number 383

*  180 hp Lycoming ) 360 A!AD engine, converted to fuel injection

*  Electronic fuel injection on one set of spark plugs

*  Hartzel 68 inch, standard Lancair prop

*  Perfomance

    -- Cruise speed 207 kts

    -- Clean stall 68 kts

    --  full flap stall 62 kts

    

I only recently became aware of the lml web site and it appears like an appropriate place to pass on this type problem.  I have not addressed this matter with Lancair.  They always seem defensive rather than proactive  in dealing with flight problems and after I drove my right landing gear through the right wing on my first right cross-wind landing attempt five years ago, the FAA had me take remedial landing lessons with a certified flight instructor.  That did not seem to fix the problem. So this is my way of getting the word out to folks who may really care.