lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> I reported the sudden dive, with negative g forces last Jan. At the time I suspected the autopilot, since I was cruising at 9500 ft using the S-Tec altitude hold. I was reasonably certain that I had to overcome the autopilot to stop the dive. The upset was especially violent since I was not holding the stick. The first investigation did not find any problem with the autopilot and left some uncertainity regarding the cause of the upset. A clue was furnished on my next cross country from BPT to LHX. I was at 10500, a little cool and pulled the heater on. Immediately the plane tried the dive manuever, but this time I did have a grip on the stick and averted a major upset. Subsequently, it appears that the problem was with the heater cable passing over a terminal strip. Clearance from an uninsulated bolt with several leads attached was about 1/32". I insulated the cable with some FEP tubing and have had no further upsets. Tracing of the leads to be certain that one of them was from the autopilot was very difficult and not successful due to the lack of ID at the terminal strip. However, another clue, my uMonitor also had failed to record the proper flight time on the first upset. Apparently this can be caused by low voltage and I can trace that lead from the terminal strip bolt to the uMonitor. It would appear the builder completed the instrument panel with the terminal strip before completing the heater cable. The terminal strip was not secured to the nose wheel well. Of course, the short of these leads could have been avoided by proper insulation or by proper placement of the cable or terminal strip. A warning to those of us who will have some else complete the instrument panel. Any of the various engine control cables can short out instruments. LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com.