Merry Christmas everyone!
3 or 4 months ago, I reported on the forum that I had found substantial movement of my engine mount around the area where Dan subsequently found a crack. Many of you asked for me to send the video I had taken of the movement that was clearly visible and occurring by simply moving the over-centre links up and down with no hydraulic pressure applied to the cylinder – other than fluid resistance forces etc. I had raised the issue with Lancair, but they had not come across this. I think there was a change in the engine mount design – probably between 2005, and 2008 when I took delivery of my kit. I had checked the pressure switch settings, cylinder rod end adjustment etc – no issues there, but if the mount moves as easily as it does as I showed in the video, and having read what happened to Dan's mount, I felt something had to be done. So I went ahead with installing a pair of knee braces behind the firewall to provide for properly anchoring the aft over centre link mounting points.
The attached pics tell most of the story, but in summary. The knee braces are 12 BID carbon with 6 BID reinforcing angles floxed to the knee brace webs making 18 BID both sides; these angles also strengthen the bond of the knee braces to the sides of the nose gear tunnel. The clamp pieces tuck right inside the weldments – quite a complicated shape dimensioned using moulds (especially so to make sure that the door closing links / bolts clear the clamps) and then drawn up in CAD and machined on a CNC machine from 10mm aluminium bar. A number of flox releases were required here and there to make sure everything sits nice and square. AN4 machine screws hold the clamps in place.
Having of course checked for clearances and done a retract test, I have now taken the aircraft for a fly. All fine… and absolutely no movement of the engine mount is evident. I feel I now have very robust nose gear bracing where flexing either forwards or aft of the engine mount is pretty unlikely.
Just thought I'd share this with you all, as I really didn't want to end up with what happened to Dan's engine mount. And I was looking for a solution that didn't require the engine mount to be removed from the aircraft and reinforced – probably a technically better solution, but……….
If anyone wants more details or the CAD file for the clamps, or higher quality pics, just let me know.
Regards,
John
John N G Smith
Tel / fax: +61-8-9385-8891
Mobile: +61-409-372-975
Email: john@jjts.net.au