lml@lancaironline.net Mailing List Archive

Michael,

From the photo, it looks as though the crack has been welded shut once already. If you repeat this procedure, you may get a better weld, but there is still a pretty good chance that it will crack again. I would consider replacing the tube to get rid of the damage and possibly going to a higher strength tube material. This would increase the fatigue resistance, but make no change to the stress/strain field so you wouldn't have to worry about the damage moving elsewhere. Competent welding and grinding the weld smooth will also reduce the stress concentrations and reduce the probability of recurrence. Just make sure that the new and improved tubing isn't more susceptible to welding effects than the original or you will decrease the fatigue resistance.

Rob

In a message dated 01/25/11 16:48:46 Eastern Standard Time, mnewman@dragonnorth.com writes:

The two attached images show a crack in the engine mount on my Lancair IV-P. #4637 shows context and #4641 details. The opposite side cracked in a similar fashion two years ago. (I have not had nose wheel shimmy.)

Larger images available at:

http://www.dragonnorth.com/pictures/dataaccess/photo.php?PhotoID=11194

http://www.dragonnorth.com/pictures/dataaccess/photo.php?PhotoID=11197

http://www.dragonnorth.com/pictures/dataaccess/photo.php?PhotoID=11198

I would like advice on appropriate repair. My mechanic is suggesting some form of gusset which could improve the overall strength and prevent a future occurrence.

I wonder if this might not be asking for trouble. Without doing some serious engineering you could create point loads that might be worse.

Rather than remove the mount I would like to fly the plane to a highly skilled welder to make this repair. Any references for someone in the Northeast.

Other comments anyone?

Michael Newman

Dragonnorth Group

401 Sandy Valley Road
Westwood, MA 02090

Cell: 617 821-4608
Home: 617 566-7975
Fax: 617 566-7975

www.dragonnorth.com

mnewman@dragonnorth.com