Forums:
RDD have issued a mandatory SB for all LX7s S/N 014 and earlier to replace all windows out of concern for cracking in flight. Apparently, the typical LNC4 build that serves as the donor aircraft may not have been fully tested to 5-psi whereas all LX7s are tested to a minimum of 5-psi. As a result, the window installation procedure published by Lancair has been found to be lacking and could cause window cracking when a cabin pressure of 5-psi is realized for a significant portion of flights. The updated procedure is to move to a "plug style" window installation versus the hard bond originally published by Lancair. I'm able to maintain a cabin pressure of 9,000' at FL210 with 4-psi so feel some margin of error for in-flight cracking. Would like to hear from any LNC4 or LX7 owner who regularly flies with a cabin pressure close to 5-psi as to their experiences.
Hello Andy
Submitted by Laurie on
Hello Andy
I have been attempting to get some data points on this for years to satisfy my need to know were the limits are.
However, I have been unable to extract sufficient information to have any solid engineering done.
The Lancair IV-P window fitment has an undesirable failure mode, yet there are not many failures reported other than door windows.
Door window failures are proven to be largely caused by incorrect adjustment of latches.
Based on the safety margin approach, composite airframes should be tested to 200% of the intended working pressure. I understand the Factory prototype was tested to 10 psi.
I tested my airframe to 7psi which was all I could achieve at the time with the compressor at at hand. So technically I should only be comfortable with 3.5psi. I have flown at max diff on numerous occasions but generally use the lowest pressure necessary and avoid unnecessary cycles.
The jury is still out on whether regular testing to pressure limits validates the working pressure or actually damages the structure.
The issue with a plug style window is that while the failure mode is less dramatic, in the absence of layup schedules for the airframe it is impossible to know whether the bonded window was engineered to meet the need for retaining skin tension and thereby contributing to the margins allowed for flight loads.
Anecdotal evidence would indicate that the airframe is robust enough to allow for floating windows but at least we know the airframe is controllable after losing windows and significant pieces of surrounding airframe.
I look forward to any additional information to assist in being confident to run max diff routinely.
I am interested in the process adopted by the certified Epic E1000 if anyone has insight, as I am sure they have had to jump through some hoops to satisfy engineers.
Post a Reply