elevated temperatures over a long period may be worse than short periods of higher temperatures. A significant obstacle to heated rotor blades are studies that show that the kind of heat needed to de-ice main rotor blades is sufficient to damage the bonding between blade skins and cores of conventional blades, and that likelihood also exists for composite blades. With more frequent use of composite structural components in newer helicopter designs, maintenance technicians need to pay attention to any defects in surface protection and probably keep a tap hammer on their belt. One major difficulty in the manufacture of composite structures is the level of quality assurance and techniques for inspection needed to assure that defects that occur during lay-up and curing are smaller than acceptable limits for inclusions, de-bonds or delamination. Ultrasonic inspection techniques work well for many applications but X-ray is not as effective as it is for metal alloy parts. In addition to the varieties of ultrasound inspection (single transducer, multiple or phased array, through transmission or pulse echo are some), there is shearography which uses light wave interference patterns or phase shifts which result from surface or subsurface defects when putting a stress (thermal, or mechanical, vibratory, acoustic, torsional etc.) on the part. Some of these techniques are better suited to looking at new parts in a controlled environment such as an OEM would have but as microelectronics and signal processing software gets better, these things will more and more be used “on the flight line” for inspecting composite structures.
If some of this sounds a bit like rocket science that is because it sort of is rocket science. For a good introduction to the training needed to use this equipment effectively see the article by Larry Schultz in the Oct/ Nov 2010 issue of Helicopter Maintenance (then called HeliMx).
August | September 2019
HelicopterMaintenanceMagazine.com 29
We are probably approaching a time when there will be more of a need to have people trained in composite inspection than there has traditionally been in the helicopter industry. This is not to say that there haven’t been lots of composites used in helicopters until recently. The day when core airframe structures are made from composite materials is already here and they are going to be more commonly found in major structural components. Twenty-five years ago I thought it would have been smart for me to have been an avionics specialist. That may have turned out to be true, and I would also suggest that getting a solid background in composite repair and inspection can probably be a path to serious job security for someone starting out in aviation maintenance today. Both are also skills that are directly transferrable to other industries.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
