Northwind produces composite components utilizing both proven aerospace design practices and aerospace grade materials. These design philosophies and materials allow us to offer products with exceptional performance and durability. However, as with all composites, our components should be routinely inspected for signs of damage and require proper personal care while modifying. Many of our products are intended for those who have basic fabrication skills or will take their parts to a qualified installer.
That said, we recognize that advanced composites are new to many people and we have provided some basic items to be aware of while using and working with our parts. This information is meant to support and help our customers and should not be considered an all-inclusive write up of technique, safety, and other issues associated with composite work.
Handling Considerations and Tips
Our parts do not require any special care or considerations when causally handling or working with.
However, special care should be taken when grinding, sanding, or cutting. All parts are fabricated from a varied selection of carbon fiber, fiberglass, various core materials, aramid (Kevlar®), and epoxy resins. These materials in dust form can be both allergens and irritants to skin and eyes. Dust masks, eye protection and gloves should worn when trimming our parts in addition to good ventilation.
Cutting our composites can easily be performed with standard rotary tools such as Dremel tools and die-grinders. Keep the RPM up and it will cut just fine. Additionally, a three flute down spiral router bit run at a high RPM will create a nice edge. We recommend 80 – 120 grit for rough sanding and 220-320 grit for final sanding. Any drilling operations should be performed with a sharp bit, medium to high RPM and a slow feed rate. Drilling composites is a subject of many, many, many debates and research papers but the general rule is still a sharp bit, medium speed, and a slow feed rate.
As a general rule, drilling tends to create very small local delaminations around the hole. Therefore, it is recommended to seal the hole with an epoxy or sealant. This sealing epoxy is meant to seal the hole to prevent moisture, grease, oil, etc. from getting between the plies and causing long term damage. Therefore, most epoxies found at your local hardware store will work for this purpose. Alternatively, any through fasteners can be installed with an RTV sealant – but be aware of silicone as it can interfere with any epoxy sealing/gluing down the road.
Inspection Practices
All parts should be routinely inspected for damage such as cracks and delaminations. Pay particular close attention to all holes and fastener locations. Cracks can be seen by looking for, well, cracks. Interlaminar crack (cracks between the plies) will often appear as milky white lines within the fiberglass though these types of cracks are much harder to visually detect in carbon fiber.
Delaminations (separation of the plies) can occur from poor trimming, drilling, and impacts. Delaminations will degrade the strength of the part and will continue to get larger over time, further reducing strength. One of the easiest ways to detect delaminations is through a tap test. Simply take a quarter or nickel and tap firmly around the area where damage is suspected. You will hear a nice crisp sound in areas where the laminate is sound and you will a dull note if the area is damaged.
Additional Resources
The information above is meant to provide a basic generalized discussion of care and maintenance of our composites for the layman. For those who wish to delve further into the subject and wish to learn more, please see the FAA links below.
http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentid/99861 *See Chapter 3