What is the principal advantage of the envelope method for covering wings?

• A. Almost all the seams are machine-sewn by the envelope supplier.
• B. It eliminates the need for any testing.
• C. Seams are completed by hand only.
• D. It uses no tape at all.

Answer: (A)

The main idea is that using the envelope method shifts most sewing to the factory, so the seams are machine-sewn by the envelope supplier. This provides consistent, high-quality seams and greatly reduces the amount of hand sewing and on-site labor. Factory sewing tends to be faster and more uniform, which helps ensure the fabric is stretched and lapped correctly, reducing rework and fit issues when the wing is installed. After the envelope is fitted, you still finish the installation with trimming, sealing, and any necessary edge work, but the heavy seam work is already done.

Why the other thoughts don’t fit: you still need testing to verify aerodynamic and structural integrity, so it’s not eliminated. Seams aren’t completed by hand only in this method, since the envelope supplier does the machine sewing. And even with the envelope method, tape is still used to seal and finish joints, so it uses tape.