FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician examining a wing box beam spar notes that the vertical member connecting the upper and lower spar caps is thin sheet metal reinforced with stiffeners. What is the primary function of this vertical web?
- ATo carry the bending loads of the wing
- BTo carry the shear loads between the upper and lower spar caps
- CTo act as the primary attachment point for the wing skin
- DTo provide the aerodynamic contour of the wing
Show answer & explanationAnswer & explanation
Correct answer: B. To carry the shear loads between the upper and lower spar caps
In a box beam spar, the spar caps (upper and lower flanges) carry the tension and compression bending loads, while the vertical web primarily carries shear loads between the caps, similar to the web of an I-beam.
Why the other options are wrong
- A. Bending loads are primarily carried by the spar caps, not the web.
- C. Skin attachment is typically along ribs and stringers, not the spar web directly.
- D. Aerodynamic contour is provided by the wing skin, not the internal spar web.
Spar Web (Box Beam)
The vertical sheet metal member connecting the upper and lower spar caps in a box beam spar, primarily designed to carry shear loads while the caps carry bending loads.
- Spar caps carry tension/compression bending loads.
- Web carries shear loads, similar to an I-beam web.
- Webs are often reinforced with vertical stiffeners to prevent buckling.
Memory trick: Caps = Compression/tension, Web = shear — 'Caps Bend, Web Shears'