Assertion: hang glider's wing | /r/HasProperty | lightweight
Facets:
value: to have external bracing struts
type: PURPOSE
value: until the 1930s
type: TEMPORAL
value: to have enough strength
type: PURPOSE
Source sentences:
text: But to be structurally efficient, and hence lightweight, a wing must have a short span but still enough area to provide lift (low aspect ratio).
text: So until the 1930s, most wings were too light weight to have enough strength and external bracing struts and wires were added.