"Tube" frames subdivide into simple beam types, such as the AC Cobra, or the Locust. The Locost has a "space" frame, using a 3-D truss instead of a pair of main tubes with some cross-connection and various extensions. The space frame is far lighter for the same stiffness.
Frames are primarily built up for stiffness, not strength. Thus, mild steel is often just as suitable as 4130 aircraft tubing, titanium or aluminum. What it lacks in ultimate strength goes into useful toughness in a crash.
For a great overview of the options, see "Structures" by J.E. Gordon - it is very readable, and not expensive on eBay.
|