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F.5.2 Bent Tubes or Multiple Tubes
F.5.2.1 The minimum radius of any bend, measured at the tube centerline, must be three or more times the tube outside diameter (3 x OD).
F.5.2.2 Bends must be smooth and continuous with no evidence of crimping or wall failure.
F.5.2.3 If a bent tube (or member consisting of multiple tubes that are not in a line) is used anywhere in the Primary Structure other than the Roll Hoops (see F.5.6.2), an additional tube must be attached to support it.
a. The support tube attachment point must be at the position along the bent tube where it deviates farthest from a straight line connecting both ends
b. The support tube must terminate at a node of the chassis
c. The support tube for any bent tube (other than the Upper Side Impact Member or Shoulder Harness Mounting Bar) must be:
The same diameter and thickness as the bent tube
Angled no more than 30° from the plane of the bent tube
Explanation
F.5.1.2 - The minimum bend radius for any tube bend must be at least 3 times the outside tube diameter (3 x OD), measured from the center of the tube. This rule is in place to ensure that the material properties of a tube are not compromised by it being bent too much.
Bent tube diagram (from the internet)
Bent tube diagram showing the relationship between the outer diameter (blue) and the minimum bend radius (red)
F.5.2.2 - Bent tubes should look smooth and continuous. There should be no wrinkles, crimps, sharp edges, or anything that could indicate tube failure.
Tube wrinkling
Tube flattening
More Subtle tube wrinkling
Diagram explaining several type of bad tube bends
F.5.2.3 - If a member is not in a strait line (either it has bends or is made of multiple tubes), it needs a support tube. This rule excludes the Roll Hoops (they have their own support requirements).
Diagram showing the correct placement of a support tube based on the endpoints of the member
a. The support tube must be attached to the part of the member that is the furthest away from an imaginary line connecting the endpoints of the member.
Using the Main Hoop Brace as an example because it follows the same rule of having to connect to a node
If the pink tube was a real tube connecting to Accumulator Protection in the middle of the member instead of a node, it would not be rules compliant.
b. The support tube must connect the bent member requiring support to a node of the chassis. This helps ensure the chassis remains properly triangulated.
The support tube is less than 30 degrees from being in the same plane as the bent tube.
The support tube is more than 30 degrees from being in the same plane as the bent tube.
c. The support tube should be the same diameter and thickness as the bent tube (excluding the Upper Side Impact Member or Shoulder Harness Mounting Bar) and no more than 30 degrees away from being in the same plane as the bent tube.
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