Spar Weight Saving

Task Description

To save as much weight as possible, we’re looking to punch out a bunch of material from our spars. A discussion and some sims/calculations were done in discord Discord - Group Chat That’s All Fun & Games to determine optimal orientation of the holes.

Brief description of our findings:

• Quick FEA was wrong to see which way would give us more strength

• Remember that wing deflection is the main concern (ie. the wing deflects in the axis perpendicular to the “length” of the spar

• Result: less deflection when hole is parallel to the force and therefore parallel to the ground (this is enough info for you to complete the task)

Open

Hole parallel to the face

Open

Hole perpendicular to the face

• If you’re curious as to the theory and reason behind it, here it is (not necessary for the task):

  • Deflection formula for simple cantilever beam:

  • Since deflection is inversely proportional to moment of inertia, increasing moment of inertia reduces deflection; moment of inertia formula for a rectangle:

    •  

    • By having a weight saving hole, we are subtracting the moment of inertia of the hole

  • When the material is removed from the parallel face, the moment of inertia for the hole is:

  • From the perpendicular face:

  • From these formulas, the perpendicular hole has a largest moment of inertia and so it reduces the overall moment of inertia more (since it is subtracted from the total)

  • This leads to more deflection based on the deflection formula

Constraints

Assignees

Task Progression/Updates

Author: @Ben Lovegrove Date: 2024/11/14

Spar Weight Saving

I added cheese holes for the spars, they are parallel to the face.

All the holes are 2.5 inches long and a half inch an inch wide. The parts are in inches per @Alison Thompson, as it will make it easier to machine.

There are 5 holes all cut through both sides, and are spaced 1 inch apart.