Theory of Flight 04
OPENING QUESTION:  Elaborate on the conflicting properties of weight versus strength for aircraft (generally).

LEARNING GOAL FOR TODAY: I will construct a tetrahedron (pyramid) of balsa and fabric to illustrate the relationship between material weight and material strength during today's class.




  • Take a moment to predict what that word means.
  • Make a sketch that you associate with that term when you say it.



Consider the evolution of the airplane materials --

  • The Wright Brothers made their Kitty Hawk Flier out of wood and fabric

  • WWII aircraft pioneered the use of aluminum

  • The SR-71 pioneered the use of titanium in airplane manufacturing. That material is so hard to work with that it basically had to be hand-assembled.... clearly not practical for commercial aviation (but it was VERY strong)

  • Aluminum was the primary material for airplane wings & fuselage all the way until the 1990's when aircraft manufacturers started experimenting with carbon fiber

  • The 787 aircraft fuselage & wings are made of carbon fiber...


Today we are going to explore the relationship between the weight of a material and the strength of that material.

    1. Please take a look at THIS document on the methods of "tissuing"
    2. Our goal is to make a tetrahedron (pyramid) structure out of balsa wood that has the highest strength to weight ratio.
      • For example: if your tetrahedron has a mass of .010 kg then it's weight is 10 m/s/s x .010 kg = .10 N
      • If that structure supports 10 N of force, then the strenth to weigh ratio is:

        10N/.10N = 100

      • Notice the ratio does NOT contain units... .because, well it's a ratio and ratios are simply a comparison, not a mesurement per se


    BASIC Procedure:
    1) Begin by drawing two 7 cm triangles. Each of the triangles will be the base of a tetrahedron. (Yes, you will build two! One is for crushing, and the other is for tissuing.)

    2) Assemble the basic tetrahedron 1st by cutting the 6, 7 cm structural members, then assemble the structural members (also called linkages) beginning with the base of an equilateral triangle.

    3) Once you have framed up your two basic structures, choose the “best” tetrahedron for reinforcement. Use the other tetrahedron for tissuing.

    4) Reinforcement (trussing) is your judgment call. You must study your structure and decide how you may best increase its strength without making it too heavy. Remember you want the greatest strength with the least amount of weight. If you are careful to truss your 4 sides so that each side is flat, you will have the option of tissuing as a means of increasing strength for your structure.

    5) When you have decided you have trussed to the best of your advantage, you are ready to test your structure. Use the back of this sheet to process the performance data for your structure.

    Write up is HERE and below:

    Tetrahedron Construction —Engineering Write-Up
    Please use this document as a guide for your write-up.  That means consistently using IQIA and responding in clear and accurate full sentences to each prompt.

      1. Provide an accurate, engineering-type diagram of your tetrahedron.  Please note:  This is NOT a sketch but your best attempt at a diagram TO SCALE (3 pts)

      2. Describe a problem that you anticipate occurring during the construction of your tetrahedron (2 pts)

      3. Provide a possible solution to that problem AND show the steps that you took to address that problem (2 pts)

      4. Show the ‘crush’ data in a data table (1 pt)

      5. Describe the effectiveness of your design.  Did it perform up to your expectations?  Why or why not.  Provide a detailed analysis (3 pts)

      6. Design Success:  2 pts if your tetrahedron performs at a 20x ratio, 1 pt for 10 – 20x ratio (this is preliminary)