• Wood aircraft propellers must demonstrate strength and durability.propeller image by Tomasz Pawlowski from Fotolia.com
  
  Airworthy wood must withstand the effects of humidity and heat. So wood grain, growth rings, strength and stiffness are what the Commonwealth of Australia's Department of Aviation considers when specifying requirements for their country's aircraft propeller wood. Suitable aircraft propeller wood pass tests, which predetermine its performance in the sky. Therefore, U.S. aviation inspectors will not inspect wood propellers unless its wood grain is visible.
  
  

Quality

• One sure-fire step to ensuring quality is that aircraft propeller wood must be made of a known species of wood. Factors such as warping planks or the wrong type of grain will render the timber unsuitable. In addition, the wood cannot show signs of decay, knots, splits, fractures and brittleness. Evidence of dirt or insect attacks is unacceptable. Yet, imperfections that will not affect the wood's strength, such as small blemishes or wavy grain, are acceptable. As long as there is a sufficient distance between minor flaws, they will not affect propeller performance.
  
  

Moisture Content

• Wood that is destined to become an aircraft propeller must be air or kiln-dried and meet aviation standards. For example, Australia's Department of Aviation requires that manufacturers test the moisture content of potential propeller wood three times. Calculating the wood's overall moisture content with the assistance of an electrical resistance-type moisture meter determines each plank's airworthiness. The average moisture content of each plank selected for making a propeller cannot vary more than 3 percent, in Australia.
  
  

Impact Resistance

• Airplane propeller wood must also demonstrate impact resistance. An Izod testing machine identifies if the wood is too brittle for use. Brittleness is determined by breaking the wood in the impact-testing machine. If the wood withstands strikes near its growth rings, it passes the test for use in the manufacturing of an Australian aircraft propeller.