Brief Engineering Design

From our President/CEO/Captain/Lead Engineer

When first asked by Colorado Rocks marketing to write about the engineering design behind The Colorado Rocks Team’s plastic blades, I wrote an in-depth section located under Engineering Design for those that want a behind the scenes in-depth look into the engineering involved. They immediately requested a shorter rewrite, which follows below.

Shape: Initially an optimized design was intended for both the flat bottom blade as well as the symmetrical blade. Research into full scale helicopters revealed that many have symmetrical blades, including Bell 209 AH-1 Cobra, Bell 212, Bell 48, Bell 61, Bell 47G-2, Bell 47J, Vertol, and many others. A helicopter blade is basically a spinning wing; however, a wing doesn’t experience as many different relative airspeeds as a helicopter blade since a helicopter can move in any direction. As a result of all the different relative airspeeds, a symmetrical blade typically results in the optimal performance, as it is affected less directionally by all the relative airspeeds a helicopter will encounter. This is one reason they are used on so many full size helicopters and why it was chosen by the Colorado Rocks Team as out first design. Upon completion, we found that we needed to develop a flat bottom blade for the stock setup.

Material: The material used for these blades is a compromise between price/durability/force. The material was choose such that these blades would be economical, much more durable than the wood blades, and would not transfer as much force into the rotor head as the carbon fiber blades when/if a strike occurs.

Lift/Drag Ratio: This is a very important number, it measures the ratio of lift (yeah, cheers!!) to drag (boo, hiss!!). There is a constant compromise in aerodynamics between lift and drag, it is difficult or impossible to increase lift without some kind of increase in drag. The question becomes how much more lift can you get versus how much more drag. In Blade CP terms, the more drag the more force the tail motor is required to generate. Since we all know the durability issues with the tail motor (especially with 3 cell li-po), The Colorado Rocks Team was challenged to optimize the lift/drag ratio in hopes of reducing the force generation required by the tail motor, which correlates to an increase in tail motor life and more tail authority. The team accomplished this by optimizing the airfoil shape, smoothing the entire surface of the airfoil, and optimizing the tip design.

Tip Design At the tip of a wing or helicopter blade, undesirable vortexes are created that cause instability and drag. The tip design of these helicopter blades is designed to minimize these vortexes.

The Colorado Rocks team used aerodynamic theory to create 7 different unique designs; each design had unique properties and characteristics that were put to the test in real world testing. Each design was produced using SLA rapid prototyping and tested in a controlled environment to determine the overall best design. You can learn more about each prototype by visting the prototype page.

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