A Balancing Act!
|Add plate weights to balance the main rotor head|
|Pitch Control Links and side view of the swashplate|
So Whats The Angle?
Now that the helicopter is flying, this is where things get a little touchy! Even though the blades have an angle set on the ground, before even leaving the hanger, the blades can take on a mind of their own when the helicopter starts flying forward. Each of these blades are hand made out of composite materials, fiberglass, resin, metal, and graphite. Because each blade is hand made and completely original, they each fly in their own unique ways. This individuality reveals itself pretty quickly after reaching cruising speed (around 100-120 knots), this is when it starts to get bumpy. The only way to get these unruly blades to fly right is to adjust their individual tabs on the trailing edge of each blade. These tabs are like tiny ailerons which control the particular angle ("angle of attack") that each blade flies. Using a special tool the mechanic can make small bends to these tabs. If the tab is bent up, the blade flies higher, if the tab is bent down the blade flies lower. The closer the blades fly to each other, the smoother the ride. The best way to explain this phenomenon is to imagine having a three legged race with someone who has a shorter leg. This would cause for a bumpy race each time the shorter leg is stepped on and used to propel the racers forward. The same is true of a blade that is not flying in the same circular path as the other blades. Thus, the closer the blades fly to each other, the smoother the ride. Simple right! Not so fast. There is one more problem the mechanic has to deal with, turbulence. Remember when you last went fishing on the lake, and those pesky motor boats kept speeding by and made such a large wake that you left in disgust? As the boat raced through the water, it created waves that reached out behind the boat as it traveled forward in the water. Well the same is true for each of these blades. As the blade passes through the air (remember it is a fluid) it creates its own wake in the air that disturbs the smooth ride of the blade right behind it in the rotor path. So you have to be careful not let the blades fly too close or the ride will get bumpy again. This final act of adjustment can be quite the feat and is a combination of art and science. After you master this, you got it! The helicopter is flying smooth and efficient!
|Blade tab adjustment tool|
|The small aileron like blade tabs. But only bend the two inboard ones, the other four are set at the factory.|
|Bend the tab up, the blade flies higher. Bend the tab down, the blade flies lower.|