Vietnam -- Balancing Rotorblades With Duct Tape

Using duct tape to align rotor blades? Sound far fetched? Not at all. In fact, its pretty common.

Technically speaking, this proceedure can occur almost anywhere in the world and at anytime;  not specifically novel to Vietnam.

From a mechanic's perspective, it is one of the most dangerous part of the job. Here's the proceedure:

First, you mark the edge of the blade where the securing hook goes -- a piece of metal about a 1/4 of an inch thick -- with one side blue and the other side red. 

A pilot gets in the back seat and starts up the helcopter. With the blades turning at 320 rpm above your head, you walk up under them, figure out where the end tip of the blades are, and mark it with your boot.

A flag is used.  This is a metal pole that has a handle at waist level and two pieces of metal sticking out from the center pole at 90 degrees to the handle. Between those two pieces of metal, are two pieces of rope. Wrapped around the rope is tape.  This tape is what the blades will strike.

So, the first time this proceedure is done, the pilot adjusts the blades so they will hit the tape and not the metal pole. The job of the mechanic at that point is to bring the pole up a few inches away from the turning blades and then turn the pole so the tape gets hit by the turning blades.

Once this happens, the helicopter is shut down, the lower blade's buckshot cap is opened and inspected for steel  balls.  Six sill move the blade up a half inch. But there is 3/4 of an inch more to get the alignment correct -- perhaps.

For a second time, the pilot adjusts the blades so they will hit the tape and not the metal pole. With fresh tape added, the blade strikes the tape. Now, there's only a half inch diffeence between the lower red and the higher blue.

This time, duct tape is applied to the blue blade near the trailing edge of it, Two complete turns of the tape. Each wrap representing 3 steel balls.

This should bring it below the red line. We test to see. Got through the proceedures and sure enough, just a little below the red line. 

Tape comes off and 4 steel balls are added to the blue blade's buckshot cap.

Aftter tnew tape is added to the flag, the pilot starts up the cobra and we bring the flag into the spinning blades. The two marks are right on top of each other/. The buckshot caps tightened down as per specifications, get safety wired and approved by the technical inspector.

That's pretty much how we used duct tape to balance rotorblades.