REDSTONE ARSENAL, Ala. -- The "corona effect" is characterized by distinctive glowing rings along metal or fiberglass rotor blades operating in desert conditions.
The glowing rings are made up of numerous small sparks resulting from grains of sand striking a normally-operating rotor blade, meaning the corona effect can be seen only at night.
The corona effect has been seen from about a half mile away on a CH-47 Chinook hovering at about 1,700 feet, said Mike Hoffman, and that without the aid of night vision goggles.
Hoffman, an engineer and manager of special projects in the Aviation Engineering Directorate, Aviation and Missile Research, Development and Engineering Center, noted that while the glow may be an interesting sight, the cause is devastating to rotor blades.
The intensity of the illumination of the individual sparks varies with the number and size of particles passing through the rotor system, Hoffman explained. The corona glows brighter as the numbers and sizes of the particles in the air increase.
A method to fix the problem can save half a million dollars per aircraft. Leading edge molded boot technology already exists and has been tested and approved on several helicopter types.
The current Task-L101 polyurethane molded form of the boot is better than its predecessor, the Task-L100, which required a brush application.
The newer molded boots prevent the corona effect and resist rotor blade erosion in desert conditions. One of the biggest pluses for the new boots is the resulting decrease in repair time and maintenance costs.
The corona around a Ch-47 Chinook provides easy detection at night, placing the rotorcraft at a tactical disadvantage. Before we had these new boots,ö Hoffman said, ôit took about 26 man hours to remove the rotor blade system, repair the blades, and replace the blade system. Now, we just put the boots on the blades and repair them without removing them, and the helicopter is ready for flying again in the time it takes for the polyurethane to cure.
The cost of protecting the blades of an Apache with boots, including the main and tail blades, is about $6,900 in material and labor. The cost of a new rotor blade system is about $500,000 per aircraft.
Hoffman said that after Operations Desert Shield and Desert Storm in the 1990s, and Iraqi Freedom and Enduring Freedom in the early part of the 21st Century, the degradation of rotor blades has become one of the single largest logistics and maintenance burdens experienced by Army Aviation. But he first saw the damage that sand was causing to rotor blades more than 10 years prior to Desert Storm.
What we saw were huge rings of white fire above the rotor head. At the time, I didn know what it was, but I knew we had to fix it. So subsequently, in 1981, at Fort Rucker, Alabama, the first tests were conducted using a polyurethane material to protect the blades from the grinding sand.
The tests were successful, but back then our focus was on Europe and the Cold War, he said. So, problems about sand erosion actually didn't come up again until about 1990.
However, in the past few months, due in large measure to Hoffman's efforts, the sand erosion problem has surfaced again in a big way.
Not only has the requirement for the boots been approved, but the funding has been approved as well.
We're really happy about receiving the funding from DA [Department of the Army], Hoffman said. ôWe received funding in both [fiscal year] 03 and FY 04. WeÆre currently planning to install the boots on the Black Hawk, Chinook, and the Apache. The Kiowa is already protected by the polyurethane coating.
Hoffman said rotor blade engineering goals continue to remain at the forefront of emerging technologies that will help and protect our Soldiers.
I'm proud of all our folks who are on the front lines, whether here at the AMRDEC, or in Iraq and elsewhere, he added. We feel good about what we are able to achieve, working together as a team, to ensure that our Soldiers have the best equipment, the best service, and the best technology in the world
