S & C Thermofluids has used their experimental capabilities to re-create the phenomenon referred to as “scintillation”, and have investigated means of preventing it from occurring.

The problem occurs when the downwash from helicopter blades stirs particles in dusty and sandy environments, causing a "brownout" situation. This problem is exacerbated in low light conditions when the particles interact with the rotor blades generating a bright halo-like effect. By being able to prevent scintillation from occurring it would vastly reduce the excessive wear to the rotor blades in dusty environments.

Possible causes have been proposed but little formal research has been conducted to date. S & C were tasked to develop a means of recreating the phenomenon under test conditions in order to investigate the causing mechanisms.

S & C made use of its Gnome Engine Test Laboratory (GETL) based in Cornwall. At the GETL, Rolls Royce Gnome gas turbine engines are utilised in a number of configurations to produce various forms of air flow for experimental purposes. In this instance, sand was injected into the flow and allowed to impact on a section of rotor positioned downstream of the rig. The experimental setup proved to successfully re-create scintillation allowing various forms of camera and sensing equipment to view the effect.

The experimental trials showed that the predominate contribution to the phenomenon is the due to the erosion of titanium leading edge protection materials, common to the majority of helicopters, creating bright spark-like emissions. Other leading edge and tip protection materials such as stainless steel and nickel did not exhibit such intense visible scintillation.

A number of counter measures were tested to determine their ability in preventing or reducing scintillation. These included the use of various types of polyurethane leading edge protection tape and an oil bleed flow onto the leading edge of the rotor blade. Both of these reduced the intensity of the effect, particularly the polyurethane tape that appeared to eliminate all visible scintillation.

Dr. Tony Smith, Director of S & C Thermofluids, commented:

“When we first saw pictures of helicopters with sparks coming from the rotors someone in the company commented – “how are we going to fix this one?”. But 6 months later and we have been able to recreate it in the lab under controlled conditions, gain a fundamental understanding of how and why it occurs and have come up with techniques which may be used to control it. It is very pleasing that by applying our capabilities, we have brought a rapid solution to this problem.”

Scintillation from a Lynx rotor blade

Leading edge with oil bleed