For Robinson Helicopter, switching from aluminum to stainless-steel skin for main rotor blades has been “a mixed bag,” said company vice president Kurt Robinson, who defended the move on the grounds that the change means lighter and stronger blades with better corrosion resistance. But critics argue that the stainless skins do not hold paint well and that the switch from aluminum
to stainless precipitated the 2007 Robinson Service Bulletins concerning main rotor blade delamination.
Robinson made the switch from aluminum skin to stainless initially on the R44, certified in 1992. These “Dash 4” blades were then sized for R22s and made available for retrofit for operators willing to exchange their Dash 2 blades.
Kurt Robinson said the company achieved its goal of minimizing weight and susceptibility to corrosion but has experienced some unintended consequences. “You get less corrosion, but where you do get it, it is intensified,” he said.
In Service Bulletins 61 and 96, issued last year, Robinson noted that main rotor blade skins can begin to debond (separate) at the skin-to-spar bond line on the lower surface near the blade tip. Debonding can occur when the bond line is exposed due to excessive erosion of the blade finish, or when corrosion attacks the internal tip cap. Robinson recommended that operators use visual inspection and “tap tests” (tapping the bonded areas on a blade with a coin) to detect delamination.
The FAA followed the Robinson Service Bulletins with an Airworthiness Directive in January. But the NTSB wants even more elaborate bond-testing methods. Citing two 2006 in-flight break-ups of R44s due to fractured blades, in June the Safety Board recommended the adoption of long-term durability testing of adhesive bond joints for helicopter main rotor blades and the requirement for Robinson to “develop a nondestructive inspection technique or combination of techniques capable of consistently detecting bonding defects, such as voids, debonds and weak (kissing) bonds, in bond areas between the skin and spar at the tip of the blade and between the skin and tip cap for R22 and R44 helicopters.”
Robinson maintains that the company had good reasons for making the change to stainless and that most blade delamination issues were successfully handled by more frequent operator inspections, keeping blades properly painted, and improved blade-manufacturing techniques. “We’ve seen no problems for well over a year,” he said.
The new blades’ reputation for shedding paint is hardly a secret in the Robinson community, with some operators reporting bare metal, and even some delamination, within months of taking delivery of new helicopters.
One R22 operator, Airwolf Aerospace, approached 3M about tape solutions and developed a kit that has now been sold to approximately 300 Robinson operators. The Airwolf tape is four inches wide and is applied on the outer 36 inches of R22 blades and the outer 38 inches of those on the R44. Tape can be applied over either freshly painted or bare metal blade sections; however, bare metal sections must be hand-sanded as power sanders can heat the blades and cause delamination.
The blades must be removed to apply the tape effectively, according to Jonny Quest, Airwolf’s technical director. Airwolf sells the kits for $1,299 for R22s and $2,499 for R44s. The blades must be retracked after re-installation. The entire process takes about a day, Quest said. On average, he expects the tape to last around 1,000 hours, about half the recommended life of 2,200 hours for a set of Robinson blades.
The tape is an approved FAA alternative means of compliance (AMOC) to the related AD. Under the AMOC, taped blades must be inspected every 100 hours. Quest said that when the tape fails, operators will know it.
“A dime-sized hole will produce a distinct whistling sound,” he said. The Airwolf tape kit does not degrade helicopter performance, according to Quest, who also said that its application would not affect Robinson warranties under most circumstances.
Company founder Frank Robinson has made no secret of his dislike for taped blades, but Kurt Robinson will say of the Airwolf tape only, “We really don’t know anything about this new product.”
Quest said that most of Airwolf’s tape customers to date have been R44 operators. “They don’t even bat an eye at the price,” he said. “The R22 operators are a little more cost conscious.”
Quest said there is a compelling economic case for the tape, as delaminated blades must be replaced at significant cost. According to Kurt Robinson, a single new blade on an R22 sells for $12,000 and on an R44 $17,000. Replacing both blades and associated components and hardware at TBO runs $29,000 on an R22 and $40,000 on an R44.
Robinson fleet operators who spoke to AIN said that the difference in cost between installing the tape kit and diligently inspecting and repainting the blades as needed was a wash; most said that it was slightly less expensive to repaint over the life of the blades.
Rick Toso, a technician at Leading Edge Aviation in Bend, Ore., said his company’s R22 and R44s need new blade paint about every 300 hours, depending on the time of year, and that cleaning, prep and painting takes about six to eight hours per blade set. “We really haven’t seen many cases of delamination,” he said.
Rick Palmer, the director of maintenance at Rotor Wing in West Palm Beach, Fla., said, on average, the rotors of their helicopters require minor paint every 100 hours and that, on average, it takes between an hour and an hour-and-a-half. Palmer also reported not seeing any cases of blade delamination.