Tuesday, November 29, 2011
Question:Good afternoon, We have recently seen the certification of the R66 to new FAA standards. I have two questions: How could they certify the blades to lightning strikes since the technology is identical to that of the R44 and R22, which have had a history of bonding issues for years with normal operation? I feel that increased heat generated by the lightning current makes it impossible for blades to allow a safe landing. Secondly, the seats are equipped with a three-point harness, which most likely forbid the restraint to be efficient, when taking into account the 10 or 20° angle in the wrong direction during the forward crash tests. Thank you for the info.
Answer:14 CFR Part 27 of the Federal Aviation Regulations defines the airworthiness standards of Normal Category Rotorcraft with maximum weights of 7,000 lbs. or less and nine or less passenger seats. The particular design requirements for lightning strike protection can be found in Subpart D of this section, titled “Design and Construction.” Similarly, the design requirements for passenger restraint can be found in Subpart C, appropriately titled “Strength Requirements.” Robinson Helicopter was kind enough to provide me with an excellent response to this question: Lightning Protection of R66 “The R66 is well protected against catastrophic effects from lightning strikes as required by FAR 27.610. The primary means of protection is the exterior of the aircraft, which is composed almost entirely of sheet metal (aluminum), allowing the current from a lightning strike to flow through the surface of the aircraft without causing any significant damage. In the specific case of the aluminum skin main rotor blades, electricity flows through the aluminum blade skin and exits at a different part of the metal aircraft exterior, leaving the main rotor blade skins undamaged. Additionally, as the electrical resistance of aluminum is very low, the aluminum skins do not heat up, and the adhesive bonds on the inside of the main rotor blade skins are not compromised. The attachment points of the lightning strike may suffer local burning and pitting which may require component repair or replacement, but the area affected would be far too small to cause immediate catastrophic failure of a main rotor blade or any exterior structural member. It is worth noting that commercial airliners, most of which are made of similar aluminum sheet metal construction, are regularly struck by lightning (approximately 1 in every 1000 flights), and do not suffer significant damage for precisely the same reasons discussed above. Additionally, an R22 parked on the ground during a thunderstorm was once struck by lightning, and suffered only the minimal, non-catastrophic damage described above.” Three-Point Harness Crashworthiness “FAR 27.562 requires, among other things, that a forward crash test be performed with the helicopter’s longitudinal axis yawed 10° right or left. As part of the FAA certification process, the R66, with 3-point seat belt harnesses, was tested (with FAA engineers witnessing the tests) in accordance with FAR 27.562 and other applicable regulations, and was found to fully comply with all the necessary crashworthiness requirements.”
Jessie K. Kearby is a Certification Engineer for Aircraft Night Vision System Integration, Modification and Repair Center at Aero Dynamix, Inc.
In addition to his established working relationship with the FAA, Jessie K. Kearby was recently recognized by Transport Canada Civil Aviation (TCCA) as a Subject Matter Expert on Aircraft Night Vision System Modification.