N6RP

HISTORY OF FLIGHTOn May 31, 2014, about 0944 eastern daylight time, an experimental amateur built Vans RV-6, N6RP, operated by a private individual, was substantially damaged in Suffolk, Virginia. The private pilot sustained minor injuries. Visual meteorological conditions prevailed for the personal flight conducted under Title 14 Code of Federal Regulations Part 91. The local flight originated from William Tuck Airport (W78), South Boston, Virginia at 0830 and was destined for Suffolk Executive Airport (SFQ), Suffolk, Virginia.

According to the pilot's written statement, he intended to fly from W7B direct to SFQ to attend a fly-in event. After departing W7B at 0830 the pilot climbed the airplane to 3700 ft. mean sea level (msl) and leveled off for cruise flight. The pilot then descended to 2000 ft. msl about 10 nm from the airport. At the first waypoint designated by the fly-in instructions the pilot turned to a heading of 100 degrees magnetic. The engine RPM then went to redline, the pilot lost thrust and a reddish residue resembling hydraulic fluid from the propeller covered the windscreen. The pilot pitched the nose up, pulled throttle, and turned the airplane into the wind. During the descent the pilot selected an emergency landing site. He attempted to add power, but the engine yielded no thrust. While above the trees, the pilot realized he was not going to make the landing site and slowed the aircraft. As the airplane neared the tree tops the pilot pulled the control stick aft and the airplane stalled before making contact with the tree tops. The airplane subsequently fell through the trees, impacted the ground, and came to rest nose first, which resulted in substantial damage to the wings and fuselage. PERSONNEL INFORMATIONThe pilot held a private pilot certificate with ratings for single engine land. He had accumulated about 1,418 hours of total flight time, of which 242 hours were in the accident airplane make and model. His most recent third class Federal Aviation Administration (FAA) medical certificate was issued on September 3, 2013. AIRCRAFT INFORMATIONAccording to FAA records, the RV-6, a two-seat, all-metal, low-wing airplane with tricycle configured landing gear was issued an airworthiness certificate, in the experimental category, on August 25, 2006. It was built from a series of kits provided by Vans Aircraft and Eggenfellner Aircraft, Inc. The airplane was equipped with an Eggenfellner Subaru H4 modified automobile engine, which included a Gen 3 V4 propeller speed reduction unit (PSRU) gearbox that was used to drive the Vari-Prop VP 01 propeller assembly that consisted of three hydraulically actuated wooden propeller blades. The propeller was designed as a closed, airless hydraulic system, independent of all other aircraft systems and rated at 165 HP and 6500 rpm. The airplane had 158 total flight hours when the Vari-Prop assembly was installed. The blades were replaced at 221 total flight hours.

The propeller system was designed for in-flight adjustment of the propeller. Power was transferred from the engine gearbox to the propeller hub through a propeller drive shaft. The aft end of the propeller drive shaft bolted to the output shaft of the gearbox and the opposing end was inserted through a slave servo into a female key slot in the propeller hub. The blade pitch angle was adjusted through a non-rotating slave piston cup and a rotating blade pin spool that were separated by a needle thrust bearing. Hydraulic fluid was provided by a separate reservoir located in the fuselage that would feed hydraulic fluid to an expandable hydraulic fluid chamber in the slave piston. The piston moved the blade pin spool fore and aft along the shaft to change the blade pitch angles. The blade pin spool consisted of two bolts that extended beyond the propeller hub. The bolts were equipped with two nuts to provide a mechanical low pitch stop in the event of a loss in hydraulic pressure. According to the builder/pilot, the stop nuts that provided the mechanical limit to the low pitch angle were tightened so that the washers were slightly loose when the propeller blade pitch angles provided the required static rpm. The builder was responsible for positioning the blade angles to achieve 2520 rpm while the airplane was stationary.

According to the pilot, the airplane had accumulated a total of 247 flight hours at the time of the accident. The propeller was last inspected and serviced about 28 flight hours prior to the accident when the pilot/builder cleaned and lubricated the bearings. The propeller blade bearings were lubricated with either Sig Wurth 3000 grease, a highly viscous lubricant, or a mixture of Honda Moly 60 and Sig Wurth 3000. The pilot subsequently reported that he used only Sig Wurth 3000 grease to lubricate the needle thrust and slave servo bearings. According to the lubrication manufacturer, the Sig Wurth 3000 grease is advertised for use on fleet and heavy equipment for the automotive and trucking industries. An internet search revealed several public videos that demonstrated use of the Sig Wurth 3000 grease on the fifth wheel of an eighteen wheeler. The manufacturer also remarked that the company's policy is not to sell its products for use in flying applications. METEOROLOGICAL INFORMATIONThe 0935 automated weather observation at SFQ included winds from 020 degrees at 7 knots; visibility 10 statute miles; sky clear; temperature 21 degrees Celsius (C); dew point 15 degrees C, and an altimeter setting of 30.16 inches of mercury. AIRPORT INFORMATIONAccording to FAA records, the RV-6, a two-seat, all-metal, low-wing airplane with tricycle configured landing gear was issued an airworthiness certificate, in the experimental category, on August 25, 2006. It was built from a series of kits provided by Vans Aircraft and Eggenfellner Aircraft, Inc. The airplane was equipped with an Eggenfellner Subaru H4 modified automobile engine, which included a Gen 3 V4 propeller speed reduction unit (PSRU) gearbox that was used to drive the Vari-Prop VP 01 propeller assembly that consisted of three hydraulically actuated wooden propeller blades. The propeller was designed as a closed, airless hydraulic system, independent of all other aircraft systems and rated at 165 HP and 6500 rpm. The airplane had 158 total flight hours when the Vari-Prop assembly was installed. The blades were replaced at 221 total flight hours.

The propeller system was designed for in-flight adjustment of the propeller. Power was transferred from the engine gearbox to the propeller hub through a propeller drive shaft. The aft end of the propeller drive shaft bolted to the output shaft of the gearbox and the opposing end was inserted through a slave servo into a female key slot in the propeller hub. The blade pitch angle was adjusted through a non-rotating slave piston cup and a rotating blade pin spool that were separated by a needle thrust bearing. Hydraulic fluid was provided by a separate reservoir located in the fuselage that would feed hydraulic fluid to an expandable hydraulic fluid chamber in the slave piston. The piston moved the blade pin spool fore and aft along the shaft to change the blade pitch angles. The blade pin spool consisted of two bolts that extended beyond the propeller hub. The bolts were equipped with two nuts to provide a mechanical low pitch stop in the event of a loss in hydraulic pressure. According to the builder/pilot, the stop nuts that provided the mechanical limit to the low pitch angle were tightened so that the washers were slightly loose when the propeller blade pitch angles provided the required static rpm. The builder was responsible for positioning the blade angles to achieve 2520 rpm while the airplane was stationary.

According to the pilot, the airplane had accumulated a total of 247 flight hours at the time of the accident. The propeller was last inspected and serviced about 28 flight hours prior to the accident when the pilot/builder cleaned and lubricated the bearings. The propeller blade bearings were lubricated with either Sig Wurth 3000 grease, a highly viscous lubricant, or a mixture of Honda Moly 60 and Sig Wurth 3000. The pilot subsequently reported that he used only Sig Wurth 3000 grease to lubricate the needle thrust and slave servo bearings. According to the lubrication manufacturer, the Sig Wurth 3000 grease is advertised for use on fleet and heavy equipment for the automotive and trucking industries. An internet search revealed several public videos that demonstrated use of the Sig Wurth 3000 grease on the fifth wheel of an eighteen wheeler. The manufacturer also remarked that the company's policy is not to sell its products for use in flying applications. WRECKAGE AND IMPACT INFORMATIONThe propeller, wings, and tail section were accounted for at the accident site. According to information provided by the FAA, the airplane came to rest in a nose down attitude in an area surrounded by trees. Photographs provided by a recovery service showed the airplane was supported in an upright position by the left wingtip and nose and the fuselage rested against a tree. Both wings exhibited significant leading edge damage; a tree was embedded in the right wing about mid-span about eight inches from the leading edge. The left wing displayed horizontal crush damage along the outboard section of the leading edge. The vertical stabilizer and rudder displayed some compression wrinkles. All control surfaces remained attached to their respective airfoils. All three propeller blades were separated from the propeller hub and only two of the three propeller blades were accounted for at the accident site.

Additional examination of the propeller assembly was performed at a secure recovery facility under the supervision of NTSB investigators. Severe thermal damage was present throughout the servo unit; the non-rotating portion of the slave servo had seized to the rotating portion at the needle thrust ...