Wichita Falls, Texas: Wednesday, 21 November 2001

By Jeff Keaton. Edited by Jay Carter, Jr. and Kenneth Hibbs

FLIGHT-TESTING STATUS UPDATE

New Flight Crew Training

During the last two weeks of flight-testing the CarterCopter Technology Demonstrator (CCTD), the new team of Larry Neal (pilot) and Brad King (co-pilot) has progressed from high speed taxi runs, to low altitude flights down the runway - to flying the traffic pattern and making smooth takeoffs and landings. Rusty Nance was able to attend for three days and his instruction greatly accelerated Larry and Brad's learning process, although minor problems with the aircraft shortened Rusty's time as instructor. Although frustrating at times, debugging these problems after a major repair was a significant accomplishment. Improved configuration control and flight record documentation facilitated pilot training and corporate learning -- preventing mistakes that have slowed flight-testing in the past.

New copilot Brad King

Repairs and Modifications

The CCTD was repaired after damage that occurred September 18, 2001 (see Previous Press Release) when a newly constructed propeller (made with a KEVLAR^® spar instead of carbon) failed during testing in the "pit." Repairs included: a new carbon spar prop with a newly added carbon shear web, a new spinner with a new heat-treated support bracket, repairing the starboard tail boom, machining 17 new aluminum and steel parts, repairing the rotor blade and fuselage damage, and repairing and calibrating several sensors for telemetry data.

Other modifications were made during this period, including: changing the collective range (From: 0° to 12°, To: -2° to 10°), adding a 0° collective detent, installing new cyclic control cables with a more direct routing to the rotor linkage, streamlining the aft lower section of the fuselage and associated cooling air exhaust, designing and manufacturing a new rotor hub and pitch horns to change the rotor delta three from 30° to 10°, changing the prop RPM controller algorithm, adding 4 layers of KEVLAR^® armor around both tail booms in line with the prop plane of rotation, changing the ratio of engine-to-propeller RPM from 2.75:1 to 2.387:1, and replacing the collective cable in the cockpit.

Old aft fuselage with cowl flap

New streamlined aft fuselage (no cowl flap)

Flight-testing October 26 to October 28, 2001

In order to train the new flight crew, the pilots first practiced procedures in the flight simulator. With the help of the Golden Arms Associates, detailed flight test records and data were analyzed and used to modify procedures and checklists that the new pilots studied and practiced before attempting to fly the CCTD. Then several high-speed taxi runs were made in the CCTD that allowed the pilot to practice pulling collective and capturing pitch in preparation for takeoff. During this period, flight time was sometimes interrupted by small problems. This has come to be expected after major repairs that require the removal and reinstallation of numerous components. Although most problems were found during static testing in the "pit," some problems didn't show up until taxi tests - including loose connections, failed switches, brake cylinder leaks, sensor malfunctions, bad circuit breakers, and coolant leaks. Even though outside air temperature was around 70° F, the engine would occasionally overheat during periods of repeated pre-rotations and taxiing.

At the completion of the first high-speed taxi run on Sunday, October 28, 2001, the aircraft was stopped using normal aerodynamic braking. After the aircraft had stopped, the cyclic was inadvertently positioned full aft with the collective at 9.5°. This control position, combined with a headwind and low rotor RPM (approximately 100), resulted in excessive rotor flapping which caused the rotor blade to hit and damage the top portion of the both rudders.

Damage to rudders

Flight-testing November 8 to November 15, 2001

After repairing the rudders, flight-testing resumed on November 8 in Olney. Changes were made in order to prevent a future rudder strike. A voice alarm was added to warn when the sum of aft spindle tilt plus flapping is too high. A mechanical stop was also added to limit aft movement of the cyclic to 10°. Flight operations procedures were changed for the co-pilot to more closely monitor flapping and rotor RPM and call out values to the pilot more frequently. This situational awareness feedback is most important when the pilot's workload is high, for example when learning new flight procedures or being distracted.

Rusty Nance, who was only available for three days, began the flight tests in the left (pilot) seat. After a few high-speed taxi runs to refresh his feel for the aircraft, he flew five low-altitude flights down the runway. During these short flights, a small vibration in the cockpit and a stick oscillation were noted. Rotor balance and tracking were adjusted to minimize these problems.

Rusty then traded seats with Larry, who practiced eleven high-speed taxi runs before flying four low-level flights down the runway. Larry was able to reach this competency level in a tenth of the time that it had previously taken new pilots to learn to fly the aircraft for a few reasons. An experienced pilot was in the right seat providing real-time instruction. Flight operations procedures are now well defined and documented. Training for takeoffs utilizes a build-up approach where more familiar procedures (similar to autogyros or fixed wing aircraft) are used before more aggressively pulling collective to shorten takeoff rolls.

Problems with the aircraft continued to interrupt flight-testing. A serpentine belt came loose due to the failure of the air pump bracket. This belt also drives the water pump and alternators. Overnight, the bracket was redesigned and repaired.

The next day a few more low-level flights were conducted. The engine tended to overheat with repeated rotor pre-rotations and slow speed, full throttle flights. A water mist spray cooling system was added to the aircraft and provided some improvement.

Three traffic pattern flights were then made; the longest was for 9 minutes at 1000 ft AGL. The aircraft reached an airspeed of 117 mph with the rotor slowing to 190 RPM. The rotor was unloaded to a point where the wings were providing over 85% of the lift (500 lbs. on the rotor and 3000 lbs. on the wing). This data is encouraging because it indicates that recent changes in trim (relationship between the horizontal stabilator and spindle angle) will unload the rotor and allow rotor RPM to decrease with increased airspeed as designed -- and still keep flapping to a minimum. As rotor RPM drops, the aircraft accelerates. Trimmed for a target airspeed of 100 MPH with constant throttle, the airspeed quickly reached 117 MPH as the rotor RPM decreased. A speed increase was expected, but the amount of increased airspeed still surprised the pilots.

Engine overheating continued to be a problem, so overnight more misting nozzles were added to increase the injection rate of cooling water. However, two days of bad weather (high wind, then rain) prevented further flight tests. Additionally, while diagnosing an erratic reading on one sensor, it was discovered that the main ribbon cable that interconnects all the aircraft computers was worn out and intermittent. The aircraft was returned to the shop to build and install a new cable.

Flight-testing is scheduled to resume in late November. Before then, the rotor will be rebalanced and tracking will be adjusted to minimize a one-per-revolution "cabin bounce" reported by the pilots. The air intake area will be increased 80% and the air exit increased by 20% to improve engine cooling.