Wichita Falls, Texas: Thursday, December 13, 2001

By Jeff Keaton. Edited by Jay Carter, Jr.

NEW FLIGHT RECORDS SET

Flight testing of the CarterCopter Technology Demonstrator (CCTD) continued for seven consecutive days during the period from November 30 to December 6, 2001. A good portion of that time was spent waiting for the weather to improve (mostly low ceilings and high winds). Overall system reliability is improving and downtime due to maintenance is declining.

Three new flight records were established:

·   Highest airspeed: 142 MPH
        ·   Longest duration: 39 minutes
·   Highest Mu*: µ=0.46
 

Larry Neal is becoming more comfortable in the aircraft and now has over three hours of flight time (in the air, not including taxi time). Take-off and landing procedures are now standardized and touchdown speeds and landing rolls are decreasing. The last landing was at less than 20 MPH with calm winds - and this was without over-speeding the rotor prior to flair.

    * The Greek letter "µ" is used to designate the ratio between the forward speed of the rotorcraft and its rotor tip speed relative to the aircraft.

The availability of a chase aircraft with a removable door provided the opportunity to get more air-to-air photos:

Significant progress made in solving some chronic problems

Changes to increase the area of the air inlet and exit have reduced the temperature rise over ambient so that engine cooling is excellent. At 65° F ambient temperature, a full power climb at 80 MPH produced a water exit temp of only 190° F - an improvement of 45°.

The prop controller RPM is much more stable after isolating the problem to noise on the sensor signal. After a couple of flights, it appears that cleaning up this signal has eliminated the surging problem. In fact, on the last flight the pilots made a point to note that they did not feel any engine surging.

Increasing the amount of dampening on the spindle reduced a two per revolution vibration due to rotor flapping to essentially zero.

Fine adjustment to the rotor tracking improved the cabin bounce (one per revolution) felt by the pilots. This required adjustments as small as 0.016 inch - about the thickness of four sheets of paper. This works out to be a change in blade pitch of about 1/8 of a degree.

One hundred tufts were installed on the aircraft and videotape from the digital video tail camera was studied to analyze airflow. Above 130 MPH, the tufts are starting to lay down indicating the modification to the aft lower fuselage and the air exit has improved air separation around the fuselage.

Tufts

Problems to solve before flying again

The engine driven air compressor failed. An air leak caused the compressor to run continuously (which it is not designed to do). The leak was traced to some tubing that has now been replaced and a new air compressor has been installed.

The landing gear is retracting so quickly that oil is pumped out of the landing gear cylinders into the accumulator, which then blows out with the vented air. An air lock (like the drain on a bathroom sink) prevents the oil from refilling the cylinders. As a result, the nose gear collapsed on one landing but no damage occurred. The system has been redesigned to insure that all the oil quickly flows back into the cylinders when the gear extends.

The biggest problem is an oscillation that occurs at a rotor RPM of 200 that is not dependent on airspeed. Every 3 revolutions of the rotor blade, the pilots feel a "beat-beat" or sometimes a "beat-beat-beat." This rotor system oscillation has the appearance of a blade weave and prevents us from sustaining airspeeds above about 140 MPH. The working theory is that the aerodynamic center is shifting as the blade goes through one complete revolution. This causes the spindle to oscillate back and forth, resulting in a 150-pound fluctuation in lift that is felt in the cockpit and through the cyclic - a very uncomfortable vibration. After analyzing the problem, the counterweights on the rotor have been increased from 12 to 30 lbs.

We hope to resume flight-testing within the next few days.