Wichita Falls, Texas: Tuesday, November 23, 1999.

Photos of CarterCopter retracting its landing gear. (photos by: Brad Redding)

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CarterCopter Flying Again

The CarterCopter successfully completed the third two-day test flying session since the installation of the new engine. The six days of flying were done over a two-week period. The first two sessions were devoted mainly to fine-tuning and troubleshooting.

Between the 2nd and 3rd session, a 9-inch nose gear extension was installed and the wheel-well lengthened so the gear could retract. The extension allows the aircraft to rotate back and results in less weight on the front gear, which makes it easier for the pilot to lift the nose for a jump takeoff. It also helps him to gently lower the nose after landing.

Mark holding the rotor blade preparing for prerotation. Note the new 9-inch nose gear.

The third two-day session logged quite a bit of flying with emphases on three areas: 1) shortening the rolling jump takeoff, 2) verifying elimination of the severe vertical oscillation the aircraft experienced during the early June flights, and 3) observing the lift transition from the rotor to the wings. Progress was made on the first two areas.

A technique is being developed which has shortened the jump takeoff roll to approximately 30 feet in a no wind condition. Further technique improvements may ultimately result in a zero roll takeoff. However, due to a heavier gross weight than planned, a larger diameter rotor will likely be necessary to achieve the desired jump takeoff results. It is important to note here that very little attention to weight reduction has been made on the prototype, except in certain patented areas including the propeller, rotor blade, rotor head, landing gear, pressurized door and windshield structure.

Indications are that the severe vertical oscillation problems have been resolved. Flight recorder data shows that the CarterCopter flew up to 120 MPH with varying degrees of collective (blade pitch relative to the rotor plane of rotation) without a reoccurrence. A lower frequency beat has been observed, which comes and goes at varying rotor collective pitches above 80 MPH airspeed. It seems to last only for short periods (seconds). While it is not severe enough to show up on any of the recorder channels, it is noticeable by the pilots and is, therefore, of concern. It appears to be about the same frequency as the tail boom's natural frequency. Due to the uncertainly of the cause of this vertical beat the aircraft has not been flown any faster than 120 MPH during the last three sessions.

Some other notable observations during the last flight sessions were:

• Because of the increased gross weight, more collective must be pulled during the 550 RPM rotor overspeed to lift off the ground when forward speed is very low. This higher angle of attack in conjunction with the high rotor tip speed (mach 0.86) causes very high compressibility drag and causes the rotor RPM to drop from 550 to 450 very quickly. This 100 RPM drop occurs in about the same time that it takes to drop from 450 to 400 RPM with 8 degrees of collective. Consequently, we are wasting a lot of stored energy due to compressibility drag. We would be much better operating the rotor at a lower disk loading so the coefficient of lift and corresponding blade angle of attack could be lower at the high tip speeds for a given lift.

• The minimum HP required to fly straight and level at a gross weight of 3050 lbs was 120 at 75 MPH. At 50 MPH the HP had increased to 160. However at 50 MPH the nose is pitched up so much that the pilot has to look out the side of the cockpit to see the ground.

• The aircraft flies quite smoothly at 50 MPH with 8 degrees of collective.

• HP available for takeoff at sea level conditions was 300. Static thrust was over 1400 lb.

• Data collected continues to confirm our patented control and aircraft configuration is operating as designed such that as the aircraft speed increases, the rotor RPM decreases, yet the blade flapping does not increase. For all other rotary wing aircraft, the opposite occurs where flapping increases with either an increase in speed or a decrease in rotor RPM. The increased flapping is a factor which limits the aircraft's forward speed. Our concept not only allows us to fly faster because we are not limited by excessive blade flapping, but we can also do so efficiently by slowing down the rotor RPM. The drag on the rotor is essentially a function of RPM³. Therefore, a reduction in rotor RPM from 300 to 100 will reduce the rotor drag by a factor of approximately 27 - MAJOR DRAG REDUCTION!