Wichita Falls, Texas: Friday, June 11, 1999.

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

Click on all Photos for a Larger Version

SUCCESSFUL FLIGHTS FOR CARTERCOPTER:

Following three previously mentioned delays in the May 17 press release, the CarterCopter was trailered to Olney, TX, on Monday, May 24. After extensive pre-flight checks, a small crack was found near one prop tip, and flight test series #8 was postponed. The repair was made the same week and was relatively simple. Follow-up tests revealed that the necessary reinforcement of the prop-tip area had reduced maximum prop thrust by approximately 50 pounds. The next generation prop will include the reinforcement, making the repaired area several times stronger than before, and the lost thrust will also be recovered. On June 2, 1999, flight tests series #8 resumed.

THE FLIGHT TEST GOALS ARE PRIORITIZED:

The flight-testing was divided into two areas. Priority was given to goals considered most important to the program and to those least likely to cause a mechanical failure that would stop the flight-testing. The high number of recent delays had everyone being particularly cautious.

It was decided that the first priority would be to explore the flight speeds between 100-125 MPH while flying extended patterns around the airport. At the higher speeds, we could observe the ability of the aircraft to unload and slow its rotor while continuing to maintain rotor stability. This stability issue is the key design feature that will permit the aircraft to fly fast and efficient.

Zero-roll takeoffs and landings would be done last. Previous flight tests have convinced the test pilots that more than sufficient energy can be stored in the CarterCopter rotor system to do these maneuvers. All that remains is for the test pilots to develop the necessary techniques.

The reason for putting these tests last was the concern that the strain from a large number of prerotations might cause the spindle shaft spline to fail. This is not a safety concern because the spline is only loaded during prerotation when the aircraft is on the ground. Its failure would stop the flight tests but not cause other damage. The spline carries all the prerotation torque and it has suffered extensive wear from the accumulated rotor testing of the past 4½ years. Also, the spline carries a heavier load than it did originally because the HP required to spin the rotor up to its maximum jump takeoff RPM of 550 has increased by 33%. This is due to the blade chord being increased 25% to eliminate a blade weave problem (Press Release, January 28), and a special shark-fin tip being added to increase the rotor diameter/swept area and to reduce rotor-tip noise. A new spindle shaft has been designed that eliminates the spline.

FIRST FLIGHT PATTERN:

Being two months since the last flight (Press Release, April 5), the first morning was limited to a repeat of previous flight tests. This not only allowed test pilots, Don Farrington and Jay Shapley, time to become familiar again with the aircraft's startup, prerotation and basic flying characteristics, but also to become comfortable with the numerous changes made since the last flight. Don and Jay were to proceed with the scheduled program at their discretion. During a mid-afternoon flight down the runway, the CarterCopter, suddenly raised its landing gear and flew its first traffic pattern. The flight lasted 4 minutes 13 seconds. The aircraft flew to an altitude of 400 feet and to a speed of 116 mph.

SIX MORE TRIPS AROUND THE PATTERN ON SECOND DAY:

The following day, six more traffic pattern flights were made lasting between 4 minutes 0 seconds and 6 minutes 35 seconds. Maximum speed was 126 MPH, maximum altitude was 800 feet and maximum rate of climb was 600 feet per minute at 260 HP. Interestingly enough, the current world speed record for a gyroplane over a 3 km course (piston, 1986) is 120 MPH. The CarterCopter was flying patterns that were 6-8 miles in total distance.

FLIGHT TEST DATA SUPPORTS MAJOR PREDICTION:

The plan was to set the trim relationship between the horizontal stabilator, rotor spindle and flaps so that the rotor initially carried a higher percentage of the aircraft's weight relative to the wings than in the expected final configuration - for any given airspeed. Over 50 channels of data were collected during each flight, permitting us to compare actual data against our predictions. Once our predictions were confirmed, we reset the trim relationships for the subsequent flight so that the wings provided a slightly higher percentage of the overall lift for any given air speed. As expected - the rotor RPM and drag became less as the rotor was unloaded. Most significant was the fact that the rotor flapping did not increase as the air speed increased and the rotor RPM decreased. This situation is the opposite that occurs on other rotary wing aircraft, and indicates the patented, flapping control concept is working and will eventually allow a jet powered CarterCopter to fly as fast as 500 MPH true airspeed.

The rotor RPM and drag were so high on the 1st traffic pattern flight that the maximum speed at full HP was only 116 MPH.

By the 5th traffic pattern flight, the trim relationship had been changed so that at zero degrees of rotor pitch, the aircraft flew at 126 MPH using less than full throttle - and at a rotor RPM of 320 instead of the previous 400.

At this point we still planned to make more incremental trim changes in order to additionally unload the rotor in the hope of achieving a calculated desired rotor RPM of 225 at 125 MPH.

VERTICAL OSCILLATIONS AT 320 RPM:

During this 5th traffic pattern flight the aircraft experienced vertical oscillations at 320 RPM and 126 MPH. We could not see anything from the data to explain what had happened, but felt it might be RPM related. We decided to make some more trim changes that would allow the rotor to slow to the same 320 RPM at a lower air speed.

During the 6th traffic pattern flight the aircraft again briefly experienced vertical oscillations at a lower air speed and at a RPM of both 320 and 340 - with slightly different rotor collective settings. Again we could not explain what was happening, other than it seemed to be RPM and/or collective pitch related.

We decided to fly the 7th traffic pattern, but this time hold a little more collective so the rotor could slow down to 320 RPM at an even lower forward speed. When the rotor hit 320, RPM severe vertical oscillations occurred that lasted 15 seconds. The pilots saw double vision and inadvertently turned the radio and intercom off.

LANDING GEAR COLLAPSES WITHOUT CAUSING STRUCTURAL DAMAGE:

Photos of Slight Damage by Brad Redding and Rod Anderson

The pilots were so surprised by the sudden oscillations that between trying to analyze what was happening and making the landing approach, they forgot to lower the landing gear. Halfway down the runway and with 10 feet of altitude remaining, they noticed the radio switch was off. When they turned it on, the first thing they heard was ground control shouting for them to lower the gear. Although the gear fully lowered before they touched down, the air pressure had not built up to the point where it would fully support the aircraft. The gear collapsed just before the aircraft rolled to a stop. The patented tail boom configuration kept the prop from hitting the ground, so damage was limited to non-structural scrapes. The landing gear was aired up and the aircraft taxied off the runway - something very few pilots have been able to do after having their gear collapse with the prop turning.

ENGINE PROBLEMS:

The engine did not sound right, therefore, it was turned off once the CarterCopter cleared the runway. When a restart was attempted the engine locked up. The aircraft was towed back to the hanger. Initial inspection showed two spark plugs destroyed. When the engine was disassembled it was revealed that the intake valve to the #5 cylinder failed - for still unknown reasons. The intake valve had broken into pieces and bounced around the inside of the intake manifold and was ingested by the other cylinders. One large piece had wedged in the intake manifold chamber of the #1 cylinder. Further inspection revealed a crack in the crankshaft which probably occurred when the prop shaft broke (Press Release, May 17). A decision will be made next week whether to rebuild the V-6 or to replace it with a V-8.

OTHER CHANGES NECESSARY BEFORE THE NEXT FLIGHT TEST SERIES:

After a review of the rotor collective data, the collective slave cylinder control, and further thought, everyone seems confident that the vertical oscillations were caused by excessive deadband in the collective hydraulic system and by a reduction in the collective linkage preload at low rotor pitch settings. We will not fly again until the collective hydraulic slave system is changed to a ball bearing push-pull cable control system. This change is the same that was made earlier to the cyclic control system (Press Release, November 14).

The temporary tail-rudder extensions are another consideration for change. They are not "mass balanced" and can be expected to flutter at some point above 125 MPH. Plans are to trim a few inches from the trailing edges - followed by test flights. Once the optimum length for full rudder control at takeoff and landing speeds is determined, the rudders can be rebuilt to the correct size and then correctly balanced.

Photos of Mark, Stan, Jay, & Joe performing Inter-Flight Inspections, Rudder Extensions, and Stan Inspecting the Rotor Head & Linkages by Rod Anderson

CARTERCOPTER APPEARANCE AT OSHKOSH 1999:

We are hoping to complete aircraft modifications and the phase II and III flight tests (Press Release, March 3) to enable us to take the aircraft to Oshkosh. There is still a slight chance we can complete the required hours on the aircraft in order to fly at Oshkosh.