Wichita Falls, Texas: Tuesday, August 24, 1999.

ENGINE PROBLEMS KEEP CARTERCOPTER GROUNDED

The GM V-6 engine was rebuilt following its failure on June 3 (Press Release, June 11). After the CarterCopter returned from Oshkosh on August 2, a week was spent mapping the engine. The spark advance and fuel-air ratios of the ignition/fuel injection modules were optimized at five different throttle settings and eight different engine RPM settings. During the engine endurance runs that followed in the test pit, oil pressure was lost when the oil pump drive shaft broke.

The data collection system recorded the moment of oil pressure loss, but the fatal alarm was overlooked. The engine was running at 5000 RPM, and our attention was focused on engine calibrations having to do with exhaust temperatures and HP output. The engine continued to run for an extended period without oil pressure and was once again damaged.

TIME IS A CRITICAL FACTOR

We are now faced with decisions similar to those we faced after the engine failure on June 3. We need to start flying the CarterCopter again as soon as possible. Only by flying can we prove our concepts. We are very close to proving that the CarterCopter is a safe, simple rotorcraft that can use energy stored in its high-inertia rotor for zero-roll takeoffs and landings. In addition, the high-inertia rotor and patented control system will demonstrate its inherent stability and very low rotational drag at 100 RPM, with rotorcraft forward air speeds exceeding 150 MPH.

ENGINE OPTIONS ARE LIMITED

Detailed technical information has been requested for each of the following options. Once the information is available, we will do preliminary design studies to determine the feasibility of each option and the probable time required to install the option.

GM V-6: The quickest option is to once again rebuild the existing V-6 engine. We hesitate to do this for the following reasons:

· The V-6 is under powered for the 3000-pound weight of the CarterCopter. For our HP needs, it can be utilized only at very high RPMs with high compression ratios or by employing a turbo charger.
· The V-6 is rough running due to its odd-fire crankshaft and its inability to be perfectly balanced. We suspect some of our problems result from metal fatigue caused by the inherent engine vibrations.
· The odd-fire V-6 requires the use of a sophisticated engine controller that needs to be calibrated for optimal power output. Engine calibration is time consuming and tedious, and leads to other problems if not done properly.

CORVETTE LS1: The second option is to switch to a V-8 engine. The selection is limited due to the length of the CarterCopter engine compartment. A V-8 that appears to have the right size, weight and HP is the LS1 engine used in Corvettes. This option would allow us to buy the engine and all necessary accessories as a complete package; including intake manifold, throttle body, fuel injectors, ignition system, engine controls, etc.

The LS1 can provide 375 HP without any engine modifications and can be purchased at a relatively low cost. Fitting this engine into the existing engine compartment will still present problems. At the minimum it will require new motor mount supports, drive shaft support plates, drive pulley, prop drive shaft, and obtaining a special Kevlar double-groove belt (used to pre-rotate the rotor) that is 8-inches longer than the current belt. This belt requires a 6-8 week delivery time. We estimate the LS1 option will take 8-9 weeks from the "go" decision until the next flight.

GAS TURBINE: A third option, currently our first choice, is a gas turbine engine. The advantages are less engine weight, increased reliability, and a healthy amount of HP. This combination would produce outstanding CarterCopter performances.

The disadvantages are high cost, our inexperience with gas turbines and the unknown amount of time required to perform the installation. Any gas turbine will cause major re-design problems due mainly to its length.

If the right turbine can be found and the manufacturer is willing to provide factory support, we would consider taking 1-2 months longer on the installation than with the Corvette LS1. The 4-bladed prop necessary to absorb the added HP from a turbine has already been designed. It is essentially 2 - 2 bladed props mounted 90 degrees to each other.

OTHER CHANGES SINCE THE LAST TEST FLIGHT SERIES

Numerous improvements on the aircraft were made at the same time work was being done on the engine.

COLLECTIVE: The rotor collective pitch control no longer uses slaved hydraulics. It was redesigned to use the same kind of ball bearing push-pull cables used earlier in the redesign of the rotor cyclic control (Press Release, January 28). With this installation now complete, no slaved hydraulic systems remain in the CarterCopter. The only remaining hydraulics is the air-over-hydraulics found in the patented landing gear system.

The pilot's collective stick force is now nearly constant throughout the entire collective pitch travel. This nearly constant collective force is due to the patent pending blade pitch spring toggle being re-designed to provide almost 3 times more collective linkage preload at zero degrees collective. This modification along with moving the collective stop from the cockpit to the rotor head should eliminate the vertical oscillation experienced at a given rotor RPM as reported in the June 11th press release.

WIRING HARNESS: Because of numerous, on-going electrical problems caused by poor connections, inadequate strain relief, incomplete documentation, and other gremlins -- the wiring was completely re-designed and installed from the instrument panel back. The new wiring harness is commercial grade and professional in every aspect.

DATA COLLECTION SYSTEM: Once the new wiring harness was installed and we began checking the system, we found more problems in our data collection system. Keeping the data collection system working has been a major time consumer. This time we decided to use our excellent in-house capabilities and build our own system rather than send the system back to the manufacturer for the 6th time.

FUEL SYSTEM: The fuel system was improved again (Press Release, May 17). As before, one low-pressure fuel pump sucks from the front of the main tank and the other from the rear of the main tank. Both low-pressure pumps are capable of re-priming themselves.

Both low-pressure pumps now feed into a common fuel-air separator. Both high-pressure fuel pumps feed off this separator into another high-pressure fuel-air separator. The low pressure separator contain enough fuel volume to run the engine at full throttle for 20 seconds. This fuel volume buffer gives the pilot sufficient time to switch low-pressure fuel pumps if a pump fails or runs dry for any reason. The high pressure separator allows the use of only one fuel flow meter for increased accuracy. Yet, it still prevents any air from going through the injectors causing a lean fuel-air mixture.

BRAKES: The brakes were re-built with larger pads and larger cylinders to reduce the braking force required from the pilot during maximum static thrust.

REAR SEAT: A rear seat was added to cover dual pilot controls that are soon to be installed (see below), and miscellaneous electrical components.

NOSE BOOM: The nose boom was shortened 18 inches, eliminating the need for a skid pad at the end. The true airspeed and aircraft pitch indicators were relocated to the right wing tip.

ROTOR DRIVE SHAFT: A larger, stronger rotor drive shaft U-joint (used for rotor pre-rotation) was built and installed. A new, elastomeric-supported, movable mast section was then rebuilt to provide more room for the larger U-joint.

The rotor shaft spline remains as before (Press Release, June 11) -- but the female half was re-machined and then heat-treated. The male half had been heat-treated originally and showed no signs of wear.

SEVEN DAYS AT OSHKOSH '99

The CarterCopter was trailered to Oshkosh, arriving Sunday, July 25th. Before leaving Texas, it received some cosmetic touch ups. We could not fly at Oshkosh this year because we had not accumulated the required 40 hours of unmodified flight time. The CarterCopter was displayed just inside the archway entrance to the "new design and custom-built aircraft" area.

Click on photos for a larger version. Photos provided by Rod Anderson

CarterCopter appearence at OSHKOSH 1999

ADDITIONAL CHANGES SCHEDULED

DUAL FLIGHT CONTROL SYSTEM: The delay caused by the engine problem will provide the time needed to finish building and installing the new dual flight control system. Dual controls will provide an extra safety net for the pilots. The dual controls will also facilitate qualifying pilots to fly the CarterCopter.

EXPANDED DATA COLLECTION SYSTEM:Our new data collection system (see above) will be expanded from the current 28-channels to its maximum capability of 84-channels. We will incorporate additional features such as three separate instrument panel displays: one for each pilot and a larger one in the center. Each display will show information from the same or different channels as needed by the pilots.