Archive of Weekly Updates

January - March, 2004

2004-03-29

  • We ran the aircraft in the test pit to locate any problems, especially those associated with heat and the cooling system. After several cycles of running at full throttle until the water and oil temperatures reached 250 degrees (both occurred at about the same time), everything seemed to check out except that during one of the runs, the propeller drive belt failed. Examination of the belt revealed that the failure was due to excessive heat. We believe the source of the heat was the engine exhaust, which although insulated runs about 2 inches above and down one side of the belt. We installed an insulated heat shield between the belt and the exhaust to eliminate any radiating heat. Subsequent testing indicated this kept the belt from being any hotter than the engine block temperature.
  • Installed the new prerotator yoke with a heat treat method that produced a tougher core. Proof tested the yoke to 3100 ft-lbs.
  • Company president, Jay Carter, went to Washington, D.C. and made a presentation at the FAA Forecast Conference, a conference looking at the future of commercial and civil aviation. While in D.C., Jay also visited with several military and government personnel.
  • Completed the molds for the internal shear webs and ribs of the scimitar propeller.

 

2004-03-22

  • We took the aircraft to Olney for flight testing. On Wednesday, the pilots felt a vibration related to propeller rpm. The vibration was caused by an interference between the prop pitch mechanism and the thrust measurement system. The interference was caused by the thrust measuring system being low on oil, and the prop drive shaft being at a slight angle relative to the mounting bracket due to the belt change the week of 2/23/04. We modified the prop mounting bracket to put the shaft back in line with the bracket, and will more closely monitor oil levels in the thrust measurement system.
  • We still had a problem of high oil temperatures (>220º F) in flight. We suspect that part of the problem is due to the installation of one of the oil coolers, where the airflow into the cooler is not uniform. We are modifying the oil cooler installation to ensure a more uniform airflow to the cooler.
  • Modified wiring to improve radio communications.
  • Added two new pages of information to main pilot display.
  • Created a new warning for the landing gear, which warns the pilots if the gear is taking too long to extend because of the drag on the gear due to airspeed.
  • Laid up the leading and trailing edge spars of the scimitar propeller. Began work on the plugs for the internal shear webs.

 

2004-03-15

  • We have added a new page to the website, Frequently Asked Questions about the CarterCopter. The page answers many of the common questions people have about the CarterCopter, and will hopefully clear up some misconceptions about the aircraft.
  • When we tested the aircraft in the test pit with the new prerotator yoke, the part failed, this time at a lower load than the previous design. Examination of the broken part revealed that the new method of heat treating made the part very fragile. We have machined a new yoke using a different steel alloy, which will be heat treated with a method that will leave the core tougher. Since the prerotator is used only on the ground, and is not under load in flight, we installed a spare of the current fragile yoke to use until the new, tougher yoke is completed. We will limit prerotator drive torque to keep the part from failing.
  • Modified automated control programs to improve operation.
  • Completed the root block of the main spar for the scimitar propeller. Made the tooling to align the main spar in the skins. Completed the leading and trailing edge spar molds.

 

2004-03-08

  • After examining the rotor head, the prerotator yoke was the only part that needed to be replaced because of last week's prerotator failure. We talked with a metallurgist about the part, and it turns out that the method of heat treating that we had used on the part was very prone to cracking. We think that the part had cracks introduced during heat treating, which caused high stress concentrations, with the torque spike during rotor stopping being a contributing factor. We redesigned the yoke with a larger fillet to reduce stress concentrations, had it machined, heat treated with a different process, and installed back into the aircraft, all in one week. We have also modified our rotor stopping procedure to eliminate the large torque spike when the rotor stops.
  • Modified the cyclic links to give more spindle travel.
  • Modified the collective links and linkages to give more collective travel.
  • Made a simpler manual override for the automated collective control, allowing the pilots to easily pull more collective on landing if they want to.
  • Laid up the upper and lower skin for one blade of the DARPA funded scimitar propeller; completed the leading edge and trailing edge spar plugs; and laid up the root block of the main spar.

 

2004-03-01

  • We took the aircraft down to Olney for flight testing. We had several good flights on Thursday. The pilots performed several simulated landings at altitude, and the automated controls worked wonderfully. Our best rate of climb with the landing gear extended was 750 fpm.
  • On the last flight on Thursday, the engine quit running in flight, just as suddenly as if the pilots had turned off the ignition. The aircraft was at 1200' AGL, so the pilots had their choice of runways. They made a nice dead stick landing without cyclic or collective hydraulic boost. Thanks to the backup air boost, the controls were still very manageable. Inspection on the ground after the incident revealed that wires connecting the engine crank sensor to the engine computer had become too hot, melting the insulation and shorting the wires. Without the signal, the computer could not control the engine. The wires were repaired and wrapped with thermal insulation.
  • During spin up prior to taxiing for our first flight on Friday, the prerotator u-joint yoke failed. We believe that the yoke cracked the previous day, when we enaged the prerotator with the engine off to stop the rotor from spinning. Right at the instant when the rotor stops, a very large torque is generated- much larger than our operational torque when prerotating the rotor. We have redesigned the yoke with a larger fillet to reduce the stress concentration, and have modified our rotor stopping procedure to eliminate the large torque spike. Once we disassemble the rotor head this week, we will know the extent of the damage. The prerotator is only used on the ground to spin up the rotor, so it would not have failed in flight, nor is it a necessary system in flight. We are also running the prerotator system at a higher stress level than originally designed, since we are using a larger rotor than the original CarterCopter rotor.
  • Completed the final bonding operation on the second blade of the DARPA funded extreme mu rotor.
  • Laid up the spar for the DARPA funded scimitar propeller. This was the first spar we have designed using the three dimensional solid drafting program, Solidworks, which we used to design the spar and its mold, and to calculate the number of carbon strands needed to lay up the spar. The mold was machined on a five axis CNC machine using an electronic file generated by Solidworks. This was the smoothest layup operation we have ever had for a spar.
  • Began preparing the molds and making templates to lay up the blade skins for the DARPA funded scimitar propeller.

 

2004-02-23

  • Finished tuning the engine with the turbo. Peak power was 385 HP at 4800 rpm and 2.5" of boost pressure.
  • After tuning the engine, an inspection of the propeller drive belt revealed that it was beginning to split, even though we had kept horsepower down from the previous week's tests when we failed the belt. We decided to go back to a belt system which we had used in the past which has a higher capacity. This meant changing the drive pulleys, as well as modifying several brackets to accomodate the new center distances necessary between the pulleys.
  • Began replacing the numerous Molex connectors in the aircraft's wiring system with more reliable AMP connectors. Because of the large number of connectors, this will be an ongoing process.
  • Completed all of the internal components of the second blade of the DARPA funded extreme mu rotor, and bonded them to the lower skin of the blade. We expect to bond the upper skin to the blade this week.

 

2004-02-17

  • Made a modification to the newly installed oil thermostat.
  • Reassembled the rotor head after making the several modifications already noted in last week's update.
  • Made several modifications to the automated control software to improve its operation based on lessons learned in flight testing.
  • Began tuning the engine with the turbo. Partway through the tuning process, the prop drive belt failed. We are going to examine the aircraft this week to determine the cause of the failure. We currently suspect two possibilities- either that the pulleys were misaligned or that we put too much power to the belt at too low of an rpm. If the failure was due to overloading the belt, we will limit the turbo boost pressure to keep horsepower lower, and will consider installing a different set of pulleys and belt to give us a greater capacity.
  • Took the first blade of the DARPA funded extreme mu rotor out of the blade molds. Laid up the skins for the second blade.

 

2004-02-09

  • Reinstalled the turbo. We expect to put the aircraft in the pit this week to calibrate the engine and check the other modifications we have made. We hope to be back in Olney for flight testing by the end of the week.
  • Installed a redesigned oil thermostat. This will keep the oil going to our boosted controls at a constant temperature independent of the outside air temperature.
  • Modified the rotor head to allow more clearance between the collective control tube and the prerotator u-joint. There had been a problem of interference between the two when the pylon was forward and the pilot pushed forward on the stick.
  • Installed strain gauges in the rotor head to measure rotor lift and collective control force.
  • Completed the final bonding operation of the first blade of the DARPA funded extreme mu rotor.

 

2004-02-02

  • We spent three days flight testing in Olney, without the turbo installed on the engine. Our goal was to gather data on the automated controls, which appear to be working wonderfully. The automated collective pitch control worked great for takeoff and cruise through 142 mph. It appears that it will work for automated landings as well, but since we were not able to practice any simulated landings at altitude due to a low ceiling, we continued to do conventional landings by manually operating the collective. The automatic rotor rpm control also appeared to function correctly, tilting the spindle back 50% of its travel at 140 mph to maintain the rotor rpm at 150. We did not stay at this speed long enough to confirm that the controller would continue to be stable. Our best rate of climb during these tests due to the reduced horsepower available from the non turbo charged engine (12 lb. aircraft weight per hp) was 500 ft/min at 100 and 110 mph with the gear extended, and the fastest we went was 142 mph (mu of 0.63). Once we adjusted the blade pitch to get the rotor to track, our pilots reported that the aircraft was ultra smooth. With their eyes closed, there would have been no clue that they were in a rotary wing aircraft. We plan to continue flight testing in one to two weeks once we reinstall the turbo. Our climb rate will be significantly better, and we should be able to start expanding the speed envelope.
  • We installed an additional oil cooler, which should keep our oil temperatures fine even on hot days, but our oil thermostat did not function correctly. The temperature it sensed was more influenced by the cool oil coming from the oil coolers than from the hot, bypassed engine oil, so the thermostat sensed a temperature cooler than the engine oil and continued bypassing the oil coolers most of the time, keeping the engine oil temperature high. We were forced to remove the thermostat in order to complete the flight test. We will install a redesigned thermostat before flying again.
  • We experienced a problem trying to extend the landing gear at 110 mph. The drag on the landing gear was high enough to open a pressure relief valve in the gear's oil lines. Once the craft slowed to 80 mph, the drag was low enough that the gear extended. We will increase the preset pressure on the relief valve before future flights.
  • Finished all the tooling and internal parts for one blade and began the final bonding operation of the first blade of the DARPA funded extreme mu rotor.

 

2004-01-26

  • Removed the failed turbo and sent it off for a failure analysis. Failure was due to a lack of oil to the bearings caused by blockage of a flow control needle valve due to Teflon tape. Received a rebuilt turbo.
  • Recalibrated the engine controller for natural aspiration. The engine without boost produces only 340 HP at 5200 rpm. (At 1 psi boost the engine produces over 400 hp).
  • We may fly some this week if our rate of climb with the reduced hp is at least 500 ft/min. Test weight without the turbo installed will be about 3900 lbs. Our intention is to continue to check out and tweak the automatic controls – initial take-off collective pull, initial rotor rpm energy management, cruise rotor rpm, and rotor flapping (maintain balanced lift moments between the advancing and retreating blades). Next week while our copilot is on a skiing vacation, we plan to reinstall the turbo with a few modifications.
  • Modified the collective boost system to remove the dead band regardless of the load direction.
  • Modified the flapping sensor so that it measures only flapping due to lift differences between the advancing and retreating blades, and not due to spindle movement.
  • Completed the trailing edge spar for one blade of the DARPA funded rotor.
  • Finished casting second blade tip weight, cut and machined the tip weights for both blades and laid up the carbon uni pockets for the first blade weights.
  • Held our annual shareholder's meeting over the weekend.

 

2004-01-19

  • President Jay Carter spent another 2 days in Washington, D.C., meeting with government and industry.
  • Replaced prop drive pulleys. Used a harder surface coat to keep them from wearing as rapidly.
  • Increased the inner diameter of the hoses and fittings connecting the oil cooler to reduce its pressure drop and increase the engine oil pressure.
  • Designed, built, & installed an oil cooler thermostat.
  • Recalibrated the engine computer for 400 HP at 1 psi boost.
  • The harmonic balancer & drive pulley came loose at max horsepower, causing the belt to ride up over the pulley, failing part of the belt. The engine was shut down from max horsepower to a stop and zero oil pressure in less than 4 seconds. The turbo continued to spin down without oil pressure and failed its bearings.
  • We plan to fly the aircraft without the turbo until the turbo can be replaced. This engine should be capable of producing nearly 400 HP with natural aspiration.
  • Hired a second electronic/mechanical technician- Alex Dobek.
  • Completed mold for the trailing edge spar of the DARPA funded rotor.
  • Laid up shear webs for the DARPA funded rotor.

 

2004-01-12

  • We have found the cause of our sudden loss of oil pressure- the rear main bearing had spun. This was due to too low of an oil pressure (50 psi) and too high of an oil temperature (235 degrees) for the given load on the bearing. The bearing sees a higher load than in an automobile because of the overhung drive pulley load. The crankshaft also had a crack at the corner of the main bearing and the throw. The Auto Shop had finished rebuilding the larger, 427 cu. in., racing version with a stronger, forged crank, so we can now install that into the aircraft while we decide what to do with the smaller, basically stock 347 cu. in. engine. To keep oil temperatures lower, we are going to install an additional oil cooler.
  • The drive belt wore through the hard anodize on the drive pulleys, and had begun to eat into the pulley teeth. We have machined new pulleys, and are using a different surface treatment to improve their wear resistance.
  • Finished the molds for the internal shear webs of the DARPA funded rotor.
  • Made the plug for the trailing edge spar of the DARPA funded rotor.

 

2004-01-05

  • We have not yet determined the cause of the oil pressure drop described last week. After a partial dissassembly of the engine, not including removal of the turbo exhaust system, the prop drive nor a number of other components, we thought we had found the cause. An 1/8 in. gap in the oil suction tube had been sealed with silicon, instead of an o-ring as designed, which could have caused a leak. Repairing this did not correct the problem. This week, we are going to completely dissassemble the engine, including those components that were not included last week, to determine the cause of the pressure drop.
  • Repaired nose gear. During transportation on the trailer, one of the supports broke loose from the fiber glass because of the way the aircraft was tied down. This is not the type of load the landing gear would experience in flight operations.
  • Added an air/oil separator tank below the turbo to ensure that the oil does not back up in the turbo and get lost in the exhaust or compressor.
  • Installed an oil pump pressure relief to the auxiliary oil pump to keep the pressure from getting too high on cold weather starts.
  • Moved turbo air inlet to the top of the engine compartment, which should decrease inlet temps by about 15ºF.
  • Stiffened the oil pump support.
  • Made the plugs for the internal shear webs of the DARPA funded extreme mu rotor.
  • Carter receives its first Publication Cover! The first published photo of the newly restored CarterCopter will appear on the cover of the 1st January issue of Trade-A-Plane (TAP). The TAP Cover photo was taken during recent flight-testing in December. Trade-A-Plane has more than 132,000 readers and has been the leading aviation marketplace publication for more than 60 years.
Q 4, 2003
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