Subject: NAS2-99090 June monthly report

Date: July 5, 2000

The following items were completed or worked on during June.

• Installed new oil cooler, 2 new radiators and 2 turbo air coolers in aircraft. Required support structure and baffles.
• Finished fabrication and installation of variable opening cooling air duct.
• Prefinished wing, booms, rudder, horizontal stabilator and tip extensions.
• Updated web site with info on CC Heliplane Transport
• Fabricated electric cooling fan support and duct.
• Finished as much of the rotor testing as possible on the test stand. Most of the month's effort was spent modifying the test stand and rotor drive in order to test the rotor.

Rotor test comments:

The original prerotator design is no longer adequate for the larger dia rotor. Not only is the rpm lower - requires greater torque, but the hp and additional torque requirement is greater because of the nearly 1.5 times blade area increase. In order for the engine to turn at the higher rpm and hp needed for prerotation, the drive ratio needed to be increased. There was not room on the end of the vertical rotor drive shaft for a larger pulley, so we installed a smaller pulley on the prop drive shaft. The smaller pulley also allowed us to use the original special belt length, as the belt manufacturer would not make us the longer low stretch belt required for larger pulleys (upper management found out the belt was going on an airplane). This was not an ideal situation, but in the interest of saving time and to confirm the rotor system was stable, we had hoped the belt and pulley diameters would be adequate for short duration runs. The small pulley at the high loads produced so much scuffing (inner radius of the pulley will try to turn the belt slower than the outer pulley radius), that the belt would start smoking and wear very fast after only a short run. We went through 8 belts. To obtain a little better belt life, we had to go back to the larger drive pulley. This reduced the engine rpm and hp needed to obtain the desired rotor rpm and reduced the pulley center line distance to the point where the belt misalignment was so far off that the belt would sometimes climb up and over the pulley groove, destroying the belt, belt guard and aluminum support. Under these conditions there was only enough hp to get the rotor up to 420 rpm.

In addition to the prerotator belt problem, we had a problem with the high lateral stiffness of the test stand. A little lateral softness as is in the aircraft is desirable and greatly reduces these loads. A relatively simple modification to the test stand to provide some lateral softness (still different than in the aircraft) caused another problem. Any out-of-balance caused by rotor flapping, or u-joint drive whip (caused because the u-joint is not on the spindle tilt axis) and amplified by the increased distance between the blade teetering axis and the blade center of gravity at low coning/lift (distance needed due to the larger rotor dia and lower centrifugal force) had to be carried by the cyclic push rods. If a disturbance under power (in this case when collective is increased) causes the U-joint angle to exceed approximately 1 degree, then the spindle whip starts to diverge and increases cyclic loads until the control rods bend. This whip is not rpm dependent, but rather on u-joint deflection and torque. When the aircraft is flying there is no torque load on the u-joint. For the tests we would have preferred to pull collective after the clutch was released, but because of the belt misalignment problem with the belt being too short, this was not possible.

It is apparent the rotor drive will have to be redesigned and it seems we will need to finish the rotor proof testing in the aircraft while it is anchored to the test pad. We had hoped to take the rotor to a minimum of 450 rpm on the test stand and satisfy ourselves that everything was OK before a final confirmation test was done in the anchored aircraft.

As a result of the time required to design and fabricate a new prerotator, it will take at best 3 weeks before we can start the rotor testing again. Therefore next flight will not occur until after Oshkosh. We have known for some time that a better prerotator design was needed, but since it had nothing to do with flight safety and in the interest of proving our concepts as soon as possible it has had a low priority. We hope to complete the design and detail the drawings by July 12^th.

The following items need to be completed before the rotor can be tested. Essentially the aircraft will be ready to fly after completion of the rotor tests, provided no modifications are necessary as a result of the rotor tests.

1. Finish rotor test.
2. Remove engine from test stand and re-install in the CarterCopter.
3. Complete installation of all electrical systems including the voice alarms.

Installation of the prop with a new spinner will take place after the rotor testing.