Wichita Falls, Texas: Monday, July 14, 2000

Edited by Rod Anderson

PROOF TESTING ALMOST COMPLETE
CARTERCOPTER BEING REASSEMBLED

EXCITEMENT ABOUT RESUMING FLIGHT TESTS GROWING

Proof testing of individual components is completed with the exception of a final rotor test. Most of June was spent modifying the test stand and rotor drive in order to properly proof test the new rotor. Final testing of the rotor will take place once the CarterCopter is reassembled and the aircraft is anchored to the test pad inside the pit. It will be tested using the new pre-rotator mechanism now being built (see below). If no additional modifications are found necessary as a result of the test, the CarterCopter will (essentially) be ready to fly.

Final assembly of the CarterCopter is proceeding smoothly. The engine was installed on July 17th. All of the new body parts (right wing, horizontal stabilator & extensions, tail booms, air scoop and rudders) have been finished and painted. All electronics have been installed but not checked. To maximize the HP available to the rotor, the new prop and spinner will not be installed until after the final rotor test.
 

NEW PRE-ROTATOR

The original pre-rotator design is no longer adequate for the 10 feet increase of the rotor diameter (43½ ft vs. 33½ ft previously). Not only does the lower RPM require greater torque, but more HP and additional torque is needed because of the nearly 1.5 times greater blade area. We have known for some time that a better pre-rotator design was needed. Before the recent rotor tests, the redesign had a low priority because it did not affect flight safety and we wanted to prove our rotor and rotor-wing interface concepts as soon as possible. It was apparent from the start of the new rotor tests that a new pre-rotator system was needed.

The new pre-rotator design has been completed and the necessary materials have arrived. The highest priority has been given to machining the new parts.

On another positive note, testing showed that the collective pitch forces have been reduced by a factor over 3 in spite of the larger blade diameter and area. As expected the collective boost will be eliminated.

Click for larger view

The engine is re-installed showing the new prerotator belt drive/clutch. Also shown is the new horizontal stabilator extension outside the booms and the cooling air exhaust duct on the bottom of the fuselage. Located in the bottom rear of the fuselage are 7.2 sq. ft. of turbo inter & after coolers plus 7.2 sq. ft. of radiators.

 

PROOF TESTING USING THE ORIGINAL PRE-ROTATOR

In order for the engine to turn at the higher RPM & HP needed for prerotation of the larger rotor, the drive ratio needed increasing. There was insufficient room on the end of the vertical rotor drive shaft for a larger pulley, so we opted to install a smaller pulley on the prop drive shaft. A benefit of the smaller pulley was that it allowed us to use the original (custom built) belt length that we had in stock. Upper management at the belt manufacturing company had discovered the belts were being used on an airplane and refused to make us the longer low-stretch belt required for a larger pulley.

The smaller pulley was a less than an ideal situation but if the belt and pulley diameters proved adequate for short duration runs we would save time in confirming the rotor system was stable. Unfortunately, at the high loads we were running, the small pulley produced so much scuffing (inner radius of the pulley tries to turn the belt slower than the outer pulley radius), that the belt started smoking and wore very fast after only a short run. We went through 8 belts quickly.

To obtain a little better belt life, we had to reinstall the larger drive pulley on the prop drive shaft. This reduced the engine RPM & 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, sufficient HP was available to spin the rotor to a maximum increase of only 420 RPM.

We had hoped to take the rotor to 465 RPM (tip speed of Mach 0.95) on the test stand and satisfy ourselves that everything was OK before doing a final confirmation test later using the anchored aircraft. Now we plan to use the anchored aircraft to reach 450 RPM minimum. The expected maximum jump take-off RPM is 425. During the recently completed tests we would also have liked to pull collective after the clutch/drive belt was released. This was not possible due to the belt misalignment problem caused by the belt being too short. This will be done using the anchored aircraft.

TEST STAND PROBLEMS

In addition to the pre-rotator 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 provided some lateral softness (still different than in the aircraft) but unfortunately caused another problem. Any out-of-balance caused by rotor flapping or U-joint drive whip (caused by the U-joint not being 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) caused the U-joint angle to exceed approximately 1 degree, then the spindle whip diverged and increased the cyclic loads until the control rods bent. This whip was not RPM dependent. Instead, it was dependent on U-joint deflection and torque. When the aircraft is flying there is no torque load on the U-joint.

SAMPLING OF ROTOR TEST RESULTS

 

OTHER NOTABLE BENCHMARKS FOR JUNE

1. Installed the new oil cooler, 2 new radiators and 2 turbo air coolers. The installation required support structure and baffles.
2. Finished fabrication and installation of the variable opening cooling air exit duct.
3. Pre-finished the wing, booms, rudders, horizontal stabilator and tip extensions.
4. Fabricated the electric cooling fan support and duct.

OSHKOSH / AIRVENTURE 2000

With Oshkosh / AirVenture 2000 so close, we now plan to wait until after AirVenture to fly again. Those of you attending AirVenture are invited to attend Jay's forum. Jay will be available some of the time from Friday morning through Sunday noon at Booth # C-3096 (Hanger "C"). If not there and you wish to discuss a business matter, leave a note at the booth or call him on his cell phone (940) 704-2577. You may also make an appointment with Jay in advance of the fly-in.

Jay's Forum Date & Time: Saturday, July 29, 2:30 PM.
Location: Tent 5A

At Other Times Booth: # C-3096 (Hanger "C").
Company: Advanced Technology Products, Inc.