Wichita Falls, Texas: Monday, December 21, 2000

Edited by Rod Anderson

First the Good News

A press conference and award presentation was held on Thursday, 14 December 2000 in Wichita Falls, Texas. The Popular Mechanics' Design and Engineering 2000 award was presented to CarterCopters, L.L.C. for the design of the CarterCopter Heliplane Transport (CCH-T). PM's Editor-in-Chief, Joe Oldham, presented the award. Jay Carter, Jr., president and principal engineer / inventor, accepted the award for CarterCopters.

The PM award was highlighted in the December 2000 issue of PM. The CCH-T is considered by PM and many others to be the first significant new aircraft design of the 21st century. According to PM the CC gyroplane / Heliplane concept could reshape the face of aviation. PM is published in four languages and sold in 11 countries.


 

(from left to right)
Jay Carter, Jr. - President
Joe Oldham - Editor-in-Chief of P.M.

TEAM MEMBERS
Stan Clines - Composites expert
Mark Robinson - Welder, mechanic,machinist
Brad Redding - CNC mill programmer, machinist
Loi Tran - Electrical engineer, website, computers
Shane Teeter - CNC lathe programmer, machinist
Troy Tally - AutoCad draftsman

More Good News

Flight-testing of the CC prototype resumed at Olney on Wednesday, 13 December (the day before the PM award presentation). The pilots made 12 flights down the runway. During the takeoff and climb portion of each flight the pilots' effort was directed towards understanding how best to use the stored energy in its rotor. They also wanted to see how quickly rotor rpm would increase during flight once the collective was reduced. Both pilots were delighted with the results. The first few landing sequences were used to confirm the ease of performing zero-power landings with the incredible amount of rotor inertia available. The pilots were more excited than ever before about the aircraft's responsiveness and the obvious potential for performing zero-roll landings (the 2nd of NASA's 5 goals). They felt the first zero-roll landing would come before the end of the day. They commented that the prototype flew so smoothly they could not tell by feel that they were flying in a rotary wing aircraft. They compared the sensation to flying in a sailplane in smooth air. There was a complete lack of rotorcraft-type vibrations or shake of any kind. This perception of smoothness included the controls. There was absolutely no stick shake. This is very unusual -- especially in a direct control rotorcraft with no boost.

Aircraft ready to taxi during November testing &
fly-by during December 13th, 2000 testing.

Bad News: Non-event Causes Major Damage

At the conclusion of the 12th flight, the totally unexpected happened again. The CC slowly ran off the end of the runway at 20 MPH. In the span of just a few seconds, the non-event landing suddenly turned into a nightmare. The damage to the aircraft can be repaired in 3-4 weeks. It will take 2-3 months to build, balance, & install a new rotor and then proof-test everything in the test-pit.

Aircraft after pulling nose boom out of ground.

The CC landed gently at 30 MPH with plenty of runway remaining. For reasons unknown to the pilots at the time, the brakes were not effective. One pilot later commented that the only options he could see were to swerve sharply left to the taxiway and risk blowing a tire and dragging a wing or hope the overrun was firm enough and speed slow enough to support the aircraft. The result was -- it wasn't. It was a tough, spit-second judgment call that went the wrong way.

Blades broke at hub with minimal damage to hub & rotor head.
Blade spar will handle 500,000 lbs. of centrifugal force but will
break off at the hub on both blades if one blade hits the ground solidly.

Rolling slowly off the runway at 20 MPH would have been a non-event as the pilots hoped except for the fact the ground was very soft from recent rains. As a result, the front landing gear sank to its axle. The intense drag this created caused the (long) front landing gear to fold back as though it was retracting. Even with the gear folded back the incident would have remained a non-event except for the 4 feet long nose boom (part of the ballistic chute system) that speared the ground with the 3,000 lb aircraft pushing. The sudden stop from 20 MPH caused the CC to pitch over on its nose to a near vertical position -- allowing the rotor to strike the ground. The aircraft looked like it might remain in the vertical position like a dart stuck to a dartboard (quite a sight), but after a brief hesitation it rolled onto its right wing. The wing prevented the aircraft from rolling further. After a few more breathless moments the aircraft finally fell back onto its landing gear.

Top of rudders chopped off when aircraft nosed over.
Booms were undamaged.

If the nose gear had not folded under -- the nose boom could not have speared the ground and nothing serious would have happened. The nose gear had folded under during the December 1999 accident with similar results. That time it had folded due to the forward pitching moment cause by the hard landing and the brakes being applied hard. To prevent the same thing happening again an excess amount of oil was added to the front gear. This caused the front gear to bottom out before it could compress enough to allow the nose boom to (again) dig into the ground. Every time the gear is retracted (either fully or partially) the current oil-air separator permits a fine mist of oil to escape into the air. The oil is automatically replaced from a reservoir each time the gear is fully cycled in flight. During each of the numerous trips to and from the pit to proof-test the rotor and gearbox, we had to partially retract the front gear to clear the top of the door opening at the CC shop. Apparently enough oil escaped into the air from these numerous retractions to let the nose gear compress too far -- again. During our subsequent flight-testing, the flights down the runway were too brief for the pilots to retract the gear which would have automatically replaced the escaped oil.

Blade 30 ft. from aircraft. Tip came off when
the blade first hit the ground.

Damage to the CC prototype includes the following: (1) the rotor was destroyed, (2) the rotor mast was damaged, (3) both rudders were clipped off near the top by the rotor, (4) the right wing was broken about 5 ft from the tip and (5) several parts of the rotor head and prerotator drive will need to be replaced. The reinforcement we added to the rear wing spar attachment after the December 1999 accident kept the wing from failing again at the root.

End of outboard 7 ft. of 2nd blade buried in ground.

Brake Mystery & Solution

When the pilots emerged from the aircraft they both thought the brakes had failed. The aircraft had not slowed down when they pushed hard on the brake pedals. Until this landing the brakes had worked without any problems. They appeared to work fine when the aircraft was rolled back onto the runway.

Looking at the data transmitted from the CC during flight-tests solved the mystery. Once reaching 400 ft altitude the pilots had progressively lowered the collective a little more than they did the previous flight. This allowed the rotor to speed up before they started the landing flare. The pilots were surprised at how slowly the rpm dropped as collective was pulled to keep the aircraft in the air -- and how far they were able to float down the runway. As they got closer to the end of the runway, they decided to let the aircraft settle onto the runway by not pulling any more collective. At this point the rotor rpm was 180, the airspeed 30 mph and the collective 8.5 degrees. At touch down, the pilots were discussing the beautiful flight and the energy remaining in the rotor. Collective was inadvertently not lowered before applying the brakes and with the rotor still providing a lot of lift, the wheels just slid lightly down the runway without providing the needed braking action.

An alternative braking solution (beside the brakes) was available but was not used soon enough. The rotor on any gyroplane can be tilted back to provide a rotor brake during the landing procedure. The method was used in this case but only after rotor rpm and lift had dropped off -- permitting the brakes to become more effective. The aircraft is normally tilted forward 3.5 degrees, so the rotor has to be tilted back 3.5 degrees just to be level with the runway. To provide enough rotor tilt to be effective at stopping the aircraft, the CC must be rocked backwards onto its tail boom training wheels. In this case it was not tilted back far enough or soon enough to overcome the forward pitching moment of the brakes.

Probable Reasons

The question was why the collective had not been lowered after touch down. This is standard procedure that had been followed previously without fail. The most likely answer is that the pilots were distracted (excited) as to how much energy was in the rotor and how long they were able to keep the aircraft in the air. The collective itself could have been a contributing factor. It has a spring that toggles over center at approximately 3 degrees of collective. As the spring toggles over center it applies a force to help the pilot pull more collective easier. This is necessary because the high centrifugal force on the blades caused by the 65 lbs of rotor-tip weights per blade provides a moment to keep the blade pitch in the rotor plane of rotation. The pilot has to overcome this moment in order to change the blade pitch. For any given pitch this moment will increase or decrease as a function of rpm squared. This means that by the time the rotor rpm has dropped to 180 rpm, the collective force at 8.5 degrees is negative -- requiring the pilot to now push the collective down to reduce pitch instead of having to hold it up. Collective force was therefore not available to remind the pilot to lower the collective after landing (as would be on most other rotorcraft).

Steps Taken to Prevent a Third Reoccurrence

This is the second time the aircraft has suffered major damage as a result of the nose boom digging into the ground after the nose gear compressed (the December 1999 accident was the first). In this case if the nose boom had not dug into the ground, the nose of the aircraft would have slid across the ground and little if any damage would have been done. To prevent the possibility of this happening a third time, the boom will be shortened so it cannot dig into the ground.

A new oil-air separator has been designed for the nose gear that prevents any oil from escaping when the gear is retracted. This should prevent the nose gear from being able to compress and fold under due to a shortage of oil -- should a similar emergency occur in the future.

A Pilot Operating Handbook (POH) for the CC gyroplane has been under development for some time by our pilots. Now they intend to include a new section on fast stop procedures while taxiing. An effort will be made to brainstorm as many other emergency scenarios as possible and work out the best procedures in advance. At some point in the future when finances permit, the ideal solution might be to develop a CarterCopter flight simulator and incorporate these scenarios for training purposes.