Wichita Falls, Texas: Wednesday, 30 May 2001

Edited by Jeff Keaton*

Persistence Leads to Breakthrough: New Takeoff and Landing Procedures Developed

The third time IS the charm -- at least this past weekend when flight-testing of the CarterCopter Technology Demonstrator (CCTD) resumed at Olney, Texas. By the end of the third day, the pilot developed a takeoff and landing procedure that was smooth, relatively simple and fully repeatable. This long awaited breakthrough in pilot training procedures opens the door for rapid progress in the coming weeks. Everyone still hopes that sufficient time remains to complete the required flight-test program by mid-July so we can fly the CCTD to AirVenture 2001.

Fig. 1 - 28May01 Flight Testing

The flight-test team was persistent in its determination to resolve difficulties that caused early termination of the two previous flight-test series (see below). They chose to take the necessary time at this point in the program to simplify flight procedures and better understand the involved flight dynamics so that later flight-testing can proceed with more confidence. The persistence has paid off.

First Flight-test Series Ends in Sudden Pitch-up: Causes No Damage

Olney, Texas, 14 April 2001: The CCTD was repaired after the minor accident on 25 March 2001 that occurred during an aborted short field takeoff (see Press Release 28 March 2001). Flight-testing on 14 April began with numerous taxi tests that gradually increased in speed. The CCTD momentarily became airborne with an unexpected pitch-up. The test pilot quickly brought the CCTD back under control and landed with a hard touchdown. The high-energy absorbing landing gear worked as designed and there was no damage to the aircraft. The test team then spent the following two days determining the cause of this pitch-up. Careful analysis of flight-data (including telemetry from the heavily instrumented CCTD and high definition digital video from both on-board and off-board locations) provided the following analysis.

Analysis: The pilot was requested to hold a predetermined pitch attitude that would provide the necessary amount of lift at a relatively low airspeed and preset collective. The technique was designed to allow a standard (acceptable) test build-up approach in speed and flight altitude. The build-up approach permits the pilot and flight-test director (monitoring telemetry) to evaluate the aircraft performance and dynamic handling qualities before climbing to a higher altitude and flying a normal traffic pattern.

The technique that was designed and agreed upon for this test-flight unknowingly resulted in the rotor's lift vector being ahead of the CCTD's center of gravity (CG). As speed increased, the elevator's unusually high positive lift (due to a positive angle of attack in ground effect) had to be balanced by the rotor lift vector being ahead of the center of gravity. Once airborne and with the elevator out of ground effect, the lift on the elevator dropped off quickly -- resulting in the unexpected pitch-up. This momentary imbalance would have eventually equalized as the pilot shifted the rotor's lift vector back into balance with the lift from the elevator. The sudden change in elevator lift allowed the nose to pitch up more than was comfortable for the pilot and he successfully aborted the flight.

After a detailed analysis of flight data and much discussion, the test team developed another technique intended to facilitate flight control familiarization before actually flying. Using rotor pitch as the control variable, a similar build-up approach was agreed upon for the next sequence of flight tests. As noted above, the efforts finally paid off. Details of the first two flight-test series follow:

Second Flight-Test Series Ends with Rotor Airfoil Damage: Easily Repaired

Olney, Texas, 28 April 2001: Flight-testing resumed. Several low-speed taxi runs were made while gradually increasing the amount of collective (increasing the pitch angle of the rotor blades). As rotor lift increased, the aircraft became easier to control in pitch. The test team decided to have the pilot increase collective until airborne and hold this collective for a few seconds before setting back on the runway. If the pilot felt uncomfortable at any time, he was told to lower collective and settle back on the runway.

The technique did not work as planned. Anticipating the rotor would tilt to the left slightly as the aircraft pitched up (due to the rotor delta-3), the pilot pushed the cyclic too far to the right -- causing the aircraft to roll right sufficiently for the wing-tip to graze the runway. The pilot then overcorrected by moving the rotor spindle 9 degrees to the left in 1/2 second. The aircraft made almost a 90-degree bank to the left and headed toward an open field at the center of the airport. The aircraft landed safely in the rough field, but as it slowed the nose landing gear (again) folded back causing the nose to dig into the ground -- momentarily pitching the aircraft over on its nose and allowing the rotor to strike the ground. No one was hurt. Damage was primarily to the airfoil shell of the rotor, with minor damage to the right wing caused when a section of the (nearly stopped) damaged rotor blade struck the aileron. The rotor blade spar was intact.

Fig. 2 - 29Apr01 After rotor strike accident

Analysis: Although the pilot over-controlled the aircraft, a detailed analysis of flight data showed it was not pilot error. At low speeds, it is difficult for the pilot to balance the aircraft on the main wheels because the elevator is not yet effective and the CG is so high above the wheels that slight pitch changes cause the CG to significantly move fore or aft over the wheels - in turn causing the aircraft to unexpectedly pitch up or forward.

This is further complicated whenever the lift from the rotor is not through the aircraft CG. Then as the aircraft pitches, the lift on the rotor changes and produces another pitching moment. As the aircraft quickly accelerates in a high-speed taxi with increasing prop blast over the elevator and additional rotor lift added with collective -- the more stable the aircraft becomes. But as the CCTD reaches this stable condition, it can unexpectedly become airborne without the pilot wanting it to. Therefore, a gradual buildup to this point is necessary to give the pilot time to learn the required control response before committing to flight.

Several techniques have been tried to achieve this, but none have demonstrated the desired characteristics of low pilot workload and minimal aircraft pitch change at lift-off. For the next flight-tests, temporary changes will be made in the landing gear to permit the pilot adequate time to develop the proper technique necessary for a smooth takeoff. The nose landing gear will be extended seven inches and the main landing gear pressure will be increased to fully extend the main gear. This will provide the pilot with a more standard tricycle landing gear configuration and help reduce shifts in the CG during high-speed taxing.

Analysis of Detailed Flight Data Resolves Doubts: Leads to Success This Past Weekend

Data analysis shows no indication of an instability or natural frequency resonance problem. Recent flight-test problems were being caused primarily by the fact that the CCTD was designed for zero roll (jump) takeoffs -- not conventional rolling autogyro takeoffs. Those who have climbed into an unfamiliar aircraft and taught themselves to fly will understand the situation. The tendency to over-control in this unfamiliar environment is natural. Learning the correct techniques to use with the CCTD was complicated further by the fact it is a hybrid aircraft. The flight-test team decided that developing the necessary training methods at this point in the program was worth the time, risks and expense.

 

Fig. 3 - 28May01 Flight Testing -- getting ready to fly

Our continued success will depend heavily on having good techniques that pilots can use to familiarize themselves with control responses and to develop a feel for flying the CCTD without fear of unexpectedly becoming airborne. Takeoffs during training should always be smooth without any sudden control movements required upon liftoff. The procedure must be repeatable. Smooth takeoffs had (eventually) been accomplished in earlier test flights, but not without incident and only after several weekends of flight build-up. Once pilots have become accustomed to flying the CCTD, they indicate the aircraft is very responsive and easy to fly.

Fig. 4 - 28May01 Flight Testing -- taxiing out

Additional training problems are caused by pilot (preflight) preconceptions concerning potential control problems due to (1) the high-inertia rotor system, (2) the interaction between the rotor and conventional fixed-wing controls and (3) the 30-degrees of delta-3 flapping (where any large, rapid, cyclic movement causes the rotor for a very brief time to move in a direction approximately 30-degrees from the direction the stick is moved).

Complicating the situation further is the fact that our pilots work with us on a part time basis and must schedule around their full time jobs. The flight-test program (unfortunately) cannot afford the luxury of having a fully trained pilot always available when we are ready to fly or to help with the training of a new pilot. In hindsight, the lack of a fully trained pilot always available to fly and to train other pilots has been very costly and may have contributed to several mishaps that damaged the aircraft. We remain confident that once our test pilots have gained flight time in the CCTD and the new flight-training methods are fully developed, they can teach inexperienced pilots to quickly and safely fly the aircraft.

On the positive side, the causes of these unexpected events are now better understood and will result in safer flight-testing during later phases of the test program. In flight-testing, we prepare for the unexpected and then take advantage of what we learn. Our carefully planned build-up approach and our disciplined CC crew members dedicated to following that approach has permitted us to methodically collect data and conduct valuable analysis. Our success this past weekend validates the effort.

Fig. 5 - 28May01 Flight Testing -- view from chase vehicle

Washington, DC, Officials Welcome Jay's Briefings

Jay made two trips to Washington, DC, this month to brief military and government officials on CC progress and goals. Jay hopes that once the CC program proves flight above Mu-1 is feasible, government agencies will provide the $10 million needed to build a prototype CC Heliplane - either in the utility or UAV category. Any assistance that readers of our web site can provide to further educate members of our military, Congress and the aerospace community - is greatly appreciated. Please let us know about your efforts in our behalf.

In four days of briefings, Jay met with the following people:

MILITARY

1. Lieutenant General Fred McCorkle, Deputy Chief of Staff for Aviation, US Marine Corps. He recommendation that we work to make the CC project one that is supported by several branches of the military.

2. Major General Bill Whitlow, Director of Expeditionary Warfare Division, US Marine Corps. Attending was CDR William Condon, Executive Assistant, Expeditionary Warfare Division and Peg Tysiak, Deputy Branch Head, Aviation Systems.

3. Rear Admiral John V. Chenevey, Principal Deputy Assistant Secretary of Navy (Research, Development & Acquisition) Act'g. His major interest was the adaptability of the CC concept to UAVs.

CONGRESS

1. LCDR Dell Bull, an active duty USN F-18 pilot serving as Navy fellow to Senator John McCain.

2. Thomas L. MacKenzie, a senior staff member for Senator John Warner. Senator Warner is on Senate Armed Services Committee. Tom clarified that even ACTD and ATD funds are already allocated for fiscal 2002 and 2003. The earliest that a CCH-T project could be funded in his view is in the 2004 cycle. He emphasized the importance of CC support from hometown senators and congressmen.

3. Melissa C. Wojciak, staff director for Congressman Tom Davis. Tom Davis is Chairman, Republican Congressional Campaign Committee and Chairman, Technology & Procurement Subcommittee.

4. Kim Kotlar, Legislative Director for Congressman Mac Thornberry. Congressman Thornberry represents the Texas district that includes Wichita Falls.

5. Other staff members of the Texas delegation that met with Jay include Thomas Sevier for Senator Kay Hutchinson, Trey Bahm for Congressman Mac Thornberry, Ryan Hightower for Congressman Tom Delay, Jim Richards for Congressman Henry Bonilla, and Amanda McPherson for Congressman Chet Edwards.

Amanda McPherson suggested that once the CC breaks the Mu-1 barrier, a joint letter signed by each member of the Texas Congressional delegation in support of a CC funding initiative would be possible.

AGENCIES

Ronald E. Mutzelburg, Deputy Directory, Air Warfare, Office of Under Secretary of Defense (Acquisitions, Technology & Logistics). Attending was an assistant, Joe Potts.

Jay Presents Paper at SAWE International Conference

Jay was invited by Berlin Benfield, co-chair of the V/STOL Committee of the Society of Allied Weight Engineers (SAWE) to present a paper at their International Conference held in Arlington, Texas, 21-23 May 2001. This was the third paper Jay has presented on CC technology at a major conference. It was titled "The CarterCopter Heliplane Transport (CCH-T): A new high-speed and long-range V/STOL for heavy and bulky payloads". The other four papers presented in the V/STOL session were by Sikorsky on the H-60 derivative, by Bell on the Quad Tiltrotor and Eagle Eye tiltrotor UAV, and by Boeing (Mesa) on helicopter preliminary design.

SAWE promotes the design and manufacture of optimum weight equipment, development of new materials and improvements in the state of the art. A very heavy emphasis is on aerospace. Membership is international and includes individuals in industry (both manufacturers and users), government and academia. More information on the organization is found at www.sawe.org

SAWE members are interested in CC technology because it is inherently lightweight - a fact that will permit the CCH-T to be the largest rotorcraft every flown. Until now, the combined weight of rotorcraft components has effectively prevented the existence of a large rotorcraft with a useful load. There are no upper limits to the size of a rotorcraft except those caused by the fact that as size increases, the weight tries to follow the cubed law; i.e. double the rotor diameter and the lifting capacity increases 4 times -- but the rotor weight increases 8 times (the same cubed law applies to wings). As they are scaled up in size, all aircraft designs eventually become so heavy that although they can fly - they cannot fly and still carry a useful load.

Using CC technology, the initial weight of any CC Heliplane design will be much lighter than previously possible for any given useful load. This permits the CC Heliplane design to be scaled to a larger size and retain a larger useful load than previously possible before the cubed law catches up. It makes the CCH-T possible. Lightweight CC technology includes the rotor, rotor head, props, prop hubs, landing gear, and the composite construction of the airframe. The largest rotorcraft currently flying have disk loadings as high as 15-lb/ft² to reduce the rotor diameter and the torque on the drive - solely to help get the aircraft's weight down. By comparison, the relatively lightweight design of the CCH-T will permit a disk loading of only 8.5-lb/ft².

*NOTE: Jeff Keaton joined CC on 20 April as General Manager. He is an instrument-rated private pilot and holds a BS in Mechanical Engineering from Oklahoma State University. Jeff is an accomplished manager with 13 years spent managing mechanical, electrical, and software engineering teams in various roles -- including product design and development, research, project management, and worldwide manufacturing and service support. His 23 years of professional experience as a Mechanical Engineer encompasses mobile information, wireless communication systems, computer, manufacturing, and music industries.