By Jay Carter, Jr. and Rod Anderson

MU 0.87: CCTD EXCEEDS NASA GOAL OF MU 0.8

Under CarterCopters' (CC) former NASA SBIR Phase III contract, NASA offered $50,000 per goal for five goals. We reached only the first goal -- performing a zero-roll takeoff with the CarterCopter Technology Demonstrator (CCTD) -- before the grant period expired early last year.

The most significant goal was for the CCTD to fly at Mu 0.8. This was the highest Mu-ratio previously achieved by large aerospace companies after years of major effort. Mu is the 'Greek letter' designating the relationship between the forward speed of the rotorcraft and its rotor-tip speed relative to the aircraft. Tremendous benefits occur from drag reduction when the rotor slows as the aircraft goes faster - which is indicated by the resulting higher Mu-ratios.

Last Friday, 3-22-02, Larry Neal and Brad King flew the CCTD to mu 0.87 - exceeding the NASA goal by a large margin. This historic achievement bears comparison with some of the all-time greatest aviation accomplishments. The CCTD is now flying in a realm of rotorcraft flight never before explored. The Mu 0.87 flight began at 170 mph with a rotor rpm of 125. The CCTD then maintained Mu 0.87 as it slowed to 163 mph and a rotor rpm of 120. The rotor remained stable.

NASA provided $870,000 total in SBIR Grants to help us achieve this major breakthrough in aviation technology. The goal took longer than expected - but the CC team's primary objective was to do it safely. The potential benefits of a VTOL aircraft that flies with efficiencies now found only in conventional fixed-wing aircraft - are enormous.

In addition to exceeding Mu 0.8 and doing a zero-roll takeoff, we have also completed two other of the NASA goals: zero-roll landings and flight above 10,000 feet MSL.

On two different occasions, zero-roll landings were made when the pilot flared too high with the aircraft dropping in from 3 ft and 10 ft. The extreme energy absorbing landing gear performed as designed, prompting a pilot comment "couldn't believe how soft the landing was". On two other occasions, a sticking valve prevented the main gear from extending. Both times the CCTD landed on its tail booms with zero-damage to the aircraft. All four landings were non-events.

On Tuesday, 3-26-02, Larry and Brad climbed above 10,000 feet MSL looking for calm air so we could obtain repeatable flight-test data from our 60-channel telemetry system. The flight lasted 45 minutes - which broke our previous time-aloft record. When a turbo is added (soon) to our standard Corvette LS6 engine, 30,000 feet should be possible.

The only remaining NASA goal is to fly 600 miles non-stop Our fuel capacity during flight-testing is limited to 18-1/2 gallons in a special fuel tank used for safety reasons. We calculate this is sufficient for a one-hour flight. The CCTD is designed to hold 160 gallons -- giving it a range of more than 1,000 miles at already demonstrated efficiencies. With additional drag reduction modifications, higher Mu-ratios and higher altitudes possible with the addition of a turbo, the range should exceed 2,000 miles. We expect to eventually fly at Mu 3-4. If we fly the CCTD to Oshkosh in July, the NASA goal will be met.

Other recent accomplishments include:

• Max speed of 173 mph in a shallow dive. With a turbo and additional drag reduction modifications, 250 mph should be possible in level flight at 25,000 ft.
• 800 fpm climb-out below 3,000 ft MSL with 3500 lbs gross weight, using 325 hp. A turbo will greatly improve this performance.
• 90-92% prop efficiency above 170 mph. 94-95% efficiency is possible above 200 mph.

DETAILS OF HISTORIC FLIGHTS

Friday, 3-22-02: Larry, our Chief Test Pilot, and Brad, our flight-test engineer, flew three flights on this historic day. Each flight broke our previous Mu-ratio record. The first flight achieved Mu 0.73. The second flight achieved Mu 0.8. On the third flight we achieved Mu .87 as mentioned above. The highest speed for the day was 171 mph. We stopped after the third flight because the CCTD began yawing back and forth at the higher speeds. This same condition had occurred previously. We had increased the speed at which yawing occurred by 20 mph by cutting 2-inches of the rudders -- moving the aerodynamic center (AC) of the rudder closer to the pivot point. We decided to cut an additional 1-inch off the rudders before continuing flight-testing the following morning.

After achieving Mu 0.73 on the first flight -- we decided to see how slow Larry could fly the CCTD. As he descended through 4000-ft AGL, he reduced the hp to 240 (approximately 85 hp less than the maximum available) and began slowing the CCTD concurrent with increasing the collective to keep flapping at around 4 degrees. At 30 mph the CCTD was climbing at 100 feet-per-minute (fpm) with the rpm at 210, the flapping at 3 degrees and the collective at its pre-set maximum of 7.4 degrees. Had Larry been able to pull more collective, the CCTD would have slowed even more. Holding 240 hp, the CCTD flew a short distance at 20 mph while descending at around 300 fpm. These results were a great confidence builder for the pilots. They saw that even with 7.4 degrees of collective, the CCTD rotor continues to autorotate without the rotor rpm dropping too low or the flapping increasing too high.

Saturday, 3-23-02: Larry and Brad flew the CCTD at sun-up hoping for calm air. They climbed to 8000 ft MSL before beginning flight-tests. Larry then flew for a while at Mu 0.85 (it is still a little hard for the CC crew to believe these Mu-ratios), at 165 mph and a rotor rpm of 125. He was delighted that he was able to control flapping and rotor rpm exactly as the system was designed. In the post-flight debriefing, both pilots commented they were thinking this was going be the day to break the Mu-1 barrier. However, they encountered wind gusts that cause first the rotor and then the entire aircraft to precess slightly like a spinning top that has been disturbed. This event was then followed by heavier gusts. Everyone had agreed during the pre-flight briefing that we must have calm air at this point in our flight-testing, so the flight was aborted.

The maximum speed reached during the flight was 170 mph. The additional 1-inch we cut off the trailing edge of the rudders cured the yaw oscillation problem until the aircraft started precessing. The yaw oscillation stopped as soon as the precession dampened out. We decided to trim just a little more off the trailing edge of the rudders to put the AC exactly on the rudder pivot axis. The problem with the precession is harder to band-aid. It is caused by the extra weight we added to the rotor stabilizer bar to keep the rotor inherently stable at these high Mu-ratios. Unfortunately, these same weights make the rotor act like a gyroscope when it sees a disturbance. Our new cyclic reverse lock works just as designed -- permitting the CCTD to safely experience these precessions.

Mu > 1.0

Exceeding Mu-1 is our next goal. A new rotor and computerized rotor-controls will be installed over the next 3-4 months to greatly reduce the pilot workload for this event. The recent flight-tests made it clear that at high Mu-ratios the rotor's plane-of-rotation is at a very shallow angle to the air stream. When Larry inadvertently lets rotor lift drop too low as the rotor slows, the slightest stick movement (or wind gust) causes the rotor plane-of-rotation angle to go negative - causing negative lift on the rotor. This in turn causes the rotor to start precessing due to the gyroscopic effect of the weights on the rotor stabilizer bar. Once the precession starts, Larry must input a positive lift during the following 3.5 seconds or the precession amplitude will increase. Larry found he could dampen-out the precession once it started or help prevent it getting started (except for wind gusts) by pulling a little collective to maintain positive lift. However, if he accidentally pulled too much collective - then flapping got out of control and he had to lower collective, slow the aircraft and abort the attempt to reach higher Mu-ratios.

The dynamics of the situation kept Larry too busy controlling flapping with collective and rotor RPM with spindle-trim for him to be effective. The solution is to computerize the process so that the necessary split-second corrections are made automatically. Utilizing our patented controls, we do not feel the current situation is dangerous - just too demanding of the pilot to stay on top of developing trends as required to reach the higher Mu-ratios. Many modern aircraft use computerized controls for just this reason - to compensate for the relative slowness of human reflexes. The design, programming, installation and proof testing of the computerized controls hopefully will be a relatively simple process.

The new rotor will not have weights on a stabilizer bar - which solves the precessing problem. Without a stabilizer bar, the spinner enclosing the rotor hub can be small - greatly reducing parasitic drag. The surface area of the new rotor will remain about the same but its weight should be about 80 lbs less. 50 lbs of this reduction comes from removing the stabilizer bar. A side benefit of the new rotor is that its design looks very strange. This will help set CC rotorcraft apart from helicopters at a glance. The unique look will fit right in with the unique CC prop, landing gear, twin tail booms and the other unique CC innovations.

While we are at it, we will install a small turbo so we can produce 400 hp up to about 20,000 ft and 300 hp to 30,000 ft. We will also install dual flight controls for the co-pilot. We still hope and will try our best to make it to Oshkosh this summer, even if all the new changes have not been incorporated.

MOST RECENT EFFORTS TO IMPROVE PERFORMANCE

Improving flight efficiencies through drag reduction modifications and other tweaking is an ongoing effort. Some of the recent efforts follow:

We recently modified the back of the engine cowling (above the prop spinner) to reduce parasitic drag. The vent below the prop spinner provides more cooling exhaust area than needed in cruise. Plans include adding an automatic closure to the vent to reduce parasitic drag at cruise.

Yarn tuffs were taped to the fuselage to study airflow during flight. The tuffs are recorded during flight-testing by the Mini-DV camera located in the top part of the right vertical stabilizer. The videos show that we still have airflow separation around the rear of the fuselage and the bottom-rear of the tail booms. A slight redesign of these areas should correct these problems.

CC PROP: Prop efficiency climbed from around 85% at 160 mph up to 90-92% at 170+ mph and 320 hp. The dramatic increase in efficiency was caused by the prop root coming out of its stall (high drag) condition. 94-95% efficiency should be possible at 200+ mph. We invite prop manufacturers who consider this high efficiency impossible to visit and go through the calibrations and test procedures with us.

The calibration of the prop thrust and engine hp was carefully checked twice and found to be accurate. The checks were made because the static thrust has dropped -- causing suspicion that calibrations were off. We now suspect that the static thrust has been reduced due to the computerized prop controller (CPC) being programmed to hold the engine rpm at a maximum of 5000. The CPC may position the prop pitch too high in its effort to hold the rpm at 5000. The static thrust prop-map (thrust vs. rpm and hp) will be recalculated when time permits to see if best static thrust occurs at a still-higher rpm.

CC PAPERS PRESENTED TO PROFESSIONAL ORGANIZATIONS

SETP: Carl Hawkins and Paul Smith, two members of the GAA, presented a paper 15 March on the subject of the CCTD and extreme-mu flight at the West Coast Symposium held by the Society of Experimental Test Pilots in San Diego, CA. Their presentation was well received by the 75-85 test pilots who attended - representing the US Air Force, Navy, Army and various aerospace companies. There is a chance that Carl and Paul may present the paper again at the East Coast Symposium being held next month in Washington, D.C. and at SETP's largest symposium taking place in Los Angeles this October. The SETP web site is found at www.setp.org.

AUVSI: Rich Kraemer's paper was selected as a Poster Session / Presentation Alternate at Unmanned Systems 2002 (July 9-11) - an international symposium held by the Association for Unmanned Vehicle Systems International. The designation guarantees him the opportunity to present his paper at a poster session. If someone cancels at the concurrent main session, Rich will substitute. His paper details the benefits of the CC propeller system over other propellers that are currently available. The CC prop's extremely high efficiency has generated a lot of interest from UAV manufacturers wanting to increase their aircraft's performance. The AUVSI web site is found at www.auvsi.org

SUN 'N FUN 2002: 7-13 APRIL

FORUM:Jay Carter, Jr. will present a forum on Tuesday, 9 April, 12:00 noon, in tent # 3. Everyone is invited to attend. The forum will provide an update on CCTD flight-testing and includes recent videos of the CCTD. Efforts to interest qualified manufacturers in licensing CC technology for a CC kit-plane quick-build facility will be discussed. He will also show the illustrations developed by the GAA for their SETP paper explaining Mu-flight. A Q&A session will follow. The Sun 'N Fun web site is found at www.sun-n-fun.org/content/flyin/main.asp

PRESS CONFERENCE, DAY #1: The press is invited to a catered Sunday luncheon & press conference at 12 noon on April 7th. S'nF officials will provide the location when they announce the event at the Sunday morning briefing. They will also post a notice at the Media Building beginning Friday, April 5th. Contact Rod Anderson at cartercopter@earthlink.net / phone: (520) 316-0170 if you have any questions or would like to arrange an interview with any of the CC personnel attending S'nF -- including Jay Carter, Jr., Claudius Klimt, Guy Ullman, Greg Lynch and Rich Kraemer.