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Sun, Apr 25, 2004

CarterCopter Advances towards Mu>1.0 (Part 1)

By ANN Correspondent Kevin "Hognose" O'Brien

A recent CarterCopter press breakfast should have been called a "press brunch." The Carter people had so much news to put out that 2 1/2 hours after starting they were still going strong when the next outfit in line to use the media room ran out of patience entirely. As they were throwing the Carter crew out of the room, I was still learning new stuff from Carter's people, including Jay Carter Jr. and Anita Infante.

During the briefings, Carter's team had four major announcements, each of which probably justified a press conference of its own, but the Carter crowd would have to give up their research and engineering if they took on the burden of feeding the ravenous press four times.

The four announcements were, strictly in my understanding of their importance: The resumption of CarterCopter Technology Demonstrator test flights as of December 6, 2003, Carter's co-invention of a revolutionary new patented landing gear which is adaptable to many kinds of aircraft, a NASA contract for a new Personal Aerial Vehicle design, and an Army contract for test flight & test flight data analysis.

In addition, numerous details of Carter's thinking and future plans emerged from the marathon conference. It was time well spent.

The CarterCopter Flies Again

Just over a year ago, during a demonstration flight for brass hats from the world's largest user of rotary-winged aircraft, US Army Aviation, test pilot Larry Neal demonstrated something that wasn't part of the flight plan: the structural strength of the CarterCopter cabin (shown right). The gyro convertiplane, which had been flying consistently since September, 1998, and which had completed over 360 hours of groundbreaking flight, slammed hard onto the runway with gear retracted. The tail booms, belly skin, rudders and propeller were all seriously damaged or destroyed.

At Oshkosh last August, Jay Carter showed video of the accident from inside and outside the machine, complete with the callouts of "Gear! Gear! Gear!" as another aircraft entering the runway distracted Neal at exactly the wrong time. The crew was unhurt but the gyro was substantially damaged. To Carter Aviation Technologies, this meant an opportunity to rebuild and improve the machine, even if that meant it would be grounded for longer than simple repairs would take.

The rear fuselage, tail booms, wings and rotor all needed rebuilding. After the last rebuild, Jay told us, they had to add "100 lb lead in the nose… there's been so much repair and Bondo and all that we are now up to 300 lb of ballast overall to keep our mass balance." Improvements were included throughout. A new, lighter and differently shaped prop and spinner were made, the better to take the thrust of an engine increased from 5.6L (350 CI) to 7.0L (427 CI) displacement, and now turbocharged. The turbocharger is used not to boost power per se, but to normalize the new motor' 400HP up to 20,000 feet (as estimated by Garrett, who consulted on the turbocharger system). The more power isn't there just for its own sake, but to power the machine to high altitudes - and past Mu=1.0 into the unknown beyond. "We intend to expand the envelope," Jay said quietly, then, as if he realized that some of the journalists present were not aviation-oriented, and hadn't seen The Right Stuff, he translated into plain Texan: "We're gonna go pretty fast."

The sensors of the electronic flight control system were rewired and a number of previously manual pilot-workload tasks were automated, including automatic flapping control , automatic spindle trim for RPM control, and automatic collective. Jay: "Automatic controls really make this pilot-friendly. The idea is to reduce workload. We have automated it so that the collective is push-button." In other words, the pilot can simply toggle the auto-collective on and fly the machine with stick alone, like a Cessna. The flight control computers manage energy and control all parameters of the system. The system, says Jay, "looks at rotor RPM, flapping, speed; it takes that all into effect and account." What if the pilot disagrees with what the automatic system is doing? "He can push a button and override it any time."

Of course, flight control computers that advanced make pilotless flight possible. "We are leaning toward a totally autonomous vehicle - so it can fly as a UAV."

The Propeller

The propeller of the Carter Copter Technology Demonstrator is a scimitar-shaped composite structure of 8 foot diameter - the whole propeller weighs 15 lbs.

Jay Carter believes the prop has more thrust to weight than any propeller, and that it can safely be spun faster. "We could go supersonic [meaning the prop tips]. One of the things about this scimitar design is it fools the air over the tip into thinking it's going slower. So we more efficient, quieter, increased chord at tip - what ended up is a little more tweaking, it really improves our climb and our static thust. It was not something I planned but it just worked out that way."

The propeller doesn't have any bearings; it just twists. It's free to flap, which prevents gyroscopic loads. The propeller is currently If we can break Mach 1 for 10 minutes, then we may try to go to Mach 1. Difficulty goes up exponentially when you cross the speed of sound. We're looking at 600 HP, so we can absorb 1200 with four blades. We will have a turbine and this adds up to more thrust."

"We'd like to find somebody to work with us, maybe in racing. That'd be a great place to work with us."

Prop RPM is 2500 for take-off and 1700 at 300 MPH. "We actually have a computer that looks at TAS, temperature, HP going into prop, and varies RPM for optimum. It will do for prop efficiency what solid-state ignition has done for propulsion."

Data Collection

Data is collected on 84 channels of information, including some things never before tracked on a gyro, like propeller pitch, thrust and efficiency. Rotor parameters including Rotor RPM, L/D, blade pitch, flapping and Mu-ratio are also monitored.

To be continued...


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