Frank Piasecki, the aviation pioneer who invented the big twin-rotor helicopter that has carried soldiers into battle and rescued thousands from disaster, died today after becoming ill in his Main Line home.

The helicopters he developed, the Army's Chinook and the Navy's Sea Knight, are now built by the Boeing Co. Rotorcraft Division in Ridley Township, a Philadelphia suburb.

In 1943, Mr. Piasecki, who was born in Lansdowne and lived most of his life in Delaware County, became the second American to build and fly a helicopter, following Igor Sikorsky who flew his first in 1941.

Mr. Piasecki and his wife, Vivian, raised seven children. Daughter Nicole Piasecki of Tokyo is president of Boeing's operations in Japan. Two sons, Frederick and John, are vice presidents of his company and are carrying on his work.

He was an accomplished violinist - concertmaster of the orchestra when he was at the University of Pennsylvania - and a gifted amateur photographer.

Chuck Allen, head of Boeing Rotorcraft, called Mr. Piasecki "a visionary and an amazing designer. . . . He will always be remembered as a pillar of American aerospace history. His daring and courageous approach to vertical flight inspired years of advancements."

At age 88, Mr. Piasecki remained chief executive of Piasecki Aircraft Corp.

When Mr. Piasecki fell ill today at his Haverford home with his wife Vivian at his side, his chief test pilot, Steven A. Schellberg, was in the air completing a key phase of testing his latest invention - a ducted fan to replace a helicopter's vertical tail rotor and increase speed and maneuverability.

Advanced age and strokes had diminished his physical agility, but his mind remained sharp and his death came as a shock to coworkers.

"He's the father of Boeing Rotorcraft. We would not be where we are without his mind and entrepreneural skills," J. Patrick Donnelly, Boeing's director of advanced rotorcraft, said in an October interview. "He struggles physically, but we still have conversations with him about our work. His mind is very fertile."

Donnelly made the comments in an interview at Piasecki's birthday party in October. The event was held in Boeing's hanger at New Castle County Airport, where Mr. Piasecki is testing his latest invention on a modified Sikorsky Black Hawk helicopter, renamed "Speed Hawk."

"Pi," as his friends called him, "was really a visionary . . . a creative engineer with a lot of energy and imagination," said Joseph P. Consgrove, his friend and colleague since 1955, also interviewed at the birthday party.

He and others described Mr. Piasecki as a table-pounding and demanding boss who never held a grudge and would later say thank-you to those who stood up to him.

His son, John, said as a boy his father often awakened him with questions on what he planned to do that day. In his birthday tribute to his father, his son said he was always challenged to "see how he could do something, not why not."

Mr. Piasecki did not set out to find uses for ideas that came to him, Consgrove said. Instead he was always working to solve a problem or fill a need. He developed the tandem-rotor helicopter, for example, in response to the military's need to lift and transport more weight than single-rotor helicopters could handle.

The first version was dubbed "the flying banana" because of its shape. The rear curved upward to elevate the rear rotor over the forward rotor.

The Navy is replacing his Sea Knight with the V-22 Osprey, which takes off like a helicopter, then tilts its rotors to fly like an airplane.

But new models of the Army Chinook have fresh transport and special operations missions and is being pitched to the Air Force for search-and-rescue missions. Boeing says Mr. Piasecki's creation, which flew soldiers to remote parts of Vietnam in the 1960s, will keep flying well beyond 2030.

Mr. Piasecki gave up control of his first company to get funds to build the big factory in Morton, Delaware County, to mass produce the tandem-rotor helicopter. While investors pressed for financial rewards from his invention, Mr. Piasecki wanted to keep creating new technology.

In frustration, he left the company and its name was changed from Piasecki Helicopter Co. to Vertol Aircraft Corp., which Boeing acquired in 1960.

In 1955, Mr. Piasecki formed his current company, Piasecki Aircraft Corp., and went on to achieve a long list of firsts in expanding the capabilities of vertical take-off aircraft.

He was born Oct. 24, 1919, in Lansdowne, Delaware County, but he remained loyal to his family's roots in Poland. After the Berlin Wall fell, he went to Poland at urging of President George H.W. Bush to help its aircraft industry meet U.S. certification standards.

Several who attended the October birthday party said that Mr. Piasecki always pushed to create something new at a time when others have been mainly enlarging or refining existing aircraft.

His new Speed Hawk changes helicopter flight in several ways, test pilot Shellberg said. Conventional helicopters achieve speed by tilting forward and counter the rotation of the horizontal main rotor with a small vertical tail rotor, both of which creates drag. Mr. Piasecki's ducted fan, with fins to direct thrust, push the aircraft forward, counter the main rotor's torque and keep it level.

"This gives it more speed and range and it doesn't give up maneuverability," said Kenneth R. Pribyla, a retired Air Force colonel who works for Piasecki Aircraft. Unlike conventional helicopters, it doesn't "bleed off speed in turns," test pilot Schellberg said.

The next phase will be to clean up the Speed Hawk with retractable landing gear, farings and other refinements to see just how fast it can go.

The family will meet Tuesday to plan the funeral, son John Piasecki said.

Mr. Piasecki is survived by his wife and their children: Lynn Piasecki Cunningtham, Nicole Piasecki, Fredrick Piasecki, Frank Piasecki, Michael Piasecki, John W. Piasecki and Gregory Piasecki.

Contact staff writer Henry J. Holcomb at 215-854-2614 or