August 29, 2013
By Jim Moore
A Canadian aircraft maker developing a new light sport aircraft claims that flight tests have demonstrated the two-seater will not spin.
SAM Aircraft President Thierry Zibi issued a press release Aug. 27 touting flight test results, providing links to online videos, and offering brief excerpts from a test pilot’s report on the SAM LS. The aircraft is being developed as both a kit and factory-built aircraft, with deliveries expected to begin in 2014.
“Our test pilot tried to make it spin, and the SAM just spirals… He also crossed the controls; the SAM buffets and goes nose down,” Zibi said in the news release. “The SAM won’t spin -- and we tried hard to make it spin.”
Without naming Icon, which was recently granted an FAA exemption to the light sport aircraft (LSA) weight limit on the strength of a spin-resistant design for its two-seat A5, Zibi claimed there was “more than one spin-proof design at Oshkosh this year!”
It is unclear to what extent the SAM LS has been tested, and Zibi said in an email that there are no plans to seek independent validation of the results, appearing to suggest that customers will themselves validate the spin-resistant quality of the new design: “At this time, we will not ask a third-party verification, but that will be soon the case when more and more SAM will fly, this characteristic will be third-party confirmed,” Zibi wrote. He did not respond to a subsequent email seeking additional detail about the flight tests conducted.
The YouTube videos posted to demonstrate the aircraft's (attempted) spin and cross-controlled behaviors do not show clearly the control inputs applied during the maneuvers. The pilot appears to be alone in the tandem seat design, with the rear seat empty.
William J. Fredericks, a NASA aerospace engineer with the Aeronautics Systems Analysis Branch at NASA’s Langley Research Center, said with the rear seat unoccupied it would be much more difficult to induce a spin, because the center of gravity would be toward the forward end of the envelope.
“As you move the CG aft, it’s easier to spin the airplane,” said Fredericks, who is familiar with recent aircraft design efforts but not involved in the development of Icon, SAM Aircraft, or other commercial designs.
Fredericks noted that the side-by-side seating arrangement of Icon’s A5 is part of what helps it resist spins, limiting the aft excursion of the CG. Combined with aerodynamic features and limited elevator travel, the side-by-side arrangement helped Icon achieve its design goal of resisting spins. Accomplishing the same in a tandem seat aircraft is “a much more challenging bar to reach,” he said.
Dan Johnson, president of the Light Aircraft Manufacturers Association, said in an email that he considered the assertion that “SAM won’t spin” to be “merely a claim and not particularly meaningful therefore.”
Johnson softened his stance in a follow-up email: “Since we corresponded, I watched their videos and the test pilot really messed up the controls worse than most customer pilots might, yet Sam LS did not respond poorly.”
Zibi said in his email to AOPA Online that the design team did not set out to make the SAM LS resist spins.
“To be honest, spin resistance wasn’t a design goal, even though we wanted a safe aircraft, easy and enjoyable to fly,” Zibi wrote. Spin resistance “was a surprise for us, a great surprise.”
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