Diamond’s single-engine five-place D-JET prototype S/N 003 arrived Thursday at Oshkosh with blended winglets that change the jet’s look and improve its performance as the jet heads toward advanced performance testing. Diamond’s test program has flown about 70 hours since January. Test pilot Mark Elwess told AVweb the winglets have delivered measurable improvements in cruise,low-speed handling,roll authority and lateral stability. “It handles like a sports sedan,” said Elwess, “and now it’s better.” A forthcoming prototype, S/N 004, will be a conforming model that reflects the now “frozen” aerodynamic design and incorporates some changes not seen in S/N 003. Diamond hopes to take that design through certification. And the company’s specific plan for certification means some exciting flight testing may still lie ahead.
According to Elwess, the winglets have improved dihedral effect and improved roll control at all speeds, especially in slow flight. He said roll-off in stalls performed at idle in the landing configuration previously could be as much as six or seven degrees. The new winglets have cut that to three. But the company is following an approved and extensive program that allows it to seek certification with a stick pusher instead of normal spin resistance testing. The idea is that a properly applied stick-pusher system prevents stall, and without a stall there is no spin. Diamond’s task now is to show that the stick pusher performs properly in all configurations. That means Elwess will be flying abused stall entries, including a wide range of yaw rates, to satisfy regulators. Assuming success, Diamond is planning to achieve certification in about 18 months.