 Modifications were completed on the Ames model and testing resumed in April 1961. The new design demonstrated much better control in hover and considerably improved lift. The vehicle was now able to travel at up to 100 knots (190 km / h), a great improvement over the 30 knots (56 km / h) previously reached. However, it remained unstable in pitch, and exhibited a strong nose-up trim. NASA engineers attempted to modify this with a T-tail, but this proved to sit within the airflow of the turborotor and did not help. Frost's team considered two new designs, one with a large vertical tail and one with a wing with tip mounted verticals — "winglets." Both designs used two 2,700 lbf (12 kN) thrust General Electric J85 turbojets and increased the turborotor diameter from five to six ft.
