 Landing was challenging as the big wing would fly at very low speeds, and the small thrust the engines produced at idle made it difficult to reduce speed for touchdown.Even with the spoilers out and landing gear extended, the plane had a very low sink rate and pilots resorted to holding the RB-57Ds into a series of slight stalls to get the aircraft down to the runway.Only 20 RB-57Ds were built, but there were four basic variants that each had mission specific changes incorporated into the design.