Rolls-Royce and Allison Lift Engines

Both Rolls-Royce and Allison undertook significant lift engine development during the 19551975 period, initially separately and later collaboratively, culminating in the joint development of the XJ99 in the late 1960s and early 1970s. Lift engine development efforts at both engine manufacturers are reviewed, along with planned aircraft applications. A summary of the XJ99 development and its unique characteristics is included.