(U) It was originally intended to use an advanced turbojet as the baseline
engine for this concept, with a variable-cycle engine to be used as a trade
study. However, the initial sizing exercise quickly revealed the impracticality
of this approach (Figure 100). The turbojet aircraft weighs almost 9 million
pounds, which is totally unacceptable. Therefore, a variable/multiple-cycle
engine comparable to the engine discussed in the paragraphs on low-cost trades
was employed on the baseline.
(U) Also, the Rockwell multimode integrated propulsion system (MMIPS) was
examined for this aircraft. A MMIPS could provide SFC improvements of
approximately 3 percent at subsonic cruise and at penetration relative to the
VCE baseline. This would be achieved by using a fean engine with a higher bypass
ratio, approximately 2.5, sized for subsonic cruise, and sizing the turbojet
for takeoff and penetration,. The MIPS weight would be approximately the same
as the VCE baseline because the significantly higher takeoff specific thrust
of the MIPS would allow smaller engines. While SFC is extremely important in
the minimum time penetration aircraft, the modest improvement the MIPS offers
tends to be offset by the complexity of the installation. Thus, the MIPS was
not analyzed further.
