Jetrader - Spring 2018 - 21

This is a follow-up to the "Advancements in Engines" article,
written by IBA and published in the summer 2012 edition of
Jetrader. On occasion, Jetrader will revisit past content with
an eye on how the forecasts and predictions have held up
while providing a fresh look at a previously covered topic.

Rather than invest large sums of money into the development
of clean-sheet airframe designs, in recent years OEMs have
elected to redesign, improve and re-engine already successful airframes for the next generation of aircraft. In many of
these cases, the engine accounts for a significant proportion
of the efficiency savings.
Innovation in the aero engine industry is a constant process
to stay one step ahead of the competition. Take the Rolls-Royce
Trent 1000 for example. It competes against the GEnx on the
Boeing 787 platform. Six years after entering service in 2011,
Rolls-Royce developed an improved model, the Trent 1000-TEN,
with more than 70 percent of parts either new or changed from
the initial models. The Trent 1000-TEN contained technology
through research attained from the Advance3 program and its
sister engine, the Trent XWB.
There are myriad factors that an engine OEM has to consider
when designing and manufacturing an engine. The OEM must
ensure the operating and maintenance costs remain low, and
reliability is high as these are key considerations for an operator during engine selection. The OEM must also comply with
emissions and environmental regulations. These factors are
largely tied to the propulsive and thermal efficiencies of an
engine. In a nutshell, the goal is to develop an engine with
as great a propulsive efficiency - that of the fan system, and
thermal efficiency, that of the core - as possible.
Achieving these gains is proving increasingly difficult,
particularly with current engine architecture, as much of
the improvements are incremental rather than offering a
step-change in efficiency. Advanced material development
is costly and bypass ratios can only increase so much before
size and weight become prohibitive and negate any perceived
gain. However, could a demonstrator developed 40 years ago
provide the answer?

Open Rotor
A new concept was born in the 1970s at the height of the
fuel crisis. It was a marriage that brought together the performance of a turbofan and the fuel efficiency of a turboprop.
The concept was dubbed the propfan, also known as an open
rotor or unducted fan due to its shroudless, contra-rotating
fan blades. GE developed perhaps the most notable engine, the
GE36. Boeing intended to offer it on the 7J7 while McDonnell
Douglas saw it as an option for the MD-94X.
As part of a testing regime, McDonnell Douglas fitted
the engine onto the left-side fuselage of a MD-80 aircraft.
Astonishingly the open rotor was able to achieve a 30 percent
improvement in specific fuel consumption over the JT8D turbojet. With such promising results, GE and McDonnell Douglas
flew the aircraft to the 1988 Farnborough Airshow in an attempt
to market the engine, but not all was rosy. Noise and vibration
Jetrader * Spring 2018 21

Jetrader - Spring 2018

Table of Contents for the Digital Edition of Jetrader - Spring 2018