Jetrader - Spring 2018 - 23

was an issue inside the cabin even when
mounted at the rear of the fuselage. Airlines
never truly bought into the concept, public
perception was an issue and, by that time,
oil prices had plummeted. Acquisition of
the engine would be costly for a minor
operating advantage given the economic
climate and that turbofans were proving
more reliable. The open rotor was dead.
At the same time, sales of the CFM56
took off following issues with the V2500.
As a 50 percent shareholder in CFM with
Safran, GE didn't want to impinge on those
sales and shelved the project. The success
of the CFM56 would continue for the next
four decades. Building on that success, CFM
developed the LEAP engine to power the
next generation of narrowbody aircraft.
Not all was lost from the GE36 programme
though. GE leveraged the experience and
technology gained from developing composite fan blades for the unducted fan and
applied them to the GE90, and later the
GEnx. The CFM LEAP engine was able to
reap the benefits as it features 18 fourthgeneration 3D-designed carbon fiber composite fan blades. Coupled with a composite
fan case, this has enabled CFM to reduce
engine weight by around 1,000 pounds,
compared to a fully metal fan and case.
Drawing on core technology from the
GE90 and GEnx, blisks - bladed disks -
are used within the compressor of the LEAP.
This reduces the parts count, weight and
maintenance costs. Although the LEAP features extra stages compared to the CFM56,
which, in theory, should increase maintenance costs, CFM claim that costs and
removal intervals should not be much different to its predecessor due to the materials and technology used. Rolls-Royce was
able to generate a 15 percent weight saving
from the high-pressure compressor (HPC)
of the Trent XWB through the use of blisks.

such as the CFM56-7B have 24 fan blades,
while CFM56-5B engines have 36. However,
with increasingly powerful super computers
and the use of 3D air-flow-modelling software, the LEAP fan blades were designed
to require just 18 fan blades.
This trend is not restricted to narrowbodies. Large widebody turbofans such as
the Trent 7000 feature 20 highly swept fan
blades, a reduction from 26 blades on the
Trent 700. The next widebody engine to
enter the market will be the GE9X in 2020.
This will solely power the 777X and features

just 16 fan blades compared to the GE90,
which had 22. And 3D aerodynamic modelling can be seen throughout the engine.
Compressor and turbine blades are modelled
with 3D aerodynamics to ensure they minimize losses and inefficiencies and extract
the greatest work from the airflow.
To improve thermal efficiency, many
OEMs are using lean-burn combustors. GE
has developed the twin-annular pre-mixing
swirler (TAPS) combustor for the GEnx,
a second generation TAPS II combustor
for the CFM LEAP and a third-generation

Moving Forward
Advancement in materials has seen
ceramic matrix composites (CMCs) adopted
across hot sections within engine cores.
These materials require less cooling, are
lightweight and have a higher resistance
to temperatures than metals. Both LEAP
and the GE9X have components made from
CMCs in the High Pressure Turbine (HPT).
A common trend among new engines on
the market is the reduction in the number of fan blades. Existing CFM56 models
865888_Novus.indd 1

www.novus.aero

Jetrader * Spring 2018
23
4/13/17 1:15 AM

http://www.novus.aero http://www.novus.aero

Jetrader - Spring 2018

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