Friday, May 8, 2015

The 737 CFM Leap-1B Is under The Boeing Wing (Updated)

The infamous CFM-International Leap-1B is currently under a 747 wing at the start of its extensive testing. What gave its infamy is the 5% performance shortfall on the bench testing recently, which causes major concerns for the program when competing with the Airbus A-320 NEO. Boeing has already sold 2,724 Max to customers with this one only engine type. Boeing placed all its eggs in the CFM basket, as it has done for the 737 since these many years it has been flying.

Image result for CFM Leap 1-B
The next two years testing by both CFM and Boeing must improve the newly conceived engine by the 5% short fall. Heat mitigation design points, and internal inefficiencies are two areas under the engine builders’ scrutiny while it flies attached to the 747-400 test bed. Both Boeing and CFM have to make up the inefficiency metric within its 69.4" diameter. The fixed 737 engine opening is at maximum, negating any expansion of diameter compared with a similar engine found on the A-320 NEO's CFM Leap 1-A, 78" engine diameter. The "efficiency rule of thumb", suggest a bigger diameter for better performance through aerodynamic attributes. Where the additional space gives a natural and better performance with additional mechanical space. A tighter engine makes for a hotter engines losing some performance. The NEO CFM Leap 1-A engine has a 2% shortfall at this time at its 78" diameter. Boeing's tighter Leap 1-B must find ways for an additional 5% improvement during the time it sits attached under the 747 testing wing.


Several publication have suggested new ceramics for dissipating and withstanding heat build-up as one area CFM must achieve a percentage improvement. A combination of tuning the new engine through compression ratios, and engine parts modifications can go only so far when installing PIP's (Performance improvement package) derivatives. Typically a PIP cycle takes vast amount of time for implementation. The CFM Leap 1-B could be making at least two PIP's to improve the engine performance up to 5% from its bench test metric. CFM has these two years of flying test to do it in. How they can do it? Obviously through maximizing its every aspect of thermodynamic testing on composite parts and reconfiguration for the mechanical optimization of this jet engine. CFM has to stay within the lines of a 69.4" diameter. CFM can't cheat the diameter upward by making the 737 Max engine a larger opening, as found on the 777X when it meets engine efficiency targets. Boeing sold the Max to its customers on the premise it will achieve its "established" on paper "bench marks" for efficiency during the MAX project.

Both Boeing and CFM are searching for percentage points in multiple areas rather than just one area.

Here are the key areas they need to find percentage point improvement.
  • Engine Weight Reduction by a slight amount.
  • Advanced Heat resistant & ceramic-plastic parts over the current parts installation.
  • Optimal engine placement on wing moving it frontward or backward by a few mm's or cm's.
  • Tweaking compression by-pass metrics
  • Boeing helps with airplane design aerodynamics and airplane weight.
Any combination of these areas receiving a measurable testing improvements, will come off the bench, and is frozen as a test PIP. Then it's placed under -the-wing as test copy on the 747 Boeing aircraft, for actual en-flight testing.

CFM/Boeing have two years to make up this short fall by method testing each objective area.

Recent news reports show promising results: Air wise Report Link Below

"Separately, a senior industry figure familiar with the LEAP engine described the shortfall speculation as "absolutely false." Another industry insider familiar with the matter said talk of a shortfall was inaccurate."

The Airbus Leap 1-A with its 2% short fall has different testing constraints from its bigger diameter engine. They have an easier road to go where any improvement can be passed through for consideration on the 1-B. However, since Boeing needs innovation in more areas, and since the 1-B is constrained by 69.4", its innovation may not be transferable to the 1-A scenario.

Before Max

MAX Trickeration
Photo From Aviation Week

Boeing's trickle down design problem starts with aircraft landing clearance and its landing gear. It would have to redesign the whole frame for accommodating a taller gear folding into the body. Next would be a push back on all engineering space available in the aircraft. The argument for a clean sheet design would be made by having a taller landing gears for its bigger engine opening. Boeing chose to improve the 737 by a giant "Leap" step, and not change the frame configuration by doing so. 

The CFM 1-B is confined by ground clearance since its using 737 NG configuration theme of a low- to - the - ground engine placement. The question remains, will they do it?

My answer, is sort of and very close:

The engine can better itself by 3% as an instinctive estimation for CFM improvement. Boeing will chip in another 1% for its part with Aero design trimmings when the MAX flies. With a "Test PIP II" and a Boeing effort in total, will make the 4%+ offset the 5% lost indicated during its first and formal bench tests. Customers will be satisfied, since it will achieve an advantage over the competition (A-320) with a significant efficiency separation over the  the CFM Leap 1-A hung on the A-320 NEO. Maybe the 5% shortfall is a false flag operation for Airbus' sake.

A Winging It Follow-up has found CFM, also had placed a loosely fitting 1B engine on the bench representing what a worn out 1B would simulate after approximately five years of service. Having observed this important fact, I can take several conclusions on this new knowledge.

1. Having a loose  engine tolerance will significantly under perform expectations found in a new engine delivered with factory tight tolerances. CFM knew this would be an outcome from this test but it didn't know by how much. The one formally tested, was a under performing engine configuration representing what a customer may expect from an engine at the end of its life cycle.

2. Finally, lessons learned from airborne 747 testing, will include significant changes optimizing the CFM-1B configured engine, in addition with Boeing's own aero packaged, improvements mating the the 1B engine nacelle with 737 Max body dynamics, optimize a more efficient body enhancements with new lift and drag coefficients saving fuel and workload for the engine  

The claim by others who became a town cryer for a 1B -5% shortfall were only correct within limited facts about the test, and have greatly underestimated what the 1B will demonstrate on the first 737 Max in flight testing. Indeed it should meet the high expectations mapped at the beginning of this program, a 14% improvement over older 737 single aisle models. Airbus has much to be alarmed with when the situation of the block tests is exposed. Those on the project cannot say out of confidentiality, but can smile at the hubris of a -5% shortfall report.