The CFM Leap 1-B had a 5% short fall last month coming off its bench testing. Now that it is under wing several key players in its development have come forward and said those numbers misrepresented what was really happening to the CFM Leap 1B. Smiles have returned to the Boeing execs faces in lock step. It is a key indicator of a hasty news report about the CFM engine. The 68" front opening of the MAX directed engine has achieved early bench marks while under wing on the 747-400 test bed. No one has said exactly what has happened to that 5% low ball short fall number, but it appears the first tune up during its flying testing has moved the efficiency needle back closer into the 14% efficiency realm it has promised its Max customers. Quiet backslapping is a great indicator of corporate relief.
The MAX is on track again with CFM and Boeing. The testing and tweaking process has begun. Innovation is once again a hold card, once all normal progressions are completed. The CFM at 68 inches has achieved theoretical performance it had claimed when compared with the Airbus CFM Leap 1-A 79" diameter. The 1B will be lighter than the 1A. It has an Aerodynamic sweet spot compensating for the Airbus advantage of its larger 78" for the A-320 family.
The rule of thumb is a bigger diameter jet engine produces better efficiency than one with a lessor diameter. In Boeing's case they had to find a better preforming CFM Leap 1B than the Airbus Leap IA configuration. Boeing reached back in its bag of tricks for some aviation Trickeration for the 12" smaller diameter engine using wing placement adjustment and center of gravity considerations. Drag elimination on the engine nacelle with new aero design points mitigating any so called engine drag and from a lighter over-all single aisle structure than Airbus with its engine weight. Even though CFM shares its technologies with Airbus, Boeing seeks a greater performance efficiency out of a smaller engine size.
The gauntlet was laid down for CFM, where Boeing asked for more Carbon Fiber or plastic components with its engine needing a greater heat dissipating properties under its nacelle than the prior CFM's. The trend line for the Leap 1B indicates more innovation on the engine and aircraft complying with the MAX design points for having a low engine clearance on the ground. Secondly, the engine, frame fit, and performance must work more within the MAX design, as a sum of all its contributing parts equals optimal performance for Boeing and CFM. The Leap 1A with Airbus may have a role of all CFM efficiency are hung on the wing, and are found just within the engine. The Leap 1-B is a solid two team project integrating the MAX with The Leap as a Joint solution in performance.
Considering the chart above it appears the 737 NG has a 6% head start before the MAX had announced its inception for development. Now it will lead by 5% at the end of the day. The caveat is seats available is greater for the MAX. This does not include the A-321 frame which is a separate class of Single Aisle. The MAX 737-9 is also not part of this discussion as shown by the chart above.
The testing that is occurring is an epic change to the paradigm for single aisle aircraft engine building. The Boeing smiles this week indicate a self-assured positive outcome. Getting the CFM off the bench and flying was a great idea, and long over-due from a press point of view. Actual final efficiency numbers are usually understated as an error towards being conservative for all concerned until it goes on the MAX itself.