Subtle aerodynamic changes to 737MAX beyond blister

Most of the changes announced by Boeing today for the firm concept milestone of the 737 MAX are on the inside – bigger LCD displays from Rockwell Collins, confirmation of the electric bleed and revised nose gear leg retraction from Honeywell. However, there are a couple of notable tweaks to the aerodynamic features on the exterior that have come out of Boeing’s intensive high and low-speed wind tunnel campaign to shave off a few more percentage points of drag.

Nose configuration before (above) and now (below)

The most obvious of these is the elimination of the chin blister which Boeing briefly considered as part of its move to the larger, 69.4 inch fan diameter CFM Leap-1B engine. This required an 8 inch nose leg extension which, in turn, needed additional room for nose leg actuation. Boeing and Honeywell have successfully re-packaged this mechanism and revised the internal structure around the nose leg ‘dog house’ to accommodate the longer nose leg without the need for the bump.What’s perhaps harder to see are the more subtle changes around the positioning of the engine on the wing and the alterations to the nacelle configuration. Close examination of the updated firm concept for the 737-8, the first MAX version due to be assembled and flown, shows the engine location has been moved forward slightly and cantilevered further out ahead of the wing. This is likely to help offset the ground clearance issue as part of the decision to re-jig the nose leg retraction mechanism and delete the chin blister. In addition, the nacelle trailing edge and strut have moved forward, improving aerodynamic interaction with the wing. However, this also means that the aerodynamic vane on the inboard of the nacelle, which was originally deleted form earlier designs, has had to be reinstated.

Engine, nacelle configuration before (above) and now (below)

Tags: tw99, Boeng, 737MAX, Rockwell, Collins, Honeywell, CFM, Leap-1B