June 16, 2023, ©. Leeham News: This is a summary of the article Part 17P. Airframe with lower induced drag. The article analyzes Boeing 737 MAX 8-sized airliners with Truss Braced Wings versus wings with folding wingtips and the standard MAX 8 wing. We use our Aircraft Performance and Cost model to get the drag data and overall efficiency improvement for the concepts.
We run a Boeing 737 MAX 8-sized Truss Braced Wing (TBW) airliner, with a configuration like in Figure 1, against today’s MAX 8 and against a MAX 8-sized aircraft with an extended cantilever wing with folding wingtips in our Aircraft Performance model.
All three aircraft have a similar fuselage size and cabin capacity, using the MAX 8 data for all three. The TBW version has a 52m wide wing and a T-tail, like in Figure 1. Other Aerodynamic data was described in last week’s articles.
The Wide Wing (WW) version has the same fuselage and tail as a MAX 8 but has a 35.8m base wing with two 4m folding wingtips for a 43.8m wing. The wing keeps the wingarea of the MAX 8 by virtue of composite construction and advanced aerodynamics.
The MAX 8 keeps its 35.92m wing with a split winglet.
We have kept other aerodynamic data the same for all three except for a slight increase of Interference drag for the TBW. Transonic drag is the same for all three as they fly at long-range cruise speeds.
The WW has a heavier wing due to increased span and fold, whereas the TBW adds more weight due to wing flutter stiffness requirements, the truss brace mass, the unfavorable main gear placement, and the need for a larger T-tail to control the wide wing.
We flew the aircraft on the typical single-aisle average stage length of 800nm and note the differences in performance. The Truss Braced Wing showed a high single-digit percent improvement over today’s MAX 8, whereas the folding wing stayed in the mid-single digits. All aircraft used today’s MAX 8 LEAP-1B engines.
Our target was to see the ballpark improvements one can expect from technologies like folding wings using modern composite techniques and a TBW using the same techniques but combining them into a wider and more advanced concept.
We described all the challenges a TBW must overcome in last week’s Corner. The WW is less challenging. The Boeing 777X has introduced folding wingtips to civil airliners (they have been on Naval fighters for 80 years). The main challenge will be increased wing mass due to the fold and increased wing bending moment. At the same time, both aircraft get less sensitive to increased empty weights as the drag due to weight, induced drag, is significantly reduced.
Which concept will prevail? We will have to see. What we know is that the folding wing will be present on the next generation of Heart-of-the-Market airplanes. If it will be truss braced or not is too early to tell.