The production models had even more structure modifications.
"However, during production, structural strengthening is accomplished by increasing the GAGE of spars, stringers, ribs, and panels.".
"For airplanes in production, the wings are strengthened Throughout the wingbox to accommodate the winglet loads with full use of the speed brakes to the in-flight detent position. The in-production modification meets the same design criteria as those for the retrofit. However, during production, structural strengthening is accomplished by increasing the gage of spars, stringers, ribs, and panels. Rib 27 incorporates bolt hole patterns that allow attachment of either a winglet or a standard wingtip. The winglet is installed in final assembly."
I don't think anyone here has suggested that changes were actually made to the fail safe strap / pickle fork at the wing center section on the winglet models..
In fact my posted link states that inboard wing changes were minimal or unnecessary. Maybe Boeing should re-think this position.
It is apparent that the early Generation NG aircraft were designed / produced / sold without winglets in mind.
"Structural changes.
After completing the studies of the toe angle and speed-brake angle, structural material for the mid- to outboard wingbox was still required. (Because the inboard wing had sufficient strength margins, structural changes to that area were minimal or unnecessary.) To minimize the adverse effects of the wing structural modifications on flutter, wing torsional stiffness was maximized in relation to bending stiffness."
After reading the link info [#221] it appears to me that Boeing strengthened the mid and outer wing but did not make any structure modifications to the inner wing or wing center section.
[made the outer wing stronger which had the effect of transmitting more wing loading into the wing center section that was not modified]
Last edited by B727223Fan; 13th Oct 2019 at 14:09.
Reason: more info