Originally Posted by
Winemaker
I may be stupid, but I don't see how the wing load is greater with the winglet. The load is aircraft weight and g loading; that hasn't changed. I can see stiffening the wing tip as the winglet is increasing the local loading, but the final load carried by the wing box is constant. The wing load profile will change, but not the total load.
Uhhh look at the wing- with and without a winglet. Compare to lever arm pivoted about one side of the wingbox. Without a winglet, assume a ( hypothetical for ease of calculation ) load of say 1000 lbs 20 feet from pivot poInt= 20000 foot lbs acting on pivot point at edge of wingbox
Now with a winglet, assume a load ( due to aerodynamics in both cases ) of say 1000 lbs at 22 feet from pivot poInt = 22000 foot lbs .
This is because in simplified terms, the winglet changes the aero load ( lift) distribution a bit further outboard, thus increasing the ' lever' arm.
I have deliberately not counted extra weight of winglet, or tried to model actual aero lift numbers, etc. Simplified numbers for illustration only- not an aero engineer, etc.
For a detailed description- go to Aeropartners site.
"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."
http://www.boeing.com/commercial/aer...let_story.html
Then point is its the LEVER arm change in lift distribution that adds to the torque-bending loads at the junction of wing and wingbox, NOT jusrt the minimal difference in weight and slightly longer wing.
