Leading Edge Structural Calculation 1

[soldanr]

I am trying to find out the loads (force, moments, etc..) in the leading edge of a C-172. I am interested to know the loads in the landing light cut-out on the leading edge of the wing.

When Cessna made that cut-out on the wing leadnig edge of the wing did it have any impact on the structure integrity?

Does cutting as hole in that location make the wing weaker?

I am just concerned because from my research the wing of a C-172 is a stressed wing skin.

If anybody can give me a hint on this opic I would appreciate it very much!

Thankx

 

[WKTaylor]

soldanr… thumbnail look at an old Cessna wing design.

I was the investigating engineer for an O-2 [C-337] that broke-up in-flight due to over-load. Failure of the Lt Wing occurred thru the landing light "cut-out" on the LE. This wing failure was complicated by multiple factors... and failed "way-above" design ultimate loads (pilot error).

As for "weaker"... that is relative... the "stock" C-337 wing withstood 4.3-g pull-outs for thousands of hours with relatively few ill-effects (routine/rough maintenance practices appeared to abuse the wing worse than high-G loading).

Obviously, there are probably two factors that have driven Cessna to put landing/taxi lights in the cowl of newer high wing acft: reduced complexity of the light instl; and reduced complexity of wing assembly (symmetrical structural configuration).

Also, I was lead engineer for tear down inspection of a USAF T-41 (C-172) trainer at 20,000-Hrs... minor damage... mostly related to corrosion... and some buckling. Wings appeared in good condition... including leading-edges at landing light cutout.

NOTE: low-wing GA Acft that regularly fly pipeline inspections take the "worst” beating... having experienced several wing failures (spar) due to fatigue cracking.


Regards, Wil Taylor

 

[edmeister]

The wing leading edge is considered an auxilliary structure to the wing box. The wing box is the structure between the F/spar & R/spar. The structural concern relating to the leading edge is essentially the bird-strike requiremnent. It is critical that any impact into the leading edge does not 1/ adversely effect the fly capabilities of the wing and 2/ allow the impact object to contact & buckle the spar. Otherwise any structural benifit obtained from the leading edge is a "bonus"

 

[planedr]

Reverse engineer the loads applied to the area in a conservative manner. Use the material strength as the basis (way conservative) or use the adjacent fastener pattern (conservative) to derive the loads applicable to the Skin. Cutouts will increase the stress concentration in an area, and anytime you remove material it gets weaker. Although creative mathematics may show otherwise.

Typically LE's are secondary structure and designed for aerodynamics, or other certification requirements only (least conservative).

Al CET EIT

 

[aerodog]

If the leading edge was on the wing during structural testing, I would consider the L.E. structural.

Cessna is not likely to share their secret so you would have to assume the leading edge is structural. Cessna would also know if the cut-out was in the wing during the bending tests or if it was written off later but it might take Cessna some time to sort thru the history appropriate to the model you are dealing with.

This is all common in the program life of an airplane, especially true of the 172 which went into production half a century ago. Cessna probably tested various wing configutations a dozen times to account for design changes and weight increases.

If you plan on doing a mod to the airplane, you could probably approach an STC by showing your mod stronger than the original configutation.