Objective:

Demonstrate qualitatively how Monokote and similar wing skins affect wing torsion stiffness.

Description of Model:

Wing ribs were designed using SolidWorks solid modeling software. The airfoil chosen was the NACA 0012-34. Coordinates for the unit airfoil were obtained from the UIUC Airfoil Coordinate Database. The coordinates were imported into Excel and multiplied by a 10in. chord. The new coordinates were stored as .txt format and were imported into SolidWorks. The three variants below were considered for construction. The second variant was chosen initially and lightening holes were added.

Fig. 1: Three Variants of First Rib Design

Graduate assistants of Dr. Rediniotis were consulted for advice on the rib design. The students provided recommendations for how to better support the aircraft skin while maintaining the desired airfoil shape. The rib design shown below reflects these recommendations.

Fig. 2: Second Rib Design

Ribs using the second design were cut into 1/16 in. three-ply birch and 1/8 in. three-ply birch. Ribs of 1/16 in. thickness were cut such that the grain of two plies is oriented in a chord-wise direction. This action was taken in order to help prevent cracks from propagating above or below the spars. Ribs of 1/8 in. thickness were cut such that the grain of two plies would run perpendicular to the chord. This action was taken help prevent the rib from flexing when handled. The structure in Fig. 3 was constructed using the second rib design and approximately 4 in. spacing between ribs.

Fig. 3: Wing Skeleton Using Second Rib Design

The spars were created using 1/8x1/4x36in. basswood sticks as spar caps and 1/8in. balsa sheeting for the shear webs. A 1/8in.-diameter birch dowel was used to provide leading edge curvature. The balsa sheeting and balsa strings were added such that the skin material will maintain the airfoil shape. Gaps were intentionally incorporated into sections of the structure in order to make the effect of skin more noticeable.

Results:

The structure shown in Fig. 3 is quite stiff against flexure while remaining compliant to torsion. Under a torsion load, the cyanoacryllic glue may fail at certain joints.

Recommendations/Future Actions:

Epoxy will be applied to joints that receive the highest stresses. A clear Monokote skin coating was recently obtained and will be applied. Design of an experimental wing structure will continue. A test frame must be designed to hold the wing structure for experimentation.

Relevant Files and Documents:

Results and Reports, End of Summer\Wing Structure\SolidWorks Files

Results and Reports, End of Summer\Wing Structure\Photos

E:\Results Documents End Of Summer\Wing Structure\Wing Structure.Docx1