Session: Research Posters

Paper Number: 166825

3d-Printed Adjustable Angle Mount for Wind Tunnel Testing 

This paper describes and details the design of 3D-printed Wind Tunnel Mounting Solutions for use in the Tennessee Tech large-scale, low-speed wind tunnel. Mounting solutions for different airfoils are critical for the research and investigation of different performance parameters of the desired airfoils, as no such mounting solution currently exists. This paper will discuss the design criteria, use cases, and overall design and construction of such mounts.

To mount a wing horizontally in the wind tunnel, the mount must be able to hold the wing at a 0-degree angle of attack (AOA). This mount must be compatible with the currently installed load cell and the associated boom arm, which is made of a galvanized steel pipe.

The boom adapter is constructed to form a tight fit around the boom arm to prevent oscillatory fluctuation due to aerodynamic effects. The fitment on this boom is crucial to ensure good reading of the load cell data, as movement of the mount will cause fluctuation in the data. The mount is fastened to the boom arm by a bolt running through a hole cut perpendicular to the pipe and is secured further by two adjustable bolts incorporated 90 degrees from the bolt that runs through the boom arm. These secondary bolts are inserted into printed holes that have a heat-set threaded adapter to tighten against the outer surface of the boom arm to ensure that no rotation around the pass-through bolt can occur. The airfoil mount is constructed from Polymaker PolyLite PLA-LWand is designed to attach to the wing in 4 points using screws of suitable size. The two components are fastened together using a keyed shaft-like attachment with a hole through the top. The boom adapter contains a heat-set threaded insert that allows a screw to be inserted through the top of the airfoil adapter and tightened down to ensure that the two components will not separate during operation.

To mount a wing horizontally in the wind tunnel, with the option to adjust the AOA, beta angle, and roll angle, a mount must be similarly designed, with the use of servos and gears (discussed later in this paper) in separated sections to allow the mount to rotate about three different axes. In this respect, the Articulating Mount is designed in 4 sections, with the final airfoil adapter installed on the top, increasing the part count to 5 sections. The following sections are as follows:

Boom Adapter: This follows the same design as the Simple Mount, with space added for a servo to be mounted in such a way that the servo spline hub is mounted coaxially with the base

Beta Angle Section: This section contains the adapter for the servo spline on the base, and contains the servo housing and hinge component for the AOA section

AOA Section: This section is smaller and connects the Beta Angle Section and the Roll Angle Section. This section contains the hinged shaft sections that require a pin to stop the shaft from rotating relative to this section. This fixture of the shaft is crucial to the reference point for the other parts to rotate in relation to.

Roll Angle Section: This section houses the outside hinge for the shaft as well as the servo housing to rotate the section. The top of this section also contains the same keyed shaft-like adapter that connects the Simple Mount components together, allowing the same Airfoil Adapter to be used.

The ability of the AABARA Mount to articulate was due to the use of 40 kg servos that are commercially available. These were used with commercially available gears, with machined shafts to accept the gears that are not attached to the servos. The method for implementing these servos into the design was to model a rough shape of the servo and use the “Cavity” feature in SOLIDWORKS to create a hole that is the exact size of the servo. Channels for the servo wires were then implemented into the cavities to ensure that the wires were properly routed. And did not interfere with the operation of the mount. This allows the servos to fit tightly and accurately without the need for subtractive manufacturing after the mount was printed. The servos were then screwed directly into the printed components through the premanufactured holes in the servos.

Future Work

In future iterations of this mount, to reduce the drag force of the mount itself is of crucial importance. In wind tunnel testing, the drag of the mount must be subtracted from the overall drag of the system to yield the test article’s drag. To do this, two changes can be made. 

One, reduce the diameter of the mount itself. Based on the observed strength of the mount itself, and after testing articles in the wind tunnel, the force on the mount is not high enough that concerns regarding material strength arise. 

Two, it is observed that the mount can be constructed with a smaller cross section and still avoid these concerns. The mount can also be constructed in such a way that resembles an airfoil on some sections.

This combination of 3D printed wind tunnel mounts opens a large opportunity for future work regarding application specific mounting hardware to be designed and constructed by individual teams rather than to rely on commercially available solutions or specialty contractors. As the whole system of mounts that were designed are designed and manufactured in house, this reduces the amount of money spent and allows for very specific, purpose-built hardware to be utilized. The ability of this design to be implemented in other wind tunnels with the necessary modifications also allows for quick and easy collaboration between teams to implement solutions that fit the purpose of different experiments. The increased accessibility and ease of use of 3D printing and CAD design make this system very accessible and implementable to any use case.

Presenting Author: John Adams Tennessee Tech University

Presenting Author Biography: John Adams is an undergraduate student in Mechanical Engineering Department at Tennessee Tech University.
He is mainly interested in aerodynamics, astrodynamic, and wind tunnel operations. In addition, he is genuinely passionate on mechanical design and drawing.

Authors:

John Adams Tennessee Tech University
Charles Savage Tennessee Tech University
Bruce Jo Tennessee Technological University