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Universal Shaker Stand for Aircraft Modal Testing
Universal Shaker Stand for Aircraft Modal Testing
MAE 156B Sponsored Project - Spring 2013
University of California, San Diego
Sponsored by:
ATA Engineering, Inc.
ATA Engineering, Inc.
This project involves the complete design and fabrication of a universal shaker stand. During the design stage, finite element analysis was used to predict the structure’s first modes in the lateral axis and second lateral axis. Analysis was performed to verify that the design of the structure to ensure that no flexibilities exist near the realm of input forces (e.g., the frequency of vortex shedding of wind over a bridge). Once the structure was built, the modal analysis was validated by testing, using a shaker to provide a known excitation input force to the structure and then measuring the resulting vibration responses.
Specifications & Constraints
Stiff in one lateral axis (back and forth) (15 Hz 1st mode)
Stiff in the other lateral axis (left and right) (9 Hz 1st mode)
Reconfigurable from 1.22m (4') to 4.27m (14') with a minimum height increment of 0.15m (6”)
Easy to assemble, reconfigure, and stow (should be assembled by 1-2 persons in less than 15 minutes)
Ability to stow four units in a standard shipping crate (max size of 1.067m x 0.432m x 0.457m or 42”x 17” x 18”)
Light weight for shipping - under 45 kg
Each leg must support at least 890N of force
Manufacture with COTS (commercial off the shelf) components as much as possible; i.e. minimize use of parts that are machined, molded (if plastic or composite) or welded
Try to reduce the amount of hardware (nuts and bolts) required for assembly to minimize FOD (foreign objects and debris) risk on the flight line
Existing/Similar Devices
One of the existing solutions for shaker stand is shown in figure 1. The overall structure is a truss structure with three telescoping legs that is very similar to a camera tripod. The truss structure has diagonal beams which makes the stand structurally sound and ideal for modal testing. Wheels are placed at the bottom of each leg which allows the stand to move easily. Although this design is superior in terms of stability and rigidity, it is unable to be collapsed into a small size for transport and does not have as wide a range of adjustability.
During modal testing, shakers are typically placed near the tip of the wing, so it is desirable for the stand to be adjustable to accommodate the different wing heights of various aircraft. An example configuration of the shaker stand during aircraft modal testing can be seen on the right. The shaker is placed near the tip of the wing and the pushrod from the shaker connects the wing to the shaker. The structure is then excited by the shaker and the frequency response is collected through accelerometers attached to the wing.
Background & Objective
Modal analysis testing is a critical aspect in structural design of aerospace and industrial systems. It allows the designer to avoid any undesirable structural flexibilities that could lead to failure. ATA Engineering, Inc. is an engineering consulting firm that provides solutions through test and analysis driven design by focusing on manufacturing needs, quality control, and time-to-market challenges for mechanical and aerospace systems. The firm is currently in need of a stowable equipment stand that can support a shaker for aircraft modal testing.
Figure 1: Example shaker stand
Final Design
The final design solution for the shaker stand is an A-frame truss structure. The stand consists of four stainless steel telescoping legs that are able to extend from 1.07 meters to 4.42 meters. The telescoping legs are secured and locked into position with shaft clamps that tighten the two pipes together. These clamps can quickly and easily be released or tightened using an allen key. The stand has four lever-lock hinges that connect the legs to a top plate that holds the shaker. The hinges allow the A-frame to be adjusted to multiple configurations by changing the angle of the legs relative to the plate. The hinges can be locked into position using a hand lever. Moreover, a ratchet strap with webbing is attached at the bottom of each of the telescoping legs to prevent them from migrating outwards. Telescoping truss members are connected to hinged joints on the telescoping legs to help make the structure more rigid. The hinged joints can be removed to allow the structure to collapse to a smaller footprint. The top plate has the correct bolt pattern to secure the shaker on the top plate.
Figure 2 (left): CAD model of the shaker stand
Figure 3 (Right): The shaker attached to the top plate of the shaker stand
Figure 4 & 5: Collapsed Final shaker stand. The height of the collapsed stand is only 1.07 m (3.5') for ease of transportation.
Figure 5, 6 & 7: Extended final shaker stand design. The stand reaches a height of 4.42 m (14.5').
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