Most integral to this team’s responsibility to Solar Turbines is the investigation and selection of a viable linear actuation mechanism that can be deployed to the field on their new T-250 six-strut mount design package. The early stages of this project consisted of deep research in the best solution for actuation. Several designs were weighed against each other according to the following criteria: ease of alignment, speed, accuracy/precision, reliability, envelop, and cost. A summary of our findings is presented in this Pugh chart. As seen in the chart, the jacking bolt and the worm gear screw jack scored the best and were both considered as final solutions for the actuation mechanism. 

The first solution to Solar Turbines is the jacking bolt. A base serves as a linear guide for the foot to slide on while two opposite facing jacking bolts adjust the position of the foot through the input of a torque wrench.

The chosen jacking bolt for actuation is ¾” in diameter with a tenth of an inch pitch. The jacking bolt is highly accurate and boasts a maximum required torque of 36 foot pounds to operate. 

Due to overall scale of this project and financial restrictions, a full scaled model was not produced. However in order to test the how the effects of the stick-slip phenomena will hinder our design's positioning capabilities, a scaled down model was produced. Due to its accessibility, the jacking bolt solution was chosen as the actuation mechanism for our test. In order to simulate the 12,000 lbf loading that the aft strut will experience, a hydraulic press was utilized to apply extreme vertical loading. To simulate the horizontal loading that the strut will experience in reality, the vertical load from the hydraulic press was increased.  

• The cause of stick-slip:

  • Difference between Static and Dynamic coefficients of friction.

  • The pushing force required to break static friction is higher than the force required to move during dynamic friction resulting in a step-rise in acceleration and thus potentially imprecise adjustments of the foot

Multiple tests were ran with with various loads applied by the hydraulic press; also, assorted combinations of greased vs non-greased surfaces were applied on the threads and sliding contact surfaces of the test rig. A 20 inch wrench was used to rotate the jacking bolts. After observing and recording the required input torque, the distance of foot travel, as well as the motion profile for each test it was determined that stick slip would not be an issue. Specifically, under the worst conditions the required input torque was still less than 45 lbft. The movement achieved could be described as like cutting a hot knife through butter, it was both smooth and consistent. As a result, precise movements in increments of 1 thou were easily achieved during testing with maximal load. Equally as important and worth mentioning was that our experimental results validated our torque and precision estimations.

The foot mount was modeled using ANSYS with maximum loading during alignment of 48,000 lb. The result was a maximum deflection of 1.5e-5 in. This analysis has helped verify the performance of the foot mount and that the deflection will remain within the allowable tolerances.

The foot's natural resonance frequency's were estimated using SolidWorks. Avoiding resonant frequencies will ensure the foot will not oscillate uncontrollably and jeopardize the integrity of the foot mount. It is difficult to gauge the frequency and amplitude of vibration each strut will be subject to, but as the six-strut mount design matures through the design phases, these are the natural frequencies to avoid during engine operation. 

The binding ratio of a linear rail system was examined to determine the forces the foot would encounter if there was an offset distance between the applied force and the center of the rail. These forces could create added friction or bind/lock the foot on the rail.