All Terrain Lifting Assistance System (ATLAS)Aggies That Lift Armored Vehicles (ATLAV) Team

C. Crandall, D. Webb, P. Le Goubin, N. Hawkes, L. Williams, J. Singleton, T. Christensen, A. Landon, A. Gerber, L. Nielsen, B. Wood, D. Magda

Low Fidelity BladderA low fidelity polyurethane bladder was chosen which will provide enough strength to withstand the pressure and also be thin enough in order to be folded easily inside of the constraint layers. The thickness of the bladder is 1/32”. The bladder will expand to 200% of its original size before the polyurethane rips but our bag design only allows the bladder to stretch 10% of its initial size before being constrained by the Vectran layers. When it is constrained bythe Vectran Layers it will be relieved from the hoop and axial stresses in the bag.

VectranThe exterior layer of the airbag will carry the hoop and axial stresses. Equations 2 and 3 present the equations used for the analysis. In order to calculate the hoop and axial stresses it was assumed the airbag was completely inflated and that it resembled a rigid, cylindrical pressure vessel. The hoop and axial stresses were calculated with a wall thickness of 0.1 inch and a 24.0 inch radius. Figure 5 plots the hoop and axial stresses as pressure inside the bag increases as well as the yield strength of Vectran.

Camlock ValveThe Cam lock is a product of testing of the first prototype bag. The first prototype bag had a Schrader Valve that was used for inflation. The Schrader Valve has a 1/8” opening that allows air to flow in and out of the bag. When the bag was inflated to operating pressure we noted that it took approximately 20 minutes to completely deflate before we could inflate again. In order to decrease the deflation time we introduced the Cam Lock Valve with a 1” diameter. This decreased the deflation time to 30 sec and greatly improved the overall performance of the lifting bag.

Compressed Air TankOur design will use a High Pressure Air tank (HPA) which will allow for the gas to move from high pressure to low pressure through a regulator and hose. Both Compressed air and CO2 were considered as mediums for inflating the airbag. The HPA tank was finally chosen for the fact that it has better performance throughout a larger range of operating temperatures, and for the fact that more mass of CO2 would be needed than for air. It is also noted that in field operations it is assumed that compressed air is more readily available that compressed CO2. The ATLAS uses a Luxfer T71R tank, size 6.8 in. diameter by 18.3 in. tall, that has a 4945 psig capacity. The tank however will only be able to be filled to 4500 psig. At this initial pressure, the tank will provide the sufficient air to operate the airbag for two full lifts at 75 psig. A regulator that can reduce the HPA pressure from 4500 psig to a variable pressure range of 0-300 psig was chosen to allow the operators to more precisely control the lifting speed, giving added safety for the operator and rescuee.

Assembly Testing

In order to ensure a good working prototype, physical testing was critical. Testing was performed under many different conditions. Vehicle loads of over 30,000lbs were used in varying types of terrain as well as inclined surfaces. Different lifting configurations and vehicle contact locations were performed as well. A maximum clearance of 3” was provided. Cyclicla testing was also conducted to evaluate inflation time capabilities in different configurations. The testing proved valuable and showed how the design can perform well over a wide range of scenarios.

Lessons LearnedThe final bag was a product of the numerous tests. We learned that stability became an issue when lifting with a low clearance. We were able to counter by placing the bag in different configurations. Our knowledge about the placement and configuration of the bag greatly increases the stability. We also noticed that the Schrader Valve didn’t stand up to the requirements since we were to lift quickly. The Schrader Valve inflated and deflated slowly so a Cam Lock Valve replaced the Schrader Valve. This change greatly decreased the lifting and deflation time of the bag. The most important lesson we learned was about the bladder. The bladder was designed to be low fidelity and hold only the air, but we learned that the bladder would puncture due to the movement of the bag inside of the constraint layer. This will be fixed in future iterations.

For future developments the bag diameter and pressure should be optimized to decrease mass and optimize lift capacity. The mass can be creased by reducing the weight and size of the inflation system. Chemical inflation designs were considered in the design of this bag, and should further to reduce the inflation systems weight. Vectran also is a developing technology, and it has potential to become lighter and stronger with additional research.

2014 Air Force Research Lab Design Competition Design and develop a system to lift aircraft and armored vehicles weighing 45k-55k lbs from uneven sloping shale terrain to aid in extrication of wounded personnel in a rescue situation. The Utah State University (USU) design team Aggies That Lift Armored Vehicles (ATLAV) has designed, built and tested the All-Terrain Lifting Assistance System (ATLAS) that satisfies this mission statement. ATLAV zeroed in on a lifting bag design that greatly improves upon the current system in use by the military. At full inflation via a compressed air tank, ATLAS will raise upwards of 45,200 lbs, 24 inches into the air. ATLAS is lightweight, packable, deployable by a single operator, and deploys in less than two minutes, dramatically increasing the chances for the victim pinned beneath the target vehicle.

Features

What is Next?

Special Acknowledgements

Design & Configuration

Bag SpecificationsDiameter 24”

Height 24”

Max pressure 150 psi

Operating Pressure 75 psi

Bag Weight 13lbs

System weight 41lbs

Max Lifting Capacity 68,000lbs

Minimum Lifting Clearance 2”

Average inflation time under max load <3min

Testing and Development

• USU Department of Mechanical/Aerospace Engineering• USU College of Engineering• Federal Fabrics-Fibers• Logan City Fire Department• Arnold Airforce Base• Air Force Research Lab• United States Air Force Pararescue