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
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
Design & Configuration
Testing and Development
Low Fidelity Bladder
Assembly
Testing
A 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 by
the Vectran Layers it will be relieved from the hoop and axial stresses in the bag.
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.
Vectran
The 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.
Bag Specifications
Camlock Valve
The 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 Tank
Our 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.
Diameter
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
Lessons Learned
The 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.
What is Next?
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.
Special Acknowledgements
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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