Flotation Systems
General Goals of Flotation Systems
Retrofitting the 2006–2007 project car started with calculations of what kind of volume was required to make the car float with the heaviest team member in the cockpit. The goal of flotation was to ensure that buoyancy of the vehicle could achieve an 800 lb. load without relying on the buoyancy of the tires or sealing the cockpit. Sealing the cockpit would require sealing panels onto the car, which is disadvantageous due to maintenance requiring removal of those panels. Further, a sealed cockpit can weigh the vehicle down if water is able to enter the cockpit over the sides.
The flotation system must be contained within the top-down profile of the vehicle. The team is trying to avoid placing flotation farther away from the body than the tires extend. This constraint is to provide damage safety for the flotation system that could possibly cause it to be torn from the vehicle. The idea is that if the tires hit an object first they will take the impact without critical damage whereas the flotation may be torn off removing amphibious capabilities.
Flotation attached to the underside of the vehicle should inhibit clearance as little as possible. To facilitate this constraint a limited thickness of flotation material can be attached to the bottom. The rest must be attached to the sides of the cockpit, the front bumper, and the engine compartment.
Making it Float
The prototype retrofit of the 2006–2007 car started over the December break. The flotation system is six inch layers of foam sandwiched between pieces of plywood. The flotation attached to the underside of the vehicle was limited to a single six inch thickness of foam between two half inch thicknesses of plywood. This removes, an allowable, seven inches of clearance form the vehicle. Further flotation is attached to either side of the cockpit as another thickness of foam with another thickness of plywood on top.
The flotation is attached to the vehicle body through the floor of the cockpit. Seven bolt/washer/nut combos are used for this. Flotation to the sides of the cockpit are attached to the underside flotation using nuts, washers, and long threads running through all 13.5″ of flotation. The flotation retrofit can bee seen in Figure 1.
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| Figure 1. Progress photo of flotation retrofit to the 2006–2007 project car; car awaits installation of foam under the engine compartment and front bumper. |
For further flotation foam will be attached to the front bumper and under the engine compartment in the back. After final attachment of the prototype retrofit the team will test the vehicle in a body of water. First will be an unmanned test then a manned test using a light weight team member.
Propelling it Forward in Water
After all buoyancy materials were installed to ensure the safety of an 800 lb. load the team began work on a fender design. The fenders were first designed to inhibit the flow of water upward and forward on a fully submerged tire. Redirecting those flows downward and more importantly backward will propel the vehicle forward in water.
The fender design has a large tail to facilitate directing as much of the water flow coming off the tire backwards. This tail is also angled upward as a completely horizontal fender tail would have much of the water bounce off and be directed downward; not providing propulsion. The prototype fiberglass fender can be seen in Figure 2.
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| Figure 2. Adam Collins and Ryan Dark work to mount the prototype fenders on the 2006–2007 project car. |
Flotation Testing on Warm Springs Road
On January 11, 2008 the Mini-Baja team did its first flotation field test in a pool beside Warm Springs Road in North Salt Lake. The purpose of this field test was to test if the Baja could float and if it could float whether it could propel itself or not in the water. Figure 3 illustrates the process of testing these systems.
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| Figure 3. The Baja is anchored to a truck with a tow cable (1), driven into the hot spring (2&3), propelled in the water (4&5), then pulled back out of the hot spring by the anchor truck (6). |
A suitable entry point into the hot spring was scouted and the team set up along a shallowly inclined shore of the hot spring. The test began by anchoring the Baja to a truck for easy retrieval should the untested water propulsion system fail or if the car runs aground. The test pilot, Taylor Halford (and later Mike Madsen), then drove the Baja into the hot spring. Some problems were immediate such as entry into a muddy water system was easy to get stuck in with the Baja.
The team was not sure if the flotation was working properly until the Baja had made it a significant distance into the hot spring. Specifically the team knew the Baja was floating by testing how easy it was to pull the car back into the shore. The flotation system had succeeded and as far as the team can tell is over designed as much of the foam remained out of the water. Also, the cockpit was raised high enough from the water that it did not fill with water.
Once the Baja was determined to be floating the test pilot tried to tip the Baja to see if the flotation provided enough stability to meet the ± 30-degree tilt reset requirement. No measurements were taken on the exact tilt angle however the pilot was unable to tilt the Baja far enough to capsize.
The propulsion created by the fiberglass fenders was underwhelming. The Baja barely seemed to move at all and got stuck on sand bars more often than not. The fender design is being revisited and at the time of the test better solutions to the fender design had been found. Valuable insight into the materials used on the mounting of the fenders as well as the fenders themselves was gleaned from the field test. The fender mounts were different on the left and right sides showing that three attachment points on the wheel upright provided the better stiffness and that steel angle iron the better choice compared to aluminum slats.
Lessons learned from the field test
- Fiberglass is not stiff enough alone to make directional fenders. Fiberglass should simply be the shell on a steel skeleton.
- The flotation foam mounted to the bottom needs to be trimmed to an angle in the front and back to decrease snag issues on entry and exit from bodies of water.
- A new directional fender design is required to harness more water flow to make the car move faster in the water.
- The fenders need to be more concentric to the tire itself as well as drop lower on the front and back of the tire to direct water more effectively.
- Foam needs to be shaved off the bottom of the vehicle to better balance the vehicle in the water. The vehicle sat higher in the front making steering in the water more difficult.