other tables and stations. A plexiglass sheet was placed on a table top to provide the smooth flat surface to lay up the fiberglass on.

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Florence Hudson
5 years ago
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1 Fiberglassing After hot wire cutting our four airfoils for testing, it was decided that greater strength was needed. The foam airfoils do not have the required strength to withstand the forces of the wind tunnel. Due to the ease of manufacturing and its strengthening properties, the team decided to cover the foam airfoils with a ply of fiberglass. Fiberglass work can be summarized in six simple steps. The first step is to get all the correct materials and tools together. Without the correct tools and materials the final product will not come out correctly. Suggested materials and tools needed are: Epoxy, fiberglass, a plastic squeegee, scissors, a single edge razor blade, mixing cups, a yard stick, rubber gloves, paper towels, and a drop cloth. If the work surface is glass, a drop cloth is not required, but can be helpful. For the MAV airfoils to be strengthened US Composites Epoxy was used as well as US Composites 0/90 degree woven fiberglass cloth. Once all the materials and tools are acquired it is possible to move on to step 2. The second step is to size up the job. The fiberglass cloth should be cut down to a size slightly larger than what is required to cover the airfoil. Usually an extra inch and a half in each direction will provide a sufficient amount of fiberglass to account for anything being off center when applying the fiberglass to the foam airfoil. In some cases it is feasible to use strips of fiberglass to work with. Working with multiple strips, however, usually results in more sanding after the lay up is complete. Therefore, it seemed only fitting to use a single piece of fiberglass to laminate the airfoils with. Sizing up the job also helps to provide for the correct amount of epoxy resin that should be used, cutting down on waste. The third step is to lay out all of your tools in the order in which they will be used, or at least within an arm s reach so that time is not spent searching for tools while the epoxy resin is curing. It is important that the drop cloth, or glass surface is at least two and a half times the size of the fiberglass cloth being used. Following this standard will provide that there is enough room, not only to work with the fiberglass, but also for all of the tools and supplies to be within quick reach throughout the lay-up process. For the MAV team a fiberglass station was set up in the wind tunnel area, away from all of the

2 other tables and stations. A plexiglass sheet was placed on a table top to provide the smooth flat surface to lay up the fiberglass on. The fourth step begins the actual fiberglass lay up process. Before starting this step it is very important that the fiberglass cloth is on a smooth flat surface and all the tools are in order. With rubber gloves on the epoxy resin can be mixed. It is essential that the 3:1 ratio is kept between the resin and hardener. The RIT Aero Team and MAV team have observed that the US Composites Epoxy can be very temperamental and if the ratio of resin to harder is off slightly, the final product will not turn out as desired. To achieve an optimum mix of hardener and resin the MAV team will use calibrated ratio d pumps or a scale. Once pumped into the mixing cup the resin and hardener should be mixed for two minutes, making sure to scrape the sides of the cup to ensure all the resin is in solution. Once the epoxy is thoroughly mixed, the fiberglass cloth can be saturated with the epoxy. The plastic squeegee should be used to ensure that the fiberglass cloth is thoroughly and evenly saturated with epoxy. The fiberglass cloth will begin to turn clear when it s completely saturated with epoxy. During step five the saturated fiberglass is placed on the foam airfoil. Before applying the fiberglass to the foam airfoil, if any epoxy is remaining after saturating the fiberglass, it can be applied to the surface of the foam airfoil. Through the MAV team s experience, however, this does not improve the quality of the final product, but can add extra variable to the process, therefore extra epoxy will be used for saturating more fiberglass, or disposed of. The saturated fiberglass sheet can be applied to the airfoil and air bubbles or imperfections can be smoothed using the plastic squeegee. Step six is when the fiberglass laminated airfoil should be stored so that it can be left to cure for twenty-four hours. The extra fiberglass around the edges of the airfoil can be trimmed. Once the airfoil looks satisfactory it can be placed back into the foam block it was cut from. The foam block provides a structure that helps the fiberglass bond to the foam airfoil as weight is applied to compress the foam mold around the fiberglass laminated airfoil. After twenty-four hours the epoxy is fully cured and the airfoil can be removed. During curing, the foam mold must be covered with something to keep the epoxy saturated fiberglass from adhering to the mold. For the MAV team s first trials cellophane was used to cover the foam block. The surface roughness of the airfoils using

this method was not satisfactory and we approached the Aero Team for suggestions. It was suggested that the MAV team use Mylar in between the airfoil and foam block.

3 this method was not satisfactory and we approached the Aero Team for suggestions. It was suggested that the MAV team use Mylar in between the airfoil and foam block. The first trial with Mylar resulted in a disaster. The Mylar stuck to the fiberglass at some areas on the airfoil. In searching for a reason, the MAV team members concluded that the Mylar stuck due to the fact that as epoxy cures it experiences an exothermal reaction and heat is expelled. To combat this, the Mylar was waxed, and all trials utilizing the waxed Mylar have produced promising results. Wet sanding can smooth out any imperfections and help produce a smooth surface for the fiberglass laminated airfoil. Laminating the foam airfoils with a ply of fiberglass gives each airfoil a substantial increase in strength, with minimal weight gain. Depending on the airfoil, the fiberglass laminate adds twenty to thirty grams to the weight of the airfoil. For future lay ups, the MAV team hopes to make use of the vacuum bagging equipment available to hopefully improve the uniformity of our airfoil manufacturing. Step 1: Obtaining supplies. Figure 7.7: Layout of supplies

4 Step 2: Sizing up the job. Figure 7.8: Sizing fiberglass Step 3: Laying out Tools and Supplies. Figure 7.9: Laying out fiberglass Step 4: Saturating the Fiberglass. Fiberglass will become clear as saturated. Figure 7.10: Saturating fiberglass with epoxy

bubbles. Figure 7.11: Laminating airfoil with fiberglass Step 6: Curing.

5 Step 5: Laminating the airfoil. Fiberglass must be smooth over airfoils, so the plastic squeegee is used to remove air bubbles. Figure 7.11: Laminating airfoil with fiberglass Step 6: Curing. Weight is applied to the top of the foam mold with fiberglassed airfoil inside for 24 hours to cure Figure 7.12: Weight applied to airfoil during curing process

Vacuum Bagging Wings Instruction Manual Purdue University

Vacuum Bagging Wings Instruction Manual Purdue University Note: Do not leave the vacuum pump running unattended! Revision: Original Release 10/31/15 Vacuum bagged wings are quick to build, light weight,