Amity Blimp
Amity High School Robotics Team
May 30, 2010
Enhancing the fan experience at a base ball game… This is a very open-ended problem to solve. Depending on ones life experiences, you will have different ideas on how to solve it. We came up with the idea of dropping something on the crowd. The idea came from seeing a blimp at the Rose Garden. Everyone on our team thought that dropping t-shirts would be a cool idea. The only logical flying machine to have over a crowd of people would have to be lighter than air. At this point we did not realize all the complexity that comes with loosing large amounts of weight (t-shirts) from a lighter than air, craft. Devising a blimp to fly over the crowd at PGE Park with t-shirt “bombs” would require some expertise as we knew next to nothing about envelopes (the lighter than air part), propulsion, and buoyancy.
Envelopes:
The first quandary that we had to overcome was that of creating a blimp envelope. An envelope is the film that contains the lighter than air gas (commonly Helium). The film must be lightweight but still strong and resistant to the permeation of helium. Because we knew that helium balloons where made of “Mylar”, we thought that we could do similar. We also knew that emergency blankets are made from “Mylar” (polyester film). With all this in mind, we stopped at Wal-Mart and picked up a “Mylar” balloon, an emergency blanket, a clothes iron and some other materials. Cutting open the balloon, we found that we where able to heat-seal it back together. Then we tried to do the same with the emergency blanket. It did not work so we tried to attach a piece of the balloon to the emergency blanket this also did not work. Frustrated but armed with this new information, we went online and found two things. First, that we could use double-sided tape or, find a company that makes film that is heat sealable. While we where doing this research, we also found that blimp envelopes are made is by piecing together “gores” which are long, thin, shaped pieces of material. We decide that the tape would be cheaper, easier and more available. So we started on a 1/3 scale model of the envelope using emergency blankets to create gores and then taping them together with double-sided tape and a ½ inch overlap seam. This was not easy and we had many leaky seams. After they where sealed, we filled it up with helium and started doing some tests. It was a lot of trouble to create the small envelope with double-sided tape and we realized it would be almost impossible to create a larger blimp out of safety blankets and the double-sided tape.
The first quandary that we had to overcome was that of creating a blimp envelope. An envelope is the film that contains the lighter than air gas (commonly Helium). The film must be lightweight but still strong and resistant to the permeation of helium. Because we knew that helium balloons where made of “Mylar”, we thought that we could do similar. We also knew that emergency blankets are made from “Mylar” (polyester film). With all this in mind, we stopped at Wal-Mart and picked up a “Mylar” balloon, an emergency blanket, a clothes iron and some other materials. Cutting open the balloon, we found that we where able to heat-seal it back together. Then we tried to do the same with the emergency blanket. It did not work so we tried to attach a piece of the balloon to the emergency blanket this also did not work. Frustrated but armed with this new information, we went online and found two things. First, that we could use double-sided tape or, find a company that makes film that is heat sealable. While we where doing this research, we also found that blimp envelopes are made is by piecing together “gores” which are long, thin, shaped pieces of material. We decide that the tape would be cheaper, easier and more available. So we started on a 1/3 scale model of the envelope using emergency blankets to create gores and then taping them together with double-sided tape and a ½ inch overlap seam. This was not easy and we had many leaky seams. After they where sealed, we filled it up with helium and started doing some tests. It was a lot of trouble to create the small envelope with double-sided tape and we realized it would be almost impossible to create a larger blimp out of safety blankets and the double-sided tape.
Heat Seal Film:
Back to the internet to do more research and we found a company that makes a heat sealable film. When we contacted them, they told us that they had some “left over” Polyester film with a heat seal coating. This new film is 0.0009”thick, that makes it extremely light. The ability of it to be heat-sealed meant that we no longer needed to use the tape. Instead of an overlap joint, one of our mentors suggested a butt joint with a four-inch “seam piece” overlapping both sides. A representative of the film company told us not to use a clothes iron to heat seal the film because they do not provide an even heat. He recommended that we get a “Monokote Iron”, that provides consistent heat.
After receiving the poly film, we made a jig that would help us seal it together. This jig started out as a 4-inch wide 3 foot long inclined smooth wood surface that we covered with a cotton cover. Because we where sealing a curve we added a hump to the jig that allowed us to seal the curve that we needed.
Back to the internet to do more research and we found a company that makes a heat sealable film. When we contacted them, they told us that they had some “left over” Polyester film with a heat seal coating. This new film is 0.0009”thick, that makes it extremely light. The ability of it to be heat-sealed meant that we no longer needed to use the tape. Instead of an overlap joint, one of our mentors suggested a butt joint with a four-inch “seam piece” overlapping both sides. A representative of the film company told us not to use a clothes iron to heat seal the film because they do not provide an even heat. He recommended that we get a “Monokote Iron”, that provides consistent heat.
After receiving the poly film, we made a jig that would help us seal it together. This jig started out as a 4-inch wide 3 foot long inclined smooth wood surface that we covered with a cotton cover. Because we where sealing a curve we added a hump to the jig that allowed us to seal the curve that we needed.
Propellers:
Another challenge that we faced was the propellers and thrust. We originally went to Wall Mart and looked at household fans for lift. But, those kinds of propellers are just for pushing air, not for generating lift. We met with NW UAV Propulsion Systems, and found out about propellers and Motors. We learned we would need to use brushless motors because brushed motors are much heavier per RPM/Power. So we ordered propellers and brushless motors for RC planes. When they arrived from Hong Kong, we had 4 types of propellers, and 3 brushless motors.
When we first tried to test lift on the props, we realized that we had them on backwards, which doesn’t work too well. These props were designed to pull air, not push it because they are an airfoil and create high and low pressure. So once we got that figures out, we wired up our little assembly to a multi meter, and we measured current and volts. We ran 12 volts through our motors and watched to see if they would catch on fire or not. Thankfully, they didn’t.
Another challenge that we faced was the propellers and thrust. We originally went to Wall Mart and looked at household fans for lift. But, those kinds of propellers are just for pushing air, not for generating lift. We met with NW UAV Propulsion Systems, and found out about propellers and Motors. We learned we would need to use brushless motors because brushed motors are much heavier per RPM/Power. So we ordered propellers and brushless motors for RC planes. When they arrived from Hong Kong, we had 4 types of propellers, and 3 brushless motors.
When we first tried to test lift on the props, we realized that we had them on backwards, which doesn’t work too well. These props were designed to pull air, not push it because they are an airfoil and create high and low pressure. So once we got that figures out, we wired up our little assembly to a multi meter, and we measured current and volts. We ran 12 volts through our motors and watched to see if they would catch on fire or not. Thankfully, they didn’t.
Thrust:
Another problem we had was when we were trying to measure thrust. We were using a kitchen scale, which is about 10 inches wide. Our propellers that we ordered had a minimum diameter of 10 inches. The biggest propeller that we ordered was a 15-inch prop with a 7.5-degree pitch. We decided not to use this one because it was too big. We measured all of our props; and then realized that we weren't covering all of the prop’s potential thrust. So we put a big piece of plywood over the scale and cut the weight. Then we got our real reading.
When we finally figured out the real thrust of the propellers, we wondered why they all had about the same amount of thrust. The 3-bladed 11.5-inch prop with a 4-degree pitch generated about 750 grams of thrust, which is about 1.5 pounds. With two of these, we could lift about 3 pounds, or 1.5 kilos. A two bladed prop with a 6-degree pitch had about the same amount of thrust as the 3 bladed prop. Eventually, we decided to go with the 2 bladed prop, which didn’t max out our motors and make them explode.
Another problem we had was when we were trying to measure thrust. We were using a kitchen scale, which is about 10 inches wide. Our propellers that we ordered had a minimum diameter of 10 inches. The biggest propeller that we ordered was a 15-inch prop with a 7.5-degree pitch. We decided not to use this one because it was too big. We measured all of our props; and then realized that we weren't covering all of the prop’s potential thrust. So we put a big piece of plywood over the scale and cut the weight. Then we got our real reading.
When we finally figured out the real thrust of the propellers, we wondered why they all had about the same amount of thrust. The 3-bladed 11.5-inch prop with a 4-degree pitch generated about 750 grams of thrust, which is about 1.5 pounds. With two of these, we could lift about 3 pounds, or 1.5 kilos. A two bladed prop with a 6-degree pitch had about the same amount of thrust as the 3 bladed prop. Eventually, we decided to go with the 2 bladed prop, which didn’t max out our motors and make them explode.
Ducting:
The next thing that we had to figure out was a lightweight ducting. We used a big square of polystyrene foam insulation from Home-Depot. We cut a hole in the middle after gluing two on top of each other to be only slightly bigger that the prop. Then we put it on a wood lathe and carved it out to look like a duct. After that was all said and done, we put fiberglass on it, to make it more durable. We have PVC arms that come out and we fiberglassed them around the duct too. The foam was a great weight savings suggestion from a mentor and we had fun creating “pink” fluffy shavings on the lathe.
The next thing that we had to figure out was a lightweight ducting. We used a big square of polystyrene foam insulation from Home-Depot. We cut a hole in the middle after gluing two on top of each other to be only slightly bigger that the prop. Then we put it on a wood lathe and carved it out to look like a duct. After that was all said and done, we put fiberglass on it, to make it more durable. We have PVC arms that come out and we fiberglassed them around the duct too. The foam was a great weight savings suggestion from a mentor and we had fun creating “pink” fluffy shavings on the lathe.
Buoyancy:
We had to understand how the law of buoyancy affects helium. Helium is much lighter than air, so when in the same environment, the helium would move upward and the air would move downward, trying to find equilibrium. Buoyancy occurs when an object that is lighter than another object rises, attempting to reach the place above the heavier item. If the helium-filled balloon weighed more, altogether than the weight of the air it would be floating in, itwouldn’t float at all, due to gravity. Our goal was to find neutral buoyancy of the blimp, without any T-shirts attached. Then, once the weight was added, it would sink. To lift the loaded blimp into the air, we planned to use thrust from our motors. This way, when we lost all of the weight of the T-shirts, we would be able to sink safely to the ground again by gravity.
American blimp told us to have the balloon slightly negatively buoyant, so that when we dropped the T-shirts, we wouldn’t rise up into the sky. If everything was balanced, we could gently fall back to earth after the T-shirts were dropped. We already had an idea, to some extent, of how large it had to be to lift our gondola for neutral buoyancy, but we weren’t very certain.
In our experiment to understand the concept of buoyancy, we built a scale model of our blimp about 6 feet long and filled it with helium. Next, we weighed and taped a tin can to the bottom of the filled blimp, adding BB pellets to the can until it finally leveled out. After we weighed the pellets, adding that number to the weight of the can and the tape, we knew the weight at which the balloon would be at neutral buoyancy, just the amount of weight it took to keep the balloon from rising or falling.
Moving to the full size blimp, we needed to find the volume of helium needed to carry the amount of weight of our gondola with motors, ducts and the T-shirt dropping mechanism (as seen in Table 1 of the appendix). We weighed all of the parts we needed on the blimp, the duct assembly, the dropping assembly, the batteries, etc. Being certain we would need to add “something else”, we added in a 20% buffer in additional weight. Then we used Microsoft Excel to find the amount of lift created by our envelope. First, we did it as a rough estimation using a perfect cylinder and found that it should be 16 feet long. Then we drew out the pattern of the actual gores for a more exact calculation. From there we calculated volume more exact by taking measurements at each foot. These numbers where used to calculate the area of each of the 1-foot cylinders in the envelope. If we kept the blimp at 16 feet it was not a larger enough volume so we added a foot to the center making the total length 17 ft and giving us an area of 7.8m and a lift of about 15.45lb (as seen in Table 2 of the appendix).
We had to understand how the law of buoyancy affects helium. Helium is much lighter than air, so when in the same environment, the helium would move upward and the air would move downward, trying to find equilibrium. Buoyancy occurs when an object that is lighter than another object rises, attempting to reach the place above the heavier item. If the helium-filled balloon weighed more, altogether than the weight of the air it would be floating in, itwouldn’t float at all, due to gravity. Our goal was to find neutral buoyancy of the blimp, without any T-shirts attached. Then, once the weight was added, it would sink. To lift the loaded blimp into the air, we planned to use thrust from our motors. This way, when we lost all of the weight of the T-shirts, we would be able to sink safely to the ground again by gravity.
American blimp told us to have the balloon slightly negatively buoyant, so that when we dropped the T-shirts, we wouldn’t rise up into the sky. If everything was balanced, we could gently fall back to earth after the T-shirts were dropped. We already had an idea, to some extent, of how large it had to be to lift our gondola for neutral buoyancy, but we weren’t very certain.
In our experiment to understand the concept of buoyancy, we built a scale model of our blimp about 6 feet long and filled it with helium. Next, we weighed and taped a tin can to the bottom of the filled blimp, adding BB pellets to the can until it finally leveled out. After we weighed the pellets, adding that number to the weight of the can and the tape, we knew the weight at which the balloon would be at neutral buoyancy, just the amount of weight it took to keep the balloon from rising or falling.
Moving to the full size blimp, we needed to find the volume of helium needed to carry the amount of weight of our gondola with motors, ducts and the T-shirt dropping mechanism (as seen in Table 1 of the appendix). We weighed all of the parts we needed on the blimp, the duct assembly, the dropping assembly, the batteries, etc. Being certain we would need to add “something else”, we added in a 20% buffer in additional weight. Then we used Microsoft Excel to find the amount of lift created by our envelope. First, we did it as a rough estimation using a perfect cylinder and found that it should be 16 feet long. Then we drew out the pattern of the actual gores for a more exact calculation. From there we calculated volume more exact by taking measurements at each foot. These numbers where used to calculate the area of each of the 1-foot cylinders in the envelope. If we kept the blimp at 16 feet it was not a larger enough volume so we added a foot to the center making the total length 17 ft and giving us an area of 7.8m and a lift of about 15.45lb (as seen in Table 2 of the appendix).
Conclusion:
Using our own tests, research, and formulas, our team of three was able to bring together this blimp project. We determined how to make an envelope, what kind of motors and props to use and what volume of helium the blimp would need to hold. We have learned about the buoyancy of helium, heat sealing, aerodynamics, brushless motors and how a blimp really works. We have received a great deal of knowledge from our mentors and have applied it successfully. This has been a very fun challenge, with lots of problem solving, teamwork, and a lot of pink fluff from our ducting! We are looking forward to the Beaver game at PGE Park.
Using our own tests, research, and formulas, our team of three was able to bring together this blimp project. We determined how to make an envelope, what kind of motors and props to use and what volume of helium the blimp would need to hold. We have learned about the buoyancy of helium, heat sealing, aerodynamics, brushless motors and how a blimp really works. We have received a great deal of knowledge from our mentors and have applied it successfully. This has been a very fun challenge, with lots of problem solving, teamwork, and a lot of pink fluff from our ducting! We are looking forward to the Beaver game at PGE Park.
Northwest UAV Propulsion Systems – McMinnville
Troy Klopfenstein – Brushless Motors
American Blimp – Hillsboro
Rudy Bartel – Blimp envelope
Near Space Corporation – Tillamook
Eric Byers – Heat seal process
Griff Paper and Film – Penn
Tim Roche – Polyester film
Evergreen Space Museum – McMinnville
Larry Wood – Test facility
Garmin – Kansas
Noel Duerksen – Foam ducts, monokote iron
Garmin AT – Salem
Bob Myers – Fiberglassing
Troy Klopfenstein – Brushless Motors
American Blimp – Hillsboro
Rudy Bartel – Blimp envelope
Near Space Corporation – Tillamook
Eric Byers – Heat seal process
Griff Paper and Film – Penn
Tim Roche – Polyester film
Evergreen Space Museum – McMinnville
Larry Wood – Test facility
Garmin – Kansas
Noel Duerksen – Foam ducts, monokote iron
Garmin AT – Salem
Bob Myers – Fiberglassing
Team Coach
Garmin AT – Salem
Craig Hudson
Craig Hudson