Remote Sensing: Winch System
Your winch system was designed to be a light-weight, portable device to ground your blimp where you choose, while easily and quickly winding to adjust the length of the tether. The metal bars offer a space to place a sandbag to weigh down the system so high winds can't pull it around.
- Mechanical Advantage
- Line Length
Pulley: Your winch system uses a fishing downrigger to allow for smooth operation of the tether line that holds your blimp. The tether line is wound up in the large central pulley, strung along the downrigger arm and placed in the groove of the small pulley at the end of the arm. This offers several advantages. First, pulleys are useful for redirecting the force required to let out or reel in the line. This is particularly useful if the wind is tugging your blimp in different directions.
Torque: The second advantage of a pulley system is that it allows you to apply torque with the attached hand clutch. Torque is the amount of twisting force you have to exert to reel in or let out the line. The long handle of the hand grip gives you more torque, meaning you have to exert less force with your body and therefore have more control.
Tension: Your blimp is influenced by a variety of forces when it is flying. We talk about the buoyant force and the force of its own weight on the blimp page. And it is also being pulled and pushed by wind currents, however these do not blow the blimp away because your winch is exerting force through the reel line to hold the blimp close. We call forces that are exerted by strings "tension" forces.
Tensile Strength: The fibers that make up your tether can regulate only a certain amount of force from the tug-of-war between the weight of the winch and the wind pulling the blimp. The ability of a material to handle stress is measured by the weight it can hold right before breaking, called the tensile strength. Your tether is made from durable spectra line with a tensile strength of 800 pounds. It can handle 150 pounds of pull from the blimp, which should be plenty to allow for some windy days.
Your winch system also has a line counter so that you can measure how much line has been released. This is particularly important for staying within the Federal Aviation Administration (FAA) guidelines, which regulate that a commercial blimp stay within 150 feet of the ground.
You can determine how long your line can be to reach an altitude of 150 feet with the Pythagorian Theorem or with the sine function. If we assume your tether line is at a 45 degree angle with the ground, then you can release 212 feet of line. For angles smaller than 45 degrees, you can release even more line. A good rule of thumb for you to be close to an altitude of 150 feet is to release 250 feet of tether line.