Whether you are a new or experienced user of outdoor movie screens, safety is of paramount importance for all users. Insurance really doesn't matter if someone is hurt or killed. With the average screen sizes used by Parks and Recreation and professional outdoor movie operators getting progressively larger, the risks increase. In terms of the loading on an outdoor movie screen, there are two engineering terms that apply. These are "moment" and "shear. The moment of a force is a measure of its tendency to rotate an object about some point. so wind has the tendency not to come either the front, back or sides of a screen but from an angle. this means that wind load on each anchor point is not equal to the others. In our outdoor movie applications with inflatable screens, this means that anchors must be significantly stronger than if each anchor point were to equally bear wind force. Shear is simply strain and refers to stretch factors of the screen and it's anchor tethers under strain. Nylon rope has a stretch factor of 10%, webbing has varying ratios. Many outdoor screens flex or bend under wind load. An AIRSCREEN with its RF sealed seams and higher pressure blowers tend Have less shear but wind is a powerful force nonetheless.
In simple terms, what does this mean to the outdoor movie screen user? Very simply, follow manufacturers guidelines for anchoring, and then add some! If staking, place your anchors further away than recommended if possible. Drive stakes all the way into the ground. learn proper rigging knots, or use caribiners or ratchet straps. Recognize that loose or sanyasi soil does mot offer much holding power. Substitute sand stakes if anchoring into this type of surface.
If anchoring using ballast as opposed to earth anchors, use more weight than recommended. Three 55 gallon drums on each corner for a 24'x13'6" wide screen placed one and a half times the height of the outdoor movie screen frame away from the screen is recommended. For instance an AIRSCREEN AEROPRO 24'x13' frame is approximately 19' tall, so anchor placements 30' away is a good placement.
Remember that anchor specs are for normal conditions and not storms! If in doubt and weather is approaching, get your screen deflated and on the ground ad quickly as you can. The best accident is the one that did not happen!
By Bob Deutsch
Www.outdoor-movies.com
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