Physics of Half-Turn in Straps?

I do a full turn on each side of my straps. Never had a problem and they never move in the wind

 

Same force that makes a reed in a saxophone vibrate when you blow across it. Or the reed in the squeeker of a dog's squeeky toy. Or a blade of grass between your thumbs.

The reeds are small and stiff so the vibrate at high enough frequencies for us to hear.

Your cargo strap is not tight enough to cause audible pitch. I should say unless it is overtightened it might.

 

:smt017 Do what?

 

I have been in many a rest area walking the dog and heard a truck coming way before the engine could be heard. Cracks me up when they come by and the straps are a singing!

I just have a habit of putting the twist in even when it's under the tarp. Twist one, twist them all!

 

This is only a part of it. A strap is never perfectly flat to the wind because it rolls, bounces and buffetts along the load as it moves past, bouncing off the straps from a variety of directions causing the vibrations.

The other part of "why the twist works" is that the shortest distance between two points is a straight line. So when you tighten a strap without a twist you are tightening across the entire width "evenly", however we don't operate in a perfect world so the strap is not evenly tightened across the width due to some strands being slightly shorter &/or longer than each other, excess webbing on the winch, slight deviations in the load, etc.

By putting a half turn twist into the strap, you are now compensating for those imperfections by pulling harder on the outside edge reducing ever so slightly towards the center because the center is the shortest distance and due to the twist the outer edges actually cover more distance and therefore the outer strands get "pulled harder" by more of a degree than the imperfections of the uneven strand lengths.

You can create the same effects with a chain and binder...if you pay attention to the details of the chain links and make sure they are straight and all lined up, you will find that your chains do not come loose or not as frequently as the ones you don't line up straight...all else being equal; blocking crush, load "squeeze", tire inflation on loads with tires, etc.

 

In Australia we get fined if we have a twist in the strap. They claim it reduces the strength of the strap.

 

I'd like to visit Australia some day. But your government seems to take a LOT of the fun out of life....

 

Colonel Sanders....

Everybody "knows"...He invented chicken...

 

So DOT Down-Under "knows" as much as the DOT here does.....

 

if that sounds good to you then go with it, but guy asked about the physics of what causes it, and its the wind passing over and under the strap, even a tight strap will vibrate at times. a four foot wide load ,8feet tall with straps across the top will vibrate there behinds of without a twist, due to physics.

there is a show on pbs about a skyscraper they are building in shanghai china, th ey have a typhoon season with high winds and rain. this is one of the tallest buildings in the world. the design has and outside shell of graden space away from the office space about 30 feet wide around the building enclosed by glass windows. this desin if different , instead the outside garden space being supported by whats underneath instead they are suspended from the top down. this design was going to lead to a motion in the building under high winds or story weather. guess how they solved this problem?? they did wind tunnel testing and found by "twisting the building it stopped this. the optimum amount was 180 degrees of twist ( half twist in a strap, full is 360 degrees) but this building desing would only allow 100 degrees but it solved the problem.

same principle believe or not as a half twist in a strap. and its physics, no matter how you see it.