Statement about Wind Slits

Happy spring, all! It’s Sarah here. I know it’s technically been spring for a few weeks, but it hasn’t truly begun to feel like it until this past week. We can finally shed our heavy sweaters and parkas and let our skin be rejuvenated (and hopefully tanned, if you’re anything like me) by the warm sun. Ahh, what a beautiful thought.

Today’s discussion is about why we at About Flags do not recommend wind slits in avenue banners and across-the-street banners. We are often asked about the subject, and here’s our explanation and reasoning for our response. We compiled this information from trusted vendors–it’s legitimate!

acrossthestreet

Example of an across-the-street banner

Wind holes/slits in avenue banners and across-the-street banners are meant to allow wind to pass through and hopefully reduce the total wind load on the banner.

wind_lg

Sounds like a great idea, right? Here’s why we don’t think so:

  1. In both of our full-size wind tunnel tests in 1984 and 2002, we tested banners with and without wind slits on our hardware.  It both cases, it was visually obvious that these wind holes became detrimental to the banners due to vibration and fabric stress within the banner. They tended to increase the wind load rather than reduce it.  The holes allowed the fabric to ripple and catch more wind which increases the drag factor.  The fiberglass arms deflected more rather than less indicating more force on the system with the holes than without.  The banners vibrated considerably more at 60mph to 100mph with the holes than without them.
  2. The typical hole or half-moon pattern that we are asked to cut into the banners, do not allow enough wind relief to make a difference, regardless of the rippling effect.
  3. The slits often interfere with the designs and artwork on the banners. Things get even more dicey when it’s a double-sided banner, because it’s challenging to find a bare spot on both sides.

But, there is hope! We have an alternative for you: mesh! You will typically find mesh banners hung on fences (see below), advertising construction, etc. Mesh is highly recommended by us because the holes are small enough that they don’t interfere with the design, and they have a 30% blow-through wind rate that reduces the stress put on the banner. The only downside to mesh is that it can only be used on one-sided banners.

meshbanner

Mesh closeup ruler (2)

close-up of mesh banner

Have we changed your mind about wind slits yet? We hope so! Now get out and enjoy the wonderful weather!

-Sarah

 

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