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Re: Flag Loads

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I have a copy of the Building Standards article and the testing was
performed by NAAMM ( National Association of Architectural Metal
Manufacturers ) using a small airplane.  They found the winds loads to be
significantly less than the loads calculated with the Navy and/or Hoerner's
formula.  It seems that NAAMM was also concerned about the significantly
lower results and did a second round of testing to confirm thier findings.
They do provide one interesting note at the end of the article.  The Navy
formula produces a load of 1136# for a 20 foot by 30 foot flag in a 100mph
wind.  This would equate to 303 horse-power to overcome the drag,  however
the plane used for the testing had only a 150hp motor and towed the flag
with ease.    The NAAMM  formula results in a 65 hp motor or 256#.

Robert Shaffer, PE
Santa Cruz,  CA

----- Original Message -----
From: <mkrakower(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Tuesday, May 09, 2000 11:00 AM
Subject: Flag Loads

> I recall using a drag force of 1 pound per square foot applied to the
> surface area of the flag. This value corresponded to wind velocity of
> around 90 miles per hour at normal air density at around 70 degrees
> temperature. The drag coefficient used was around 0.1 to account for the
> summation of skin friction and a dynamic component representing flutter
> separation. The weight of the fabric and the flag aspect ratio affected
> drag force. I will be curious to read the 1986 Building Standards article
> referenced by Rodger Turk. The office reference I used was from work done
> by Hoerner on drag of flags around 1965.
> Michael Krakower SE