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Re: Flag Drag

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On 9/11/06, Neil Moore <nma(--nospam--at)> wrote:
Use ANSI/NAAMM FP 1001-97.  I don't think that there is a later edition.

Equation 4 will give you the wind load for nylon or cotton flags.
Equation 5 will give you the wind load for polyester flags.

You certainly need to know what the height of the building is and then use the appropriate formulas for that.   You also need to know what the governing wind speed is.  For unknown areas we usually use 130 mph with no flag.  (We consider the flag gone at that wind speed).  Then we check the flag and the pole combined at 90 mph.  The flag poles that we design are usually 400 feet and higher, free standing single poles.

The above mention code provides sample calculations in Appendix A.   If you are concerned about buckling, we then reference Section 4 of the Standard Specification for Structural Supports for Highway Signs....ect, published by AASHTO.

Neil Moore, SE, SECB
neil moore and associates
consulting structural engineers
shingle springs, california
530 677-4308

At 10:58 AM 9/11/2006, you wrote:
Wouldn't it be waving in the plane of the wind? 
I think that the wind blowing on the surface area of the pole would govern the design.
Sharon Robertson, P.E.
Arcon Engineers
5625 Ruffin Rd, Ste 130
San Diego, CA  92123
858/503-7858 fax

Visit us on the web at

From: David Maynard [ mailto:DMaynard(--nospam--at)]
Sent: Monday, September 11, 2006 10:55 AM
To: seaint(--nospam--at)
Subject: Flag Drag
Here's what I got.
A flag pole wants to be installed on top of a Structure.  I want to make sure that the flag pole on hand is capable of the loading.  Therefore, I need to know how to calculate the wind load on the waving banner.  Is there a spec out there, or can someone point me in the right direction, as to a design procedure for this.  I'd appreciate it.
David Maynard, PE
Gillette, Wyoming

Sorry I'm so late to the thread....I found this eariler today but didn't have time to post it.

Thje projected area of the flag might seem overly conservative but a flag can have much higher drag forces than a simple vane.

here is a rather geeky  treatment of  the  phenomena

note referenece 3.....would be a great resoucre if someone could track down a copy

I also found this  posting on an engineering  forum

14 May 03 18:54
I came across this thread like a few others who wanted more information on the wind drag of flags and streamers - and there is not a whole lot out there. I am pleased to report that I have found a good reference on this subject: an article by J. M. Roehm in the Jan-Feb 1986 issue of Building Standards Magazine, page 10. (You can obtain a fax copy of this article by calling the nice folks at, who run the magazine).

The article presents drag force results from towing flags behind an airplane and they come up with the following formulae which are DIFFERENT from the Hoerner and previous estimates, and generally give lower drag force values:

V = wind speed, Area = one-sided area of flag

Nylon: Drag(pounds) = 0.0010 x (V,mph)^2 x Sqrt(Area, sq. ft)

Polyester: Drag(pounds) = 0.0014 x (V,mph)^2 x Sqrt(Area, sq. ft)

For those of you who prefer MKS units, like myself, this converts to:

Drag(Newtons) = 0.073 x (V,m/s)^2 x Sqrt(Area, m^2) for nylon, with polyester flags giving a force 1.4 times greater.
Note that unlike traditional formulae for aerodynamic drag, here the force is proportional to the _square-root_ of area, not area directly, so a "drag coefficient" is not really appropriate.

hope this helps