Tuft Demonstration


Copyright 2008 WindTripper

WindTripper Is Patent Pending.


WindTripper - Tuft Testing
December 2005 - Woodstock, Vermont

 In December 2005, we set up the following demonstration to prove the effect of the WindTripper* wind spoiler system on wind flow over a roof.  This test method is typically employed to determine airflow over, and lift generated by, an airplane wing (airfoil).

 The test apparatus consisted of a 12:1 scale model building with a WindTripper* model installed along the windward eave, and a large, variable speed air blower.   The building was scaled exactly, and constructed with standard trusses, sills, and sheathing.

The roof was set upon, but not attached to, the building side walls.  Two padded vertical stops were mounted at opposite ends of the downwind side of the roof to prevent the roof from blowing off downwind.  A tether (shown above) was also installed to keep the roof from blowing over the vertical stops.

A WindTripper* spoiler system was mounted on the eave closest to the wind source.  Note that the model WindTripper* was constructed in a continuous piece.  In full-scale, WindTripper* spoilers are constructed in shorter segments for reliability in case of mechanical blockage or damage by a fallen tree, for example, and for ease of installation. 

 Since the continuous length spoiler lacked longitudinal stiffness, we attached it to the eave mid-span with duct tape.  This prevented it from moving away from the eave under wind load.

The blower employed in testing allows scale winds to the equivalent of 200 mph.

Blower speed was controlled with a variable speed, 50:1 ratio. 90 VDC SCR drive which included a calibrated, ten-turn potentiometer.  Output was monitored with a current meter and confirmed by blower shaft speed.

The relative wind was tested at various elevations and angles of incidence in relation to the roof line and to the horizontal and vertical planes of the building.  Wind flow over the building caused the roof and roofing material to lift.  In order to show the effect, we installed tufts of yarn in the pattern shown.

 The controller was used to increase fan speed to produce an 85 mph wind (at scale). 

Although the WindTripper* spoiler normally deploys at a scale wind speed of approximately 60 mph, for the first part of the demonstration, the WindTripper* was manually fixed in its stowed position.

 In the first photograph below, note the smooth airflow over the roof.  This airflow pattern is sought after in aircraft wing design because it is known to produce maximum lift.  However, it is also the most harmful to the integrity of a roof in high winds.  A smooth flow produces maximum lift of the roof structure, and maximum lifting of roofing material off of the sub-roof.

WindTripper* under 85 mph wind stowed position

 The WindTripper* spoiler was then allowed to rotate into its deployed position, as shown in the two photos below. 

 Note the significant disturbance of airflow, and its resulting lift, over the roof.

 The maximum effect of the deployed WindTripper* occurred in the critical leading edge portion of the roof, with flow reversal occurring at some locations.  The yarn tufts wandered without significant energy, indicating a substantial reduction in harmful lifting force on the roof and roofing material.

 This conclusion was further borne out by the significantly greater wind speed required to lift the roof structure off the side walls with the WindTripper* deployed.

WindTripper* under 85 mph wind deployed position

WindTripper* under 85 mph wind deployed position

* Patent Pending.

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Copyright 2008 WindTripper - WindTripper Is Patent Pending.
Last modified: 03/19/08