Industry Testing Protocols Further Explained:
As mentioned, fleets typically road-test trailers only under near no wind conditions, since no wind conditions are at least somewhat repeatable from test-to-test. And no wind conditions happen to show that short trailer skirts can be somewhat effective, since the rear wheels are still at least somewhat shielded from headwinds in the absence of any crosswinds.
Fuel Economy road tests of our deflector panels with M-V-T-Solutions in Pecos, Texas, fall 2021.
(NWT has conducted both standard industry protocol road tests in low wind conditions, as well as engineering tests in afternoon high wind conditions in order to confirm the major differences that our panels produce under the windy conditions common in many parts of the country.)
But testing in the windy conditions under which many fleets actually operate is quite problematic, since windy conditions are very unrepeatable from test-to-test, and is therefore avoided in standard testing protocols. And since shielding the upper wheel is much more effective in windy headwind conditions than under null or no wind conditions, standard industry road testing protocols (including wind tunnel protocols) simply will not show just how effective our deflectors are under real world windy conditions.
Therefore, fleets should not rely solely on standard low-wind road tests of shorter trailer skirts in determining just how effective these skirts are in real world windy conditions. With the rear wheels being exposed to crosswinds, the wheel sets become very high drag inducers on the vehicle, largely negating much of the benefit that these short skirts yield under null wind test conditions.
However, by adding our deflector panels to these trailers already having shorter trailer skirts, fleets can then correct for this savings degradation by also shielding the upper wheels under windy conditions. In fact, this combination is likely the most efficient and cost-effective deployment of both technologies under the windy conditions common across most of the country.
Furthermore, wind tunnel testing will also not show the magnified effect that wheel drag has on the vehicle, since the complex mechanics of the freely propelled vehicle on the road is negated by the wind tunnel model being instead fixed to the ground by attachment to a force-measuring stinger. Rather than power dissipation being directly measured inside the wind tunnel, drag forces acting on the body of the vehicle are instead measured to only infer what effect measured vehicle body drag has on overall vehicle efficiency. Actual vehicle efficiency is then simply estimated from measured vehicle body drag by using a rough 'rule of thumb' estimate, as explained by test engineers at ARC while we were testing our Inner Wheel Skirt invention.
(This reliance on simple vehicle body drag measurement protocols in the wind tunnel at ARC in Indianapolis was quite surprising to us when we tested our Inner Wheel Skirt invention in 2021, since we assumed ARC would be a bit smarter in measuring the efficiency of open wheeled vehicles. But the racing industry has likely grown accustomed to this comparative approach of body drag measurements, apparently satisfied in ignoring the highly magnified drag effects of the exposed wheels.)
While this rough 'rule of thumb' estimate can be useful for vehicles with covered wheels shielded from headwinds, it becomes quite inaccurate for vehicles with large open wheels exposed to headwinds.
As a result of these testing limitations being largely inaccurate for measuring the effect of shielding only the upper wheel, we invented a more accurate method for vehicle wind tunnel testing that instead has the vehicle being self-propelled and unrestrained on the rolling road inside the wind tunnel, just as it would be on the actual open road, in order to directly measure the power being dissipated in drag on the entire vehicle, including the wheels.
In this patented method, rather than relying on any estimated effect based on body drag forces on a restrained vehicle that is effectively attached to the ground via a force-sensing stinger, the total power being dissipated in drag including the otherwise unmeasured magnified drag loss on the wheels is measured directly through the power being delivered through the wheels by the rolling road itself. This power being delivered is then equivalent to total drag power being dissipated on the vehicle.
This new wind tunnel testing method can then capture the true effect of shielding the upper wheel, whereas standard wind tunnel protocols measuring only drag forces on the vehicle body will not. However, employing this patented method would require a retrofit of the rolling road controller, an expensive modification wind tunnels have yet to adopt for increased measurement accuracy specifically for testing open-wheeled vehicles.
We confirmed these standard protocol testing limitations while testing in the ARC wind tunnel in Indianapolis in 2021, where we also confirmed the enhanced crosswind gains produced by our Inner Wheel Skirt invention. We tested our Inner Wheel Skirts on both a semitruck model and on a pickup truck model using standard wind tunnel drag force sensing testing methodology.
Both tests showed dramatically enhanced gains in crosswind yaw angles of only four degrees, reducing vehicle drag up to 10X more than in simple headwind conditions. We expect those gains to increase even further in larger yaw angles often encountered under windy conditions, since rear wheel sets directly facing headwinds become major drag inducers on the vehicle.
As previously discussed, wheel sets exposed to crosswinds exacerbate the turbulence developed immediately behind the vehicle. Turbulent swirling winds developed behind the vehicle include a momentum component of force within the moving air currents, thereby reducing the effective static pressure component in the swirling air. Reduced static air pressure behind the vehicle then increases the effective differential pressure developed between the front and rear of the vehicle, increasing overall vehicle drag.
For this reason, reducing turbulence developed behind the vehicle is also critical to reducing overall vehicle drag. And Inner Wheel Skirts are also effective for this reason.