Shielding the Critical DRAG-INDUCING Uppermost Wheel
Our numerous patents show that all open-wheeled vehicles needlessly waste fuel by exposing the top portion of the wheel, whose surface necessarily moves forward directly against the wind at twice the vehicle speed. Thus, if the vehicle speed is at 65 mph, the top forward-moving surface of the open wheel is exposed to at least 130 mph winds plus any additional headwind that may be present at the time.
Orange arrows show the effective wind speeds on wheel surfaces under null (no) wind conditions. Blue extensions show the effective wind speeds on wheel surfaces under headwind conditions equal to the vehicle speed (An extreme condition for an automobile at highway speeds, but quite common for a bicycle).
(It is only the side-view outline of the wheel that appears to move forward at the vehicle speed. The individual wheel surfaces actually move forward anywhere between zero at the stationary ground contact point to up to twice the vehicle speed at the top of the wheel.)
And most importantly, since power loss due to drag force is actually proportional to the wind speed cubed—a very sensitive exponential relation—the much faster surface at the top of the wheel is dissipating at least 8X more power than any equivalent slower surface on the deflector panel. Moreover, this highly magnified power loss on the exposed wheel increases rapidly with any additional external headwind present. For this reason alone, our minimally sized deflector panels become far more efficient in windy conditions, a non-obvious relation supporting our numerous patent allowances.
Orange arrows show the effective wind speeds on wheel surfaces under null (no) wind conditions (up to twice the vehicle speed). Blue extensions show the effective wind speeds on wheel surfaces under headwind conditions equal to the vehicle speed (Up to 3X the vehicle speed, an extreme condition for an automobile at highway speeds, but quite common for a bicycle).
(While wind tunnel testing has focused on the measurement of drag force, rather than power loss, it is actually power loss that directly affects fuel efficiency. Power loss is difficult to measure in a wind tunnel, while drag force on the vehicle body is quite simple. Then a simple 'rule of thumb' is used to estimate fuel efficiency. This method is fine for measuring the relative effects of aerodynamic efficiency on body surfaces of the vehicle, such as an airplane, but is quite lax in estimating the true drag effects of headwind-exposed wheels on an open-wheeled vehicle.)
Our wind shielding deflector panel is simply fixed directly to the vehicle frame, and is therefore moving forward at only the vehicle speed (not up to twice the vehicle speed like the uppermost wheel surfaces), dissipating much less power than equivalent uppermost wheel surfaces that are otherwise exposed to much higher wind speeds.
Thus, it is only logical to shield the drag-sensitive top of the wheel using a slower-moving, more efficient deflector panel in order to shift the highly magnified drag otherwise induced on the faster upper wheel surfaces onto the slower moving vehicle frame, thereby reducing the effective drag on the vehicle considerably, especially in headwind conditions which exacerbate the effective vehicle drag on exposed wheels. As a result, our deflector panels are optimally sized to minimally shield only the uppermost portion of the wheel, and should always be used in order to actually minimize vehicle drag.
Proof of concept and performance testing was initially done on bicycles, the vehicle most affected by headwinds.
Furthermore, since the lower wheel rolls easily over any bumps in the road, the lower portion of the wheel likewise rolls just as easily against any headwind (affecting form drag on the wheel outline), much more easily than any lower wheel deflector panel plowing through the wind at the vehicle speed.
Thus, the lower wheel should ideally remain exposed to headwinds, a non-obvious relation not yet appreciated even in auto racing where airplane wind tunnel testing protocols are erroneously applied to open-wheel vehicles (see above), thereby having misled an entire industry for many decades.
(Simply demonstrate the mechanical advantage/disadvantage effects of form drag on a vehicle wheel, by pushing along a toy model along the ground while resisting first on the lower and then upper portions of a wheel. Note how much easier the wheel rolls through any wind resistance located below the level of the axle than any 'air plow' fairing positioned in front of the bottom of the wheel!)
(Formula One and IndyCar do not seem to truly care about minimizing drag...they have rules against changing the car appearance too much. So they shield the lower part of the wheel, the opposite of efficiency, in order to produce down force and keep the style 'looking' fast.)
And making the deflector panel much larger in size also defeats the fuel savings potential, since larger panels induce too much drag on the vehicle without providing any gains from reducing drag on the upper wheel, since the lower wheel should ideally remain exposed to headwinds. Our panels are then optimally sized to shield just enough of the critical upper wheel surface to yield a substantial reduction in vehicle drag even under our worst case null wind conditions.
(Shielding the upper wheel when an extreme headwinds is present dramatically reduces over 90% of the drag on the wheel from the red curve to the green curve. Still for lesser headwinds, the gains lie in between these curves, still providing substantial gains in vehicle efficiency.)
And as discussed above, whenever headwinds are present, vehicle efficiency actually increases quite rapidly, this predicted effect having been confirmed through numerous road tests on bicycles. So for vehicles operating frequently on the highway under windy conditions, fleets can expect even more savings, reducing payback time considerably.
Bicycle Downhill Coasting Test demonstrates potential gains of shielding only uppermost wheel surfaces into headwinds.
(Years of instrumented road testing on bicycles has shown that achieving repeatable headwind conditions is virtually impossible, rendering road test results in windy conditions nearly useless. The only practical road test that we were able to achieve were numerous side-by-side downhill coasting tests, which yielded very consistent results, proving the advantages for shielding only the upper wheel in order to actually minimize vehicle drag.)
And as mentioned above, development testing was first conducted on bicycles in order to confirm the math model for drag reduction on open-wheeled vehicles. The model plotted under varying headwind conditions (below) shows that efficiency gains rise quite rapidly (left side of chart) from a minimal level with only minor headwinds present. This indicates that even large trucks with exposed wheels will quickly gain in fuel efficiency under even only moderate wind conditions (and also at higher vehicle speeds). In fact, class 6 box truck drivers have reported even feeling the difference and noticing a speed gain on long hills (a test any fleet can easily conduct without having to spend thousands for fuel economy road tests).
(The quite complicated 15-term math model of open-wheel vehicle drag mechanics predicts that shielding the upper wheel increases vehicle efficiency quite rapidly in only minor headwind conditions (as well as with higher vehicle speeds). These curves have been verified through extensive road testing in windy conditions on bicycles, and will be similar in trend for larger vehicles such as trucks. That is, in windy conditions where some headwinds are present, we can expect a quite rapid rise in the effective gains in fuel efficiency by minimally shielding only the uppermost portion of the wheel.)