Fill it with helium balloonsI wonder how efficient my Cybertruck will be when towing my little Casita. It's fairly aerodynamic, but my Ram 1500 Hemi averages 13 mpg towing it at 65 mph. I have never towed it with my MYP.
I was agreeing with you, right up until you said âThe v front does not reduce drag.â Yes, it does. In a trailer, its impact on drag reduction is not as great as the back (as you point out), but it DOES reduce some of the drag. The only possible exception to that would be if it were being towed by a van, the same size or larger, so that the trailer could sit in the âshadowâ of the van.
It is possible to increase drag via the taper at the back.
Love that diagram and I feel like I intuitively understand the impacts of the different shapes with one exception - why is the half-sphere LOWER drag than the full sphere? The way Iâve always thought of aero, conceptually at least, is in terms of a âvacuum shadowâ behind the shape moving through the air. In other words, if you had a wind tunnel and string/ribbons so you could see the air flow, at the point where the laminar flow detaches from the shape, the area between the boundary layer and the object represents a complex shape filled with different layers of vacuum pulling back on the object (drag). And filling in that shape with more âobjectâ would effectively reduce the area of the vacuum shadow, reducing the drag. So basically the reason a airfoil has such lower drag than a sphere is that the vacuum shadow behind the widest point of the foil is âfilled inâ by the trailing structure of the air foil, so there is no vacuum shadow, at least at certain speeds. Given this, Iâd almost expect the half-sphere going backwards (flat side first) to be close to the sphereâs Cd, but higher, and the half-sphere with the curved edge going first and the flat side trailing would be much higher. Why is the half-sphereâs CD Lower than the full sphere? That makes no sense to meâŠ
en.m.wikipedia.org/wiki/Drag_coefficient
Notice the "angled cube" vs "cube". Despite the angled cube presenting a wider total cross section to the wind at its mid point, because it gets to that maximum cross section and back more slowly and evenly, it actually has a lower coefficient of drag.
This is due to the "area rule" concept I talked of a few posts back.
https://en.m.wikipedia.org/wiki/Area_rule
There's actually one more shape missing from that chart, which is the "streamlined body" with the curves after it's maximum width point inverted. I remember papers on that shape claiming it was actually lower drag per unit volume. Apparently, detaching a toroidal wake at just the right size actually causes some air to push forward again on the rear end. This effect has been documented in fish, as an explanation for how they can stay mostly motionless in a flowing stream. Good luck utilizing that effect in the automotive world though, with all the complications like varying speed, cross wind, and the incompressible ground below you.
Yep, and quick look at the actual chart on Wikipedia indicates that the shapes all have the same Reynolds number. But that number is calculated from four values, 3 of which are based on the fluid through which the object is passing. As pointed out, velocity is one of those values. And the two publications from which the numbers appear to be derived, are Dynamic response of pipe rack steel structures to explosion loads and Explosion Hazards and Evaluation. The former is a masters thesis, the latter is a published book. If youâre looking at lift and drag during an explosion, youâre looking at supersonic flow, where the behaviors are much different. I didnât buy the book, but I did go over the paper. This chart appears to bd derived from a chart in the paper which is evaluating the backside load on small pipe and other construction materials when compared to the shock load on the frontside.
Helicopter definitely beat the air into submission⊠but one show of weakness, and down you goâŠHelicopters are proof that with enough power applied, anything can fly.
