Quote:
Originally Posted by Shepherd777
I completely agree. This is why I designed my aero semi truck this way. Here is a quote from my web site:
One can see by these fiberglass pics that the rig does not have the traditional look of a other class 8 rigs. Other Class 8 rigs slope-in the hood starting at the firewall under the "A" pillars. Then they highly swoop the wheel wells over the tires and then drop-off the swoop in front of the doors. This "old-school" automotive design is based on 70-80 year old automotive theories and mind-sets.
One of the best examples of those old-fashioned designs is shown by the pic below on the left of a 1941 Willys. Obviously, contemporary Class 8 trucks don't have the pointy nose like the Willys. They just cut-off the point of the hood and have that big, dumb, square diesel truck radiator as part of the body! At least back in 1941 they got it right and placed the radiator inside that pointy nose. They ducted the radiator engine cooling air through that lower horizontal lower body grill. So all other modern Class 8 trucks took the best part of the 1941 Willys design and destroyed it, by cutting off the pointy, aerodynamic front end, and exposed those big, dumb, square radiators.
This rig is based-upon the more modern 21st. century design of a Bullet Train. After all, if you were building a new design Class 8 rig, and you wanted superior aerodynamics and fuel savings, what would you base your design upon? A 70- 80 year old design, or a 21st. century design that travels up to 350mph on a bullet train???
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Hi,
I'm going to throw something into the mix that is not so obvious....
"If we go to an extreme with the mentality of covering protruding wheels from our vehicles at any cost, then we should do the same thing with airplanes currently sitting at the airport".
Discussion:
1) Let's look at an airplane with a tadpole configuration..... The wheels are mounted about 3 feet from the bottom of the fuselage and without any covering, breaking a fair amount of wind. Let's further say that this amount of air drag needs to be dealt with.
a) Do we make small pants to cover the wheels?
b) Or do we (now get this), extend the bodywork all the way down to cover most of the wheels, and resultantly make the fuselage longer to accommodate the huge rise in cross-section? Note: we are not even addressing the weight gain and increase in skin friction from doing this!
The above conversation is an extreme point, but something that is being missed in this entire thread.
At what point do you simply add "pants" to exposed wheels/tires, or make the entire structure of the body shape larger to accommodate the protrusions?
I think there IS a rule-of-thumb for this effect, but no one has addressed it yet.
My three-wheeler, with a primary body with of 27 inches, and tires that stick out to the sides, at 60 inches, I believe is beyond the threshold of expanding the body shape to accommodate these "extensions". And I have already provided some basic math that shows this point fairly well.
The airplane example above is also in this same realm. No one would think to extend the bodywork to cover wheels...... wheels that extend away from the main shape that far.
I agree that as the main body shape is made larger relative to the track width, at some point it makes more sense to extend the bodywork to cover the leading tires. And when we look at the "bullet" train shown above, it makes perfect sense to cover the wheels with the body shape, since the body shape is already the same width (or wider) as the track width. This makes sense because it's so obvious!
No, a rule of rule-of-thumb for this breakpoint would be helpful to all who are eager to read topics such as this one!
But I don't think that a body shape that is fully, one-half the width of the tire tracks is at this point. Can we be a little more scientific than just "speculating"? Let's see some math or at least some nice pictorials showing why your design merits "automatically" covering the wheels with a body shape.
Developing a rule-of-thumb for anyone designing road going vehicles with different body-width to track-width ratio's would be very helpful.
Another consideration is what happens to the clearance between the main body and wheel pant, when the wheel is turned 30°, as in the example below... It appears that if a very streamlined pant is utilized, then either the wheel needs to be moved out, OR the body needs to be narrower. If this is not possible, then truncating the pants may need to be improvised.
It's obvious that if the body is another couple inches wider per side, there may be no option but to make the entire structure the same width as the tires, unless someone has other ideas....
Yet another option is keeping the pant "secured" (non-rotatable) and making cutouts for the wheel to make turns, similar to the front wheels on most cars. Obviously higher drag, but still gives the option of not having to drastically increase frontal area to cover the wheels, with much longer body shape as well. Slightly less unspring mass too.
Another way to allow getting the outboard wheel closer to the main body is to allow the rear of the wheel pant to pivot as shown below.... Just an idea, but could be useful.
Rule of Thumb:
3-Wheeler Design ----------
Track Body - Ratio Wheel -- Math
Width Width ------ Pants
-60 --- 27 - 0.45 -- Yes -- Post #22 and CAD Dwg
Bullet Train (estimated) ----
Track Body - Ratio Wheel -- Math
Width Width ------ Pants
-48 --- 80 - 1.67 -- No -- See picture above
Jim.