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If Tesla made "weirdmobiles"... introducing the Model W.

Discussion in 'Model 3' started by KarenRei, Jul 31, 2017.

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  1. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    It's well known that Tesla has a rule against making "weirdmobiles" - cars with an unconventional appearance. Many "weirdmobile" traits offer no practical driving benefits, such as excess fins, bubble domes, etc. However, few people are calling for things that limit the market and hurt range/performance. In general, a "weirdmobile ban" generally is a ban on just one thing: streamliners. Cars with more airplane-like styling rather than traditional car styling, in order to lower the drag coefficient.

    Here we will not address the challenges of getting the market to accept a streamliner (aka, a "wierdmobile"), except to note that Tesla has already started taking some steps that people might consider "weird", including elimination of the front grille, keys and fobs, the traditional dashboard, and numerous other details. We will simply examine what the Model 3 had been like if physics had been allowed to take a stronger role in its design instead of tradition, basing our numbers on the Model 3 as-is.

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    Model W Type 1

    In this variant we only incorporate basic streamlining principles, while keeping the front and rear wheels inline and the materials unchanged. All four wheels are skirted with quick-open skirts with abrasion-resistant pads at their bottom; the front skirts must rotate along with the wheels, in shrouds. The bottom of the vehicle is elevated (the optimal ride height increases significantly for vehicles with a high rear taper). The hood becomes a flattened egg shape, allowing for the hood rake angle to blend directly into the windshield rake. Side mirrors are eliminated in favour of cameras (to Tesla's credit, they already want to do this; regulations have been the holdup). The dimensions change (w=-5%, h=-10%, l=+15%), from (w=1849mm/72,1"; h=1443mm/56,1"; l=4694mm/184,8") to (w=1750mm/69,2"; h=1299mm/51,1"; l=5398mm/212,5"). The corners are rounded in to a greater degree, cutting off about 10% of frontal area. The vehicle reaches maximum dimensions around the driver. By the rear passenger bench seating, there has been a small vertical taper but only minimal horizontal taper. Behind the rear passengers, taper continues on both axes but primarily vertically, getting close to forming a line on the rear. On the rear end, the lights, the license plate, and bumper come as close to forming a line as can be met while also providing for safety and meeting legal requirements. The overall shape from the side is a zero-lift airfoil atop shrouded wheels. Cabin and cooling air vents through the rear bumper, helping to fill in the minimal wake.

    Negative consequences:

    * The small loss of passenger width (99mm / 2,9") and more rounded corners means that while two rear passengers can still fit in comfort, it's a little tighter (~1 inch less per person) for three. The height loss is more significant - 144mm / 5" in the front, and greater in rear. However, the height (1299mm/51,1") is still much greater than for a vehicle like the Tesla Roadster (1127mm / 44,4"), and the SUV-like higher ride height of the vehicle makes it easier to get in and out. Passenger seating is more reclined than for a Model 3. Vehicle length is now more similar to a pickup truck.
    * Available battery pack volume is similar to the Model 3, but shaping is more complicated.
    * The CG is higher than for the Model 3 (although still lower than for a typical vehicle)
    * There is somewhat more weight in extra glass and length (although offset to varying degrees by reduced width and height). The windshield may be more difficult to manufacture.

    Positive consequences:

    * Passenger legroom increases.
    * The vehicle gains a long, almost pickup truck-like bed in the rear, particularly when the rear seats are folded down. Contrarily, an additional mini-row of seating could be made optional for one or two child seats (headroom is too small for adults).
    * Frontal area decreases to around 77% of that of the Model 3, while the drag coefficient drops to around 0,17 (from 0,23), leading to a drag area 57% of the Model 3.
    * Assuming that pack capacities and vehicle mass remain the same, the short-range variant has an EPA range around 320 miles, while the long-range variant has an EPA range of around 470 miles. Contrarily, pack sizes could be dramatically reduced, reducing mass and purchase price significantly.
    * Top speed increases to 172mph for the short-range pack and 185mph for the long-range pack, from 130 and 140mph, respectively (assuming gear ratios and limits are matched to the lower aero resistance).
    * Wall-to-wheels energy consumption decreases from ~256 Wh/mi to around 170 Wh/mi. The base vehicle switches from charging at 30mph on 240V/30A to charging at ~45mph on the same socket. The long-range vehicle goes from 37mph on 240V/40A to 56mph. Even on 120V/15A the vehicle charges at 11mph.
    * The high ground clearance improves performance in snow and potentially allows for offroading.
    * The greater windshield rake and slightly more reclined position keep the A pillars further away from the driver, reducing the blind spot and improving the "glass canopy" aesthetics. The smaller nose makes the road more visible.

    Model W Type 2:

    Starting from the Type 1 base, we take streamlining further and combine the rear wheels into a single central pod, forming a delta trike. We assume that there remain two wheels rather than one to keep the vehicle classified as a car rather than a motorcycle, and thus avoiding criticisms of skirting safety regulations. Contrary to a delta trike (narrow forward, wide at the back), a "tadpole" configuration (wide forward, narrow at the back) has excellent stability on the road, similar to that of a traditional inline four-wheeled configuration. This is because when braking and cornering, the CG lies nearly between the front two wheels. The Cd drops to around 0,15, an extra 13% decrease in aerodynamic drag, increasing range and charge rate even further (or correspondingly, pack size, weight and cost). Weight drops slightly. If the vehicle can be shown to be stable driving at moderate speeds and payloads with only one rear wheel for a few dozen miles, the spare tire can be eliminated, further saving weight and increasing interior room.

    Model W Type 3:

    Starting from the Type 1 or Type 2 base, we switch from aluminum / steel construction to foam or honeycomb composite construction. Fiberglass panels have long been used in consumer-grade vehicles in this price range, usually with polyester resin. Vinyl ester costs only marginally more than polyester and significantly improves mechanical properties and durabilities. The most expensive traditional option, however - carbon fiber and epoxy - has generally been priced out of the midrange. While carbon fibre prices have been falling, new composites have presented interesting possibilities - for example, carbon/UHMWPE (spectra/dyneema) hybrid weaves combine the strength of carbon fibre with the energy-absorbing (non-brittle) properties of UHMWPE, at a lower price than pure CF, while simultaneously decreasing density and thus increasing the area moment of inertia (bending / breaking resistance). Foam and honeycomb composites greatly increase the area moment of inertia, and thus the strength to weight ratio; they simultaneously add insulation (reducing parasitic losses) and noise dampening. The lighter weight allowed by a composite body reduces rolling and braking losses (dominant in city driving) while improving acceleration.

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    In conclusion: show some heart for the humble "weirdmobile" and its airplane-like looks. It's not "weird" for it's sake - it's "weird" for your sake!
     
  2. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    To reiterate: I don't blame Tesla for going for "mainstream" looks, even though the consequences for range / battery size are severe. That said, I do hope that styling trends continue to move in a more aero direction in the future. Once upon a time, cars with raked windshields (rather than vertical) were "weirdmobiles". So were cars with horizontal grilles. Cars with curved windshields were once weirdmobiles. So were cars without chrome bumpers. And cars with lights embedded in them rather than sticking out. So much of what we see as "normal" once made a car a weirdmobile. From a marketing perspective, beyond the range and battery size advantages, I think the high clearance could be a good selling point on its own. One could even, for example, have an option for an integrated tent into the rear, for "glamping" out in the middle of nowhere just by popping the hatch (like a pop-up trailer). Potentially made of flexible solar material to trickle charge the car while you camp.

    But as it stands: I get it that people see streamliners as "weird". And thus, I know that we will continue to get vehicles like Model 3s and not Model Ws. :)
     

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