The conclusions of this video have far-reaching implications towards consumer attitudes towards battery-electric vehicles and potential bias if considering a purchase.And it deserves its own thread.
While I do believe that Jason Fenske is trying to empower viewers with information,specifically about the upcoming Tesla Cybertruck of 2021,Mr. Fenske has left the conversation open to additional insights into the world of towing that may presently elude him.And in his presentation,he has openly invited networking,for which, in this thread,we may flesh out new contributions.
I recommend all Fossil Fuel Free forum participants to watch the 'Why Tesla's Are Bad At Towing' YouTube video if they haven't already done so.
I'm in my seventh week of preparing materials in the wake of a firestorm of controversy,following Tesla's launch of Cybertruck,and hope to have those available soon.
Please watch the video,then we'll 'talk'.Thanks!
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..................................... COMMENTS.......................................... ...
*The first comment I'd like to make is,that since aerodynamic drag dominates the power equation for highway towing, if we're going to tow a trailer through the air at the same velocities at which some airplanes fly, we might want to give the process the same consideration as the aeronautical engineers.
*The second comment I'd make is,that the typical towing/towed combinations offered to us, better resemble an aircraft flying backwards,with trailing edges leading,and leading edges trailing.
*And to add insult to injury,these 'aircraft' have enormous holes punched through the middle of fuselage and wings.
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............................... TOW VEHICLE BASICS..........................................
For any given trailer,the performance of the towing/towed combination will be affected by the tow vehicle:
*Vehicle type: notchback,squareback,fastback,pickup,van,SUV,CUV,f airings,air deflectors
*Length
*Height
*Width
*Ground clearance (active suspension)
*Frontal area
*Coefficient of aerodynamic drag (in the combination)
*CdA
*Tire type(P,LT),inflation pressure,Crr
*Weight
*Distance to trailer
.........................................TRAILER BASICS........................................
For a given tow vehicle,the performance of the combination will be impacted by the trailer's:
*Distance from tow vehicle (tow bar length)
*Type of trailer ('box',sloped-nose,V-nose,bullet-nose,NASA-shoebox,tongue-pull,fifth wheel,gooseneck,tapered-roof,..........)
*Length
*Width
*Height
*Ground clearance (active suspension)
*Frontal area
*Coefficient of aerodynamic drag (in the combination)
*CdA
*Excrescences (exposed-protruding wheels/fenders,vents,skylights,A/C unit,antennas,satellite dish,LP tanks,cargo boxes,bicycles,awnings,hay bales,........... )
*Weight
*Tire type,inflation pressure,Crr
...........................................TRAILER GAP............................................
*If the tow/towed combination is considered as a single,but mutilated form,any existing gap can have a profound impact upon performance.
*From Abbott and von Doenhoff's 'Theory of Wing Sections,' we know that a gap (slot) constituting only 3% of wing cord can introduce a drag penalty,from 7.9%,to 31%,depending upon location.
*NASA's Class-8 tractor-trailer research demonstrated that a gap constituting 7% of total length introduced a wind-averaged drag penalty of 17%.
*Hucho published data for a commercial tandem rig in which the gap was responsible for a drag increase of Cd 0.073 (13.7%).
*Box trucks with cab-to-box gaps of 1.2% of length can equal the drag coefficient of an Airstream trailer in train.
*Chrysler Corporation's research of the NASCAR,2-car draft, revealed that a 'trailer' of zero draw-bar length reduces the solo coefficient of aerodynamic drag of the trailer by 37.1%.
*Hucho shares similar research for buses,in which the trailing bus enjoys a 66.6% drag reduction.
*In 1982,the 'Trailer Dome',of Fibrelock Fabrics Ltd,of Dorset,England,demonstrated a drag reduction,from 32%-to-52%,by eliminating all but 2.8% of trailer gap, with an inflated bulbous nose on a caravan trailer.
*In the United States,since 1951,intracity and intercity buses have used articulated,accordion closures to completely eliminate gaps between the towing bus and trailer extension.
*Imagineers later adopted this technology for their 'Tomorrowland' monorail,at Disneyland,Anaheim,California.
*Sloped-nose and V-nose trailers have deceptive drag liabilities,as beneficial stagnation bubbles of 'blunt-nosed' trailers are absent,to the detriment of both towing vehicle,but trailer as well.Hucho illustrates the lack of any drag advantage of sloped-nose trailers.Owner testimonials relate the same observations concerning V-nose trailers.
*Presently,in the world of RVs,the least offensive gap belongs to motorhomes, pulling toy haulers of smaller frontal area,such that the trailer becomes a wake rider,stuffing the wake, approximating a solid box cavity;organizing the motorhome's wake and delivering the resulting flow to a separation point of smaller cross-section and higher base pressure.
*In the world of fully-submerged bodies,as with dolphin,fish,squid,projectiles,airships,blimps,sub marines,torpedoes,electric trolling motors,fuselage,high-speed rail cars,medium and heavy trucks,only light vehicle and trailer design remain the outlier with respect to fluid mechanics.
.................................. TRAILER DRAG REDUCTION.................................
*Anyone with Hucho's text will already have his depiction of the VW Passat and Golf/Caravan wind tunnel studies incorporating a rooftop air deflector,good for a 15% drag reduction.
*Online,an RV owner shared his experiment with a 2007 Toyota Tundra,pulling a Layton Skyline travel trailer.His original 8-MPG improved to 9-MPG with the addition of a full tonneau cover,then by tilting the tonneau up,as a air-deflector,fuel economy rose to an average 11.5 MPG.
*The 'Trailer Dome' has already been mentioned,32%-to-52% drag reduction.
*Pat Nixon of Texas Tech, put some video together for me back in 1991,when we were doing the Becker-Lyon BMW LSR Bonneville motorcycle streamliner project.It included video of the T-T truck research,in which the fifth wheel bulbous nose did about as much good as anything the crew experimented with.A lesson not lost on Airstream,Casita,SCAMP,Happier Camper,ARGOSSY,..................
*Both BamZipPow and I are running zero-gap trailers.I'll let him tell his story over at his thread.So far,with an incomplete project,I'm sitting at delta-zero mpg pulling mine.
*Trailer-Tail is out there.And they're petitioning governments to allow even longer units.
*The 'baby' template car came in at Cd 0.121 at DARKO,so there's a high probability that the boat-tailing is a sure thing, as far as drag reduction goes.
*Between the two trips to DARKO,there's enough data to show Spirit at as low as Cd 0.218,so we know pickups have some wiggle room.
........................... TOW VEHICLE/TRAILER RELATIONSHIPS.......................
*Hucho presents a sedan/box trailer combination.As a 'train',the presence of the trailer behind the sedan lowers the sedan's Cd by 43.4%,with its wake embedded within the positive pressure of the trailer's forward stagnation bubble.The trailer itself,gets a small drag reduction of 4.8% by riding in the small wake of the sedan,less dynamic pressure impinging on its forebody.
*Hucho also presents D.M.Waters research of a Morris Minor 1000 notchback and squareback pulling the same caravan trailer,both with different tow-bar lengths (gaps).Overall,the squareback demonstrates a drag advantage compared to the notchback,with the aftbody of the tow car more closely matched to the frontal area of the caravan,and trailer training inside a larger wake.
*Hucho also offers two different fastbacks towing,a Golf and Passat,which are of particular interest with respect to the Tesla Model X.Since the fastback body's flow produces the smallest wake,it imparts more dynamic pressure to the face of the trailer,while offering the face of the trailer the least shielding from the onflow.The sloped aftbody of the fastback also presents less ability to telegraph positive pressure of the trailer's stagnation bubble onto the fastback.It is the least matched configuration,frontal area for frontal area.
*Hucho also presents Romberg et al.'s NASCAR,2-car draft,of the Cd 0.315,45-degree backlight,200-mph,Dodge Charger Daytona development vehicle.Within the train,the lead car realizes Cd 0.22,a 30.15% drag reduction,with no wake,while the trailing Daytona realizes a Cd 0.198, 37.14% drag reduction,having no forward stagnation point,however ,all the wake.Representing a trailer towed at virtually zero tow-bar length.
*Hucho also shares a NASCAR,two-bus draft,which,like the Chargers, presents a similar but different drag relationship,with lead bus realizing a 15% drag reduction,while the trailing bus enjoys a 66.6% drag reduction,as with a Class-8 tractor-trailer,or railroad train,with narrow gaps.
*From Sighard Hoerner we have gap-less,streamlined railroad cars,also with streamlined,boat-tailed, tail cars.
*Additionally,Hucho offers a constellation of commercial vehicle combinations,including buses (motorhomes) and associated drag data,including aerodynamic add-on devices.
*The SAE has published entire books on fuel economy,with data for both rolling resistance and aerodynamic drag.
*Baron Reinhard von Koenig-Fachsenfeld's Aerodynamiks des Kraftfahrzeugs is a power-house of aerodynamic data, from his years with Wunibald Kamm's FKFS,next door to Daimler-Benz.
*Same for Hoerner's 1951,'Aerodynamic Drag,' in which about every imaginable geometric shape has been tested and documented,subcritical,supercritical,and supersonic.
............................. TFLcars 'Can Electric Cars Tow?................................
*First up on the Tesla Mode X tow test was the 16-foot,Cimarron,tandem axle, Showstar,V-nose,horse trailer. Some observations:
*We have no idea what the tow-mirror drag contribution is.On the Tesla owners forum,trailer widths appear to garner greater consideration.Tesla probably has the lowest drag side mirrors in the industry,and more closely matched frontal areas of trailers keep it that way.Cybertruck is 83.36-inches wide,compared to the Model X's 79-inches.
*The Showstar was towed to LOVES behind a HUMMER H2 with roof-mounted cargo carrier.We might consider the frontal area ramifications of the H2 and its wake,compared to the Model X.
*The Ram pickup which was highly praised for its towing prowess is wider,taller,and is basically a full-separation vehicle,compared to the Model X,providing a larger wake in which the Showstar may ride.
*The V-nose of the Showstar does not produce a stagnation bubble and high pressure benefit to the aftbody of the Tesla,as would a more blunt-nosed trailer.
*The wider wake of the Ram would minimize the impact of Showstar's exposed fenders,compared to the Tesla.Not an issue with Cybertruck.
*The taller Ram,and its turbulent wake exposes less of Showstar's forebody to dynamic pressure,an advantage lost on the Model X,but not Cybertruck.
*I estimate Showstar's frontal projected area at approximately 62-sq-ft,compared to an estimated Af 30.777-sq-ft for the Model X,and approx. 35.5-sq-ft for Ram.Cybertruck is approx. 38.53-sq-ft..Cybertruck would not require mirror extensions,perhaps no mirrors at all.
*If one is going to pull a trailer up the 'Gauntlet at 70-mph,it would be good to enter the incline at 70 mph.
*If your going to pull a trailer up the incline at 70-mph with an electric truck,you might want to also descend at 70-mph on account of regen.Another oversight with the testing.
*And since aerodynamic add-on devices can cut drag up to 52%,one might want to consider using the thirty-eight-year-old technology if you're going to tow at these velocities.
*Another curiosity with the TFLcars tow tests,would be the calculus that,a 4.8-mpg ICE pickup is superior to a 48-mpg-e BEV passenger car,both towing the same trailer,up the same mountain pass.
*It's 2,899-miles from New York,to San Francisco on I-80.Why does an 8-mile stretch of I-70 get to define the sum total capability of any SUV or pickup?
*And if only 5% of truck owners actually carry a load,or pull a trailer,why is towing even a problem for 95% of pickup owners? Are we obsessing over a problem which doesn't exist for most people?
*Oh,and how about beginning the test with the trailer first and get the big load out of the way while you've got most of the battery capacity available?
....................... THE BOREAS SERIES XT OFF-ROAD TRAILER ...................
Some observations:
*It's an 'off-road' trailer,and that's where it belongs.Crawling behind a 4WD,dropping mpg below 8-12 mpgs.
*Analyzed by components,as per Hoerner/Messerschmitt,I give the trailer Cd 0.924,solo in a wind tunnel,at approx. 38.18-sq-ft frontal projected area.How it performs in train,will be decided by the tow vehicle.
*A major portion of the tires are exposed to the airflow.
*The axle and suspension is completely exposed.
*The bottom of the frame is about 25.5-inches off the ground,making it's belly useless for any airflow.And with zero belly pan,it's just as well.
*The fenders extend a foot from each side,merrily shredding the air as she goes.
*The envelope which rides ahead of the spare tire is Cd 1.11.
*The spare tire basically rides in it's wake.
*Between there and the actual trailer body is a rectangular cuboid cargo/toolbox,virtually embedded in turbulence.
*The 'face' of the trailer is a full 75-inches from the tow vehicle's stern,making any hope for pressure relief a hallucination.
*The sharp leading edges spell immediate and full flow separation,which will reattach 77-inches down the driver's side (except for near the fender),however the attached storage and propane bottle on the passenger side destroy any chance of flow recovery on that side,and forcing asymmetric flow and wake.
*The roof-mounted rack,tent,vent,and tubular carrier are the coup de grace for the flow over the roof.
*At 93.25-inches in height,it's just as tall as the Cimarron horse trailer.Behind a HUMMER H2,not so offensive.Behind the Tesla it has nothing going for it.If you intentionally wanted to destroy the performance of the Tesla,I can think of no better candidate trailer.The Cybertruck will fair better.
*It's good that ICE pickups have up to 1.2-MegaWatt fuel tanks.They'll need them,pulling sky-scrapers like that around.
*If TFLcars has done one thing,it's not so much that it's illustrated the weakness of electric vehicles,as it has the inappropriateness of some contemporary trailer products sold in the USA,when paired to a Tesla Model X.
*There exists,trailer technology,which, while doubling a tow vehicle's weight,returns 100% fuel economy,and battery economy.Even better economy!This should be considered when making broad brush stroke appraisals of BEV performance.It's all in the aerodynamics.
-----------------100% mpg trailer images............................................
I located what's left of the zero-loss trailer images from Photo Bucket.
If you'll GOOGLE: Phil Knox's gap-filled full boat-tailed trailer,on the second line down you'll find a rendering based upon the 1st-gen HONDA Insight,and Alan Cocconi's EV sports car.
................... Tesla Model-X/Bowlus Road Chief NASA/MIT 'testing'.............
I modified the 1934,Bowlus-Teller Road Chief, with the 1980 NASA roof deflector,gap-filler,and added the 1987 GM Sunraycer/1990's Goro Tamai, MIT,solar racer's full wheel fairings.
*At the 'California' 55-mph speed limit,on level highway,the 'rig' returns 291.5 Wh/mi,for 103.6 mpg-e,and 316.3 miles range.
*In Denver Colorado,on the TFLcars' I-70 'loop,' and 75-mph,she drops to 393.7 Wh/mi, 234-miles range,at 76.8 mpg-e.
*We can discuss the 'Gauntlet' later.
I'm in my 14-week of Cybertruck calculations.I've been putting in 50-hour weeks,doing numbers and images which will go to AeroStealth for You-Tube.
*The most interesting 'experiments' are derived from Chrysler's R&D of the Dodge Charger Daytona,NASCAR,2-car Draft.They can produce pop-up,or telescoping trailers of negative drag coefficient,which actually increase the driving range of the towing vehicle,overcoming a 'doubling' of weight,rolling resistance penalty.
*And by retaining a battery pack,the electric heat pump,and air suspension,a Tesla-based trailer can double the range of the rig,help it up a mountain, at up to 130-mph (if the tires could take that),regen on downgrades,and supply power once to the campsite,if off-grid.There'd be no charging en route,unless you planned to drive up to over 1,000-miles in one sitting.The cheapest Cybertruck would have 500-miles towing range,away from mountain grades.
*At state and national parks,plus area RV parks,the available 220-V would handle daily loads plus recharge the rig while fishing,hiking,....whatever.
*I doubt that you could flip one on it's side in a crosswind.The whole rig would hug close to the ground,as there's no need of ground clearance on the open road
------------------Tesla/Cimarron on the 'Gauntlet'--------------------------
*I streamlined the Model-X/ShowStar combination as per NASA,MIT,GM,and was able to scale the Gauntlet without falling below 135-miles range.I entered the grade at 70-mph,letting velocity fall during the climb,to 40-mph in the climbing lane to finish the 8-miles,then resumed 70-mph.Supercharger stations are to be located 134-miles apart for the time being.Knocking 5-mph off velocity and streamlining allowed the rig to just eek by.
*At California's 55-mph speed,the Model-X/ShowStar returned 180-miles range,also doing the 7% grade at 40-mph.
*Un-modified,Cybertruck will have a slight aerodynamic advantage over the Model-X,due to it's larger frontal area,and even with a 1,100-pound penalty,should mimic the Model-X's performance pulling.Rolling resistance is essentially meaningless compared to aerodynamic drag.Streamlined,Cybertruck is essentially the same as the streamlined Model-X,as both are married to the ShowStar at identical frontal areas.With 184.484 kW-hs of usable battery capacity,Cybertruck should do the Colorado 'Gauntlet' with 271-miles range,and California's with 387-miles range.With a minimum drive time of almost 4-hours,if people continue to urinate,hydrate,and eat;there remains the opportunity to make regular 'rest' stops,while catching some kilowatts at the same time.
I'll post more as I complete it.
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