Engineering Explained:Why Tesla's Are Bad at Towing

[freebeard]

I retrieved the book I mentioned in Permalink #168.

The pages are 92 [Utility core] and 93 [schematic]. A three-story structure that integrates a solar roof, with two distribution rings and inclusive of the ashes that go from the fireplace to the compost digester that surrounds the hot gray water tank.

I'll likely take it to the library and scan some sample pages.

[Golden Ears]

@redpoint5 this might be the most egregious thread derailing I have ever witnessed.

Slowmover was banned instead of you? If I was a mod I’d ban those who contribute the least to solving problems.

Ok let’s get to the meat of this.

The real issue here as we all recognize it is efficiency of towing by improving the aerodynamic relationship of the tow Vechiles and trailer.

It has absolutely zero to do with whether the tow vehicle is powered by gasoline, diesel, cow farts, hydrogen, electricity ,hybrid or your bunch of hot air blustering tomfoolery. Oh you’ll all hate me now. But maybe you’ll stay focused by channeling this into the original discussion.

Solve the aerodynamic relationship or coupling relation of trailer to tow vehicle and every single person on the planet benefits from the efficiency (except the fuel sellers and makers of solar panels ) .

Most of the energy is translated to heat. Better aero means less waste heat per mile no matter the energy used.

So here’s a personal experience .

In 1993 I won a silver medal for downhill speed skateboarding from the French & Spanish Olympic committees in adventure games held in the Pyrenees mountains. Without improving my own aerodynamics by wearing a rented wetsuit, I might’ve placed third or worse.

Gravity is a great equalizer when it comes to gravity powered vehicles.

So let’s talk a little bit about aerodynamics with skateboards. I am also the world longboard champion.

Here are some different speeds attained on the same hill using the same gear, but with different configurations. The hill is the Harvard’s Arnold Arboretum in Jamaica Plain near Boston. A spiral hill of mild grade.

Speeds attained: gear is consistent. 55” Gravity brand Ed Economy Longboards with 78a hyper rollo wheels. Speed at bottom of hill is in mph. Hill length is identical for all runs.

1. Standing upright turned sideways 19mph
2 . In a “ Hut Tuck” bent at waist , hiding one legs behind the other. 24 mph
3. Two boards , two people identical weight and build in Catamaran 27mph ( 4 legs hide in the frontal area of about 1.25 legs , torsos present the same frontal area as a person sideways standing…if the hill were faster the hut tuck might win if speeds exceeded 5-0 mph.)
4. Two boards , 4 people with a space between the front row catamaran and rear 2nd row. 32 mph
5. Same but all bunched up near the front , no gap 36mph
6. 6 people 3 rows , holy crapolla 53 mph ! We nearly destroyed the 8 wheels employing a reverse ski snowplow stop ( all leaning outwards legs locked)

So what’s interesting to learn here is as the frontal width becomes less significant relative to the length we have DRAMATICALLY faster speeds despite exponential drag increase.

12 legs hide in the frontal area of 1.25 legs.

Also interesting to note was the speed seemed ( totally subjective here) to pick up the most rapidly at speeds over 20mph. It’s was pretty insane . Mostly because I was the only skilled person in this directing 5 inexperienced people 2 of whom have never skateboarded and had to keep them calm when I was flipping out inside my head wondering if I could stop them before we ran the possibility of colliding with a random patrolling park ranger car around a blind curve breaking up to 12 legs at once.

So melding the gap here to me seems akin to what little I know about sailing and “ hull speed”. Apparently long thin boat hulls can hit a higher speed if their waterline length is long relative to their frontal area. My prom dates father owned “Circus Maximus” a long fast sailboat.

So if we want to solve this equation , I think what we need is a stretchable yet very firm relative to highway speeds …uhhh “Linking shrouded fairing” that connects the tow vehicle to the trailer front in an aero shape (Better than the bendy bus ridged accordion linkage )

I own a 2017 Model X 90d which already has a battery capacity of about 85.5 which maybe about 81kw (at 100% charge) is usable (4kW is hidden reserve ). It’s “Ideal range when new was 313m and now is 299m thanks to a tow yard letting the battery go dead. So let’s say I have 79kw available.

Now I need to tow an airstream or similar build tin can .

1.So I think the best I could manage is to put a sail type cord ridge in some stretchable sail type cloth …and slam that down under/inside the trunk lid hinge.

2. Take the other end and secure that to the airstream top stretching it over the roof with a slight bulge and then taper that back down to the roof line of the airstream.

3. Wrap under the trailer as well linking the underside of the car to the underside of the trailer.

4. Add some sort of taper to the airstream end or aero diffuser , maybe try to channel some air to fill in the turbulent end.

5. It might not all be stretch materials, some might have to be segmented almost like an armadillo to have enough range of rotation for turns.

6. The airstream has to loose all the crap HVAC vents antennas on the roof and smooth out the bottom. Go to a mini split, or just use a larger compressor/heat pump on the Model X and duct the air inside so trailer weight increase is marginal . Charge the entire trailer off Model X traction battery , but also have a similar battery arrangement in the trailer ..(I was thinking the entire Tesla battery and rear axles salvaged out of a red drive Tesla and plunking the trailer shell around that ) .

Now when you go off exploring in the tow car you can return and replenish the batteries in the trailer. If you hit a flat grade you could draw upon the trailer battery if needed for the flattest sections using an inclinometer switch and regen proportionally more than Model X on small,downhills to charge the trailer battery and not need thermal management of that battery , and save the Model X high output traction battery for high current hill climbs ( which might need battery thermal management ) and steep hill Regen (also higher current) . Trailer could also do Regen down hills to reduce trailer sway, as sway is increased if the trailer tries to go faster than the tow vehicle. In a typical configuration with model x and a trailer with trailer brake controller , slowing the trailer adds friction drag to model x and reduces Model x regen form the tow/trailers combo. If the trailer has regen set ever so slightly higher than Model x and this in cases slightly for steeper declines, this would make for a very safe and efficient recapture of energy and perhaps allow for slightly more safety margin for quicker descents.

Lastly, the trailer should have slight taper both in height going towards the rear and width . Not much is needed. I used to own (2) 1994 Mercedes E500 sedans (.01 worse than Tesla Model S, and a big part of that was taper and managed airflow. The w/124 chassis were the first aero Mercedes’ passenger cars…slippery bricks.

And the trailer should be able to shrink in height 9maybe not like the trail manor, but certainly shrink another way to be below the height of the roofline of Model x. And if not you will need that trailer “Bow bulb

[redpoint5]

I don't know if I should take a bow, or try harder.

aerohead's posts are non-sequitur *footnotes.

My specialty is identifying what's dumb. That doesn't mean dumb things aren't fun, or that a lot of thought can't be expended doing dumb things. In the end, it's all dumb, so enjoy the journey.

[Golden Ears]

Originally Posted by redpoint5

I don't know if I should take a bow, or try harder.

***Bravo! If that's your life purpose.you have accomplished it and can move on.

aerohead's posts are non-sequitur *footnotes.

*****I found a lot of valuable info in his footnotes. But if you don't see whole picture it would appear to be random blasts of consciousness when in fact they are useful pieces to solving the puzzle.

My specialty is identifying what's dumb. That doesn't mean dumb things aren't fun, or that a lot of thought can't be expended doing dumb things. In the end, it's all dumb, so enjoy the journey.

***Anyhow to keep thison topic instead of calling it dumb. Towing efficiency isn't dumb any less than aerodynamics or hydrodynamics are dumb.

When I would street luge in 1975 against a much bigger taller standing opponent (Silver medalist Nelson Vales aka Cheetah or Tea-ba , I could draft him but he could not draft me,

The less turbulent wake an opponent left the more easily they could escape my dafting and the closer I had to be to lock in, sorta like having a shorter distance between the tow vehicle and the trailer.

If a person was standing, and they still,left little turbulent wake , some of them could be harder to draft when luging behind them than another liger, because they airstream heights did not match.

When locked behind someone in a draft, it is almost as if you were coupled like a trailer.

So all these things factor in , again coupling the two and making the undercarriage heights similar and roof heights similar and width all,should play in, but over all the trailer should slightly taper behind the tow vehicle , fart powered or gravity powered.

Fuel economy for any fuel would improve, and if you aren't interested in that , well ... I guess you just like typing gibberish. It's like taking Spanish about taco folding to someone who only speaks Korean who is interested in designing televisions , no one really cares.

[ldjessee00]

On the Cybertruck forum, there has been lots of talk about a battery pack on a trailer, even motor for regen and drive capability...

I am not a fan of the trailer providing motive power, but I am a fan of regen, especially down hill.

I think for the ultimate aerodynamics some kind of physical aerodynamic 'bridge' between the tractor and the trailer makes sense... but I think low hanging fruit would just be making the trailer fit as much as possible into the wake of the tractor.

If the trailer was narrower and as close to the height as possible than the tractor that would be something more easily achieved without recreating a lorica segmentata for towing.

[redpoint5]

The topic of the thread is why Tesla's are bad at towing, and the conclusion is that batteries suck and need to get better, much better.

I expanded the topic by mentioning it's not just energy capacity that matters, but how quickly it can be replenished. If it could be replenished very quickly, it matters less how big the "tank" is.

The point of a trailer isn't to be as aerodynamically efficient as possible, but to haul the intended cargo in a given footprint and weight rating. There's no "solution", only trade-offs.

The reason trailers don't have regen is because only 3% of vehicles are EV in the first place, and they already have regen built in. Redundantly adding it to a trailer adds weight, complexity and cost. It's not that it hasn't been thought of already, it's that people thought about it and then realized it was dumb.

[ksa8907]

TLDR

Electric towing will be limited to local deliveries and day cab trucks. Heavy and long distance transport will be diesel and natural gas for a long time.

[hayden55]

I mean we get off topic here a lot but I don't see where anybody is wrong. I wouldn't wanna mess with 40mpge in a vehicle carrying essentially less than 2.5 gallons of gas. 33.7kWh = 1 gallon of gas. In example 33.7kWh will get you ~40miles. Sounds like a range of less than 100 miles. I mean thats perfectly fine for towing your mid sized wakeboat to the local lake and back, but long distance towing that would suck so hard. I've heard that fast charging has increased in price as well and if thats the case it sounds like the cost/mi isn't really an advantage anymore.

https://www.youtube.com/watch?v=jhX3...TheFastLaneCar

[Piotrsko]

I think your estimate of KWH to gallon is a bit understated. I have 12-18 (depending) kwh to do 40ish in the ranger which used to get a solid 20mpg

[ksa8907]

Originally Posted by Piotrsko

I think your estimate of KWH to gallon is a bit understated. I have 12-18 (depending) kwh to do 40ish in the ranger which used to get a solid 20mpg

It's the energy content, not the effective use of the energy. Gasoline engines are inefficient in vehicles whereas electric motors suffer none of those inefficiencies.