2G wrote on 12/14/2019 5:54 PM:
On Saturday, December 14, 2019 at 2:22:32 PM UTC-8, Martin Gregorie wrote:
On Sat, 14 Dec 2019 12:59:37 -0800, Eric Greenwell wrote:

Oooh, Life is Good! Electric glider AND electric car! But did you mean "3
kwhr/mile" when NOT towing? Because "2 Kwhr/mile" when towing sounds like
the trailer improves your mileage.

More to the point, units of stored energy and power are being confused here.

If the battery capacity is 100 kWh and the car gets through 2 kWh per mile,
apparently regardless of speed, then its maximum range can't exceed 50
miles.

This car and trailer normally averages 160 miles on a charge. If we assume it
is running at 60 mph then it will take 2.67 hours to cover the distance and
will be drawing less than the 37 Kw, given by a simple calculation, during
that time. Which works out at 50hp (1hp = 0.748 kW).. In real traffic the
travel time is likely to be more than that and no sensible driver will plan
to arrive at the next charger with a totally empty battery. Consequently the
averaged power consumption will most likely be rather less than 37kW.

I should declare an interest in towing with either an electric or a hybrid,
and so am interested in how they compare with a petrol car: this is why I'm
interested in analysing these numbers and/or any other information about
towing with these vehicles.

I tow a fairly light tube trailer containing a light glider (201 Libelle)
with a 2 litre petrol engined Focus Estate. This combo is limited to 60mph by
both UK road rules and stability above that speed. I generally guestimate
travel times at 3 hours/100 miles after allowing time for coffee breaks and
pertol stops, so am interested to see if that can be matched with an
equivalent electric or hybrid vehicle. Relative costs would also be
interesting, as, on a cost/kW basis, our electricity appears to be 15% more
expensive than petrol.


-- Martin | martin at Gregorie | gregorie dot org

I think Scott meant that he gets 3 mi/kwh not towing and 2 mi/kwh while towing.
The 100D has a 100 kwh battery, making the range roughly 300 mi.

I found a better example of towing with an electric car (Tesla X):
edmunds.com/tesla/model-x/2016/long-term-road-test/2016-tesla-model-x-range-and-charging-while-towing-a-trailer.html

This was a 1,000 mi test towing a 1,260 lb trailer (he didn't mention the
weight of luggage, water, etc.). A glider trailer would probably be
significantly heavier, making the performance worse. The results were much
worse than what Scott indicated, averaging just 1.63 mi/kwh. This gives the
100D model just a 163 mi range (no reserve). A more realistic range would be
130 mi. He mentioned several complicating factors:

* heat (degrades range) * elevation (degrades range going uphill) * wind
(headwinds degrade range) * uncoupling trailer (most charging stations are
back-in) * tow speed was limited to 53 mph to maximize range

His average travel speed, including charging time, was just 24.9 mph over the
entire trip! And he never had to wait to use a charging station and only had to
uncouple his trailer once (you could not pull the trick he did with a glider
trailer). You can add another 10 min per stop to uncouple and recouple the
trailer, including the time necessary to find a parking spot. This would have
reduced the average trip speed to 23.9 mph.

At times he would have to turn off the AC to ensure getting to the next
charging station - in 100 F temperatures! His average travel distance between
charging stations was just 91 mi. On top of that, one shorter route was
unavailable to him because of the very marginal reserves he would be facing.
And the Tesla range app does not factor in heat or wind.

The answer is yes, you can tow a glider trailer with a Tesla X (to some
locations), but would you want to?

What's missing from his report is how much the trailer affected things, other than
accessing the charger. The other issues were not trailer related (heat and
grades). Also, while the trailer is lighter, it is taller and wider than a glider
trailer, so I think a 15m glider trailer would actually be easier to tow.

Scott's experience may reflect the effect of a glider trailer better than Edmunds
report. Still, heat and cold affect an electric vehicle more than ICE vehicles,
and charging is going to be a problem with a trailer as long as you have to back
into places. Better get an electric car with a front charge port!

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1