Won't it also make a large difference overall, depending on the tow vehicle ? If the trailer fits in the trailing vacuum, I would think there would be less resistance than if it were punching a new hole. I suspect this could have a larger difference than the frontal area and Cd.

Peri

<< Want to know about the effects of leaf blowers ? https://quietcleanseattle.org/ >>

------ Original Message ------
From: "Lee Hart via EV" <ev@lists.evdl.org>
To: "Electric Vehicle Discussion List" <ev@lists.evdl.org>
Cc: "Lee Hart" <leeah...@earthlink.net>
Sent: 18-Aug-20 11:09:11 AM
Subject: Re: [EVDL] [External] EVLN: Tesla-Y feels like it’s not towing anything

Luke Scharf via EV wrote:
We need a way to rate the trailer's drag, as well as its weight.

One possibility is a roll-down test. Accellerate the vehicle to speed, put it 
in neutral, and measure the time and/or distance to coast down to a lower speed.

Obviously, do it on flat ground when there is no wind. It's best to repeat the 
test in both directions to cancel out any effects of wind or incline.

If you want more data, you could record the speed and distance every second or 
so right down to a standstill. The drag of a vehicle has 3 factors: friction 
(constant), rolling (proportional to speed), and aerodynamic (proportional to 
speed squared). With some math, the 3 factors can be separated out. This can 
give you the actual aerodynamic drag coefficient.

Lee Hart

-- A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
        -- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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