Reply To: Hypermiling the Aptera

[curtis-cibinel]

Unfortunately I am not a mechanical engineer and I’m sorry if I failed to describe that. I simply found calculations accounting for air resistance, weight and rolling losses and plugged it into a targeted spreadsheet I converted (originally for a GEO metro EV). The numbers are “back of the napkin” estimates. The 2000 mile claim was a bit sensationalist I admit and perhaps when someone really tried to stretch it the real value might be 1700-1800 miles which is still an impressive feat.

Even when released most production vehicles don’t provide all specs for all of the values needed for high speed efficiency calculations so they are estimates. Frontal area for example is not available as a shown spec but can be estimated and has little impact at low speed (I used the spec for an F150 to approximate the Rivian as a point of comparison). The data seems to fit real world measured values for the reference vehicles well enough to be a point of comparison (varies only 1-3%). See https://teslike.com/

I now realize one fundamental flaw was failure to account for engine efficiency losses and my coefficient of tire resistance may not be precise enough. I do not know the efficiency of the wheel motors (apart from the reasonable assertion they are above 90%). For rolling friction I simply took the assumption from articles that low rolling resistance tires with coefficients in the range of 0.006 and 0.008 were available (low rolling resistance tires) and plugged the higher (worse) into the equation. From Wikipedia this seems to be the case but I could not find specific low rolling resistance tires rated measured in coefficient of rolling resistance for the specific size for Aptera (195/45 R16).
https://en.wikipedia.org/wiki/Low_rolling_resistance_tire

I believe that a ultralight car with ~45% of its mass being high density batteries (based on the rough 10lb / kwh number that is often quoted) can reasonably be assumed to have strong hypermiling potential. It stands to reason that if a Tesla driven slowly can exceed its rating by over 70% that an Aptera can similarly. Controlling all variables and maintaining a constant low speed at high elevation with a lightweight operator would logically exceed what can be done with two guys driving a loop on a public road.

One thing in the numbers that I find non-intuitive (potentially wrong) is that when I compared the range degradation at speed between the model 3, rivian and entry level aptera (with some assumptions for both) they are nearly identical rates of degradation. This could be a coincidence in the data given the areas, weights and drag values or a flaw in my equations.

Here are my operating assumptions for the Aptera:

1. The described 1800 lb aptera is the 600 mile version. The weight be kwh being ~10lb would result in the 1000 mile version being ~2200lb +-100lb

2. The testing would be performed at a high elevation track reducing air density. This accounts for a ~2.5% (65 mile) increase in range but could be ignored due to practical challenges.
3. Tires for the Aptera with coefficients of road friction of 0.006 to 0.008 (see linked wikipedia are available). This seems reasonable given the common assertion of typical tire-road friction being 0.01. I actually used 0.12 for most of my charts as it seems to better align with mileage ratings but those losses are more likely due to breaking efficiencies. Small differences in this value result in huge swings in effective mileage at speeds where aerodynamics are negligible.

4. The frontal area of the aptera is ~20 ft squared. Honestly this might be high but the model 3 is 25 and it is clearly less than that. I believe it should be in the 17-22 range.

5. Coefficient of air drag is exactly 0.13 as stated. This could be higher or lower in reality but at low speed is relatively minor. +- 0.05 ?
6. The driver is 90lb. Honestly this is just me putting a 90lb jockey into the calculations for my own amusement. If the driver is 150lb instead this accounts for ~50 miles in the calculator which tracks within reasonable error with the statements that 30lb = 1% range.

7. For engine power conversion efficiency I would defer to anyone with more engineering background. Currently my chart fails to account at all which is obviously flawed. Not a ton of detailed specs exist for wheel motors in general. 95%?

8. I also made the assumption that ~8% of the pack would not be available to the user to preserve longevity. This was used more or less in all the numbers presented. At the end of the day actual pack sizes are not something we know for most EVs. By tuning based on other vehicles 55 mile theoretical ranges to exceed their epa ranges by approximately 7-10% the data seems to track with this fairly well.

In general I found most vehicles I entered exceeded rated ranges by too wide a margin but by a fairly consistent amount for each. This seems reasonable given the pure physics rather than real world nature of the calculations vs practical driving (turning = losses, breaking = losses, etc).