Aptera efficiency

[GNiessen]

I am sure there will be a sweet spot speed. But at least the Aptera will be less affected by wind speed and direction.

[christopher-morehouse]

Depends. Need to balance drag, motor efficiency and battery efficiency to find your peak driving speed for max range. As you go up in speed, drag term goes up exponentially.

Electric motors will have a peak efficiency operating condition based on physical speed and power draw. Batteries will have a peak efficiency based on power draw and temperature.

Your drag characteristic can also change depending on speed. If the aero forces cause a change in body position for example….

However, the drag difference between 60mph and 90mph is going to be considerable. For a 50% increase in speed your drag force, all things being equal, is going to go up by 125%. So unless your motor and batteries combined are at least 74% more efficient at that speed, you aren’t going to be better off.

Drag is a bitch.

[christopher-morehouse]

Not sure I am following why you would want to generate lift. Downforce is good for traction, it doesn’t make the car heavier though. Lift is not a good thing in a fast moving vehicle, it unloads the suspension and can make the vehicle unpredictable to control. That is why fast cars have wings to generate downforce in the first place.

You are correct that wings increase drag. Anytime you have an airfoil generating lift (or down force which is just negative lift) you get an induced drag term. This is why super cars have active aero surfaces. So they can optimize downforce and drag at different driving conditions.

[curtis-cibinel]

It will obviously seem counterintuitive that the most aerodynamic vehicle made would not want to go fast but its true. Aptera will lose more of its rated range if going fast than other EVs. Aptera is always super efficient with energy the extent to which it beats others substantially. Aptera Owners Club recently released a video presenting the Aptera as a rural EV due to the need for lots of long distance highway travel. While Aptera can definitely do this and with far less energy than any other vehicle it might have even less range than you expected if trying to stay in that goldilocks 20-80%

Aptera has a few superpowers that make it so amazingly efficient:

• Drag Coefficient: Aptera has an amazing stated 0.13 Cd drag coefficient. This blows everything else out of the water. Unfortunately NHTSA has required the addition of mirrors and with Aptera being tight lipped about stating a number since I am operating under the assumption of a 0.15 Cd.; Still substantially ahead of the Lightyear 0 at 0.175 or Model 3 at 0.23. Total air drag is impacted by the frontal area, air density (functionally a constant), drag coefficient and speed.
• Weight and Rolling Resistance: The Aptera is amazingly light vehicle. We haven’t got any firm numbers for a long time but switching to CF-SMC is definitely not making it any heavier. Regardless of speed the rolling force for a vehicle is based on the coefficient of friction to the roadway, gravity (a constant until the first Aptera on mars), and its weight. For the purpose of examining this I have used a weight of 1200lb plus the driver and batteries. At low speeds rolling force is the biggest thing holding a vehicle back but at 110 mph it is only 14.6% of the force Aptera needs to overcome to maintain a constant speed.
• Auxiliary Load: All EVs need to use some power beyond that turning the wheels to overcome drag. This energy runs microcontrollers, displays, cameras and climate control. Aptera is a small vehicle and is taking steps to limit the auxiliary load; we don’t have all the details but we do know some things. The vehicle is powered by a small power efficient computer similar to a cellphone (possibly Toradex i.MX8); by comparison Tesla is putting actual computers with gaming GPUs in its cars. Aptera will hopefully have heated seats shortly after release (feature delayed for now) and a heat pump eventually to reduce energy for heating/cooling; it is worth noting that the interior volume of the Aptera is still lower than a normal sedan (less air to warm).

At low speeds (20 mph) the weight of Aptera means it is only using about 38% the wh/m of a model 3. This is also the speed at which any auxiliary load will have a greater effect since it is a larger percentage of your overall energy use. Aptera is actually a very good vehicle for low speed driving since it is light and like all EVs it has regen.

As the speed increases other variables become more negligible and we get closer to simply 0.15 (assumed drag of aptera with mirrors) / 0.23 (drag of a model 3). This is 65% the energy use of a model 3. Still better but worse relative to low speeds(this is simplified and requires ludicrous speed beyond what either vehicle can achieve); at 110 mph the number is actually 56.9% of the energy needed for the model 3.

Note: Some have pointed out that I should have compared near equivalent range vehicles. The 23 kwh / 250 miles actually amplified the range loss with speed since it loses just as much energy to aerodynamic drag but has a smaller battery relative to its range. Based on the math it seems likely the 23 kwh Aptera will either struggle to reach 250 miles or (my preferred possibility) the 45 kwh will greatly exceed the expected 400 miles of range. I prefer not to speculate to much on the 600 mile and 1000 mile Aptera models since we do not have enough information on the batteries yet.

My Advise:

• If you want to go fast get at minimum the 45 kw Aptera. The vehicle will always be efficient but this will offset some losses from speed or bad weather. It is also unclear if the smaller pack of the 23 kwh will be able to output the over 6c discharge to power the AWD with 150 kw of motors will want for optimal performance.

Calculations:

• https://docs.google.com/spreadsheets/d/1Tuu7avKH2dS_JPk7aiP2av09a1f1WE0OvvNH6fdHpiQ/edit#gid=1285203539
• Please make a copy if you want to play with the numbers.

Assumptions:

• Both Aptera and Model 3 have a 23 sq ft frontal area.
• Aptera has an aux load of 200w and Model 3 has an aux load of 350w
• Aptera has a 0.0085 coefficient of road friction and Model 3 has 0.011
• Both drivetrains are 90% efficient
• A single 150lb driver
• Testing is at earth sea level

IMPORTANT: Please understand that Aptera is not released yet and not all numbers are from official sources. Despite many numbers being estimates the trends are quite clear and while specific values may be (and likely are) inaccurate the general trend is clear. A very light and efficient vehicle will lose more range as speed climb despite extremely good aerodynamics. Without the advantage of good drag vehicles like the Avvenire Spiritus are likely to see ranges plummet as speeds increase.

• This reply was modified 1 year, 5 months ago by  Curtis Cibinel. Reason: Added charts
• This reply was modified 1 year, 5 months ago by  bbelcamino.
• This reply was modified 1 year, 5 months ago by  Gabriel Kemeny.

[paul-kirchner]

This is like long for play. All of this guessing and postulating this and that for years. Will be super interesting to see the real numbers on things when the Aptera is actually born and brought into the world.

Thanks for the effort it took for all your analysis of the murky waters.

[ab-reitsma]

You could also look at it from the bright side, you will gain a lot more range if you are not in a hurry 😄, given that the current range estimates are probably simulated EPA averages.

[curtis-cibinel]

Looking just at the pack sizes simply multiplied by 10 it seems clear that if the 250 and 1000 mile make there epa rated range the 400 will overperform by 10-15%. As you factor weight of packs bigger will do worse but the 400 isn’t huge. Keeping super basic:

23 kwh x 10 = 230 miles (20 under)

45 kwh x 10 = 450 miles (50 over)

66 kwh x 10 = 660 miles (60 over – likely worse due to battery weight)

99 kwh x 10 = 990 miles (10 under – likely worse due to battery weight)

[david-marlow]

It may loose more in tearms of % of range, but not in actual range when comparing the same abount of charge.

[david-kingsley]

How many miles per kWh are they getting?

[993cc]

The projection has alway been about 10 miles per kWh. or 10 kWh per 100 miles if you prefer. That hasn’t changed to my knowledge.

• This reply was modified 1 year, 3 months ago by  Bob Kirchner.
• This reply was modified 1 year, 3 months ago by  Gabriel Kemeny.

[seth]

Is anyone amazed that Aptera hasn’t started showing proof of their efficiency claims? It would only make sense to me for Aptera to make headlines uses only 43% of the power of the most efficient Tesla’s even using gamma. That’s assuming their numbers are near the original estimates…

Or do you think they’re waiting for the newer more efficient slow motors to have a chance to meet or exceed the original estimates.

I doubt they’d need more than 2 days at a track near a lvl2 charger to prove or disprove the claims. Now is the time to make headlines that make it onto mainstream news to motivate masses of potential investors.

[BigSky]

Yes and no. Their claims were theoretical and I am sure real life changes like the additional side view mirrors will increase drag. I am going to assume they have not yet finished the refining in Gamma to their liking and they had been working on further improvements to Delta (such as more efficient motors). If you collect and post data in the interim, then it becomes the new number everyone anchors to versus what you are aspiring to. They avoid all of the noise by publishing when they are ready to share the final results that will go to market.

• This reply was modified 1 year, 1 month ago by  Steven Montana.
• This reply was modified 1 year, 1 month ago by  Gabriel Kemeny.

[kerbe2705]

@seth-feldman I’m guessing you don’t realize that there isn’t an actual production version of the Aptera – because running such tests on a pre-production prototype would be pointless: The resulting data would be invalid.

[Jeff]

I just hope that Aptera will have enough funds to build a few Deltas and actually do these efficiency (and other) tests before folding.

If I was a potential big money investor, I would want to see these types of concrete real-world data before investing millions to finance building out the production facility.

[jerry-kingzett]

Aptera wins the efficiency test in my Vehicle comparison

Why-Do-I-Have-an-Insatiable-Need-for-an-Aptera-2.pdf 366 KB PDF - Click to view

• Copy Download Link

[john-trotter]

I agree with all those noting that real measured results need a real production vehicle. Even with a production vehicle, scientifically accurate measurements would need an understanding of temperature, wind, weight, speed profile(!), tire condition, etc., etc., etc. And repeat several times. That said, as long as Aptera is better (= more efficient) than any other two-person production vehicle, numerical results do not matter much. The bragging point is “most efficient”.

[elden-housinger]

Aptera is all about efficiency, but it seems to me that its efficiency would be maximized having only one of these motors.

[Mike-Mars]

Two front motors would be more efficient than a single rear motor, simply because the motors are used for regenerative braking, and the bulk of braking effort always goes on the front wheels.
Three motors would be less efficient than two, but we don’t know exactly how much. 10% has been suggested, but that sounds high to me.

Simply cutting the power to a motor would not help isolate the efficiency impact of the motor from the vehicle – unless there is a clutch to let the wheel spin freely, or something similar, you’d still get the extra frictional resistance, and the effect of the spinning magnets which would create stray electrical currents. As I see it – you might be able to turn off a motor, but whether that would help with efficiency is unclear.

It might make sense to have a ‘local delivery’ version of the Aptera with two S400 Elaphe motors, instead of the 2 or 3 M700 motors on the mainstream vehicle (provided that they spent the time optimising the S400 for efficiency … they’ve already done that on the M700).

• This reply was modified 1 year ago by  Michael Marsden.
• This reply was modified 1 year ago by  Michael Marsden.

[curtis-cibinel]

Efficiency yes but they would lose a ton of performance and rain/winter viability. Aptera still needs to be a practical vehicle for people. They could definitely make a RWD only (just like the Daymak spiritus) but it would only save a small amount of cost/energy and would be a far worse vehicle for it.

[daniel-crotty]

Assuming that you have 2 EV’s, driving at constant 70mph on the highway. Is a 2 wheel version more efficient than 3 wheel?

My first thought seemed to be obviously 2. But the more I think about it, it seems that while you are using 3 motors, each is having to do less work. Totaled up the same amount of battery should be being used.

There is the extra weight issue. But it seems that 2 motor version has to “run harder”, so I am not sure how much that extra weight is an affect.

Seems to me that while 3 motors may lose, it would not be by much. And in the long run, the motors may have a longer life span due to not having to work as hard.

I do NOT claim this to be true.

[Mike-Mars]

Aptera themselves have said that 2 motors is more efficient than 3.

The exact drop in efficiency is unknown.

[craig-merrow]

The dual-motor Tesla’s were purported to be slightly more efficient than the single motor variant because of the increased regenerative braking. Of course, this also depends on your driving habits – YMMV.

[Jeff]

I don’t think that’s why. IIRC, I think it’s because earlier versions of dual motor Model S’s used 2 induction motors and Tesla was able to tune and gear the rear one for power/acceleration and tune/gear the front one for efficiency while cruising, and that’s why the dual motor versions got better efficiency ratings than their single-motor counterparts despite the added weight.

https://www.greencarreports.com/news/1102834_all-wheel-drive-tesla-electric-cars-rated-more-efficient-but-how

I doubt increased regen from the second motor played into it at all since the deceleration rates in the EPA test drive cycles are quite modest and should be handled fine with one motor.

In contrast, the Model 3 and Y have a type of permanent magnet motor in the rear that is already very efficient, and so the addition of an induction motor up front in dual motor versions does not improve efficiency ratings, it actually drags it down.

[Shawgrin]

Tesla’s Most Efficient model is the Model 3SR (standard range), it only uses a single motor.

[robert-wakeman]

Yes they said this but they also said they found less of a drop than they expected in early testing. And they are still working on the drive software. If you look at the physic of a three point system two in front one in back the opportunity to drive them in ways that would maximize traction, handling, and efficiency. The ability to drive one, two, or three wheels Is unique. Cannot wait to see what they come up with!

• This reply was modified 1 month, 2 weeks ago by  Robert Wakeman.

[john-trotter]

Two months ago, in the “Battery & Power Train” YouTube, Aptera was enthusiastic about the efficiency of using Silicon-carbide inverters. (“97% efficient versus industry standard of 92%”) In the more recent “Production Tooling Progress”, they seemed more in favor of IGBT inverters, for cost and availability reasons. This is a great example of the difficulty of real life engineering decisions.

My two cents would be to err on the side of efficiency. That is, after all, the basic ethos of Aptera. My own experience with engineering compromise in the fundamentals of a project is that it leads down a dangerous and slippery slope. Any number of changes can be justified, a few dollars at a time. (In fact, that may be one of the basics of engineering itself.)

Three-percent waste heat versus 8% is significant. It affects cooling as well as range. Sure, one can design for it, but that in itself increases cost.

<font face=”inherit”>I assume Aptera Engineering has numbers on overall cost differences, and I </font>would<font face=”inherit”> certainly not think </font>efficient-at-any-cost is the right answer, but …

What do you think?

[BigSky]

Hard to say. I don’t really know what the true tradeoff is. I understand Steve’s point about the low current distributed across the 3 motors really minimizes the effect, but I just don’t know how much of a true efficiency hit, vs. the cost benefit/gross margin challenge vs. risks due to component availability are. On the surface, it would be a shame to put all of that care into the engineering and, then to give up range on the inverters. Given the trickle solar, you’d think they wouldn’t easily give up those loses.

[Greek]

I guess my response would be…What ever gets the vehicle into production quicker. Make improvements as you continue to grow and expand as a company. Just as Tesla has been doing.

[ray-holan]

If availability of the improved inverter delays production, I would easily forgo it. If it were available and at the same cost, it would be a no-brainer, consistent with the Aptera Ethos of efficiency. Personally, I would be willing to pay a little more for the significant improvement in efficiency. If it added $300 to the price I could swallow that. If it added $1000,I’d probably take a pass.

[Mike-Mars]

I would want to know the actual effect on efficiency and range on the Aptera, and the relative cost of the two options. Right now the only people who know that data is Aptera themselves.

• This reply was modified 10 months, 3 weeks ago by  Michael Marsden.

[Myk]

I would say it depends on the engineering differences. If it would it be possible to have the more efficient inverter as a drop-in replacement, I’d definitely say go with the more available one for launch. If there are significant changes to other parts of the vehicle required, I’d be more inclined to want to wait.