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Wind Tunnel testing
Aptera has spent a lot of money on CFD simulations but have apparently not put any of their vehicles into a wind tunnel to verify the sim. So, claiming a Cd of 1.3 is ludicrous until they actually put real wipers on the vehicle, with real, usable side view mirrors, and stick into the wind and measure the Cd. For those crying that such testing is absurdly expensive, guess again. The price as of 2019 I think was about $20,000 per day. You only need one day to get a number.
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51 Replies
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Wind Tunnel testing
updated 2 months, 2 weeks ago
28 Members
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51
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I think there is a good reason for this and many would not like the answer. They have the theoretical right to claim a Cd of 1.3 until they get new data to the contrary. There are so many variables they are managing and it doesn’t help their marketing claims to get new information early and risk what they are able to claim today. I suspect once Gamma is released, it will be time to do that test since the production intent is established and, theoretically, all of those Cd variables will be locked. There is little value in running wind tunnel tests that may jeopardize the 1.3 Cd hype unti that point. I’ve had the same curiosity on the 100 Wh/mi claim based on all the different battery sizes/weights. I would not expect them to be equal which would bring into question whether they will adjust the battery sizes to meet the 600 and 1000 mile variants to pull the additional weight. Maybe the claim is based on the 1000 mile variant and the results are better for the smaller batteries, but such a conservative marketing claim is not typical. I’m expecting some clarifications as they learn more, but I would expect them to be in the ballpark of what they are claiming.
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You stated the wrong Cd in your post. The Cd claim is 0.13 not 1.3. You are an order of magnitude off.
Similarly incorrect, gamma is not production intent. The delta prototype is production intent. There is one more prototype to go to establish production intent.
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Many a solar car race team have learned the value of full scale wind tunnel testing.
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Why don’t you pay for it then? Oh, you need to do two tests: one with those supposed external mirrors and one with the default side cameras.
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It is possible to measure the Cd by getting the vehicle to speed and let it roll to a stop measuring the speed/decel/time and putting it into the formula or models. The computer simulation on the other hand is great for finding the rough spots to smooth them out for the finer details, but nothing is better than reality.
The only issue with this approach for Aptera is the cutting of the drive current would lead to some high voltages coming back into the drive electronics leading to breakdown or arcing on the cables, I am sure that they can get help from Elaphe on this. Or use only one motor (rear, set it up as a non-permanent magnet synchronous motor and cut the field windings) to get it to speed and just wheel bearings elsewhere, on a mule. A _lot_ cheaper than a wind tunnel, and will give them the data they need and they can break the runs between modifications as they please.
They can setup the drive for non-interference station keeping on the PM motors, but there will always be FUD if they can not free wheel. This is where Elaphe can help I am sure.
NB: my company has software to do this on an Android phone. Done.
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Mark, what you propose is how you would measure the total drag on a vehicle, including rolling friction and aerodynamic drag. That’s a useful piece of information, however the Cd is only a part of the formula for the total drag. Also included in the total drag is the drag of the tires on the road, the drag in the motors and bearings, and anything else.
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Who cares? I mean, unless there is a change to the machine, let Aptera claim whatever they have SOME basis for. Computer models are actually pretty good for evaluating design options and that’s what is more important. Save the money, time, and distraction.
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Lightyear just reported wind tunnel results of its Lightyear 0, which has already seen units hit the road. If Lightyear waited until now, it’s fair that Aptera is waiting until at least the Paradigm Editions hit the road.
(For the record, the Lightyear 0 came in at 0.175, making it the current placeholder for most efficient production car.)
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Jason Hill posted on LinkedIn:
“Pininfarina Wind Tunnel…”
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I thought they tested the design with NASA’s either wind tunnel or simulation computers. I also seem to think the Jeff Bezos let them use his computing power as well for the same thing. Nasa told them it was the most aerodynamic shape they’d ever seen/tested.
The recent fluid dynamic programs are good enough for me and I’m sure the production intent vehicle will be tested again but why not put that $20K a day to getting cars made?
You need more proof?
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$17,000 is not a lot of money, however it was one to the first checks written, to NASA, for Langley to test out the design. The NASA engineers were baffled by how low the drag was, so much so that Steve and Chris taught them about ground effect. Wing suit pilots count on the compression of the air as they skim past a mountain. Aptera takes into account the strange effect of ground interaction of air stream with the body of the Aptera. Airline pilots glide into a landing, and almost have to push down at the last to overcome the ground clearance effect.
This topic should not worry us, the design is better than Lucid, and they claim to be the best currently at .20. This needs it’s Launch Edition to provide the naysayers the information they simply do not believe. Getting Aussie Idea man, (even though I doubt he has any ideas,) an Aptera. He said he would buy one if they make them, I want to see that.
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Yeah, Aussie isn’t buying one – that claim is as full of feces as he is.
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This testing is not yet possible, as we do not yet have a production intent vehicle to test.
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As long as the shape of the vehicle doesn’t change, the aerodynamics won’t change. They could for example test a model made out of wood or clay carved to the same shape. Well, I guess any vents on the vehicle also need to be modeled accurately.
From my understanding, computer modeling is now so accurate that you can get more consistant results from computer simulations than from moving from one wind tunnel to another.
I’d love to know the impact of the side view mirrors and off-road wheel pants.
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I would guess the main purpose of the current tests is simply to validate that the result is consistent with their simulations.
It would be interesting to see what they’ve done in the area of the suspension arms & whether they’re using a boot where the suspension arms go into the wheel pants.
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This reply was modified 6 months, 2 weeks ago by Michael Marsden.
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This reply was modified 6 months, 2 weeks ago by
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Another pic from Jason:
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Major cool factor right there!
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So, since that is the rough-built Gamma that has a lot of gaps which increases the drag, what are the results of the testing (unless that is just a PhotoShopped pic)?
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Yeah, a little dicey doing wind tunnel testing with the gamma and with the wind tunnel in the released pictures. The wind tunnel is old tech and a sucking wind tunnel. Not sure how accurate or applicable to a production delta the results will be.
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> Not sure how accurate or applicable to a production delta the results will be.
I think the point is to validate how close their simulations are to the real thing. If their Gamma CAD model generates the same numbers in a simulated wind tunnel to the real Gamma in a real wind tunnel, then that’d be counted as a success, since it would imply that the Delta model is probably also accurate in the simulation. If they get different numbers then that means that they have screwed something up in the simulation.
Very similar to the track testing where they were comparing simulated kerb strikes versus real kerb strikes.
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This reply was modified 5 months, 2 weeks ago by Michael Marsden.
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This reply was modified 5 months, 2 weeks ago by
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Anyone heard any news about wind tunnel tests last month?
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As soon as some new info becomes available, you’ll see it in this thread.
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BMW designed the original R100RS in the same wind tunnel in Italy. It’s my desktop screen on my old G5 Mac Cheese grater in the basement.
Day after BMW left, Moto Guzzi showed up. “Come on in…” and the 1000SP was the result.
Had two RS BMWs. Whereas a normal BMW will give you 200 miles easily, the RS’s would go 230-240 before I hit reserve 1 or 2.
Aerodynamics do make a world of difference. That’s what has kept me compelled with Aptera going on the second decade.
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Post the original results of the gas powered version and how far it was able to go on a gallon of fuel. Made me a believer.
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Before it went to be crated-up for its return flight to the US, Aptera’s Gamma prototype visited the Pininfarina Wind Tunnel in Turin, Italy.
Prof A Morelli – who designed this wind tunnel in 1972 – also designed the aerodynamic shape upon which Aptera’s body is based: Talk about a “family affair”!
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That’s a really cool picture!
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This is an interesting 2022 article about the most aerodynamic cars. For you math wizards what would be the percent less drag coefficient between Aptera’s .13 and Tesla Model 3’s .23? I presume it’s logarithmic?<div>
https://www.carwow.co.uk/best/most-aerodynamic-cars#gref
</div>
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I can see how the elongated tail, recessed door handles and tight wheel covers help, but still, 0.212! How is this possible? Very impressive.
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Roof & windows closed of course, but I suspect if the roof was solid, they might’ve achieved .200 al the least. The head lights didn’t help, either.
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> I presume it’s logarithmic
Linear I believe (the Aptera would have 56% of the aerodynamic drag of the model 3 if the frontal surface area was the same, which it isn’t).
The effort involved to improve it beyond a certain point is exponential 🤣 but that’s simply due to diminishing returns.
The really important figure is cdA, which is the coefficient of drag multiplied by the frontal area (which includes things like the wheelpants and the struts). Total aero drag is cdA times speed cubed (and what we care about is speed squared not cubed, because we want to know how much drag there was over a distance). I don’t think we know the frontal area precisely, but the people generating 3d models probably have the best idea of that.
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This reply was modified 5 months, 1 week ago by Michael Marsden.
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This reply was modified 5 months, 1 week ago by Michael Marsden.
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This reply was modified 5 months, 1 week ago by Michael Marsden.
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This reply was modified 5 months, 1 week ago by Michael Marsden.
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This reply was modified 5 months, 1 week ago by
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Posted on LinkedIn by Pininfarina:
“We are always excited to take part in the development of innovative vehicles, especially when they share such a strong link with our wind tunnel’s history”, Alessandro Aquili, Head of Wind Tunnel at Pininfarina.
Solar electric vehicle manufacturer Aptera Motors entered the validation phase for its aerodynamic shape last month at Pininfarina’s world-famous wind tunnel. This first step in its validation underscores Aptera’s commitment to progress, continuous innovation, and the pursuit of revolutionary mobility solutions.
At the forefront of ultra-efficient transportation, Aptera has designed the most aerodynamic vehicle possible – with three wheels, outboard in-wheel motors, and a striking teardrop shape. Now Pininfarina, with its rich heritage and exceptional aerodynamic prowess, will be working closely with Aptera to validate the unique shape of its cutting-edge solar electric vehicles.
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Below generated by chatGPT on Coefficient of Drag value range
The range of values for the coefficient of drag (Cd) can vary significantly depending on the specific object, flow conditions, and the reference area used for calculations. Here are some approximate ranges of Cd values for different objects:
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Streamlined Bodies:
- Cars: Cd ranges from around 0.20 to 0.45 for typical passenger cars. Some modern aerodynamic cars can achieve even lower values, approaching 0.25 or below.
- Aircraft: Cd ranges from about 0.02 to 0.10 for streamlined commercial aircraft.
- Rockets and Missiles: Cd can vary widely depending on the specific design, but it can range from 0.1 to several times higher.
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Blunt Bodies:
- Buildings: Cd can vary depending on the shape and size of the building. Typical values range from 0.5 to 1.0 or higher.
- Square Plates: Cd is approximately 1.17 for a square plate perpendicular to the flow.
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Spheres and Cylinders:
- Spheres: Cd for a smooth sphere is approximately 0.47, while a rough sphere can have a higher value, around 0.5 to 0.6.
- Long Cylinders: Cd for long cylinders perpendicular to the flow can range from 0.7 to 1.2.
It’s important to note that these values are approximate and can vary depending on factors such as Reynolds number, surface roughness, and flow conditions. Additionally, the Cd values mentioned above represent a single orientation or specific flow conditions, and the Cd can change if the object’s orientation or flow conditions are altered.
Furthermore, Cd values for irregular or complex shapes may not fit within these general ranges and often require specialized testing or simulations to determine their drag coefficients accurately.
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Aptera has designed the most aerodynamic vehicle possible….
Hmmm…….
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A video of the testing:
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Thanks for sharing that one – very impressive!
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I see finally some real testing but have not seen the real values. I wonder from where Aptera’s Cd values were coming from, computational or testing of models. Aerodynamic drag is not only dependent on Cd value but also front surface area. I have not seen any value of that as I expect that the front wheels separated from the main body and their suspension will increase the surface area.
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This reply was modified 4 months, 2 weeks ago by Jakob Bogenberger.
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As I remember, it came from NASA.
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This reply was modified 4 months, 2 weeks ago by
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A video with a couple of seemingly new bits of video during the testing:
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Does anyone have any word on when we might expect results of the wind-tunnel testing to be available publicly?
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There likely won’t be any more info released about this testing – it was only for set up and validation of the correlation between the simulated work and actual wind tunnel results. Don’t expect any results until well after the first Deltra prototype is available in Europe,
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After a break from posting, Jason Hill has this on LinkedIn:
Gamma tuft testing Aptera Motors
Following soon with the full video thread…
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hmmm…..not sure what tuft testing of gamma accomplishes. Not sure what it accomplishes if it was a delta or LE. Certainly anticlimactic after the highly hipped wind tunnel run in Italy.
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It would be validation of their CFD computer models. Maybe not the exact same numbers as the Delta and production items but would give them greater confidence in their predictions.
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There is so much that can be learned from wool tuft testing, that I can’t guess which specific reason(s) they would do so now. Could be checking for something noticed in the wind tunnel. Even with that one low res shot above , there’s a lot to observe. I hope the forthcoming video clarifies.
Despite how the internet generally bags on tuft testing vs CFD, tuft testing provides (real) data, not just theoretical.
