-
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.
-
20 Replies
-
Wind Tunnel testing
updated 3 weeks, 3 days ago 17 Members · 20 Replies
-
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.
-
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.
-
-
Many a solar car race team have learned the value of full scale wind tunnel testing.
-
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.
-
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.
-
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.
-
-
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.
-
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.)
-
Jason Hill posted on LinkedIn:
“Pininfarina Wind Tunnel…”
-
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?
-
$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.
-
Yeah, Aussie isn’t buying one – that claim is as full of feces as he is.
-
-
This testing is not yet possible, as we do not yet have a production intent vehicle to test.
-
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.
-
Yep, the CFD analysis is solid. The estimates of rolling resistance and the efficiency of the drive train likely have more error. Then there’s wind and weather effects. Oh, and the variable that will have at least an order of magnitude greater effect on real world performance and efficiency is the loose nut on the wheel. 😀
-
Hey! Get off of there! I am sure it says “no step” somewhere in the manual.
That’s what we get for letting those nuts loose…😅
-
-
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.
-
This reply was modified 3 weeks, 3 days ago by Michael Marsden.
-
This reply was modified 3 weeks, 3 days ago by
-
-
-
Another pic from Jason:
-
Major cool factor right there!
-
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)?
-
