Is lift a problem at high speeds?Posted by fgSOL24 on January 7, 2023 at 9:02 am
Very aerodynamic cars with low drag coefficients may suffer lift, an upthrust force that causes under or over steering due to reduced downward load and tire grip. Lift increases significantly the higher the speed. Does the aptera suffer lift at high speeds?
- 24 Replies
- MemberJanuary 7, 2023 at 12:03 pm
Early in the program, one of the engineers stated that there was a small amount of down force at speed.
- MemberJanuary 8, 2023 at 8:31 am
This was addressed in an interview recently with Chris Anthony – at 38:25 in this video:
- MemberMarch 14, 2023 at 11:49 am
Great, thanks! Just what I was looking for. There’s SO much focus on coefficient of drag, that coefficient of lift gets forgotten… but it also becomes a factor of drag, and can really make for instability at high speeds, so this is good to know.
I do really wonder what the actual figure is of CL, though. Just how negative is it? Maybe -.05 or something?
- MemberMarch 12, 2023 at 7:43 pm
I have not found it mentioned anywhere, yet. What happens to this vehicle design if it gets sideways at highway speeds? My thought is in the event of an accident and the vehicle is sliding or spun sideways. It is very aerodynamic with little down-force and it is relatively light. With my limited understanding of aerodynamics, there does not appear to be anything to stop up-force from lifting and flipping the vehicle. Thoughts?
- MemberMarch 12, 2023 at 10:32 pm
I would think that there won’t be very little danger of flipping with a large lateral airflow component. Traveling backwards at very high speed might be an issue, but even that is just a guess.
- MemberMarch 13, 2023 at 12:11 pm
“I would think that there won’t be very little danger of flipping with a large lateral airflow component.”
So you are saying while there is a high danger with a large lateral flow, but it is not as high as a backwards flow?
- MemberMarch 13, 2023 at 12:10 am
Official sources from aptera have mentioned that even high speed lateral wind will not effect stability. As for reverse the only way I would be totally convinced would be if I saw an aptera drive in reverse at 100mph
- MemberMarch 13, 2023 at 9:14 am
Probably good reason to govern the reverse to a reasonable speed; Prevent some Darwin awards. Despite the drivetrain being capable of 100 mph in reverse I cant see any good reason they should allow it.
- MemberMarch 13, 2023 at 12:30 am
@scott-sment In aerodynamics, both lift and drag (downforce) are functions of air pressure. Lift is generated when there is higher pressure pushing up than down and drag occurs when the opposite is true. Bernoulli’s Equation is used to explain how airplane wings work: In effect, the underside of a wing is flat while the top surface is humped so air takes longer to flow over the top of the wing than it does the underside. If you look at Aptera from the side, you’ll see that BOTH the upper and lower surfaces are humped: Air will flow over both surfaces at approximately the same rate, although there is some drag built in to help keep the rear wheel firmly planted.
- MemberMarch 13, 2023 at 8:40 am
Kerbe2705. drag is not the opposite force to lift. It is the opposite force to thrust in aerodynamics. gravity (weight/mass) is the opposite force to lift.
- MemberMarch 13, 2023 at 11:00 am
@john-malcom All downforce is drag but not all drag is downforce: I was using the shorter word as – for some reason – the “f” key on my keyboard is going wonky.
- MemberMarch 14, 2023 at 2:46 pm
No, all downforce is NOT drag. One of the unavoidable components of lift (be it up, down, sideways or whatever) is drag. Generating lift does also generate an amount of drag, but Lift is not the same thing as Drag.
- MemberMarch 14, 2023 at 12:31 pm
No, the major source (or parameter) of lift for a wing is not Bernoulli’s principle, it’s the angle of attack.
As long as the apparent angle of attack stays negative, Aptera should have downforce.
- This reply was modified 8 months ago by Robert Klasson.
- MemberMarch 16, 2023 at 10:44 am
Here’s a video of a formula one ‘crash’ that shows what can happen with an aero-optimized race car that gets weird in the air at high speed.
That first image in the video is one of the few flying formula one crashes that seemed particularly influenced by the reverse aero design. Most of the airborne F1 crashes occur when the driver is closely following a vehicle ahead and crests a hill (or runs over the back tires of another vehicle) and the front rises and the car literally turns a backward somersault typically crashing its backside on the pavement.
It is important to remember that race track speeds are on a whole new order of magnitude from highway travel. The strength of the racer’s cockpit and the protections it provides are the key to racing being a sport instead of a suicide pact.
It is Aptera’s execution of the CF safety cell that will determine its ultimate safety and on that score, I’m confident.
- MemberMarch 16, 2023 at 5:48 pm
Not F1, but as the video title says, Le Mans cars, prototype class at that. Their aerodynamic design is so very different from the Aptera that there is essentially no comparison. Race cars are designed to generate large amounts of downforce through carefully controlled airflow from front to back. When that airflow is disrupted (including coming from a significant angle off axis) and the car is traveling at racing speed nasty things can occur – as shown in this video. Since the Aptera is designed to generate near zero downforce and the vehicle is designed for essentially equivalent airflow underneath and above, it will not suffer the same catastrophic effects even if you were to get it up to the speeds of the racing cars.
What Aptera does have in common, as you suggested is a carbon fiber safety cell, certainly more durable than almost any other passenger vehicle available today. Being properly belted into an Aptera will likely be one of the safest places to be in the event of an accident.
- MemberMarch 17, 2023 at 4:15 am
A lot of the crash safety in race cars is due to the 5 point harness and neck protection. Probably the reason why drivers can walk away from a crash which doesn’t look survivable.
- MemberMarch 17, 2023 at 5:29 am
This is true. Fortunately most civilian accidents are at much lower energy levels than racing accidents. 1/2 to 1/4 the impact speed means 1/4 to 1/16 of the energy levels. 5 point harnesses are not needed in our vehicles to maintain comparable safety levels to race cars.
- MemberMarch 23, 2023 at 11:28 pm
I was watching that lemans race live when the cars took flight,
I have a 52 MGTD. And it gets very sketchy at highway speeds The big sail like fenders lift the front end off the ground a little, Being shaped like a wing. Aptera should fly like a bird
- ModeratorMarch 24, 2023 at 7:11 am
Yes, Aptera’s shape acts like a wing somewhat, but that wing shape is angled slightly down, so it pushes down to hug the road rather than lift it up. Also, Aptera weighs the better part of a ton and has a top speed of only 101 mph, much slower than those race cars.
If the road is slippery, I suggest you keep your speed down to much less than that. 😉
- ModeratorMarch 25, 2023 at 7:25 am
My first car was a 1952 MGTD. As I recall, it was “sketchy” at all times! Rebuilt it 2x.
I’m sure Aptera is far more well engineered for aero.
- MemberMarch 25, 2023 at 7:21 am
So. If I read that correctly. The car is designed to create downforce will affect its range. More road resistance. Less range
- MemberMarch 25, 2023 at 8:26 am
You have to steer that narrow path between most efficient design and flying off the road into a ditch.