Active Aero -- A waste of time?
07-11-2014, 11:22 PM
#31
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I say go for it. Worst case it doesn't change your lap times, best case you have found something new.
07-12-2014, 01:55 AM
#32
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I take the point about the wing not running parallel to the ground and the general fastback situation. I deal with it myself. Looks like Jack's struts are higher off the rear screen than mine and I would suspect that there is enough separation to perhaps look at the point of reference somewhere inbetween the angles of the road and rear screen. It would be a guess. The endplates moving with the vane, perhaps that's a good thing, perhaps not. I'd be inclined to try it all out too as Matt says. Hope it works very well for you. Lucky to have the flexibility in the rules to run this. Something I'd really be interested in comparing is running with a stock engine cover vs the ducktail which I think will react adversely with your wing.
07-12-2014, 04:30 AM
#33
Yes, I commented that airflow was likely going to be somewhere between the rear window angle of the ground angle. Jack confirmed that with a specific number.
How are you going to make it so the end plates don't move with the wing? This is a simple single wing element setup here with the wing element attached to the uprights. The answer is that you are not.
How are you going to make it so the end plates don't move with the wing? This is a simple single wing element setup here with the wing element attached to the uprights. The answer is that you are not.
07-12-2014, 06:05 AM
#34
I think you will need a s**tload of sensors and loggers on that car in order to be 100% sure about the effects this thing has on your car and its handling, in an objective way.
IMO.
IMO.
07-12-2014, 06:08 AM
#35
Rennlist Member
Yes, I commented that airflow was likely going to be somewhere between the rear window angle of the ground angle. Jack confirmed that with a specific number.
How are you going to make it so the end plates don't move with the wing? This is a simple single wing element setup here with the wing element attached to the uprights. The answer is that you are not.
How are you going to make it so the end plates don't move with the wing? This is a simple single wing element setup here with the wing element attached to the uprights. The answer is that you are not.
Agreed. Suspension pot sensors really aren't difficult or expensive to mount. Worth it in this case I feel.
07-12-2014, 02:54 PM
#36
Race Car
Thread Starter
Well you could, but I realise that this is all mostly shadetree mechanics and not F1. It's fine and I enjoy what Jack does with his car and showing it to the world, good or bad.
Agreed. Suspension pot sensors really aren't difficult or expensive to mount. Worth it in this case I feel.
Agreed. Suspension pot sensors really aren't difficult or expensive to mount. Worth it in this case I feel.
And more than most, I'm in a position to see the results right away from the driver's seat, since I've been driving the one track for 14 years now, visiting it around 8 times a year. There isn't a whole lot of driver variability left. Based on the ambient temps, I can pretty reliably say what my lap time is going to be before I go out.
According to an aerodynamicist I've spoken to, even after some fudging for uprights and other mitigating factors, I probably have about 20-30 lb of drag at 130 mph, which consumes about 10 horsepower -- that's just for the wing. He says I could potentially cut that about in half, which chould be worth a little bit of top speed on the straights.
Now, we all know that 5 hp is a pretty small change -- I still suspect the real-world change might be negligible. But for the cost of a couple of salvage-yard Miata pieces, it's worth a try.
07-12-2014, 03:36 PM
#37
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C
According to an aerodynamicist I've spoken to, even after some fudging for uprights and other mitigating factors, I probably have about 20-30 lb of drag at 130 mph, which consumes about 10 horsepower -- that's just for the wing. He says I could potentially cut that about in half, which chould be worth a little bit of top speed on the straights.
Now, we all know that 5 hp is a pretty small change -- I still suspect the real-world change might be negligible. But for the cost of a couple of salvage-yard Miata pieces, it's worth a try.
According to an aerodynamicist I've spoken to, even after some fudging for uprights and other mitigating factors, I probably have about 20-30 lb of drag at 130 mph, which consumes about 10 horsepower -- that's just for the wing. He says I could potentially cut that about in half, which chould be worth a little bit of top speed on the straights.
Now, we all know that 5 hp is a pretty small change -- I still suspect the real-world change might be negligible. But for the cost of a couple of salvage-yard Miata pieces, it's worth a try.
Now, the million dollar question is what the drag is for just the wing, when not providing lift. (or downforce). generally, drag due to lift is the majority, but if you are still getting lift at 0 AOA, that will be some significant drag. to neutralize the lift , you have to know the angle of the air coming off the roof line. you might have 7 -9 degrees of deflected air to work with, meaning the wing has to be angled up quite a bit to produce 0 lift. Then, you are dealing with just the parasitic drag, which might be 5-8lbs. or 2 or 3ft-lbs at the engine (or 2-3hp) . this brings the net of the solution down to around 5-7hp if i was to guess.
It will be interesting to see the results, and if you get the straightline benefits that you can measure. 5hp change on a straight, might be tough to detect due to a lot of other factors. same day, same turn exit speed to start, and you might be able to see something, i hope.
07-12-2014, 03:39 PM
#38
Rennlist Member
I had a contraption that measured the downforce that used a calibrated spring scale. i would calibrate it by putting 300lbs of weight on pywood on the rear wing, as max , and then in 20lb increments, marked the scale. i think i got 275lbs of downforce at 120mph.....i have to check my notes and pictures.
07-12-2014, 03:48 PM
#39
Rennlist Member
I think this experiment is a waste of time because the speeds aren't high enough to make the difference significant. Even at venue like the Big Track at Willow Springs. Heck, one of the areas where you are carrying a lot of speed is a turn so you need the wing in it's high downforce position anyway.
The air flow coming on to the wing is not parallel to the ground. The shape of the 911 has the air coming onto the wing roughly parallel to the rear window angle. Well, probably a bit in between the ground angle and the rear window angle. In other words, the low drag setting would have the leading edge of the wing higher than the trailing edge relative to the ground. I don't see how the end plates moving with the wing would have any effect since their job is to keep the air from spilling off to the side of the wing. If anything, it is better that the end plates move with the wing.
The air flow coming on to the wing is not parallel to the ground. The shape of the 911 has the air coming onto the wing roughly parallel to the rear window angle. Well, probably a bit in between the ground angle and the rear window angle. In other words, the low drag setting would have the leading edge of the wing higher than the trailing edge relative to the ground. I don't see how the end plates moving with the wing would have any effect since their job is to keep the air from spilling off to the side of the wing. If anything, it is better that the end plates move with the wing.
Yes. The incoming air moving over the back half of my car is at an angle of about 10°, which is less than the 17°-19° of the (old) fastback shape, but also a long way from parallel to the ground. I tested it with wool tufts suspended from wires.
So if I run a 0° angle of attack relative to the road surface, I'm actually running the wing at 10°. I'm planning on running a slightly more agressive AOA (than usual) with this set-up, because the overall drag trade-off should be reduced. But then, drag isn't the only factor in setting a wing. Fore-aft balance and how it changes the car's handling is more important. So I'll be ready to go back to the original angle if the car is pushing through the high-speed corners.
Odd as it might look, the wing is still generating downforce at an AOA of 0° or even into negative AOA numbers. Regarding turn 8 (a 130-mph sweeper), I expect to go through it with the wing in the low-drag (and low downforce) position, assuming all this nonsense works. I frequently run at Willow with no aero bolted on (just the ducktail), and I am still flat on the gas through 8 without the wing in place. With the wing in its rocked-back, low-drag position, it will still be pressing down on the car in addition to the amount the ducktail spoils.
Lift force, drag force, and aerodynamic moment all scale with the square of speed. And the power required to overcome drag scales with the cube of speed. So I think there's probably some value to looking at whether reducing drag will help on the two portions of Willow that are 100-133mph -- which is about half the track. That said, I'm still skeptical that it's going to make a significant difference on a car that's as much as an aero nightmare as my widebody early 911 with all of its home-made aero pieces and what-not.
Still, it's interesting to take a look at something like this. Because so few sanctioning groups permit active aero, it's one of the few aspects of racing a 911 that hasn't already been tested and worked out to death.
So if I run a 0° angle of attack relative to the road surface, I'm actually running the wing at 10°. I'm planning on running a slightly more agressive AOA (than usual) with this set-up, because the overall drag trade-off should be reduced. But then, drag isn't the only factor in setting a wing. Fore-aft balance and how it changes the car's handling is more important. So I'll be ready to go back to the original angle if the car is pushing through the high-speed corners.
Odd as it might look, the wing is still generating downforce at an AOA of 0° or even into negative AOA numbers. Regarding turn 8 (a 130-mph sweeper), I expect to go through it with the wing in the low-drag (and low downforce) position, assuming all this nonsense works. I frequently run at Willow with no aero bolted on (just the ducktail), and I am still flat on the gas through 8 without the wing in place. With the wing in its rocked-back, low-drag position, it will still be pressing down on the car in addition to the amount the ducktail spoils.
Lift force, drag force, and aerodynamic moment all scale with the square of speed. And the power required to overcome drag scales with the cube of speed. So I think there's probably some value to looking at whether reducing drag will help on the two portions of Willow that are 100-133mph -- which is about half the track. That said, I'm still skeptical that it's going to make a significant difference on a car that's as much as an aero nightmare as my widebody early 911 with all of its home-made aero pieces and what-not.
Still, it's interesting to take a look at something like this. Because so few sanctioning groups permit active aero, it's one of the few aspects of racing a 911 that hasn't already been tested and worked out to death.
best of luck. watching with much interest.
07-12-2014, 03:52 PM
#40
Race Car
Thread Starter
The odd thing about my car and this track -- it had better not do too much. I can usually hit 132 on the straights. My car's gearing it limited to 135 at redline in 5th. I don't want to be bumping off of the rev limiter, but I doubt the 4hp difference is going to get me there. But we'll see.
12-29-2014, 05:00 PM
#41
Race Car
Thread Starter
Junk data can live forever on the internet. So I did some more testing, and here's a comparison between two runs on the front straight at WSIR, one (red) with the wing going to low drag on the straight, and one (blue) with the wing remaining in a fixed position. The rear ride height sensor wasn't working, so this shows the front, which drops down when the rear wing is switched to the low drag position (note: the line going higher on the graph means the nose of the car was moving lower to the ground).
So that would seem to show that leaving the wing in the high-downforce (high drag) position on the straight meant losing ultimate high speed.
But then here's the flipside. This is the same two laps, but looking at the back straight. This time the high drag (and high downforce) speed starts out slower, but then catches up to the low drag run -- which doesn't make any sense, if the low-drag position is lowering a significant amount of drag.
The difference could be as simple as the prevailing winds during the two (sequential) laps. Or one of many other factors.
So the jury is still out...
So that would seem to show that leaving the wing in the high-downforce (high drag) position on the straight meant losing ultimate high speed.
But then here's the flipside. This is the same two laps, but looking at the back straight. This time the high drag (and high downforce) speed starts out slower, but then catches up to the low drag run -- which doesn't make any sense, if the low-drag position is lowering a significant amount of drag.
The difference could be as simple as the prevailing winds during the two (sequential) laps. Or one of many other factors.
So the jury is still out...
12-29-2014, 09:15 PM
#45
Rennlist Member
One thing we noticed once back in 2013 was that we shifted the smaller of the dual elements on our wing to a higher AoA and actually went faster down the main straight of this shorter track. If my memory serves me correctly, we also measured the '2 notch' move to equate to an extra 300lbs of rear downforce. Our assumption was that the extra rear downforce allowed a higher exit speed out of the preceding corner therefore a higher top speed on the following straight. This would still be classed as anecdotal but thought it worth mentioning.