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Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
4/27/20 2:48 p.m.

During the Current Unpleasantness, the task of shooting the weekly Facebook Live video for FM has fallen to yours truly. Some of them are of more interest to GRM than others. Last week, I showed off my active aero proof of concept using Miata headlight motors and I thought the GRM folks might find it interesting. Audio level is a little low for the intro, but that sorts out once I get closer to the camera.

We need more DIY active aero.

 

boxedfox (Forum Supporter)
boxedfox (Forum Supporter) Reader
5/8/20 11:19 a.m.

That's very cool. And highly attainable for the DIY racer.

It's giving me all sorts of bad ideas, like using a towing brake controller as a g-sensor to fine-tune the threshold for when the wing would activate, or hiding the motors in the trunk and running the turnbuckles through a larger pipe so no one knows that you have an active wing.

NOT A TA
NOT A TA SuperDork
5/8/20 12:43 p.m.

Thanks for putting it up here.

I got a couple linear actuators and a pair of trunk hinges a couple years ago to fabricate something similar but hadn't found a wing yet. Now I've got a wing to play with but unfortunately the wing project isn't near the top of the project list.

 

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
5/23/20 8:53 a.m.

My sport bike powered datsun roadster build isn't going to use the exhaust Vale actuator in the exhaust. 

That leaves an actuator that is controlled (and programmable) by the ecu...

Map the wing(s) to rpm and throttle position? Sounds really cool.

BrianC72gt (Forum Supporter)
BrianC72gt (Forum Supporter) New Reader
12/19/20 3:36 p.m.

Here is another nice chap in the UK doing diy active aero with a prototype arduino controller.  He's already got a version of it fitted to his AW11 MR2.    The control motors give you all kinds of precise movement options, just have to gear it for the right torque I'd guess.  I wonder would this help with throttle of oversteer...of course so would learning how to drive better (speaking for myself).   

 

NOT A TA
NOT A TA SuperDork
12/20/20 9:14 a.m.

In reply to BrianC72gt (Forum Supporter) :

Looks pretty cool. I'd think he needs to put vents in the sides of the case to allow air flow to cool the heat sinks for the linear sub power supplies.

MrFancypants
MrFancypants Reader
12/20/20 6:45 p.m.

Julian Edgar messed around with this on his Insight. He used compressed air to adjust his air brake. He has a series of videos documenting the development on his channel, here's one of them...

 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
12/20/20 8:44 p.m.

The servos in that video are 25 kg each, which means two of them are rated for a 55 lb load. Put them near the center of pressure of the wing and that should be enough. They look fast enough in the video.

That video is the second stage of evolution. Mine was very much a proof of concept - "what's the easiest way to make this happen?" The rabbit hole of asymmetrical flaps with arduino control was often brought up, but never by anyone who had actually made the first step.

Compressed air would be fun, do you use it to retract as well?

SVreX (Forum Supporter)
SVreX (Forum Supporter) MegaDork
12/20/20 9:15 p.m.

My next project involves active aero. I will post when I make some progress. 

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
12/20/20 9:36 p.m.

I actually had a couple back and forths with Julian via posting on his youtube videos. Smart guy, for sure. I like his aerodynamics book too.

I'd like to see active aero on a challenge car, but more importantly I'd like to see the proof of effectiveness.

Unfortunately I can't really think of a good case for active aero in the challenge... You want downforce for the autox and you want less for the drags. Plenty of time to manually make adjustments if needed. I just don't really see where the very few times you want less downforce in autox (and could therefore reduce drag) are going to help you times much.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
12/20/20 9:43 p.m.

Everyone always goes to drag reduction because that's what F1 has. What about air brakes? Slow speeds just means bigger surfaces.

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
12/20/20 9:46 p.m.

In reply to Keith Tanner :

Fair, but would you trade downforce for extra drag and expect to get faster?

I'd think you're slowing down best by maximizing tire grip. Maybe not?

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
12/20/20 9:59 p.m.

To maybe explain a bit better. Any active aero device will have an impact to both drag and downforce. In autox situations, if it increases downforce you probably want to just run it all the time. No need to be active.

If you want it to increase drag (air brake), then the drag increases but the downforce either goes down, stays about the same, or increases. As we said before, if the active movement increase downforce, you're probably already running it full time. If it decreases downforce, then you might be adding aero braking but you are losing tire braking. So you're only left with active aero being a benefit when the air brake doesn't substantially change downforce. 

Just a very narrow design goal range for the challenge is all I'm saying. Probably bigger fish to fry.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
12/20/20 9:59 p.m.

You're getting most of your braking off the front wheels, so turning your rear wing into a parachute isn't really costing you much useful tire grip. It also acts to stabilize the car by moving the aerodynamic center way back. I've felt this on my car when the air brake kicked in, it was a lot more stable. This is probably a lot more appreciated in the triple digit range when the consequences are a little bigger than a few cone scuffs.

And usually downforce keeps increasing with AoA. It just gets really inefficient. But that's okay, because that inefficiency is giving us our braking effect. So we get more downforce AND more braking force. It's a win/win.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
12/20/20 10:02 p.m.

So you're suggesting a challenge car has power to spare and will not benefit from decreased drag relative to the maximum downforce and maximum drag setting. For certain cars with a lot of power, this is undoubtedly true. But those who are playing the low power/light weight game may be able to take advantage of being able to trade off acceleration and cornering. I can tell you that my 148 rwhp, 1200 lb Locost saw a massive fall-off in acceleration with the windshield installed. 0-60 in 4.7, 0-90 in 10.8. Take the windshield off and it improved markedly.

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
12/20/20 10:08 p.m.

In reply to Keith Tanner :

Yeah I'm suggesting that in autox basically every car has "power to spare" and that's why miatas can compete with corvettes. 

Edit, and both cars improve more from handling improvements than acceleration improvements. 

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
12/20/20 10:15 p.m.

I don't know any of this to be universally true of course.

But in general, for autox you need to maximize cornering speed over just about anything else. Tradeoffs giving something up for more cornering speed usually make the car autox faster.

Sure, could a CP miata gain a bit by dropping the spoiler flat on the maybe 5 seconds of pure straight on course? Yes I'd think so. But would your $2k challenge budget be better spent finding bigger chunks of time elsewhere? Also probably yes.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
12/20/20 10:56 p.m.

People keep trying to prove how aero doesn't work until someone beats them with it :) The wing on my car was designed for NASCAR use, which everyone tells me means it's for 200 mph use and is not appropriate for Miata speeds. And especially not for a kart track that is basically a permanent autox course. But on a track that has a 63 second lap time with an average speed of just about 50 mph - it was worth two seconds.

So I'm always willing to experiment with aero and not write it off until I know for sure.

If drag is irrelevant on an autox course, then active aero doesn't make any sense unless it's doing some torque vectoring which is an interesting use. But as noted with my light, low power car, drag certainly does come in to effect in autox speed ranges. So maybe if someone manages to find a way to have max downforce (and/or max drag) when they need it and low drag when they don't, that seems like a benefit when tenths of a second count. My own setup was done with a relay and Miata headlight motors, so any NA Miata going to the challenge could implement it without a cent of the Challenge budget being affected because all of those parts come included with the car. Could a 2'x4' sheet of plywood going vertical in the braking zone help add a little more braking power to what the tires can produce? Maybe. Would it get you written up in the magazine? Quite possibly. Would it be interesting to try? Definitely.

Besides, there's a whole lot more to life than the Challenge. Even for Challenge cars.

Appleseed
Appleseed MegaDork
12/20/20 11:53 p.m.

Also, if you have limited strength in an actuator or servo, look into employing a servo tab. You think a human has the bare strength to muscle something like a B-17 rudder without help? 

Not 100% the same as if we treat the wing like an all moving sabilator in the animation,  nor are we using it as a trimming device,  but the mechanics are similar. 

sleepyhead the buffalo
sleepyhead the buffalo Mod Squad
12/21/20 4:35 a.m.
Keith Tanner said:

And usually downforce keeps increasing with AoA. It just gets really inefficient. But that's okay, because that inefficiency is giving us our braking effect. So we get more downforce AND more braking force. It's a win/win.

There's something about this that sounds wrong to me...

edit:
I think that's maybe more true for spoilers, as a rear downforce treatment.  And, I reckon it's even more true cars that have diffusers.  I'm still a little hesitant to think it applies to "wings"... (and again, is maybe more true for cars with wings and diffusers, than just a wing and no diffuser).

Still, I reckon there's a limit with spoilers of deflection increasing downforce.  I suspect it'd be found somewhere around 115deg from horizontal.  I think a "wing", would top out closer to 60-75deg.... depending on (a lot of things).

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
12/21/20 9:00 a.m.

Most lift/drag calculations come from aircraft, and I'm thinking about a true wing with airflow on both sides. A moving spoiler is more akin to a flap on a wing - which is used to increase lift at the expense of high drag, of course.

If you look at lift/drag charts, you'll find that the peak in lift often comes after the drag curve gets ugly. Even after that peak, the lift stays high. I'm recommending staying in that range.

ProDarwin
ProDarwin MegaDork
12/21/20 9:09 a.m.

To jump in on the aero discussion re: autox

I would suspect that in autox you are under max cornering loads such a high percentage of the time that active aero does not make sense.  Just set it to full grip and run it.  That said, its just wild speculation and I would love to look at some data and see if that is the case.

It would be interesting to take a data trace (after run 1) and run it through a simulation to calculate what the best possible tradeoff is for drag/downforce for a particular wing and then set it for that :)

 

Also, because I didn't watch the entire video of Professor Keith - what is the reaction time of the aero?  like max to min - 1 second?  .1 second?  .01 second?

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
12/21/20 9:10 a.m.
Keith Tanner said:

Besides, there's a whole lot more to life than the Challenge. Even for Challenge cars.

You're entitled to your opinions, no matter how wrong they are. cheeky

I never said I don't think active aero is a benefit. Nor did I ever say that its not really cool. In fact I did say I wanted to see it at the challenge and see the proof of its effectiveness. I only said that I couldn't think of a good case for it in the challenge. The main reason for that is that I see only small places for it to be effective, and therefore I see many other much more lucrative areas to spend your time and budget in a challenge sense. 

And this is all coming from a guy who has spent a huge amount of time compared to most other competitors on aero at the challenge over the last few years. 

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
12/21/20 9:21 a.m.
sleepyhead the buffalo said:
Keith Tanner said:

And usually downforce keeps increasing with AoA. It just gets really inefficient. But that's okay, because that inefficiency is giving us our braking effect. So we get more downforce AND more braking force. It's a win/win.

There's something about this that sounds wrong to me...

edit:
I think that's maybe more true for spoilers, as a rear downforce treatment.  And, I reckon it's even more true cars that have diffusers.  I'm still a little hesitant to think it applies to "wings"... (and again, is maybe more true for cars with wings and diffusers, than just a wing and no diffuser).

Still, I reckon there's a limit with spoilers of deflection increasing downforce.  I suspect it'd be found somewhere around 115deg from horizontal.  I think a "wing", would top out closer to 60-75deg.... depending on (a lot of things).

Yeah, I don't know about the answer to this in the sense of the whole car, but I do try to run the wings I attach generally at their 'downforce peak'. as seen in pictures like this in other threads. I am shooting for the AoA that nets the largest downforce, drag be damned. 

Whether this is the fastest way to do it or not, is of course debatable!

SVreX (Forum Supporter)
SVreX (Forum Supporter) MegaDork
12/21/20 9:31 a.m.

In reply to Robbie (Forum Supporter) :

I'm not convinced you are viewing this right.

Keith was pretty clear in his video that he sees the greatest opportunity with this as an air brake, not as a contributor to aero.  

As you have noted, in autoX, we never generate speeds high enough to be massively concerned about the drag generated (drag be damned).  However, the ability to dive deeper into the corners before braking because of the increased stopping power of the air brake also gives the ability to get OFF the brakes quicker, and get out of the corners faster.

"Active aero" might not even be the right name.  

Consider a well designed wing (like you have developed) to be a great advocate to downforce (as you have shown).  But once there is a good wing on the car providing, the ability to use it secondarily as a nearly free component as an air brake to assist in braking force may also have merit.

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