The Great FD3S Under-body Aerodynamics Thread: Photos, Products, Ideas, Results
11-15-09, 05:48 AM
#29
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The Rx7 is a front engined rear wheel drive, sorry to state the bleeding obvious here, however it isn't such a stupid statement!
I'm sure that Mazda had all of the money in the world to develop their flag ship model, but remember this is a road car, and not a race/road car. With the engine in the rear, then you don't need to worry about prop shafts, exhausts, gearboxes and anything else that generates heat and generally would make it difficult to service.
So with that in mind, looking at the Lotus Elise, Ferrari 430, Porsche GT3, these all have the flat floors and are rear engined. Also they are probably taken to a main dealer....and owners expect to pay more money for their servicing.
Our system was designed by a company who specialises in aerodynamics We are going to test it...logging the suspension with linear pots to see what extra loading we get with the aero.
I'm sure that Mazda had all of the money in the world to develop their flag ship model, but remember this is a road car, and not a race/road car. With the engine in the rear, then you don't need to worry about prop shafts, exhausts, gearboxes and anything else that generates heat and generally would make it difficult to service.
So with that in mind, looking at the Lotus Elise, Ferrari 430, Porsche GT3, these all have the flat floors and are rear engined. Also they are probably taken to a main dealer....and owners expect to pay more money for their servicing.
Our system was designed by a company who specialises in aerodynamics We are going to test it...logging the suspension with linear pots to see what extra loading we get with the aero.
11-15-09, 12:30 PM
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No one is saying anything in this world is perfect. But the FD has a .29 drag coefficient (.31 R models) and it's stable throughout its speed range. So how much better are you going to do?
Check that CD figure against current performance cars. It's as good or better than most of them. A number of supercars have significantly higher CD numbers. (Higher is worse.)
You can try adding more downforce, but how much drag are you adding? And without wind tunnel testing it's going to be difficult to tell how balanced that downforce is. And how often are you driving over 100 mph anyway? Is the added drag canceling out the claimed downforce advantage in most all of your driving?
So we've got some backyard engineers and small aftermarket firms with no access to extensive wind tunnel testing claiming they can make incremental improvements on the FD's already good numbers. Well, I say prove it.
You can be sure in most of these cases you're adding cost and weight and probably aerodynamic drag too. Let's be honest about the motivation --- you're scratching an urge to tinker and looking for an appearance item to set your car apart.
11-15-09, 02:06 PM
#35
No one is saying anything in this world is perfect. But the FD has a .29 drag coefficient (.31 R models) and it's stable throughout its speed range. So how much better are you going to do?
Check that CD figure against current performance cars. It's as good or better than most of them. A number of supercars have significantly higher CD numbers. (Higher is worse.)
You can try adding more downforce, but how much drag are you adding? And without wind tunnel testing it's going to be difficult to tell how balanced that downforce is. And how often are you driving over 100 mph anyway? Is the added drag canceling out the claimed downforce advantage in most all of your driving?
So we've got some backyard engineers and small aftermarket firms with no access to extensive wind tunnel testing claiming they can make incremental improvements on the FD's already good numbers. Well, I say prove it.
You can be sure in most of these cases you're adding cost and weight and probably aerodynamic drag too. Let's be honest about the motivation --- you're scratching an urge to tinker and looking for an appearance item to set your car apart.
Check that CD figure against current performance cars. It's as good or better than most of them. A number of supercars have significantly higher CD numbers. (Higher is worse.)
You can try adding more downforce, but how much drag are you adding? And without wind tunnel testing it's going to be difficult to tell how balanced that downforce is. And how often are you driving over 100 mph anyway? Is the added drag canceling out the claimed downforce advantage in most all of your driving?
So we've got some backyard engineers and small aftermarket firms with no access to extensive wind tunnel testing claiming they can make incremental improvements on the FD's already good numbers. Well, I say prove it.
You can be sure in most of these cases you're adding cost and weight and probably aerodynamic drag too. Let's be honest about the motivation --- you're scratching an urge to tinker and looking for an appearance item to set your car apart.
also, how does under-body paneling have anything to do with appearance? no one will ever see that...it's under the car.
the weight argument is also pretty silly. anytime you add/replace parts on any car you're affecting the weight one way or another. when adding new parts (adding weight), the additional weight can be easily offset with things like swapping out the stock battery, lighter rims, etc. when people add trunk spoilers to a wingless car, do you tell them that they're doing more harm by adding additional weight? no, because for certain types of cars, having a rear spoiler helps (where's that video of the wingless FD vs the stock wing FD vs the FD with the RE-Amemiya GT wing?)
i think you're missing the point of this thread.
not every mod/part is for every car. each person builds their car for a specific purpose. people choose parts and configurations specific to their goals. while not everyone needs to worry about under-body aerodynamics, some people might be interested in the r&d of products specific to that subject. some people street drive their cars, some people drag them, some people auto-x them, some people build them for "show", some people track them, some race them professionally - there are configurations for each of these, and i'm sure there are some people who have cars that can benefit from some under-body aerodynamics r&d.
if you have such a problem with this, stay out of the thread instead of bringing all that negativity.
11-15-09, 02:12 PM
#36
You all maybe the first aero manufacturer I've seen to have numbers to go along with their products.
Just as manufacturers' claims of horsepower improvements should be backed up with real numbers, so should manufacturers of aerodynamic enhancement products. That's all I'm saying! I'm not bashing any improvement in aerodynamics or saying that it's not possible to improve the aerodynamic properties of any car.
11-15-09, 02:57 PM
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i wonder how hard it is to get ahold of 3d fluid dynamics software?
theres a few very detailed 3d models of FDs out there, mabey if they could be transfered to that program, we could actually give it a "test"..
theres a few very detailed 3d models of FDs out there, mabey if they could be transfered to that program, we could actually give it a "test"..
11-15-09, 03:29 PM
#38
It's funny that engine parts are more expensive and harder to manufacture yet you can just go down to your local workshop to test the performance of these parts on dyno, aero parts are easier to manufacture but your local shop doesn't have a wind tunnel so we can never be sure of the performance of these parts as black and white as in other parts of the car. Most of the time ppl go by common sense like more downforce the better, lighter the weight the better etc. but of course when someone asks for proof they can't pull out a wind tunnel sheet like they can quickly pull out a dyno sheet.
Now when it comes to drag coefficient I don't know but I always thought the major factor is the design of the bodywork of the car not underbody. Underbody of most cars look like they are not designed with any performance benefit in mind. Since the RX7 has .29 dc with a messy looking underbody I don't think a flat underbody will improve on that dramatically. It might be better (which I can't prove it) but I don't think anyone here can really tell the difference. On the contrary anyone remember the Mercedes in LeMans flipping on air on the main straight (of course at a very high speed which a regular RX7 won't do)? A flat undertray may contribute to wind under the car acting as one and giving more power to lift the car at high speed (flag with holes vs. flag with no holes).
Now when it comes to drag coefficient I don't know but I always thought the major factor is the design of the bodywork of the car not underbody. Underbody of most cars look like they are not designed with any performance benefit in mind. Since the RX7 has .29 dc with a messy looking underbody I don't think a flat underbody will improve on that dramatically. It might be better (which I can't prove it) but I don't think anyone here can really tell the difference. On the contrary anyone remember the Mercedes in LeMans flipping on air on the main straight (of course at a very high speed which a regular RX7 won't do)? A flat undertray may contribute to wind under the car acting as one and giving more power to lift the car at high speed (flag with holes vs. flag with no holes).
11-15-09, 03:37 PM
#39
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No one is saying anything in this world is perfect. But the FD has a .29 drag coefficient (.31 R models) and it's stable throughout its speed range. So how much better are you going to do?
Check that CD figure against current performance cars. It's as good or better than most of them. A number of supercars have significantly higher CD numbers. (Higher is worse.)
You can try adding more downforce, but how much drag are you adding? And without wind tunnel testing it's going to be difficult to tell how balanced that downforce is. And how often are you driving over 100 mph anyway? Is the added drag canceling out the claimed downforce advantage in most all of your driving?
So we've got some backyard engineers and small aftermarket firms with no access to extensive wind tunnel testing claiming they can make incremental improvements on the FD's already good numbers. Well, I say prove it.
You can be sure in most of these cases you're adding cost and weight and probably aerodynamic drag too. Let's be honest about the motivation --- you're scratching an urge to tinker and looking for an appearance item to set your car apart.
Check that CD figure against current performance cars. It's as good or better than most of them. A number of supercars have significantly higher CD numbers. (Higher is worse.)
You can try adding more downforce, but how much drag are you adding? And without wind tunnel testing it's going to be difficult to tell how balanced that downforce is. And how often are you driving over 100 mph anyway? Is the added drag canceling out the claimed downforce advantage in most all of your driving?
So we've got some backyard engineers and small aftermarket firms with no access to extensive wind tunnel testing claiming they can make incremental improvements on the FD's already good numbers. Well, I say prove it.
You can be sure in most of these cases you're adding cost and weight and probably aerodynamic drag too. Let's be honest about the motivation --- you're scratching an urge to tinker and looking for an appearance item to set your car apart.
The thing about underfloor aerodynamics is that it doesn't sacrifice downforce for drag. Sticking a great big wing on the other hand doesn't!
The CD factor really isn't that much of an issue here. We are looking to improve our ability to win races, and so downforce is the main goal.
You don't need to take the car to a wind tunnel, to gain results. For one, good old fashioned experience plays a part also.
Tomorrow morning is getting closer...so there will be some photos
11-16-09, 11:58 AM
#40
Please somebody help!!!
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No one is saying anything in this world is perfect. But the FD has a .29 drag coefficient (.31 R models) and it's stable throughout its speed range. So how much better are you going to do?
Check that CD figure against current performance cars. It's as good or better than most of them. A number of supercars have significantly higher CD numbers. (Higher is worse.)
You can try adding more downforce, but how much drag are you adding? And without wind tunnel testing it's going to be difficult to tell how balanced that downforce is. And how often are you driving over 100 mph anyway? Is the added drag canceling out the claimed downforce advantage in most all of your driving?
So we've got some backyard engineers and small aftermarket firms with no access to extensive wind tunnel testing claiming they can make incremental improvements on the FD's already good numbers. Well, I say prove it.
You can be sure in most of these cases you're adding cost and weight and probably aerodynamic drag too. Let's be honest about the motivation --- you're scratching an urge to tinker and looking for an appearance item to set your car apart.
Check that CD figure against current performance cars. It's as good or better than most of them. A number of supercars have significantly higher CD numbers. (Higher is worse.)
You can try adding more downforce, but how much drag are you adding? And without wind tunnel testing it's going to be difficult to tell how balanced that downforce is. And how often are you driving over 100 mph anyway? Is the added drag canceling out the claimed downforce advantage in most all of your driving?
So we've got some backyard engineers and small aftermarket firms with no access to extensive wind tunnel testing claiming they can make incremental improvements on the FD's already good numbers. Well, I say prove it.
You can be sure in most of these cases you're adding cost and weight and probably aerodynamic drag too. Let's be honest about the motivation --- you're scratching an urge to tinker and looking for an appearance item to set your car apart.
My car has no appearance items, my body is bone stock. I am a form follows function kind of guy. My interest in the underbody is purely utilitarian, if I can add 5-10lbs and get better mileage I'll do it. I need to replace my missing oem undertray anyway.
11-16-09, 01:01 PM
#41
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OK some photos of the floor.
The weight of the system, excluding any brackets is 13.8 kgs. That is for the front splitter (including brackets shown) Flat floor pieces and rear diffuser.
We will test the overall effect that the floor gives, and I can promise you it will be extensive! To quantify the level of downforce we are expecting, we shouldn't need to run a rear wing. We are still going to run one, but the angle of attack can be less so therefore not producing as much drag.
As already pointed out in a previous post, aerodynamic effects are a proven quantity. LMS, FIA GT, GT Open and ALMS are the top flight cars currently running today, and all of these cars run flat floors. These are tied the regs, and so limit the amount of bespoke tuning to the individual cars, so in theory pretty much all of the cars run a similar ground effect concept of a full flat floor with an extruded diffuser.
The weight of the system, excluding any brackets is 13.8 kgs. That is for the front splitter (including brackets shown) Flat floor pieces and rear diffuser.
We will test the overall effect that the floor gives, and I can promise you it will be extensive! To quantify the level of downforce we are expecting, we shouldn't need to run a rear wing. We are still going to run one, but the angle of attack can be less so therefore not producing as much drag.
As already pointed out in a previous post, aerodynamic effects are a proven quantity. LMS, FIA GT, GT Open and ALMS are the top flight cars currently running today, and all of these cars run flat floors. These are tied the regs, and so limit the amount of bespoke tuning to the individual cars, so in theory pretty much all of the cars run a similar ground effect concept of a full flat floor with an extruded diffuser.
11-16-09, 01:09 PM
#42
Racy looking parts there.
Would this be appropriate on a street car? I wonder about the effects of sealing off the exhaust. Seems like the engine bay heat also follows the trans tunnel to be evacuated. I would think more of the heat would be radiated into the cabin as a result of this on a street car.
Would this be appropriate on a street car? I wonder about the effects of sealing off the exhaust. Seems like the engine bay heat also follows the trans tunnel to be evacuated. I would think more of the heat would be radiated into the cabin as a result of this on a street car.
11-16-09, 02:01 PM
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we are going to ceramic coat the exhaust right through to the end....but also we are going to be adding ducts to bring air in. This will be done without compromising the ground effect.
We are also running oil coolers for both gearbox and diff.
Also we line the transmission tunnel with an aluminium weave shielding, as previously after an hour of constant running, even without the flat floor, the tunnel was so hot it burnt my leg.
It will be suitable for both race or road cars, as we have built in strengthening sections which are strong enough to jack off.
We are also running oil coolers for both gearbox and diff.
Also we line the transmission tunnel with an aluminium weave shielding, as previously after an hour of constant running, even without the flat floor, the tunnel was so hot it burnt my leg.
It will be suitable for both race or road cars, as we have built in strengthening sections which are strong enough to jack off.
11-16-09, 03:25 PM
#46
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11-16-09, 03:41 PM
#47
Also working on some aerodynamic pieces myself. Currently working my front splitter with wheel well diffuser sections. Due to Redline Time Attack rules I can't go flat bottom like AtomicRex is doing, but I will be making a tranny tunnel plate and rear diffuser, amazingly very similar in design, lol.
11-16-09, 04:00 PM
#48
If all goes well I may get access to the wind tunnel here at work later next year when all my aero parts are made. Provided at a limited capacity and air speed. More of a verification of attached air flow than actual down force numbers.
11-16-09, 04:40 PM
#50
Interesting thread.
It shouldn't be too difficult to quantify changes in aerodynamic drag by doing coast-down testing. Google it, you basically put the car in neutral and record vehicle speed vs time: lots of drag will slow the car quickly. Should be a pretty simple test if you've got an aftermarket ECU that can datalog vehicle speed. Slightly less easy would be to use a camcorder (or digital camera or fancy cell phone in movie mode) pointed at the speedometer.
Someone on these forums once claimed that removing the front fender liners improved their 3rd or 4th gear acceleration times by a significant margin.
Unfortunately measuring actual downforce isn't nearly as easy... the best most of us can do may be to infer 'more grip' or 'less grip' from very controlled testing. If you've got some way of measuring actual cornering g's that's a step closer. If you've got a lot of resources you might be able to measure suspension travel... find a straightaway and compare ride height with and without aero. You might take this a step further and compare those numbers against ride height with ballast.
Don't forget the weight of fuel if you're testing over an extended period of time... a 5-gallon fuel jug is pretty heavy when full.
It shouldn't be too difficult to quantify changes in aerodynamic drag by doing coast-down testing. Google it, you basically put the car in neutral and record vehicle speed vs time: lots of drag will slow the car quickly. Should be a pretty simple test if you've got an aftermarket ECU that can datalog vehicle speed. Slightly less easy would be to use a camcorder (or digital camera or fancy cell phone in movie mode) pointed at the speedometer.
Someone on these forums once claimed that removing the front fender liners improved their 3rd or 4th gear acceleration times by a significant margin.
Unfortunately measuring actual downforce isn't nearly as easy... the best most of us can do may be to infer 'more grip' or 'less grip' from very controlled testing. If you've got some way of measuring actual cornering g's that's a step closer. If you've got a lot of resources you might be able to measure suspension travel... find a straightaway and compare ride height with and without aero. You might take this a step further and compare those numbers against ride height with ballast.
Don't forget the weight of fuel if you're testing over an extended period of time... a 5-gallon fuel jug is pretty heavy when full.