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Old 08-16-2003, 11:51 PM   #1
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Default Diffuser for RC?

well...being the European racenut that I am..I always noticed that the cars have rear diffusers on then..(F1/ASTCC/BTCC/GTCC etc etc..I know that Tamiya makes a rear diffuser for their old style F1 cars but have never seen one for the newer cars..being that in theory RC Cars run thru the air the same way full size cars do I was thinking if a diffuser would be an advantage or not?..I have some 1/8thinch CF and was curious what youre thoughts were before I begin building one....Thanks.
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Old 08-17-2003, 01:58 AM   #2
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I remember something like 7 years ago, Tamiya made a prototype of a lexan under chassis for the TA03 which took all the surface of the car and had a rear diffuser, then they just added one of their 11T and a 7 cells batt, I think they clocked the car at 95 kph (45 mph??)....not so sure it was a long time ago
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Old 08-17-2003, 01:59 AM   #3
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that is perhaps why all this kind of under chassis aerodynamic stuff are forbidden during competition .
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Old 08-17-2003, 09:43 AM   #4
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I really dont know that they would help all that much. The bottom of the chassis is perfectly flat on 95% of the cars made, so the wind should just cut right underneath it. You'll get more noticiable results by playing with body selection and wing, because that is what creates the real drag and downforce.
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Old 08-17-2003, 11:42 AM   #5
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a normal flat chassis just take 50% of the surface under the car, the one I saw just had holes for the wheel, it was folded in the middle to create a ground effect too(V-shaped)
HPI made a while back a prototype with a molded carbon chassis with the same kind of shape (the chassis were V-shaped and were totally closed (like a flying saucer!), had a diffuser too in the back, has something like 20 cells...but weren't able to make any record since the diff ball melted. very fast
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Old 08-17-2003, 12:00 PM   #6
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Why the heck would you run a ball diff with 20 cells...
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Old 08-17-2003, 12:07 PM   #7
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never see those oval cars using something else than a ball diff...
maybe i am wrong but they are all using pan cars (RC10Lx, RS10G......)
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Old 08-18-2003, 12:02 AM   #8
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In the past I have experimented with diffusers and undertrays on my RC cars, and they DO work (depending on design of course).

However, now all sanctioned race meets have banned them, so there was no point in me continuing.

And for those wondering, the bad part, aerodynamicaly speaking, is all the holes and cutouts underneath the chassis creates drag and turbulence. If you ever get to look underneath any groung effect racing car, or high end road car, you'll see that the bottom is very smooth, with no gaping holes,(and if anything, naca ducts for cooling on some road cars), with a rise, generally restrained by the rear suspension, so that when the floor clears the rear wishbones, the rake picks up further. Also, once the diffuser section becomes too large, you need to add spill plates to stop the air from getting too messed up.
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Old 08-18-2003, 11:13 AM   #9
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Quote:
Originally posted by BagofSkill And for those wondering, the bad part, aerodynamicaly speaking, is all the holes and cutouts underneath the chassis creates drag and turbulence. If you ever get to look underneath any groung effect racing car, or high end road car, you'll see that the bottom is very smooth, with no gaping holes,(and if anything, naca ducts for cooling on some road cars), with a rise, generally restrained by the rear suspension, so that when the floor clears the rear wishbones, the rake picks up further. Also, once the diffuser section becomes too large, you need to add spill plates to stop the air from getting too messed up. [/B]
Bang on, except for the restraining effect of the wishbones. For F1 the rear diffuser is regulated so it can only begin in-line with the front of the rear wheels, and cannot extend farther back than the wheel axle (about 13''). There is also a central diffuser, however, which can extend as far back as the trailing edge of the rear wing. In CART the tunnels are also restricted, and again cannot extend behind the rear axle line. The old Group-C cars were permitted tunnels, and these were normally extended right through the line of the rear wishbones and axles.

We've been debating this question on another forum; http://www.rcracechat.com/forum/inde...;threadid=2524
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Old 08-18-2003, 05:35 PM   #10
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I've got an idea for you. What if we copied the Chapparal 2J/Brabham "fan car" concept instead! Seal off the bottom of the car and mount one of those small Radio Shack fans
(that many use to cool their motors and batteries) on the back of the car facing to the rear so that it sucks the air out from underneath the car, thus creating a perfect vaccume that works at ALL speeds!!! You could couple the fan with a rear diffuser so that you are not only sucking the air out from under, but also creating the venturi effect by accelerating the low pressure air
through the curve of the diffuser. Should work great!!!
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Old 08-19-2003, 01:10 AM   #11
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Simple diffusers were used in teh 1/12th scale racing a few years back. They increased the rear end traction in fast corners, but didnt' really help with lap times as they introduced pushing in high speed corners, decreased top speeds, more weight and added battery consumption. I haven't seen any for years.
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Old 08-19-2003, 07:04 AM   #12
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Quote:
Originally posted by JesseT
Simple diffusers were used in teh 1/12th scale racing a few years back. They increased the rear end traction in fast corners, but didnt' really help with lap times as they introduced pushing in high speed corners, decreased top speeds, more weight and added battery consumption. I haven't seen any for years.
I actually found them quite useful on 10th and 12th pan cars when racing on Asphalt. On asphalt they helped to lock-in the rear, thus reducing tire wear and actually increasing corner speed by keeping the vehicle on line with out an over-abundance of mechanical grip required from the tires. Obviously they'd be of limited benefit on a short, high bite carpet track.

Of course with today's advances in chassis design, they're not really necessary.
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Old 08-19-2003, 09:01 AM   #13
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We used to run lexan diffusers religiously with the F103. Tamiya's diffuser was really nice. It helps with rear down force and stability with its strakes. Most importantly, it shielded the spur gear from rocks Some drivers even left the points on the strakes (spill plates) sharp so that if another driver plows them, they might get their tires cut up haha evil. Personally, I always rounded my corners off...I don't like pointy things jabbing me when I work on the car.
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Old 08-19-2003, 11:34 PM   #14
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Quote:
Originally posted by JesseT
Simple diffusers were used in teh 1/12th scale racing a few years back. They increased the rear end traction in fast corners, but didnt' really help with lap times as they introduced pushing in high speed corners, decreased top speeds, more weight and added battery consumption. I haven't seen any for years.
Did anyone try using a front Splitter as well? I don't know if anyone remembers but a 90mm extension to the McLaren F1 GTR's splitter eradicated the understeer it had back in 1996/7.
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Old 08-20-2003, 08:00 PM   #15
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I guess no one is interested in my "fan car" idea which would solve all of your diffuser issues. The beauty of the fan car concept is that it works at any speed, even standing still!! Scale size of the car and air density do not matter with this concept, as the fan does all the work by creating a constant vaccume suking the car to the track. Too bad no one seems interested.
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