# Aerodynamics?



## cagee (Apr 20, 2007)

Is aerodynamics important on a slot car. If it is which chassis is it important on?

Also the lower the body the better the lap time?


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## coach61 (Sep 6, 2004)

Lower body will give better center of gravity to avoid roll overs, as for aero I am not so sure on such a small scale.. if someone can show me I will start adding winglets to my f1's lol


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## zig (Mar 11, 2004)

coach61 said:


> Lower body will give better center of gravity to avoid roll overs, as for aero I am not so sure on such a small scale.. if someone can show me I will start adding winglets to my f1's lol


Theoreticly the faster the car is the more important aero is I'll bet your f1's are a lot faster than a rectangle shaped box of the same weight.


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## coach61 (Sep 6, 2004)

zig said:


> Theoreticly the faster the car is the more important aero is I'll bet your f1's are a lot faster than a rectangle shaped box of the same weight.



You have a good point there.. Guess I will have to fix up a shoe box with a computer fan and exhale cigar smoke through it to see what the little aero flaps do.. and you think I put a lot of aero tweeks on the Honda...lol...


Dave


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## dlw (Aug 17, 1999)

Here's a few good XT bodies for racing:

Chevelle Stocker
Mitsubishi Eclipse
Mazda RX7
Toyota Supra
GT40

These are decent handling bodies:

57 Nomad
Plymouth Barracuda
Dodge Pickup
77 Firebird
71 Camaro
Javelin
57 Corvette

I've never ran these (much), but the look like they would be ok:

Monte Carlo Stocker
Shelby Mustang
55 Nomad


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## SplitPoster (May 16, 2006)

With most slot car applications, I would expect the aero part would be more about frontal area than the finer points of flow, more the drag aspect than positve or negative pressure, lift or downforce. 

Relative drag could be pretty easily measured by mounting bodies/cars on a slide in an airstream, a scale oriented horizonally to measure the "pull" in that airstream. Zero everything with the fan off, get a value with it running. You'd need a good air source and smooth chamber, not real "gusty", and a very accurate scale to get any value from the data.

Who is up to building a t jet wind tunnel?


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## 1976Cordoba (Sep 20, 2000)

I think the idea of aero-efficiency is made null by the force of the traction magnets.

Body shape is not so much about aerodynamics as it is about center of gravity and getting that body shell low to the chassis and thus the track.

Aerodynamics are very important in radio control racing and that is 1:10th scale (largest segment). I am sure there is some merit to aero at 1:64th scale but it is really more about the magnets and CG.

My $.02 worth.

'doba


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## JordanZ870 (Nov 25, 2004)

I am not sure it means getting the body down to the track, either. 
Seems to me that we should be trying to center the body "mass/weight" to the center of the rotating (arm)mass/force. Like a gyro-top? 

I can see it in my minds eye. Now my brain hurts. LOL


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## SplitPoster (May 16, 2006)

Doba, you are exactly right, with all else equal I am sure you would be measuring any advantage in the thousandths of a second. Now, a couple thousandths a lap for x number of laps, and, just like with any other form of racing, you have that one or two car-length victory. 

One very serious 1:1 showroom stock driver I knew meaured and found that a clean, very slippery waxed car was worth almost 1/2 mile per hour at the end of the longest straight at one track, nothing in the slower sections. It translated to a certain number of feet per lap. Splitting hairs and looking for every advantage big or small is all part of it. 

JoeZ, I can picture your thought, what about the polar momentum ahead of and behind the pin? Low CG keeps weight transfer down. As there is almost no "lean" and weight transfer laterally like a 1:1 or an R/C car, and the guide pin provides the lateral force to turn the car..... now my brain hurts too.


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## Scafremon (Dec 11, 2006)

Unless you can go WOT around a portion of a track with a slot car, or, have a need to conserve the amount of voltage you are allocated, then IMO aerodynamics has no advantage in slot cars.


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## *MAYHEM* (May 4, 2007)

Trust me,aerodynamics plays a big part. I have a Lancia Stratos body for T-jet from Alfaslot1 (I've posted pics before) that I run in Mod Tjet classes. I originally did it up with a fairly small wing and fairly flat angle. It was fast but it did tend to lose the back end a lot. I redid it, mainly because lane tape peeled my paint, and added a bigger wing with about a 35 degree angle. Now, with all other componants being the same, it tends to lose the front end.

At one time I actually had an HO scale wind tunnel and you could see just how the air flowed over the bodies and how it was affecting them. 

yes aerodynamics does play a part in how your car handles. Try this sometime: Take a Porsche 917/10 body and remove the rear wing, run a couple dozen laps (timed of course). Then put the wing back on with a shallow AOA and run a couple dozen more. Then jack the wing to a steeper AOA and run a couple dozen more. Now compare your average times.

The first time I noticed aerodynamics having an effect was years ago running on a friends Tyco Loop track, my Ferrari 512M wouldn't go through the loop without coming away from the track at the top of the loop. Added a 3/8" piece of lexan to the rear spoiler and angled it up. Guess what? it stayed glued to the track all the way through the loop.


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## *MAYHEM* (May 4, 2007)

BTW: Center of Gravity and Roll Center play a good part too. One of the reasons I went to this Stratos body for Mod class is the fact that it's set up for the middle axle position. Since the middle position is higher than SWB or LWB it changes the roll center. More of the weight of the car is now below the axle mounts in the front. It tends to roll less in the corners and therefore keeps all four wheels firmly plated. 

The body also sits pretty low and is bottom weighted and has lexan glass. The top has been thinned so the wieght is mostly down low. Combine the low CG with a high RC and you have a car that actually leans INTO the corners.

I think shaving a little wing off the back will balance the car out and then it will be damned tough to beat.


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## martybauer31 (Jan 27, 2004)

It makes a difference even with the lexan bodies. I can take .2 seconds off a lap total switching from a Plymouth Roadrunner Nascar body to a Porsche 917 body. You would think that something that light would be negligible, but it really does make a big difference.


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## A/FX Nut (May 28, 2004)

cagee said:


> Is aerodynamics important on a slot car. If it is which chassis is it important on?
> 
> Also the lower the body the better the lap time?


Areodynamics is a factor. Take cars with an opening in the front like the A/FX Nomad. Air can flow through and aid in motor cooling.

Some rules don't allow for any openings in the front of the car.

But I've found that the lower the body and center of gravity is best. A/FX Mecury Stocker is a very good handling car for me. So is the A/FX Camaro, but it's a lighter body than the Merc.

I think the lower body thus lowering the center of gravity is going to improve aerodynamics automatically. Randy.


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## SplitPoster (May 16, 2006)

Very interesting thread, neat to know that a lot of the work has been done. Yes, lowering the body automatically decreases frontal area, covering more of the exposed chassis, overall displaces less air. Air moving under the car is turbulent, has to go around pins, shoes, tires and the crown gear. Air moving over and around the car has unimpeded flow aided by smooth body shape and surface.


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## TK Solver (Mar 18, 2004)

This might be a good one for the Mythbusters show. It would keep me watching. I am certain that the center of gravity is an important issue in the corners but I'm having a very hard time believing that a relatively dense object like a slot car with magnetic downforce would be significantly impacted by airflow when traveling 20 mph in a short burst.

On the other hand, we all know that when the wind's blowing in, baseballs have a harder time clearing the fence. And baseballs are relatively dense objects.

Reading Mayhem's examples, it might be difficult to differentiate the impact of the added weight in the rear from the possible increased downforce from air. The angle of attack of the wing would be the crucial experiment. 

I love to learn. I work with lots of engineers. I'll bounce this one off a few of them and report what I hear.


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## 1976Cordoba (Sep 20, 2000)

It is my understanding that the aero bits on 1:1 cars don't actually affect a thing until about 90 mph or so. So, a slot car travelling at 20 mph should be unaffected.

Unless you count it as _scale_ mph, which we know to be anywhere from 500 - 1,000 mph. Then aero efficiency would be crucially important as the cars would be travelling at airplane speeds.

I still think, however, that CG and magnet strength are the real keys to going fast.

OK -- Now my brain hurts too. :freak: 

'doba


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## cagee (Apr 20, 2007)

Everybodies brains hurtin except mine..........and its just breakin wind. I'd say this is a split decision so far on the aero of the cars.


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## A/FX Nut (May 28, 2004)

This is a real good thread. Here is a paragraph from page 58 of Greenberg's Guide To Aurora Slot Cars.

" Aurora's final Ca-Am racers were the RC Cola Porsche 917-10K and Porsche/Audi 510K (1747, 1786). Aurora markerters cut a deal with Sears to produce the super-hot Porsche/Audi. Jim Keeler took the first shot of the 510K to Watkins Glenn and showed it to owner Roger Penske and driver Mark Donahue. Keeler was amused when the conversation turned to whether the slot car's tiny movable rear spoiler was functional. "I wish I had a tape recording of that conversation." Keeler recalled. Interesttingly, Penske's real-life Porsche proved so dominant on the Can-Am circuit that it may have contributed to the series' 1974 demise."

A/FX's Road Racing HandBook also talks of aerodynamics and center of gravity. Shows drawings of a Bre-Datsun 510 Trans-Am compared to a Porche 917-10K. 

Very good thread indeed. Randy.


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## jeremy1082 (Apr 27, 2004)

aerodynamics is important for a slot car just as it is for a real car. I find the '57 Nomad a great car for racing as is the original AFX Corvette (I have the spirit of 76 set).
For some reason they just go faster and the Vette is lesss prone to tipping over in a curve.


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## LeeRoy98 (Jul 8, 2005)

I prefer the 71 Camaro and the 71 Plymouth Roadrunner. Both bodies are among the lightest AFX bodies and I have found both to be superior in handling. 

Gary
AKA LeeRoy98
www.marioncountyraceway.com


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## AfxToo (Aug 29, 2003)

Aerodynamics definitely comes into play with the faster HO slot cars, but it tends to be overshadowed by other influences such as static and dynamic magnetic downforce, center of mass, pin location, wheelbase, and balance. To a certain extent driving style matters as well. Some people like cars setup a little looser, i.e., more prone to tail wagging, than others. I've had cases where I've mounted a larger body and ended up going faster because I was more comfortable with the car's balance with my driving style. But generally speaking, a low slung, wedge shaped body that does not have a lot of rear end overhang is a good racing body. I've also found that body front end overhang, anything forward of the pin, does not detract from the handling at all and may actually help. I always mount my lexan bodies as far forward as I can legally get them (the body has to cover the chassis when viewed from above). This pushes as much body mass as possible forward of the pin and in turn leaves as little body mass as possible hanging off the rear where it hurts you. 

I also like the 917 hardbody because it fits the basic criteria for a good race body. The 512M has that big wing way up high in the back and that detracts from its handling. I cut the wing off one of my old beater 512Ms and it improved the handling a ton. The Charger Daytona body is definately a tail wagger with that wing. The Ferrari 612P is a good handling body, sans wing of course. The JL pullback #94 stock car body is a good stock car body. The AFX 'Vette and Camaro T/A are good handling bodies. The LL 'Vette is pretty good if you can't find a Rokar Datsun body.

On the TJet side the Lola GT works very well, as does the Corvette Grand Sport. The one TJet body that shocks me with its good balance is the old Willys. It really works well with the short wheelbase. Even though it looks top heavy and wags its tail with ease, it seems almost self correcting and I can run one around the track for hours with relative ease. The fact that a Willys was one of the first HO slot cars I ever drove may have something to do with my opinion of it. I also love the way the regular (non sand van) dune buggies handle, again a car I spent many, many hours driving around my first HO track many moons ago. Neither of these two would win a race against a race inspired body, but they are very well behaved.


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## Bill Hall (Jan 6, 2007)

It would be interesting see some comparative data on drag coefficients for HO bodies. Undoutedly at the national level any shaving of lap times is desireable, but for the average home schmoe like me making use of any aerodynamic advantages is really not a consideration.

Funny I always thought the same thing about the topless buggies...not half bad at all. To your list I might add the t-jet Dino and the much maligned 904. Although the 904 has some considerable tail hang compared to the Dino, I've always found it to be very predictable, especially if your allowed to drop the ride height a bit. The Dino is no secret as there's nothing topside and the bulk of it's weight is down under.

Now I'm gonna go way off in left field for some crazy talk, LOL! Take a look at the venerable splitty vette. In a lowered state those slab sides and armoured car doors are like super ll outrigger weights. 

Interestingly if ya take a gander at todays resin fray bodies you'll note that the vast majority are pretty chunky down low and have very little body work above the gear plate. I generally draw an imaginary line at the gear plate and ballpark estimate how much coachwork is above the line relative to how much mass is below.

Now the Willys is an enigma, but if you draw the line just above the fenders you'll find that there's not much chunk on top relative to the amount below and a good bit of it is right over the wheels and wide. Interestingly the Willys seems to handle more friendly/consistently with the stock gasser stance. Should you take the front post down and shift the ballance forward, roll overs at the limit increase and their inherent tendency to slide out and recover is severly dimninished.

This is also my theory on the dune buggy roadster. Although fenderless it has a good chunk of it's total weight between the wheels with the slab sides. Again it is rather wide by comparison and what additional coachwork it does have is wrapped fairly tight to the gear plate.

Same with the AFX 917 bods and the Can Am bods. Fairly "Bertha" in weight, but most of it in the right places. Rather wide with slabsides and although they have a third again as much plastic top side, a fair chunk, say 2/5th's, of that hangs over the hubs. Combined with the fact that a good percentage of the frontal weight is at or below axle center it's little wonder they drive beautifully when properly set up.


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## AfxToo (Aug 29, 2003)

One of the things I absolute love about stock bodied TJets and AFX cars (on stock or hot rod chassis) is just how markedly different each body makes the car handle. I have an ingrained familiarity with many of them. The TJet Dodge Chargers are some of my favorite model cars, but boy are these long and skinny beasts a handful to keep in line. The back the front end don't want to follow the same track on any track with turns. Very twitchy and squirrelly. If I had to describe how the Charger handles my first response would be "take a look at the flippers on a pinball machine, that's what the Charger looks like on the track." There are a few bods that throw me for a loop because they work better than you would think at first glance. Besides what I already mentioned, the TJet GTO convertible is a body that I am very comfortable with at speed. The TJet Vega Pro Stock is a great all around body that would be even better if they cut off the hood hump. Then there's bodies that surprise you the other way. Like the JL Camaro, which handles like a long boat compared to its Aurora Camaro cousin which is a nimble little car. 

Magnet cars have similar differences, but the differences tend to be experienced at the upper end of the velocity curve. With TJets/AFX you know before you are one quarter way through the first turn what kind of hand a body has dealt you. On the magnet car front, limiting it to stock cars, some of the shorter and wider Tyco stock cars like the wonderful #30 Pennzoil Pontiac with full air dam are a joy to drive. The Tyco 908 short nose is way high on my list of favorite bodies, whether on a TycoPro or a 440-X2. 

Fray Jets are an entirely different beast. They have with their own set of unique behaviors. The bodies for these have become a bit of a black art, or maybe just a gray art. Everyone knows that the bodies are manipulated in ways that transform them into what can be described as a somewhat aesthetically pleasing car-shaped handling pan, with the outrageously thick bottoms, thin roofs, crudely integrated lexan windows, etc. At least most groups now put a limit on just how thick the bottom skirt can be. I don't mind the cockroach like stance of these cars at all when they are run as a group, although I don't like seeing the top gears on display and uncovered in the panorama rear windows. 

In fact, it's the differences in the performance and handling of each body that inspires me to buy even more cars. Each new body and chassis style is a unique driving experience. It never gets old.


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## oddrods (Feb 6, 2007)

Interseting observations on the Tjet Charger body. In my group(all 4 of us at the most) the Charger and the Daytona are some of the easiest cars, and fastest to drive! They do hang out all over the track but they are very easy to control in a slide. Seems as if they are more apt to slide out rather than roll over. We don't have a timing system on Bob's track yet so I can't tell if they are faster or slower than other bodies but they "feel" faster than most to me. I have a crude timing system on my door track ( a Zip Zap lap counter) but the times don't translate in the slightest to Bob's much larger track. I also find that a body that I like the looks of, either the body style itself or the paintjob, is easier for me to drive. When we get together to race we all run the same body so it's more a tuning/driving thing than a body advantage.


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## SuperFist (Aug 7, 2005)

For BSRT G3, AFX Turbo & Magnatraction cars.
I like to use the Johnny Lightning Thunderjet pull back car body #_84_.









It's low and real light.

















__________________


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## Dslot (Sep 2, 2007)

*Aerodynamic Test*

Seems it shouldn't be hard to test whether aerodynamics has a significant effect. Create a clip-on body with 50/50 weight distribution front to rear, give it good aerodynamics from one direction, bad from the other. Put it on a track with a good long straight and an accurate timing system, and run a lot of timed laps with the body facing forward and then backward. Compile the best lap times. 

Since aero effects are negligible at low speeds and increase greatly as speed increases, the test track needs to be a high speed circuit or dragstrip. I don't have the track, superfast cars or timer (or driving skill, for that matter) to do the tests, but I can contribute the body design. Here's the layout - anyone can make it from sheet styrene or even heavy card. 

It'd be neat if several people did independent tests and compared results.

Gosh, Mr. Wizard, ain't science fun?
-- D


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## hartracerman (Jan 9, 2005)

Now if we could scale air density to match the cars it would get real interesting


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## NTxSlotCars (May 27, 2008)

*Aerodynamic Engineering*



dlw said:


> Here's a few good XT bodies for racing:
> Chevelle Stocker
> Mitsubishi Eclipse
> Mazda RX7
> ...


It seems to me that a lot of the testing has already been done. It's different because of the Magnet downforce, but didn't the big three battle it out in the sixties for supremecy on the high banks and road corses of America and beyond? Let's take the Magna Traction cars. It seems that you can get one of those to handle about as realistic as a scaled down car can get. From the old AFX stock car bodies, we have ....
*71 Plymouth Road Runner
72 AMC Matador
73 Chevelle
73 Mercury Montego
73 Dodge Charger
74 AMC Matador
77 Monte Carlo
77 Tbird
78 Dodge Magnum*
and from JL/AW we have ....
*75 Ford Gran Torino*
and not so great repros of the afx cars.
All of these bodies are legal in our 70s Magna traction Nascar class.
I run some tests with the same chassis (which isn't exaclty fair because different chassis can work better with different bodies.) The obvious dogs are these, in this order....
*75 Ford Gran Torino* (which actually sits _on top _of the chassis)
*78 Dodge Magnum* (which is why Petty left Chrysler for the second time)
*75 AMC Matador *(which didn't have the funding to compete)
and the not so great repros. I find on my track that the lap counts are down from 3 to 5 laps and lap times are up to 4 seconds slower. The late 70's cars just didn't have aero in mind. On the other hand, the *71 Road Runner *and the *73 Charger *bodies were designed when Chrysler was still in Nascar racing _with both feet_. Just having the wings stripped of thier RR and Chgr, this was the best aero package they could come up with to go head to head with Ford. Scaled down, shouldn't that technology translate? The *72 AMC Mat *is balanced well, but it's just too big and boxy. The *Chevelle* is balanced too, but the tail hanging out so far at speed seems to be a disadvantage. The *Montego* is fast and balanced, but is prone to engine failure. This leaves the Chryslers. There's just something about running a Chrysler product. In the pack, the aero really plays out. The flat nosed *Chevelle* is unstable, as is the *AMC*, both tending to spin out, a loss of downforce on the rear when next to another car. The *Montego* can't keep with the pace. The *Road runner* is great, super stable in a pack, but it's exposed tires are a weakness against other cars. It tends to roll. Ahhhhh, the *Dodge Charger*. It's super stable aero package in a pack shines. The rear of the car is short, the nose is low, and the bulgy sides give it plenty of push when the going gets tough. It's why _Richard Petty _won 280 races in the 70s with this car. I snap the *Dodge Charger *body on, and I pick up 4 tenths of a second before I set my car on the track. I found that if I wax and polish the body real good, I can pick up another tenth. YES, it does translate. I'm sure it does in sport car bodies as well.

Another win for Petty Enterprises:woohoo:








Rich _*43*_

www.myspace.com/northtexasslotcars:thumbsup:


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## NTxSlotCars (May 27, 2008)

Other than that, they all run about the same.


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## jeremy1082 (Apr 27, 2004)

The best body (aerodynamicly) that I have found is the original AFX '57 Nomad. For some reason every chassis that I have put it on has managed to go faster than with no body at all.


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## NTxSlotCars (May 27, 2008)

That's because the front of it looks so mean, the air divides in front of it. Kinda like a school of fish in front of a shark.


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## NTxSlotCars (May 27, 2008)

Any other aerodynamic cars out there?


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