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Aerodynamics in off road racing

Suhaib Kiani

Well-Known Member
#21
I realize that the type of course and car would determine a lot of stuff, but feel that even if one is not doing 100mph better/smoother airflow (particularly over the top end) would keep things calmer and give less of a feeling of total chaos all the time. Have looked carefully at desert racing aero stuff on the net including vintage style wings of the past, but saw none of that stuff in today's trucks and buggies and got the impression that aero was probably deemed less important for some reason.....

And since there are no pics on this thread I thought that the newbie should stick his neck out :) Essentially wanted to do more, but got such great encouragement from everyone around that decided to leave it alone after this:


Do believe that aero doth play a role in keeping the Mitsubishi Pajero Evolution planted at speeds above 80mph:


Anyways, thanks for the great thread and discussion, look forward to more! BTW I do believe that there is the traditional taped threads alternative method of doing it without the wind tunnel (some articles on the net on that). Obviously not as good, but probably better than blowing smoke with an air blower/pump on the face of the car (which is what we were doing at some stage, ssssshhhh :))
 

mike mcqueen

Well-Known Member
#22
Right again rocket man At the caltech wind tunnel I learned that a 4"x4" with a rounded front will promote laminar air flow on the lee side up to 15 degrees before seperation. And the extended lip like I said. I was just on the 110 and saw a tractor trailer with air evacuation dams under the trailer. Due to spring trvel on a TT it would be hard to get it to work. For a stable trailer im sure it works fine. By the way we have glass splitters for the front of 7200 & 6 trucks.
 

DanMcMillin

Crane Motorsports
#23
Didn't RG claim his Hummer to do 150+ on the lake bed at the 500 and 1000 because of the aero of a closed cab and his gearing? Anyone know if he really did? That would be insane to see on video!

I know Andy and Scott went back East and did some wind tunnel stuff on their old RG truck, but I am not sure what the accomplished exactly. The only thing I can think of is you see a lot of Trophy Trucks today with that piece hanging below the front bumper, usually black... (Can't think of the exact term at the moment), to keep the hood and front end lifting at high speeds.

Worrying about aero is, in my honest opinion, the least of your worries in a Baja 1000 or Baja 500. I mean you can only do 60 mph on the hwys, so 100+ there is long gone, and where do you really go that fast for aero to make a huge impact? A 10-15 mile dry lake bed on a 250, 500, 1000 mile race? Maybe leaving Bay of LA to San Ignacio on some of those roads, MAYBE? This isn't the Indy 500 where it's 500 miles of 200+ mph and it makes ALL THE DIFFERENCE. Taking care of your tires and drivetrain are, to me, the more important things to worry about, from a TT perspective. Class 1 would be tires as well, and the transmission and CV/Axles. I think it's always interesting to see and hear about how or what aero factors are being used in off-road racing, but to me, I don't know, it's doesn't really make a lot of sense.

Just my opinions on the topic of aero. Did you guys hear about Sam Berri and Brandon Aurther?
 

dirtdudeaz

Well-Known Member
#24
it seems like the course would be the factor as to how much aero would make a huge difference..on tight, technical, difficult courses, aero would be less of an advantage than the longer more wide open courses. kind of like bristol vs. daytona.....armin swartz [sp] runs a rear spoiler on his bmw tt and i don't know how much of an advantage he's attained. but i'm still having problems trying to figure out why the dimples on a golf ball make it go further than a smooth ball in tests so what do i know?
Simply put....the dimples cause the air flow to stick to the ball longer which reduces the drag. The dimples also create lift and allow the ball to be controlled in direction by the spin. If you want the long version I think they have some good websites with pictures that get into some depth on the principals of laminar/turbulent flows/seperation/drag/etc...


when i asked an aero guy here at work what would make our truck better(class 7 unlimited) he said front spoiler with a splitter min 1/2 extending forward of the spoiler, move all the coolers so air can flow through the cab, add a splitter to the bottom front edge of the roof (see above size),and tear drop any tube that is in the air flow....a brick has better aero properies than a round tube/cylinder ......
The teardrop shape to tubes yes...bricks being more aerodynamic than a tube, I don't think so.... A brick would be over 1.0 Cd (I've heard close to 2.0) and a tube (depending on Re) at max is around 0.5. Now, as the brick cross-section decreases and it becomes a flat plate (parallel with the air flow) the drag would be less than a tube, but that wouldn't be a brick anymore. Also as mentioned, if you round the front...but then this is also not a brick... If this weren't true, the shuttle/airplanes/salt-drag bodies would not be cylindrical. (This doesn't apply to Spaceballs flying the motorhome of course \m/)


This is a good thread! I have often wondered myself where the sport could be with a more aerodynamic outlook on vehicle design. The problem as someone mentioned was how much useful application will you get compared to the money you spend. Engineers/R&D don't come cheap. Of course if you can save gas/time/etc...maybe it would add up. It would be neat to be able to control the amount of lift on a car and be able to change it on the fly for terrain changes.

If anyone would like to hire me as their aerodynamicist consultant please feel free to PM me!! But seriously, when I get a vehicle of my own, or a trusting friend...., I have a couple designs catia drawings I messed with when I was in school. Maybe one of the TT guys will let me slap some wings on their truck so they can literally fly over whoops...
 

bajaxp

Baja Bobsled Team
#25
'Did you guys hear about Sam Berri and Brandon Aurther?'

^^^jajaja...yes, I did! BTW everyone needs to quit picking on Pete and yes you need a passport in Mexico!

Back on the subject of off road Aero. I wonder how much more fuel efficient a more slippery car would be. Fewer pit stops, in theory would be faster. Right?
 

down4glamis

Well-Known Member
#26
with a clip on or off on my 7200/1450 was close to 10mph! adding the light bar on slowed me down almost 15mph total! if thinking aero and planning accordingly can help a stupid truck go from 70 to 85 like it was nothing would sure change a bunch of peoples minds!

i would love to add the front lip to my truck and see how it goes. who needs wind tunnel testing?!?! our plan was to bring some of the 3/8" abs out to a lake bed and start making runs. simple runs on a fire road and then on evan hughes proved the point of the clip/light rack.

you guys talk about 120+ being critical, but if your 12 car tops out at 100 but cant reach it not because of gearing but because of the motor/wind factor, maybe taking a weekend/day to start blocking off sections of the cab/bumper/sides.
 

randy68

Well-Known Member
#27
Simply put....the dimples cause the air flow to stick to the ball longer which reduces the drag. The dimples also create lift and allow the ball to be controlled in direction by the spin. If you want the long version I think they have some good websites with pictures that get into some depth on the principals of laminar/turbulent flows/seperation/drag/etc...




The teardrop shape to tubes yes...bricks being more aerodynamic than a tube, I don't think so.... A brick would be over 1.0 Cd (I've heard close to 2.0) and a tube (depending on Re) at max is around 0.5. Now, as the brick cross-section decreases and it becomes a flat plate (parallel with the air flow) the drag would be less than a tube, but that wouldn't be a brick anymore. Also as mentioned, if you round the front...but then this is also not a brick... If this weren't true, the shuttle/airplanes/salt-drag bodies would not be cylindrical. (This doesn't apply to Spaceballs flying the motorhome of course \m/)


This is a good thread! I have often wondered myself where the sport could be with a more aerodynamic outlook on vehicle design. The problem as someone mentioned was how much useful application will you get compared to the money you spend. Engineers/R&D don't come cheap. Of course if you can save gas/time/etc...maybe it would add up. It would be neat to be able to control the amount of lift on a car and be able to change it on the fly for terrain changes.

If anyone would like to hire me as their aerodynamicist consultant please feel free to PM me!! But seriously, when I get a vehicle of my own, or a trusting friend...., I have a couple designs catia drawings I messed with when I was in school. Maybe one of the TT guys will let me slap some wings on their truck so they can literally fly over whoops...
Great thread!


(Just FYI, and useless in this thread, but, interesting, a 1.0" dia. X 12" rod
below a 50' racing sailboat has more drag than the ENTIRE wetted surface
of the hull.)
 

y2kbaja

Well-Known Member
#28
Maybe we're not talking getting over 150mph, maybe we need to push 7200 trucks above 85. At the VORRA USA500 last weekend we had a 10+ mile long straight accross a valley, down the slope we could reach 83mph, starting up the other side I had to downshift from 5th and couldn't pull 74mph. Light bar above windshield, lower valance. Other trucks in our class were pulling 110mph. We lost 1st oa by 6 minutes.
 

down4glamis

Well-Known Member
#30
what i learned from some of the guys i talked to about the wind tunnel was 2 things

one was the pressure and pockets, the other was cooling. low pressure areas build up and deflect a high pressure force and start making a ton of "disruption". the smoother you could get the air to flow into and out of the vehicle the faster it could "cut" through the air. the other thing on that was cooling, seeing that the air rolls up the hood and hits the cab and stops, it forms a pocket in there and air does not flow through it as fast as the vehicle is traveling. with radiators in the back window it creates a huge pocket, doesnt allow air flow, and doesnt make for a smooth air flow through the vehicle, or through the radiator. there are a ton of ways to work around it, but those were the things i heard Robby and Andy both learned from the wind tunnel (besides what was posted about a sealed cab/windshield/ or the front lip)
 

Nessy

Well-Known Member
#31
it seems like the course would be the factor as to how much aero would make a huge difference..on tight, technical, difficult courses, aero would be less of an advantage than the longer more wide open courses. kind of like bristol vs. daytona.....armin swartz [sp] runs a rear spoiler on his bmw tt and i don't know how much of an advantage he's attained. but i'm still having problems trying to figure out why the dimples on a golf ball make it go further than a smooth ball in tests so what do i know?
On Mythbusters they took a Taurus and put clay all over it and shaped it like dimples on a golf ball and got better gas mileage even though the car weighed an extra 1000lbs or so.
 

200MPHTape

Well-Known Member
#32
Heard the same story from Robbie Goerke from Collins. Robby Gordon has also done wind tunnel testing and you can see the added material behind the "cow catcher" down to the bottom of the front skid plate, i believe BJ has the same sort of design. Light bars up top are almost like a mini parachute but with the Rigid/Vision X type lights being used now it helps.
Rumor was when Challenger IV was first built did a 150mph on the asphalt at the Mexico races (Per Danny Thompson and John House the builder) but was VERY squirrely and scared the hell out of Mickey Thompson. They kept playing with the narrow wing on top of the car then finally took off the back of the narrow part and put on a "top fuel" type wing and that seemed to calm it down. Talking with Bob Gordon and Parnelli about wings, they said they worked great but you constantly had to adjust them (electric actuator) for the terrain or it would upset the vehicle. Not sure what a wing would look like on a TT but 'd love to see some on a couple class 1 cars.......
I think he had a front wing on it at one time, that might be those TI parts you where trying to figure out.

On Mythbusters they took a Taurus and put clay all over it and shaped it like dimples on a golf ball and got better gas mileage even though the car weighed an extra 1000lbs or so.
It did not get better mileage then without the clay, remember they added the clay,test, dimple the clay and put the cut outs in the back seat so there was no weight diff. with the clay, and with dimples it did get better mileage.

This is a great subject, I will add that the more closed up, the better the aero, who will be the first TT to add a windshield for the extra MPH? RG's hummer don't count. I will dig thru some old fotos of winged cars.

Back in the days lots of cars had wings, think it just turned into some thing else to worry about.
 

HDRA1

The Godfather
#33
We have been workinng on Billy Worthing's New class 1 car light weight and small openings we even Frenched in the rigid lights into the top visor just to reduce some of the drag
 

Ol' Curmudgeon

RDC's resident crackpot
#34
On Mythbusters they took a Taurus and put clay all over it and shaped it like dimples on a golf ball and got better gas mileage even though the car weighed an extra 1000lbs or so.
Maybe hail-damaged vehicles should command a premium.
 

green787

Well-Known Member
#35
On Mythbusters they took a Taurus and put clay all over it and shaped it like dimples on a golf ball and got better gas mileage even though the car weighed an extra 1000lbs or so.
That's because the little dimples catch pockets of air.... Air glides over air better than air glides over vinyl....
 

ScottyA

Well-Known Member
#36
Probably more advantage for the small horsepower classes. Formula Fords made huge gains with aero back in the 80's. A car called Swift came out and basically made it a spec class. On the pavement the back of the car is more important than the front. You put the air back together to reduce drag. Kinda hard on an off road car with spares and lights etc.. But not impossible! If I have a 10 or 16 car I would put some effort into aero for sure. If you have a 1 or TT just buy more horsepower.. Just kidding! I'm sure it's a balancing act between aero and downforce in unlimited classes. You have to factor many variables like suspension, ease of spare removal, lights ect. Great thread... Anybody seen Dan Mc wearing a dress lately. JK again, back to the aero talk.
 
#37
There is more of a focus on air flow to the engine, coolers, and shocks than aerodynamics. If people put winsheilds in their cars the air would move over them easyer than without.
 

Zambo

Well-Known Member
#38
The problem with desert racing as compared to almost any other form is the variety of speeds that the cars go. When you're slogging thru the silt, up some gnarly rutted out hill climb or whatever, you're going slow AND you need a ton of cooling. That means big exposed radiators with scoops etc. These things act like a big drag chute at high speed. Plus, nobody else runs that much light, another huge source of drag.

Maybe some sort of adjustable scoop behind the cab of a truck that raises up to grab more air at low speed, but lowers down at high speed would help. Stuff like that.
 

CRAIG_HALL

Well-Known Member
#39
Lots can be learned about aero, cooler ducting, high & low pressure areas from some simple reading in many of the a ails or race car books. Testing the known theories is difficult as testing is needed. Wind tunnels are ideal but costly. Tell tales taped all over a body with multiple cameras would be very useful.
 

MCM MOTORSPORTS

Well-Known Member
#40
We used to see over 220 kph in one of the earlier jimco a arm cars over here is OZ (clocked on a speed camera on a graded road). However i find our tracks are more flatter with less large holes. So we were able to lower the car right down for more stability at higher speeds. Plus it was a light car with a turbo 4 putting out 500 at the wheels.
 
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