Race car aerodynamic help?
I am after some help, please can you see our website,
www.bennettracing.co.uk I am after some aerodynamic advice on our race car, we simply want to reduce drag and were open to ANY ideas or suggestions. Thanks Luke |
Hi Luke -
For which car? Can you post a link & photo? |
Put light fairings on the roll cage and wing support tubes and any similar bits cutting air. A simple tail of folded cardboard and two wraps of hundred-mile-an-hour tape can cut the drag of those parts to a third. Light, well-shaped fiberglass wraps could be much better still. You might even get to laminar flow in clean air, if the vibration isn't too bad.
A thin metal wrap on those headers could give both streamlining and downforce, especially if the pipe angles are adjusted with that in mind. |
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Well, with how aerodynamically dirty that thing is, you'll need to start from the front and work your way back. Everything will need to be enclosed in a fairing. Avoid any abrupt angle changes. I'd try to tilt the windshield back to reduce the angle there. Once everything in enclosed, add a boat tail to the end. Tuft testing is really going to be your friend on this one.
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Got that book just reading through it now.
Really after things we can add without hugely changing the look of the car. But to help it through the air a little better. The rear wing struts we are going to change to the aero tubing which is basically tear drop shaped rather than round. I was thinking of making an undertray for the front section too |
race car
Luke,is it the AA Fuel Altered that you want help on? Your all-up weight would be useful ( wet ).Are you at full lock-up with the clutch at the timing light? Is there any horsepower to spare? Is the body of the car already carbon-fiber epoxy? Does the rule-book allow any enclosure of the body/chassis for that class? Are the wrinkle-walls slipping presently at speed ( roof-top negative-lift airfoil )? Can the driver see around the engine/blower/bug-catcher at present time? Do you have your front/rear axle weight bias ? Do you have a sense of the car's dynamic weight distribution at upper speed. Do you have a time/velocity table so we can see your residence time through a velocity regime? Can you show us where the center-of-gravity of the car is. Have you ever put a model of it in a windtunnel to determine it's aerodynamic center-of-pressure. Does the car do a wheel-stand,with chassis-flecture at launch? If so,at what distance and velocity does the front wheels touch down? Do the small outboard winglets at the front axle keep the wheels firmly planted near top-speed? Can you say how much the cabin raises as the drag slicks grow to full sidewall height? Is the length of the car at it's maximum or could it be any longer? Can the wheelie-bars be enclosed? These are some considerations one would need to appraise where you presently are,and potentially where you could get to.We don't have to tell you how dynamic a dragster is,from launch to the finish line,and your driver's safety is paramount.If your going to "experiment" with the "real thing" you sure want to be safe about it.
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Thats a few questions ! I will try to answer them the best I can. is it the AA Fuel Altered that you want help on? Yes the black Relentless fuel altered Your all-up weight would be useful ( wet ) 2200lbs race ready with driver Are you at full lock-up with the clutch at the timing light? Do you mean top end finish line? Or the start line? Is there any horsepower to spare? How do you mean? Is the body of the car already carbon-fiber epoxy? No fibreglass but its fairly lightweight, we were concious of this when we made it. Does the rule-book allow any enclosure of the body/chassis for that class? Pretty much do what we want...thinking an undertray? Are the wrinkle-walls slipping presently at speed ( roof-top negative-lift airfoil )? Don'y get this one...sorry Can the driver see around the engine/blower/bug-catcher at present time? Yeah has about an inch over the injector Do you have your front/rear axle weight bias ? It is around 800lbs over front and 1400lbs rear end Do you have a sense of the car's dynamic weight distribution at upper speed? None Do you have a time/velocity table so we can see your residence time through a velocity regime? Not sure what you mean... Can you show us where the center-of-gravity of the car is? Not sure how can I find out? Have you ever put a model of it in a windtunnel to determine it's aerodynamic center-of-pressure? I am currently trying to get it sorted, have someone ready to put a model in there but need a CAD drawing done first. Does the car do a wheel-stand,with chassis-flecture at launch? Yes, chassis must flex to enable it to put the power down If so,at what distance and velocity does the front wheels touch down? Front wheels come down at around 60 feet out or about 100mph Do the small outboard winglets at the front axle keep the wheels firmly planted near top-speed? So far yes, we have only tested the car so far but at 160mph the car was very stable. Can you say how much the cabin raises as the drag slicks grow to full sidewall height? The tyres grow about 8-10 inches in total Is the length of the car at it's maximum or could it be any longer? We are restricted by wheelbase (centre of wheels) which is 125 inches. Everything else we can do what we want. Can the wheelie-bars be enclosed? Yeah I agree safety is paramount its my dad in the car so I'd like it right. Even if there are some little things I can do/make it might be the difference between a 6.200 and a 6.1999 Thanks again all appreciate your time. Luke |
I am watching this with interest as I feel that aerodynamic changes can give you the improvement in times you are looking for in a field where everyone just tries to increase horsepower.
My only question is, would an undertray be safe on a vehicle that already does wheelies? That aspect seems to present a problem IMO. - more surface area to cause drag while in the wheelie, which will strain those wheelie bars even more, thus actually slowing you down. But I will other those that know break that down better. BTW, without altering the wheelbase can you change the shape of the cab. Imagine a dragster with a boat tail ... |
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While a 12 inch wheelie looks good, going up means your not going forward... An inch is plenty...but the point it def to do a small wheelie as it transfers ALL the cars weight over the rear slicks which aids in traction. As for the boat tail, could you post a simple drawing please? We made the body and added the arches and also the part for the parachutes to go onto, as any lower its just dead air. We can make and fabricate anything so any ideas are very welcome. Thanks |
Why not cover the engines with fairings?
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I get you, see what you mean but that would mean a totally new body, we need to really keep the overall look of the car really. Hope that makes sense. We could enclose the whole car but then its not a fuel altered, it near enough becomes a funny car. Thanks |
Luke,
Your 2007 body had a engine cowling...can you reuse it, or make a similar? I would also suggest making the front wing wider if it is allowed in the rules, to put the front wheels in the wind shadow of the wing. Also, some fender flares in the back to smooth the flow around the rear wheels. You'll have to check the rules there for "open wheel". Solid Moon disks instead of mag wheels also might help a bit. Since you are concerned about the look as well as drag, starting at the back instead of the front might be a better approach. Is your rear wing actually doing you any good? You might be able to get rid of it altogether and get the same effect by moving the engine a few cm forward on the chassis. We would need to see some pictures of the rear-end. If the air stream is creating a vortex "trailer" you are pulling down the track, putting a boattail with a sharp edge on it could help to reduce the size, or allow for better separation of the flow off the rear. I think the other guys are requesting dynamic data to try and understand where in the run the aero loads are hurting you. For example, static wind tunnel testing might suggest increasing the angle of the front wing. But if you do this, it won't hurt your performance at the start, but once the front wheels come down, it might put your blower in the wind shadow, and rob your horsepower in the last half of the run. Darren |
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We can make similar but would look odd with the front end body work? Front wing wider was an idea I thought but I don’t understand aerodynamics enough yet, I thought an inch wider than the wheels? Rules wise, backs can be enclosed fronts cant Rear wing def def works, when we started to get upto 180mph+ in 1995 the car was getting out of control so the wing was added and now drives perfectly but I do want to change the tubing for aero tubing later this year Seen photos of a boat tail, how could we add this to the car ? Totally understand that, the only part that needs to be in clean aie is the injector (3 holes at top of motor) Thanks all il post some photos of rear end asap |
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A few musings,
What deploys the parachute? What conditions are acceptable for its deployment airflow wise? Could the front wings be extended vertically in a narrow strip to shade the front tyres from air flow? Both up and down. Would there be any advantage in making the nose more like a cowcatcher -to move air to the sides and higher to cover more of the block. When the rear tyres grow - do they still stick out of the body? |
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2 levers deploy them seperately, or both together (depends on speed) On our 2007 body shown on the site, we kept having the chutes fall right onto the wheelie bars, we solved it by simply moving the chute mount up only 1 inch and sorted it. must have been in dead air... Not sure what you mean airflow wise? As long as they work we can try anything, its got to be safe. The front wings? you say a narrow strip? can you explain please? We have played with the idea of making the front bodywork come further back nearer to the engine to 'hide' more of it from airflow They grow a fair bit, here is a photo of the car during burnout to give an idea as they grow about the same amount. http://i40.tinypic.com/or4c5x.jpg |
Relentless
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Phil, Sorry for delay in replying…thanks for the post, made good reading! One thing regarding our clutch, it does not use timers or anything, it’s a 2 plate pedal clutch from Crower. Due to the nature of the fuel and the blower we use, it will pull hard till about the 1/8th the the rest is down to taking fuel away to keep the AFR good I mean it still pulls but not a strongly. To give an idea, it will do 175+mph at the 1/8th but will only gain another 40ish mph to the finish line. (1) I have thought about adding a slim wing to the front of the car, infront of the bodywork to smooth the whole front, (2) What about making some angles pieces that sit to help with the bulkhead? (3) I think for now with this body we will have to make the best of it…. (4) Good point, how can we help this? (5) We need a wing tunnel I think (6) We will definetly be making the wing struts from areo tube this year I hope. (7) Would a canard style wing in front of the rear slicks help this??? (8) I remember the wing, everyone laughed till he went 260mph! Thanks for the info I will try these and try to get the car in there. Also thanks for the post, appreciate it Luke |
Forgive my bit of drag racing ignorance specific to classes/rules etc, but I did notice you were working on your wheelie bars to keep your wheelstands under control and that doesn't seem like something that would be as beneficial as other courses of action.
I used to work with a guy who was deeply involved in drag racing a similar class in southern California back in the 60s and he was heavily into the unintuitive tricks to tune the cars. He did a lot of work on rear suspension and engine placement optimization as well as clutch slippage and blower speed modification. They were running mechanical FI at the time and stopped rejetting fuel for the conditions and started changing blower speed to achieve AFR with a fixed fuel flow to improve consistency. If you have AFR problems try adding more blower rather than pulling out fuel. This will mean you're always putting out about the same horsepower and will reduce the variability of your suspension/clutch setups. You're better off setting up your rear suspension so that the instant center is vertically higher as this would improve squat resistance, changing the force transfer from chassis to tire to plant the wheel more so than rotate the chassis. Ideally the car will accelerate without changing attitude, but if your move your rear instant center too high your rear end will lift up and the front will dive which is about as bad as doing wheelstands. Another option is to dial in more clutch slippage off the line to keep your front end down. If you're bogging in the last 1/8 you might need more clutch slippage there, or your geared for a higher trap speed than you're currently achieving. Maybe this won't be an issue if you can solve the problem that's forcing you to pull out fuel past the 1/8 mark. Another thing that may help is varying your valve clearance. If you're getting tire spin at launch you can run a step or two tighter valve clearance which will increase valve overlap and lift (reducing low-RPM torque and improving high-RPM power). The opposite is also true; launch bog can be helped by running a step or two looser valve clearance to improve low RPM torque at the expense of high rpm power by loss of lift and loss of overlap. |
MechEngVT,
Thanks for the reply, we still run mechanical FI but this cars has no suspension. We have to slip the clutch to a degree but this car is 2500 horsepower + so it harder to control. The reason for pulling fuel is due to the design of a roots type blower. Its an ineffeciant blower in its design (made better now as we use a hi helix, which means it has a 120 degree rotor twist) But in essence the faster you spin these blowers the faster they become ineffiecent on the track and will then actually heat the air. We spin ours fairly slowly, 1/8th marker was just to give an idea, this car is an animal and will pull hard probably until the 1000foot marker but we have yet to do a full pass with this combo. Initial testing though is so promising, we did a soft half pass and it still ran a 7.60 at 133mph |
From looking at the pictures, I think you could blend the body lines of the gas tank back to the tub with the body material of your choice. Obviously leaving a hole for the motor & what ever accessories need cooling.
Rear fender flairs. You could move the front edge of the flairs forward allowing you to reduce the abrupt angle of the flair. I think moon covers are out of the question, but if you make your outer beadlock ring "full disk" as possible (current F1 cars as an example) it should help aerodynamically. if you have the resources you could screw on a carbon fibre plate to the beadlock ring to reduce rotating mass. Don |
just got your post
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Air/Fuel Ratio
Luke,I've been thinking about the richening problem on the race car and wanted to toss out the following.---------------------- I found four articles from HOT ROD Magazine dealing with mixture issues which went in a direction I would not have thought.------------------ The racers were experiencing water pump cavitation which led to uneven combustion chamber temperatures,which played hell with mixtures.--------------- Their solution was to use old-tech cast-iron impellers,with more efficient hydrodynamic vanes instead of stamped-steel impellers.----------- Sometimes they used smaller diameter pumps to reduce angular velocities at the vane tips,and lastly,they might under-drive the pump a bit to keep speeds below what would cause cavitation.------------------- The modern electrically-driven pumps may do away with these issues,don't know.----------------------------------------------------------------- The other thing I noticed is that the flat-faced driven pulley of the blower,and brackets behind it,near the bug-catcher,look like they could actually interfere with airflow into the throttles,and lastly,the throttles on some bug-catchers have virtually no radii at all ahead of the openings,just a sharp-edged corner.----------------------------------------- All elementary fluid dynamics textbooks would say this was a no-no,and lead to what they call a "vena-contrata" entry loss,where the air cannot flow anywhere near the walls of the opening due to flow separation at the inlet,effectively squeezing down the flow at a point where you need it the most.--------------------- If you have this,not only will you have an immediate flow restriction,you also raise the power necessary to impel the air into the blower which will add heat to the compressor,expanding the charge,and requiring a leaning of the fuel supply to maintain stoiciometrics.------------------------------------------------------- I can't tell as much as I'd like from the photos of the car and your hardware may be better evolved than others,but if the problem with the mixture persists you might consider a second look there at the inlet.Best to you,Phil.
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Back from our first event of the year, and good news is that we won.
Also we can a new personal best, a 6.6352 but most importantly at only 181mph This would of been a low 6.5 or high 6.4 but as this was only our 2nd run and were still testing, came off of it early and still ran the 6.63 We have also added a gurney flap to the rear wing and also to the rear wing spill plates too. Another addition is some 1" angle alloy to the sides of the body to get it lower to the ground and added strength Any more tips and hints please help us go faster! Thanks |
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Thanks! we were very happy.
Well the injector that we run was designed and built by us, we took an 80's designed injector and brought it right upto date, it is working extremely well so far, few bits we have tried inside which will help power too. |
Bit of an update.
We won our 2nd meeting of the year and have now also ran another PB of 6.4261 at 191mph We were getting to approx 195mph and the rear slicks were rubbing on the inner arch so we need to raise the body up some more. I have bought a nice wing that I intend to add to the very front of the car at a shallow angle to help the whole front end to be more efficient. But we will still keep the canards on there too. So that the smaller narrow wing helps to get the air over them. Also stability of the car has always been very good and has not changed since we changed the body from the 2007 design. Any more suggestions are very welcome. Thanks :thumbup: Luke |
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