Quote:
Originally Posted by Bennett_Racing
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
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Luke,apology for late response and thanks for the data.Since many dragsters have so much power that they might go through 32-partial clutch engagements before actually reaching lock-up close to the finish line,to avoid wheelspin.----------- If that were the case for your car,then,perhaps you might have some power available for some additional mass,in the form of aero add-ons.------------------- Or,with substitution of carbon-fiber epoxy,you could add structure and simultaneously LOSE weight.------ If your clutch is fully engaged by the finish line,and you are not experiencing wheelspin,is the car still accelerating strongly? or is the power and gearing playing out?---------------------- With respect to the time/speed curve,some drag racers believe that they're at speed so briefly,that power-to-weight is the most important parameter and to hell with aerodynamics.-------------------------------------- I have very little data regarding dragsters and what I have is from the work of Don and Gerald Arivett who were developing a low-drag AA Fuel Dragster,fully-enclosed,with Cd0.20 ( Cd 0.18 @ 12-degrees yaw ).This was 1987,and at that time,no complete windtunnel tests had ever been performed on a dragster.--------------------------- They looked at Indy cars,since they were also open-chassis,so to speak,and the best of those cars had Cd 0.69,and they believed the best funnycar had Cd 0.60.---------------- The Arivett Bros. believed that their car,in 250-mph territory,would free up over one thousand horsepower.------------------------- So it looks like drag reduction does pay.--------------------------------------- Looking at Relentless,my thought is that (1) the integral nose/wing combination lowers the efficiency of the wing.My intuition tells me that a smaller front wing,moved forward,would provide as much downforce with less drag penalty,operating in "cleaner air". (2) The abrupt chopping-off at the back of the nose section is accompanied with complete flow separation and turbulent wake trailing back to the engine.(3) The engine itself poses a "torture-chamber" to the air,both in it's leading aspect and flow separation behind it.(4) The firewall of the altered's body is so sharp-edged,along with the windscreen frame,that I'm fairly confident that you've got complete flow separation at that point,with little recovery if any,which may be why you had to raise the drag chutes up so their droque-chutes could catch some "clean" air.(5) The rear fenders are sharp-edged enough that flow is torn up there,although it may not be a problem due to the separated flow ahead of them.(6) As mentioned by others,the tubing and padding for the roll-cage could be streamlined like aero struts on aircraft,along with the support structure for the rear wing.(7) The Goodyears,as exposed wheels,have been windtunnel-tested and themselves have a drag coefficient of 0.57.------------------------------------------- If any of these areas can be faired in,or enclosed without violating class restrictions,especially the rear wheels I think it would pay you dividends.The entire wheelie bar,if enclosed like a boat-tail,tapering to 50% of the cross-sectional area of the body ( like drag-bikes )with some fairings in front of the wrinkle-walls would dramatically reduce drag,but also might violate rulebook.(8) My final thought for now,is the rear wing.And you may have fully investigated this already but back in the 1980s,Joe Amato ran an Eldon Rasmussen "high-wing" spoiler which is credited for Joe's victory and 260+ mph runs.The wing was small,placed very high,and behind the car,operating in very clean air,with max downforce,minimum drag,and more "leverage".If Relentless is stable now,your starting from a good place.------------------------------ If you can get that windtunnel model going you could do a lot of "safe" shakedown runs without risk to your dad.I don't know if you'd have access to the MIRA facility.There is a Donald Campbell tunnel at London's Imperial College and at Southampton.Williams Grand Prix Engineering has it's own tunnel.If these can't help,perhaps another university with Mechanical Engineering Dept.and windtunnel might take your car on as a undergraduate or graduate project if you threw a few hundred Pounds their way.Keep us posted,and we'll keep thinking about Relentless.Race safe,Phil.