Aerodynamics

[Kev]

Yeah, Mark! This is what I want to talk about! I was starting to think that people like Splinter or Alan Simms had bolted wings on their cars just to appease the Halford's Sponsorship!

[Anonymous]

When my mates pro mod rear wing collapsed just before crossing the 1/4 line at 200mph, it was the loss of the wing which caused loss of down force & major contributor to cause the car to roll & total the car, so think he may disagree

Without knowing what the wing design looked like I couldn't possibly comment, but I am willing to bet the significant factor in the crash was not the loss of a wing but the sudden change in handling characteristics when it fell off. Of course if any part of it was still clinging to the car then that would precipitate another aerodynamic force which would create a shift in handling beyond the controllable realms.

If he needed a wing to stay on the floor at 200 mph then there was something fundamentally wrong with the design of the car that it was actually creating lift at such a low speed.

Some car desgins do create lift, and it's generally ones that were developed before a good understanding of aerodynamics was held. For me it is a much better solution to solve the lift issues rather than bolting on attachments to counteract that force.

There seems to be a commonly held view that you should block any airflow under the car, then when air inevitably gets under the car, it flips! Why not design the underside of the car so that it aids the aerodynamics? If you want downforce why not use a diffuser instead of a wing? That way you can keep the top surfaces clean for attached flow.

[Dave-R]

Keep the centre of mass of the car IN FRONT of the centre of aerodynamic pressure.

yep. Another reason for trying to reduce the amount of lift at the front of my car. The center of gravity moves towards the back so far that it actually gains 75lbs at the rear. But there is only a little you can do without spoiling the look of a classic like ours.

A flush grille on the Challenger would help loads. Even if it was just a fine wire mesh as high speed air would see it as being almost solid and deflect away from under the leading edge of the Challenger hood. Yet it would allow enough air through to cool the radiator.
But it would look like Bananarama!.

[mopar_mark]

Without out question the car was destabled due to the loss of the wing. I agree with you that this caused a complete change in its handling charecterstics, the lack of down force caused the rear of the car to unload.

The video clip below demonstrates this very well

If he needed a wing to stay on the floor at 200 mph then there was something fundamentally wrong with the design of the car that it was actually creating lift at such a low speed.

As for something fundamentally wrong with the design of the car, well lets say even the best of the engineers/R&D can get this wrong, you must remember the case of the flying Merceds at Le Mans

[Anonymous]

I am currently working on something to evaluate the blockage ratio of radiators. we use mesh or drilled plates to replicate radiator blockage in the wind tunnel models.

Are you certain that shift in mass is from the aero alone? Did you use a data logger to get that figure? Obivously under hard acceleration at the beginning of the run you would see a significant shift in mass rearwards, this will tend to settle out as the run progresses.

Stopping the airflow through the engine bay is probably not the answer, encouraging it to exit through hood vents or similar rather than going under the car would reduce lift. That way it might also aid in keeping attached flow along the windsheid. If you were to block the grille you would only want to do it as a temporary attachement at the track to aid aero during a run, then take it off to drive home.

[Anonymous]

As for something fundamentally wrong with the design of the car, well lets say even the best of the engineers/R&D can get this wrong, you must remember the case of the flying Merceds at Le Mans

Of course I remember that. And engineers the world over learn from the mistakes made in the design of that car. So do you think that if the Mercedes engineers managed to miss a major floor in their design that drag racers in UK are somehow doing it better?

If you have a resonant frequency in the front of a car the way that Merc was bouncing around and you are coupling that with a significant use in undertray diffuser downforce, there is only going to be one outcome when the two finally catch up with each other. Donald Cambell fell to the same scenario.

Now I know that UK drag racers don't have the budgets to spend on rolling road scale wind tunnel models or CFD analysis. But I have never seen techniques like ink dotting or teathers used on a UK drag car and rarly seen data logging to asses forces.

There are inexpensive techniques out there that help engineers to understand what is happening in a car. sadly the general mindset amongst the UK drag racing fraternity (and other racing fraternities as well) isn't very receptive to actually thinking about what is happening. 'Just bolt on another part that Summit says works, that'll fix it'.

[mopar_mark]

So do you think that if the Mercedes engineers managed to miss a major floor in their design that drag racers in UK are somehow doing it better?

Exactly my point

If you have a resonant frequency in the front of a car the way that Merc was bouncing around and you are coupling that with a significant use in undertray diffuser downforce, there is only going to be one outcome when the two finally catch up with each other. Donald Cambell fell to the same scenario.

I completely agree with you

Now I know that UK drag racers don't have the budgets to spend on rolling road scale wind tunnel models or CFD analysis. But I have never seen techniques like ink dotting or teathers used on a UK drag car and rarly seen data logging to asses forces.

Definitely some chassis builders are using CFD analysis, but to what extent I could not say. Without question, this is a big area of growth for drag racing in general

There are inexpensive techniques out there that help engineers to understand what is happening in a car. sadly the general mindset amongst the UK drag racing fraternity (and other racing fraternities as well) isn't very receptive to actually thinking about what is happening. 'Just bolt on another part that Summit says works, that'll fix it'.

This may be true, but it takes time to change mindsets. A lot of people copy other car combination without understanding the reasons for the change, I'm sure we all have been guilty of this at some point.

When people see the & understand the benefits of aerodynamics this will eventually change.

People will always be scepticle about spending money & time if they are not sure what they will get in return, so opt to spend cash in other areas, such as places you mentioned likeSummit

[Kev]

Think I'll just gun it through the traps and see how it feels, as this techno babble ain't helping me cause...........Started a reasonable debate though, eh?

[mopar_mark]

Think I'll just gun it through the traps and see how it feels,

Seat of the pants testing gives immediate results

[Anonymous]

Glad to see someone actually agreeing with me for once

There are teams out thinking about what they are doing, and unsurpirzingly they tend to be the ones doing well, although sometimes those benefits take a while to filter through. But it has to be said that those who consistently adopt a sensible engineering attitude to their racing will tend to do better than those who don't.

Without saying too much, we have recently had a well known 7 times (or is it 8 now) NHRA championship team on our 7 post. Now you wouldn't think a car without suspension would need that sort of analysis, you would be wrong. I was impressed at the level of thinking going on in the team. And it's that sort of attitude that will bring about success, you don't have to spend millions to achieve it (although that will always help IF spent in the right direction - Just look at Toyota F1), it's just a method of working. That doesn't mean things don't go wrong, but it does mean that when they do you will have an understanding as to why and be able to rectify it.

I would like to see what was achieveable with one of these cars if someone was to really think about the aero package. I reckon Duncs Bird has the potential out of all the UK cars to really go far. It's just a case of how far he wants to deviate from the norm.

[MrNorm]

Kev, I would think the prime application of some aerodynamics for you would be to make sure the front end doesn't go light at high speed. So stopping aerodynamic front end lift. Obviously you want the front end lift off the line for weight transfer (presumably you have 90/10s or similar?) which I would think would make the car less resistant to lift at high speed. So having something (spoiler, splitter etc) that will progressively counteract the lift is a good thing - but only adding enough downforce to keep you where you want to be, without adding excessive drag.

If it were me I would determine how much lift I am getting by some Heath Robinson device to measure shock or suspension travel at the top end - webcam in the wheelarch with a graduated scale logging to a laptop off the top of my head (or maybe could get someone to film you through the traps) and then start adding downforce with the device of your choosing and repeat - see how much lower the front gets and tune from there. I'm guessing here but I would assume that if you aim at a neutral ride height you won't go far wrong, as long as your geometry/alignment is stable at that height.
I'm assuming that by that part of the track you won't be too worried about losing traction at the back.

Anyway, just some thoughts. This is all taking me back to the days when I actually got out and did vehicle testing in proper windtunnels instead of sitting at a desk planning stuff......mind you, I was less involved with pure aerodynamics and more cooling systems......

[Cannonball]

kev why are you worried, about lift at 130 are you doing somethin your not tellin us about that is low 10 second speed,
and james you can get my car quicker anytime once its out

[Blue]

You must have missed this then Dunc...

http://www.moparuk.com/forums/viewtopic ... sc&start=0

[Cannonball]

yep not spotted that, thats tweety old mtr in it ??? go for it kev boy

[Dave-R]

Yeah thats right. Andy Neal managed to offload that racing junk off onto Kev.