Wings or ground effect?

Open formula where anything goes. What would perform better a ground effects car with no wings or a wing car with a flat bottom?

The numbers suggest that you could generate lots of downforce without wings but how could you control it? 

GE with skirts will produce far greater L/D than wings.

No need to control it if drag is minimal and the aero is unsprung.

Speaking of unsprung.. if I recall correctly, in the late 60s, F1 cars had their rear wings attached directly to the rear hubs, and this was later banned.  Was the ban safety-related?  I know there were some catastrophic rear wing failures at the time - are unsprung wings more likely to fail due to the pounding from bumps in the road etc?  If so, surely with today's materials, such effects could be avoided?

Speaking of unsprung.. if I recall correctly, in the late 60s, F1 cars had their rear wings attached directly to the rear hubs, and this was later banned.  Was the ban safety-related?  I know there were some catastrophic rear wing failures at the time - are unsprung wings more likely to fail due to the pounding from bumps in the road etc?  If so, surely with today's materials, such effects could be avoided?

Yes & Yes. I doubt modern materials would make the principle safe enough to be useable.

Did the Lotus 88 ever have any major suspension collapse brought on by having one unsprung tub which housed the floor ?

Unsprung aero is definitely feasible. CF allows much lighter aero components plus a somewhat compliant connection to the uprights would combine to produce manageable inertia loads - even for a full aero undertray. The Lotus 88 had bump stops (rubber?) transferring the DF to the uprights.

Speaking of unsprung.. if I recall correctly, in the late 60s, F1 cars had their rear wings attached directly to the rear hubs, and this was later banned.  Was the ban safety-related?  I know there were some catastrophic rear wing failures at the time - are unsprung wings more likely to fail due to the pounding from bumps in the road etc?  If so, surely with today's materials, such effects could be avoided?

In F1, these were flimsy last minute lash ups, retro-fitted to cars that had never been designed to have them.  It was not very surprising that they collapsed under load, especially at circuits like Montjuich Park.  However, the Chaparral 2E sports racer had a hub mounted wing designed into it from the outset and properly engineered.  AFAIK, this never failed, but was swept away anyway in the furore over the F1 failures.

 Thanks to all.

Unsprung aero is definitely feasible. CF allows much lighter aero components plus a somewhat compliant connection to the uprights would combine to produce manageable inertia loads - even for a full aero undertray. The Lotus 88 had bump stops (rubber?) transferring the DF to the uprights.

Does anyone have any ideas how you could engineer a connection to the uprights from a full aero undertray?  How could you fine tune the undertray? 

Is there a formula for working out the drag from an undertray? 

Workshop argument now in full flow because I have suggested throwing the wings away and instead running a full aero undertray.

Venturi ground-effect in F1 was never unsprung, didn't need to be with sliding skirts, the ride wasn't that uncomfortable either as springs at the time were pretty linear. 

Edited by Rasputin, 30 August 2013 - 16:21.

Why wouldn't you just use sta bar drop links, or the equivalent? Somehow you have to top it squirming around in plan view, so use two drop links in a V arrangement off one axle.

The only datapoint that springs to mind is a reverse engineered aero model of the 2000 Ferrari car, where the undertray has an L/D of about 10, rear wing 4, front wing 3. I'm sure there are references in Katz which could lead to better estimates for your particular setup.

Thanks again. 

Still lots of unanswered questions as to whether an unrestricted car with ground effects but no wings could be faster than a car using only wings. Numbers say it could easily be but the practical side in me doubts it is that simple. Perhaps it is time to try out the theory.

Depends on the car and track too. You might not be able to make enough downforce with just ground effects if you have a twisty circuit and a powerful engine.

Correct me if I am wrong but aren't ground effects better for a following car.  Less turbulence to disturb the car behind.  Ground effects less sensitive to turbulent air?  It would be nice to see a very clean car with hardly any wing.  What would be a front nose design with pure ground effects? 

It would be nice to see a very clean car with hardly any wing.  What would be a front nose design with pure ground effects? 

Brabham BT49?

http://www.inderscie..._Fig3_small.jpg

Venturi ground-effect in F1 was never unsprung,. 

Lotus 88.

 Workshop argument now in full flow because I have suggested throwing the wings away and instead running a full aero undertray.

What sort of car - Formula Libre hillclimb?

The ultimate aero package would have both (and wouldn't be open-wheel either). A rear wing will pump the venturi, increasing underbody DF as well as adding DF of its own. Aero development in FSAE is worth studying, FSAE being a very open formula in terms of aero (open wheels mandatory however). http://www.fsae.com/....php?1948-WINGS

Lotus 88.

If I remember correctly the unsprung part of the 88 aero was just the side fences and skirts, so basically zero plan area.

You're probably right, although the "unsprung" chassis gained enough DF (from somewhere) to pull it down to the bump stops from its relatively high static position.

Brabham BT49?

 

http://www.inderscie..._Fig3_small.jpg

That was my first thought after I hit Post

Deltawing. 

I had no formula in mind when I posed the question.

The interesting thing is that regulations have always interfered before a "proper" ground effects car has been fully developed.  Most of the information I can find is on F1 and as we all know there never were full ground effect cars due to the regulations that were already in place regarding wings, skirts etc and for that reason most cars that we think of as being ground effect cars are flawed.

I would think a ground effects car to an open formula would have large diffusers under a full width nose, perhaps exiting at the side of the cockpit behind the front wheels and have other rear diffusers with their exits at the rear of the car. Skirts would be ideal but since most formula stipulate a minimum ground clearance (to save track damage if nothing else)  another method might need to be found. Certainly there would have to be wheel shrouds and various other aero managing parts to aid the performance of the under side.

I know a wing car creates downforce at the cost of drag but does a ground effects undertray create more drag than that of a wing car with the same level of downforce. The figures suggest it does not due to the large area of the floor pan.

"I know a wing car creates downforce at the cost of drag but does a ground effects undertray create more drag than that of a wing car with the same level of downforce."

I don't understand what you are getting at, those figures I posted show exactly what the situation is. GE is better than wings for L/D.

Beware of terminology. "Wing car" was used for the F1 ground effects cars - the whole chassis was a wing.

ground effect exaggerates center of pressure movements where as wings go against them. if you fix your ground effect devices tot he unsprung mass then thats a whole new area of play 

So what is the difference between a 'wing' car and a one that uses GE?

I thought the convention (and it's not really grounded [as it were] in fact since 'conventional wings' are often in significant ground effect) was that aero where the sun don't shine (underbody) is "ground effect" and the stuff on top that looks like wings is "wings". A front wing isn't a ground effect device (even though it clearly is) essentially because it's in plain view and sort of looks like an aircraft wing.

Oh well, once people define what they actually mean then we can have a sensible conversation.

Oh well, once people define what they actually mean then we can have a sensible conversation.

Do you think so?  You lost me when you referred to the 2000 Ferrari.  What one and in what spec were your numbers referring too or is it something you lifted from the KATZ book?

I have spent a bit of time over the weekend trying to get more information on the subject and it is fair to say there is little to be had because most of the cars are compromised by the regulations they are built too. The workshop debate is now closed.

The 2000 Ferrari is the one in the Peter Wright's Ferrari Formula 1 book.

Edited by Greg Locock, 09 September 2013 - 23:09.

This is easy, wings.

Given that you've said anything goes, we'll assume this is a high powered car, and also that our race track (very important) is a typical F1 circuit. A ground effects car will ultimately be limited by the area underneath the car, so whilst being many times more efficient, will run out of downforce it can create.

Not so easy if you have a human driver on board. A no-rules GE car could be built to produce cornering and braking forces beyond human limits and require a lot less HP than wings to do so. I guess if you wanted the massive grip at lower speeds as well, you would need to add wings so the answer is still probably "both".

Edited by gruntguru, 10 September 2013 - 11:17.

I think in a no rules formula we decided a fan car would be a better bet than passive aero

Yep.

You only have to look at the F1 cars of 1980, the peak-year of venturis with sliding skirts, to get the answer to the original question, they barely ran any wing at all.

As for a fan-driven sucker-car would beat them both, I doubt it, the weight, complexity and power-consumption would probably have made it impossible today.

You only have to look at the F1 cars of 1980, the peak-year of venturis with sliding skirts, to get the answer to the original question, they barely ran any wing at all.

 

As for a fan-driven sucker-car would beat them both, I doubt it, the weight, complexity and power-consumption would probably have made it impossible today.

I think the Brabham fan car example suggests otherwise. If the perimeter is well sealed, the fan power requirement is low. The big advantage over conventional aero is at low speeds.

The other big advantage is at high speeds. On the straight.

The other big advantage is at high speeds. On the straight.

Yes I image with effective skirting the fan power required could be less than the drag power of a high L/D GE car.

Well i was thinking of switching it off until the brakes or steering are needed, but that might be a bit of a high risk low reward activity.

For practical systems even without skirts the power draw is not ridculous, 40 hp or so, so compared with current aero drag power it is low.

The other big advantage is at high speeds. On the straight.

Edited by Kelpiecross, 13 September 2013 - 05:00.

From original question= 

Open formula where anything goes. What would perform better a ground effects car with no wings or a wing car with a flat bottom?

 

...and assuming fan-cars out, we have a not-completely open formula....  

So presumably the question is=

What would perform better a ground effects car with no wings or a wing car with a flat bottom?

 

Fan cars will always perform better, just by the fact that, as Kelpiecross stated, it provides Fz from 0 v...but excluding them, and again having a completely free formula for wings or ground effects only, can be very close, imagine a winged car but with moveable surfaces, or even retractable, giving low drag on straights and massive drag under braking, plus variable downforce in corners, balancing braking and traction needs. On the other hand ground effects are always better in L/D, for a given Fz, but would be also massively improved with a variable geometry (shape if you will). It all depends on how far you would go, presumably we are talking ultimate? All the developments, including active (or rather re-active, although Lotus had started working on predictive suspension before the whole shebang was banned) suspension was just a way of controlling flat bottoms, themselves a product of regulations. Nice for a bench discussion but needs far too much work to answer accurately, not to mention that track variables (I.E. cornering speeds, corner radius/straight line lenght ratio/amount of braking/traction and surface quality/size of curbs/system weight and control complexity) would bias towards one or another despite optimization. A HUGE can of worms...  

As quoted once "Include me out" of this discussion...

From original question= 

...and assuming fan-cars out, we have a not-completely open formula....  

So presumably the question is=

 

Fan cars will always perform better, just by the fact that, as Kelpiecross stated, it provides Fz from 0 v...but excluding them, and again having a completely free formula for wings or ground effects only, can be very close, imagine a winged car but with moveable surfaces, or even retractable, giving low drag on straights and massive drag under braking, plus variable downforce in corners, balancing braking and traction needs. On the other hand ground effects are always better in L/D, for a given Fz, but would be also massively improved with a variable geometry (shape if you will). It all depends on how far you would go, presumably we are talking ultimate? All the developments, including active (or rather re-active, although Lotus had started working on predictive suspension before the whole shebang was banned) suspension was just a way of controlling flat bottoms, themselves a product of regulations. Nice for a bench discussion but needs far too much work to answer accurately, not to mention that track variables (I.E. cornering speeds, corner radius/straight line lenght ratio/amount of braking/traction and surface quality/size of curbs/system weight and control complexity) would bias towards one or another despite optimization. A HUGE can of worms...  

 

As quoted once "Include me out" of this discussion...

Good points all of which entered the workshop debate. One smart Alex decided all those variables could be electronically controlled and the missile that would then result would win any race hands down.  

Well i was thinking of switching it off until the brakes or steering are needed, but that might be a bit of a high risk low reward activity.

 

For practical systems even without skirts the power draw is not ridculous, 40 hp or so, so compared with current aero drag power it is low.

I beg to differ, a typical axial blower can't create much more than 2 kPa pressure diff anyway, a proper venturi can easily top that,

Moreover, you would need to seal a fan-car off in the front as well, which is not such an easy thing to do.

Hold your hand against the bare vacuum nozzle at home, 2 kPa over 12 cm^2 equals 0,24 kg (0.5 lb) force, about right, isn't it?

I would have thought the main advantage of the fan car (compared to other forms of down force) is that the down force is always there - not dependent on forward movement. So even standing motionless (on the starting line for example) or in very slow corners where the normal methods of DF would be absent or very low the added tyre grip of the fan suction is always present.

I have read that racing drivers driving a F1 car for the first time comment on how frightening they are due to the varying DF with speed. Apparently you have to attack the corners at what seems to be ridiculous speed to develop enough DF not to go off. But if you tackle the same corner at a lower and apparently saner speed you certainly will go off due to lack of DF. The fan car presumably would not have this problem - DF being much the same at all speeds. I know which I would prefer.

If you've got a separate engine for the fan like the Chaparrals then you can count on the suction being relatively constant, but if, like the Brabham, the fan is run by the engine, you've added the variable of engine speed. I think I remember a quote from Lauda about the Brabham being very unintuitive to drive - something like the response to understeer was to give it a bunch of throttle. 

There are stories from Anderstorp, the only track where the BT46B was ever raced, that you could see the car squatting in the pits when Lauda blipped the throttle.

Venturis with jet engine(s) to speed up the airflow.

All you would need is to inject the exhaust in the right positions at the venturi expansion, imagine an extra 500 kW into that diffuser?

another angle to argue, pure speculation. fan car would work very well at lower speed corners much more effectively but when speed rises and drag increases to produce downforce, how much horsepower does it take can be equivalent how much horsepower needed to turn a fan and maybe more. I mean, how much horsepower does it take to spin a racing Porsche aircool engine's fan?  eventually at high speeds the efficiency of how race cars are designed today, drag downforce ratio might catch up and meet at a point where the fan simply would be more drag. if we to unban ground effects, it might even increase this possibility. a fan car will not win in every track

Edited by Powersteer, 14 September 2013 - 01:51.

Powersteer- eventually at high speeds the efficiency of how race cars are designed today, drag downforce ratio might catch up and meet at a point where the fan simply would be more drag. if we to unban ground effects, it might even increase this possibility. a fan car will not win in every track

 

...comes back to the argument that it's always horses for courses...where and how you race will determine what equipment you use. The bottom line in engineering is determined by cost, practicability, what is available and how far you want to take an idea, there is always the optimal crossover point of pros and cons. Why limit your fan to a fixed ratio to say, engine rpm? why be tied to a single engine (see Brabham fan vs. Chapparal), why be limited to a reciprocating engine, after all the quote was completely free regs.

If one uses, say a fan-jet engine, the by-pass could be used to evacuate the under car plenum, thus providing downforce, whilst the central spool drives the wheels, if you take the drive mechanically to the wheel, it could be a pure thrust car, or the turbine could turn a generator that in turn would drive separate in-hub motors computer controlled to work at the limit of slip in each individual wheel, possibly with individual steer to improve handling, effectively a real drive-by-wire, with the computer changing parameters to make car follow a driver determined trajectory. Think big...  

The spectre of car performance outstripping human physical capability will always be a barrier, we were coming close to it in the skirted ground effect cars, if only on the non-assisted steering of the time, plus the lateral and longitudinal G forces being developed, think the evolution of fighter planes, from fly-by-wire to the ultimate (well, for a while) transition to drones and missiles. Thanks to Moore's law, the silicon side of engineering will very quickly outstrip the evolution driven development of this all too mortal flesh. Yikes, we are sliding into philosophical ground here...    

 (or rather re-active, although Lotus had started working on predictive suspension before the whole shebang was banned) 

I am happy with re-active suspension but predictive?

Were they somehow measuring the chassis to road distance in front of each wheel to deduce the magnitude of bump/yump to come and, with reference to forward speed, modulating the actuator accordingly?

...actually running several laps to map surface, and then predict the ground profile for subsequent laps...was quite early days on this process. Interesting idea for closed circuits, but the sheer amount of data to be processed could be daunting.