Ground effect coupled with suction fan

[riff_raff]

isn't passive aero (in a race car) inherently less efficient than a fan ?

Tommy Cookers,

Whether or not the overall efficiency of an active fan downforce system would be better than a passive system would depend on how each was employed. For example, a fan that operates with insufficient mass flow at high speeds is not really a "fan" anymore. Instead it's more specifically a "turbine", that is absorbing power, rather than imparting energy/momentum into the underbody airflow.

You should also consider conventional wing airfoils. They are entirely passive aero devices.

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[Greg Locock]

I might argue that using an engine-driven fan to create downforce by scavenging air from the underbody would only be more "efficient" under certain conditions. For sure it would help in low speed corners. But on high speed straights the engine power diverted to drive the fan would hurt top speeds. Before fans were banned, I believe the designers were using variable speed drives precisely for this reason.

My bad, I'd assumed they'd modulated the air pressure as required, as it is the obvious thing to do.

[riff_raff]

My bad, I'd assumed they'd modulated the air pressure as required, as it is the obvious thing to do.

If only it was as simple as modulating air pressure. The downforce is a product of the relative dynamic airflow pressure difference existing between the upper and lower body surfaces, right? These dynamic pressures are greatly affected by turbulence, velocity, mass flow, etc. Not very easy to "modulate the air pressure as required". A fan works by transferring momentum to the passing air mass, thus increasing the energy/velocity of the air mass. The velocity of the air mass as it exits the fan should be equal to or greater than that in the slipstream. Otherwise very little meaningful work is achieved by the fan. When one considers the very wide range of airflow velocities that an F1 underbody operates at, it becomes apparent just how difficult it would be to design an efficient fan system for this application.

[Greg Locock]

Um, you may be right in some instance, but experience with hovercraft and observation and calculation leads me to believe that it is not very difficult to switch the fan in a fan car on and off, and it would have the desired effect.

[matt21]

Um, you may be right in some instance, but experience with hovercraft and observation and calculation leads me to believe that it is not very difficult to switch the fan in a fan car on and off, and it would have the desired effect.

I rather would adapt a hydraulic drive for the fan. Then you can adjust the speed of the fan more precisly. Or you can vary the AoA as on a aircraft propeller.

[Tommy Cookers]

isn't passive aero (in a race car) inherently less efficient than a fan ?

You should also consider conventional wing airfoils. They are entirely passive aero devices.

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FWIW I've always thought eg that an Indy 500 spec engine in a suitable airplane could do the 500 much quicker than the car
(plus, operating a (lifting) wing of airplane AR in ground effect almost doubles its L:D ratio)

reasonably, the efficiencies of a (mainly) ground effect car, a WIGE vehicle, a fan car, and a hovercraft are closely related

my suggestion (IMO based on the idea underlying the OP) was that (the effectiveness of) the fan car would be invincible if engine power available (in principle, by diversion)) at the end of a straight was used for temporary very high downforce via a high-power fan high-downforce system (for enhanced braking and cornering grip only)
this would surely have resulted (from a Can-Am 'arms race'), and was the cause of the fan car ban ?
people have even 'proved' on paper that tyres (or rolling belts) with integral vacuum pad effect etc are very efficient

the race driving position is better for 'g' tolerance (cornering anyway) than the fighter pilot position
(strangely though, pilots get tunnel vision at about 8 'g' , but race drivers get it at the first corner !)

[flynfrog]

The chaperall used a snowmobile engine to run the fans. No added drag on the drive motor.

[Tommy Cookers]

that was about 60 bhp for the fan (continously) and about 600 bhp for propulsion (intermittently) ?

speaking crudely, the next step IMO was more like 600 bhp switched from propulsion to fan and back, as required
(hence the ban)

the car has say a 5 speed transmission and the driver matches the engine to the current task via the gears and (diff) torque balance
he could also select built in combinations of fan and drive torques (if the designer had arranged this)

there was a lot of 4 wd transmission interest/hardware around at the time
we were so near !

[Greg Locock]

"reasonably, the efficiencies of a (mainly) ground effect car, a WIGE vehicle, a fan car, and a hovercraft are closely related
"

That may seem reasonable to you but it is misleading, the variation in efficincy between those is about 400%, wig being worst

[Tommy Cookers]

a glider flown in ground effect (WIGE) can show a L:D of 80, that's 'efficient' by one (engineering) criterion

by a broader criterion (eg lap time), there's nothing very efficient (or effective ?) about having an 800 bhp propulsion engine going largely unused approaching and negotiating slow corners

'computer controlled' fan lift transport vehicles (all-speed flight out of ground effect or hover, only in ground effect ?) have been advocated for general public use by eg the Senior Scientist of NASA Langley, as a viable engine for development of eg the Amazon region, in preference to road vehicles and roads (although they are presumably less 'efficient' than helicopters)

this encourages my view that the fan car could usefully (ie for racing) have much more than 60 bhp driving fans for DF

[olefud]

The comparisons seem to be of rather differing ways of obtaining similar results. A fan car to my mind isn’t an aerodynamic device other than the fan blade moving air. It merely creates a vacuum in a skirted volume and creates down force as a result of the pressure deferential with the lower pressure also reducing shear drag under the car. This is fundamentally different from a wing which creates down force as an opposite and equal reaction to accelerating air upward in accordance with Bernoulli and Newton.

WIGE is a bit different in a plane and a car, I think. A car wing moving close to the ground generates a shear zone between the laminar air layers on the ground and on the under side of the wing. This enhances the low pressure area under the wing in the fan car manner while still substantially maintaining the wing updraft force.

WIGE with a plane is more the effect of the lifting downdraft from the wing getting a reaction from the ground as well as compression of air between the wing and the ground. It’s effective up to 1.5 to 2 times the wing span.

I can testify to WIGE in a plane having lost a cylinder upon rotation for take off in a Cessna 150. The plane could fly fine up to 20 or 30 ft altitude, i.e. over strung wires, but that was it and would lose altitude with slight banking – which was a concern since the Rocky Mountains a couple miles off the end of the runway.

[riff_raff]

olefud-

The principle of ground effects is different when considering an aircraft or a race car. Anyone that has ever experienced landing on a commercial jet flight has felt the ground effect between an aircraft wing and runway surface. Then there is the additional lift effect produced by helicopter rotors operating in ground effect. The ground effect experienced by an aircraft during landing or a rotorcraft HIGE is momentarily increased lift. The ground effect sought by race cars is continuously greater levels of downforce.

A better comparison to a racecar with a suction fan would be a STOL fixed wing aircraft that uses exhaust-blown wings for additional lift during take-off.

[Tommy Cookers]

The principle of ground effects is different when considering an aircraft or a race car.

Then there is the additional lift effect produced by helicopter rotors operating in ground effect. The ground effect experienced by an aircraft during landing or a rotorcraft HIGE is momentarily increased lift. The ground effect sought by race cars is continuously greater levels of downforce.

IMO ...... the ground effect is continuous
ie there is continuous availability if much greater Cl and thereby much greater L:D ratio

eg the power required to hover a helicopter above ground effect is much higher than for hover in ground effect
the minimum power to sustain aeroplane flight in ground effect is much lower than minimum power for sustained flight outside GE
(the Dornier X spent maybe half its flight time in GE crossing the Atlantic in 1928?)

GE is available all the time, the aeroplane pilot accesses it only briefly (for various good reasons)
aeroplane pilots who accessed it longer are very few, .... well done olefud !

GE adds 50% - !00% to the efficiency to rotary or fixed-wing flight, that's why they invented WIGE vehicles
the modern helicopter HIGE lift is about 4 times its core minimum weight
(that is the notional weight of the minimum possible structural and lift system without redundant engine(s) fuel etc etc)

HIGEs everse analog ie 'super fan-car' capability
am I the only person who thinks that fan power in fan-cars would not have greatly increased but for the fan-car ban ?

[Greg Locock]

The L/D of a WIG when used on an F1 car is 4. I assumed we were talking about cars, not gliders.

[Tommy Cookers]

For me it would make sense to couple a fan AND ground-effect.
The fan can provide larger downforce at lower speeds until the aerodynamic flow takes over and at higher speeds you can use the not needed fan-power to reach higher top speeds.

If I remember correct, Colin Chapman sketched a Lotus 79 coupled with a fan after the Swedish GP 79.

there must be ways of combining the two ?
(eg reconfigure GE tunnels into 'vacuum pads' with front & rear doors, then deconfigure)
in a fixed system, surely the fan could be somewhat helpful to the tunnels ?

and running the fan is the best way to use all that recovered electrical energy !