Ground Effect - Bring It Back

[bhall II]

I´m tired of your patronising attitude Bhall, specially since you ignore most questions related to the thread...

When I jumped into this conversation, it was on the assumption that everyone knows current front wings operate in ground effect in a way that's functionally identical to underbody venturis. As we now know, that assumption was wrong.

I've been asking you to describe the structural basis for your opinion in order to find a common ground that can be built upon, because I have no idea what you mean when you just say...

I´ve never questioned front wing work as a venturi tunnel, but I think it also work as a wing while you reject or ignore this. It´s not posible for the wing to work both ways?.

...or...

It´s logical, they´re wings so, what´s the reason to stop using downforce created by wings-bernoulli effect? Teams spend millions looking for ways to improve DF, it would be absurd to not use front wing as a wing.

Without context, I don't want to respond to your questions, because incongruent definitions are exactly what tangled up this mess in the first place.

Now I'll just pick Andres125s's cue and leave you to your ranting.

I've also asked you to explain your opinions, and you have not. All I see are isolated theses and seemingly random citations that appear totally irrelevant, because you've failed to explain them.


I've put forth my ideas in detail and with sources so they can be scrutinized. Neither of you seems to agree with them, which is fair enough. But, how can you possibly expect me to agree with you on anything if you won't give me a reason?

So, yeah, my frustration boils over. It's annoying as hell to be asked for something from someone who isn't willing to give it himself.

[Just_a_fan]

There are better ways to produce DF than wings..... or to be more precise, for the amount of DF rules will ever admit (to limit cornering speed as we all agree more than 5-6G would be too dangerous on most tracks) I´m sure it would be possible to create that amount of DF with less dirty air.

Just been watching a video about the Blackburn Buccaneer. Lovely aircraft. Seen the video a number of times because it's a proper film about the subject rather than a modern "flash and bling" type with no content as favoured by modern broadcasters. Anyway, one of the clever things the Buccaneer had to improve low speed performance was a boundary layer control by means of blowing. Air was ducted (from the low pressure compressor I think) out to various points on the wings and tailplane. This allowed for lift to be maintained as if the aircraft were flying faster than it actually was - localised airspeed was higher than the actual airspeed of the vehicle.

One could conceive of doing something similar on a car. It's a bit like the idea already stated of going back to fan cars but without the hovercraft type fan on the back. One could run a lower camber wing and get the same downforce as today. This would reduce wake issues too. You could even use it to blow the underside of the car I suppose. It would need an engine driven fan, at a guess, or an electric one in order to maintain performance in off-throttle situations.

In effect it would be the exact opposite of this:
http://www.racecar-engineering.com/tech ... echnology/

[Tommy Cookers]

this blowing at low airspeeds (also in the Starfighter etc) increased the lift coefficient by about 50% (without increased AoA)
would (or wouldn't) this correspondingly increase the tip vortices ?

doesn't it give (in military use) from single-slotted flaps the same result as a double or triple-slotted flaps do in civil use ?
(flap blowing etc in not permissible in 'public transport' civil aviation, as it relies on the engine working)

and how does eg the Cl of an F1 rear wing compare to either of the above ?

[Nickel]

I'd like to bring up a few things. First, it's the tip vortices that are used downstream to benefit. The venturi vortex is simply directed in such a way as to reduce front tire drag.

Second, what strange assumptions about dirty air lead one to believe under floor GE would be less affected by it? A moving car generates a wake. Say the air behind a car is pulled forward at 30kph at a distance of 5m(as an example). The following car has an effective airspeed of 30kph less if its 5m behind. Therefore less downforce. No amount of imagination will negate this.

Solution would be to cap downforce and focus development on drag reduction.

[Just_a_fan]

this blowing at low airspeeds (also in the Starfighter etc) increased the lift coefficient by about 50% (without increased AoA)
would (or wouldn't) this correspondingly increase the tip vortices ?

doesn't it give (in military use) from single-slotted flaps the same result as a double or triple-slotted flaps do in civil use ?
(flap blowing etc in not permissible in 'public transport' civil aviation, as it relies on the engine working)

and how does eg the Cl of an F1 rear wing compare to either of the above ?

I guess I was really thinking about the front wing - which is most affected by the wake of the car ahead. Blowing would give back some of the lost downforce without the need to redesign the entire aero concept of F1. Whilst selective blowing of the rear wing would allow for a DRS-style effect on the straights by turning off the blow you reduce lift and hence drag.

I would expect that a blown wing would still exhibit tip vortices in proportion to the lift being produced. A thought occurs - could one blow the end plate in such a way as to disrupt the tip vortex? No idea if one could and if it would work, just a thought.

The idea is really a fleshing out of my earlier suggestion of applying active aero to the problem. One thing about blowing the wing to allow closer running to the car ahead is that if the system fails then you're no worse than you are now. The problem with a fan driven underside aero system is if the fan fails; you're in to serious downforce loss in an instant. And that's not going to be good news for the driver.

[Andres125sx]

I´m tired of your patronising attitude Bhall, specially since you ignore most questions related to the thread...

When I jumped into this conversation, it was on the assumption that everyone knows current front wings operate in ground effect in a way that's functionally identical to underbody venturis. As we now know, that assumption was wrong.

.... because we all are stupid and you had to return to our mortal´s world to be able to understand our limited minds


BTW, nobody questioned that ever

I've been asking you to describe the structural basis for your opinion in order to find a common ground that can be built upon, because I have no idea what you mean when you just say...

I´ve never questioned front wing work as a venturi tunnel, but I think it also work as a wing while you reject or ignore this. It´s not posible for the wing to work both ways?.

...or...

It´s logical, they´re wings so, what´s the reason to stop using downforce created by wings-bernoulli effect? Teams spend millions looking for ways to improve DF, it would be absurd to not use front wing as a wing.

Without context, I don't want to respond to your questions, because incongruent definitions are exactly what tangled up this mess in the first place.

Both questions were in context, and you never asked for any clarification, simply ignored everythink not related to your repetitive argumentation about front wings working as VTs

I´m construction engineer. When someone ask me a question (interesting or stupid) about a building, I reply the best I can trying to use the proper language for the person I´m talking to, it´s not the same talking to an arquitect than talking to a philologist. If the question is stupid I clarify it trying to explain the reason it has no sense. But ignoring a question is a sympthom about you don´t have a clue about that but don´t want to admit you don´t have a clue.

[Andres125sx]

There are better ways to produce DF than wings..... or to be more precise, for the amount of DF rules will ever admit (to limit cornering speed as we all agree more than 5-6G would be too dangerous on most tracks) I´m sure it would be possible to create that amount of DF with less dirty air.

Just been watching a video about the Blackburn Buccaneer. Lovely aircraft. Seen the video a number of times because it's a proper film about the subject rather than a modern "flash and bling" type with no content as favoured by modern broadcasters. Anyway, one of the clever things the Buccaneer had to improve low speed performance was a boundary layer control by means of blowing. Air was ducted (from the low pressure compressor I think) out to various points on the wings and tailplane. This allowed for lift to be maintained as if the aircraft were flying faster than it actually was - localised airspeed was higher than the actual airspeed of the vehicle.

One could conceive of doing something similar on a car. It's a bit like the idea already stated of going back to fan cars but without the hovercraft type fan on the back. One could run a lower camber wing and get the same downforce as today. This would reduce wake issues too. You could even use it to blow the underside of the car I suppose. It would need an engine driven fan, at a guess, or an electric one in order to maintain performance in off-throttle situations.

In effect it would be the exact opposite of this:
http://www.racecar-engineering.com/tech ... echnology/

Like blown diffussers... interesting, didn´t know it

[Smokes]

Blown wings are used to compensate for lack of prop wash over the wing that you would you get with prop planes.

https://www.youtube.com/watch?v=Nz6niKjJuXQ

[bhall II]

When I jumped into this conversation, it was on the assumption that everyone knows current front wings operate in ground effect in a way that's functionally identical to underbody venturis. As we now know, that assumption was wrong.

.... because we all are stupid and you had to return to our mortal´s world to be able to understand our limited minds


BTW, nobody questioned that ever

Ease up on the self-righteous indignation. I've asked you repeatedly to clarify your opinion, and that still hasn't happened.

By default, ground effect has always been the driving force behind front wing design. Its very nature makes that unavoidable, and limiting such influence is why wing tips were steadily raised throughout the '90s and '00s in order to slow down cornering speeds.



But, even then, it remained a design focus...








(None altered to scale)

So, when you ask a question like this:

I´ve never questioned front wing work as a venturi tunnel, but I think it also work as a wing while you reject or ignore this. It´s not posible for the wing to work both ways?

To me, it reads like this:

I´ve never questioned front wing work as a [wing], but I think it also work as a wing while you reject or ignore this. It´s not posible for the wing to work [as it always has]?

And I dunno what to say, because I don't think these cars work the way you seem to think they do.

[Tommy Cookers]

Blown wings are used to compensate for lack of prop wash over the wing that you would you get with prop planes.
https://www.youtube.com/watch?v=Nz6niKjJuXQ

I had been avoiding this topic - and can only guess at the subject of your link
the Cessna is operable like a parachute - a good exercise (rudder to keep it dead straight and don't touch aileron) with spare height
there's a range where the flaps tend to blanket the elevator (ie if high power and high AoA is used with significant flap)

a 4 cylinder Pitts can be held continuously (with full power) at 45 deg 'AoA' (pitch attitude really) and zip all airspeed
a 6 cylinder similarly at 52 deg
an Extra 230 at 60 deg
in these cases (no flaps of course) you have a symmetrical section that gives useful Cl at abnormal AoA but huge Cd
presumably the part of the wing in propwash is working at significant airspeed and the rest is stalled and bumps around
the indicated oil temp goes off the clock in seconds (but means what ?)
dance on the rudder pedals to keep perfect 'heading' or you'd be in a shocking power-on spin entry
spinning + AoA or - AoA and have to work out which

yes, the propwash over the wing(s) can do a grand job

[Just_a_fan]

Blown wings are used to compensate for lack of prop wash over the wing that you would you get with prop planes.

https://www.youtube.com/watch?v=Nz6niKjJuXQ

Cessna did some work on blowing the flaps in the mid/late 50s but never put it in to production - there were too many issues for a "cheap" general aviation aircraft. Blown flaps were apparently patented in the UK in the early 50's and the system was first flown in production on the F104 Starfighter. Wouldn't be surprised if the idea had been looked at during WW2 when the possibility of patents might have been far from the designer's mind.

[Andres125sx]

Maybe in that case propwash is more necessary to keep control surfaces into an airflow so you still have control on the plane than to keep the wing under an airflow

The max AOA probably depend more on the max thrust of the engine (your examples show that tendency) than the airfoil or type of plane itself. While the AoA increases, lift depends more on engine thrust than wings lift, to the point in vertical position lift is equal to engine thurst. If max thrust is higher than plane TOW it can hover on the prop, if not the max AoA will be low if total thrust is far from TOW or high if max thrust is close to TOW.

I´m saying this because in RC world there´s a category wich obviously do not exist in real aircraft world wich is 3D aerobatics, some sort of radical aerobatics. Here there´s a sub- category called shockflyers wich are planes built as light as posible, with depron sheets, even the wings, so the lift is only achieved due to motor thrust and the AoA of that wing, whose airfoil is a perfect rectangle, so there´s no lift at all due to direct propwash, and they´re very easy to hover and do high AoA (we call to that maneouver "harriers")

[Andres125sx]

I´ve just realiced about this, it´s a jet so no aiflow on any surface (wing, elevator, etc.) but he manage to do high AoA harriers and even a hover thanks to thurst vectoring

Jump to 3:20

[amc]

tl;dr: An F1 car's front wing is a wing which works in ground effect. This is not the same as a venturi tunnel. The wing is designed to have similar effects to a venturi tunnel, but due to a number of factors it does not work in the same way.

The primary difference between a venturi tunnel design and a front wing design is the presence of multiple flaps, which are not seen in venturi tunnels. The front wing is designed to work in ground effect, as is a venturi tunnel. But the front wing cannot be a venturi tunnel, because it needs flaps to:

• Prevent stalling. The front wing must cope with differing levels downstream blockage, due to tyre and suspension movement. When the tyre moves in behind the wing, there is a greater adverse pressure gradient on the back of the wing (read: flow slows down more) and can become separated. Slot gaps allow boundary layers to remain energised.
• Prevent choking. The height above the ground of the wing varies while the car is in motion, which varies the downforce production of a venturi tunnel significantly. Multiple elements keep downforce production more consistent.
• Control downstream flow. A venturi tunnel will produce inconsistent downstream flow patterns as the downforce varies, so using elements makes the rest of the car easier to model accurately.
• Produce tip vortices. The ends of the flaps are designed to interact with the Y250 in some way (I can't qualify or quantify exactly what way). A venturi tunnel, sealed at the edges, would not allow this possibility.

One could imagine the first element of a front wing to be a venturi tunnel, with subsequent elements forming a 'wing' behind it. The downforce produced by a tunnel is a function of the height of the wake at the point it returns to atmospheric pressure. The additional elements behind the wing are making this height greater, and therefore producing more downforce.

Finally, a venturi tunnel is not in itself 'low drag'. The reason a venturi tunnel is seen as 'cheap downforce' is that the drag is normally attributed to the car placed on top of it. It still creates induced drag, and will produce about the same amount of induced drag as a wing scaled to provide the same downforce. If you wanted a lot of downforce and really low drag from an object in ground effect, the longitudinal cross section would be a streamlined aerofoil profile, to reduce the profile drag (total drag = profile drag + induced drag). It would, in fact, look a little bit like a wing.

Good reasons were brought up a while back about sporting reasons for re-introducing underfloor venturis (driver mistakes, variance in performance due to ride height changes). The aerodynamic reason it would increase overtaking is because, being primarily exit driven, the tunnels suck through all sorts of warm, turbulent, airflow. Unlike putting a current car into the wake of another, it won't totally mess up the carefully engineered flow patterns generated by the front wing and cause the barge boards to stop working (for example, I have no idea if this actually happens), so there won't be a step change in downforce.

[rjsa]

Thanks for putting it so clearly.