Blowing the Wing - what is it?

[hardingfv32]

Pressure switches are a great idea and have been used (experimental passive front wing stalling of Mercedes last season). I also see no reason for Lotus to not use such a pressure switch in their currently developed passive rear system.

We still to this date have no idea if Mercedes was experimenting with a passive switch. If they were, it would seem they had poor success as they went to the DDRS which adds a lot of complication.

The McLaren F-duct had a strong on/off signal. There is no indication that this is the case with Lotus. Any ideas what would make for a operable pneumatic switch 'signal'?

Brian

[olefud]

What’s needed is low downforce/drag on the straight and the opposite through turns with the latter often at high speed.

That's not strictly true. The cars operate in the area of 80 to 300 kph, with the fastest turn exits somewhere on the good side of 200 kph. So they need downforce at rather high speeds (10 kph more carried through the corner are more worth than 10 kph more top speed). They would like to have switching aerodynamic characteristics (and did with F-Ducts), and operating the rear wings at stalling AoA is too risky (i.e. no precise switching speed).

Pressure switches are a great idea and have been used (experimental passive front wing stalling of Mercedes last season). I also see no reason for Lotus to not use such a pressure switch in their currently developed passive rear system.

PS Aren't pneumatic (same as hydraulic) logic devices all fun and games with no real implementations?
(At least none you could call a computer.)

I agree that the need for down force is turn rather than speed related.

There’s another problem even if a proper signal condition could be identified for switching. The driver isn’t going to be too happy with the car making decisions on its own. An example is the WWII Bf-109. It had leading edge slats that deployed when airspeed and AoA were in a certain domain. It actually worked rather well. However, the better pilots disabled the system since the slats tended to deploy while they were execution their aiming solution when attacking and upsetting a delicate maneuver.
Down force switching in and out would be even more disconcerting to a driver.

The DRS approach has the advantage of driver control though with a rather limited available duty cycle.

[superdread]

I agree that the need for down force is turn rather than speed related.

There’s another problem even if a proper signal condition could be identified for switching. The driver isn’t going to be too happy with the car making decisions on its own. An example is the WWII Bf-109. It had leading edge slats that deployed when airspeed and AoA were in a certain domain. It actually worked rather well. However, the better pilots disabled the system since the slats tended to deploy while they were execution their aiming solution when attacking and upsetting a delicate maneuver.
Down force switching in and out would be even more disconcerting to a driver.

The DRS approach has the advantage of driver control though with a rather limited available duty cycle.

Therefore the system needs to be as predictable as possible and they need to be able to adjust it under parc ferme. Otherwise to be on the save side they must tune it for best weather, highest head-on wind and qualifying. Better still, being able to adjust while pitting (similar to McLaren's brake ventilation). The driver must be very attentive to head on winds (and changes in air temperature) as the activation speed will wander and if that falls too low (or the racing speeds get too high) then the system can seriously hamper performance.

[Cam]

Good point. I was reading up on Airspeed indicators and wondering whether Lotus or any other teams have consider this as a switch using a pitot tube to measure pressure. Aircraft must allow for differences and errors - so an F1 car using a similar system would also?

A Pitot Tube seems like a pretty simple system to switch on/off - completely without driver input.

A pitot tube is a pressure measurement instrument used to measure fluid flow velocity. The pitot tube is used to measure the local velocity at a given point in the flow stream and not the average velocity in the pipe or conduit. The basic pitot tube consists of a tube pointing directly into the fluid flow. As this tube contains fluid, a pressure can be measured; the moving fluid is brought to rest (stagnates) as there is no outlet to allow flow to continue. This pressure is the stagnation pressure of the fluid, also known as the total pressure or (particularly in aviation) the pitot pressure.

http://en.wikipedia.org/wiki/Pitot_tube

[superdread]

Good point. I was reading up on Airspeed indicators and wondering whether Lotus or any other teams have consider this as a switch using a pitot tube to measure pressure. Aircraft must allow for differences and errors - so an F1 car using a similar system would also?

The aircraft has a big advantage, it only moves through air, so airspeed is all the information they need (on the other hand they adjust for height, humidity, temperature...). A car moves relative to a volume of air, but also relative to the ground and the need for drag reduction depends on the position on the ground (i.e. turn exit).

When using road speed as a representation for the turn exit the influencing factors are for example fuel load, tyre state,....
But there is no way of accessing the road speed for switching an aerodynamic device (due to some FIA rules).
So, representing the road speed is the air speed, and that brings a whole lot more factors to be considered. Compensation environment changes by modifying the trajectory through the corner is possible but has a very limited impact (e.g. late apex -> higher exit speed can compensate to a very small degree for higher fuel load or worse tyres).

So when determining the activation point around two corners and not being able to recalibrate for any of the influencing factors changing, the system suffers. But with a little bit of cleverness, caution and pure luck you could utilise a passively activated blown wing.

[bhall]

Thoughts?



It's an open-ended question, because I just don't think this thing worked the way it was generally accepted to work at the time.

[fussell]

Hi Guys,

It seems all these blowing devices used in F1 'blow' the underside of the wings to reduce drag and/or downforce.

Is there a way of blowing the top surface of the wing to increase downforce and then shedding this effect at higher speed? Could you then use a lower AoA?

[bhall]

[...]

Is there a way of blowing the top surface of the wing to increase downforce and then shedding this effect at higher speed? Could you then use a lower AoA?

Maybe not exactly in that manner, but that's precisely the area of discussion I'm hoping my question about the MP4-25 initiates.

Moreover, I think the front wing of the W03 operates with a design that's diametrically opposed to what's currently held as "conventional wisdom" on the subject.

[gato azul]

Thoughts?
It's an open-ended question, because I just don't think this thing worked the way it was generally accepted to work at the time.

Looks like a combination of this:

with an F-Duct

Trying to make more downforce by "blowing" and then, when not needed, killing the downforce by "more blowing" so to speak
Blowing - all a question of why, when, where and how

[Tommy Cookers]

The driver isn’t going to be too happy with the car making decisions on its own. An example is the WWII Bf-109. It had leading edge slats that deployed when airspeed and AoA were in a certain domain. It actually worked rather well. However, the better pilots disabled the system since the slats tended to deploy while they were execution their aiming solution when attacking and upsetting a delicate maneuver.
Down force switching in and out would be even more disconcerting to a driver.

...(automatic (wingtip/outer wing) slots aka slats to raise stall AoA in that region of natural lower stall AoA due to chord)
the essential point was to get both slots opening at the same time, this was factory checked, standards were sacrificed later
experienced pilots made good use of them in combat, to tighten the turn briefly and particularly to point tighter/higher
they increase Cl (opening at high AoA) only if more AoA is then used
high speed + high AoA = high 'g' and drag, so they were cycled in and out in combat (someone who did this wrote it up)
they would likely open on landing, one only opening was bad then (British evaluations always avoided this region)
confidence was needed to get them out and keep them out

the whole point was to enable greater AoA, but design progress was towards lower AoA operation related to nosewheels replacing tailwheels and more lavish flaps, so fixed slots (with lesser AoA enhancement) took over


anyway, there shouldn't be a problem on a car ?

[olefud]

The driver isn’t going to be too happy with the car making decisions on its own. An example is the WWII Bf-109. It had leading edge slats that deployed when airspeed and AoA were in a certain domain. It actually worked rather well. However, the better pilots disabled the system since the slats tended to deploy while they were execution their aiming solution when attacking and upsetting a delicate maneuver.
Down force switching in and out would be even more disconcerting to a driver.

...(automatic (wingtip/outer wing) slots aka slats to raise stall AoA in that region of natural lower stall AoA due to chord)
the essential point was to get both slots opening at the same time, this was factory checked, standards were sacrificed later
experienced pilots made good use of them in combat, to tighten the turn briefly and particularly to point tighter/higher
they increase Cl (opening at high AoA) only if more AoA is then used
high speed + high AoA = high 'g' and drag, so they were cycled in and out in combat (someone who did this wrote it up)
they would likely open on landing, one only opening was bad then (British evaluations always avoided this region)
confidence was needed to get them out and keep them out

the whole point was to enable greater AoA, but design progress was towards lower AoA operation related to nosewheels replacing tailwheels and more lavish flaps, so fixed slots (with lesser AoA enhancement) took over


anyway, there shouldn't be a problem on a car ?

The Bf-109 example related to a device that actually worked well but was disabled as not appropriate for the delicate positioning of a gun platform for an attack –though I understand that Marseilles use the slats to good purpose during a unique prop-hanging attack tactic he developed. The point being that a driver setting up for a corner would find it disconcerting to have his down force controlled by a passive off/on switching of down force when setting up for a corner.

The problem is finding a reliable passive trigger for down force modulation. Of course it could be done easily with global positioning or other overt device that the rules would promptly stomp on. Using the varying slipstream to modulate down force would be tricky given the varying turbulence from other cars.

My best thought is allowing a bit of pitch and/or roll variation that would optimize ride height during cornering and concurrently enable variable down force –but someone else will have to refine it.

A bit more seriously – would it be all that bad to have driver enabled down force modulation. Lower down force and less turbulence on the straight sections might assist passing.

[gato azul]

for whoever is still interested in this, this is perhaps the closest to the application at hand:

ACTIVE FLOW CONTROL BASED ON STREAMWISE VORTICES FOR A BLUNT TRAILING EDGE AIRFOIL

and just for giggles, the guy N.Tomazis, mentioned as author/co-author of some papers in the reference section, is the current
Ferrari chief designer, who wrote his PhD thesis on a similar topic.

[superdread]

for whoever is still interested in this, this is perhaps the closest to the application at hand:

ACTIVE FLOW CONTROL BASED ON STREAMWISE VORTICES FOR A BLUNT TRAILING EDGE AIRFOIL

and just for giggles, the guy N.Tomazis, mentioned as author/co-author of some papers in the reference section, is the current
Ferrari chief designer, who wrote his PhD thesis on a similar topic.

Not really.
This paper describes how to prevent a Karman vortex street at a blunt trailing edge by injecting air into the wake, so to aid flow separation at the trailing edge. Nothing about separating the air flow in the middle of the wing.

[gato azul]

by injecting air into the wake, so to aid flow separation at the trailing edge.

Do you not think, that this is well worth a though?
Do you think, that the classic "thin airfoil theory", more the most part assuming laminar flow,
is a good approach to describe a F1 rear wing as a whole?
Do we assume that the Kutta condition is always met when we talking about an F1 "wing" as a whole unit at changing speeds?
What does it mean, and what would happen if it is not met, prevented to establish?

If we think about this mystic ex-McLaren guy and his "dead zone", why do you think they would call it that? For lack of a better word?

I'm sorry if this paper did not met your expectations, we may have to wait then until someone publishes a paper or writes his PhD thesis about an F-duct in a F1car. I thought, that it bears more relevance to the topic, then blowing the leading edge of a delta wing, but I could be wrong.

[superdread]

There once was a very similar topic: viewtopic.php?f=6&t=8429
(it has more pictures)

Especially this post seems helpful (a 3D simulation would be grand, but it illustrates the principle quite nicely):

Hi guys,

Just carried out a simple simulation in ANSYS of a normal and blown wing. It was at relatively low speed of 16m/s and a low aspect ratio wing typically used in FSAE cars

Boundary conditions and the mesh were appropriate. The wall Y+ returned values below 20.
The blown velocity was 75% of the free stream and at an angle of -45deg to the global co-ordinate system.at about 60-70% of chord distance. Here are the velocity contours between the same levels. the wing is at 0 AoA. Boundaries were sufficiently far to account for any blockage in the simulations.

The airfoil used is a single element one and hopefully quite relevant to the topic discussed here. I request Mods to move it to appropriate thread.

Normal airfoil


Blown airfoil 45



From the converged lift and drag values of the the 2 simulations,

NORMAL AIRFOIL
LIFT -235N
TOTAL DRAG = 62N
L/D -3.77


BLOWN AIRFOIL
LIFT -81N
T.DRAG = 18
L/D -4.5

As seen, stalling a wing is effective at low speeds as well, and just these 2 cases were tried.
The induced drag on the blown wing was 3.5 times less as seen on the normal wing.I have not considered endplate factor for this calculation. [2*H/B, I presume]
The simulations are 2D and simple wing theory calcs were used for approximations. The blown wing is effectively a 3D phenomenon.Look forward to any opinions/suggestions.

Thanks

Do you not think, that this is well worth a though?
Do you think, that the classic "thin airfoil theory", more the most part assuming laminar flow,
is a good approach to describe a F1 rear wing as a whole?
Do we assume that the Kutta condition is always met when we talking about an F1 "wing" as a whole unit at changing speeds?
What does it mean, and what would happen if it is not met, prevented to establish?

I think the flow on a F1 rear wing is mostly laminar (disregarding the vortex devices (endplates and trailing edge cuts)), having a wing with pure speed induced separation effects would be a quite unpredictable thing for the driver (sensitivity to air temperature, slip angle...).

If we think about this mystic ex-McLaren guy and his "dead zone", why do you think they would call it that? For lack of a better word?

Never heard of it, is there some context for what he described as "dead zone"?

I'm sorry if this paper did not met your expectations, we may have to wait then until someone publishes a paper or writes his PhD thesis about an F-duct in a F1car. I thought, that it bears more relevance to the topic, then blowing the leading edge of a delta wing, but I could be wrong.

Don't be sorry. It is hard to find good data on this subject, because it is very specific and F1-teams will do hell to publicise theirs. All the proper research engineers are interested in and write about is planes.
Scarbs has done something with pictures but also no drag data: http://scarbsf1.com/blog1/2010/03/04/bl ... -stalling/