In free practice for the Indian GP, we saw a violent fluttering of Felipe Massa’s front wing. This is a higher frequency movement than the flex we commonly see on front wings – in fact, the movement is enough to cause the endplates to hit the ground, sending up showers of sparks. Bearing in mind that the wing is around 75mm off the ground when the car is at rest, we can appreciate the amount of movement that’s occurring here.
This movement is not an aero benefit in itself, but may be symptomatic of other flexibility in the wing.
Ferrari Flexi Wings 2011 Indian Grand Prix FP1 by Mattzel89
This clip shows the Ferrari crest the hill before braking into a turn (4s into the clip). As the car crests the hill at high speed with DRS open, it’s clear that the wing is bowed from the aero load. It’s possible to see the side spans of the wing bend down from the central section. At this point there is some vibration in the wing, but not an excessive amount. As the car starts to go down hill (DRS still open) and passes a shadow across the track, the wing starts a rocking motion (5s into the clip). This rocking soon increases in violence until Massa closes the DRS and starts to brake as usual for the corner (at 9s), so this episode only lasts three seconds. I counted around 20 movements of each endplate, which increase to the point where the endplates’ skid blocks strike the ground.
The cause may be explained as follows: the wing is bowed at speed, but as the car crests the hill the wing is unloaded slightly. Then, as the car starts to move down hill, that load would reverse and the wing (which was already vibrating) is sent into a rocking motion. One endplate moves down, while the centre section and wing mounting pylons appear to be rigidly fixed to the car and are not moving. The load passing from the endplate must have been transferred across the central spar of the wing to the other endplate, which now drops. This movement resonates in a wave from one side of the wing to the other, increasing in frequency and amplitude until the wing actually hits the ground.
I can’t explain why closing the DRS and braking calmed this resonance so quickly, but the wing rapidly returns to the low-amplitude, high-frequency vibration seen elsewhere on track.
Also, I’m no expert on composites but my limited knowledge does suggest that carbon fibre structures are relatively well damped (compared to, say, a metal structure), the rebound effect of flex being relatively well damped and not prone to oscillating.
Ferrari introduced the new front wing in Korea. Alonso ran the wing as it was clear that it displayed the accepted level of flex as used by many other teams. The wing is legal as it meets the more stringent FIA 2010 deflection test. Last year Red Bull set a precedent when its wing, which openly appeared to bow downwards at speed, passed the tests and was declared legal, even when the test loads were increased mid-season.
This bowing effect – where the tips of the wing move downwards at speed – is commonly used as the front wing then sits closer to the ground and can generate more downforce. Despite a lot of theories about mechanisms or heat being responsible for the flex, the answer is much simpler: it is down to the way you want the wing to work i.e. the tips to bend down without the wing twisting and thereby reducing the wing’s angle of attack. This is all done with the lay-up of the composites – I’m told it is a “nightmare“ and have heard of composites technicians spending weeks trying different lay-ups to get this effect, but once worked out it is very effective.
Of course F1’s knowledge of carbon structures has been used to create very stiff parts, but now that we are starting to allow controlled flex, we will start to see resonance becoming an issue. There is a new field of knowledge to be understood and controlled.
It seems the wing was tried again in FP3 and the FIA has taken an interest in the wing. The wing was removed and one would assume that it will not be raced for fear of mechanical failure or a post-race ban, although Ferrari’s Friday press release may suggest that the wing is a development item not planned for use in the race, but as part of the 2012 programme. Pat Fry: “We continued with the now usual parallel programmes: on the one hand looking for the best set-up for the car at this circuit and on the other, working to get a greater understanding of the latest aerodynamic updates, with the new car project in mind.”
We have seen extreme movement of front wings before in super slow motion, such as wing tips fluttering, wings swaying sideways on their mounting pylons and endplate devices flapping. All of these movements, although highly visible, have been accepted by the FIA because the tests have been passed. All of which is to the detriment of the overriding regulation that bodywork should be rigid and immovable.
Thanks to Andrew Biddle (andrewbid@gmail.com) for his assistance as Copy Editor
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For me looking at the video seems clear that that part of the track is pretty bumpy, and as everything what is flexible has their own self frequency of resonation, the track and the cars speed made the car resonate at the wings own frequency, making its amplitude hit the extremes, as every object kind of amplifies the resonation it gets if hitting that sweet spot of frequency. This can be tuned easily or damped down.
“I can’t explain why the closing of DRS and braking were so quick to calm this resonance”
Is there another possibility?: That the oscillation is initated by a bump induced contact with the ground, then subsequently sustained by friction-induced torsion and flexing of the wing. The only analogy I can think of is chalk sqeal on a blackboard (or even the squeal of tyres). This might explain why the vibration stops quite abruptly once the wing-ground separation increases sufficiently.
Were Alonso and Massa running the same wing during practice because it seemed only Massa had this problem and not Fernando.
The reasonance stops under braking because the aerodynamic load is highly reduced with reduction of speed.
This is my assumption as well. Perhaps the construction was slightly off, side-to-side. That is, perhaps the construction on one side was not perfectly mirrored on the other, in which case that might set off an oscillation that passed back and forth. At the top of 7th and with the DRS open, it was above “normal” 7th gear loads.
Mep maybe is right, to my knowledge.
Anyway, I think Ferrari has planned to race the wing in the race also, because we are pretty sure Massa had it in quali, as he said: “Now I find myself with one less set of Softs and with a broken front wing. It was the new one, which we had here for the first time and it delivered a bit extra in terms of performance”
Adrian must be annoyed that Ferrari had taken Red Bull’s tech and is replicating at least 80% of the results. The uncontrollable resonance might be the fibre alignment is not precise enough on critical places. You can simulate this in FEA software.
If I’m not mistaken the load comes from underneath the wing not from the top down.
I would have thought the load was distributed top and bottom. As it is simply high pressure on the top side and low pressure on the underside. I suppose it is difficult to say if the low pressure sucks the wing down or the high pressure pushes the wing down.
Refering to the flex test:
http://www.formula1.com/news/technical/2010/836/782.html
The 100kg test does not actually double the bending moment load as it is not placed on the edge. This means that the deflection could be lesser than 2x compared to the 50kg test.
My hypothesis about this flexi wing that is able to pass load test is this. The front wing has 2 structural parts that takes the loading. Notice there is a slot main body wing. The front structure can be made weaker than the rear. This allows the front to twist a bit under aero load and thus increasing the angle of attack. This leads to larger negative lift coefficient (-C_L). This provide the extra loading to bend the wings even more.
The rear structure is strong enough so that it alone would be sufficient to pass the loading test. the front bit is the key to allow flexing.
I guess the tricky bit is to not allow the wing to generate aero-resonance (or vortices).
One other question could be the method which FIA applies the load test. Do they hang a 100kg load on a string that is loop onto the wing? how and where exactly is the load applied?
I’m sure it’s entirely unrelated to Webber’s front wing never making it back to the pit lane after his Imola whoopsie 😀
It isn’t actually resonance, despite what first year physics text books tell you, what we seem to be seeing here is aeroelastic flutter, something we see quite often in high speed racing model airplanes, the most famous example is probably the tacoma narrows bridge though
Yup, that’s classic binary flutter. At high speeds the bending and torsional stiffness modes couple, and the change in angle of attack and position produce aerodynamic loads that feed the harmonic motion. The fact that the wing’s movement is limited by hitting the ground meant that the oscillations could not grow beyond the structural limits of the wing and cause a failure. Braking instantly reduced the velocity of the airflow, and hence the aerodynamic loads, meaning that structural damping could overcome the induced oscillations.
I have just finished an undergraduate thesis on composite tailoring for improved flutter response and aim to work in F1 in the future so seeing that on the TV made me very happy!
“Fluttering is a physical phenomenon in which several degrees of freedom of a structure become coupled in an unstable oscillation driven by the wind.” – in our case, the wind was the aero load under braking.
Alonso had this problem too but his front wing didn’t flutter but the whole front wing was oscillating up and down at high speed, but just for few laps. The French TV commentator suggested it was the combination of hard front damper + too low pressure in front tyres that made the car resonate !
What’s your opinion about that ?
This remiand me the accident between Jason and Vetel last year..
Surely the FIA must question its testing now? I agree that the wing is legal according to the FIA rules as it is passing the test (although according to my rules that does not automatically make it legal, but I am not the governing body so my view is irrelevant). However the FIA must be asking themselves why cars passing their flex tests are showing significant flex during the race. The tests clearly are not working.
I would like to offer a another explanation and wonder what you think of it: When DRS is closed there is an area of high pressure. This high pressure could be used and to transferred into the front structure to pump up and thus stiffen the front wing. It would certainly alter the spring properties of the front wing structure. When DRS is open drag is reduced by flexing when closed the front wing is stiffer and can transfer more downforce onto the chassis. The excessive rocking is still an inefficiency of the system and unwanted.
Here is a simple theory for the on-off nature of the flutter. Basically, the DRS opens, reduces rear downforce, increases rake, makes the front wing closer to the ground, increasing the aero loading of the wing (Ferrari now knows this increase has some undesirable side-effects – flutter).
Then DRS snaps closed and while the speed is reduced and over-all aero performance goes down, the aero balance still does shift rearward, reducing rake, lifting the front wing, and eliminating the flutter.
You might think that dive under braking would have a similar effect, but dive is likely engineered out of the car with suspension geometry, and anyhow with the lower speeds there is less aero potential.
Regarding, “…my limited knowledge does suggest that carbon fibre structures are relatively well damped, compared to say a metal structure.”
This is correct. If not in all cases, it is certainly possible given various construction options. A real world example is that many road bicycles (including mine) have an aluminum/aluminium frame (fairly light but less expensive than CF), but the front forks, the handlebar stem, and the seat post are carbon fiber/fibre to reduce vibration. Came that way from the factory.
I watched the replay many times in slow motion, and one thing I noticed is that the wing ends moved in opposition to each other. When one moved up, the other was going down, and vice versa. The center section appeared rigid and immovable, so I wonder by what method the wings were moving in sympathy with each other. Is it because the attachment is like a teeter totter, or is it that the loads are being passed back and forth as a result of the properties of the wing construction and materials? Aerolastic tailoring is relatively new to Formula one, and I wonder just how that front wing is constructed.
I do not know how does it work but the thing is it works (at least the Red Bull system). The regulation says that any specific part of the car influencing its aerodynamic performance must remain immobile in relation to the sprung part of the car. The problem is the same regulation allows certain flexibility, and measurements are made when the car is stationary. Do you think it is possible another kind of test (by changing the regulation, of course)? Which one? In my opinion if we are not able to measure this flexibility we should forget all about the current limits (sorry for my bad English, I am Spanish but I hope you will be able to understand)
What is the total downforce created by the front wing?
I think I’ve heard claims that F1 car can travel on the roof of a tunnel above 200km/h, which means total of ~600kg of downforce. The speed at which this flutter occurred was above 300km/h. Is it possible that the front wing generates a lot more than 200kg of downforce at that speed and hence flexes a lot more than in the tests?
I’m not surprised that the flutter stops very quickly under braking, with a deceleration of 40-50m/s^2.
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