OT ... but may be of interest to those interested in detailed information concerning aeroelasticity.
Probably we have all read about the NASA F-18 testing aeroelastic wing geometry in 2001: http://www.nasa.gov/centers/dryden/news ... -DFRC.html
Smokes wrote: I also cannot think of any examples of aero/hydro elastical bodys in nature apart from the flying squirrel. .
A gale blows through a forest. A leaf on a tree is blown into a new position, reducing the drag on the tree. Aerolastic
A jellyfish pulses its umbrella to move forward. It then relaxes, the umbrella collapses, reducing the drag on the jellyfish. Hydrolastic.
If you definition of XXXolastic is that a structure is deformed elastically by an impinging fluid and moves in such a way as to usefully modify the forces it sees, then I think it is actually quite common, bird's feathers being the most common example.
Good point. Mother nature have the tendency to use 'soft' approach for large creatures. The features on bird's wings are beautiful in design, very clever and efficient at the same time.
Small creatures like bees, fly uses hard shell because of their size. Aero-elasticity is not so much used there.
I thought birds could control their feathers in flight? therefor not completly passive.
And jelly fish have to move there body back using a electrical energy hence not Aero elastic. more like Aero plastic.
tree leaves yes.
Incidentally, & more or less on topic, I guess that RBR's "flexi" front wing would be an example low energy consumption, whilst Ferrari's attempted copy would be an example of high energy consumption, & presumably high drag. (In RBR's case, the front wing was on its way to "Divergence", whilst Ferrari's front wing "Fluttered", drawing it's energy directly from the airflow).
Edit: in classical aerolasticity, the difference between the two would be the position of the centre of mass relative to the elastic centre - wing mounted engines are located ahead of the wings in passenger aircraft to avoid wing bending-torsion flutter.
IIRC Massa's car wasn't any slower because of the fluttering wing. Maybe that effect is desidrable, but instead of flapping the wing rocks back and forth in a similar frequency.
I still think all the fast teams will have flapping wings in common, just like Red Bull. There is absolutely zero evidence that flapping reduces lift. The fact that every flying animal must flap or vibrate their wings to get off the ground suggests quite the contrary. They can tune the CF so that the wing rotates on the hinge of the mounting pylons, this rocking can be triggered by the car moving, going over bumps etc. I remember reading a recent paper on the subject and in fact flapping wings tend to generate more stable vortecies, which would be especially helpful to the wing seeing as how the tire can very easily disrupt the FW vortecies.
Similarly there are no real rigidity rules for the rear wing endplates, so if parts of the endplates were allowed to flex and vibrate under aero load, like where the area by the main plane where the cheese graters are.
According to this article if you could make the rear diffuser flap then theoretically you should be able to run a more aggressive diffuser ramp, seeing as how a flapping motion makes angles of attack over 45 degrees less prone to stalling.
Your argument is convincing, godlameroso, and your reference is very interesting. The abstract mentions a Reynolds Number of around 2000. Do you think the conclusions would still be valid if the experiment was scaled up by, perhaps, 500?
I have yet to see RBR's front wing flutter, by the way.
What I see is the front wing apparently pitching, more or less as a rigid body about a horizontal axis located close to the lower edge of the end plate and roughly 50 percent aft of its leading edge. The nose camera mounts appear to be moving in phase with the motion, suggesting that it is the nose box that is allowing the motion. The under-tray appears to be relatively stable. I also see the rear tyre deflecting laterally, again more or less in phase with the front wing - possibly caused by the tyre stick-slipping over the kerbs.
It is difficult to see how that motion can be explained without a significant compliance, as you suggest - but of the nose box?
Which leads me to ask, do you have any other similar clips?
...led me to believe Red Bull might have used the bendy nose in conjunction with the front wing as a mass damper similar to Renault's 2005-06 proper tuned mass damper. You see all sorts of oscillation on the other cars' tires, but not nearly as much on the Red Bull.
Last edited by bhall on 07 Dec 2012, 23:51, edited 1 time in total.
If you notice in the slow motion shots you can see that there is horizontal as well as longitudinal flapping, unfortunately due to regulations it seems RB can only induce the longitudinal flapping
Here you can see the vortecies forming under the beetle wings and how the longitudinal flapping seems to add more energy to the natural vortex generated by the horizontal flapping.
Thanks to both bhallg2k & godlameroso for interesting contributions.
It is a characteristic of classical aeroelastic "flutter" and "divergence" that the effect increases with airspeed. Both have a "critical" airspeed, below which they are stable, and above which they are increasingly unstable. It follows that an effect that is visible at low airspeeds and not catastrophic at higher speed is probably not flutter or divergence.
The clip of Massa's Ferrari I referenced earlier, showing a violent instability at the start of a braking manoeuvre, decreasing, and finally disappearing, as he shed airspeed would be a good candidate for flutter. On the other hand, the RBR clip you included, godlameroso, whilst it was very interesting in several ways, was probably not flutter, in my view (more a forced oscillation caused by the kerbs, I thought).
I have sympathy for your conclusions, bhallg2k, and you may very well be correct. However, bearing in mind that a mass damper is a "tuned" device, is difficult to make work reliably (think about Ferraris failed attempt which ultimately caused the device to be banned), and it works most efficiently with a completely locked front suspension, I suspect that is not the reason for the very obvious compliance. Rather, I think it is just one of many attempts (which have systematically been banned by regulation) to lower the mean running height of the front wing.
Your comments on the effectiveness of the RBR front suspension are well made. It should, perhaps, be observed that they probably have a "decoupled" front suspension, very stiff in "heave", but very soft in "roll", and run a "heave" inerter (which, amongst other things, reduces the effective dynamic spring stiffness).
On the subject of compliance, it would be interesting to know exactly how the FIA performs its front wing "compliance" test. Is it, for example, performed on the car as a whole, or using a fixture to which the nose box is fitted. If on the whole vehicle, exactly how do they measure the compliance of the suspension and tyres.
