Rear Wing Vibrations

Here are our CFD links and discussions about aerodynamics, suspension, driver safety and tyres. Please stick to F1 on this forum.
thepowerofnone
thepowerofnone
23
Joined: Wed Apr 24, 2013 4:21 pm

Re: Rear Wing Vibrations

Post

flyboy2160 wrote:I was thinking about the airflow in yaw vis a vis the endplates. That is, a big yawing direction could make them bluff/stall in that direction. But the more I think about it, the less likely that seems.

Flyboy Steve
The more I think about this the less I think its caused by aero effects, regardless of whether its intentional or not. The footage of the Williams pitting proves for me that 1) there is a non aero related source of significant vibration because that car isn't travelling fast enough to have significant aero forces and 2) the rear wing oscillates readily without much input. Another argument against aero causes is that the frequency with which the vortex sheet shed is a function of velocity, so you would expect the natural frequency to be hit for only a portion of your trip down the straight, not the whole way. The yaw idea occurred to me too but I pretty much ruled that out on the basis that this effect is most pronounced when the car is travelling in a straight line then braking. I think a lot of us like discussing aero so we are just jumping to it like aero engineers rather than vehicle dynamicists.

Which leads me to my latest theory (I know I've had many, I speak too soon without thinking any of them through it seems, I'll probably be throwing this theory out in the next few hours): this seems to occur most under braking, especially heavy braking, which got me thinking how can you get a vibration that big from a mechanical component - my guess is the way the energy recovery systems work this year the flywheels are pretty big and have a fair bit of inertia, as well as having a huge non-axisymetric fitting on the end. From a packaging perspective I imagine they aren't perfectly centred in the car and it would also explain why this year the vibrations are so significant.

flyboy2160
flyboy2160
101
Joined: Mon Apr 25, 2011 4:05 pm

Re: Rear Wing Vibrations

Post

thepowerofnone wrote:..... CFRP isn't meant to flex at all a lot and some delimitation probably occurred.....
Aerospace/F1 carbon fibers have much lower strains to failure (essentially the % they stretch before failing) than typical aerospace/F1 metals, but they do still have a range through which they flex before breaking.

https://www.youtube.com/watch?v=sA9Kato1CxA

https://www.youtube.com/watch?v=M6Kd9zJEucM

These fibers don't all have the same stiffness. Typically, the stiffer the fiber, the lower the strain to failure. I wouldn't be surprised if the F1 teams are using very stiff fibers for the endplates to minimize the types of deflections we just saw. But they still have some working flex to them.

User avatar
flynfrog
Moderator
Joined: Thu Mar 23, 2006 9:31 pm

Re: Rear Wing Vibrations

Post

On a mildly related note. When I was working flight line the flutter test envelope might have been the craziest test we did. You outfit the plane with exciter motors basically a motor with an offset shaft and weight. Get the plane to max Alt. Put it into a dive max out air speed all with the exciters doing sine sweeps trying to put the wing into a flutter mode. The test pilots earned their pay that day.

thepowerofnone
thepowerofnone
23
Joined: Wed Apr 24, 2013 4:21 pm

Re: Rear Wing Vibrations

Post

flynfrog wrote:On a mildly related note. When I was working flight line the flutter test envelope might have been the craziest test we did. You outfit the plane with exciter motors basically a motor with an offset shaft and weight. Get the plane to max Alt. Put it into a dive max out air speed all with the exciters doing sine sweeps trying to put the wing into a flutter mode. The test pilots earned their pay that day.
That's pretty awesome. I've seen videos of those tests on YouTube with the pilots wearing parachutes, you can sorta understand why. I assume at the bottom of the dive you pull up hard and try to encourage buffet?

flyboy2160
flyboy2160
101
Joined: Mon Apr 25, 2011 4:05 pm

Re: Rear Wing Vibrations

Post

thepowerofnone wrote:.....
Which leads me to my latest theory (I know I've had many, I speak too soon without thinking any of them through it seems, I'll probably be throwing this theory out in the next few hours): this seems to occur most under braking, especially heavy braking, which got me thinking how can you get a vibration that big from a mechanical component - my guess is the way the energy recovery systems work this year the flywheels are pretty big and have a fair bit of inertia, as well as having a huge non-axisymetric fitting on the end. From a packaging perspective I imagine they aren't perfectly centred in the car and it would also explain why this year the vibrations are so significant.
NONONONONO - don't throw out this original hypothesis just yet. If the MGU thingies are rotating along a longitudinal axis, won't a change in that direction induce a torque 90 degrees to that change - just like the side to side motion we're seeing. I'm going to have to twist my thumbs around to check the Right Hand Precession rule. It will be easier after a beer or 2......

Just_a_fan
Just_a_fan
726
Joined: Sun Jan 31, 2010 7:37 pm

Re: Rear Wing Vibrations

Post

thepowerofnone wrote: this seems to occur most under braking, especially heavy braking, which got me thinking how can you get a vibration that big from a mechanical component
Uneven road surface, poorly damped tyre under load at one end, poorly damped tyre under less load at the other end thanks to "weight transfer". By poorly damped tyre I mean that it relies solely on its own inherent damping properties rather than the dampers within the sprung part of the suspension system.

I think the principal exciter for the rear wing endplate flex is the road surface. If it was part of the car's mechanical package then it would be exhibited all the time to some degree. If it was aero then it would occur every time that aero situation occurred. That it occurs under heavy braking in one location suggests that is the cause.

Occam's razor and all that...
Turbo says "Dumpster sounds so much more classy. It's the diamond of the cesspools." oh, and "The Dutch fans are drunk. Maybe"

thepowerofnone
thepowerofnone
23
Joined: Wed Apr 24, 2013 4:21 pm

Re: Rear Wing Vibrations

Post

Just_a_fan wrote:
thepowerofnone wrote: this seems to occur most under braking, especially heavy braking, which got me thinking how can you get a vibration that big from a mechanical component
Uneven road surface, poorly damped tyre under load at one end, poorly damped tyre under less load at the other end thanks to "weight transfer". By poorly damped tyre I mean that it relies solely on its own inherent damping properties rather than the dampers within the sprung part of the suspension system.

I think the principal exciter for the rear wing endplate flex is the road surface. If it was part of the car's mechanical package then it would be exhibited all the time to some degree. If it was aero then it would occur every time that aero situation occurred. That it occurs under heavy braking in one location suggests that is the cause.

Occam's razor and all that...
You're probably right, and it wouldn't surprise me if road surface were a large part of it, but if you watch zork's videos from Melbourne you can see the Williams rear wing oscillating when the car is stationary and off the ground during a pit stop. That alone doesn't say a lot because when stationary the engine will rock the car a bit when just ticking over, but when we exits the pits there is significant vibration there too. Those pit lanes are almost always perfectly graded, its not like its a complex piece of tarmac to lay, unlike a corner, and I can well imagine its important to use the engine to recharge the ERS as you exit the pits - you have to discharge it for the mechanics to work on it so it would be desirable to recharge it when your speed is limited and your engine isn't being stretched.

Anyway, yeah, you're almost certainly right, I am probably just seeing something that isn't really there.