Shakeman wrote:turbof1 wrote:Any ideas how they are able to run that kind of rake? They must have found a method to seal the diffuser without the exhaust.
Do you have to "seal" the diffuser for that amount of rake to be effective?
Gordon Mccabe has a very interesting article about this:
http://mccabism.blogspot.be/2011/08/dif ... -rake.html
Basicilly bigger rake does 2 things: increase the angle of the diffuser, increases downforce, but also increases height, decreases downforce.
Why does downforce decreases under a higher height? The edges of the diffuser generate vortices that energize airflow, sucking air more quickly out of the diffuser and speeding up airflow. These vortices weaken the higher they are above the ground.
There's also an issue with tyre squirt: the tyres inject turbulent low energy in the diffuser. The higher the diffuser is above the ground, the more of this energy gets into the diffuser.
To mitigate that, teams used the highly energized exhaust plume to strengthen the vortice and to seal off the diffuser from the tyre squirt. Imagine this to be the equivalent of stretching the edges of the diffuser back down to near the ground. The latter is Illegal to do so, but the former is a nice workaround for that.
Seemingly, mercedes found ways to strengthen the vortices enough without exhaust gasses to run such a rake again. I'm curious though how this will act at low speed, when vortices are weaker and when downforce is needed the most.
