Michael Benno

This weekend I replaced the rear wing on my car with one from the salvage yard. My rear wing was drilled for mounting a removable Gurney Flap. Which looks pretty cool with big P O R S C H E lettering across the back but sadly I am not brave enough to drive around town with that on the car, especially now that the roll bar has been removed.

Anyway, the replacement wing was from an early 87 model and has the flip up feature, which I didn't think I cared for. Upon mounting, I noticed what looked like an angle adjustment so one can raise or lower the trailing edge of the wing presumable to influence downforce, or possibly tidy up the looks when messing with front/rear ride height.

Am I correct with this? I didn't see any mention of this in the archives.


Here is a shot of the wing lifted. Left side of the photo is the rear of the car.

Benno
1988 928 S4 5spd

Michael Benno

I found a thread that explained it pretty throughly so never mind :-)

Speedtoys

Can you let us in on the secret thread?

Hilton

Its not for angle adjustment - just for adjusting the lock mechanism to take up any play and stopit rattling

PHIL928

The wing doesn't generate any downforce, it's merely a spoiler to reduce drag and reduce lift to some extent.

Hilton

It must produce some - it reliably closes itself at around 50mph if you don't latch the flip-up one down properly.. With a large "clunk"

GUMBALL

Isn't "reducing lift" and "providing downforce" the same thing? Either way, the wing DOES function.

Speedtoys

Wings on planes are simply anti-gravity devices too.

OR..to some extent the wing provides downforce.

PHIL928

A wing generates a force in either direction, whether lift force (airplane) in the upwards direction, or down force (race car wing) in the downwards direction, relative to gravity.
A spoiler disrupts the airflow from laminar flow to turbulent flow. The turbulent air is better able to fill the void of negative relative pressure behind a vehicle that is generated at higher velocities. In other words it allows the air to bend behind the car to fill in the area of vacuum.
This void of negative relative pressure literally sucks the car back, which is another way of saying drag force. There is also a similar void of negative relative pressure above the rear hatch, but much, much smaller which causes a tiny amount of lift.

If you would like to form a more grounded understanding of vehicle aerodynamics, there is a great book by Hucho on this subject. ( Titled: Aerodynamics of road vehicles)

stuartbrs

Spot on Hilton! It scares the crap out of me whenever it goes THUNK because I haven't latched it down properly!

Michael Benno

So upon further review and inspection of this mechanism, I can conclude that the adjustment on the rear wing latch mechanism does not impact the angle of the wing. In the down position the wing ALWAYS rests flush to the rear hatch.

Adjusting the position of the release block does not impact the wing angle. The adjustment of the release block impacts the gap between the the down rest position and the contact to the release block.

On inside of the wing there is a nub that acts in two ways. It catches on the release block on the down position to prevent lifting. The nub is rounded so excess force pushes the spring loaded block out of the way. In the up position the nub on the wing pushed the release block out of the way so it can be put in down and locked position.

Popoboy944

any chance you can share the thread on the rattling? Would like to try to fix on my 87.

Hilton

My comment came from experience - not a thread. Its pretty easy - if there's play in the wing, you can loosen the little screw on the back side (see above picture), and then the recangular block with the rounded edges can be moved down to remove slack, or up if the wing isn't quite catching and holding down, and hence rattles on the outside of the mechanism. The block has serrated teeth on the back side of it. Move it a couple of teeth in the desired direction, tighten the screw, and done

Popoboy944

thanks! i took a quick look, and see what you mean, but i think i may attempt a different kind of fix. the black part of the wing had been rubbing on the paint already, making some nasty marks and low spots in it. maybe this is the source of the loosness? i plan on putting a piece of helicopter tape (the stuff clearmask uses for their clear paint protection film there. its the right thickness to take up the looseness, i already tested with some painters tape. hopefully that will protect the paint and keep the adjustment in the wing correct for the long term. will put a couple posts here once i get it done.

Adamant1971

You are missing the PP film that should go between the bracket and the hatch. That may stop your rubbing as the latch will be slightly raised from the surface of the hatch.