Hood splitter for my vw

[bestclimb]

Originally Posted by BamZipPow

From a safety aspect...don't do that. There are specific safety catches on the fenders that are there to prevent the hood from flying over the vehicle in a front end collision.

Yer better off building it up from foam/Coroplast sheeting...

Not over the vehicle but through the head/neck area of the passenger compartment.

Originally Posted by Christ

That's not really a deflector... The hood just happens to cover up the wipers in the parked position.

That may be most of what a window deflector does, is puts a draggy item (the wipers) under a fairer surface.

[Varn]

I would invite others to make a hood splitter like I did and check your mileage. Imagine your vehicle from the top down rather than just from the side. My design was not intended to cover the wipers. Using coroplast is a very crude way of testing. I am going to make one that blends into the hood next.

Here is my trike at speed, it has the same canopy as my varna.


Ever stick your fingers out the window and feel the air flow at the surface of the roof line your car. At the windshield the air is strong right at the surface. As you drift your fingers back a foot or two back from the windshield top; you can feel the major flow move outward a couple of inches. Anything we do to help keep the flow attached is going to make the car go through the air better.

If you want to prove this wrong then start recording your mileage and doing your own testing.

[Christ]

Originally Posted by bestclimb

Not over the vehicle but through the head/neck area of the passenger compartment.

No, they actually place the trailing edge of the hood at just above the dash... In line with your head. They're there to ensure that the hood crumples, rather than just disconnecting at the chassis and becoming a projectile.

[bestclimb]

Originally Posted by Christ

No, they actually place the trailing edge of the hood at just above the dash... In line with your head. They're there to ensure that the hood crumples, rather than just disconnecting at the chassis and becoming a projectile.

Yea to keep it there rather than flying off, or coming straight back. I have looked at mine several times, and that's the best I can come up with. Departing the vehicle is not much of a concern, departing and impinging into the occupants that's worth the engineering effort to put hooks on the hood.

[Frank Lee]

I can't tell enough from the Camaro pic to comment on it, but that region is known to not have high attached flow.

By all means, let's see some rigorous testing, and by that I mean, testing that lasts further than half a tank, is repeatable, and is accurate. Or, let's see data from the pros; either one will do.

[winkosmosis]

Originally Posted by Frank Lee

I can't tell enough from the Camaro pic to comment on it, but that region is known to not have high attached flow.

By all means, let's see some rigorous testing, and by that I mean, testing that lasts further than half a tank, is repeatable, and is accurate. Or, let's see data from the pros; either one will do.

Well of course it's not known to have attached flow-- because on most vehicles it's a sharp transition, so a bubble of air forms there.

This truck didn't have attached flow from the front to the sides until NASA put curved fairings on it

[Frank Lee]

Those are two different situations. Completely different.

So I'd wager hood blisters don't really affect the flow upstream and downstream... so then what?

[winkosmosis]

I can't find any better pics of the Camaro hood and windshield.

[winkosmosis]

Originally Posted by Frank Lee

Those are two different situations. Completely different.

So I'd wager hood blisters don't really affect the flow upstream and downstream... so then what?

Well the blister looks too narrow, but I think a gradual transition between the hood and the windshield would obviously allow air to flow smoothly and stay attached, rather than forming a high pressure bubble. I've seen people on this forum say that the bubble means aerodynamics in that spot don't matter, but it seems to me that it's the opposite.

Look the Aptera, Prius, and other aerodynamic cars. The hood is almost the same angle as the windshield so there probably is smooth continuous flow. The question how close to the same angle ideal you can get with a fairing that doesn't connect to the windshield.

Making the transition gradual with a curve has to help. It takes energy to force air to change direction, but less energy if you direct it gradually. Just look at intake pipes, sewage pipes, etc etc... Gradual curves, not right angle elbows.

[Frank Lee]

Look at any wind tunnel image with the smoke trails... they sure look to be arcing smoothly up at the hood/windshield to me...