Help designing a wind fairing for roof rack

[Arv]

IMHO a full height wind fairing is often unnecessary (but not always since they do have their applications). Don’t shoot me! :ak472: It’s just my take on this and hence this thread to find out what people have on their roofs and their experience with their wind fairing. My Whitson full rack is going to be delivered soon and I’m thinking a shorter fairing that hugs the roof and just goes past the lower front bar should suffice. The question is the angle, distance from the rack, and height. The fairing will be curved to match the top of the windshield/roof line so it will be pushed out more in the middle which should also push some air to the sides.

Ok, so just imagine splashing water from a hose on a flat surface like a plate. At low water pressure, the water will just flow and drip over the edges of the plate. As you increase the water pressure the water starts to stream away from the edge of the plate before dropping off. I’m thinking this should be the same case with a wind deflector, as your speed increases the wind will be pushed way past the top of the wind fairing that it does not have to be the same height as the roof rack. Hopefully at highway speeds 65mph the shorter wind fairing at the proper angle and distance from the rack will push the air high enough that it clears the top of the rack and over to the back.

If you have something tall (12” +) on your roof rack all/most of the time. Then a full fairing might be ideal but most of the time that roof rack will be empty and the objective is to eliminate wind noise and reduce drag while the rack is empty and get decent performance when the rack is loaded.

Remember the bigger the wind fairing the more drag it creates on its own.

Plus you can always run roof lights and the short fairing will block reflections off your hood.

Maybe even have 2 fairings? One for daily use when the rack is empty and one for full loads. I’m going to have to install the sunroof insert for camping trips so what’s a few more screws to replace the wind fairing.

The challenge here (apart from finding the right setup) is that the roof rack sits so close to the roof that you might not have enough height between the roof and just above the lower front bar to put a decent fairing.

Please let me know what you think, what you have, and did you try other setups before settling with what you have. Any aerodynamicists out there?

Sorry no pics mounted on my rig as I don’t have the rack yet, but there’s a ton of pics on this thread. http://www.toyota-4runner.org/3rd-gen-t4rs/120808-roof-rack-special-august.html

Thx!
Arv

 

[Arv]

70+ views - cool!
No replies - not so cool.

Does anyone have one of those Yakima, Gobi, etc... wind fairings that sit pretty low? Does it help? Works well?

 

[WastedAccount]

I made this one for my Whitson rack. It cut down wind noise a lot.

 

[4-Ripcord]

I dont really understand what you are asking here, but I have the yakima fairing. I never have anything on my roof except for snowboards in the winter in the snowboard holder.

So all my fairing does is create drag, lol.

 

[Arv]

I made this one for my Whitson rack. It cut down wind noise a lot.

Wasted,
What I'm thinking is a wind fairing that goes up maybe up to your lower fairing hardware. So its just slightly above the lower front bar. It wont be attached directly to the rack but it will be held in place by brackets that would also push it out to curve and match the windshield shape. I really didn't want to go the full height fairing route as it creates too much drag on its own.

Just a thought, maybe if you eliminated (or reduced significantly) the wind that goes under the fairing and rack that it will reduce noise more. I think a lot of air makes it under your fairing and through all the bars and mesh thats makes that extra noise. OR maybe the windshield pushes the air past that gap between the fairing and roof so the gap is really not an issue.

Favor, I'll understand if you're not up to it and I know it'll look ugly but can you pust some duct tape to seal that gap between the fairing and roof then drive on the freeway to see if it helps?
Thanks!
Arv

 

[Arv]

I dont really understand what you are asking here, but I have the yakima fairing. I never have anything on my roof except for snowboards in the winter in the snowboard holder.

So all my fairing does is create drag, lol.

Ripcord,
What I'm asking basically is what people have as wind fairings. Either full height or a short ones like what Yakima and Thule sells for peeps who have towers and crossbars.

So how's the wind noise without the fairing compared to with it on? Is yours one of those where you can adjust the angle? I bet at the right angle yours should do its job for your app. If you think yours creates drag, imagine how much a taller fairing creates.

 

[Arv]

I made this one for my Whitson rack. It cut down wind noise a lot.

BTW, thanks for posting all those pics and walk around video. That helped a lot in making my decision in purchasing the rack!

 

[WastedAccount]

Glad my pics and walk around helped. I won't be duct taping the fairing though, I drive 90 miles on the freeway several times a week and I'm quite pleased with how the fairing works now. Before I put it up there the rack was noisy. It hasn't given me back any gas mileage though. If I do anything, I'll be making a slightly shorter on since this one is BIG up there. I also mis-measured and it's 1/2 inch to wide. The material I have is brittle so it sucks to work with and I"m not to excited about making another right now. A lot of work went into shaping that one.

 

[Arv]

How much drop in mileage did you get? How fast do you normally drive on the FW?
So you think its BIG eh? Same here that's why I'm trying to figure out how to get away with a shorter fairing.

 

[fish0281]

A fairing works more like a bridge abutment in a flowing river than a hose hitting a flat surface. It creates a high pressure zone (read: stagnation pressure) and thereby re-directing the "upstream" flow around it. If you really want to get all sciency, you'd have to create a fluid model. If your fairing only went up to the lower bar (which would be a pretty small fairing), it would basically only direct the flow up over the first bar.

Wind noise is a result of turbulent flow. The purpose of a fairing is to try and maintain laminar flow over the vehicle (that high pressure "bubble" that deflects oncoming air over any turbulence-inducing objects). With that in mind, your mini-fairing idea doesn't seem to me like it'd keep the "moving" air from passing through the latter portion of the rack. Considering that the rack has that wire mesh stuff (definitely would cause turbulence), I'd think the best way to reduce wind noise would be with a fairing more similar to Wasted's.

You could also fill the front with lights... ;-)

 

[Arv]

A fairing works more like a bridge abutment in a flowing river than a hose hitting a flat surface. It creates a high pressure zone (read: stagnation pressure) and thereby re-directing the "upstream" flow around it. If you really want to get all sciency, you'd have to create a fluid model. If your fairing only went up to the lower bar (which would be a pretty small fairing), it would basically only direct the flow up over the first bar.

Wind noise is a result of turbulent flow. The purpose of a fairing is to try and maintain laminar flow over the vehicle (that high pressure "bubble" that deflects oncoming air over any turbulence-inducing objects). With that in mind, your mini-fairing idea doesn't seem to me like it'd keep the "moving" air from passing through the latter portion of the rack. Considering that the rack has that wire mesh stuff (definitely would cause turbulence), I'd think the best way to reduce wind noise would be with a fairing more similar to Wasted's.

You could also fill the front with lights... ;-)

A full fairing is definitely the standard or normal way of addressing this issue but I really want to avoid it if I can becuase of 2 things. 1 - creates to much drag on its own, 2 - its HUGE! I really think and hopefully I am right that a properly setup shorter fairing would do the trick (height, angle, distance from front of rack) otherwise I'll end up with a full fairing or like you said filling up the front with lights! LOL!

 

[Arv]

Fish,
About the full fairing creating too much drag, I think its evident in Wasted's fuel mileage. Sure the fairing reduced wind noise but it also creates too much drag. That's why I think he didn't gain any fuel mileage after installing the full fairing. I don't have the tools or enough info to make a definite conclusion plus I've never had a fairing on any of my vehicles.

 

[fish0281]

What I was saying is this: I don't think you'll get the desired affect from the fairing unless it's at least half-way up the face of that rack. The deflected flow length will have some relationship to effective height (height perpendicular to the flow) and flow speed... since the rack is pretty long, you're going to need a tall fairing.

I don't think you'd get noticeable drag (i.e., fuel loss) from the fairing even if it were perpendicular to the flow and full height. Also, unless you plan on driving about 100 mph, anything less than 45* isn't going to cut it either.

Not sure a mini-fairing would look all that cool either, but beauty is subjective!

 

[fish0281]

Fish,
About the full fairing creating too much drag, I think its evident in Wasted's fuel mileage. Sure the fairing reduced wind noise but it also creates too much drag. That's why I think he didn't gain any fuel mileage after installing the full fairing. I don't have the tools or enough info to make a definite conclusion plus I've never had a fairing on any of my vehicles.

From what Wasted said, it sounds like the fairing didn't change his fuel mileage, the rack did. That being said, I think you're either going to battle drag from the fairing or the rack itself...

I'll say that my fairing, same as 4Ripcord's, didn't affect my mileage at all. It's about 6" tall (effectively) and I am not sure what it will do to help when I have snowboards up there... I mostly got it hoping it'll help keep the road grime off my snowboard and cause it looks cool. :bluejump:

 

[Arv]

What I was saying is this: I don't think you'll get the desired affect from the fairing unless it's at least half-way up the face of that rack. The deflected flow length will have some relationship to effective height (height perpendicular to the flow) and flow speed... since the rack is pretty long, you're going to need a tall fairing.

Yes, very true and that is why the height and angle of the short fairing are two critical things. You might be able to achieve the same thing with a 4" fairing set at lets say 60 degrees from horizontal compared to a 6" fairing set at 30 degrees.

 

[Arv]

From what Wasted said, it sounds like the fairing didn't change his fuel mileage, the rack did. That being said, I think you're either going to battle drag from the fairing or the rack itself...

I'll say that my fairing, same as 4Ripcord's, didn't affect my mileage at all. It's about 6" tall (effectively) and I am not sure what it will do to help when I have snowboards up there... I mostly got it hoping it'll help keep the road grime off my snowboard and cause it looks cool. :bluejump:

Looking cool is definitely on top of our priority list!
Good to know that your fairing didn't affect your mileage.
Oh see i interpreted his post another way, I thought he meant that installing the fairing didn't increase his mileage after the decrease when he installed the roof rack.

 

[Arv]

Fish,
A question for you, so if i did a full fairing BUT leave a gap underneath the rack, so basically the fairing only goes from the top front bar to the lower bar with the gap between the rack and roof open, do you think a lot of air will go under the rack the cause turbulence on the crossbars and mesh flooring? OR would the windshield push the air past the gap so little or no air will go through that gap?

 

[fish0281]

I think this would be a good baseline, considering the rack geometry similarity and that Gobi probably invested some* amount of time/energy into optimization.


*considering the cost of those things, they better have!

 

[fish0281]

Fish,
A question for you, so if i did a full fairing BUT leave a gap underneath the rack, so basically the fairing only goes from the top front bar to the lower bar with the gap between the rack and roof open, do you think a lot of air will go under the rack the cause turbulence on the crossbars and mesh flooring? OR would the windshield push the air past the gap so little or no air will go through that gap?

I think the high pressure region created by the fairing and windshield would over-lap, preventing flow from going between the rack and roof... assuming the rack sits pretty close to the roof.

 

[Arv]

I think the high pressure region created by the fairing and windshield would over-lap, preventing flow from going between the rack and roof... assuming the rack sits pretty close to the roof.

Yes, I've seen the G rack fairing. I found that when I was researching on wind fairings since I really didn't want a HUGE fairing on my roof.

The Whitson rack does sit much closer to the roof than the G rack. So if all else fails on a low profile wind fairing I might just have to try a fairing that just covers the front of the rack leaving a gap betw the rack and the roof. Being so close to the roof (not that I'm complaining) also presents the problem of not having enough height to play with. Since the G rack sits higher, their fairing height works out, but with the W rack sitting so low, you'd have to at least go past the lower front bar or even almost half way (hopefully not).

Hey thanks for all your input!