wind deflector mods

[twobone]

So I've been on a mission to reduce wind buffetting on my outboard ear.

 

I took the standard caterham wind deflectors and bent them outward.

 

Then I added 4 inch extensions. That helped a bit. It moved the buffeting epicentre back a few inches.

 

I then swapped out the extensions for 6 incvh versions. Interestingly that did not make a difference. I would have thought that it would move the wind epicentre back further. Now I'm wondering if the source is more the top corner of the windscreen.

 

Perhaps there is a vortex at that point that is unaffected by the size of the wind deflector.

 

I would prefer to run without a half hood.

 

I once met a guy who had a device that directed air from the toip of the screen down into the cabin. He said that this negated the negative pressure wave within the cabin.

 

Anyways, the modification experiment continues.

 

 

Ideas?

[Croc]

Sounds complicated. I just took my standard wind deflectors and shoved them into a big pot of boiling water on my stove. I heated up the perspex this way and gradually made the curved end even more sharply curved.

 

This makes the wind deflector stand out more perpendicular from the body. The boiling water did make me lose my silicone bumper but I just stuck another on.

 

This modification shifted the buffet point backwards from my face to beyond my ear and makes it more comfortable for running without half hood or doors. Adding the half doors to this improved things further.

[drew...]

I have always thought that the cause of the buffeting around the outer ear (drivers or passengers) was actually the air flow over the rear fender. That's why the half door can make such a difference. What would happen if you started moving the air over the rear fender with the use of something like the carbon fiber wickers that are used on the nose cone, locate it about even with where the lower frame changes from angled to parallel / straight?

[coffee break]

Has anyone had any luck with adding a clear panel across the roolbar?

[breezy7]

No experience with it but Soft Bits for 7s makes a rollbar wind deflector. http://www.softbitsshop.co.uk/the-draft-reducer-10-c.asp

I have a wind deflector in my Miata that does help, it is a solid piece but similar idea to what Soft Bits is doing.

Mike

[scannon]

Has anyone had any luck with adding a clear panel across the roolbar?

I made a test version out of press board and it made no difference at all.

 

Has anyone followed up on the theory someone proposed about cutting a 4" hole in the center of the windscreen to negate the low pressure area that forms in the cockpit? I plan on replacing my windshield after the GBB so maybe I will try cutting that hole at that time.

[timax]

I made a test version out of press board and it made no difference at all.

 

Has anyone followed up on the theory someone proposed about cutting a 4" hole in the center of the windscreen to negate the low pressure area that forms in the cockpit? I plan on replacing my windshield after the GBB so maybe I will try cutting that hole at that time.

 

 

I have read a fair bit about that.Good thread about it here..

http://http://www.hdtalking.com/general_harley_davidson_topic/37241-holes_in_windshield_for_buffeting.html

 

Also interesting section on aerodynamics here.

 

http://http://www.calsci.com/motorcycleinfo/Fairing.html#Windshield

 

I made my own defectors a put a little reverse flick on the outer edge to try and "flick" the air out a bit more. The info on Von Karman vortices explains why my idea didnt work.

[slomove]

I agree with Skip on the panel across the roll bar. I tried that, too without much if any difference.

 

It is actually pretty easy to see with a few threads of wool on a stick what is happening in various places. Mostly it is the accelerated air stream up and over the windshield that creates a slight vacuum in the cockpit area. With the open "doors" of the Seven, the air rushes into this vacuum from the sides, and since the side and top edge of the windscreen are a bit abrupt, the whole area is full of vortices and swirls. As we all know such swirls can occasionally grab some exhaust from the rear and get back into the cockpit. When a passenger with long hair rides along, I can see the hair flowing forward sometimes.

 

The proven methods are AFAIK

 

- side screens (does not allow air to rush in from the side but is too claustrophobic for me)

- Brooklands or aeroscreens (avoid or minimize the vacuum bubble and keep the air stream laminar but lacks some rock protection)

- large wind deflectors or half doors (will not completely eliminate the buffeting but move the turbulence backward behind the face)

- hood or Bimini top (I noticed some improvement when used by itself but better with half doors)

 

I don't think it has much to do with the rear fenders. However, I did not try to drive without them. The 4" hole may help but I can not imagine it to solve the problem. After all I am quite happy with my slanted half doors.

Edited June 3, 2013 by slomove

[IDreamOfChapman]

with respect to the ear discomfort - I found that my wind deflectors simply moved the turbulence so that it hit me directly in the ear (not comfortable) no matter what I did. So I removed them completely - this moved the turbulence significantly forward. So, it is still turbulent, but my ear is much more comfortable.

[Dave W]

If you are considering a rear wind deflector, it should not be a solid panel across the back between the roll bar tubes. I had tried that several years ago and it really did not help. Since then I've installed a rear window for colder weather. The window has a sliding center section, and what I found is that with the center section opened about 3 or 4" it does an excellent job of cutting down the buffeting, because the center area has a high vacuum area with a constant draw to the low pressure area behind the window. So if you go that route, design the panel to have an adjusting section or plan on using a hole saw to get enough open space to bleed off the air in the cockpit. Also the side wind deflectors seem to work best for me when adjust to about a 40* angle to the windshield. Dave W

[rx7locost]

It would seem that there is no "silver bullet" for wind buffeting in a Seven. Some problems have been identified due to the distance of driver to windscreen (worse on a Locost) One builder actually moved the windshield closer to the driver with success. Others find that 1/2 doors help. Myself, a hardtop helped but did not eliminate it. I'm in the process of adding 1/2 doors. But twobone prefers no top, and I assume that that also means no doors. With all the minor variations in cars, it seems that any change might be successful on one car but not on another.

 

For a visual idea of what we are up against, there is an old thread on the LocostUSA site where CFD analysis was done on the Locost. It should look similar for most makes of sevens. http://www.locostusa.com/forums/viewtopic.php?f=23&t=13379

[Dave W]

Chuck

I think you will find that the half doors will cut down the buffeting just as much as the your new top, plus you will be bring home a lot less stones in the cockpit. My half doors are on 90% of the time. Dave W