The XV-JP Needs Help, Please, from a Jeep Aerodynamicist. (Really)

[mhiscox]

There are lots of people, and lots of expertise on the Portal, so I'm sure we must have dozens of aerodynamanics experts. Or perhaps at least one.

Here's the problem . . .

Earthroamer built the XV-JPs cabin with an extension that goes over the cab, and then replaced the remaining section of the Wrangler roof with a fiberglass panel. It looks like this from the front:




and like this from the side:

.


The gap between the top of the roof panel over the cockpit and the bottom of the cabin overhang is about an inch and a half.




and there are some front-to-back ridges molded into the fiberglass roof.




So . . . here's the problem: When the truck is headed at 50 mph or more into a quartering wind, or when there is a crosswind, there's occasionally, not always, a loud variable banshee-type howl that sounds as if it's the result of air turbulence right above the roof. Not just buffeting, more of a screechy noise. The noise is not present with a tailwind, dead calm, or when headed straight into the wind (when you just get the basic barndoor-into-the-wind rumble).

So I'm thinking I need to do something to change the flow of the air getting stuck under that overhang. My thought was to stick maybe four heavy rubber strips, about 3/4 inch tall and an inch wide, longitudinally at even intervals on the rooftop. But I've no reason for this strategy, except that it should change something.

If someone out there has an idea to tame the noise that's based on something more efficient than my rank experimentation, I'd be eager to hear it.

 

[Shawn]

A rubber gasket or molded plastic to fill the void.

 

[digitaldelay]

It must be just hitting a resonate frequency under certain conditions, like blowing across a beer bottle opening. You are probably on the right track to just "change something". You may just need something to disrupt the airflow enough to prevent that resonating.

Jason

 

[reece146]

Could also try throwing on some air tabs to keep more of the boundary layer attached for longer.

Are you sure the noise is at the front of the structure and not at the back?

 

[nwoods]

Clearly one thing you do not want to do is fill that gap with anything non flexible. The body of the jeep and fiberglass ER top flex, move, expand and contract at very different rates. You need that separation. But you might try stuffing in a compressible backer rod (made of foam), with some silicone sealant such as DOW 795, and see if that resolves it. The silicone is very flexible, adheres tenaciously, and can be tooled smooth while curing. There is a gray color designed to match clear aluminum that might be close in color to your silver rig. I think you'd want to do all three sides.

 

[Clutch]

Clearly one thing you do not want to do is fill that gap with anything non flexible. The body of the jeep and fiberglass ER top flex, move, expand and contract at very different rates. You need that separation. But you might try stuffing in a compressible backer rod (made of foam), with some silicone sealant such as DOW 795, and see if that resolves it. The silicone is very flexible, adheres tenaciously, and can be tooled smooth while curing. There is a gray color designed to match clear aluminum that might be close in color to your silver rig. I think you'd want to do all three sides.

Or bulb seal, some already have an adhesive backing (don't have to mess with messy silicon), our local PepBoys even sells it.



Backer rod, may deteriorate quicker over time (and does) since it is an open cell foam, I use it on the leading edge of my dash to keep from rattling.
Which reminds me, I need to replace mine, since the AZ heat/sun has destroyed it.

 

[CTD-WAGGY]

you might try covering those lights with 100mph tape as well.

 

[Rexsname]

As an experiment you might try some swimming pool noodles shoved into the space. Shouldn't cost more than a few bucks.....


REX

 

[mhiscox]

Thanks for the ideas, everyone. Much appreciated.

I'd agree that some strategy that (flexibly) filled the void would work, but I was worried that the results might look kinda tacky and homebrewed. Hence my preference for something subtle, and easy to implement to see if I'm on the right track.

My first move, I think, will be to see if I can force a couple of pieces of foam pipe insulation into the gap temporarily as an experiment to see what happens. Could get better, could get worse, but something ought to change. But that might be the easiest way to run some tests until I catch on to what would be a good permanent fix.

Are you sure the noise is at the front of the structure and not at the back?

Seems to me to be mostly at the front, just aft of the windshield header, equally on the left and the right.

 

[bobholthaus]

I do not mean to hijack this thread, but what fog lights are those in the first pic? I'm dying for a better fog light solution for my 2012 JKU. Thanks.

 

[1stDeuce]

I just did a quick search and didn't find what I was looking for, but they make an inflatable boot that's designed to go between the cab of a truck and cabover camper to eliminate exactly what you're talking about. It's thin when it's flat, so you just slide it in, then blow it up. I think the foam, either noodles or just strips would work fine too. You just need to get the air to slow down when it's forced through there.
Good luck!
Chris

 

[mhiscox]

I do not mean to hijack this thread, but what fog lights are those in the first pic? I'm dying for a better fog light solution for my 2012 JKU. Thanks.

Sadly, I'm not going to be much help. The lights where the foglights should go are actually Hella HID projector lamps that go on with the stock high beams. They're really bright and make a big difference.

This strategy, though, means that I no longer have any foglights, and the foglight switch on the stalk does nothing beyond light the panel indicator light. Sorry.

 

[nwoods]

As an experiment you might try some swimming pool noodles shoved into the space. Shouldn't cost more than a few bucks.....


REX

Rex for the win! I love it!
How you been man? Missed you on our recent Mojave trip.

 

[mhiscox]

I just did a quick search and didn't find what I was looking for, but they make an inflatable boot that's designed to go between the cab of a truck and cabover camper to eliminate exactly what you're talking about. It's thin when it's flat, so you just slide it in, then blow it up.

Thanks for getting me thinking in that direction, Chris. Looks like a topic of discussion by truck camper owners, with lots of different ideas. (Even one made with perforated gutter screens.)



I also saw that it's easy to buy an inflatable boot meant to go between the camper and the pickup cab's rear window. They're pretty small, but so is the Jeep's space, so that might be a very simple solution.

Anyway, thanks to all for the help. I'm thinking I best get started trying different stuff.

 

[mtnbike28]

"I also saw that it's easy to buy an inflatable boot meant to go between the camper and the pickup cab's rear window. They're pretty small, but so is the Jeep's space, so that might be a very simple solution."
Be very careful, I read where these scrape the paint off the truck and camper very fast! I would bet the swim noodle would do the same. I like the idea of two bulb seals (one attached to the Jeep roof and one to the camper) and let the rubber parts rub on each other. Clean up if it did work would be easy with Goo Be Gone.