Truck rack " whistle " Advice needed

[tasslehawf]

Gonna build my first truck rack in 2 or 3 weeks (when my pipe bender comes in). My union instructor showed me things to look out for (all the racks on their trucks are all schedule 40 round pipe, round being stronger than rectangle or square stock):

Rule #1: Don't have your bar shorter than the top edge of your front window, sticking out a little is better. If it is exactly above it might be ok, but just a little behined, it'll start to whistle. Funny this thread came up about that! He said the air coming off the windshield hits the pipe and makes it whistle. You could make it higher, but we both agreed it doesn't look nice... He makes all his around 3" above the top point of the cab...
my .02 (pick it apart, but that's what I was told, and that's how I'm going to make my 1st pipe rack)

I think round would make a huge difference and probably gives you more leeway with what you can get away with. If you're doing it square, you probably do have to take it 5" above the cab.

I guess that's why all the commercial racks are round. My rack is square and doesn't extend over the cab, but I can hear the wind noise.

I bet you could still make the vertical support off the bed in sqauare and make the top out of round. Or how about fab'ing a sheet metal form to fit over the front which mimics the shape of one of those car top carriers.

[weldckr]

Gonna build my first truck rack in 2 or 3 weeks (when my pipe bender comes in). My union instructor showed me things to look out for (all the racks on their trucks are all schedule 40 round pipe, round being stronger than rectangle or square stock):

Rule #1: Don't have your bar shorter than the top edge of your front window, sticking out a little is better. If it is exactly above it might be ok, but just a little behined, it'll start to whistle. Funny this thread came up about that! He said the air coming off the windshield hits the pipe and makes it whistle. You could make it higher, but we both agreed it doesn't look nice... He makes all his around 3" above the top point of the cab...
my .02 (pick it apart, but that's what I was told, and that's how I'm going to make my 1st pipe rack)

Bert you are right, we used to build them in the pipe shop that I ran and when we built them as your instructor stated no whitle, but if the guy wanted it back on the cab whistlemania. also some of the units for vans (Weatherguard MFG) had small spoilers with them to stop the whisling but they uasually got tore off the first time a piece of 2" pipe got loaded on the rack.

[scott-n-montana]

Well thanks for all the replies. I will say that it doesn't matter if it is round or square, because I had a rack with a round bar and it did the same thing. I did some more looking into it and learned that if the front bar is disturbing the airflow over the top of the cab then you get the noise or vibration. I might try a piece of angle on the front bar and if that don't work I will make or buy a small fairing. I'm sure a fairing would do the trick. Thanks again. Scott

[monte55]

I'm not sure what the diameter of your metal...........why not try a section of
insulation foam for pipes that is split lengthwise than be put over said bar. Whistling is generally caused by fast air movement over sharp edges.

[Bert]

Whistling is generally caused by fast air movement over sharp edges.

Monte, what kind of "round bar" do you have that has sharp edges????
lmao!!

Monte is probably right, but I also think it's a HUGE difference too, of where you place it!!

-bert-
p.s. Monte, package shipped as you requested. This time, I put air holes....
Hope she faires better than the first one did!!!!!!!
Did you bury the body yet???

[monte55]

Monte, what kind of "round bar" do you have that has sharp edges????
lmao!!

Monte is probably right, but I also think it's a HUGE difference too, of where you place it!!

-bert-
p.s. Monte, package shipped as you requested. This time, I put air holes....
Hope she faires better than the first one did!!!!!!!
Did you bury the body yet???

My chisel
I didn't know if it was round or square. Even small round can create noise at certain speeds. When relative wind hits a an object it splits and speeds up to meet at the trailing edge and depending on the shape will dictate how much turbulance as in an airfoil. Even aircraft wings make noise as they slip through the air.

PS I thought it was going to be two months...air holes will be great

[FusionKing]

Gonna build my first truck rack in 2 or 3 weeks (when my pipe bender comes in). My union instructor showed me things to look out for (all the racks on their trucks are all schedule 40 round pipe, round being stronger than rectangle or square stock):

Rule #1: Don't have your bar shorter than the top edge of your front window, sticking out a little is better. If it is exactly above it might be ok, but just a little behined, it'll start to whistle. Funny this thread came up about that! He said the air coming off the windshield hits the pipe and makes it whistle. You could make it higher, but we both agreed it doesn't look nice... He makes all his around 3" above the top point of the cab...
my .02 (pick it apart, but that's what I was told, and that's how I'm going to make my 1st pipe rack)

I agree with about everything here...it sounds plausible enuff except the part about round being stronger than square...a piece of square the thickness of that sch 40 pipe would be awfully heavy duty

[Bert]

I agree with about everything here...it sounds plausible enuff except the part about round being stronger than square...a piece of square the thickness of that sch 40 pipe would be awfully heavy duty

FusionKing, yeah, I thought it should be just as stong also, but I've talked to a lot of old timers, and they all say that because the pipe is round, then it's stronger. More even weight distribution......

[DSW]

Rule #1: Don't have your bar shorter than the top edge of your front window, sticking out a little is better. If it is exactly above it might be ok, but just a little behined, it'll start to whistle.

One thing you might think about. If your rack extends past the front of the top of the windshield by much you can expect it to drip on the windshield all the time. Especially if you make a solid top like some have. We have one at work this way and it is annoying to say the least. Looking back at it, just a little bit farther forward and it would drip on the hood rather than the windshield.

I'm looking at building a new rack for my truck so have kinda been keeping an eye on this. Noise shouldn't be a problem as the body is at least 18" over the cab. I am thinking about going over the roof so I can get at least 14-16' on the rack (11' body) but hate the way I think it would look. My first thought is to use 3" alum channel. Anyone ever make a rack that telescopes out sort of like what some of the chopsaw tables do? I don't need to hold a lot of weight, just support long items like molding, light steel bar in full lengths or PVC pipe. Any suggestions on what alum sq tube sizes slide in/out togther well? My other thought is to make a removable rack that would go all the way to the front bumper. The 9' 6" height to the top of the body makes installing this a PITA by myself. Any suggestions and picts would be appreciated.

[Bert]

DSW, wow! never though of the drip thing, as I've never had a truck rack before!! THANKS! I guess I'll be extending mines out a little furthrer like you did though!!!
Far as your "front rack" thing. I see a few guys here that make a frame off their bumper (bolted on to the bumper), and that helps support the piece. If I see one again, I'll send you a pic.