I have a GMC 2500, extended cab. I get a lot of noise from the flex of the lid on the truck when I am behind a big rig. Do you think this would eliminate that? I have about 5 inches between truck and cabover. Also, I was thinking of putting a tool rack in there.
J&S~B wrote: I have a GMC 2500, extended cab. I get a lot of noise from the flex of the lid on the truck when I am behind a big rig. Do you think this would eliminate that? I have about 5 inches between truck and cabover. Also, I was thinking of putting a tool rack in there.
John
I think it might help out with that, I've heard it called "oil canning" here on the forum. I like the tool rack idea, a good use of wasted space. I did get a chance to drive about 60 miles today with the deflector installed. I didn't have any noise or bug splatter on the camper. I'll have to wait for my first big trip to see what it does for mileage.
Pat
'98 Chevy K2500HD 4x4 454 3.73
'06 S&S Montana Bitterroot 8.5 ASC
'00 FR Sandpiper 30SPCS 5er Toy Hauler
J&S~B wrote: I have a GMC 2500, extended cab. I get a lot of noise from the flex of the lid on the truck when I am behind a big rig. Do you think this would eliminate that? I have about 5 inches between truck and cabover. Also, I was thinking of putting a tool rack in there.
John
It will make a more neutral pressure area there and should help.
Any kind of rack in the area will create more turbulance... more truck roof flex, and more noise.
Reason enough to not have a unused rack on the roof of the camper for "just in case"... hurts your coefficient of drag... and mpg.
2003 Lance 1161,/slideout/AGM batteries/255W Solar/propane generator/Sat dish/2 Fantastic Fans model 6150/AC/winter package
AirFoil, Trimetric, LED lights
I had the same problem with the roof flexing, when I installed the airfoil it stopped. The other solution is to remove the head liner and install some insulation.
Sleepy,
Very nice design.
I was looking at the sketch and comparing it to the pictures of the assembly. The drawing calls for a 22" flat area in the front. Yet it appears you made it only about 12". Was the 22" a prototype?
Also, do you get any flex or noise in the foil in the long unsupported expanse between the anchors in the front and the anchors at the sides?
Last question, what type of glue did you use for the construction?
Plan to construct one this weekend. Can't waite to try it out. Have had a lot of noise from the roof flexing.
Thank you for sharing this.
PJ Colahan wrote: Sleepy,
Very nice design.
I was looking at the sketch and comparing it to the pictures of the assembly. The drawing calls for a 22" flat area in the front. Yet it appears you made it only about 12". Was the 22" a prototype?
Also, do you get any flex or noise in the foil in the long unsupported expanse between the anchors in the front and the anchors at the sides?
Last question, what type of glue did you use for the construction?
Plan to construct one this weekend. Can't waite to try it out. Have had a lot of noise from the roof flexing.
Thank you for sharing this.
On mine I used the existing screws in the trim... they are 5" apart... plus 1" outside to the bend. I have built them many ways... and posted picture of many of them.... and many of you have adapted them to your campers and trucks.
Use an existing scres hole on the outer trim also.... even though you might change it later slightly.
I use clear PVC pipe glue and clear PVC cleaner from a store (home depot or lowes)that sells a lot of pvc glue (it has about a 6 month shelf life).
PM me with your phone number if you need help or have questions. I have those good old Cingular/att weekend minutes and after 9 of course.
sleepy - thanks for the answer(s). I suspected you were looking for an approach with a bit less pressure differential across the flow boundary. The complexity of the fluid dynamics of an aero fence with holes requires a more empirical approach to solving these sorts drag problems, in which you have what appears to be a very good solution if there is not a noise artifact (I'm assuming we aren't in the high speed environment where shock wave artifacts are a concern!!!).
Do you have a copy of Hoerner's Fluid Dynamic Drag (the NASA Cd figure you have is from Hoerner data)? He describes bluff body drag (Chapter XII) and that might give you some ideas with the rear-camper drag/pressure issue(s). In many speed/environment profiles we get an actual "push" by having our large TC's entraned in the airflow, but we also get all of the dirt/debris plastered to the rear of the camper as well. Since we don't care about lift (either positive - i.e. aircraft wing - or negative - i.e. race car airfoil) we probably want to keep the flow laminar over as much of the camper as possible (less induced drag) but keep the high pressure in the rear via turbulence with the tradeoff being the amount of turbulent area (which contributes to induced - form - drag). So we're waiting for your next invention!
middlecalf wrote: sleepy - thanks for the answer(s). I suspected you were looking for an approach with a bit less pressure differential across the flow boundary. The complexity of the fluid dynamics of an aero fence with holes requires a more empirical approach to solving these sorts drag problems, in which you have what appears to be a very good solution if there is not a noise artifact (I'm assuming we aren't in the high speed environment where shock wave artifacts are a concern!!!).
Do you have a copy of Hoerner's Fluid Dynamic Drag (the NASA Cd figure you have is from Hoerner data)? He describes bluff body drag (Chapter XII) and that might give you some ideas with the rear-camper drag/pressure issue(s). In many speed/environment profiles we get an actual "push" by having our large TC's entraned in the airflow, but we also get all of the dirt/debris plastered to the rear of the camper as well. Since we don't care about lift (either positive - i.e. aircraft wing - or negative - i.e. race car airfoil) we probably want to keep the flow laminar over as much of the camper as possible (less induced drag) but keep the high pressure in the rear via turbulence with the tradeoff being the amount of turbulent area (which contributes to induced - form - drag). So we're waiting for your next invention!
By tweeking the airfoils at the sides of the cabover you can get the air that slides off the foil to push away from the camper to return just at the rear of the sidewalls and "fill" some or the area behind the camper... again... use dirt as the method to observe what is going on.
To observe this airfoil functioning... it's fun to tie ribbons on the air foil and let your wife or friend drive you down a straight stretch of highway while you bounce from window to window to observe them.
I realize the air foil induces some small amounts of drag to the sides of the camper... it's a small trade off. I've made subtle changes to the ends of the airfoil but nothing worth mentioning.
There is no noticeable noise induced at legal speed limits.... the majority of the air molicules are part of the laminer flow that crosses the holes and exits at the ends of the airfoil.
As far as other ideas.... I am concerned about the drag at the rear of the camper.
I'd like to put the Air conditioner in the basement... get everything off the top. That would help a lot.
My favorite idea to minimize the drag on the back of the camper is to use verticle fixed wings with holes mounted on each verticle corner in the back... some air goes through the holes... some is diverted into the area immediately behind the camper. It doesn't take much... just a few inches mounted an inch or two from the corner.
Any thing to fill the negative pressure area with air.
I've actully played a little with channeling some of the turbulant flow across the top to a down spout at the rear edge to break up that drag. too complicated... simplicity wins every time
I assume that you are into aero engineering at Boeing... this is blacksmith engineering... trial and error based on mind experiments and a lot of experience.
A lot of it actally comes from our knowledge that a propeller blade is nothing but a rotating wing that produces thrust instead of lift. Our goal when working on propellers was to "eliminate" cavitation... and minimize noise... all while increasing efficency. One of our propellers and some applications were exhibited at the U S Patent Office a few years ago at their invitation.
* This post was
edited 04/30/08 03:17pm by sleepy *
sleepy-
If you're ever in North Carolina in the vicinity of Kitty Hawk, I recommend spending some time going through the Wright Brothers exhibit. One of the things that struck me most was their work on propellers. In fact, they did a lot of the early design work for wind tunnels so they could test their propeller theories. Interesting, using a propeller driven wind tunnel to test propeller designs. Kind of like you using your TC to investigate new low aerodynamic drag concepts! Yeah, I'm an engineer at Boeing, but not for long. I'm headed to Sweet, Idaho and some non-engineering fun (and fewer "Kerry-Edwards" bumper stickers).
middlecalf wrote: sleepy-
If you're ever in North Carolina in the vicinity of Kitty Hawk, I recommend spending some time going through the Wright Brothers exhibit. One of the things that struck me most was their work on propellers. In fact, they did a lot of the early design work for wind tunnels so they could test their propeller theories. Interesting, using a propeller driven wind tunnel to test propeller designs. Kind of like you using your TC to investigate new low aerodynamic drag concepts! Yeah, I'm an engineer at Boeing, but not for long. I'm headed to Sweet, Idaho and some non-engineering fun (and fewer "Kerry-Edwards" bumper stickers).
It sounds like you might approve of the airfoil concepts.
I have been to kitty Hawk, (my best friend from 50 years ago is Vice principal of the brand new Kitty Hawk High school. Also been the Aerospace Museum in DC, USAF museum in Dayton, The Wright Brothers Bicycle shops in Dayton, Blue Angles navy museum in Pensacola....
It took years to learn how to describe out propeller concepts to others. It turns out that I had to go back to the Wright Brothers airplne to describe our props so that people could understand them.
At one point our drive way was home to a large water loop that we used to test the props...we tested them as props and as turbines. Water is non compressable... we moved the water... not the props.
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