Don't drop the tailgate - Montana Owners Club

Dave e Victoria · 01-16-2006, 09:51 AM

Found the report on this site to be very interesting.

http://sitemaker.umich.edu/um.gm.truck

The report is some wind tunnel tests trying to figure out what helps reduce drag on a pickup truck (not towing of course) They conclude removing the tail gate actually increases the drag. The best improvement is a flat bed cover. Probaby explains why GM is offering a bed cover as a factory option.

Dave

Parrothead · 01-16-2006, 11:25 AM

Dave, Where is your new GMC? You have to keep us updated here.
Happy trails....................

richfaa · 01-16-2006, 01:08 PM

Quote:

quote:Originally posted by Dave e Victoria

Found the report on this site to be very interesting.

http://sitemaker.umich.edu/um.gm.truck

The report is some wind tunnel tests trying to figure out what helps reduce drag on a pickup truck (not towing of course) They conclude removing the tail gate actually increases the drag. The best improvement is a flat bed cover. Pro baby explains why GM is offering a bed cover as a factory option.

Dave

We have the Fold-a-cover on our F-350. A couple of weeks ago we had a fresh snowfall of about 3 inches and of course the snow was laying 3 inches deep on the fold-a-cover. I thought what a good chance for a little wind tunnel test.Took the truck out on the interstate. 1/4 of a mile from our driveway and let er rip. The snow largely remained on the Fold-a-cover except for right at the tailgate about a 1 inch strip was clean down to the cover. Not bad airflow.Now with the cover folded up and the camper attached..different story.
Hummm just looked at that report link..Perhaps the spoiler would help when hooked up to the camper..Wonder what the effect of the spoiler would be WITH a fifth wheel attached...What do you think Dave..

Glenn and Lorraine · 01-16-2006, 01:19 PM

Quote:

quote:Originally posted by Dave e Victoria

Found the report on this site to be very interesting.

http://sitemaker.umich.edu/um.gm.truck

The report is some wind tunnel tests trying to figure out what helps reduce drag on a pickup truck (not towing of course) They conclude removing the tail gate actually increases the drag. The best improvement is a flat bed cover. Probaby explains why GM is offering a bed cover as a factory option.

Dave

Thank you Dave, I bookmarked that one for future discussions on the tailgate question.

Dave e Victoria · 01-16-2006, 01:51 PM

Sue & Ed,
After train car exchange and paperwork catching up, the traincar left Kansas City this afternoon and has Just past McPherson KS about an hour ago. Just heard a trestle burned in southern AZ forcing a lot of reroutes through Utah. My stomach dropped until I found out the trestle is near Yuma. Anyway, it is due into rail yard here on Wednesday at 0955. Already alerted the dealer to watch for it. Now it is getting exciting.

Rich,
There is another link that I have followed that is putting vortex generators on the tops and sides at the backend of Semi Trailers. They have dramatic effects -- just as good as putting a dove tail on the back. As you are probably aware, vortex generators on aircraft have dramatic effects on aircraft stall performance. If I get time this spring before we leave here for the summer, i plan to experiment with some short vortex generators at the rear of the truck roof. After reading the subject report I think they may help both towing and not. I plan to weld up a very narrow headach bar and attach some staggered fins to the top. The fins will only be about a n inch or so tall. The idea is to disturb any laminar flow over the roof there by reducing the energy in the airstream. (anybody have an idea of how to make a smoke generator to help in the evaluation?)

As to the fin on the back of the truck, there is so many things going on what with the air compression under the front of the fiver and all of the wierd angles, I would be hard pressed to speculate on the effects. I do, however, suspect what ever was positive in one installation might verywell be negative in another. It would be a fairly easy experiment to perform in the real world.

Glenn,
Don't you just love things that are counterintuitive? I am told the "Mythbusters" also featured the tailgate effect recently and came to the same conclusion.

Dave

richfaa · 01-16-2006, 03:04 PM

When we were doing wake turbulence testing in Oklahoma city we just used commom old smoke bombs along the runway. was thinking of a smoke bomb in the back of the Tv when hooked up to the camper to see what was going on back there. I suspect that there is no real solution to reducing turbulance when hooked up. The design between the tv and the camper is just too dirty.As we were flying to Fla last month I was looking out at the wing trying to figure out how/ where I could place some fins to break up the tubulance..way out of this old tech's realm of knowledge.

Dave e Victoria · 01-16-2006, 03:50 PM

Rich,
I agree that the area between cab and trailer is "dirty". That's why it needs work by techs as well as engineers. But, take a look at this site.

http://www.airtab.com/

I think it has some fasinzting possibilities for fivers. The vortex generators these guys are using are much more "aero" than i am thinking of. I'm more inclined to stick a 1x1xo,i25 ab up into the airstream. Each tab would be 3 inches or so apart and alternatively canted 20 degrees to the right or left. You probably saw some on that aircraft wing as you looked out of the window going to Florida.
Dave

richfaa · 01-17-2006, 02:46 AM

Yes sure did notice the tabs and was wondering where you would place them on the camper/TV.That's the part that is out of this tech's range. Can you see this picture..we are doing wind tunnel test using smoke , we are careening down the interstate , Big truck and big camper with clouds of smoke pouring out of the truck/camper, vortexes everywhere with a lady hanging out the rear sliding window with a video camera recording the event.How long before we are arrested. Will check out the website.

Dave e Victoria · 01-17-2006, 03:30 AM

Rich,
a bit more dramatic than what i had in mind. Primary test will be three mileage checks over 100 mile closed circuit. First test with out modification, second with and third with out. Refill tank before each run and drive at constant speed. First and third runs are control.

For the "smoke test" I propose a small smoke jet somewhere forward of the cab. I would have the video cam in a car driving alongside. All we would look for is how the stream is affected as it passes over the vortex generators.

This whole project may have to wait until fall as I have lots of other interesting projects going right now.
Dave

Sweetfire · 01-17-2006, 12:48 PM

Ask your local Fire Dept. if they have a positive ventilation fan. It looks like a small engine off a swamp boat on wheels. It may generate enough air flow that you could put the smoke bombs on a long pole and insert it into the air flow where you wanted to watch the flow. Or you could park your rig on an airport ramp and talk some pilot into doing a high power run up in front of you. Might be safer than running down the freeway.

Sweetfire · 01-17-2006, 12:56 PM

By the way, I just put the OEM tailgate back on my truck to see if there was any difference. I'll be refueling tonight so it will be about 6 days before I need to refuel again. I'll let you know what I find out.

richfaa · 01-17-2006, 01:51 PM

Oh I was just kidding around with the freeway thing. We set up the control Tower for our County air show and we were on the air show board.We could use a runway if we ever decided to do something like that and the fire chief lives a few doors up the street...

Northstar · 01-17-2006, 03:05 PM

I like the idea of running up a small aircraft to generate enough air flow for your experiment.

Dave e Victoria · 01-17-2006, 03:20 PM

actually, not a bad idea. I have to look into the smoke systems they use for quarter scale aerobatic aircraft models. Might be able to mount it under the hood. It would be an appropriately small stream. Thanks for the idea.
Dave

Sweetfire · 01-17-2006, 04:18 PM

I've seen wind tunnel tests on auto adverts here they have a smoke generator pushing smoke out the end of a long tube. That's why I thought a smoke bomb tied to a pole might be a poor man's alternative.

Dave e Victoria · 01-17-2006, 04:41 PM

Dennis, That would probably work. I need a small stream of smoke to avoid reduced visibility and it has to be cheap. Anyway, thanks for this idea too. My son and I were just talking about how to do this. A pole out front with an oil can and a gopher smoker inside. We can set the smoker off with a small squib made from niochrome wire. Think we may have a winner. But, you all may have to wait until fall to see the results. Standby one as they say.
Dave

Sweetfire · 01-19-2006, 05:01 AM

Well, after 2 trips to work (96 miles round trip) I seem to be getting .5 to 1 MPG better mileage. Will have to wait to see how the numbers come out when I fuel up.

Sweetfire · 01-23-2006, 11:45 AM

Just filled up today. Crunched the numbers, they were almost exactly 1 MPG better with the OEM tailgate then the vented, V tailgate.

Dave e Victoria · 01-23-2006, 02:03 PM

It's nice when science meets up with actual experience. Your numbers are almost exactly what the wind tunnel experiments suggest. Thanks for the data
Dave

Trailer Trash 2 · 01-24-2006, 03:36 PM

That report is great if you are not pulling a trailer, I saw that or a simular report on the dish and the trucks of today are more airodinamic form years past, and having your windows down will also cause drag and cause your milage to decress too. I would like to see that test done on a truck pulling a trailer or a 5th wheel with the gate up and down.

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