Here is one for the weight police! I was going through some of my old photos the other day and found this. Taken in the early 80s it shows my rig....a F250 + 11 1/2 foot camper + 3500 lb boat on a 48" extension.
I knew nothing about GVWR or axle weights or tire loading. Cannot believe I did that! Took my family several times across the Rockies from Alberta to BC. Mind you, I was not the only one doing this sort of thing in those days.
One time my father-in-law borrowed the camper and loaded it on his 1/2 ton dodge and drove out to Vancouver for the worlds fair in 1986. It must have been a little hard to handle!!!
.....I'm one of the ones people hear about but never actually know - I had a factory Class V hitch fail.
I had a nice ski boat, about 4500lbs on a factory installed Reese Class 5 hitch running a 48" extension. One day I went in to Superhitch to have my Torklift tie downs installed, and they pointed out that the welds on the receiver had cracked and only had about 50% of the weld left holding it on.
I didn't even think twice about fix/re-weld vs. replace. I immediately had it removed and bought a new Superhitch.
I need to change my statement regarding oem hitch & ext. I just returned from a trip with the cargo trailer to find it sagging about 2", no cracked welds but it concerned me enough that I ordered a reese titan. Better to have to much hitch than try and squeak by. Glad I made it home safely and no harm was done to the load or ANY ONE ELSE ON THE ROAD!!!!!
Thanks Boatycall & meatwagon for sharing some real world experiences! Always better than "guestimates"
Using an extension in a receiver greatly reduces the capacity due to the leverage which magnifies the force on the bolts and welds.
I have estimated the de-rating of standard receivers based on the length of the extension. The following graph must only be used as a guideline as it is an estimate only, but it will give you some idea of what the maximum loading should be.
I have more info on using a hitch extension at http://www.visualsc.com/hitch_calc.htm. It includes a calculator to estimate the impact on your truck when you tow a trailer (increased axle and tire weights, etc.)
Only way to tell is to test it. Take your rig to an area where you can make lock to lock turns forward. Then drive forward and keep turning the wheel while watching to see if the corner of the trailer comes close to the rear of the camper/truck. If you can make tight turns without contact then you are good to go. Remember to consider uneven ground. If the corner of the trailer clears under the camper, but might hit if it was raised, then that is not good. Once you have tested going forward, try backing into a turn and ensure you can see when you will make contact....if you do.
I really need to go back and take another look, as I have been saying for years "when they stick the big emena tube in Earth, it is going in real close to Yuma!"
And that may not be fair!
No, the emena tube will go in near Cold Lake, Alberta, Canada. Proof??? Many people from Cold Lake snowbird in Yuma and think it is the best place going? :R. This includes a good freind who loves it there.
Personally, I'll stick with Gold Canyon, AZ! Great scenery, lots to do, relatively clean air. Water is not great, but who cares when you have an RO.
I can talk from personal experience as I was stopped at the Coutts/Sweetgrass border a couple of years ago. They asked me to prove I had a permanent fixed address in Canada. I had my passport, drivers license and my Alberta healthcare card. They said that was not good enough as "they were too easy to get without proving where you actually live". They wanted something like a utility bill or property tax bill with my name and address which I did not have.
It looked like I was struck and would have to head back into Canada and get them. By chance, They saw that I had a paystub in among my papers. They took that and allowed me in to the US. Funny thing, was that it was from a US company for some consulting work I did!! However, it clearly showed my Canadian address. Go figure.
Now I always carry some recent utility bills and my current property tax receipt. Have not been stopped since then though.
I am also carefull about filing my 8840 form. And yes, I had reported the consulting fees previously and paid the appropriate tax...to both the IRS and my friends at Revenue Canada.
Great work on the pitot tube and testing!
So, what you're saying is that the air tabs do not seem to make as much difference in reducing the air speed in that space as does the dam designed by Sleepy?
Thanks for your diligence, honesty and interest!
What I am thinking is that based on the testing to date and my current understanding of the physics behind the air tabs, I cannot see that the air tabs would provide as good a result as the air dam. I can see that they might have some impact due to the created vortex, but not sufficient to choose them over the air dam
That said, I will do some more testing and will continue working an alternate design and will share it on the forum. But for now, if I wanted to install something now, I would choose the dam...even though I have already purchased the air tabs and they are sitting on my workbench as I write this.
OK.... after a bit of a delay due to some family issues, I was able to do some testing with a Pitot Tube above my truck cab.
As mentioned in previous posts, I was wondering if there was a Bernoulli effect going on between the cab and camper overhang, and if so, what was the effect.
What got me thinking about this was that I had observed that there were a lot more bugs accumulated on the center of the front bulkhead of the camper than on the front. This suggested to me that the air flow above the cab was stronger in the center and therefore would exert more force (drag) at this point.
Front of overhang
Center of bulkhead
So, as suggested by some, I decided to test this hypothesis by building a Pitot Tube and taking some measurements.
The Pitot tube has a static port on the side and I used a Phidget analog differential pressure to USB device to measure the pressure differential and then calculate an air speed. I validated the results by testing the unit held about 3 feet away from the side of my car. The measurement was consistent with the speed of the vehicle (and yes, my wife thought I was weird as she drove me down the highway hanging out the window!!)
I then mounted it on my truck and camper and with the help of my grandson, we ran it up and down the highway while he took readings.
At first, I thought the results failed to support the hypothesis. However, after some further study, I realized what was happening is that the air was piling up in front of the bulkhead creating a high pressure area and therefore increasing the drag.
Note that as actual speed increases, the measured speed increases but the differential to actual speed gets larger and larger. I am interpreting this to mean that as speed increases, there is a resultant increase in the build-up of air in front of the bulkhead.
At this point, I think this data (and other observations) supports Sleepy's (and abslayer's among others) design. Although I love the idea of the air tabs, I just do not see that they would give as good a result. They may help by creating turbulence that will tend to move the air to the sides, but not sufficiently to warrant using them exclusively.
I plan on doing some further testing, and have an idea for a different air dam design that will utilize a few air tabs which I will share at a later date.
First thing this morning I went out with the TC and stuck the hose straight into the wind a foot ahead of the mirror and only got 2" WC at 55 mph. I will try some new tubing and a little alcohol, metal tube as suggested and see if I can get accurate data. If not I will look around for better test equip..
The 2-inches water column is pretty much what you should see. I am currently building a pitot tube to do some testing on my truck. I worked out the calculations this afternoon to see what kind of pressure range I would need and I found that at 60 mph, the pressure should be about 1.8 inches WC.
Also if measuring the air speed above the cab (assuming my musing about the Bernoulli effect are correct) having the low point static sensing side in the cab would give a misleading result. If the hypothesis is correct, the static air pressure will be reduced above the cab and therefore you need the static point there.
I sent a PM to Sleepy with some thoughts, but he suggested I should post it here as well......
I have been following the air tabs / air foil discussion with great interest. I cannot buy the materials here in Canada to make Sleepy's design so I thought I might try the air tabs so purchased some which I now have in hand. However, when I thought about it some more and read all the posts, I am not sure which way to go.
I asked Sleepy to answer a couple of questions.
1) From Sleepy's posts, I understand that the only reason you use perforated material is to prevent a low pressure area forming behind the air foil and sucking in dirt and bugs. Is this correct??
2) Have you considered the Bernoulli effect resulting from the alignment of the cab and camper overhang??
I am thinking that this effect will greatly intensify the force exerted on the camper bulkhead behind the cab. Probably several times higher that that exerted on the front of the camper overhang and truck itself. This is a result of the dynamic pressure (kinetic energy) which is a function of velocity squared.
Is it possible that the air foil works in part more by slowing the volume of air between the cab and camper overhang and therefore reducing the velocity and thereby the dynamic pressure? This should enhance the improved fuel economy being experienced.
Also, the lower velocity above the cab would draw in more air and bugs from the sides before "splattering" them on the bulkhead. This might explain what I have observed where the density of the bugs on the bulkhead on my camper is much higher than on the front of the truck or camper overhang.
At this point, I am thinking that dampening the Bernoulli effect might have more of an effect than the displacement of air to the sides (like your barge analogy). Although displacing the air sideways also reduces the air volume and therefore velocity!
I am going to work this some more, but for now, I will hold off on installing my air tabs until I understand the physics a little better. :? Where is Sheldon Cooper when I need him!! :D
Not sure how flying geese relate to a V-shape deflector on my camper! If you read this articleClicky. It says the benefit is from vortex generation....air tabs???
Just kidding...I think everyone recognizes that Sleepy has a great design. Why would anyone want to depart from a proven idea? :B
First, go get your rig weighed while it is loaded and ready for a trip. Get weights for all four corners (if possible) or at least front and rear.
Second, go to the Michelin tire weight inflation chart HERE and download the PDF file.
Third, match up your actual weights and the size of your tires and find the correct inflation pressure.
Forth, Inflate the tires to the recommend pressure while the tires are cold. Any pressure increased during driving is taken into consideration with the chart.
Hope this helps
I can't understand how a trailer tongue extension is a viable option. It will still hit the camper or jacks on turns or uneven terrain. Sure doesn't seem like a very good solution to me.
Good point. He definitely would want to check clearances on his jacks and rear corners if he was to extend it. All depends on where everything is. I am pretty sure others have talked about having extended tongues on the forum. Maybe someone who uses one can chime in???
Been there, done that!! Really rocked the camper, but luckily no damage except I broke the tie-down points on the rear of the truck. I was using fast guns but not sure if that helped. I replaced the hooks on my rear tie downs with larger/heavier hooks and was good to go. In hind sight, not sure that was a good idea as I would rather have the tie-downs fail that bend the frame on my truck or damage my camper!!
You would be far better off to have the tongue on the trailer extended would be safer also and probably cheaper.
This is good advice if you are trying to keep costs down. Although more money than just a hitch extension, it may be a better option IMHO. A local welder can extend your trailer tongue in a couple of hours or less. Check out the comments in the next reply on potentially hitting your jacks and camper when turning or going over bumps, etc.
When you use a hitch extension, there are other things you need to be aware of. First off, the receiver on your truck is rated for a specific tongue weight. When you install a hitch extension, you will be de-rating your receiver due to the high torque that it experiences due to the length of the extension. For example, the max tongue weight on a 36" extension in a 500# receiver will only be around 150 lbs. Depending on how you load your trailer, you can easily exceed this.
Secondly, you need to watch the total load on your rear axle. Using a hitch extension can increase this considerably. Not sure of what your loaded weight is without the trailer, but it is something you should consider.
That said, something that will mitigate this to some degree is the use of a weight distribution hitch. Properly installed, it will reduce both rear axle weight and load on your receiver.
For information on using a hitch extension, check out THIS LINK. There is a chart showing the effect of different hitch extensions on receiver load at the bottom of the page.
I did not want to spend the money on a super hitch (much higher here in Canada) so I designed my own. You can read about it HERE Also, several other members here have built their own as well and have excellent designs. Hopefully they will post here and share the info with you.
I'll give you Canadians the same answer that you like to give Americans who want to pass through Canada with their firearms......."If you don't like our laws, stay home".
X2!!! I have worked in the US and also snowbirded for many years. Yes, I have paid US Income taxes and also submitted the 8840. Never had a problem. And yes, it takes a bit more effort to file in both countries, but that is the rules and I knew that going in.
Being one of the guys who always says that Campers will not tip forward under normal conditions, I am going to have to qualify that advice in the future by saying it does not apply to 3 Jack set ups! That moves the fulcrum rearward.