Air resistance vs weight

[crumbs]

I'd appreciate your thoughts on the following.

Assuming two different campers:

One weighs 350lbs LESS, with approximately 13 sq ft MORE frontal area exposed to the air-stream than the heavier camper. Assuming speeds no greater than 65mph I think the lighter unit would be an advantage to me, considering the payload of the truck will be close to its limits.

Pictures not of units involved in topic

I wish I could delete this entire message. You folks are in a different league than me, making my questions less important here. Sorry. I have to look for a different forum.

 

[smlobx]

I think it depends on the truck.
13 SF of additional frontage area is not insignificant, particularly on a smaller rig.
The same could be said about the additional weight...

On a full size rig like my F-350 the increased frontage would impact me more at highway speeds than the weight.

 

[cwdtmmrs]

I disagree about 13 SF not being significant on a smaller rig. My Toyota pickup will vary 3-4 MPG either way with a headwind/tailwind with the camper. Not so without the camper and equal weight in the bed.

cwd

 

[Bigfoot Dave]

Everything factors in but I have found that hard corners on the back of the camper tend to create more of a suction going down the road and having a significant effect. Weight alone has little effect.
I remember reading a study related to carrying a boat on the roof of a vehicle and they found that if the transom was forward it was more efficient. An empty 14' x 6.5' x 6.5' vee nose enclosed trailer always yielded the same mileage as a 25' Bigfoot travel trailer with rounded edges all around. The Bigfoot was 4 times as heavy as the enclosed trailer and the "v" didn't help. My Bigfoot truck camper gets the same mileage if the 50 gallon water tank is full or empty.
Welcome to the forum! This is a great group of travelers, Bigfoot Dave

 

[Rockcod]

I'd appreciate your thoughts on the following.
Assuming two different campers:
One weighs 350lbs LESS, with approximately 13 sq ft MORE frontal area exposed to the air-stream than the heavier camper. Assuming speeds no greater than 65mph I think the lighter unit would be an advantage to me, considering the payload of the truck will be close to its limits.
Pictures not of units involved in topic
I wish I could delete this entire message. You folks are in a different league than me, making my questions less important here. Sorry. I have to look for a different forum.

Crumbs, don't sell yourself short, you've posted pictures and asked a good question. No doubt there is a formula to put your inquiry in a math equation ? myself, I would be inclined to go with a smaller heavier unit just for the sake of portability and access to smaller roads.
I will also be near max pay load, a little suspension work and I should be good to go... Consider crosswinds as they have and impact on drivability. I am also considering a lightweight wind deflector roof mounted in front of the camper.

 

[Atlin]

As has been alluded to here, with regard to aerodynamic drag, frontal area is less important than the shape of the item. There is an old video online about some aerodynamic testing that explores drag on a wire and an aerodynamic (teardrop) shape airfoil. The drag is equal on a wire and a teardrop shaped airfoil that has 10x (you read that correctly) the frontal area. The basic issue is the turbulence (suck) behind the item. The airfoil allows the air to close smoothly downstream whereas the wire has downstream eddies. This may be one reason why the roof rack people have gone to airfoil shapes rather than the old round bars (another reason is probably whistling and other noise associated with the old round bars).

This effect is greater at higher velocities. I've seen a few semis on the road with the "tail" panels and have always wondered how much that helps their mileage.

I would surmise that the frontal area is more important than the weight unless you created a "tail" of some sort for the camper to help with the drag issue.

Just my thoughts.

 

[ntsqd]

You have to accelerate and decelerate both, but the heavier unit takes more power (fuel/brakes) to do this at the same rate, or will accel/decel slower for the same power consumption (heat generation in the case of the brakes). Once moving on flat & level it takes no more power to maintain a steady state. Some might argue that the heavier weight results in more friction and therefore will take more power to maintain a steady state. I'll counter that and say the difference will be small enough to be lost in the "noise" of the calculations.

I once had a '66 Econoline long body van with a carb'd 300c.i. six in it. Anyone familar with these vans knows that they are very flat-faced, flat-backed, and sharp edged. A literal brick. It got 10-12 mpg at 65 mph. I used it to flat tow the dune buggy in my avatar. With the dune buggy in tow it got 11-13 mpg at 65 mph. The dune buggy is not exactly aerodynamic in the least. What it did do was fill in the space behind the van and make the whole assembly more aerodynamic.
Frontal area is important, but it is far from being the sole determiner of how efficient the body moves thru air.

There was a study done in a wind tunnel and the results were (at the time anyway) published on the internet. What was studied was the effect of tail-gate up or down with regard to drag of an empty bed pick-up. What was found was that tail-gate up had less drag than tail-gate down. We all know that air is compressible, what we don't often realize is that you don't need an enclosed container to compress it. With the tail-gate up the air flowing off the top of the cab was compressing the air in the bed, effectively creating a "tonneau cover". With the tail-gate down this didn't happen, making the "rear-al area" at the back of the cab the height of the bed plus the height of the cab. With the tail-gate up this area was only the height of the cab above the bed. The bed height area occurred further to the rear making the whole rear shape much more tapered and aerodynamic.

 

[Squatch]

Unless you are pointed uphill. Wind drag will be the bigger factor on anything with wheels. Once you start climbing you can add the weight factor to wind drag.

My Trooper is also a brick. With my boat behind it the airflow tends to get better and the truck becomes much more stable on the road.

That Gypsy Vardo slide in is pretty cool!

 

[smlobx]

I disagree about 13 SF not being significant on a smaller rig. My Toyota pickup will vary 3-4 MPG either way with a headwind/tailwind with the camper. Not so without the camper and equal weight in the bed.

cwd

If you go back and carefully reread my post you'll see that's not what I said....

 

[cwdtmmrs]

smlobx, You are right, my mistake. Should have cleaned my glasses!

cwd

 

[PackRat]

There are several things in play here.....you are concerned about overloading the GVWR of your truck but (secret!!!) plenty of guys are running with more GVWR than their truck is rated for. Springs, air bags, torsion bars may make it LOOK to ride like it should, but basically you have too much weight.

So...if either camper is close or a tad over, that isn't a deal killer here.

Secondly, wind resistance tells me you are concerned with fuel economy I think. Unless you are running an engine with not enough horsepower so you are pedal-to-the-metal all the time what you are probably looking at is 2-3 MPG difference. So, you take a 500 mile trip and get 10 MPG and use 50 gallons of gas or you get 13 MPG and use 39 gallons of gas. The difference at say, $2.50 a gallon and 11 gallons of gas is $27.50 for the weekend....basically the cost of lunch along the road somewhere.

Thirdly, one of the campers is better fitted out and provides a better level of comfort for you.

Lastly, one of the campers costs a lot more than the other.

It is up to you to weigh all those considerations and see which are more important to you. As long as you have "enough truck" to carry either camper and you and passenger comfortably you should be able to decide which of those is more important to you and decide from there I think.

I myself have rated fuel economy pretty low as my F-250 gets 10 MPG....but a comfortable driver/pass compartment and being able to carry a camper that has what I want in/on it ranks next since the F-250 can handle a lot of weight and I am looking for an 8' CO AK right now myself. It carried a longer, heavier Lance with no problems (the big hard sided Lance campers do sway however, especially when a semi goes the other way at 65 MPH!).

For us, a half-day drive or so to get to a place where we can spend a few days is no big deal so having a camper that suits us is more important that gas mileage....

 

[crumbs]

I sure do appreciate all of your thoughts and encouragements.

I still wanted a shell, but that is proving difficult to obtain. Basically I'm starting the TC search again.

My little 4.3l Silverado with it's 1962 lb of payload is what I'm working with.

Currently I have a new lightweight hardside and a preowned pop-up to choose from. Both units are within a reasonable distance of me. These two are the reason for the question.

I had started this thread to see what you folks thought of air resistance vs weight. It's probably true that a majority of you are off roaders -therefore a lower center of gravity is a very important attribute. My truck will not see anything as extreme and still it will be near its limits with either camper. Additionally, the camper will be on the vehicle more often than not. This being the case, I'm thinking weight is probably more of an issue since it will experience stop n go as well as long trips.

Patience is what I need most. I guess I'll have to keep my eyes out for a shell. The furnace being the most important option.