Frontal Sq'

Old-Biscuit wrote:

mountainkowboy wrote:

Old-Biscuit wrote:
Use the 'flat figure'.....width x height

Curves will just make it less.

Besides..frontal area is least of concerns.
Trailer GVWR, tongue weight are more important factors when it comes to 'can it be towed'

So would that be "I don't know? I didn't ask if I can tow it, I was looking for a formula.

Actually I do know......

Here's the formula for a curved surface. Have fun!
Curved surface formula------- 2 pi r^2 + 2 pi r h.

And after you get it worked out you will realize it doesn't matter all that much.....just use the simple 'flat' formula ----W X H

That is true I got the formula PM's to me and it isn't a significant amount of change. As others have stated the curve is mainly for less drag while towing.

To calculate the aerodynamics involved with every towing combination would require an army of engineers with unlimited time in the wind tunnel. Ford came up with a simple and reasonable rating for its dozens of models. We can choose to respect them or not. Fuel mileage is not the only factor involved but I get about forty percent better mileage towing a 5 X 8 cargo trailer loaded to about the same weight as a conventional travel trailer. (16 mpg compared to 12 mpg with the TT)

SoundGuy wrote:
I suspect what the OP is trying to justify is towing a 192RBS like mine with his V6 Ranger rather than his F250.

drsteve wrote:
I suspect you are correct, since Ford says the 2011 Ranger is limited to 50 sq ft of frontal area.

SoundGuy wrote:
I'll bet he's asking this question because he's given it some thought and may realize this just isn't the best idea.

drsteve wrote:
I think he's asking this question because he wants to do his homework, which is a good thing. I suspect he'll find that while the Ranger will do what he's asking of it--short, lightly loaded trips--the F-250 with it's longer wheelbase is way more capable, and it'll be the truck of choice for every trip.

In another thread started by the same OP about the Coachmen Freedom Express 192RBS he said -

"We are looking at it for a full-time unit for travel in the lower 48 and possibly Canada and Alaska if we want. It will be towed by an F250 diesel with a Harley in the truck bed for the most part. I also like that it can be towed by our Ranger, 5,900lb tow capacity, with a moderate load out for local and weekend play too."

He later declared in the same thread he's not concerned at all about towing a 192RBS with his Ranger so this isn't "homework", if anything this question about frontal square footage is really an attempt to justify that it will work to his satisfaction. My belief is he'll be disappointed.

Not a calculus problem, but a geometry problem as pointed out by Old Biscuit. Really just a cylinder wrap question. Figure out the % of the wrap that is the front of the camper and you got it.

Cylinder wrap= w(2pi r) Width times Circumference

SoundGuy wrote:

I suspect what the OP is trying to justify is towing a 192RBS like mine with his V6 Ranger rather than his F250

I suspect you are correct, since Ford says the 2011 Ranger is limited to 50 sq ft of frontal area.

SoundGuy wrote:
I'll bet he's asking this question because he's given it some thought and may realize this just isn't the best idea.

I think he's asking this question because he wants to do his homework, which is a good thing. I suspect he'll find that while the Ranger will do what he's asking of it--short, lightly loaded trips--the F-250 with it's longer wheelbase is way more capable, and it'll be the truck of choice for every trip.

Good answers on this thread! I also got an A in college calc...so consider that contouring the frontal area actually increases the square footage...like cutting a square out of a ball and then flattening it out.

However this doesn't tell the whole story because even though the actual sq footage is greater, drag coefficient is reduced as a result of the contour. Further complicated by the fact that the actual drag created by the TT is a function of how much air is already being moved out of the way by the tow vehicle.

Vehicle manufacturers have already done the heavy math and distilled their recommendations down to a surface area limitation that we can calculate as simple HxW...getting into the short strokes on this won't materially change the answer. As Cramden said, if you're going to ignore that part of your owners manual, just do it, you don't need a loophole to justify your decision.

mountainkowboy wrote:
Is there a formula for calculating it for a curved front TT? I called Coachmen to get the frontal sq' of the 192RBS during my researching and they don't have any idea. All they could tell me is "if it was flat it would be 56sq'" Well it isnt flat, in fact it's only flat to the end of the diamond plate then takes a curve to meet the roof. Anyone know???

Ralph Cramden wrote:
If you're going to throw manufacturers recommendations to the wind, throw them and forget about it. Coming up with some type of half arsed justification changes nothing.

I suspect what the OP is trying to justify is towing a 192RBS like mine with his V6 Ranger rather than his F250, which I've suggested (having tried a similar setup myself years ago) may not be the best idea. His response has been a categorical "no worries" (my words) but I'll bet he's asking this question because he's given it some thought and may realize this just isn't the best idea. In another discussion about the 192RBS I asked owner Last Train about his Honda Ridgeline V6's fuel mileage returns when towing his own 192RBS and his numbers which are noticeably worse than my 5.3L Silverado's when towing my own 192RBS support the argument that when towing the same load, with the same frontal area, a smaller V6 is going to be working a lot harder than a larger V8. Big surprise, there's no magic to any of this, and no amount of complicated calculations are going to change it. :R

Ralph Cramden wrote:
....snip.......
Now if your trying to justify being within some manufacturers frontal area limitation, say 50 sq ft as an example, by splitting hairs and doing reduction calculations, it would be way easier to just ignore all of it to begin with. I only say that because over the 10 years I have been visiting RV forums, when such a question comes up thats usually the case. If you're going to throw manufacturers recommendations to the wind, throw them and forget about it. Coming up with some type of half arsed justification changes nothing.

Ralph nailed this one. Buy a popup if you want to stay under 50 square feet. Otherwise, 8 ft wide X 9 ft tall = 72 square feet.

mountainkowboy wrote:
Is there a formula for calculating it for a curved front TT? I called Coachmen to get the frontal sq' of the 192RBS during my researching and they don't have any idea. All they could tell me is "if it was flat it would be 56sq'" Well it isnt flat, in fact it's only flat to the end of the diamond plate then takes a curve to meet the roof. Anyone know???

As others have said, you do not deduct for any slope or curve to the trailer. Frontal area includes everything punching into the wind including the tow vehicle. That's using Fords definition of it, as I don't know if GM or anyone else even defines it, which is "Frontal area is the total area in square feet that a moving vehicle and trailer exposes to air resistance." They also go on to say............."Selecting a trailer with
a low-drag, rounded front design will help optimize performance and fuel economy." I would not take that to mean you do a wind tunnel test of drag reduction due to slope or curve, and then deduct the supposed results? But thats just an opinion.

I would say a Coachmen 192RBS which has a 10'-3" advertised height and 8' width to be 82 sq ft of frontal area. If you want to split hairs just deduct clear area under tow vehicle/trailer, for say 8 sq ft roughly?
74 sq ft. But you better add back in the 3 sq ft for the rooftop air. 77 sq ft.

Now if your trying to justify being within some manufacturers frontal area limitation, say 50 sq ft as an example, by splitting hairs and doing reduction calculations, it would be way easier to just ignore all of it to begin with. I only say that because over the 10 years I have been visiting RV forums, when such a question comes up thats usually the case. If you're going to throw manufacturers recommendations to the wind, throw them and forget about it. Coming up with some type of half arsed justification changes nothing.

mountainkowboy wrote:

Old-Biscuit wrote:
Use the 'flat figure'.....width x height

Curves will just make it less.

Besides..frontal area is least of concerns.
Trailer GVWR, tongue weight are more important factors when it comes to 'can it be towed'

So would that be "I don't know? I didn't ask if I can tow it, I was looking for a formula.

Actually I do know......

Here's the formula for a curved surface. Have fun!
Curved surface formula------- 2 pi r^2 + 2 pi r h.

And after you get it worked out you will realize it doesn't matter all that much.....just use the simple 'flat' formula ----W X H