Gladiator on fire, burned to the ground…

[jimbom]

Total aerodynamic drag = frontal area x Cd

Frontal area describes the size of the item.
Cd describes the efficiency of the shape.

As Papa already detailed, it's not this simple. But to your point, it could said that drag is proportional to the product of frontal area X Cd, the two things you have control over when designing for drag. Velocity is the biggest factor as the drag quadruples when the speed doubles.

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[LittleFish]

I looked at page 16 of the Ford Brochure that ShadowsPaPa linked in post #103.

Driving back from the Dodge service department today (my rear passenger axle seal is leaking and the parts are backordered until October). I spied my 1st 2 door Bronco. That is a stunner of a vehicle. Not practical for my needs but it's definitely a sweet looking vehicle.

Note the trailer Frontal Area limitations of the Ford Bronco:
Without Towing Capability 20 SqFt of frontal area
With Towing Package 30 SqFt of frontal area

As many have already said, there will be some major growing pains with this new Bronco platform. I wonder if the Ford Engineers are aware that the Bronco is +/- 6 ft wide and +/- 6 ft tall. So.... +/- 36 SqFt. Forget the trailer... the Bronco by itself is over the frontal area limitations .

 

[dcmdon]

As Papa already detailed, it's not this simple. But to your point, it could said that drag is proportional to the product of frontal area X Cd, the two things you have control over when designing for drag. Velocity is the biggest factor as the drag quadruples when the speed doubles.

I realize that drag quadruples with a doubling of speed.

I stated that in my previous post

The force of aerodynamic drag increases as a square function of air speed. That means that if you reduce speed by half you reduce aerodynamic drag to 1/4 its original value.

More practically speaking it means that in order to cut aerodynamic drag in half. You only need to reduce your speed from 70 mph to 50.

It is also EXACTLY that simple. We said the same thing. I just said it differently, in a way I thought might be clearer for others. I did this by eliminating the variables for velocity and fluid density since if we are comparing shapes, we can hold each of those constant.

 

[jimbom]

I realize that drag quadruples with a doubling of speed.

I stated that in my previous post

The force of aerodynamic drag increases as a square function of air speed. That means that if you reduce speed by half you reduce aerodynamic drag to 1/4 its original value.

More practically speaking it means that in order to cut aerodynamic drag in half. You only need to reduce your speed from 70 mph to 50.

It is also EXACTLY that simple. We said the same thing. I just said it differently, in a way I thought might be clearer for others. I did this by eliminating the variables for velocity and fluid density since if we are comparing shapes, we can hold each of those constant.

Sorry, came in late and missed your earlier post about V^2.

But when I saw your statement: "Total aerodynamic drag = frontal area x Cd", the engineer in me had to correct that overly simplified (and incorrect) formula. Pappa gave the full and correct formula for drag.

 

[jimbom]

If I remember right if the angle is 45 percent or greater it doesn’t count towards the total area

Frontal area is independant of shape or angles. In essence it is the 2 dimensional shadow cast in the direction of airflow/drag.

 

[dcmdon]

Sorry, came in late and missed your earlier post about V^2.

But when I saw your statement: "Total aerodynamic drag = frontal area x Cd", the engineer in me had to correct that overly simplified (and incorrect) formula. Pappa gave the full and correct formula for drag.

Yeah. I left the fluid density (or is it viscosity?) and speed stuff out because I wanted to make it more intuitively obvious.

I mean it just makes sense that an object's drag is dependent on its size and its shape. Right?
But then again, its also obvious that its drag goes up with velocity. Ha.

Engineering is full of simplifications for the sake of simplicity / clarity and when you can hold a variable constant. Surely you are aware of the mythical "spherical chicken". Ha.

(I never finished my ME degree, switched to economics instead. But still a Newtonian physics geek).

 

[jimbom]

Frontal area question - Other than a pop-up or small teardrop are there any trailers that would fit the bill of less than 40 SF or 55 SF? I ask because Jeep shows the Gladiator pulling an Airstream in their ads which has a frontal area of ~72 SF, which is well beyond both. Also, for kicks I checked the Ford Super Duty "Frontal Area Considerations" and they show 60 SF for bumper pulls and 75 sf for 5th-wheels. I think you would be hard pressed to find a 5th-wheel less than 75 SF and as far as I can tell, there aren't very many travel trailers smaller than 60 SF. Is the calculation something other than height x width of the trailer?

You have it right. Frontal area is simply a rectangle with the height (highest point) x width (widest point.)

 

[jimbom]

Yeah. I left the fluid density (or is it viscosity?) and speed stuff out because I wanted to make it more intuitively obvious.

I mean it just makes sense that an object's drag is dependent on its size and its shape. Right?
But then again, its also obvious that its drag goes up with velocity. Ha.

Engineering is full of simplifications for the sake of simplicity / clarity. Surely you are aware of the mythical "spherical chicken". Ha.

(I never finished my ME degree, switched to economics instead. But still a Newtonian physics geek).

Density.

As I offered before, it is correct to say Drag is proportional to Cd and Area. I see now that's what you were going for and not trying to contradict Pappa's equation.

Real story: I once had a manufacturing engineer come to me asking what he should use for Cd for a fence he was designing that had to meet certain wind loads. I told him to use 1.0 (flat plate) and asked to see his calculations. He obviously hadn't studied aerodynamics and from somewhere came up with a formula for wind load (aka drag) that was totally bogus, something like Drag = Velocity X Area x Drag coefficient. His calculated loads were ridiculous (and the resulting units made no sense.)

 

[Gvsukids]

Well that was fun. So if OP would've been driving slower, his truck wouldn't have burned?

 

[Pergrem]

Could have been the regen system. It could have failed or something could have got too close to it and caught on fire. After owning one, I am not a fan of modern diesels and will not own another one. The regen system on my Colorado would get extremely hot and you could smell it inside the cab. Looking at it during an oil change, I could tell the system had gotten too hot by the color. Regen systems themselves are not really reliable and too many trips less than 30 minutes is hard on the system.

 

[heftysmurf]

Imagine being the fella who came in here to chime in with the truck in question being his, having to deal with a burned truck/canceled travel plans and whatever else entailed...Only to have a bunch of folks speculate on the cause of the fire....

 

[Maximus Gladius]

Imagine being the fella who came in here to chime in with the truck in question being his, having to deal with a burned truck/canceled travel plans and whatever else entailed...Only to have a bunch of folks speculate on the cause of the fire....

We sound like claims agents figuring out how we aren’t paying out.
But seriously, I am considering pulling my first trailer and all this info is new to me. Very much enjoyed reading the science even though most of it goes over my head.
I wish the survivor of this tragic event well and hope it all goes in his favour!

 

[dcmdon]

Density.

As I offered before, it is correct to say Drag is proportional to Cd and Area. I see now that's what you were going for and not trying to contradict Pappa's equation.

Real story: I once had a manufacturing engineer come to me asking what he should use for Cd for a fence he was designing that had to meet certain wind loads. I told him to use 1.0 (flat plate) and asked to see his calculations. He obviously hadn't studied aerodynamics and from somewhere came up with a formula for wind load (aka drag) that was totally bogus, something like Drag = Velocity X Area x Drag coefficient. His calculated loads were ridiculous (and the resulting units made no sense.)

Correct me if I'm wrong, but his equation would have been right if the velocity was a square function and there was some constant applied to get the unit values where they need to be.

Right?

 

[Klutch]

You don't really know what the drag is unless you put it in a wind tunnel. There are just so many variables. I used to work at NASA Langley where they have some seriously high-tech wind tunnels; some can be super-chilled to allow scale models to simulate very large aircraft.

Every year NASCAR teams would bring their cars in for wind tunnel testing. It's a lot of expensive effort. If they could figure it all out with mathematical formulas, no doubt they wouldn't bother with the wind tunnel testing.

And, yeah. I wish the owner of the flaming JT all the best. I'm wondering if anyone will bother to find out the cause and, if so, report the results where we could see them. Perhaps the insurance company figures it's cheaper to just pay the claim and move on?

 

[MaysvilleStig]

Same thing happened to my Ram Eco diesel which is why I went with the gasser. This is not uncommon for that motor.

My old post
Good while it lasted... | RAM 1500 Diesel Forum

https://www.ram1500diesel.com/search/154942/?page=1&q=Fire&c[searchProfileName]=control&o=relevance

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