Semi Truck Engine Hot Air Exhaust Vent Aero I.Q.

[Shepherd777]

Originally Posted by drmiller100

Be VERY careful about the rpm you try to spin it at. Axial flow fans (traditionally a boat's propeller, but a traditional car fan sort of acts like one) the amount of air is a function of the RPM, the diameter, and the pitch of the blades.

An aside. What would be REALLY cool would be to drive the fan with a hydrostatic pump - the logic would be to measure exit temp coolant out of the radiator, and drive the fan faster until the coolant temp drops.

Horton made me sign a waiver not to operate the fan higher than 2200 rpm's. So I know it is good for at least that. But that high an rpm in this truck is a moot point. We will be operating the 450hp Cummins diesel in this truck just like an electric motor. That is, at almost a constant speed, in the most optimal range of 1100-1300 rpm. Procedure: go up a hill, drop to 1800ft. lb. torque peak @ 1100 rpm, split the 13 speed transmission to the next lowest gear, rpm's will climb to only 1300, go up the hill some more. Rinse & repeat. No grade rpm @ 55mph will be 1150, if I remember the math correctly.

Horton has supplied the hardware and software for a viscous unit. The WindMaster Revolution fan is controlled by Horton's wonderful Stratis viscous device. And the Stratis is also a very intelligent fan clutch. Fans and Fan Drives - Stratis® / Viscous Fan Drives | Horton It constantly monitors the engine computer (ECM) and if the engine only needs 5% cooling from the fan, that's all the fan puts out. Why use that other 95%, and waste all that fuel, if you don't have to?

[drmiller100]

holy crap.

that thing is neat! From the peanut gallery, they need to sell it to the heavy equipment and farm equipment market.
Those markets have MASSIVELY oversized fans for extreme conditions, which suck a lot of fuel when they are not needed.

Horton has a homerun with that product. Simple, elegant, and effective.

[Shepherd777]

Originally Posted by drmiller100

holy crap.

that thing is neat! From the peanut gallery, they need to sell it to the heavy equipment and farm equipment market.
Those markets have MASSIVELY oversized fans for extreme conditions, which suck a lot of fuel when they are not needed.

Horton has a homerun with that product. Simple, elegant, and effective.

Thanks. Yep Horton has some way-cool stuff. I'm pretty sure they are heavily involved in that off-road stuff already.

That Stratis viscous drive sits in between the beautiful billet adapter they made for me that bolts onto the crankshaft, and the rear of the fan.

[3-Wheeler]

Originally Posted by Shepherd777

Thanks Jim, but I'm not sure if I agree with your postulate. The air at the top of the tire is going forward, not towards the rear. Only the area of the tire that is below the axle goes rearward, correct? We will have a small wheel-well over the tire to hopefully mitigate the effect you are describing......

Yes, the air from the top of tire is going forward, while the radiator is going backward, and passing right over the top of the air from the tire, and that is why I mentioned the ductwork, to keep the to flows separated from each other.

Jim.

[Shepherd777]

Originally Posted by 3-Wheeler

Yes, the air from the top of tire is going forward, while the radiator is going backward, and passing right over the top of the air from the tire, and that is why I mentioned the ductwork, to keep the to flows separated from each other.

Jim.

Okay, I agree that the air on the top of the tire is going forward, but I'm not sure how much volume or velocity it has going forward.

We will have that small wheel well and the duct I spoke of earlier to hopefully mitigate any effect of the tire air going forward. If a tremendous amount of air went forward off that tire and under the hood, I agree it would fight with the engine cooling air coming rearward from the radiator and the engine cooling fan.

It reminds me of the old line by comedian Steven Wright where he put a humidifier and a dehumidifier in the same room to fight it out.

But think of a steering tire in the rain. The vast majority of the splash and spray is going rearward, not forward.

Please refer to the last image below.

I always thought this splash & spray was most attributable to the speed of the vehicle through the air, and the tires picking up water from the pavement. Not as much due to centrifugal force slinging the water droplets off of the tire itself. I understand the centrifugal force is a contributor to the splash and spray. Just not as much as the water splashing off of the pavement, combined with the slipstream traveling rearward.

Fortunately we have XZA2 Anti Splash Steering Tires from our major sponsor, Michelin Truck Tires. The XZA2's have a circular protrusion that extends outward about an inch on each sidewall, to vastly reduce splash & spray.

[3-Wheeler]

Originally Posted by Shepherd777

....But think of a steering tire in the rain. The vast majority of the splash and spray is going rearward, not forward....

I would agree that the water spray from the tire "appears" to be going backwards.

Now the question is:

1) Is the majority of the spray really going "backwards" off the tire from centrifugal force?

2) Is the spray really going forward on top of the tire in the wheel well, hitting objects inside the inner fender, dropping toward the road surface, and the wind catching it and "pushing" it backwards? (this is my choice).

One way to find out would be to utilize a tire testing circular drum and test water spray on that, and measure water droplet propagation with a stroboscope. However, the rotating drum itself has air moving across the top of that, and compounding the research.....

I doubt anyone has that apparatus available, so onward with speculation on what is really happening.

If it was my truck, and I'm looking for aero gains, I would certainly make a specialized duct from the radiator back to the exhaust opening, and keep it separate from the tire well area if possible.

Jim.

[slowmover]

Are those MICHELIN tires only for the Steer Axle, or is this also a feature of their single-wides (which I assume this truck is using)? A long overdue and welcomed bit of tech!

[Shepherd777]

Originally Posted by 3-Wheeler

I would agree that the water spray from the tire "appears" to be going backwards.

Now the question is:

1) Is the majority of the spray really going "backwards" off the tire from centrifugal force?

2) Is the spray really going forward on top of the tire in the wheel well, hitting objects inside the inner fender, dropping toward the road surface, and the wind catching it and "pushing" it backwards? (this is my choice).

I can ask the engineers at Michelin. I'm sure they know. But the tire is basically smooth on the footprint surface. If I spin my Dremel tool at 10,000 rpm with even a rough sanding wheel on it, I can't feel any air spinning off of it. And if I recall the math correctly again, truck tires spin at like 500-600 rpm. If truck tires were built like water wheels on Mississippi steamboats, I could see a lot of water spinning off it due to centrifugal force. But again, tires are smooth. I think the tires are picking up the water from the road only, and then slinging it out.

Originally Posted by 3-Wheeler

If it was my truck, and I'm looking for aero gains, I would certainly make a specialized duct from the radiator back to the exhaust opening, and keep it separate from the tire well area if possible.

Agreed.

[Shepherd777]

Originally Posted by slowmover

Are those MICHELIN tires only for the Steer Axle, or is this also a feature of their single-wides (which I assume this truck is using)? A long overdue and welcomed bit of tech!

Correct. Only the steering tires have the protruding ring on each sidewall, inside and outside, and are true AntiSplash.

We do have 8 (four on the tractor and four on the trailer) of Michelin's wonderful X-One Super Singles on the truck. They are completely covered by skirts on both units, so road-side rain splashing of automobiles or other vehicles will not be an issue.

We even have aerodynamic mud flaps on both units as well to reduce splash & spray, and of course, to save fuel.

[brittanycmpbl]

Wow! nice car.. i love the red one