MCI Front End Aerodynamics

[RVMan]

Has anyone tried to reduce the wind resistance by redesigning the front body of the big coaches?

[Busted Knuckle]

I found some pics of Bill Glenn's Eagle on his Facebook page.






He's a member here maybe he'll chime in and give you the gory details and some better pics.
  BK 

[Busted Knuckle]

one more!
  BK 

[Dreadnought]

I've done lots of calculations on this and built up a simple vehicle simultation model- it's a low resoultion model thats really accurate. I've cross correlated it to real world data.

I've measured  that my 64 MC5 can reach about 73 mph top speed with it's 280 bhp in 4th. So I made sure the model correlated to this and the shift points.

From that I estimate the drag coefficient to be around 0.67. It could be lower but it's unlikely.
The frontal area is easy- its about 80 sq ft - as my bus is about 8 ft wide and 10 ft tall.

I've found that the frontal area predominates compared to all these later buses that are approaching 13 ft 6 tall and 8 ft 5 wide.

Doesn't matter how much lower their drag coefficient is- they still need more power to attain the same top speed due to their collosal frontal areas!

Don't forget that forward power requirement is directly proporational to the frontal area multiplied by the drag coeeficient. A modern MCI is probably closer to 110 sq ft frontal area.

That's why I have zero interest in these monster roof lifts. It helps that I'm only 5 foot 7 so dont need it.

It probably also explains why I get between 8-10 mpg- along with having a manual trans and, to a lesser degree, the weight of only 28,000 lbs (has a bearing on rolling resistance- it factors in more than a car but no where near the aerodynamic drag).

If I were to practically make something- I would add some sort of a chin spoiler or air dam-take a look at a early 90s Prevost XL40. Something like that to minimise the airflow going under the bus and being buffeted around.

Then I'd smooth out the wheel hubs, may be get alcoas and have those smooth hub caps like a prevost luxury marathon or liberty.

May be do something with the mirrors.

I don't have access to a wind tunnel, so Id undertake each modification and do a coast down test to estimate actual real world improvements.

The other practical way to gauge each improvement is glue little tufts of wool at targeted areas of concern, have someone drive the vehicle and film or take pictures and see how the tufts allow you to visualise the airflow around the vehicle. That's what Jaguar did in the 60s for the Jaguar XKE (in the absence of Computational fluid dynamics). The tufts of wool should never be pointing forward as that indicates an energy sapping reverse flow.

[luvrbus]

What do you gain with all the expensive  resherch for aerodynamic, the commercial world of buses and trucks just overpower the flaws with higher HP and torque fuel efficient engines. It is common to see the 600 + hp Cummins in RV's pushing a 45 ft ,13 ft tall and weighing over 50,000 lbs averaging 8 to 10 MPG.My ISX 600 Cummins would average over 8 at 70 to 75 MPH all day long lol @ 180 degrees. The cooling fan draws the most HP from the engine but the new Hyd and electric fans are taking that out of play now on the newer stuff

[Jim Blackwood]

Fuel efficiency has long been a lead concern and oem's have the budget to fine tune where it's practical, so it makes sense that they would put their money where it will do the most good. Whenever it looks like maybe they didn't, the first step is to question what hidden factors make it look that way to you. Pretty much guaranteed there are some things you haven't considered.

Jim

[windtrader]

Adding to Jim's comment. Let's assume there is sufficient free market drivers in the commercial bus space; that might not be the case as Prevost and MCI seem to be the only ones in this space in the USA/Canada market.


Fuel efficiency is a top expense in operating buses and one would think that if a new model that improves mileage with a reasonable value proposition that this would provide them to invest in research and retooling to bring new models to market, much like tractors have evolved with all sorts of aero improvements.


So, why nothing in buses? On a 45' platform, you'd have to loose interior volume for a sleeker front end. On a 40' there is 5 added feet to provide a sleeker design and retain interior space. Only problem is hardly any new buses are 40'. 


What would be interesting is to know what the actual improvements would be. For example, I wonder what MPG the two decker MegaBus achieves? Common sense says it is less but how much better; maybe the difference is not enough to do the work on improving aero flow?


I agree there is a market based rationale that nothing has been brought to market. One last thought is look at bus design across the globe, whey do they all look the same?

[luvrbus]

Trucks  have added a few aerodynamics over the years mostly for looks and  all look the same now pulling a 13ft tall x  102 wide x 53 ft long  trailer with no aerodynamics, Here in US the trucks conventual with the engine in front in Europe they are cab over the engine designed like a block no aerodynamics to those   

[Jim Blackwood]

I think the problem is probably a combination of things like mostly what the airflow looks like around the end of a big ole brick moving at 75 mph. The air will stack up in front to some extent and flow around the edges. That stack-up probably creates it's own dynamic profile in front of the bus, much like the bottom side of a rain drop, and the biggest differences are going to be made at the edges, or corners where it affects laminar flow. There is probably more to be gained by promoting smooth continuous flow around the corners and down the sides and top without flow separation than there is by profiling the front end. This is probably why we see the designs we do. Any flow separation will result in turbulence, which results in drag and decreased economy. Anything you have projecting into the airstream is going to trip and destroy that laminar flow. AC units, vent covers, photocell arrays, awnings, etc. All the things we love to add on. It looks to me like more effort has been spent in the last couple decades on maintaining laminar flow than has been directed at vehicle front end design. Sure, we still have lots of cars with highly raked windshields but we also have a goodly number with nearly vertical ones that achieve remarkably good Cd numbers. Treatment at the rear can also have a large effect, but is a difficult problem to solve, as evidenced by those semi trailers we see with the tent on the back that is always folded up and not used. But racing has a long history of aerodynamic rear corner treatments that may eventually find their way onto buses if there is any mileage to be gained from them.

Jim

[lostagain]

Little improvements in aerodynamics are measured in fractions of a mile per hour. Insignificant for the bus nut with a fleet of one vehicle. It only benefits the big fleets with hundreds and thousands of tractors and trailers that rack up millions of miles a month. The best way to reduce fuel consumption is to slow down. That is why the big companies have their trucks governed at 62 mph.

[buswarrior]

The dashboard of a Megabus Van Hool double decker typically shows a crack over 6 US mpg.

Model of operation is running full of people and their chattels, as fast as foot to the floor line run operations will go, governed in the 67-69 mph territory.

I am reminded of the roof cap change in the MC12 vs the MC9, and the similar leading roof edge shape of the highway going D models. Regional transit wants their big destination signs, and aren't worried about aerodramatics.

cleaning the edges can have big impacts, as can subtle rear end touches.

happy coaching!
buswarrior

[windtrader]

Interesting thought. Maybe having a taller front facing the wind may not make much difference. I've run my bus for nearly 7 years now and I swear it ALWAYS gets the same 5.5 MPG. It doesn't make any sense so being a foot taller might not change it either.

[luvrbus]

To get head room nothing is going to change on buses ,they just use HP to keep the fuel mileage in check now all the buses are over 500 hp and the exhaust smoke is non existence they burn so clean   

[Dreadnought]

Here's a post I did that covers real world testing completed on older MC7s and mc8s as well as fairings to improve the aerodynamics.
The work was done by Purdue university and MCI back in 1980

https://www.busconversionmagazine.com/forum/index.php?topic=37583.0

I don't have interest in changing the appearance to pursue aerodynamics myself with the limited mileage I do but I'm interested in the science,