Good place to get started ? want to get at lest 40-45MPG.highway.

[aerohead]

https://ecomodder.com/forum/member-a...ed-micro-r.jpgGreg Fadler, Group Manager, GM Aerodynamics Engineering, shared the following with MOTOR TREND:
* aero drag constitutes about 30% to 40% of energy consumed on the freeway
* 20% more at 70-mph than at 60-mph
* ( Between 60 and 70, drag increases by 36.1% )
* delta-36.1% / delta- 20% mpg = 10% = 5.54% ( similar to 1963 GM Lab metric for 70-mph aerodynamics )
* the Tahoe's Cd 0.379, vs Cd 0.416 for the typical SUV means 1+ mpg on the highway.
* the Tahoe hybrid's Cd 0.36 comes from its airdam, fascia, and mirrors.
* I couldn't find an official frontal area for the Chevy/GMC/Cadillac variants of this vehicle. Perhaps 34.88 sq-ft ( 3.24 meters-squared ) would be a reasonable working number.
* a curb weight of 5,907- pounds is given.
* from my own experience pulling trailers, I would suggest that any added weight and rolling resistance penalty of an aero trailer is essentially meaningless, compared to the aero advantage.

[ksa8907]

Originally Posted by aerohead

https://ecomodder.com/forum/member-a...ed-micro-r.jpgGreg Fadler, Group Manager, GM Aerodynamics Engineering, shared the following with MOTOR TREND:
* aero drag constitutes about 30% to 40% of energy consumed on the freeway
* 20% more at 70-mph than at 60-mph
* ( Between 60 and 70, drag increases by 36.1% )
* delta-36.1% / delta- 20% mpg = 10% = 5.54% ( similar to 1963 GM Lab metric for 70-mph aerodynamics )
* the Tahoe's Cd 0.379, vs Cd 0.416 for the typical SUV means 1+ mpg on the highway.
* the Tahoe hybrid's Cd 0.36 comes from its airdam, fascia, and mirrors.
* I couldn't find an official frontal area for the Chevy/GMC/Cadillac variants of this vehicle. Perhaps 34.88 sq-ft ( 3.24 meters-squared ) would be a reasonable working number.
* a curb weight of 5,907- pounds is given.
* from my own experience pulling trailers, I would suggest that any added weight and rolling resistance penalty of an aero trailer is essentially meaningless, compared to the aero advantage.

Certainly not empirical evidence but when we moved south, we towed a 4x8 uhaul trailer behind our hybrid (denali, so none of the aero treatments) and mileage was unaffected, still did 18mpg at 80mph. We also had two bicycles on the roof so maybe aero was much better with the trailer and bicycles brought it back down to zero net gain/loss.

[freebeard]

It's possible. HHOTDI got better-than-stock mileage by repositioning a roof-top camp tent.

aerohead -- Was it a caveat?

Unfortunately the key word there is could, I agree, that with vast modification and streamlining, full undertray and near full boat tail the Cd could be near to 0.1, but realistically this person is looking for easy mods to get to at least 40-45mpg highway, even if you count 45mph as highway, it is still a tall order aerodynamically to even get to 45mpg without significant rolling resistance decrease.

[aerohead]

They are one of the few corporations to take advantage of the taxpayer-financed, socialist, aerodynamic research, conducted by NASA, at Edward's Air Force Base, California, in the latter 1970s.
Had the trailer tires been 'inside' the trailer body, you'd have seen even higher mpg.

[ksa8907]

Originally Posted by aerohead

They are one of the few corporations to take advantage of the taxpayer-financed, socialist, aerodynamic research, conducted by NASA, at Edward's Air Force Base, California, in the latter 1970s.
Had the trailer tires been 'inside' the trailer body, you'd have seen even higher mpg.

I didn't have the proper drop on the hitch, so the back of trailer was about 6-10 inches lower than the front. It made a great angle for boat tail!

[aerohead]

Originally Posted by ksa8907

I didn't have the proper drop on the hitch, so the back of trailer was about 6-10 inches lower than the front. It made a great angle for boat tail!

Not too long ago, Don Sherman, of CAR and DRIVER Magazine reported that their long-term, 40,000-mile test Denali, non-hybrid, returned 20-mpg ( and I'll guess it was at around 70-mph ), absorbing 44-horsepower at 70-mph. He did not specify whether this value was 'Road Load-hp' or SAE-hp. If it was SAE-hp, that would yield a BSFC = 0.4882-pounds/ bhp-hour, at 70-mph.
18-mpg @ 80, pulling, is something to talk about.

[ksa8907]

Originally Posted by aerohead

Not too long ago, Don Sherman, of CAR and DRIVER Magazine reported that their long-term, 40,000-mile test Denali, non-hybrid, returned 20-mpg ( and I'll guess it was at around 70-mph ), absorbing 44-horsepower at 70-mph. He did not specify whether this value was 'Road Load-hp' or SAE-hp. If it was SAE-hp, that would yield a BSFC = 0.4882-pounds/ bhp-hour, at 70-mph.
18-mpg @ 80, pulling, is something to talk about.

Well, it only does 16mpg with an empty car dolly at the same speed so... As we all know, aero is king on the hwy.

[Ecky]

My thoughts:

The rear of a vehicle is significantly more responsible for drag than the front. Boat tails work extremely well. But, they're often not practical or aesthetic.

The next best thing is a short kamm and full underbody paneling. Throw in a partial grille block and you might buy yourself a few mpg. Change to the lowest RR tires you can find and pump them up, and you just might hit your goal.

[freebeard]

Boat tail just haven't been done right.


https://i5.walmartimages.com/asr/2a1...2&odnBg=ffffff

[aerohead]

I ran back-of-the-envelope calculations for Don Sherman's data, presented for the above, non-hybrid stable mate of the Tahoe.
1) using the reported 20-mpg, and using 70-mph ( 115- km/h ), yielded 3.5-gallons per hour.
2) multiplied by 6.138-pounds/ gallon ( reformulated E10 Regular Unleaded gasoline ) = 21.483- pounds/ hour.
3) 44- horsepower Road Load / 85% driveline mechanical efficiency ( a value used in the past by CAR and DRIVER, and perhaps from the BOSCH Manual ) = 51.7647 brake- horsepower at the flywheel.
4) 21.483- pounds fuel / 51.7647-bhp = BSFC 0.415 pounds/ bhp-hour.
--------------------------------------------------------------------------------------
5) the 2008 Tahoe's reported projected frontal area is 88.413% of Gross frontal area.
6) using the Width and Height of the Denali, and the 88.413% relationship from the Tahoe yields an appox. Af 36.772 square-feet ( 3.416 sq-meters ).
7) plugging in Cd 0.36 yields CdA of approx. 13.237-sq-ft
8) using the drag power formula at 102.666-feet/second ( 70-mph ) yields a road load aerodynamic horsepower = 30.9948- hp.
9) subtracting 30.9948 from 44.0 = 13.00515 hp due to rolling resistance.
10) using the rolling-resistance power formula yields a rolling friction force coefficient of 0.010954543- pounds/ pound ( for the set of four (4) tires, @ an SAE test-weight of 6,360-pounds .
--------------------------------------------------------------------------------------
11) lowering the Cd to 0.10, and using the velocity-squared fraction, compared to Cd 0.36, yields an aerodynamic horsepower of 8.609666-hp.
12) adding in the same rolling-resistance horsepower ( the tadpole's all-up weight is equal to a single passenger ) yields a new total road-load horsepower of 21.6148-hp ( compared to 44.0-hp ) @ 70-mph ( 115-km/h )
13) 21.6148-hp / 85% mechanical efficiency = 25.42919 bhp at the flywheel.
14) 25.42919 bhp x BSFC 0.415 = 10.553- pounds/ hour.
15) 10.553 / 6.138-pounds/gallon = 1.719-gallons/ hour.
16) 70- miles per hour range / 1.719-gallons = 40.71-mpg @ 70-mph ( 115-km/h ), for the non-hybrid Yukon.
--------------------------------------------------------------------------------------
This is for 40,000-miles of driving, under four-seasons conditions, wind spectra, and topographical elevations changes.
--------------------------------------------------------------------------------------
So, shooting from the hip, it looks like the Tahoe ( with the hybrid advantage ) would have a shot at 40-mpg, even at 70- mph, @ Cd 0.10.
This assumes a constant BSFC, which requires matching the engine load to that of the original OEM 'Map' conditions, typically resolved with taller gearing.
--------------------------------------------------------------------------------------
While ' technically feasible', at 100-years on now, we can stand back and watch the arguments fly.