Fairing Well,NASA truck aerodynamics

[Frank Lee]

I seriously doubt it.

Bob's patent does describe using lift to reduce Crr: http://www.google.com/patents/US5908217

I still doubt it because it takes power to create lift. It seems like it would take more power to create enough lift to lighten a trailer 15% than it saves in Crr reduction.

Best case (heaviest) scenario:
Tractor: 18,000 lbs., trailer: 17,000 lbs., load: 45,000 lbs.
Loaded trailer 62,000 lbs x 15% = 9,300 lbs lift.

Calculator says 94 rolling HP @ 55 mph @ 80,000 lbs.,
@ 70,700 lbs with the lift = 83 rolling HP and +.3 mpg WITHOUT accounting for the HP and fuel required to generate 9,300 lbs of lift.

http://ecomodder.com/forum/tool-aero-rolling-resistance.php?Weight=70700&WeightUnits=lbs&CRR=.0 08&Cd=.6&FrontalArea=100&FrontalAreaUnits=ft^2&Fue lWh=33557&IceEfficiency=.35&DrivetrainEfficiency=. 95&ParasiticOverhead=0&rho=1.225&FromToStep=5-200-5

[kach22i]

Originally Posted by aerohead

http://history.nasa.gov/monograph46.pdf

That's a 172 page wonder.

[freebeard]

Frank Lee -- It may be one of his less credible claims.

I like the idea* of being able to blow the left or right slot to compensate for crosswinds, but now you have me doubting that: What good would blowing a slot on the lee side do anyway?

*Mainly because I have 1500 cubic feet/minute of hot air just being dumped into the wake right now.

[Frank Lee]

Actually I do like the crosswind thing.

[aerohead]

Originally Posted by freebeard

Frank Lee -- It may be one of his less credible claims.

I like the idea* of being able to blow the left or right slot to compensate for crosswinds, but now you have me doubting that: What good would blowing a slot on the lee side do anyway?

*Mainly because I have 1500 cubic feet/minute of hot air just being dumped into the wake right now.

The only thing my pea-brain can come up with is that the 'jet' created by blowing would be low pressure,and induce surrounding air towards it,perhaps reducing the leeward separation and magnitude of the wake.
The 1966 Kawanishi Shin Meiwa PS-1 and US-1 uses a 3,060 hp GE turbine engine to provide high-pressure air for boundary layer control at flaps,rudder and elevator for full control at extremely low flight velocities.
The truck,at crosswind,is like a STOL aircraft at steep angle-of-attack,and the blowing must help as with the aircraft.
http://media-cache-ec0.pinimg.com/73...ceb79115b3.jpg

[Piotrsko]

When did they get a tunnel at Edwards? Yes it's really windy there, but it ain't laminar

[ECONORAM]

I've spoken with a pilot or two about retracting the gear on take-off. Each one said they'd get the gear up and take the additional altitude that comes with that--good in the event an engine goes out.
What I found interesting was that the hp required increases with V cubed. I'd already done the math for the drag equation for my truck...to see what drag I needed to aim for in order to achieve the fuel mileage I'm after. But v^3? Wow. Some good reading. Thanks for sharing.

[aerohead]

*A SAE,75th-Anniversary, "Springboard" article, by Norman Chew,Executive Vice President, Freightliner Corp.,1980 SAE paper shared one of the NASA images and a drag breakdown for the mods.
*I've 'colorized' the schematic to better segregate the mods.
*The base truck was around Cd 0.717.
*After NASA got through with it,it was around Cd 0.289.
*Wind-averaged drag reduction was 67%.
*Zero-wind drag reduction was 59,6%.
*NASA's tests were duplicated in Freightliner's wind tunnel (Daimler-Benz's FKFS tunnel,Stuttgart,Germany),and they essentially found agreement with NASA's numbers.
At zero-yaw ........................................... wind averaged
*Nose = delta 4.8%.................................. 7%
*Cab roof spoiler 15.7%............................. 9%
*Gap = 19.7%......................................... 17%
*Side skirts 8.7%..................................... 19%
*Belly pan 5.9%....................................... 5%
*Boat tail 4.8%........................................ 10%

[aerohead]

Originally Posted by Piotrsko

When did they get a tunnel at Edwards? Yes it's really windy there, but it ain't laminar

All the testing at Edwards was coastdowns on the South Base runway using stopwatches and accelerometers.A 312-mile driving loop through the Mojave Desert was used for mpg testing.No mirrors,no cooling system drag for coastdowns.
Rolling force coefficients were obtained before any aero work was initiated.
Tabulated results were compared to those of Sighard F.Hoerner with very close agreement.
In later follow-on research,the University of Kansas at Lawrence,KS, scale wind tunnel was used.
Later,the Dryden Flight Research Center did get a small wind tunnel,but it wasn't used for the automotive testing.

[aerohead]

Originally Posted by ECONORAM

I've spoken with a pilot or two about retracting the gear on take-off. Each one said they'd get the gear up and take the additional altitude that comes with that--good in the event an engine goes out.
What I found interesting was that the hp required increases with V cubed. I'd already done the math for the drag equation for my truck...to see what drag I needed to aim for in order to achieve the fuel mileage I'm after. But v^3? Wow. Some good reading. Thanks for sharing.

Walter Korff of Lockheed explained the power increase from a doubling of velocity as:
*you're hitting twice as much air
*you're hitting it twice as hard
*and you're hitting it twice as often.
*2X2X2=8 or, 2-cubed (velocity-cubed)