Phil Knox's aero-modded 1970 VW van

[aerohead]

Originally Posted by bondo

That is over a 25% reduction in Cd! That is substantial. I thought I was doing good with a 10% reduction in Cd with the aerocap for pickups!

No wonder you know a little about aerodynamics, you have been doing neat stuff for 30 years now!

Thanks for sharing with us,

Bondo

Yeah,and this is 6-years after the first "Energy-Crisis." You can imagine my reaction to automakers claims that high fuel economy was just too hard to pull off.

[aerohead]

Originally Posted by MetroMPG

Did you make any changes to permit engine cooling? Didn't the original design use the low pressure at the back to draw air through the engine compartment, exiting through vents on the back of the van?

Thanks for posting this, Phil.

Darin,as Frank has mentioned,the air-cooled VWs dump their cooling air under the rear body valence into the wake.My boattail extended down to the top of the rear bumper and was completely open underneath to allow the original engine cover to be opened for servicing and allow the engine cooling air to communicate with the low pressure of the wake.I did get protection from the weather under there while checking the dipstick.As always,I could have done more,but budget and calendar conspired to end the work as you see it.----------- With respect to cooling,the drag reduction allowed the engine to operate at a lower load,thereby helping cooling that way.

[aerohead]

Originally Posted by ShadeTreeMech

I suspect some of the increase in efficiency was helped by it having a really bad .455 cd. When you start bad, any improvement is substantial. I suspect if I were to do the same with my van, which already has a cd of .35, I would be lucky to net the same percentage decrease, which would be a .26

The work is indeed nice and clean, though. Reminds me of an Airstream travel trailer. Looks like the rear tailgate was completely inaccessible; wouldn't that be a problem for a VW camper come tune up time?

When I did the mods to the CRX,I was starting at Cd0.35 and got to Cd 0.23 for a 28% mpg improvement.From the speed runs at Bonneville,the boattail was the single largest contributor to top speed.Combined with the cardboard and duct tape mods derived at the Salt Flats,the trip on to the West Coast,and then back home to Texas got me an added 8.6 mpg compared with stock.The data suggest that most of that came from only 12-inches of boattail.---------- I'm certain that the VW boattail was also the singlemost contributor to mpg,later borne out of R&D by NASA,which conducted aerodynamic work on vans at Edward's Air Force Base,and published in the 1980s.-------- If you lived next door,I'd help you cobble something together for a test.I'd be very interested to know what it would do.Some of the recent van-type concepts were attaining Cd 0.19,and 146-mpg,as in the case of Renault Vesta.

[aerohead]

Originally Posted by winkosmosis

Wow, that's a huge improvement. I wonder how much of the improvement is from the boattail, and how much from the belly pan

My hand is still gimped up from the Mesquite puncture wound so will try and be productive on internet today.----- I brought my paper on the VW project.This is what I can share:*the standard baseline tank - mpg over 3668 miles of testing was 23.795 mpg,at a steady 55-mph( the Federal National Speed Limit).--------------------------------------------------------------------- With addition of all-season steel radial tires and bellypan,and after 981 test miles,the tank mileage was 26.136 mpg(a 9.83% increase).---------------------------------------------------------------- With addition of boattail and cardboard rear wheel skirts and 589.4 test miles,the tank mileage was 30.187 mpg ave..According to A.J.Scibor-Rylski,total shielding of the rear wheels would allow a maximum 1% drag reduction( 1/2% mpg improvement).Since the boattail and wheel skirts added 15.5% mpg,deducting the half percent for the wheel skirts leaves 15%,as the contribution from the boattail,or,just over 4-mpg from the boattail.---------------------------------------------------------------- NOTE: the testing was conducted between Lubbock,Texas and Ruidoso,N.M.,along the path through Roswell,N.M.and included mountain driving on significant grades.The highest mileage (35.6 mpg) was attained on the level portions of West Texas and Eastern New Mexico.

[mikeemans]

Has anybody done work on the classic 80's Chevy vans? I've two of them (both 1990, one V6 and one V8) in Kuwait with a number of plans to play aero, however doing the underbelly I thought would give good gains, not? The van's floorpan is really a raft of cross members that stand out (or point down) like sails! I also plan to redirect air into the front wheelwells by opening the headlight housings, replacing the lights with small diameter lens-type headlights.

Of all things, I found dumping the clutch-fan (radiator fan) in favor of an electric fan (Volvo S80) not only resulted in massively eliminating engine vibration, but I also noticable improvement in performance, hence economy.

On the V6 I've added a windshield (?) between the bumper and the front axle crossmember, and the result was tangible.

Mike

[aerohead]

Originally Posted by mikeemans

Has anybody done work on the classic 80's Chevy vans? I've two of them (both 1990, one V6 and one V8) in Kuwait with a number of plans to play aero, however doing the underbelly I thought would give good gains, not? The van's floorpan is really a raft of cross members that stand out (or point down) like sails! I also plan to redirect air into the front wheelwells by opening the headlight housings, replacing the lights with small diameter lens-type headlights.

Of all things, I found dumping the clutch-fan (radiator fan) in favor of an electric fan (Volvo S80) not only resulted in massively eliminating engine vibration, but I also noticable improvement in performance, hence economy.

On the V6 I've added a windshield (?) between the bumper and the front axle crossmember, and the result was tangible.

Mike

Mike,the Chevy should react like any other bread box on wheels.If you can find the FLOW-IMAGES thread,you'll eventually see the Cd 0.16 "van" that Klemperer came up with in 1922 which remains a "benchmark for low drag today.That body would give about a 33 % mpg increase at 55-mph,more at faster speeds.
CAR and DRIVER attempted a full-size van aero-mod in the latter 1970s.Their bellypan was of no benefit unless painstaking detail was applied.
Your fan delete is one which is well known of and proven benefit.
I would mimic the front of any modern van or pickup if you can.Smaller mirrors have shown measurable results.
One and a half feet length of boat tail gave me 4-mpg.A receiver-hitch cargo box might serve you as a foundation for such a mod,with quick-on/quick-off capability.
This is something "hard to park" curbside and better suited to long highway excursions.

[mikeemans]

Thanks Aerohead. Great recommendations, and a lot of news/info for me to consider. I heard of another guy, some years back, that created a boat tail with canvass material which got "inflated" as speed picked up - it had an air inlet. This saved a lot on weight, and allowed for easy install or take down. Just a comment that jumped to mind...

Now, let me check up the recommends you sent me. Stay cool, take care. Mike

PS: Oh, and the mirrors are killers! When doing long distances I simply fold them flat or (once) turned them horizontal.

[aerohead]

Originally Posted by mikeemans

Thanks Aerohead. Great recommendations, and a lot of news/info for me to consider. I heard of another guy, some years back, that created a boat tail with canvass material which got "inflated" as speed picked up - it had an air inlet. This saved a lot on weight, and allowed for easy install or take down. Just a comment that jumped to mind...

Now, let me check up the recommends you sent me. Stay cool, take care. Mike

PS: Oh, and the mirrors are killers! When doing long distances I simply fold them flat or (once) turned them horizontal.

That guy is in Lubbock,Texas.
The Aerodynamics Laboratory at Texas Tech University did some model wind tunnel research for him.
He does use ram-air to inflate the envelope,it's clever engineering.
I wish he'd seen Walter Korff's boat tail design of 1963,or Baron von Fachsenfeld's design of 1930.They are both aerodynamically superior.
Tech published an article about the fellow around 1990/91,I'll see if I can dig it out.
There's a shot of the inflatable tail for the T-100 undergoing tuft-testing in New Mexico in the Phil Knox aerodynamic photo archive if you can find it.
They work!

[COcyclist]

I also plan to redirect air into the front wheelwells by opening the headlight housings, replacing the lights with small diameter lens-type headlights.

Mike[/QUOTE]

mikeemans, the idea is to seal up the high pressure area in the front of your vehicle. Air hitting the front of the van makes it inside through gaps and openings, swirls around and creates drag. You may want to consider making flat covers if you have don't have flush mounted headlights and "basjoos" the gaps.

http://ecomodder.com/forum/showthrea...-gap-4736.html

Phil, thanks for breaking down the aero gains on the VW. You are an inspiration and an asset to us all. I am eager for warmer weather to start on my belly pan and receiver hitch-mounted boat tail. I welded up the plug-in "stinger" over Christmas vacation. I should be able to start building from that this spring.

[Domman56]

Originally Posted by vinny1989

I'm betting the belly pans didn't help much. - those vw campers had an almost smooth underbelly anyways, same as the beetles.

Would lowering it have helped at all?

Lowering it could never hurt