Phil Knox's aero-modded 1970 VW van

[aerohead]

Hello all.There has been some interest in streamlining vans,and especially some interest in van boat tails.Al Glidewell has scanned the photos of my college project with the VW van and we're going to see if we can get them posted here.The work was done 1979/1980 for a senior project at Texas Tech.A 1970 VW Transporter was modified with 0.32-inch thick aluminum full bellypan,cardboard and duct tape rear wheel skirts,and aluminum-over-wood skeleton 18-inch boat tail extension with increasing curvature up to an exit angle of 20-degrees,as measured from the vehicles longitudinal centerline.---------------- The "kit" provided an 26.8% mpg improvement in mpg.Cd was estimated at 0.35-o.32,from an original Cd0.455.Mpg was as high as 35.5 mpg at a steady 55-mph.

[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

[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?

[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

[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.

[Frank Lee]

VWs exhaust the cooling air underneath

[Istas]

That really is an amazingly effective improvement. Thanks for sharing it with us!

[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?

[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

Sorry,I didn't expect to be back at the computer 'til next weekend and I don't have my materials with me.When the testing was done,everything was done as a "kit"and I had to rely on published relationships to help sort it out.The reason for the boattail,was that from the published literature it promised significant improvements.----------- I'll bring my papers next time and post what I deduced.

[aerohead]

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?

My van was just the standard transporter and lacked all the Westfalia equipment,which I mimicked.The original underside was a deep,ladder-type frame with deep recesses.According to R.G.S.White's Method of Estimating Drag Coefficients,it had one of the worst undersides in the industry.After studying Aerodynamics of Road Vehicles by Skybor and Rylski,I was convinced that my VW was a premium candidate for the bellypan.--------- Lowering would have certainly helped,although would effect utility for the places I'm likely to go( I still have the van).Lowering any vehicle effectively increases its fineness ratio,reduces frontal area a smidge due to cloaking of the tires,and also lowers C.G.,all good things.