Green Transportation

Moving toward a transportation system that fuels healthy people and a healthy planet.

Add to My MSN

MAX Update No. 71: Suspension Streamlining

5/4/2011 12:35:08 PM

Tags: MAX, 100 mpg, fuel economy, aerodynamics, streamlining, Jack McCornack

MU71FairingTest 

Oregonians have been flooding the radio stations with calls about a large glowing disk hovering above the ... that’s the sun, folks, we just haven’t seen it for a while.

A perfect day to take MAX out for some aerodynamic testing. The body is off for repairs, and one of my aviation friends had some related questions, so since it’s my car and I can do what I want with it, I bolted a test fixture to the chassis and built a simple drag comparitor device to show how much better a streamlined tube is than a round tube.

Yeah, yeah, I could look it up, this isn’t cutting edge research by any means, but I’m a DIY guy, so I went ahead and did it. Besides, not every effort at streamlining is as successful as every other effort, and I wanted to try an off-the-shelf product called Streamline. It’s a PVC sleeve material that’s made for sport aviation and its shape is slightly compromised so it can fit different tubing diameters (the small stuff, which I used here, fits 5/8” to 1-1/4” tubes, the larger size fits 1-1/4” to 2” diameter tubes) and as far as I know, there’s no wind tunnel data available for that specific product.

And why do I care? Because many folks like the Old MAX body better than the New MAX body, and like the visible suspension parts and other old-timey styling cues. Anyway, I measured and found that MAX has a total of eight feet of 1” tubing in its front suspension, and a quick back-of-a-napkin calculation suggests the air resistance of that tubing costs MAX about a horsepower at 60 mph. But who trusts napkins any more?

So I got eight feet of the smaller Streamline stuff, to slide over 1” outside diameter 3/4” Schedule 40 PVC pipe, and made a fixture that had eight feet of pipe sticking out one side, and eight feet of Streamline sticking out the other. I stuck the fixture on the front of the car, stuck a digital postal scale on the dashboard, and tied the two together with some nylon cord.

I’ll spare you the details but the result was, the scale read the difference in air resistance between the sleeved tube and the plain tube (times four; I used leverage to make the numbers more definitive). Then I mounted my FAA-pleasing orange and white flag and my yellow flashing light on MAX, and had the airport’s UNICOM operator listen for air traffic while I took two passes down the runway.

I’d hoped to be able to get up to 50 mph but no dice. The first thing I learned was, PVC is pretty flexible, and when I went much past 30 mph the ends of the tube and the fairing started flapping up and down like some ungainly bird with a 16 foot wingspan (the wide span is why I didn’t take it on the highway, by the way). The results came out as the textbook would expect, 1-1/2 pounds of drag reduction at 30, which means we’d save 6 pounds at 60 mph (it’s the square of the difference in speed--double the speed, quadruple the drag) which means saving that horsepower that I mentioned before...which in MAX’s case means adding 4 or 5 miles per gallon.

Of course the new body takes care of streamlining the suspension too, but it will be nice to have an improved alternative for those who are into “the look.” 

Photo by Jack McCornack 



Related Content

Health Benefits of Cycling

Discover the health benefits of cycling and how you even increase your life expectancy with this act...

No Gas at the Pumps ... No Power in the Grid

How will we live with no gas at the pump and no power in the grid?

Dear Mother: February-March 2009

Reader letters on population; tips for starting a fire; artisan bread; gourdseed corn and the Seed S...

MAX Update No. 44: Responses to Sharp Criticisms

Is MAX an actual modern-day vehicle, or just a high school shop class experiment? In this update, Ja...

Content Tools




Post a comment below.

 

Jack McCornack
5/18/2011 11:48:27 PM
Hi TDeL, Man, great minds think alike! If the car has a full body, there's no reason the chassis has to narrow so much in the footwell. Mind you, right now I'm scrambling so MAX will make a good impression at the Mother Earth News Fair in Puyallup in (gulp) two weeks, but I do have a fat-footed conversion on the drawing board and it looks like an easy modification.

TDeL
5/18/2011 12:36:22 PM
Hi Jack, I like the old Seven body style too, but your interpretation of a 50's sporty car and your eye for shape has always pleasantly surprised me. Hopefully an enclosed option will develop as well as a modded frame which gives a little more width for the legs ( I am not horizontally challenged). Looking forward to the new June unveiling. -Tom

Jack McCornack
5/17/2011 3:36:57 PM
PyroTechie, I didn't compensate. In actual use, the difference in modulus of elasticity between PVC and steel is so immense that the stiffening effect of the fairing is insignificant. In this test, all I measured was drag, not stiffness...the plain pipe didn't flex back enough to make any difference in drag that I could detect.

PyroTechie
5/13/2011 11:36:43 AM
I'm curous how you compensated for the added rigidity of the aero tubing in your measurement? The shape of the aero tube alone adds rigidity and having two layers (pipe + aero tube) creates an even more rigid structure.

Jack McCornack
5/11/2011 12:39:40 AM
Ron, I did do a full underbelly, and someday I'll have to take a 4 x 4 down the fire trail I traversed last September and see if I can find it. I intend to make another one, and this time I'll take pictures. And Jeff, Duesenberg didn't do that but their chief body designer, Gordon Buehrig, did--google Tasco or follow the link below, and Aptera does it today. http://www.aptera.com/ and http://www.pbase.com/wingman26/auburn_cord_dusenberg_museum&page=3 will give you a peek.

Ron Garnes
5/7/2011 1:23:07 AM
Jack: Your latest experiment proves again that aerodynamics is critical even at low speeds (20-40 MPH). Have you done anything to the underside of MAX? A full length belly pan or relief vents on the back side of the wheel wells would probably get you over the 100 MPG mark. If you look at the old Formula V cars the SCCA used to race, many of them had fiberglass fairings molded around the old Type I VW front suspension. This not only made them look more exotic, but probably put some downforce on the front tires, as there wasn't much up fron weight-wise. Ron G

Jack McCornack
5/5/2011 11:54:48 PM
Jason, it is indeed an arbitrary benchmark (100 mpg for ten grand) and in many ways, 70 mpg for seven grand would be more appealing...but I want to see if it can be done, and it's a number everybody can relate to. But I'm sure not going to be done designing efficient cars when MAX's mileage hits those magic triple digits. If you can get somebody out of a 30 mpg car and into a 60 mpg car, you save as much gas as if you go from 50 mpg to 300 mpg. In either case, the mileage improvement saves a gallon of fuel for every sixty miles driven.

Jack McCornack
5/5/2011 4:58:37 PM
Jeff_58, To my perpetual humiliation, I grunched the streamlined body (see embarrassing photo on MAX Update #60) before I go the chance to test it thoroughly. I'm busy rebuilding it in time for the Mother Earth News Fair in Puyallup WA June 3-5 and should have some answers by then.

jason thatcher
5/5/2011 1:15:29 PM
Hi Jack, I am actually happy to hear that there are other folks out there who are taken in with the "old" look. In fact, I would be happy to settle for the gas mileage that you were getting before - I really liked the look of the car last year! Isn't 100 mpg somewhat of an arbitrary benchmark anyway? 60+ would more than double what i am getting now, and that would be a huge improvement in itself.. thanks for the effort that you are putting into this project. jt

jeff dean
5/4/2011 5:01:34 PM
Jack, How much gain did you get with the aero-body compared to the original? HP? MPG? can you calculate how much hp it takes at 55 mph? With the old body, the open wheels appear to be the largest drag. Maybe some fenders attached to the spindles or something. Didn't Duesenberg do something like that?







Subscribe Today - Pay Now & Save 66% Off the Cover Price

First Name: *
Last Name: *
Address: *
City: *
State/Province: *
Zip/Postal Code:*
Country:
Email:*
(* indicates a required item)
Canadian subs: 1 year, (includes postage & GST). Foreign subs: 1 year, . U.S. funds.
Canadian Subscribers - Click Here
Non US and Canadian Subscribers - Click Here

Lighten the Strain on the Earth and Your Budget

MOTHER EARTH NEWS is the guide to living — as one reader stated — “with little money and abundant happiness.” Every issue is an invaluable guide to leading a more sustainable life, covering ideas from fighting rising energy costs and protecting the environment to avoiding unnecessary spending on processed food. You’ll find tips for slashing heating bills; growing fresh, natural produce at home; and more. MOTHER EARTH NEWS helps you cut costs without sacrificing modern luxuries.

At MOTHER EARTH NEWS, we are dedicated to conserving our planet’s natural resources while helping you conserve your financial resources. That’s why we want you to save money and trees by subscribing through our earth-friendly automatic renewal savings plan. By paying with a credit card, you save an additional $5 and get 6 issues of MOTHER EARTH NEWS for only $12.00 (USA only).

You may also use the Bill Me option and pay $17.00 for 6 issues.