MAX Update No. 71: Suspension Streamlining

| 5/4/2011 12:35:08 PM


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.

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.

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.

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