wind resistance

[Arne]

""I've noticed (being a newbie and not knowing how a tear is supposed to look) that few trailers have any streamlining on the underside of the tear, with all kinds of supports, etc., sticking out.

Does it not matter on the underside?""

If you look at my link, you will see that my tear has only a perimeter frame. There are 2 x-members, but they are turned flat to keep wind resistance down. The torsion axle I can't do anything about, but the spare is 'hidden' behind the torsion axle. The front of the spare is one inch behind the torsion axle. Pic on page 11 near bottom.

Also, I plan on putting a wedge on the roof in front of the fantastic to reduce the wind resistance of the front edge of the vent.

Also, I built the tear as light as I could while feeling comfortable it would be strong enough... I did not go to extremes, but I'm hoping it will be about 900 pounds.

[Arne]

So, I was crawling around under the t/d today, reinstalling the painted torsion axle...

I got thinking it looks like a 2x4 standing up the wide way.... now, I would not want to hold a piece of wood out the window going 65 mph, and suspect it has to be a 'drag'....

So, was wondering if any engineers out there could tell me the benefit of getting a piece of pvc pipe the same diameter, splitting it down the middle, and putting the half piece on the front of the axle and holding it on with worm drive clamps... while at it, I could put the other half on the back side as well...

seems like round is better than flat into the wind, but not sure how much better.

[angib]

I don't think there's much value in tidying up the undersides of trailers, unless you've got some really exotic tow vehicle - for most vehicles, once the air has passed underneath, it is all jumbled up (technical term....) and so doesn't cause as much drag.

The one thing to make sure is that the gap under the trailer is at least as high as the gap under the two vehicle - otherwise the trailer provides a 'dam' effect.

Andrew

[caseydog]

If you look under exotic sports cars, and even some sports sedans designed for high-speed driving, you'll see a pretty flat bottom. At 50 mph, it doesn't matter much. But at 150, it makes some difference.

Unless you are trying to set some speed records for a small car and Teardrop, you aren't going to benefit a lot from rounding your axle or adding wind deflectors.

As you increase speed, wind resistance goes up exponentially. So, when you double your speed, say from 30 to 60, you are not doubling wind resistance. IIRC, as you increase speed by 2X, you increase resistance by 4X.

CD