Aerodynamic trailer design

[MetroMPG]

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Sexy:

[Ecky]

Been out of town for a few days, but I'm back to drawing. Not sure yet where I want to fall in terms of compromises between absolute width (e.g. 48" plywood sheets), internal area, aero impact and turning radius, but having the box on top be replaceable means I can build several tops for different uses.

The Insight has about 28,150 cubic inches of cargo space in the hatch + hidden cargo area under the floor, or 16.3 cubic feet.

If I were to pick up a stock HF trailer with a platform of 40x48" I would have a maximum angle between trailer and car of ~82.5° with the trailer sitting 30" behind the ball. Internal area at 15" uniform height is 28,800CI, or 25,920CI if I taper it to 12" at the rear.

Widening the trailer to 48" would not affect turning much - max angle would still be ~80°. Almost all of the trailer would still be out of the windstream, with only the top corners poking out, though Cd would be increased compared to a narrower trailer. I'd have roughly 34,100CI of internal volume assuming a uniform 15" height, and 30,700CI with a taper, both accounting for recessing the wheel wells to fit the wider box. Alternatively, I could look for another trailer that already comes 48" wide, so I wouldn't have recessed wheel wells, which would give an extra ~400CI of volume.

Extending the trailer platform forward 6" and leaving it at 40" wide reduces angle before the trailer contacts the car to approx. 75°, increases the height at the front of the box to ~17" while not hurting aero and total volume ends up at ~32,880CI/30,000CI.

Extending the trailer platform forward 12" reduces the turning angle to around 55°, increases the height at the front to 19" and increases total volume to ~37440CI/34560CI.

Attaching a 20" hollow semicircular nose to the front of the trailer (as it looks like aerohead did in his CRX trailer) would give a maximum angle of ~60°, allow a maximum height at the front of the trailer to be 22", and give an internal volume of approx. 40,800CI/37,920CI. The tip of the cargo box would be 10" behind the ball.

Attaching a 20" hollow semicircular nose to the trailer and setting it about 6 inches back from the front of the platform would allow for a maximum turning angle of ~80°, a height of 20" at the front and a total volume of approximately 36,700CI / 34,180CI. The tip of the cargo box would be 16" behind the ball.


It looks like a rounded nose is the way to go for maximizing internal volume while maintaining turning angle, though it does increase the difficulty of building the trailer unless I can find something prefabricated that I can adapt.





Please excuse the slightly sloppy drawings. ^^

[Ecky]

Any thoughts on the ability of the HF 12" trailer's bearings/axle to survive many thousands of miles with 3-500lbs on them?

[aerohead]

Originally Posted by Ecky

Any thoughts on the ability of the HF 12" trailer's bearings/axle to survive many thousands of miles with 3-500lbs on them?

I went from Texas out to the West Coast and back,with over 600-lbs,and just the 8" trailer wheels.I think you'd be okay.
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Thinking about the nose.For something 'pre-made',A wheelbarrow body,whether steel or plastic,has some fine shape when inverted.This 'nose' could be cut in half to form the sides of a wider trailer nose,then just fill in the void.
It would give you side radii and top radii,plus a slope-back 'Stromform' nose,considered one of the best.
http://ecx.images-amazon.com/images/...S._SL1200_.jpg

[Ecky]

Leaving it upright might be even better. The rounded top should clear the bumper and give some extra volume with a given turning radius.

[freebeard]

I checked back through the thread and I haven't posted this here, so here:



This is what I would do before a HF folder: It steals the construction details from a 1952 Silver Streak Clipper and places it over the Sacred Template. Silver Streak used the simplest possible construction; with a central tube from the hitch, C-channel crossmembers and a carriage bolt pinning the end of the crossmember to the deck. Size the parts and compare the weight. The center tube in the pic looks fat because it was intended to be a fresh water tank.

Instead of a wheelbarrow, I'd look for a 2nd hand car-topper.

[Ecky]

Not sure what kind of vehicles would have a topper that's 40-48" wide.

[Ecky]

Found this on craigslist:

https://jacksonville.craigslist.org/tls/4791231640.html

57x38x20", 20 cubic feet of internal volume (34560 CI)



Taper isn't right, but I may find the right box.

Another:



67 x 35 x 16, 15 cubic feet.

EDIT: Does a premade cargo box exist that doesn't have a terrible aerodynamic shape? They're not even close to the profile.












Thinking building from scratch, or maybe using the wheel barrow front and building the rear from scratch would return the best results.

[freebeard]

The first example is like the one I have. Cut in half and plan-tapered it would be a good fit for a VW Beetle, which is 42" across above the rear axle line. I chose not to cut mine up.

The second one could be quartered and spread at the front, horizontally and vertically. It would be a big step ahead of the square-framed box you started with. I'd put the lower section below the deck.

I notice you haven't put the wheelbarrow to The Template. That would be a first.

[Frank Lee]

First, I wouldn't be scared of the HF trailers. I have one. The key is to remove the shipping/storage grease from the bearings and hubs and put real wheel bearing grease in them. I think people that have problems never did that. Also, quality control is spotty on any Chinese stuff; I found weld spatter on the axle where the grease seal rides. Fine sandpaper knocked that off in a jiffy.

Second, you might want to just get one and determine how close you want to shorten the hitch and everything by experimentation. I know for a fact that short lengths between hitch and trailer axle can easily "out-steer" the car, by that I mean when backing up the trailer can easily turn sharper than your ability to steer resulting in a jack-knife and/or many many fore-n-aft corrective actions. I also know we want to suck that trailer in as close as possible for aero; therein lies the conundrum. I considered all this and stuck with the stock hitch length.

Third, backing up with a small trailer can be quite a chore due to visibility as in, not being able to see it until it starts jack-knifing. My HF behind Moon Unit is almost invisible out the windows and mirrors unless it's turning.