Round vs Squarish Eggs - Page 4 - Fiberglass RV


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Old 05-11-2011, 08:35 PM   #43
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Ver-r-r-r-y interesting.
Thanks for the link back to Ken's project, Donna. I'll have to post there and ask...
I'm thinking a whole-front mod, though-

Greg, I haven't noticed the shape you describe- when you say "downward slope", do you mean sort of like what an upside-down boat looks like?
Like, starting at the coupler and traveling up and back to the peak at the roof?

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Old 05-11-2011, 08:40 PM   #44
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Well the slope is only on the V part of the trailer. Like the trailer is a box with a V nose on the front and the top, or roof of the V nose slopes down slightly towards the front.
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Old 05-11-2011, 09:16 PM   #45
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Gotcha!

Hmmm...

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Old 05-14-2011, 10:50 AM   #46
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Well, I got a Private Message from Brian B-P and he says that the V-nose shape doesn't help in the wind resistance department.
If that's true, why would the slightly more rounded corners on a Scamp's vertical walls make it more aerodynamically efficient than a Trillium of equal proportions and weight???

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Old 05-14-2011, 11:43 AM   #47
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He sent me the same thing. From what I understand the downward slope is where it gets better, not all V nose trailers have the slope and it's only a slight slope, nothing like the Lil Snoozy.
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Old 05-14-2011, 12:22 PM   #48
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Yeah- I think you said so in your other post...

So what's the big deal about Degrees of "Roundness" of Scamp/Bigfoot/Trillium/etc. upper front corners???


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Old 05-14-2011, 12:35 PM   #49
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Aerodynamics is super-complicated. That's whey companies spend hundreds of millions on wind-tunnels. Laminar flow, skin friction, parasitic drag, etc etc. People get PhDs in this stuff.

In general, frontal area is the first and most important factor.

Rounded front helps some. Note that it affects the frontal area.

Tapered back helps. Ideal taper is 5 times as long as it is wide. That's the shape of an airplane wing.

The bottom of the trailer is probably as important as the side or top. That's why the latest NASCAR wind tunnels have rolling floors.

The wind deflectors added to trucks in the 1970s don't make a big difference, but they do make a difference. With the fuel that those things drink in a year, the deflectors easily pay for themselves.

If cars were wing shaped, they would have lift and become unsafe. Seriously, Audi had to add spoilers to their hot little sports-cars 15 years ago because people were crashing on the Autobahn when they lost rear traction at high speeds.

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Old 05-14-2011, 01:56 PM   #50
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Thanks, Ron!

Whew!
It'd be interesting to calculate the dimensions of the perfect FG trailer version of this!
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Taking a look at the Original poster's question....

Quote:
Originally Posted by melissab View Post
In particular I was thinking of the Scamp/Bolers compared to the Trilliums/Escapes. I'd think the squarer FG rigs would fare worse. So is there a difference between the 2 shapes and gas mileage? And if not, why not?
Are any of the below designs measurably more aerodynamically efficient than the others?

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Old 05-15-2011, 11:18 AM   #51
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Quote:
Are any of the below designs measurably more aerodynamically efficient than the others?

Francesca
Nicely phrased question. The only way I know to answer that is by measuring. In science class we call this empirical study. Anybody have a few tens of thousands to rent a wind tunnel?

Actually, you can get some results with scale models and small wind tunnels.
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Old 05-15-2011, 03:22 PM   #52
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While we're waiting for our Government Grant to be approved, I guess we'll have to rely on the evidence of our own eyes!

The funny thing is-
When I look at those pictures I can't see much difference in shapes except-
Do my eyes (or understanding ) deceive me, or is it the Bigfoot that most closely represents an attempt to imitate the airplane wing model?
It does have the rounded horizontal leading edge that slopes rearward in both directions, and a repeat of same at the back of the trailer.
According to Private Messenger Brian B-P, the back is as important as the front!
The Casita does have a bit more of a "Buddha Belly", but then there's the flat surface of the propane tank covers that might negate its "effect".
Plus its back is flat as a pancake, as is the Scamp's back.

Am I missing something, or wrongly interpreting what I see?

....
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Old 05-15-2011, 03:57 PM   #53
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The most important factor in drag is frontal area. I believe the Big Foots are wider amd probably taller.

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Old 05-15-2011, 07:00 PM   #54
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Most eggs are shorter in height (several inches, sometimes a foot or more) than most conventional trailers. Second, the eggs have rounding at the upper corners that stickies lack. Both of these factors reduce frontal area.

Then there is the rounding around the front and rear edges. I think these surfaces may let the air make a slightly more gradual transition around the front and back than would a totally sudden 90 degree change... this curved area is relatively slight but it may help somewhat.

In the case of a modest angle (wedge) shape at front or rear, I'm not sure if it does as much as the factors I've listed previously. I can say that my previous 6x12 cargo trailer had a very slight bit of rounding at the top, whereas my current one is totally flat but adds a vertical V front; I could not quantify a change in gas mileage between towing the two.
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Old 05-15-2011, 08:49 PM   #55
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Smile Air resistance

I don't think there is that much difference between the rigs you list.

Now a Compact has sharper corners, but it is not as tall so it probably is a wash out.

Compared to a stick built like Nash or Scotty, I would think any egg would beat them. Of course, if you have all kinds of things hanging on your egg like air conditioning, awning, etc, all adds to your drag coefficient.

One of the biggest gas wasters is speed. The speed coefficient is squared so that at 50mph = 2500 but at 70 mph = 4900 nearly twice as much yields half the mileage.

I always get a kick out of these people who buy hybrids like Prius and then pass everything on the road.
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Old 05-15-2011, 09:06 PM   #56
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So-
Is it fair to assume that there's very little difference in aerodynamic efficiency between (among?) the brands of fiberglass trailers inquired about by the Original Poster?

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