Round vs Squarish Eggs

[Donna D.]

Originally Posted by Francesca Knowles

Is cutting wind resistance the purpose of the V-nose design I see on some cargo trailers?
That would be an interesting modification to contemplate for my Trillium...

Francesca

Ken would have to substantiate this, but I believe that's the reason he put the beak on his extended BigFoot: http://www.fiberglassrv.com/forums/f...tml#post234750 and if not, he got that added benefit anyway.

[Greg H]

Originally Posted by Francesca Knowles

Is cutting wind resistance the purpose of the V-nose design I see on some cargo trailers?
That would be an interesting modification to contemplate for my Trillium...

Francesca

Kinda sorta. Also some V nose cargo trailers have a downward slope in the V nose, they say that helps a lot.

[Francesca Knowles]

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?

Francesca

[Greg H]

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.

[Francesca Knowles]

Gotcha!

Hmmm...

Francesca

[Francesca Knowles]

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???

Francesca

[Greg H]

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.

[Francesca Knowles]

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???


Francesca

[Ron Stewart]

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.

Ron

[Francesca Knowles]

Thanks, Ron!

Whew!
It'd be interesting to calculate the dimensions of the perfect FG trailer version of this!



Taking a look at the Original poster's question....

Originally Posted by melissab

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?

Francesca

[Ron Stewart]

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.

[Francesca Knowles]

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?

....
Francesca

[honda03842]

The most important factor in drag is frontal area. I believe the Big Foots are wider amd probably taller.

Norm

[Mike Magee]

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.

[Roger C H]

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.

[Francesca Knowles]

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?

Francesca

[Andy B]

Originally Posted by Francesca Knowles

Are any of the below designs measurably more aerodynamically efficient than the others?

I would guess the Boler because, based on the pictures, it does not have an awning or roof vent or roof AC to create extra drag like the others and it has one of the smaller frontal areas.

[Greg H]

There should be a roof vent on the Boler, you just can't see it in the picture. The vent lays pretty low on the roof. GO BOLER!

[Francesca Knowles]

Originally Posted by Andy B

I would guess the Boler because, based on the pictures, it does not have an awning or roof vent or roof AC to create extra drag like the others and it has one of the smaller frontal areas.

Thanks, Andy!
But-
We're talking about basic design differences.
For this discussion, let's leave add-ons out of the equation!
The question is,
Does the Boler's design make it more "aerodynamic" than any other fiberglass trailer of the same size and dimensions?

Francesca

[Frederick L. Simson]

Originally Posted by Francesca Knowles

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.

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?

....
Francesca

I think you are experiencing an optical illusion re: the BigFoot. The point-of-view angle exaggerates the Lateral slope; in reality what you perceive as a slope at the back is in reality the slope of the sides. The BigFoot's back is actually just as flat as (almost) all the others.

I perceive the front (and back) of Scamp and Casita (and Boler) to be nearly identical. My tired eyes cannot differentiate what might be possibly a 1 or 2 degree difference in slope. The only "Buddha Belly" I can see is my own.

This photo of a poster gives quite a comparison. The 10 trailers pictured are:

• Top Row: Casita * Scamp * U-Haul * Casita * Bigfoot
• Bottom Row: Casita * Oliver * Scamp * Casita * Casita

The Bigfoot is in reality so much larger than all the rest. It will have much more wind drag.