Effects of Large VS Small circumference curves at upper corners

[4536]

For Aerohead, and anyone else interested.

Most vehicles have fairly short circumference curves in their transition from their sides to their top. So I suspect that little thought needs to be devoted to their taper characteristics from front to rear. However what about a vehicle with a large circumference curve?

Of course one of the advantages of the large circumference curves is its lower suseptibility to direct crosswinds which is always a concern with a trailer or high profile vehicle. Also it will presumably be more aerodynamic with any off center winds that are encountered.

Based on the Streamlined template, the following is the case for the trailer I am constructing. (see 6-14-10 "AeroTrailer from Scrap Materials" thread):
1. Each of the 24" vertical sides of my areodynamic trailer has a faster taper than the top because the D for the sides is 74" and the D for the top is 136". (53" high from floor to top at its highest point plus 15" from top of floor to pavement X 2 = 136").
2. There is a 29" radius curve that transitions upward and inward between the upper vertical sides and the top. The right and left curves account for 58" of the 74" width of upper part of the trailer at its widest point. Therefore only 16" in the center at the very top is flat (horizaontal). The trailer will be Kamm backed at about 79" rear of the widest, tallest point.
Therefore, what should the lateral (hoizontal) taper of the mid point in the circumfrance of the curve be, as it transitions to the rear?
What should the verticle taper be for that midpoint in the curve?

I ask this as that midpoint occurs at a shorter width than the sides and a lower height than the top.

Is it as simple as transitioning that mid point vertically with the roof and laterally with the sides?

Or is there some more complex equation that involves a chord perpendicular to the mid point of that curve and runs downward to the ground and is then doubled to determine D. Wouldn't this most likely provide a corner that bulged outward as it transitioned rearward due to a slower taper than the sides and top?

[Frank Lee]

I think those fillets are overly generous.

Supposedly, any radii/fillet/curve in excess of the minimum required for attached flow provides no further aero benefit. And as you can see, overly generous radii/fillets/curves really eat up interior volume vs. rectangular boxes.

[Otto]

See the NASA truck modification paper, posted elsewhere on this website by me. Evidently, remarkably low CD can be achieves vs. sharp edged box or even in absolute terms, i.e., CD < ~.3.

You also might want to consider elliptical curves, easily done with two pins, string, and pencil. YouTube for making ellipses.

[aerohead]

Originally Posted by 4536

For Aerohead, and anyone else interested.

Most vehicles have fairly short circumference curves in their transition from their sides to their top. So I suspect that little thought needs to be devoted to their taper characteristics from front to rear. However what about a vehicle with a large circumference curve?

Of course one of the advantages of the large circumference curves is its lower suseptibility to direct crosswinds which is always a concern with a trailer or high profile vehicle. Also it will presumably be more aerodynamic with any off center winds that are encountered.

Based on the Streamlined template, the following is the case for the trailer I am constructing. (see 6-14-10 "AeroTrailer from Scrap Materials" thread):
1. Each of the 24" vertical sides of my areodynamic trailer has a faster taper than the top because the D for the sides is 74" and the D for the top is 136". (53" high from floor to top at its highest point plus 15" from top of floor to pavement X 2 = 136").
2. There is a 29" radius curve that transitions upward and inward between the upper vertical sides and the top. The right and left curves account for 58" of the 74" width of upper part of the trailer at its widest point. Therefore only 16" in the center at the very top is flat (horizaontal). The trailer will be Kamm backed at about 79" rear of the widest, tallest point.
Therefore, what should the lateral (hoizontal) taper of the mid point in the circumfrance of the curve be, as it transitions to the rear?
What should the verticle taper be for that midpoint in the curve?

I ask this as that midpoint occurs at a shorter width than the sides and a lower height than the top.

Is it as simple as transitioning that mid point vertically with the roof and laterally with the sides?

Or is there some more complex equation that involves a chord perpendicular to the mid point of that curve and runs downward to the ground and is then doubled to determine D. Wouldn't this most likely provide a corner that bulged outward as it transitioned rearward due to a slower taper than the sides and top?

4536,I apologize,as I'l late to the party.
The other members have made some good comments and I'll throw some thoughts your way also.
It's important for you to think of the trailer as an organic extension of the towing vehicle.
The roof curvature and body camber of the tow vehicle are going to establish the quality of the 'onset flow',as Hucho calls it.Also,the roof-to-sides architecture of the tow vehicle will set the pattern for the body of the trailer.
After seeing triple-trailer rigs lying on their sides along US-80 at Bonneville,I understand your concern for crossswinds,although having recently doing limited tests with my latest trailer,it may not be such an issue as you think.
With respect to the taper on the roof and sides of the trailer,it will be established by the roofline and sides of the tow car,and should not be any more aggressive than what the template would allow,looking at the car/trailer as a single form.
The V-nose is actually 'inferior' aerodynamically than say a 'NoseCone '-style radiused leading edge.
The blunt face with radiused side and top is better.
The gap between car and trailer is bad,it can add up to 20 % drag.If you can figure a way to close that up it would be good.
Morphing from the back of the tow car into the body of the trailer would limit the radius in the trailer top/side,even if you had the transition panels as I'm developing for my trailer and if you're not careful,you can aggravate the velocity potential at these two areas,causing the air to spin up into attached-vortices,like an ill-designed fast-back car.
If you could post a side view and overhead photo of the car/trailer combo it would be a big help.Then we could work with your dimensions a little better.
Fun project!

[4536]

Thanks everyone. Pictures will take awhile but I will see what I can do with my finance's digital cameral when she feels better and can get over here. However I will try to get some diagrams up before next week.

I did the height and width streamlined template calculations for the mid point in the right and left arcs which have a 29" radius. Since the width and heigth (the Diameters or "Ds") in the calculations are shorter than those of the trailer, they allow for tapering back faster than those of the trailer itself thus perhaps allowing for greater attachment of flow since they will be tapering at a more gentle slope than called for as they will be tapering along with the small horizontal section of the top and the 24" vertical sides. Don't know if this is an accurate way to consider their ideal taper, but it was the only one I could calculate and it made me feel a bit better.

Here is what is already done:
1. I am completing the third of the four internal frames to which the sandwiched panels will be attached. It will be mounted 36" behind the frame at D, the highest, widest part of the trailer. The only one remaining is the back frame where the door will be.
2. The right side of the 24 inch verticle side is complete from where the rounded nose of the V will be placed to about 2/3rds of the way to the back of the trailer. The left side of the 24" side is complete from a small door toward the nose of the trailer to 2/3rds of the way back.

The trailer will be about thirteen inches higher and wider than the Subaru WRX Wagon. This is so that it can be converted to a solid pop up travel trailer later and because of the width of the axle, and because I need the space.

The nose out side of the air flow coming off the top and sides of the wagon has not been completed. One of the reasons for the V nose was to be able to more easily enclose the gap between the wagon and the trailer with transition panels that would slide along the top and sides of the trailer.

The V-nose is actually 'inferior' aerodynamically than say a 'NoseCone '-style radiused leading edge.

Actually a "NoseCone" style nose was what I had planned all along, but was trying to convene that I was enclosing the V part of the hitch.

The blunt face with radiused side and top is better.

It may be too late for this, but perhaps I can approximate it.

Its late, will be pretty busy with other matters for a few days and then will continue when able with the diagrams. Thanks again everyone.

[aerohead]

If you can get those gap-filler transition panels done it won't really matter what the nose underneath is like,but the v-nose will make for an easy mechanism to 'slip' the panels.I have the v-nose on mine only for this reason and it is contiguous to the interior space.

[4536]

How are your transition panels coming? Didn't your already have those on your aerotrailer before the unfortunate wheel mishap? ( I've been lurking for awhile). Were they destoyed or are you modifying them? (By the way I really felt for you as you had put alot of time and energy into your project, but at least your were OK.)

I was thinking that something as simple as a bungee cord attached to eyelets on the inside of the 2 verticle transition panels could hold each of the panels against the trailer sides of its nose. The bungee would be mounted in front of the nose some small distance. As you turned, the nose of the trailer would push the panel on the outer edge of the turn outward where the wind would kleep it flush against the trailer. The panel on the inside of the turn would be held even tighter against the wider part of its side of the nose due to the increased tention on the the bungee.

Another option would be to attach a bungee for each panel further back and to its side of the nose. And finally a single bungee could be attached to each panel and run thru a smooth horizontal tube in the nose to the opposite panel. In this case a funnel shaped intrance to the tube could reduce wear and tear on the bungee. Those are enough thoughts on the subject as any more and I will be approaching the complexity of pulley and cable solutions.

[aerohead]

Originally Posted by 4536

How are your transition panels coming? Didn't your already have those on your aerotrailer before the unfortunate wheel mishap? ( I've been lurking for awhile). Were they destoyed or are you modifying them? (By the way I really felt for you as you had put alot of time and energy into your project, but at least your were OK.)

I was thinking that something as simple as a bungee cord attached to eyelets on the inside of the 2 verticle transition panels could hold each of the panels against the trailer sides of its nose. The bungee would be mounted in front of the nose some small distance. As you turned, the nose of the trailer would push the panel on the outer edge of the turn outward where the wind would kleep it flush against the trailer. The panel on the inside of the turn would be held even tighter against the wider part of its side of the nose due to the increased tention on the the bungee.

Another option would be to attach a bungee for each panel further back and to its side of the nose. And finally a single bungee could be attached to each panel and run thru a smooth horizontal tube in the nose to the opposite panel. In this case a funnel shaped intrance to the tube could reduce wear and tear on the bungee. Those are enough thoughts on the subject as any more and I will be approaching the complexity of pulley and cable solutions.

4536,I'm going to dig up the trailer thread and post your answer over there,just to kinda keep things together.
It will be at the Full-Boat-Tail Trailer.................