Fineness ratio vs drag coefficient

[skyking]

I'm building a clean slate travel trailer, and plan to use it.

[JulianEdgar]

Originally Posted by skyking

I'm building a clean slate travel trailer, and plan to use it.

Yes, I can see some use of low drag, generalised shapes in that context (as I have written here before.)

[freebeard]

Originally Posted by skyking

I'm building a clean slate travel trailer, and plan to use it.

Cool. Is there a build thread or post?

I shall not repost my aerodynamic trailer design, but my current design is for a neighborhood trailer with a 25mph top speed. It would have an eyebolt for towing instead of a tongue and hitch.

It would be a pseudo-Airstream shape with Gothic arch bulkheads at the ends with an half-circular section through the middle.

[skyking]

it's all in my head and has been for a while. I hesitate to put it to paper due to many redesigns
The basic numbers are 26'-27' long by 7'6" wide, by 7'8" high with roof down.
It will have similar ground clearance as the tow vehicle at 12", with a very smooth finish on all sides.
When I start putting epoxy and glass to EPS foam on the prototype, I will get a thread going

[freebeard]

it's all in my head and has been for a while. I hesitate to put it to paper due to many redesigns

I'm with you there. Thoughts move much faster than fingers.

My target is a Shepherd's* trailer (benches over the wheels) with a 6'6"x16' floor and taper fore and aft of the two axles. I estimate $300 for a mortise and tenoned rectangle with a plywood diaphragm ready for 5" of insulation and decking. I'm agnostic about what happens above that. The big problem is I don't have space to build it.

Originally Posted by JulianEdgar

Why? For car modification, I think it is the completely wrong approach.

So where does one start then? Scott Adams emphasizes the importance of process above goals.

* Why isn't that pronounce 'sheferd'?

[JulianEdgar]

Originally Posted by freebeard

So where does one start then?

Just exactly like with any other car modifications. You measure what you have, then develop changes from those starting points and then assess the result.

If you're modifying the engine management, you don't apply some rule of thumb to altering ignition timing and air/fuel ratios - you measure what you have, make changes from those starting points and then assess the result.

If you're modifying car suspension, you don't apply some rule of thumb - you measure what you have, make changes from those starting points and then assess the result.

With car aero it's in fact easier than most car modifications, because making trial changes can be made cheaply and easily and then assessed.

[Grant-53]

The 5th edition does not list fineness in the index but does discuss d/l ratio. Since an automobile is not a body of rotation tapered to a point this is more applicable to aircraft. Compound curved panels are more costly to stamp than flat panels generally speaking. My interest is chiefly in body shells for commuter bicycles. Drag and stability are issues to be addressed.

[JulianEdgar]

Originally Posted by Grant-53

The 5th edition does not list fineness in the index but does discuss d/l ratio. Since an automobile is not a body of rotation tapered to a point this is more applicable to aircraft. Compound curved panels are more costly to stamp than flat panels generally speaking. My interest is chiefly in body shells for commuter bicycles. Drag and stability are issues to be addressed.

This is one approach to making very low drag, compound curved shapes. It was covered on a website I edited (Autospeed) but I am not sure the articles are still up. It used foam rubber heated and pulled into shape.

[Grant-53]

What makes it rigid? I've had 4 mm coroplast deflect from wind pressure at the front.

[freebeard]

There's a lot of work in that form. It reminds me of Neile Blanchard's CarBEN prototype.

I developed a plan for formless construction. Using math[s].



Pushing a simple ocathedron would be high drag. But at 4 to 6v it closely approximates a compound curve. I'm curious how a 2 or 3v would fair.