Foamie aerodynamics.

[loaderman]

Yep rounded front and tapered (boat tail) to the rear, whether full or truncated as in the kamback.

The teardrop shape is excellent at this.

[GPW]

Angib , #4 sure looks like an acceptable compromise ... drag vs. practicality ... Thanks for that info !!!! (Further validates the FoamStream design)


just thinking ... It should be all too obvious now that with the common TD shape , the flow separates too early off the extreme back taper, similar to a flat bottomed airfoil at higher angles of attack . ... so may not be the most efficient shape ..as previously mentioned,that could be improved with a Kline -Fogleman “step” which creates a circulating bubble that allows the air to smoothly flow over it ... worth investigating ...

[GPW]

Here’s a sampling of the popular drag reducing KF airfoils ... possibly adapted to trailer construction ... ??? crumbs for thought ...

[angib]

.....with the common TD shape , the flow separates too early off the extreme back taper, similar to a flat bottomed airfoil at higher angles of attack ....

Yes, that's right, all that curving down to the bumper is just 40s aero styling and that was no more scientific than any other generations' styling.

My general rule of thumb is that 15 degrees is as much of a slope as you can expect airflow to stick to and even that had better have a really smooth curve leading to it.

Most teardrops add a hurricane hinge at the top of the hatch which is a perfect flow separator - there is no way anything behind that hinge is important since the airflow won't be touching it.

[Wobbly Wheels]

15 degrees is as much of a slope as you can expect airflow to stick to

That's what is so often ignored in favour of aesthetics. Of course, the actual number is dependent on instantaneous airspeed, but there is always that point where the laminar flow lifts off the camber - now you've shot yourself in the foot and are actually creating induced drag rather than reducing it.

Re KF foils - I thought the main problem with them was specifically that they didn't scale up to full size models ?
Great for models but not for large foils (like a TD)....especially given what the interior would be like to maintain the outer shape. Same reason you don't see large shapes dimpled like a golf ball.
Now, if air had the viscosity of water or...say...maple syrup....

Dunno though: I'm not a expert, I just play one on the interwebz

[angib]

there is always that point where the laminar flow lifts off the camber

Beware - did you intend to mix up two completely different conditions here?

Laminar and turbulent are descriptions of the boundary layer - that is the thin layer of airflow (maybe 1/8" deep at the front of your vehicle's hood and 3-6" deep where the flow comes off the roof) directly affected by being near the body.

Attached and detached flow are where the airflow is closely following the contours of the body or following a totally different path of its own - so the airflow over a stalled wing is attached at the front and then detached at the back.

The use of the word turbulent is a terrible nuisance as it so nicely describes the million different directions in which detached flow travels, but they are not related. Indeed one of the aero features that really hurts my brain is that triggering a turbulent boundary layer can keep airflow attached much longer and reduce drag - which is exactly what the dimples in a golf ball achieve. Some aircraft use little studs near the wind leading edge to delay stalling by keeping the flow attached.

Aerodynamics is really, really complex. I have learnt just enough about it to know how little I know about it. If you follow me.

[Wobbly Wheels]

Yep, that's exactly what I meant, thx for keeping me honest.

[loaderman]

"Aerodynamics is really, really complex. I have learnt just enough about it to know how little I know about it. If you follow me."


Yep!!!

[mezmo]

Think of "Kammback" for use in the rear of the TD/TTT. You can
'cut' the tapered body off at the point where the cross-section is
50 per cent of the maximum cross-section of the body and achieve
almost the same results of a/the full taper - per what I've read on it.

[Bogo]

Aerodynamics is really, really complex. I have learnt just enough about it to know how little I know about it. If you follow me.

Yep! Over the years I've learned a wee bit more than a little bit. That's why I now just roughly copy known well designed aerodynamic shapes.

Aero-hydrodynamics of Sailing (http://www.amazon.com/Aero-Hydrodynamics-Sailing-Czeslaw-A-Marchaj/dp/1888671181) was a fun read. OK, I have a first or second edition copy. I wonder if that new section is worth it? BTW: This is the book to get if you want to design a sailboat and have it efficient and well behaved. It is written for the naval architect wanting to understand keel, hull, and sail design, but has surprisingly well written descriptions understandable by the layman.

[GPW]

For those interested , here’s a thread on the KF airfoils .... http://www.rcgroups.com/forums/showthread.php?t=1296458

[angib]

The book that I think is best for understanding vehicle aerodynamics (but not trailer aerodynamics) is The Leading Edge. This is about designing really low drag solar race cars (ie, electric powered by PV panels on their surface) and does contain some info that only applies to them. But its descriptions of basics aerodynamics are the easiest to understand that I've ever come across - and they are such beautiful cars that it's easy to be interested in reading about them.

[Bogo]

Second iteration... I'm going insane.


Lowered height of only 50.5" including wheels which are 31x10.5R15 off road tires. It has 12" ground clearance under all of it except where the tongue is. The wheels will have a cover plate over the wheel well to keep road spray and grime off the inside wall of the middle lifting section. 116.5" raised up which gives 7' 3" interior height. It could be shorter if smaller wheels are used. I left 2 inches above the wheel wells for bed platform, plus 6 inches for the mattress and bedding. Also the 14" high wheel wells are perfect for the Pelican 1620 travel cases I use for photo gear and clothing. The overall width is 80" which is wider than I'd like, but I traded that extra witch for more insulation. The walls have 2" foam insulation.

The interior of the lower section is 6" wider than the width of a queen bed mattress. At the front of the interior is the entry/shower stall/bathroom area. The queen bed would fold crosswise to form a sofa against the rear wall.

At strategic spots on the walls, shelf standards will be embedded, like KV Heavy Duty Designer Line. When camping, various modules can be attached. These would be for cabinets, counter with sink, toaster/microwave oven, table, shelves, etc.. When in travel mode the modules would be placed on the floor under the bed. An advantage of these modules is you can have an electric cooktop on one, and a gas cooktop on another. When you have an electrical hookup, pull out the electric one, and use it. Otherwise, leave it tucked away under the sofa/bed. Same for the gas one. Also, with some shelf standards mounted on the outside walls, it would be possible to attach them to the outside. For electrical, water, and gas hookups I was figuring on having some quick connects in strategic locations inside and out. Note: With the walls having to pass 1/2" from each other, the standards will need to be embedded flush into the walls. I was thinking of having them machined from stainless steel so mine would tie into the wall skins as well as anchor to boards built into the wall structure. I still have a bunch of thinking to do on the standards because as designed they make allot of structural changes to the walls that complicate them, reduce insulation, and reduce strength.

Window locations. I haven't decided yet. I may put some on the top part, and some on the middle section. A window high on the middle section would be at a reasonable height for looking out

Lift mechanism will be push spring in tube as that method is well suited to even lift all around. The top lifting section raises 66", and the middle section raises 33". The middle section will be lifted by a lip on the inside bottom of the top section that catches a lip on the outside top of the middle section. There will be a similar set of lips between the bottom and middle sections that will serve as a limit stop for upward lift.

Changes from what you see. I'm going to extend the nose out more in the middle so a Honda EU3000iS generator can be put on the tongue. I'd flank it with spots for two 30# or 40# propane tanks and two Jerry cans for gas. The nose area would be sculpted to cover them over when lowered. They would be exposed when the top is raised so I may make a box for them that the nose goes over. The tongue would be a three bar tongue with bars that go diagonally back from just behind the hitch point.

I need to look at the sofa seat height. Right now it is a bit high. I left 2" for the bed platform, and it could be reduced to 1" with a different structure, especially if brace legs are used. On the other hand I do like the flexibility of storage under if it is free spanning.

At this point this is a concept to show what I think is possible. I can easily see some places where changes could be made to compact it some more. Unfortunately if I wanted the portable dishwasher module, it wouldn't fit under the sofa/bed for travel. Portable dishwashers are 17.25" high. I guess you have to make some compromises for compactness and small aerodynamic size.

[GPW]

That’s a very COOL idea ....

[wagondude]

I like it.