Non-Traditional design. Looking for Pros / Cons and Faults.

[AGM_AU]

Hi all,
Just looking for some constructive feedback (both positive and negative) regarding a non-traditional design that is in the process of its own evolution. As first glace tells, it hasn't been designed for its aesthetic charm, but more to suit a set of usage parameters:

a) 4 Cylinder towable (Chevy Cruze specs). Check…at least according to the vehicle specs the GVM should come in fully loaded about 40 – 50 % under the maximum design specifications.

b) Fits in the garage. Check.

c) Maximized sleeping compartment (that doesn’t feel claustrophobic). Check…I hope. Q/S mattress, no protruding cabinetry, Trolley Top for natural lighting and air handling.

d) Aerodynamics a shade better than a flying brick. Assumption that it will (minus complex carpentry or Boat-Tails), with as much as I can read about this much debated topic which has helped no-end . And as much as I can for internal space (and still not dragging air too far above or to the sides the TV). I have no idea just how dirty the wake of the TV is and how that will translate to the Trailer. I’m winging it.

e) Reasonable storage space for items of different sizes. Check

f) A workable Galley able to take a 12v vehicle fridge & at least 2 x 20L water containers and sundry items. Check

g) Basic foam insulation in stick framed walls, floor & ceiling covered with ¼ inch Marine Ply for cooler weather. Check.

h) A reasonable turning circle when reversing. A “Looks About Right” assumption that is should be OK.

i) Axle placement correct for loaded operation on a small vehicle. Still fine tuning this one with a couple of more simulations needed to hit that 10-15% hitch weight sweet spot. With the front storage compartment, at least weight distribution can be trimmed a little fore & aft.

I have been staring at different designs for sooo long that I’ve probably got a blind spot going on when it comes to design flaws. And as this forum has more collective experience (both practical & theoretical) than I can ever hope to attain…..I’m hoping that some may chime in with something that is so obvious that I’m missing it due to DMD (Designer Mental Deterioration).

Cheers!

[Shadow Catcher]

Looks cool. The advantage of the flat rear galley is not having to lean over, the disadvantage is aerodynamics.

[angib]

There isn't an aerodynamic advantage to the steep rear slope of a teardrop - that's just 1930/40s 'aerodynamic' styling like a Chrysler Airflow. Once the airflow hits the typical hurricane hinge, it will detach so any steep slope after that is doing little good.

But I don't see the curved front as an advantage either. This would get airflow onto the sides of the trailer well, but at the expense of poor airflow on the roof where the sharp front/top corner spoils the flow. And getting good airflow onto the sides is pretty pointless since most of the lower half of the trailer body is in the tow vehicle wake, where the airflow is all disturbed already. For an aerodynamic vehicle like the Cruze, getting the airflow good over the top half of the trailer makes sense - and that is best done with a traditional teardrop-in-side-view front end shape.

If you want an actual aerodynamic back end on a teardrop, it would have no upstanding hurricane hinge and a very gentle slope, never getting more than 15 degrees from horizontal and then a completely flat Kamm tail that was maybe two or three feet high. Grant's Lil' Bear profile comes pretty close, though it still has a rounded top/back edge where square/sharp would be better.

[Steve_Cox]

Good post Andrew.

We seem to have spent years here trying to improve on the "wing cross-section" for good aerodynamic qualities, but it does always come back to that. When I built the gypsy trailer the first precept was "not aerodynamic", and it held true. It was the exact same weight as its predecessor the teardrop, but it towed like a slug, which was expected. The next incarnation will be a combination of the two, taking the best of both and incorporating them together, or maybe the worst of both.

[AGM_AU]

Thanks for the replies all.

Shadow Catcher – LOL..I did say aerodynamics a shade better than a flying brick.
I know, the negative pressure created at the rear end isn't going to be pretty and will create some drag. How much, I have no idea. I’ll find out I guess if this one gets to the building stage. Like most things, it’s a trade off from form versus function. I wanted to give myself as much galley room as possible and keep things simple. The trade-off is the trailing end airflow and a negative pressure zone. It’s not ideal. I hope it doesn't suck (pun intended) too much when it comes to mileage. I have to admit, I like the barn door idea (thanks bobhenry!) and not having to lean into a galley.

Angib – You’re right. The rounded V front was more to do with turning radius when backing up, and the vain hope that it would shed some of the air, and not be like holding a sheet of ply in a gale force wind. The top of the trailer is about 200 mm (7.87 inch) above the height of the TV. After finally finding an example of wind tunnel testing on the Cruze, I need to re-think the shape of the front end. The sides of the trailer (cabin) are about 2 inches inside the outer extremities of the TV at the widest point, effectively in the vehicles’ shadow as it were. Not sure on how to handle this one as yet, but elongating the nose section, and adding a 25-30 degree incline may help out to some degree (and probably change my CoG a direction I don’t want it to move in too). It would (I think at least) bring the front of the trailer into a dead area of air just aft of the trunk, and get the airflow up over the roof of the trailer. Like I said, I’m winging it here. Trailer design isn’t something I’m familiar with.



Steve – PMSL This thing, in whatever shape it ends up, will probably tow like a box-of-rocks as well….but at least it’ll be my box-of-rocks. Hmmm, maybe version two will be better when built (that’s of course if version 1 doesn’t lead me into the divorce courts first and leave me penniless).

Cheers.

[Steve_Cox]

Thanks for the replies all.


Steve – PMSL This thing, in whatever shape it ends up, will probably tow like a box-of-rocks as well….but at least it’ll be my box-of-rocks. Hmmm, maybe version two will be better when built (that’s of course if version 1 doesn’t lead me into the divorce courts first and leave me penniless).

Cheers.

I am with you on the "my box of rocks". The more you deviate from what is considered a normal travel trailer can be a wonderful source of campground camaraderie. Because of my homebuilt little trailers I have met people from all over the world that would not normally stop to visit. I had people walk past a guy with a sleek $200,000 custom 5th wheel and tow vehicle to come look at my teardrop once when in line checking in at a music festival. It was quite fun watching him get "hot under the collar".

As for planning #2 before you start #1, you wouldn't be the 1st guy to do that...

[Junkboy999]

Just look at it this way. After your divorce you can just live in #1 hahaha


The flat Back door is a good choice for a few good reasons. It is easier to build in most cases, if the seal leaks it is just the back that gets wet. More space for a galley , important if SWMBO and Kiddies want to camp with you. There are a few in the forums that have flat backs.


Ron and Randy are both building TD now that have that round front. They are in the build journal section. Ron's first one had a flat back door.


And there is nothing wrong with towing a brick.

[ChasCABQ]

There isn't an aerodynamic advantage to the steep rear slope of a teardrop - that's just 1930/40s 'aerodynamic' styling like a Chrysler Airflow. Once the airflow hits the typical hurricane hinge, it will detach so any steep slope after that is doing little good.
...
If you want an actual aerodynamic back end on a teardrop, it would have no upstanding hurricane hinge and a very gentle slope, never getting more than 15 degrees from horizontal and then a completely flat Kamm tail that was maybe two or three feet high.

I like your reasoning and have decided on a Kammback with a vertical recessed hatch which keeps hinges and seals out of the airflow and has improved aerodynamics. My TV has a large cross section so it blocks much of the trailer although the gap between TV and trailer can account for 25% of the total drag. May add a front box to reduce this further.

[angib]

If you go for a flat vertical hatch, be sure to check where your head will make contact with anything when using the galley. You may want to take a bit of the roof into the hatch (to give an inverted L shape) to give head clearance - and it will also stop any structure from being directly above a stove.

[mezmo]

Here are a couple threads that you may find useful:

Foamie Aero...
http://tnttt.com/viewtopic.php?f=55&t=49036
Teard(r)op Aero...
http://tnttt.com/viewtopic.php?f=2&t=61465

Things I'd do:
- Radius all the edges some [except for the kammback], even a little will help.
- Make the trolley top wider, it is much too narrow now [just doesn't "look" right]
and would be hard to use the windows. See jackdaw's trolley top builds in the
build journal section for some nicely proportioned ones.
- Make the front blunt with radiused edges so that it fits within the rear, or max
tow vehicle cross-section, then gentle a increase [<15 degrees] to the final TD body
height.
- Driving slower will help too once you're built.

Cheers,
Norm/mezmo

[rowerwet]

My latest design has a vertical hatch seam, however I plan on making the hatch itself curved so it would still give headroom inside when standing up close to the counter. Just be sure to step back a bit before walking around the side of the galley.

[RAYVILLIAN]

I like your last design for obvious reasons our trailer.


with the old one


I would get a air dam off the front of the trailer that I could feel when driving, especially when passing on coming semi's on 2 lane roads. With the new trailer I get none of that. It tracks behind the TV so well that except for the pull up hills I forget it's back there.

Gary

[working on it]

If you go for a flat vertical hatch, be sure to check where your head will make contact with anything when using the galley. You may want to take a bit of the roof into the hatch (to give an inverted L shape) to give head clearance - and it will also stop any structure from being directly above a stove.

The flat vertical hatch (or rounded, but still vertical) requires more lift/opening angle than using a standard sloping teardrop hatch. I used prop rods on the edges of my galley shelf to hold it up, @ 105 degrees, but at one campsite, that angle was compromised by ground slope, and wasn't enough for head clearance. I compensated with extensions, to raise it another 5 degrees,

finalized extension angle usage.jpg (59.23 KiB) Viewed 4680 times

but it was a bear to lift. If going with a vertical hatch, an assist may be necessary if your hatch is as heavy as mine is. I finally added a gas spring assist to mine.

finalized galley with hatch lift assist.jpg (30.29 KiB) Viewed 4680 times

The Kammback was originally in my planning, also, but my hatch opening gap seal serves almost as well.

KAMM substitute.jpg (74.59 KiB) Viewed 4680 times

[ChasCABQ]

If you go for a flat vertical hatch, be sure to check where your head will make contact with anything when using the galley...

...If going with a vertical hatch, an assist may be necessary if your hatch is as heavy as mine is...

I'm using 1/8" birch over poplar and estimate hatch weight will be less than 15 lbs. I also plan on angling the hinge attachment so hatch can open with angle above horizontal for headroom.

[Wolffarmer]

Here is what I did about reverse turning ability.



I did that mostly for back road turn about ability and not street. Have done it a few times. Of course there are many disadvantages to a single member tongue. Also the trailer could have been closer to the TV. And as I made it just long enough for this TV, this one will not work as good on a wider TV. My next trailer will cure that as it has an adjustable tongue so it can work on different TVs and be shortened up for highway use and then lengthened for back roads.

Randy