Hi Mojave Bob,
[04/09/12 Note: I was having computer problems and didn’t have any
way to scan and save to a file and then post. ‘Just got that ability back
today. I just found a couple drawings I did last summer in my “pile file” so
I thought I’d post this anyway even though it is a good bit past the
the time of the last posting in the thread.]
[Note:]
[These are just suggestions again – I’m not trying to hijack
your design or idea(s)!!! Also, this was done up before I saw any posts
after my last post of 8/12/11, and I haven’t edited it any to reflect any
subsequent posts after 8/12/11, other than this note. Therefore there
might be some of the same suggestions/considerations others have already
made included – possibly. I’m having computer problems so I didn’t
get this posted when planned.]
Since I like playing around with trailer designs:
I did a couple draw-ups of things I’ve thought about ‘RE:’ your build. –
These are how I usually try out ideas and such. Sorry if they appear to
be a bit cluttered. I always jot down any additional thing I think of
on the draw-ups when I go back and look at them again over time.
A few questions & suggestions about things that bear on the design
but haven’t really been mentioned yet specifically, from what I recall.
If they are things you’re thinking about, or already have thought about
just please bear with me. These are in no particular order, just as they
came to me.
1 – What is your tow-vehicle?- shape? - height?
2 – Will the wheels be inboard or outboard? – I think inboard is
best – out of the air flow. They should also have either a flat smooth
disk style hubcap or the wheel opening be skirted and flush with
the sidewalls. If outboard they need an aero style fender etc.
3 – The belly/underneath should be enclosed and one smooth surface
if possible, and probably the tongue top and bottom surfaces too –
that could also be integrated with a tongue box if you do one.
4 – A couple things that fellow member angib has brought up ‘RE:’
aerodynamics over time, bear on your design I think. First: If the angle
or curve of the taper used for attempting ‘areo’ is >15degrees from
the plane [surface] it is departing from, then you lose most benefit.
Second: Behind a tow vehicle, any attempt to use a design at the
front of the trailer that is ‘aero’ becomes more a styling thing than
‘aero’. Granted, there are a lot of variables, but the idea is that the
tow vehicle has already ‘punched’ through the air so the best thing
to do is try our best to have the trailer follow suit through the same size
hole/path through the air – at least for the front of the trailer.
5 - I’d suggest using 1/4inch squared graph paper to try and keep proportions
correct when sketching. The scale I use is 4 squares =1 inch for a 1 inch
= 1 foot scale. I just tape pages together if I need a larger size for the
larger drawings. [Couldn’t tell from your drawings if you already were using it.]
6 – Have you ever heard of the Kammback? It is an Austrian/German invention or idea
whereby researchers have determined that one doesn’t need a full length
‘tail’ or tapered body to achieve almost the full effect that the fully tapered body
gives. [Remember taper not >15 degrees off of the surface plane of departure.]
Their rule of thumb is: you can “cut off” the ‘tail’ at the point in the taper where
the section area equals ½ of the section area of the greatest body section area.
The ideal ‘cut’ is vertical, but most slant forward or back some in practice –
mostly for looks it seems. I’ll include some links about that at the end – quite
interesting and some good web sites.
7 – The draw-ups I’ve done use flat panels connected through curved bends of
sorts and the ‘radiused’ front walls of your initial plan, as well as ‘radiused’
joints. Sharp edges are an aero no-no it seems. If you want to get really into
it you could gently curve all the wall and roof panels similarly to how plywood
boat builders do, even borrowing some of their techniques – e.g. stitch-and-glue.
Forum member angib has some very good info on that at this link from
the design page and The Amazing Trailorboat :
http://www.angib.pwp.blueyonder.co.uk/t ... tear44.htm Don’t key on its front shape but rather the curved wall panels and such. And he
includes a link to Carlson Design that offers free shareware that’ll allow you to
figure out and cut the panels necessary to make curved walls etc.. It must also
be possible to find/Google some old boatbuilding techniques that could apply too.
The design Library also has trailer balance and tongue strength sections too if
you hadn’t checked them yet.
8 – One final thing I just realized (!) concerns the departure angle of the front sloping
roof where it meets the flat main roof. That is about a 20 degree angle from the
main roof plane. Using flat panels, as we are here, it’d be better to break the roof
into three planes so the each is 15 degrees or less off each other. Of course, I
realized this after everything was drawn, but better to discover that now instead
of after a build. Flat panels were ‘used’ for easier construction. Curved panels
may be able to get around this, but they are much more difficult and time
consuming to do, but they are doable.
9a – Finally! Here are the two draw-ups I did. The first concerns tail-end taper. I did
it in 15 degrees off the departure plane [sidewall] and off the centerline up where
they meet. This was done for both 5 & 6 foot wide. Just for the heck of it, I also
included a 30 degree departure from the sidewall plane and also a 45 degree
departure since that is what I surmised your original drawing intended. I’ve also
noted where the varying 50% of the max body sections are on the various taper
scenarios [using the 15 degree departure angle limit.], as well as where the original
12 ft end of the body is. The 12ft point shows the cut off section width as about 3ft9”
so you may as well just widen it to 4ft for ease of build since the taper for that end
width would be under the 15 degree maximum departure angle rule.
The Taper Draw-up:
9b – Here is the Foamie plan and side view. [NOTE: These are on a 2 grid square
= 1 ft scale. This is different from the Taper Draw-up’s scale.] Again, sorry if it is a
bit busy. I hope the notations make sense. On the plan on the bottom I superimposed
the 5 wide, 6 wide, and my recommendation for the frontal area being = to, or
slightly smaller than, the tow vehicle’s max cross-section. The back shows the 15
degree taper from the departure plane/side wall to centerline as the inside line, while
the outside taper line is for the 4ft end width at the bottom – these being for the 6ft
width. The 5ft width would be a very narrow end wall base of about 2.5 ft.
Just for aesthetic or looks I’ve continued the rooftop out another 18 inches using
using a 15 degree off vertical slant at the 12ft point. That will make the top end to be
~3ft wide, due to continued taper per length. So, the end wall becomes a back slanting
trapezoid shape, much less abrupt appearing than a vertical back wall. I don’t know
if it helps/hurts the aero effect much but I’d guess it doesn’t matter. On the side view
I show 4ft and 5ft tall front walls. I’d go for the 5ft just in general. It’d most likely
fit most tow vehicle’s max or departure section [depending what fits best.], but
adapt it for your specific needs – maybe 4ft6” is better? The 5ft height would
probably fit a variety of tow vehicles, in case you change them. For illustration
purposes I surmised a 3” frame/chassis height/thickness and 1” thick floor. I put an
additional 3-4” thickness by the wheels for the belly pan as I like the look of a slight
downward taper from the ends to the wheel. Flat would work too. A rule of thumb I
start with is that the wheel’s forward edge is at or just behind the crosswise centerline
of the bottom of the trailer’s body at the floor. The door could be placed to allow a
12’ to 18” wall from the door’s rear edge to the end wall base. I tried to ‘ghost in’ the
interior a bit for reference. Again, all the wall and roof and floor joints should be
radiused to eliminate sharp edges.
[Upon review, I see I may have had a problem with
stating the frontal dimensions for the trailer. I assume a 1ft ground clearance, that
I may have overlooked. But it still centers on the max section or departure section
area of the tow vehicle. The trailer frontal area could be 5w x 3h, or 5w x 4h, or
5w x 5h, or any intermediate appropriate height depending on the ‘TowVee’ height
and trailer width depends on ‘TowVee’ width and the corresponding max cross-
section that results. Whether ground clearance is part of the equation needs more
research/reading on my part.]
The Foamie Plan and Side View Draw-Up:
I’m not any kind of expert on this, I just put together what info I’ve managed to recall
on the matters involved. I think the measures/numbers are correct, but double check
them to be sure. I used a max section area of 6x6=36 square feet for 6ft wide, with
50% of that being 18 square feet for the cutoff section; and 5x6=30 square feet for the
5ft wide max section with the 50% of that being 15 square feet for its cutoff section.
[In case I haven’t mentioned it, a “section” is a vertically (usually) oriented slice view
across the building/vehicle structure width – as in cross-section.] The height used to
figure all the 50% vertical base end widths was 6ft since that is the planned interior
height at that point. Dividing the 6ft height into the 50% cross-section values gave
the widths of the end wall bases at those points. The ‘cut off’ points on the taper are
are determined by dividing the end wall widths by two and locating those distances
on each side of the centerline. Where each half-width intersects on the taper line
gives you the location of the ‘cut off’ point for each total width.
And finally here are the Kammback links I mentioned earlier. These are included as they
were a good intro to the subject. Just Google ”Kammback” and there are plenty more of them:
http://en.wikipedia.org/wiki/Kammbackhttp://scientificmethodfueleconomy.blog ... mback.htmlhttp://homepage.mac.com/christopher.z/h ... kStory.htm http://ecomodder.com/forum/showthread.p ... -3518.html[This last web site is very good RE real world aero mods.]
Sorry this got so long! I hope there isn’t a length limit on here!
Like I said earlier - just things to consider or think about – as if there aren’t
Enough of them already! Ha!
Cheers,
Norm/mezmo
If you have a house - you have a hobby.
by Mojave Bob » Sun Aug 14, 2011 1:36 pm 
