PS. im not an aerodynamicist. I'm just an engineer who has done some serious reading, and also spends time on Ecomodder forum
Fair enough, but your comments suggest you're not thinking
like an engineer...
my real point is that there could be a Huge difference if trailers were designed by proper aerodynamicists.
As you've already indicated that you understand, likely the only way to make a "Huge difference" is to significantly reduce "A" .... but that's in conflict with the primary functional requirements for 'walk-in' trailers! Those willing to accept the functional trade-offs for significantly reduced "A" pull one of the many types of 'fold-down' (either 'soft' or 'hard-sided') or 'crawl-in' (mini/teardrop) trailers, just as some folks drive a small "A" Prius rather than an Escape or a Suburban .... but each has very different tradeoffs involved and they don't meet the same overall user needs/wants.
E.g. the ability to pull off the road, walk into a trailer and make/eat a lunch, stretch-out comfortably and get back on the road with zero hassle, is a convenience that every 'low "A" ' trailer owner has envied at some point in their RV-ing experience.... a convenience they sacrifice in return for 'hugely' better aerodynamics, the ability to tow with smaller vehicles, smaller engines and with less fuel. And then there's the experience of pulling into a campground for the night during a thunderstorm .... :-0 Obviously
, based on his BTDT comments in post # 5, understands what compromises he's willing/not willing to make in that regard, as do many others who choose the 'walk-in trailer' solution.
I could imagine wheel farings, smooth underbodies, tapered tear drop rear ends. not putting blocky AC units on top, etc.
All those things make small incremental differences which even when all are applied pale in comparison to significantly reduced "A". Even then, they all also involve 'compromises' in terms of cost, ease of use/maintenance, and aesthetics. Just to choose one: why don't all cars
have skirted wheels and flush hubcaps? Because the market (and you can bet they've done market research on it) won't bear the various cost and function compromises involved even though Mfrs would LOVE what the incremental improvement would do for their CAFE ratings! It's the same for all those sorts of things (FYI, Airstreams have had full smooth belly-pans for decades with only a few waste-drain pipes hanging below). For some it's worth it, but evidence (what people buy) suggests that for most it's not if there's any sacrifice of immediate cost or convenience involved.
....ok, very slightly better than a box, not as good as their marketing implies it is....interesting point about the curved side reducing frontal area.....as long as your sides have sufficient rounded corners (not square) cross wind performance could demonstrably improve.....i agree there probably is a positive difference.....
So, when a manufacturer employs, within the constraints of the primary engineering requirements, a handful of design features of exactly
the sort that 'ecomodders' suggest for gaining incremental improvements, you discount that effort as (and I paraphrase) 'marketing hype'.
C'mon Thenorm, I'm a (retired) engineer, too. Put on your engineer hat and really think
about the challenges of meeting the requirements of an always ready walk-in RV and imagine what an aerodynamicist can do with that to make a "huge difference" in terms of towing drag or required towing power within that engineering "program". Don't forget that a significant part of the overall aerodynamic equation is a variable you can't 'fix' (the shape and size of the tow vehicle ranging from SUV to pick-up to van). Think about things like the cost of developing, implementing and maintaining a radically improved AC solution for RVs (which BTW, have become much lower profile in the last few years while still meeting the requirements of 'universal fit' on standard RV vent hatches, minimizing loss of interior space and directing most of the noise 'up' where it causes the least disturbance to neighbors in RV park/campground settings). Don't forget you need substantial ground-clearance to avoid dragging the ends on those nasty gutter-then-steep driveway approaches one encounters.... etc, etc, etc.
I don't mean to give you too
hard a time, but I honestly think you've failed to employ your smarts to develop realistic
expectations for the engineering challenge at hand and give credit to the RV industry for its efforts in this regard: there are
RV's that offer 'Prius-like' aerodynamic performance and function .... just as there are those that offer 'Suburban-like' aerodynamic performance and function. And there's undoubtedly room for incremental improvements of both. But just like with cars, the laws of nature preclude 'having your cake and eating it too' and the laws of human
drive the need/want/market for both.
No, I don't think there's much room for "Huge (aerodynamic) improvement" within the bounds of the functional market requirements for full-size walk-in RVs, even with dedicated aerodynamicist involvement in the design. And IMHO it'll take the feds stepping-in to mandate CAFE-like standards to make the incremental aerodynamic improvements that only a few RV manufacturers currently consider more ubiquitous.
@jshel101 will now surely ban me for life for finally going 'off-topic' absolutely too far :-0