Wes wrote:
I think that is an especially brilliant idea to mount the panels on the truck for ideal positioning purposes.
But I wouldn't spend too much time engineering them to also act as part-time wind deflectors... if the utilization in any way compromised solar collection dedication or their sturdiness.
My reasoning is that I don't think these type deflectors help fuel economy much, if at all. Surely some folks, and manufacturers have posted that they did it, or tested it, and it really, really helped. But I think they are fooling themselves (and customers) since frontal area remains the same and nobody ever posts honest real time data on improvement and real projected investment recovery.
One way to look at it from a rational point of view is that we might attempt to re-direct wind over the top of a trailer, or build a blunt "nosecone" dome on the upper portion of the front RV wall, or even seal all the vortex gaps between the tow vehicle (cab) and trailer, but the stubborn fuel economy still stays largely the same. To vividly conclude the possible of advantage of all these "patches" would require one to ultimately tightly attach the tow vehicle to the trailer with no gaps at all. But then the real insight comes when we realise that situation is exactly the situation of a motorhome... where the "tow vehicle" and "trailer" are already one and the same. Unfortunately the motorhome fuel economy is about the same as a stock, unmodified two-piece rig. Little or nothing in economy is gained with a sleek one-piece motorhome.
As in commercial trucks, the best bang-for-the-buck fuel economy is derived from a tapered trailer tail to reduce rear vacuum and installing air-dams and ground effect type dropsides that re-direct the turbulent slipstream away from the un-aerodynamic undercarriage/rearaxle. High fuel economy automobiles have used this tapered
Kammback trick for quite a while now. Essentially nosecones can be be pretty blunt-nosed, yet be effective, but the tail must be tapered. And note even newer 4x4 trucks usually have some sort of front airdam under the bumper.
Otherwise great idea, seems very practical and scientific. Thanks for sharing this.
Wes
I hear what you are saying, Wes. However If I'm going to mount them on the truck anyway why not use them as wind deflectors, even if it only produces a modest fuel economy gain? I do intend to build a Coroplast tail cone on the back of the TT too (an possibly on the sides of the truck at the rear too). I have built and designed many model rockets in my youth, so I understand the physics of aerodynamics better than most. A Class A has poor aerodynamics because of it's flat back more so than its flat front. If you look at the available add-on wind deflectors on the market they are far too small and have too steep of an angle of attack, and have too great a gap between the TV and trailer to be of much good.
My design solves all these problems. First instead of being perhaps 4-5 ft wide like commercial add-on units, my solar panels will be 6 3/4 ft wide, deflecting 25-35% more air over the top, but more importantly preventing turbulence produced as the air hits the squared trailer edges. Second the angle of attack of most commercial products is steeper than 45% in all cases. My design will only have 10% angle of attack, producing perhaps 1/3rd the drag of a more vertical unit. Lastly, my solar panel deflector will extend behind the truck for perhaps 10 inches, narrowing the gap to the TT somewhat - still not ideal, yet infinitely better than one mounted on the cab of the truck, which would serve little practical value whatsoever. Add the fact that it will cost little to nothing to mount the panels this way, as opposed to a strictly horizontal mount and the "pay back period" is practically zero, even if I see only minimal gains.
I totally agree that the entire aerodynamic package is important. There is a synergistic effect of both front and rear being aerodynamic (just look at the successful, aerodynamic Airstream trailers), not just the one end or the other. But remember Aerodynamics is not the primary or even secondary reason I'm moving the solar collection and storage to the TV. CCC savings on the TT and the ability to easily lift and direct the panels to face the sun and clean them to improve their energy collection capacity are of prime concern. Aerodynamics is of only tertiary importance, but if it's a possible benefit, even if minor, why not, especially for a fulltiming rig that will see many gallons of diesel burned? Ultimately, reduced vehicle speed and gradual stops and starts (basic hypermiling driving techniques) will be of greater value to fuel economy than even the best reduction in aerodynamic drag could provide.
Thanks for your thoughtful reply. I really appreciate being able to look at things from a different perspective. Knowledge is power.
Chip
