Putting rear wing on Honda truck

[Auptimist]

Hey, fellow Ridgeline owner. Glad to see I'm not the only one not taking Honda's aero marketing too seriously. Also glad this hasn't devolved into RL-bashing yet like most forums do immediately. Honda won't release the official Cd of the first gen model but they released an alleged .31 for the new one and said it's a "15% improvement in CdA", which isn't that helpful of a metric considering the frontal areas are unknowns.
I'm curious why you're going for a tonneau and deflector rather than just making an aerocap. I definitely agree with the others, a) 45° is way too steep, and b) that sort of thing adds to the "frontal area" so it's hard for an alleged Cd reduction to pay off at all. However, if you look at the side profile, the rear of the cab to the top of the tailgate does hit that aero template curve precisely, so it's probably not terrible as is, if we're talking about aft-of-tailgate aero. The biggest mitigatable rear drag is that above-tonneau vortex. Your best bet for improving the rear aero is to just increase the flow attachment in the first place with an aeroshell.
I'm making my cap out of 1/2" black steel pipe (cheaper than EMT conduit at Ace, and much stronger!) and 1/8" smoked polycarbonate in the next couple weeks, and I may make a thread about it once I get going. I'm going with the praised 12° angle, which surprisingly works well for our 5ft long bed with minimal rear edge height over the rear of the box. Hoping I can manage a pop-up top like Bondo's for more utility. My plan is to sell my tonneau to break even haha.
By the way, I don't think RL owners need to worry too much about rear lift, guys. It's a 4500lb AWD truck with a partial body-on-frame bed that drives solely in FWD over 15mph.
I'm curious what your other planned mods are! Probably to remove the rear mudflaps, at least?

[kach22i]

Originally Posted by Auptimist

....By the way, I don't think RL owners need to worry too much about rear lift, guys[/I][/I]. It's a 4500lb AWD truck with a partial body-on-frame bed that drives solely in FWD over 15mph.

I did not know this, interesting.

I like the Ridgeline and think Honda paid attention to aerodynamics.

I've read that the blended area between cab and bed was wind tunnel tested, which leads me to believe that a downward slanted roof wing would work well here to complete the envelope - as the sides are covered for the most part.

Some people do like to bash anything just a little different, as for myself I like the odd stuff.

Plain is lame.

[Auptimist]

I fully agree!
The unique utilitarian form and the sense that the engineers actually gave a **** and had some free reign from the marketing execs keyed me in, then Honda's reliability and the price drop, when the fanboys traded theirs in for the new model, sealed the deal! Its also nice to have a truck that cannot ever be misconstrued as a testosterone-outlet or a redneck's truck. My one and only complaint is that it only comes with an automatic transmission.

Cab wing: It would be hard to install without drilling into the body. I don't want to hijack or pull too hard towards an aerocap, but there are already five symmetrically placed pre-existing screw holes in the box for mounting the tonneau Honda expected everyone to have (they even lowered the tailgate height for it). It would be very easy and structurally sound to mount something to those instead...

Slightly off topic, it would be great to see what kind of ecomods could be done to the 2017+ model. That base .31 Cd plus a good aerocap and a boattail on the dual-action tailgate (only open to the side when boat tail is attached lol) would be record-worthy.

[ChazInMT]

You can't divert the air and decrease drag. Drag is a result of making the air move that was previously sitting still. Anything you do to add energy to the air will require that you add energy from you vehicle.....the air does not just move itself. I think too often we get caught up in the concept that air is moving over our vehicles....our vehicles move through the air. Subtle but VERY significant difference.

[BabyDiesel]

Use this to plan your attack on the rear of the Ridgeline -

[ChazInMT]

Yeah, what he says, build this and you'll drop your Lift coefficient AND Drag Coefficient. It'll feel like you put a downforce wing on it and improve your mileage ta boot.



You think it's coincidence that modern vehicles look like this in back????

[BabyDiesel]

I agree Chaz, but I would be more aggressive and make the top more "Kamm-back-y". Instead of making it as a typical cover with the back edge sloping front to rear, go the opposite way. If I had Wi-Fi, I'd draw a mock up of what I'm suggesting.

And rounding out the edges as you get closer to the rear helps Cd, but makes the construction a bit harder.

[freebeard]

And rounding out the edges as you get closer to the rear helps Cd, but makes the construction a bit harder.

As much as you can consider the front top and sides to be flat, you can make it out of three triangles (pointing back) and two simple curved conic sections (pointing forward).

Can anyone explain why the NASCAR Camping World Truck Series don't have campers on them?

[Auptimist]

Originally Posted by BabyDiesel

I agree Chaz, but I would be more aggressive and make the top more "Kamm-back-y". Instead of making it as a typical cover with the back edge sloping front to rear, go the opposite way. If I had Wi-Fi, I'd draw a mock up of what I'm suggesting.

And rounding out the edges as you get closer to the rear helps Cd, but makes the construction a bit harder.

I'd be interested to see an A-B-A test of the taller, more gently curved topper that follows that damn template exactly versus the 12° average slope version suggested by that one engineering thesis. I may or may not get around to that. It would be kinda neat if OP and I went with somewhat opposing designs to compare. Definitely slope the rear backwards not forwards though, I agree, and leave an overhang to get that hard edge around the convex section for the fluid tail like aerohead always talks about.

How critical is it to round the joint between the sides and top? It makes sense if the goal is to create an elliptical curve on the backside to induce the "Morelli's Fluid Tail" smoke-ring effect, but it doesn't apply as much if you intend to get the rear edge height close enough to the height of the tailgate. But I also wonder if a hard edge on those "shoulders" to ease construction and purposefully induce flow separation there like the kammbacks' rears (except on top) would be somewhat helpful too. I think it's likely there's a minimum radius for those shoulders below which you're better off with a hard edge. Though as always I'd love for someone to question and point out if/how I'm wrong. Crosswinds may play into it too. (I asked aerohead but he's only on his computer on Saturday mornings haha.)

Attached images are of a quick model from a 3d sketch I made a couple weeks ago in Autodesk Inventor (which for this I prefer over Solidworks). This represents the laziest possible geometry for the aerocap: I lofted the curve of the rear window down a straight 12° slope then trimmed it up. That would require zero heat-forming of the polycarb, just cutting shapes out of a single 4'x8' sheet and solvent/heat welding them together, and bolting them down such that the top section has that longitudinal curve that follows the window curve (which, if I choose to follow it, means I can't have any transverse curvature). Frame discussion in other posts. Sorry for the derail. Again, I'm very curious about your other planned mods!

[freebeard]

Generally, softening those edges would prevent vortex formation in cross-wind conditions, but that edge is so short the effect would be minimal. The rule-of-thumb for leading edges is 4% of the gross width.

However, a glued or welded edge in a clear material might get away from you. Can the three pieces be cut out of a 4x8 sheet without rotating one? If so, I'd consider https://www.google.com/search?q=bend...with+heat+tape.