RV rooftop air deflector (DIY: Toyota Highlander pulling 4Runner/Apex travel trailer)

[aerohead]

Just a quicky.
Gilkison phoned last night from Trinidad,Colorado to say that the Toyota Highlander rear hatch which I modified into a rooftop air deflector for his 4RUNNER/APEX travel trailer rig is recording the highest mpgs he's seen so far.
They'll go on to Denver and then home after a family visit,then we'll have about 1,200 miles of round-trip data to digest.
So far so good!
I took a defunct hatch,cut away as much steel as I could without sacrificing strength,then pop-riveted aluminum skin where the glass used to be.It's mounted by aviation grade piano hinge to a transverse 4-foot Harbor Freight level at the front and the rear support struts anchor to a bifurcated 6-foot Harbor Freight level attached in cantilever to another 4-foot transverse level which acts as the rear cross piece.
The deflector is set at the same inclination as the 4RUNNER windshield.As the dual-windshield P-61 Black Widow.

EDIT by admin - added images...

[MetroMPG]

Another success!

Think John could send a photo of the work?

[mcrews]

Pics>>>>>must have pics!!!!!!!!!!!

[KamperBob]

One of my To-Do list items was a cab roof deflector.



I delayed installation my first 11 months of full-time RV life. I didn't trust the strength of my truck cap. The sawed off aluminum topper covers the front third of my 6.5' truck bed. (The nose of my 5th wheel trailer covers the back third. The middle third gap is mostly filled by a generator mounted on the nose of the trailer.)

Cap strength was a concern because of how it was shortened. After peeling off the skin the under frame was cut down. The frame was originally all welded. I can't weld aluminum so I used pop rivets, screws and bolts. It holds itself together no problem. I'd trust that in a hurricane. What I don't trust at highway speed is additional stress from a deflector. Not until I get around to reinforcing it better.

The original plan was to use the deflector as intended. Eventually replace the fiberglass wing with a solar panel. Last month I (finally) added solar to my rig.



I scavenged the deflector for parts to mount the panel. The tilt mechanism was my objective. All this I trust inclined for stationary use but for travel I keep it folded down flat (horizontal). Highway wind loads are reasonably low that way.

What remains to do aerowise is reinforce everything to handle road winds. Whenever I get around to that I'll be in a position to experiment with different angles. It's worth doing but lower than other priorities for me now.

Even then I'm not expecting huge gains. My trailer already has generous radii (circa 12") on the top and sides. By rights bow splash should not be an issue (per work by others). A deflector probably won't do a lot of good if onset flow is already attached. Still, it's something I'll be able to do (eventually) so it remains on my someday-maybe list.

By contrast the friend's Apex doesn't have such generous edge radii going for it. If it has considerable bow splash currently then a deflector seems a prudent addition to the rig.

Here's a link to my blog post with more pix and context on the not necessarily aero facets of my deflector related project.
Solar Project – Part 5 | Recreation Engineer

[aerohead]

Originally Posted by MetroMPG

Another success!

Think John could send a photo of the work?

John's probably got some in his Zoom and I've got three in my camera,but they're from before he moved the deflector aft about 9-inches (231mm).
I'll see if Al can help me post what I have,and when John checks in,see what he's got.
It's nothing fancy and it was 101 F when I painted it,so the paint (acrylic lacquer) pretty much turned to dust.
Next time,maybe Homer Simpson will let me spray it in his control room.

[aerohead]

Yes,APEX is kinda Dark Ages design.There is a sloping and upper radiused nose in elevation,but zero edge radii in plan view.
The deflector has a bit of curvature to the sides and it was thought that some of the source flow could be directed laterally,allowing APEX' nose to ride within it's wake.
Rough without a wind tunnel and no time to do a tuft test.Sucks!
1,200 miles of data will help us appraise it's value.
Bob,sure like the PV/deflector! Two birds,one stone!

[aerohead]

I won't be able to post photos today.
Al has a new computer and is going from Windows XP to Windows 7.And it's not going well at all.I got here at 11:00 AM,it's 2:27 now and the CPU is still grinding away.
I'll try again next weekend,sorry!
P.S. I did talk to Gilkison from Denver and he was happy with numbers.
He'll be by home Sunday when I talk to him next.And we'll have all the numbers by then.I'm very curious about his return leg,southbound between Colorado Springs and Trinindad.This is where the T-100/Viking trailer pulled 47.8 mpg at 65-mph.We'll be looking for some anomaly.

[aerohead]

After 1,571 miles,Gilkison got home.
He averaged 13.08 mpg,up from around 12.5 mpg.
The new 'high' tank is 14.587 mpg,up from 13.7 without the foiler.
So about a 4.6% mpg increase on this trip.
Which is in the neighborhood of a 9% drag reduction (wind averaged).

[aerohead]

Apologies to all.Al's swamped (that's good for his business) so won't be posting images today.
Gilkison emailed three more.
I'll try again next weekend.

[Tango Charlie]

Thanks for trying, anyway, Areohead. Can't wait to see those pics!