F150 aerocap design and construction
 

Hi all,

Inspired by the aerocap threads here on ecomodder, I have been encouraged to build my own and report fully on my design and construction experiences here.

Over the next couple of months I'll be posting full construction details, with detailed photographs, and afterwards, if anyone wants to copy my design (which is, to be fair, somewhat inspired by Bondo's fantastic design, but is constructed very differently) I will even mail out templates on paper to anyone who asks.

My design will have a light wood frame, covered in strips of 1/4" plywood to make the shape, then covered in fiberglass and bondo to get a great finish. I'll then finish paint it to match my truck.

The design will have an opening lid section, and will be insulated on the inside.

So far, the only mod I have done is a fan/shroud delete, replaced with an electric thermostat and two 16" e-fans. This has bought me a small gain in FE, mostly with cold starts and in town driving, where I get around 1.5mpg improvement. From here on I'll enter details on the site, since I am no de-lurking ;)

If anyone has any questions, suggestions or support, I'm all ears :)

Dave in Austin

How I arrived at my curve:

I decided that many people have already done good research on the terminal angle for the aerolid - I think there's a consensus that the final angle in Bondo's design is perfect. However, I wanted to have a curve that happened a little later to maintain headroom inside the bed.

I took a 1x8 board, and angled the two ends so it would sit in position, with 2" of fixable surface at the front, and 1" of height at the back. There is over 4" of contact on the bottom edge.

From here, I drew a line at the terminal angle from the back, and a line level with the roof from the front. I then got a piece of PVC pipe and made it into the curve that naturally intersected the lines I'd drawn at both ends.

This gave me an even curve. I didn't want that, but wanted more of the curve biased towards the front of the lid, and the rearward portion to be a flatter curve.

I printed out a few side images of others' aerocaps, cut them out then stood back and compared them with my drawn curve. A couple of tweaks and I was happy with my curve, just by gut feel.

I rough cut it on a table saw, as straight lines within 1/4" of the intended curve. Then I created the curve on the table saw, which I find the most accurate way of making large diameter curves.

I used a belt sander and my eye to take out a couple of 1/16" variations, and ended up with a curve I am completely happy with.

Next, I'll duplicate the curve to three more pieces of 1x8. I'll make two pairs, then drill a hole for a nut/bolt/washers hinge about 3" from the front. My idea there is to let the hatch open and have an EPDM rubber strip sealed to both sides of the hinge outside so it is flexible, doesn't interfere, and is aerodynamic.

Also, I note there's a gap between the cab and the front of the cap. I intend to put a curved piece of wood in there to bring down the gap to 1/2", then fill and shape the section with foam to create a more smooth join.

My topper is a straight line in side view. The air flow is pretty good, but there is a thick boundary layer right behind the cab. Loose snow barely blows off the first foot or so of the topper.

A larger lead edge radius plus some curvature would improve it.

The photos of your shell were part of what made me take the leap of building my own. Thanks :)

I chose to not do a straight one for that exact reason. I also didn't want to exactly copy anyone's curve, or be too original either.

In the end, the way I selected my curve was quite complicated to explain, and really simple to do :)

My curve is the natural intersection of the side curve. I will take a photo that should explain it a lot more clearly when the sun is in a better position, tomorrow. What this does is make it easier to keep a uniform side profile and top profile, and just have them intersect. Words don't do it justice but one photo tomorrow will make it completely clear :)

This is a project I wish to take on soon so I will be following this closely.

Well, you're in Richmond, so next time I drive to Houston I can drop by and show you what I have done, if you like?

Meanwhile, I have been reading a couple of threads on cold air intakes. It seems a CAI is good for increasing power, which isn't my goal, but a warm air intake might do a better job of getting the fuel atomized and improve economy.

I think I will monitor intake air temps using my Ultragauge, and do some ABA testing of cold/ambient vs warm air intakes. I've looked for a definitive thread where someone has done this, but never seen one.

Ok, now to go outside and take that photo I was talking about yesterday. :)

New photos :)
 

Ok, here we go.

The first photo is standing right behind the truck. Note the line of the curve as compared to the line of the cab. The curve is the intersection of 1" inside the contour of the cab, give or take a quarter inch or so. This means I can maintain the edge contour from front to back, which I think is really clean.

Ford did a lot of work on the airflow over the top and side of the truck, so why ignore all their effort? :)

The second photo shows looking straight up the curve, so show how it and the hinged section will angle down, making the lid a trapezoid.

The third photo is a clearer shot of the curve from the side.

Progress report...
 

Today I made good use of my templates.

First, I made three copies of my main curve. This creates the two hinged sides. I pinned them together and sanded them to be uniform and match the first piece.

Next, I used the roof contour template to make a few cross-pieces. These will be used to make the opening hatch. I was careful to mark the centerline, then I pinned them together and sanded them to be nice and even.

Then I pinned the main curves into pairs, and using a temporary block, I put them in position. I made eight side templates, then positioned them and cut them to fit. That gave the curve from the bottom. I then positioned them against the main curve and made a consistent curve from the top. Now, I have all the framing needed for the aerocap.

The next step will be to glue, pin and screw the side pieces, sand them, then assemble the lid section. I'll need to go get some hardware to make the hinge/pivot - a 2 1/2" bolt, nut, and some washers for each side. The interesting part is that the bolts need to be aligned to each other, which is NOT parallel to the wood they're mounted in. I'll need to watch that carefully when I get to that stage of construction.

Great update,
Gonna be in Austin this weekend for a conference,
Msg me if you have time to show off your progress.

PM'd.

Good start, Dave!

Side-project: air intake
 

As a side project I researched here, and looked at my air intake.

At its narrowest point, my air intake is a circle 1 7/8th inch in diameter, which I think is quite small and limiting in an open throttle situation. Regardless of the Cold vs. Warm intake debate going on inside my head, I drew some conclusions, and one was that this restriction had to go.

If you look at the first three attachments,you'll see the intake restriction. I saw on here a "gotts mod" to widen that restriction out to the full diameter of the hole in the side wall. However, I decided to go a different route.

I took some A/C duct material, which is a 1.5" thick fiberglass insulation sheet coated on one side with reinforced aluminum. I removed the restriction, and made an air box like would be found on a cold air intake. I left my air filter arrangement intact.

I did this non-destructively, so when there is good weather, I can do an ABACADA test with and without the obstruction.

Here's my method, theory of what I expect to see:

METHOD:
I will note the temperature, wind and road conditions, and start with a fresh tank of gas with no additives, and a well warmed up truck.
A) I'll ultragauge my consumption at 55, 65 and 75 with the original intake. I'll note the intake temperature, fuel rate, speed, and engine load.
B) Then I will remove the restriction and repeat.
A) I'll replace the intake and repeat.
C) I'll put in the box, to in theory draw in cooler air, repeat
A) I'll replace the intake and repeat.
D) I'll remove the restriction and place some drier hose on the end, drawing air from the radiator, and repeat.
A) I'll replace the intake and repeat.

I will check that each A run is consistent, and create a graph of all the data collected during the runs and publish it here, with a photograph of each configuration.

I expect to see a baseline for A runs, a slight reduction of economy with the C run, and improvements with the B and D runs.

The EPA says that on the freeway, I should get 17mpg. Not knowing their method, I'll get those baseline consumption vs speed curves. From the baseline of 17 mpg, at 68mph that's 4 gallons/hr. That means 58.8 gallons of air would be consumed in an hour at a fuel:air ratio of 1:14.7, or a gallon a minute. That sounds like a lot less than I'd imagined, so I suspect my math is wrong? Anyone in the know want to weigh in?

I'm interested in suggestions for other things to check to improve my method, and also, any other possible configurations I could add to the test? Comments/ideas strongly welcomed!


The other attachments show how bad the underside of the truck is - it's like an aerodynamic grand canyon, and I have some firm ideas of what I'd like to do about it. More on that in a future post.

Fuel air ratio is figured by weight. That 4 gallons of gasoline weighs about 24 lbs, so 24 X 14.7 = 353 lbs of air. Next you need the density of air, which comes from a pschrometric chart (Google is your friend to find one). Air density depends on temperature, humidity, barometric pressure, and altitude. Psychrometric charts assume the altitude is at sea level, and standard barometric pressure.

Air density can range from over 15 cubic feet per lb (hot and humid) down to less than 12 cubic feet per lb (cold). Air at 70 deg F and 50% RH has density 13.5 cubic feet per lb.

Next, multiply 353 lbs X 13.5 cubic feet per lb = 4763 cubic feet per hour = 79 cubic feet per minute. And that's your air flow.

Ah, so thinking volume was a mistake, weight is correct. Thanks for explaining it to me.

I didn't have good testing conditions today. I do know that up to now my base MPG is 17. With the fan delete and the restriction removed, but no other mods, I have been getting 19.9mpg in mixed driving with a few red lights, town, some 55 and a good 65 run.

I'm hoping with the aerocap and a few other changes, I'll be up around 24-25 mpg, which means the F150 4x4 would be beating out the CX-7 for economy ;)

Of course, I'll be working on the CX-7 too, so... If I can get that over 30mpg I'll be happy.

Under body panel.
 

I have decided the method and materials I'll use to build and attach my under body tray.

I will use tape and expanding foam to make a template/mould, then make a set of fiberglass panels that will be installed from the rear to the front, overlapping. This will make for the most lightweight and easy to install/remove system, at moderate cost/effort.

I know how to work around the exhaust, and am comfortable with that side.

I also plan to leave toom for suspension travel causing the driveshaft to move lower when the suspension unloads into a dip.

Where I am unsure is the differential. Will enclosing it or putting it out of airflow cause it to get significantly hotter? What is a normal temperature for an F150 differential after some freeway driving?

I will use my infrared thermometer to collect trip temperature data after longer drives for the next few weeks and report back, but any insight would be helpful.

Yer differential will git warmer in temp when it's enclosed with a belly pan. Temperature will depend on the loading (towing/bed load). Best thing to do is run a thermometer probe on the differential and measure yer temps and git a baseline before you install yer belly pans. After you install yer belly pans, you'll be able to tell how warm yer differential will git up to and if you'll be comfortable with those temps or not. Just don't go blind and not use some sort of continuous temp monitoring setup. ;)

Something that came up recently with my pickup. At 7,900-lbs, and two destroyed tires, I had to order a rollback wrecker. We had to find attachment points to winch the thing up the bed. So, be sure to keep this in mind with any bellypan.

*nods*

I can see how that would be a problem. Also, getting under there if it was dropped the height of the tires would be an issue too. I will look at the rear attachment points and make a plan.


Good call. Thank you.

That's a nice Airstream you have there. Single axle at that length, is it a 50's pre-torsion axle one?

Late to the party, but subscribed and watching with interest.

And thumbs up for the "open source" and willingness to share approach.

Plans to A-B-A test the cap when it's finished?

I'm still designing a cap for Pablo's bed. It's a 7' x 5 1/2' flatbed with stake pockets. I'm also going to need full side skirts. It's just a little cold out there to get it done tonight.

http://img.photobucket.com/albums/v2...bloAero1-1.jpg

I drew the horizontal line 4' straight level back from the front of the cap, then angled it down to end 8" above bed level 12" back from the back end of the bed. Then I did a spline curve from the front to the midpoint of each of the lines, and then to the back end of the sloped line. I think this will give me room for a decent side door. The sides will slope so that it's 45" wide (cab top width) in front and 48" wide in back. That will involve torturing the ply on the sides slightly, but it's within doable limits.

My plan is to cut two templates out of scrap and bend a properly trimmed 4x8 sheet over them, set the side pieces in place and mark them to that curve on their angles, and then put it together with some interior framing. I'm imagining a large hatch in the roof piece to make loading easy, but I haven't worked out those details. As I said, there'd also be a side door.

Absolutely. I also plan to video the ABA tests and have anyone local along to observe/report. And tuft test.

If you get sick of that cold weather up there, feel free to come down and help ;)

Ha! Well, I've been hiding from the cold weather on the Wet Coast this year. But if you're still working on it next winter ... :D

I bought the hardware, and a cheap, sacrificial tarp from Harbor Freight yesterday. I'll put the frame together with the hardware, then cut up the cheap tarp (which has a convenient small amount of stretch) and use them as a temporary cover for the panels. That way I can do some preliminary tuft testing and ABA testing before committing to the curve and design.

Let's see if we can make some big progress tomorrow :)

Progress...
 

Today I put the sides in. The design has become a lot more rigid now there are triangles involved. This is good.

Next, I assembled the lid and dry fitted it with the retaining clips. It's a bit more snug than I'd like, but it looks right.

I attached some photos of today's work.

The one pictured is an '83 Silver Streak an upmarket cousin to Airstream. I've now a '90 model (different in appearance). Leaf sprung suspension . . for now.

Moving swiftly on...
 

Today things are really taking shape. I'm getting the luan on, getting beautiful curves...

Once that's on, I'll just very lightly bondo the seams and sand to get a professional looking finish, then seal it all in...

One thing I can't find... The mystical auxilliary brake light lead for hooking up the brake lights on camper shells. Where do they stash that?

The wire you are looking for is located under the drivers side door in the wiring harness against the frame. It will be a green wire with a black cap on it. Snip off the black cap and that is your hot lead for the brake light.

You will have to wire up a ground wire to the frame or another good grounding location also.

Best of luck to you on your project, it is looking very good.

Bondo

Found it! Wow, they really hid that well. It was tucked behind a wiring harness, behind a plastic cover. Including the 3/4" black cap, I'd say there's about 1" of wire there. I guess I'll carefully remove the cap instead of snipping it off, so I have something to work with ;)

What do you think of my rounded tail, Bondo? I'm trying to keep the airflow attached to 18" behind the truck. I will make a rounded section to fit beneath the tail, so guide and smooth out the airflow coming up from beneath -since we all know turbulent air is a bad thing.

My luan laying went fairly well. On the one side, I applied it in 3" strips and it took the compound curve very well. On the other side I got brave and put it on as one piece. Not so good. I'll take it off tomorrow and make another piece in 3" strips, and start bondoing... Is bondoing a word? I also need to put a couple of guide strips under the top of the tail piece. It has tried to dip down and I suspect it will cause the air to break away right there.

It would be best to ask aerohead about the rounded back end. A boat tail extension may be best that mounts on the lowered tailgate. That will get you another 24" back and then you can also haul 4x8 sheets of plywood laid flat in a 6.5 foot truck bed and keep the wood dry too.

Bondo

Make sure you use Bondo Gold, its what I use on cabinets when there going to be lacquer finish. I thinly coat the entire surface and then lightly sand. The finish paint is so smooth you cant tell its wood.

Normal Bondo is to much work

I saw that you did that in your thread. I don't want to do that because in this area, the police are liable to write tickets for anything they're not accustomed to, and they often write tickets for people who leave their tailgates down when not carrying a load. They twist the "nothing sticking out more than 6" from the vehicle" law we have locally.

I did the tail as a rough experiment, knowing I could easily cut it off if it didn't work. I chose the shape because it is longest in the center where the airflow is most stable, and shorter at the sides. Also, it was easy to do with two screws, a sharpie and a loop of string.

I will attach a brake light under the lip of the tail, since I don't want a ticket for an obstructed tail light either.

I drove to the airport and back last night in cold conditions with medium winds from the south, and for my round trip, including in town and traffic, plus circling the pickup circle at the airport, I got 22.5 mpg on the Ultragauge, with my 90% skinned cap. So far, I am quite happy with it.

Good advice, which I will take. A little extra expense is worth it. I've used regular bondo in some car restorations and it is time-consuming to get the perfect results...

I am curios how the project is going, any progress?

I have been tied up doing some contract work (I design parts to keep antique computers running) and the weather has been a bit.... damp... so very little progress has been made.

I will get back to it in another 3-4 weeks.

3-4 weeks ended up being 3-4 months, but I have pulled this out and dusted it off.

Updates will be posted in a couple more days.

This is exactly what I imagined.