[Greenflight]

Well, my truck is kind of a total loss when it comes to aerodynamics... I did add a homemade bed cover, which should help a little bit. Just a couple days ago, I also lowered the front a few inches, which is more of a looks thing but may also help with aerodynamics.

My Tercel is a fairly sleek car as is, but I'll probably add some body work to it once I get it going. May put a belly pan on it. We'll see.

 

[Greenflight]

OK, I got to take my truck for a test drive with the front lowered. I didn't notice much difference below 30, but I think I picked up about 3-4 mph in third gear.

Oh yeah, that was a good post Sharkey!

 

[Greenflight]

Man, this thread has really become a wealth of info... Matt, those links are great. I'm definitely planning on putting a belly pan (at least up front) on my truck.

 

[Greenflight]

I happen to have a little experience with cooling... My motor burned out at about 500 miles due to overheating.

After that experience, I decided I didn't want it to happen again, so I ducted an electric radiator fan to the motor endbell. With the fan operating whenever the ignition is on, the motor gets warm to the touch, but not quite "hot," to use technical terms.

During the summer, when it's hot and humid, the motor still gets a little hotter than I'd like, but not nearly as hot as before the fan.

The controller stays cool as a cucumber.

I'd say your estimate of about 5-6 times more airflow than needed is about right for a good quality motor. To be safe, I'd avoid blocking more than 2/3 or 3/4 of available airflow.

I think the ultimate solution is the belly pan under the front only, with small guides by the rear wheels, and maybe a few mods on the back end. But that's just my uneducated guess.

 

[Greenflight]

OK Sharkey, fill me in here. HOW does your car's controller only handle 10A?

John, I'm thinking if you place the ports at the stagnation point you won't get much flow for the drag produced. If you don't need much air, wouldn't it be logical to use flush scoops in attached (heck, maybe even laminar, if you have a smooth car) flow locations?

 

[Greenflight]

I see... so, what are the downsides? Sounds really cool...

I was thinking more along the lines of a flush scoop- one that draws the air down from the surface without projecting into the boundary layer. This type of scoop is designed to cause the least possible disturbance.

It seems like the stagnation point would split in two around the port (just guessing here ). Since the greatest loss of boundary layer energy generally occurs in the area on either side of the stagnation point, it seems as though you would end up with an excessively thick boundary layer at the front of the car, causing flow detachment sooner at the rear.

Anyway, just my $0.02...

 

[Greenflight]

Well, I used up almost a whole roll of duct tape and a couple sheets of pink (I know, I know...) insulation foam today, and I now have something that could possibly be described as a belly pan. It goes all the way back to the front axle in the middle, and it also covers the area in front of the wheels.

One of the pics also shows a lexan grill cover I put on a few days ago.

The results? Well, they don't seem to make a whole lot of difference. If I had to guess, I'd say they reduce drag a little. I can't really say for sure.

When I go to test stuff like this, I usually go about a mile one way on the flat stretch of road in front of my house, and then return, shifting into third and allowing it to reach top speed.

I noticed maybe a 1 mph increase, but it's hard to say...

Well, it can't hurt anything, right?

I'm going to do a little more work on the area in front of the wheels. I think I can get some improvement with a little tweaking.

 

[Greenflight]

Yup, NACA submerged scoop. Words weren't coming to me. I guess the concept of intakes at the stagnation point just sounds weird. Probably works fine. I'll have to look into it some more.

I run out of torque long before I run out of revs. Top speed in 3rd is pretty predictable, around 45. After I lowered the front, it went up to about 47, which is about where it is now. Tomorrow, if I get the chance, I'll add some deflectors in front of the wheels and see what happens. I'm going to try those wedge-shape deflectors. If I can get them to funnel some air towards the center of the car (where the pan extends furthest back), the pan should help more. We'll see. I'm also going to try gap sealing the top edge of the bumper to the grill, with a large fillet. Should help flow around that area a bit.

I'll let you know what I find out.

All this duct tape is creeping me out... Great for trying out mods, though.

 

[Greenflight]

I finally got the chance to throw together some deflectors for the front wheels. They seem to improve performance slightly, but it's hard to tell because it's pretty windy out. Calm conditions would be much better.

From what I can tell thus far, these deflectors are probably worth their weight. I think it would be worth making a nice fiberglass (maybe even carbon fiber? ) belly pan with molded-in deflectors. Another project for when I get bored.

If I were to lay up a belly pan, it would be easy to incorporate a new bumper cover as well, possibly picking up some more speed there.

I'm going to take it for a spin again this evening when the winds have (hopefully) calmed down and I'll post some more results, along with pics.

 

[Greenflight]

True- except the decrease in pressure would probably be compensated by upwash at the rear of the belly pan, plus the increase in pressure that would likely be caused by the sudden slowing of the air. Hard to say, though.

It is true that a lower angle of incidence would probably improve performance significantly. In fact I was just thinking about that. If I were to build a custom bumper cover I'd compensate by lowering the front of the bumper low enough to flatten out the pan. Plus it would reduce overall airflow underneath the car, which would probably also have a pronounced effect.

Kevlar might be a better choice... I just don't know much about it. I'll probably just end up using fiberglass anyway.

I drove the car a little more and concluded that there was a slight increase in performance from the deflector. A better design would probably have a much more noticeable improvement.

I like these ideas! Good, cheap ways to improve performance... Gotta love it.

 

[Greenflight]

Matt, try thinking of it this way (and please, somebody smack me upside the head if I'm getting this wrong).

Every action has an equal and opposite reaction. So each time the car acts upon the airflow to change it's direction, a force is exerted on the car as well as the air. So when the car deflects air upwards, the air exerts a downward force on the car, and vice versa. And each action/reaction takes energy. So even if the net force is zero, if the air has to go up and back down, it takes energy.

When working with air flow at subsonic speeds (I think we can all agree that this is subsonic) it is generally considered incompressible. This is not to say that air is incompressible- it's just that the effects of compression in these situations are small enough they're worth ignoring.

So anyway, when the air passes under the car, the belly pan deflects it downward (note energy loss) and then flattens it out (note energy loss). As John was saying, this reduces the cross sectional area of the "tunnel" underneath the car. Since the forces aren't enough to compress the air a noticeable amount, the only option the air has is to speed up.

Think of it as the proverbial water in a pipe. If the pipe becomes smaller, the water speeds up. Same diff.

And as far as the air behind the belly pan, it becomes a tremendously disorganized flow that my feeble mind can only guess at.

Way not to speak to the question, huh?

And BTW, thanks for that glamorous pic of my truck. To be honest, I never really looked at it that way before.

 

[Greenflight]

OK, so here's what I'm thinking of wasting duct tape on now.

Check out the pics of this car (BTW, the batteries in this car are AMAZING): http://www.austinev.org/evalbum/464

See that front bumper? I'm thinking of rigging up something like that. I would be able to lower the bottom edge of the bumper, reducing the amount of air that passes under the car, and also duct it further out to the sides, away from the front wheels. I could also bring the front of the fender closer to the wheel, reducing the excessively large gap that currently exists. I could also flatten out the belly pan quite a bit.

Plus it would be really easy to test out.

So, what do you guys think?

 

[Greenflight]

That's a noticeable effect. Very interesting.

I'll probably work on the fairing tomorrow if I have time. We'll see. I can imagine reducing the overall flow underneath the car by that much would help quite a bit.

I'll post the results when I'm done duct taping.

 

[Greenflight]

Woohoo the 50th post is mine!!!!

Good idea Matt. I'd be happy to add some pics of my experiments, along with results, etc., as long as I could figure out how. Never actually used a wiki before.

 

[Greenflight]

OK, I had some time to kill today (finally), so I started working on a bumper cover for my truck. As soon as I can get it to the point where I'm confident it will withstand 50 mph winds, I'll try it out.

I'll post some pics of this ridiculous looking contraption as soon as I get the chance.

And I keep meaning to add to that wiki but I can never seem to get around to it!

 

[Greenflight]

OK guys, here's the final rendition (sorry for the bad pic). I decided I wasn't comfortable having a huge chunk of foam on the front of the truck, so I made one out of lexan instead. Not the most elegant design ever, but hey- it works!

I might have picked up 1-2 mph. I should probably try making a new belly pan that attaches to this thing, rather than just "existing" behind it. But at any rate, the fact that it didn't slow the car down is a good sign.

 

[Greenflight]

Hmmm. 3.5%. That's kinda depressing.

Either way, this stuff is fun to play with. Plus I think it makes my truck a little more bearable for the people behind me.

Just because I'm curious- You seem pretty familiar with aerodynamics... Is that your line of work?

 

[Greenflight]

Okay, don't know how I missed that post before, but I seriously almost fell out of my chair when I saw that... Do you know if the guy got any better mileage after, uh, "tweaking" it?

I like the rear hatch... nice touch.