Aerocivic - how to drop your Cd from 0.31 to 0.17

[3-Wheeler]

Originally Posted by MetroMPG

...Just how much contemplating are you doing about an Insight tail? You definitely have my attention!...

Hi Metro,

My goal for next summer is to make a foam/fiberglass boat tail, at least this point in time.

Following your adventures with the Metro boat tail design has me convinced that another 15% reduction in air drag is something to go after.

Jim.

[3-Wheeler]

Originally Posted by basjoos

Mount the spare tire in the boattail. The boattail can add a considerable amount of cargo space to your car. Might as well take advantage of it.

Hi Mike,

That by itself is a great idea, however, as you know the Insight some *other* stuff in the trunk to consider.

There will certainly come the day when I have to do more maintenance on the high voltage battery that also sits in the trunk. It weighs 70lbs with no electronics, and I have to figure out a way to safely get this *item* out of the trunk with the boat tail in-the-way.

Or, provide a *hinge* that allows it to swing to the side and allow full access to the trunk.

This is the *contemplation* part that Metro was talking about!!

I have a feeling that others would be trying to work out a similar method for their boat tails as well.

Jim.

[RobertSmalls]

Jim,

Don't worry about the boattail getting in the way of removing the battery module. It will hardly have an effect. When I pulled the battery module out of a junkyard Insight, I stood/knelt in the spare tire well to remove most of the bolts, and for the final lift. The battery is located forward of the spare tire, right behind the passenger seat, which is out of reach of someone standing behind the car.

Worst case, you have to hire someone to lift the battery from the car for you.

I'd be more worried about getting at groceries and whatnot stored in the hatch, and whether the cargo space in the spare tire well would be accessible enough to be useful.

One other point: Insight aerodynamics are harder to improve on than Metro or Civic aerodynamics. A boattail would save you fuel, and I would be excited to see it, but I wouldn't count on a 15% improvement.

[basjoos]

Originally Posted by TOOSTUBBORN2FAIL

Mike i wanted to ask you, how thick is the lexan on the boat tails window? Im starting the design process for my car, and that would help a lot. If you have an hinge ideas that would be great as well, as my car is not a hatch back, and hinges will have to be added to add trunk space.

I used 1/8" thick Lexan. I don't know how you are planning to lay out your boattail (curving off the back of the trunk or off the back of the rear window), but you should be able to design in a piano hinge or some door or gate hinges to make an openable lid in the boattail. If you are planning to start the top of the boattail at the top of the rear glass, you could remove the stock trunk lid, then add a new trunk in the boattail section extending beyond the original back of the car. The original trunk space could be accessed by a hinged lexan hatchback and the 2nd additional trunk via a hinged lid in the top of the boattail behind the lexan hatch. This way your original trunk can be a large open cargo bin where cargo could be stacked up to the level of the lexan hatch and the new smaller trunk in boattail could be used for additional storage (spare tire, tire jack, etc.)

[MetroMPG]

Originally Posted by RobertSmalls

One other point: Insight aerodynamics are harder to improve on than Metro or Civic aerodynamics. A boattail would save you fuel, and I would be excited to see it, but I wouldn't count on a 15% improvement.

Critical point - thanks for making it.

Jim: I'd recommend testing a cardboard & duct tape prototype, to assure yourself a "good" version is worth the effort.

EDIT: however, and this is really important, we can't forget the Insight doesn't share the Metro's ICE technology. Any aero improvements to the Insight widen the lean burn window. So an Insight may not need as much of a Cd improvement to equal the Metro's 15% fuel economy improvement.

Mike may be able to speak to this since his car is now lean burn equipped.

[3-Wheeler]

Originally Posted by RobertSmalls

The battery is located forward of the spare tire, right behind the passenger seat, which is out of reach of someone standing behind the car.

Hi Robert,

Actually my battery has already been out of the car to add trickle charge capability!

And I was standing outside the back of the car, and lifted the battery out by hand after moving the battery on top of the latch, while one leg was in the trunk.

And your right, it was heavy!!

Jim.

[3-Wheeler]

Originally Posted by MetroMPG

....EDIT: however, and this is really important, we can't forget the Insight doesn't share the Metro's ICE technology. Any aero improvements to the Insight widen the lean burn window. So an Insight may not need as much of a Cd improvement to equal the Metro's 15% fuel economy improvement....

Hi Metro,

I really hope your on to something here, as the goal of 15% or even 10% will be worth it.

And your comments about widening the lean burn window is one of the goals as well.

I'm hoping someone else will be able to establish angles of curvature so I can simply copy their design in foam.

Jim.

[basjoos]

Originally Posted by MetroMPG

EDIT: however, and this is really important, we can't forget the Insight doesn't share the Metro's ICE technology. Any aero improvements to the Insight widen the lean burn window. So an Insight may not need as much of a Cd improvement to equal the Metro's 15% fuel economy improvement.

Mike may be able to speak to this since his car is now lean burn equipped.

The aeromods have enabled me to operate in lean burn to much higher speeds than a stock VX which, from what I've heard, drops out of lean burn at speeds above 65mph. So far, I've run in lean burn on a level highway at speeds up to 91mph. Based on the injector pulsewidth needed to maintain that speed, I should be able to to reach close to 100 mph before dropping out of lean burn.

[3-Wheeler]

Mike,

It looks like the boat tail will simply need to be designed to come off when having to work on the high voltage battery. There just does not seem to be a good way around this.

Is there a good way for you to take yours off if you have to?

One could imagine having quite a time trying to put the boat tail back on after working inside the rear of the car...

1) Pick up the boat tail, which if made from foam/fiberglass, would weight 20 lbs? Maybe 30 with lights and such.
2) Try to align the large end of the boat tail to "alignment" pins on the back side of the car.
3) Slide the boat tail forward until it hits some sort of "stops".
4) Now one has to hold the rear portion up and at the same time start tightening fasteners while reaching through the hatch to gain access.

No scratch that!! It sounds too difficult to handle.

a) How about picking up the boat tail on the open/large end.
b) To one side of the large end, there is a largish pin that faces toward the ground and attached as a hinge pivot.
c) Pickup the boat tail and slowly drop the pin through a corresponding hinge until the pin is fully inserted.
d) Now swing the boat tail to fully closed.
e) Tighten internal fasteners through the hatch.

In this design, the boat tail can be fully removed for sanding until smooth. For MetroMPG, this means lots and lots of sweaty sanding (grin). For me it simply means sanding, glazing putty, and primer all summer, so the boat tail will really take two summers to complete. The motorcycle fairing took this long as well.

Jim.

[RobertSmalls]

Jim,

What if, in the event of HV battery failure, you remove the passenger seat and/or the rear hatch for better access?

Or if you roll it to Buffalo, I'll crawl in, sit in the spare tire well, and remove the battery for you. I may even have reconditioned Insight cells at that point.

As to a removable boattail, the factory rear bumper cover is held on by four bolts, four hooks, and some nylon rivets. It can be removed in ten minutes. If your design has an aluminium frame, you could use the same attachment points, and maybe have the whole thing held on by eight bolts.