Need some boattail advice for the CRX-hf

[ebacherville]

Originally Posted by JJW

I would like to see any sort of diagram too, to help visualize it, but it sounds from aeroheads description (and I could be very wrong) that your design looks (as mentioned) sort of like a 240Z, but aerohead is describing something a bit more like the shape of an Audi A2 or a Prius, with the difference being instead of a solid rear the CRXs rear window angle is retained with side plates and a wing to cause the air to act as if the full rear window was there but with a bit of a tradeoff for drag. Am I even in the ballpark?

Yeah I looked at his CRX, that was his design.. Idealy however a full tail would be best ... other wise a camback would probably be the simplest bang for the effort.. However if i'm going th go through the effort I might as well make the best I can.

camback?<<think thats the right word..

[ebacherville]

I think this would be the ideal shape for a full boat tail on the CRX.. just going by eye.. however has no mathematics behind it..


AM i crazy enough to make this thing??

[ebacherville]

OK how about this its a bit less extreme.... but is it still too much for the world to accept?

Shown in the photo is the nose that I have made already .. a 1.5 " rear hood lift.. and the debated boattail..

[Cd]

Uh oh. You're starting to loose the nice looking shape you had going there.

Why not investigate a much shorter tail and just reattach the airflow at the lip of the tail ? Not only would it look better, but it would weigh less, and be less cumbersome.
Hot Rod did this sort of thing with their '79 Camaro which attained a .20 .Cd.

The last image resembles the back of a '71 Mustang Mach 1.
( Which brings up another point - If you went with a back end that steep, it would be harder to see out the back - a problem that the '71 Mach1 had )

You say that you intend to close off the entire back end and use a camera instead ?
Why ? Why not just use the stock glass mounted in your modified tail ?
If you went with a less steep angle, this would work even better.

Good luck !

[Cd]

I also notice that the underside in your illustration is now flat versus having an upward taper at the end.

[Cd]

Instead of removing the hatch entirely, you could just modify the angle of it.
Just open the hatch to the desired angle and fill in the gaps around it.
This would allow you to use the stock hatch and hinge set up.
You could then just continue the tail beyond this point.

[Cd]

Here is that Camaro. Point 209 .Cd verified in the A2 wind tunnel.

[ttoyoda]

ebacherville,
What do you envision for the top view of the tail? Do you see it coming to a point in the top view? Or just getting narrower?

Compare these two extreme designs : The m111 and the aptera.

The m111 had only one job. To go around a track. To do this, the drag had to be low, and the car had to be stable at high speeds, thus the tail fin on the back, I am sure that is not just for decoration. For an object to be stable, the center of MASS must be ahead of the center of DRAG. Thats why an arrow is stable.. The heavy head is in front, the tail feather which make drag are at the back. Try to throw an arrow backwards, it will turn around. So the m111: It is close to the ground, and a half teardrop.

The aptera has many jobs: Letting the driver see over minivans and SUVs. Allowing overweight aging yuppies to get in and out without getting a slipped disk in their back. Having a place to put the turn signals and brake lights. So aptera decided to make their vehicle way up off the road surface, on those front cessna landing gear wheels, and that giant tail-plane underneath for the rear wheel. The back of the tail was left wide for the turn signals. With the aptera up off the ground, making it a full teardrop shape made sense.

The crx is never (well, probably never) going to be up 2 feet off the ground. And it is going to have 4 wheels, not 3. So the m111 design is the one that can be most easily copied, even though their engine was in the back, and yours is in the front.

If you make your tail go down to the ground, you might worry about it scraping. But if you let it be flexible or hinged at the car, with spring preload pulling it down, (like a clamshell idea) and have a caster or two under the back (which normally does not touch the ground) then you will not damage the tail when you go up a ramp.

[ttoyoda]

.Cd,
do you have any pics or links of that camaro from the front showing more of the air dam details? And is that a reverse scoop on the hood?

[ebacherville]

Originally Posted by .Cd

Instead of removing the hatch entirely, you could just modify the angle of it.
Just open the hatch to the desired angle and fill in the gaps around it.
This would allow you to use the stock hatch and hinge set up.
You could then just continue the tail beyond this point.

With the hatch at the needed angle you wont be able to see out the rear glass anyway.. no need to keep it there if its useless... ill retail the opening hatch it will just be re-angled to fit aerodynamics.