Zulu's Build Thread (Honda CR-Z)

[bobdbilder]

If you used the stepper motor you would probably want to calculate the wind force against the vent at its closed position. You would then need to calculate the torque required to hold that vent in the closed position. The bigger the area, the higher the force against the vent and the bigger the holding torque. You would then need to use a stepper motor with a suitable holding torque. A cheaper alternative to Stepper Motors are RC Servos. Biq torky omes have metal gears.

Here is some formulas you could use. Sorry, too lazy to retype this from my blog
The force on a wing is calculated as

F = 1/2 x ρ × v ² × Cd × A

Where

F = Wind Force in N

ρ = Density of Air (typically 1.146 kg/m² at 35ºC)

v = speed in m/s

Cd = Coefficient of drag

A = Surface area in m^2

One thing that we need to understand in this equation is that the Force required to overcome air resistance is heavily influenced by speed. Now we have to look at the surface area as one that is directly being influenced by the moving mass of air. Therefore, if the surface is at an angle to the air, one has to calculate this based on the degree. Based on an freely available educational information, we know that the drag coefficient Cd;

Cd = 1.28 × sin (a)

Where a is the angle of attack or inclination of the surface. Plus as in trigonometry, we know that the maximum surface area is one where the angle is at 45 degrees. Any larger, then the Cd would need a different number than 1.28. We also know that the surface area is a plank with the size of 715mm wide by 90mm long. Having an area of 0.06435 m²

Now we have the calculated force

F = 1/2 x ρ × v ² × Cd × A

= 1/2 (1.146) (200 x 10 / 36)² (1.28 sin (a) ) × A

= 2263.7 × sin (45) × A

= 1600.68 × 0.06435

= 103N

Or approximately 10.51kg

This shall be the design constraint for the servo motor. We need one that can at the very least, generate this much amount of force to be able to move the spoiler. The HITEC HS425BB has a stall torque of only 4.1kg/cm at the maximum power of 6V. The servo arm that fits our requirement based on location of the servo and distance to the control arm is 30mm (3cm). Therefore, the available force from this servo at that distance is 1.36kg or 13N. If we choose to use the same area of spoiler the capability of the spoiler is limited by

a) Speed i which it operates and

b) Angle of attack of the spoiler

We would need a servo that generates at least 31kg/cm or 431 oz in or multiple servos just to move against that amount of wind. Therefore, we have come to another fork in the road. Single or Multiple? Looks like this is going to be costly. This then brings me back to where I wanted to do this project. A variable angle of attack spoiler meant for reducing operational cost. It was for the purpose to make life a little bit easier for normal people. We would not expect them to be running at 200km/h.

[vibrating_cake]

Subscribed .
As a fellow CRZ owner, this will be interesting!
Especially the grill block MPG gain/loss and how it's mounted, as i've always had success with grill blocks, but the crz grill being a concave honeycomb isn't the easiest of things to block without it looking silly!

How are you planning on sorting the underside aero? Honda have been extremely generous with the gaps it's given to the exhaust, so it's a bit of a nightmare down there!

Quick tip, the doors and boot (trunk) have adjustable stops on them (2 on each) if you wind them to their shortest setting, you get more pressure on the door seals and a lot less wind/road noise into the cabin.

Also i'd be interested to know how to reduce the size of the panel gaps for the boot (trunk) lid, as they are huge!

Finally, the front aero is there to push the air "past" the mirrors (reduce mirror drag)
and the foglight recesses are to make turbulant/air vortices past the front wheels to reduce the drag from the front wheels, so i'd also be interested to see what there is to gain in this department.

[oldtamiyaphile]

Originally Posted by vibrating_cake

Also i'd be interested to know how to reduce the size of the panel gaps for the boot (trunk) lid, as they are huge!

I don't know what a CR-Z looks like back there but I sealed a massive gap (12mm or so) at the rear doors of my van with self adhesive automotive seals off eBay:

[aerohead]

Originally Posted by oldtamiyaphile

I don't know what a CR-Z looks like back there but I sealed a massive gap (12mm or so) at the rear doors of my van with self adhesive automotive seals off eBay:

There is a possibility that the gaps are beneficial.
During development of the 1st-gen Golf,VW discovered that sealing the gap at the top of the rear hatch increased drag.
They were going to investigate that.(the gap may have acted as a turbulator,allowing more energy into the boundary layer and better flow attachment,or better mixing in the wake).

[vibrating_cake]

Originally Posted by aerohead

There is a possibility that the gaps are beneficial.
During development of the 1st-gen Golf,VW discovered that sealing the gap at the top of the rear hatch increased drag.
They were going to investigate that.(the gap may have acted as a turbulator,allowing more energy into the boundary layer and better flow attachment,or better mixing in the wake).

Sounds logical in an illogical way, the bootl/trunk on the crz is really long, the gaps down the sides of the lid are wide also, which in side winds creates whistling noises, which is a little UN settling when you first hear them, the gaps on mine with the adjustable stops Set fully down are still wide enough to poke a small finger through

[jamesqf]

Originally Posted by cRiPpLe_rOoStEr

It's kinda surprising to me that the CR-Z has some low mileage figures compared to other hybrids.

Maybe because it's a sports car, and so people drive it like a sports car :-) Which is part of the reason why I average "only" about 71 mpg in my Insight.

[Xist]

Awesome! You figured out how to control the vent!

I bought the largest one that I could, cut a hole for it in my grill block and air dam, and still had difficulty keeping my car from overheating as I climbed one hill.

I do not use my air conditioning, it actually does not work right now in my Civic. I just had the vent going and the temperature gauge passed the halfway mark, so I opened my windows, and turned on the heater.

That makes driving in Arizona less enjoyable...

So, I figure that the hole is not always big enough, and the vent would restrict too much flow, even when open.

[bobdbilder]

Originally Posted by Xist

Awesome! You figured out how to control the vent!

I bought the largest one that I could, cut a hole for it in my grill block and air dam, and still had difficulty keeping my car from overheating as I climbed one hill.

I do not use my air conditioning, it actually does not work right now in my Civic. I just had the vent going and the temperature gauge passed the halfway mark, so I opened my windows, and turned on the heater.

That makes driving in Arizona less enjoyable...

So, I figure that the hole is not always big enough, and the vent would restrict too much flow, even when open.

For hot weather application, perhaps you should look into removing some sealing close to the windshield. This seems to seal the engine when the hood is closed. Removing this allow hot air to escape your engine bay and move right over your windshield. I think this sealing it is to keep the heat in during winter. Since I live in the tropics I removed mine. It helps to increase air flow across the radiator as the engine bay is not entirely closed. If the engine bay is closed, there is a drop in differential pressure across the rad. When there is a drop in differential pressure, flow across the rad also reduces. Be sure to put the sealing back on in winter.

[vibrating_cake]

Isn't the opposite true about the sealing at the windscreen side of the hood? Taking that off would try venting bonnet heat into a high pressure zone, which would effectively act as an auxiliary air intake into the bonnet that bypasses the radiator?
Also the diesel civic you guys don't have in America has a tenancy to crack it's exhaust manifold and let out toxic gasses, it might be a failsafe to exhaust them out of the wheel arches like the rest of the air

[freebeard]

This suggests the control flap be on the exhaust side rather than the intake. An added benefit would be the choke cable control can be shorter.