Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 09-12-2015, 10:38 PM   #11 (permalink)
EcoModding Lurker
 
bobdbilder's Avatar
 
Join Date: Oct 2013
Location: Malaysia
Posts: 83

Knight - '03 Proton Waja
90 day: 37.15 mpg (US)

Whoopee - '01 Proton Wira 1.3 Aeroback
90 day: 38.69 mpg (US)
Thanks: 19
Thanked 25 Times in 18 Posts
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 Cd A

Where

F = Wind Force in N

ρ = Density of Air (typically 1.146 kg/m at 35C)

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 m

Now we have the calculated force

F = 1/2 x ρ v Cd A

= 1/2 (1.146) (200 x 10 / 36) (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.


Last edited by bobdbilder; 09-12-2015 at 11:01 PM.. Reason: Pasted some calculations from my blog
  Reply With Quote
The Following 3 Users Say Thank You to bobdbilder For This Useful Post:
CigaR007 (10-03-2015), MetroMPG (09-14-2015), Xist (09-16-2015)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 09-14-2015, 08:13 AM   #12 (permalink)
EcoModding Lurker
 
Join Date: Mar 2015
Location: ENGLAND
Posts: 18
Thanks: 1
Thanked 5 Times in 5 Posts
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.
  Reply With Quote
The Following User Says Thank You to vibrating_cake For This Useful Post:
CigaR007 (10-03-2015)
Old 09-15-2015, 07:49 AM   #13 (permalink)
Master EcoModder
 
oldtamiyaphile's Avatar
 
Join Date: May 2009
Location: Australia
Posts: 1,314

UFI - '12 Fiat 500 Twinair
Team Turbocharged!
90 day: 43.3 mpg (US)

Jeep - '05 Jeep Wrangler Renegade
90 day: 18.09 mpg (US)

R32 - '89 Nissan Skyline

STiG - '16 Renault Trafic 140dCi Energy
90 day: 31.99 mpg (US)

Prius - '05 Toyota Prius
Team Toyota
90 day: 50.25 mpg (US)

Premodded - '49 Ford Freighter
90 day: 13.48 mpg (US)

F-117 - '10 Proton Arena GLSi
Pickups
Mitsubishi
90 day: 36.8 mpg (US)
Thanks: 267
Thanked 327 Times in 239 Posts
Quote:
Originally Posted by vibrating_cake View Post
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:

__________________






  Reply With Quote
Old 09-15-2015, 05:09 PM   #14 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 8,781
Thanks: 11,622
Thanked 4,646 Times in 2,618 Posts
gap

Quote:
Originally Posted by oldtamiyaphile View Post
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).
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
The Following User Says Thank You to aerohead For This Useful Post:
oldtamiyaphile (09-15-2015)
Old 09-16-2015, 04:19 AM   #15 (permalink)
EcoModding Lurker
 
Join Date: Mar 2015
Location: ENGLAND
Posts: 18
Thanks: 1
Thanked 5 Times in 5 Posts
Quote:
Originally Posted by aerohead View Post
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
  Reply With Quote
Old 09-16-2015, 01:07 PM   #16 (permalink)
Master EcoModder
 
Join Date: Jun 2008
Location: Earth
Posts: 5,037
Thanks: 218
Thanked 751 Times in 549 Posts
Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
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.
  Reply With Quote
Old 09-16-2015, 02:25 PM   #17 (permalink)
Ecomuggler
 
Xist's Avatar
 
Join Date: Jun 2012
Location: Mesa, AZ
Posts: 6,537

Chorizo - '00 Honda Civic HX, baby! :D
90 day: 34.82 mpg (US)

Mid-Life Crisis Fighter - '99 Honda Accord LX
90 day: 37.34 mpg (US)
Thanks: 3,799
Thanked 1,184 Times in 886 Posts
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.
  Reply With Quote
The Following User Says Thank You to Xist For This Useful Post:
CigaR007 (10-03-2015)
Old 09-21-2015, 09:38 AM   #18 (permalink)
EcoModding Lurker
 
bobdbilder's Avatar
 
Join Date: Oct 2013
Location: Malaysia
Posts: 83

Knight - '03 Proton Waja
90 day: 37.15 mpg (US)

Whoopee - '01 Proton Wira 1.3 Aeroback
90 day: 38.69 mpg (US)
Thanks: 19
Thanked 25 Times in 18 Posts
Quote:
Originally Posted by Xist View Post
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.
  Reply With Quote
The Following User Says Thank You to bobdbilder For This Useful Post:
Xist (09-21-2015)
Old 09-21-2015, 11:12 AM   #19 (permalink)
EcoModding Lurker
 
Join Date: Mar 2015
Location: ENGLAND
Posts: 18
Thanks: 1
Thanked 5 Times in 5 Posts
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
  Reply With Quote
The Following User Says Thank You to vibrating_cake For This Useful Post:
Xist (09-21-2015)
Old 09-21-2015, 02:22 PM   #20 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 10,944
Thanks: 2,476
Thanked 3,481 Times in 2,755 Posts


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.

  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com