jlparsons
|
| posted on 11/1/07 at 02:40 PM |
|
|
More aerodynamics!
Hi folks, opinions please! (Yes i'm still ill and have nothing better to do than post speculations on here...  )
Looking at that last post on aerodynamics, something else occured to me. Given that a builder decides he must have a windscreen (road car), would it
not improve the airflow over the car to put in a rear screen too? I've seen folk put polycarbonate between the spars of their roll cages and
I've seen that funky dutch 7-a-like manufacturer whose name i forget doing fully hard-topped cars. Something inbetween might be more what
I'm thinking, so you're end up with a kind of T-bar top like the old mr2 convertible. My gut tells me this would reduce drag, no idea
what it would do with regard to lift/downforce though. Would also make wet weather gear far simpler and easier, a good plus for those of us
who'd like to use their cars every day. Weight increase should be minimal if you've already got a roll cage with supporting struts and
you use polycarbonate instead of glass (SVA?).
What do you think?
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
|
|
|
|
|
macnab
|
| posted on 11/1/07 at 02:48 PM |
|
|
you could even make a super light roof as a space frame with poly triangle window panes...but I think it would look pants
|
|
|
jlparsons
|
| posted on 11/1/07 at 02:57 PM |
|
|
Would look like the lunar lander. I'll leave that one for you!
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
|
|
|
02GF74
|
| posted on 11/1/07 at 03:01 PM |
|
|
hmmm, not sure if will; the wind screen cuases drag at the front and air wants to curl round the top to get inside, then air will be hittin the rear
screen.
the mr2 you mention has almost a completely enclosed high side windows and a much more racked front screen.
thge small mnesh screen you see on BWM, mec and others is to prevent the air curling round so as not to mess the trophy blonde's hair.
you could try simulating this on a small model, a joss stick and hair dryer?
but then maybe I;m wrong
|
|
|
jlparsons
|
| posted on 11/1/07 at 03:09 PM |
|
|
Think there's a fair chance I am too, but hey!
I do follow you, you can never know till you test it, but my gut feeling is it would prevent more turbulence than it causes. It depends on wether the
opening between windscreen and roll bar is small enough that the airflow won't curl round into the cabin once you're doing a decent
lick.
And yes, it might save some money in hairspray. 
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
|
|
|
macnab
|
| posted on 11/1/07 at 03:20 PM |
|
|
I know where this is going...
 
Rescued attachment bat.jpg
|
|
|
jlparsons
|
| posted on 11/1/07 at 03:50 PM |
|
|
Proof positive! I want that one.
Saw the batmobile outside HMV in cardiff once, some boyband had turned up to sign albums. Was a bit of a backfire, even those who knew who the band
were would rather stand and oggle the batmobile...
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
|
|
|
macnab
|
| posted on 11/1/07 at 03:59 PM |
|
|
sorry but the old style is just not my cup of tea, I have only eye's for this one...
 
Rescued attachment batmobile.jpg
|
|
|
jlparsons
|
| posted on 11/1/07 at 04:09 PM |
|
|
Hhhmmm, think batman was compensating when he penned that one.
Will never be the icon the first one was, though it is less camp.
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
|
|
|
Rob Palin
|
| posted on 11/1/07 at 04:46 PM |
|
|
I think there's a bit of a trade-off between smoothing the flow over the passenger compartment and increasing the frontal area of the vehicle.
It really doesn't help that the cockpit is so far back in the body. There is no space for the air to recover after negotiating the blockage of
the windscreen/hood/whatever before it leaves the rear of the car.
Ideally from an drag perspective you want the maximum cross-sectional area of the car somewhere around a quarter of the way along its length.
Overall for a 7-shape car i'd reckon you're better off with a minimal aeroscreen just to skip the air over the cockpit area and leave it
at that.
|
|
|
novacaine
|
| posted on 11/1/07 at 05:20 PM |
|
|
theoreticaly a roof and a rear screen that gentaly tapers towards the ground as to prevent flow detachment would reduce turbulance, a more streamlined
windcreen would help too, i was planning on setting the winscreen base further forward on the car and mounting it 45 degrees from vertical and have a
rear screen that tapered towards the ground which would encourage air to stay in the slipstream over the car's bodywork
matt
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
|
|
|
novacaine
|
| posted on 11/1/07 at 05:25 PM |
|
|
have a look at this car, its the morgan aero 8, headlights are a bit on the ugly side, but it shows how to manage the airflow of a car with the
cockpit set so far back
http://car-reviews.automobile.com/images/cars/ArtImages/17641/01.jpg
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
|
|
|
Rob Palin
|
| posted on 11/1/07 at 05:47 PM |
|
|
Hmm, yes, but having had that car in our wind tunnel at work i can tell you it doesn't actually do a very good job of managing that airflow.
The problem is that you need a *very* gentle curve to keep the flow fully attached - not much more than 20 degrees is realistically possible, and you
simply can't package that in the tiny length available to you at the back of a 7. Sorry. The best you can do is minimise the cross-sectional
area at the back of the car, though normally people opt for the mechanical benefits of a wider track and just live with the aero penalty.
[Edited on 11/1/07 by Rob Palin]
|
|
|
novacaine
|
| posted on 11/1/07 at 05:52 PM |
|
|
thanks for clearing that up for me, would you say that making the winscreen at a more shallow an angle would give a better drag coefficient?
cheers
Matt
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
|
|
|
jlparsons
|
| posted on 11/1/07 at 06:01 PM |
|
|
That's pretty much what I had in mind. Would like to sweep the windscreen more too, not sure about 45 degrees, think that might be too much
unless you use a custom curved windscreen, not even going to guess how much that would cost. I would have the rear window slope down from the roll
bar to the lip of the boot, though I wouldn't slope the back panel as I want to make a boot box for tesco bags etc and that would lose that
space. Again this is a day-to-day use consideration, which would be more the reason for doing this than aerodynamics, reduced drag being welcome
though of course!
Another thought, if this will reduce turbulence in the cabin your heater will be more effective too. Janurary motoring!
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
|
|
|
Rob Palin
|
| posted on 11/1/07 at 06:05 PM |
|
|
For a full-height one, definitely yes. For an aeroscreen it's less clear-cut since a small but steep one can deflect the air as much as a big
but angled one.
Steep screens also effectively increase front lift, since the drag they cause acts at a fair height and that causes a nose-up pitching moment. On a
standard 7 it's worth around 25% of the total front lift.
|
|
|
Dale
|
| posted on 11/1/07 at 09:56 PM |
|
|
I am going with a different arse end on mine - hoping to smooth out the rear wings as they will be molded to the back - its actually the rear of a mgb
re done. A split and raked front screen will be going on as well.
Dale
Thanks
Dale
my 14 and11 year old boys 22
and 19 now want to drive but have to be 25 before insurance will allow. Finally on the road
|
|
|
jlparsons
|
| posted on 12/1/07 at 01:29 PM |
|
|
Looks interesting, that's got to smooth things out a little better than the brick shaped back end, nice styling too.
That plus a rear screen blended into the rear shape could be interesting, I bet that would cut the drag plenty.
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
|
|
|
