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Learning how to build Lotus Seven replicas...together!
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PostPosted: Sun Aug 31, 2008 3:55 pm 
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olrowdy_01 wrote:
Some people have mentioned exiting the radiator hot air upwards through the nose cone behind the radiator. It looks like that would be a high pressure area since it is exposed to the direct air stream.

It's actually the other way round; the faster the air is moving the lower the pressure.

Somewhat related, placing the radiator exit on the top of the hood will heat the air that comes up over the top of the windscreen, into the passenger compartment, heating up the cockpit somewhat.

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PostPosted: Sun Aug 31, 2008 5:59 pm 
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KB58 wrote:
olrowdy_01 wrote:
Somewhat related, placing the radiator exit on the top of the hood will heat the air that comes up over the top of the windscreen, into the passenger compartment, heating up the cockpit somewhat.


helps with extending the winter driving season ;)


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PostPosted: Sun Aug 31, 2008 11:09 pm 
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KB58 wrote:
olrowdy_01 wrote:
Some people have mentioned exiting the radiator hot air upwards through the nose cone behind the radiator. It looks like that would be a high pressure area since it is exposed to the direct air stream.

It's actually the other way round; the faster the air is moving the lower the pressure.

In that case shouldn't the windshield be sucked -forward- at high speeds? :roll:

Seriously.............
Ahh, but "faster" than what? It depends upon the shape that the air is flowing over/around.

As I'm sure you know, on an airfoil it's the speed of the air flowing along the top of the wing compared to the air flowing under the wing that develops the lower pressure (lift) on the top surface. The speed difference is due to the fact that both air streams meet (eventually) a some common point, one traveling over a longer distance in the same unit of time.

I don't think that a Locost nose cone is going to have much lift. The air under the nose cone is going to be all disturbed because of the ground affects/clearance etc. so that effectively takes out the smooth meeting of the air flow behind the nose cone. That's why I think the front part of the nose cone would almost act as a slight down force surface.

If we compare the air flowing along the top of the nose cone compared to inside the upper surface of the nose cone (in front of the radiator), the air inside the nose cone is going to be slowed down quite a bit and will probably be turbulent due to the shape of the opening. That air can't meet up with the longer top flow at the same time due to the radiator/car being in the way.

The air behind the radiator is going to be slowed down even more and hopefully there would be a slight vacuum in that area (with a radiator shroud installed).

That's why we put the small, roughly trapezoidal shaped piece of sheet metal on the bottom of the frame behind the radiator, to prevent the air under the car from filling/expanding into the area behind the radiator and hindering the air flow through the radiator.

Compare that situation with the following.
If you hold your hand out the window of a moving car with your palm angled slightly downwards towards the front of the car your hand gets pushed -down- even though the air is traveling further (Cosine of the angle of attack * width of palm), hence going faster over the top of your hand compared to the bottom. The upper and lower air also don't meet at the same time due to turbulence.

Depending upon the angle of attack I think that it would be possible for the air under your hand to be slowed down quite a bit due to the turbulence. In this case the slower air under your hand is probably where the lower pressure is located.

Faster air might not always be best.


Somewhat related, placing the radiator exit on the top of the hood will heat the air that comes up over the top of the windscreen, into the passenger compartment, heating up the cockpit somewhat.
On my a air scoop I have a good sized gap between the air cleaner and the opening in the hood. I did that on purpose so the hot air could escape from under the hood (especially at slow speeds etc). I haven't noticed any heat affect while driving the car with the occupant air cooling that is cleverly designed into these cars. :)

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PostPosted: Sun Aug 31, 2008 11:45 pm 
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There is clearly high pressure at the windshield. I think you can find lower pressure near the seam between the nose and cowl. This is the setup used on the first Formula Ford I owned a Crossle 16f. This isn't that unusual, GT40 also is a pretty version.

Quote:
If we compare the air flowing along the top of the nose cone compared to inside the upper surface of the nose cone (in front of the radiator), the air inside the nose cone is going to be slowed down quite a bit and will probably be turbulent due to the shape of the opening. That air can't meet up with the longer top flow at the same time due to the radiator/car being in the way.


I don't think airfoil analogies or explanations apply here. When people vent out the top of the nose there is a baffle behind to direct the flow. It doesn't matter wether the air meets up with neighbor molecules. It could come out 10 minutes later, and the story will still be the same. It will work or not...

mr.peopbody.d, I agree with most of your comments. I don't really see a roof, it would be way past my abilities to actually make a real car body. I like that a Seven is almost a formula car. One thing that is great about that is that they are easier to work on.

Figuring out what to do with heat when you have a full belly pan will be a challenge. But there should be a good advantage in drag and I think you should be able to get some downforce.

They should have smaller nose openings. And possibly the radiator in back, but it seems somewhat a plumbing and logistical nightmare.


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PostPosted: Mon Sep 01, 2008 9:12 am 
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Rear aero has a greater effect than frontal aero. The car in the photo would have a lower cd with the bodywork stripped from the front and only a tail fairing. Rear radiators make the rear aero worse. Not beautiful, but it works. Of course, aero on both ends would be even better.

Another way of saying what everyone seems to be saying: The steeper the windscreen angle, the lower the pressure will be, relative to the undercarriage at the same point.

Maximizing aero means minimizing lift and downforce. I think the shape with the lowest cd we could hope for is a symetrical, horizontal, airfoil body with lots of ground clearance, using small, vertical, symetrical airfoil shapes around each wheel. Crosswinds should not be a problem either. That electric trike in California is a good example of this. Pretty weird, but it seemed everyone hated the cheese grater Testarossa when it came out. It has to grow on you.

Acrobatic aircraft typically have symetrical airfoil wings, but most aircraft do not. This allows control input at a certain trim setting to be about the same when inverted. A symetrical airfoil does not produce lift when headed straight into the wind, just like a persons hand out the car window.

Ideally, pumping as much air as possible underneath to match whats happening on top would reduce lift. Airdams reduce turbulence from a rough undercarriage, reducing drag. If the dam is lower than the undercarriage, it is creating additional drag. I could probably raise my airdam an inch and still have enough low pressure underneath to keep it cool through my tiny grill opening.

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PostPosted: Mon Sep 01, 2008 10:58 am 
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MV8:
Quote:
Rear aero has a greater effect than frontal aero. The car in the photo would have a lower cd with the bodywork stripped from the front and only a tail fairing. Rear radiators make the rear aero worse.


I think your statement is only true for a solid object. If you have a square plate, it is better to fair the back then the front. But if the front is a space frame with all those individual tubes, brackets, and unfaired bulkheads like the dash - the sum of the individual pieces, none of which are faired might be greater.

I don't really know how to compare the radiator placement in back vs. front for qero reasons. My thought was the rear of the car has a large blunt bulkhead. putting the radiator on the rear face, using cycle fenders on the rear wheels and allowing high pressure air from in front of rear wheels to flow thru, would help fill in the vacuum at the back. Not exactly low drag, but perhaps an improvement in cross section area and minor drag reduction.

What do you think about changing the belly a bit to get some ground effects downforce? Maybe it's not really doable without raising the driver too much...

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PostPosted: Mon Sep 01, 2008 12:04 pm 
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i have a sujestion that won't alter the look to much and will only include light weight sheet metal to do!

take off ur fenders, mount your light infront of the tire and rebuild the fender to hold the light! this will resembel the gt cars fenders, close to the ground bulged out at the center then tight against the whells... this will reduce drag on the light and put at airfoil around the front wheels increasing downforce at higher speeds, the faster u go the more downforce u get!

next don't put a airdamn up front... use a formula 1 spoiler... put a little bit of sheet metal on steel braided wire and just tighten it... this will give u a cool look and some folds in the metal and u could stretch it to pull air up over the front suspension piece like he f1 guys do!

adressing the issue of tire grip at the back, again re-design the rear fenders to a air foil shape! pull the forward more, and keep the tight against the rear wheel... pull it forwardtowards the front cab and taper it towards the back, this is a airfoil that at high speeds makes more downforce, the faster u go the more downforce!

things about roofs, look at the 911 models, curve the windshield and the roof line needs to taper up to the highest point (i.e. were ur head is) and then taper it back down to the rear... and u could make a hatch back roofline or model the fast back, and then throw on a "modest" 928 s4 or gt spoiler, plz don't throw on a ugly thing!

and bam u just did little changes (exept the roof) and increased the downforce significantly, this is what i had in mind for my lotus... unfortunetly i don't have the time to build one :( but maybe i do...

could anyone tell me were i could find a Busa or zx14r engine?? i might be able to afford one!
thanks



ill draw a few pics of my ideas and scan them to show u what i mean, give me a day or two to do that


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PostPosted: Mon Sep 01, 2008 11:01 pm 
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chetcpo wrote:
Jack at Kinetic is currently making fiberlass bits to assemble a more aerodynamic body for the book chassis for his "max" project.


Yeah, and if I hadn't spent the summer building Son of MAX v.2.0, the Sequel, I'd have that done by now.

chetcpo wrote:
I figure he will offer them for sale to us Locosters after that.


Good figuring, that. It's a tough challenge, keeping the essential se7enness while trying to reduce the parasite drag--and meanwhile keep it cheap. I'm fortunate to have a good drag testing hill nearby, since I don't have a wind tunnel.

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PostPosted: Mon Sep 01, 2008 11:56 pm 
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NOTE TO EVERYONE:
Please don't take offense to my comments and dragging these conversations out. I think there is some misconception of why some things happen the way they do and I'm presenting my views on the subject(s).

horizenjob wrote:
There is clearly high pressure at the windshield.

Of course, I said it as a joke.

I think you can find lower pressure near the seam between the nose and cowl.

I agree. But my comments were about the nose cone where a duct would be located. There really isn't room in the engine area for duct work etc.

This is the setup used on the first Formula Ford I owned a Crossle 16f. This isn't that unusual, GT40 also is a pretty version.

Earlier today I looked in my GT40 book/photos and there are two things that you immediately notice on the final racing form of the car;
1. The back of the radiator is sealed and ducted directly upward and backwards to the base of the windshield
2. the front edge of the duct has a small "bug deflector" lip that extends the width of the duct and extends down the sides of the duct back to the windshield. Some cars had two smaller ducts that also had the bug deflectors.

This lip clearly is flipping the air stream upwards creating a vacuum which causes the air from behind the radiator to be pulled into the air stream.


Quote:
If we compare the air flowing along the top of the nose cone compared to inside the upper surface of the nose cone (in front of the radiator), the air inside the nose cone is going to be slowed down quite a bit and will probably be turbulent due to the shape of the opening. That air can't meet up with the longer top flow at the same time due to the radiator/car being in the way.

I don't think airfoil analogies or explanations apply here. When people vent out the top of the nose there is a baffle behind to direct the flow.

Of course a duct is needed, BUT if the air pressure in the duct isn't -higher- than the air flowing -over- the duct opening the hot air would not leave the duct.

The GT40 seems to have resorted to the use a bug deflector to lower the outside air pressure below the pressure IN the duct to get the hot air out.


It doesn't matter whether the air meets up with neighbor molecules. It could come out 10 minutes later, and the story will still be the same. It will work or not...
[snip]

My original comments were in relation to KB58's statement, "It's actually the other way round; the faster the air is moving the lower the pressure." (Bernoulli's law.)

This lead me to consider what might cause the air to speed up along the curved top surface of the nose cone. An airfoil immediately came to mind since there is no other object or venturi causing object around the upper area of the cone.

I then presented reasons why an air foil could not exist around the nose cone.

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 Post subject:
PostPosted: Tue Sep 02, 2008 12:33 am 
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Assphalt Kicker wrote:
i have a sujestion that won't alter the look to much and will only include light weight sheet metal to do!

take off ur fenders, mount your light infront of the tire and rebuild the fender to hold the light! this will resembel the gt cars fenders, close to the ground bulged out at the center then tight against the whells... this will reduce drag on the light and put at airfoil around the front wheels increasing downforce at higher speeds, the faster u go the more
downforce u get!

Shouldn't we first determine if a Locost needs any [more] down force? Anybody spinning their wheels at 100+ MPH?

next don't put a airdamn up front... use a formula 1 spoiler... put a little bit of sheet metal on steel braided wire and just tighten it... this will give u a cool look and some folds in the metal and u could stretch it to pull air up over the front suspension piece like he f1 guys do!

Couldn't this cause more air drag than the suspension parts?

adressing the issue of tire grip at the back, again re-design the rear fenders to a air foil shape! pull the forward more,

Pull what "the forward" more???

and keep the tight against the rear wheel...

!!!! ...... ?????

pull it forwardtowards the front cab and taper it towards the back, this is a airfoil that at high speeds makes more downforce, the faster u go the more downforce!

Unless you have the curved surface facing DOWNWARD you are going to create LIFT with an airfoil. Unless of course you just use a lot of negative angle of attack (which would make a strange looking fender)!

Do like the dragsters used to do, just aim your exhaust pipes so they blow hot air just over the top of the rear tires. The downside is that if you go more than 1/4 mile your tires will probably overheat.


things about roofs, look at the 911 models, curve the windshield and the roof line needs to taper up to the highest point (i.e. were ur head is) and then taper it back down to the rear... and u could make a hatch back roofline or model the fast back,

Hatchback = more aerodynamic drag than fast back.

and then throw on a "modest" 928 s4 or gt spoiler, plz don't throw on a ugly thing!

More drag.

and bam u just did little changes (exept the roof) and increased the downforce significantly, this is what i had in mind for my lotus...

Why do you want to emphasize down force over streamlining? At what speed do you want the down force to occur?

unfortunetly i don't have the time to build one :( but maybe i do...

I used to be indecisive, but I'm not sure now.

could anyone tell me were i could find a Busa or zx14r engine?? i might be able to afford one!
thanks

craigslist, ebay, motorcycle junk yard, follow a guy doing a high speed wheelie.............

ill draw a few pics of my ideas and scan them to show u what i mean, give me a day or two to do that

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PostPosted: Tue Sep 02, 2008 1:09 am 
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ya after posting what i said, i looked over it while sketching my ideas out for ya to better under stand, then remember the airfoil is the opposite direction of down force, so i went awww i screwed up the explination... :(

take the whole fender as airfoils and reverse that thought,

use the pressure of the air going over the fenders as a way to compress the suspension down into the pavement...

the whole point of making the fenders to produce more downforce, is beacuse they would be aerodynamic then those shapeless un-aerodynamic fenders that u have on ur lotus7's... the downforce issue is just something that comes with aerodynamic asspect of the re-designed fenders!

i believe the whole point of the front balance is to divert air away from the suspension pieces and throw air going under the car into the radiator (increasing cooling) and also throw it over the car... this would create a massive amount of air flow over the top of the car, and basically almost no air under the car, and this stops air pockets getting under ur car and flipping u end over end


now this is in general car speak, i don't know any lotus7 that was thrown end over end cause it had too much low pressure under the car and threw its front end into the air, but im just speaking openly, im pointing what creates the most drag on a lotus7 and how it could be adressed to improve aerodynamics, which will create downforce

also the downforce on the fenders is created by the amount of airlow over the fenders, and unfortunetly the more air over the fender causes downforce, and that huge amount of air is due mostly at high speeds, were u don't really need the downforce! but it is aerodynamic


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PostPosted: Tue Sep 02, 2008 7:51 am 
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horizenjob wrote:
the sum of the individual pieces, none of which are faired might be greater.

I don't really know how to compare the radiator placement in back vs. front for qero reasons. My thought was the rear of the car has a large blunt bulkhead. putting the radiator on the rear face, using cycle fenders on the rear wheels and allowing high pressure air from in front of rear wheels to flow thru, would help fill in the vacuum at the back. Not exactly low drag, but perhaps an improvement in cross section area and minor drag reduction.

What do you think about changing the belly a bit to get some ground effects downforce? Maybe it's not really doable without raising the driver too much...


In keeping the comparison apples to apples, the rear is not unlike the front. A tapering tail similar to the length of the tapering front should have less drag.

The pressure does not have to be so high at the rear fenders. 12 degrees seems to be the maximum agreed upon angle for tapers and flares. The rear fenders could extend forward, down, and in to the body near the windscreen.

Engine and upper control arm framing limit aero changes in the front end to a taper the longitudinal width of the nosecone.

Downforce is more drag, but the rear fenders extended as mentioned above, could generate some downforce if they were skirted from the outside and the high pressure tire well, with a ramp toward the center of the rear, just inside of the rear tire. It would be difficult to have a decent flow path to the rear without raising the driver's seating position. I think everyone has seen the rear ramps that start behind the seats.

Regarding fenders in general, in side view, the forward fender lip should cover the front of the tire, while the rear lip should have a reasonably large gap. In overhead view, the forward fender lip should extend outboard of the tire, while the rear lip should be closer inboard, closer to the vehicle centerline than the tire bulge. If a person wanted to use a clamshell, the shell could be vented on the sides and have a vertical rear wall near the tire. The wall should prevent the reverse facing ramp from generating lift.

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PostPosted: Tue Sep 02, 2008 8:55 am 
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KB58 wrote:
slantvaliant wrote:
Maybe rig sliding scales to suspension components, put a camera where it can record the motion?

The problem is measuring perhaps 1/10" movement masked by inches of noise from road irregularities.


There might be inches difference between the at-rest and at-speed ride heights, but not when measuring at steady speed on a smooth, straight surface - unless you have some real suspension issues.

Lift measurements would best be done in steady state driving on staight, smooth surfaces. Consider wind, measure in both directions, etc. Certainly, there would be some movement over a few seconds, but not inches. Sampling the video frames and averaging would get some reasonable data. Obvious motion from bumps can be removed from you figures.

This little beast had significant lift:
Image
At rest, the front was almost dragging on the ground.
("72 Landry Saab" driven by Paul Romano in the Big Bend Open Road Race. SBF, I believe. Around 180 MPH)


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 Post subject:
PostPosted: Tue Sep 02, 2008 9:21 am 
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slantvaliant wrote:
There might be inches difference between the at-rest and at-speed ride heights, but not when measuring at steady speed on a smooth, straight surface - unless you have some real suspension issues.

Yes, measuring a gross amount of lift is obviously much easier to see. That's a great example of having real issues!

OTOH if you're trying to measure downforce it's much much difficult. Since glass-smooth roads don't exist, signal noise is a big problem. With any downforce at all, it means that the suspension springs will be stiff. A typical "smooth" road surface has irregularities greater than the downforce so the signal noise will be greater than what's being measuring. I speak from experience.

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 Post subject: AERO TUBING
PostPosted: Tue Sep 02, 2008 12:34 pm 
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What about making aero tubing like they did in the olden days. round steel tube with leading and trailing edges of balsa (or basswood) and then wrapped. Easy, cheap and repairable.


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