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Learning how to build Lotus Seven replicas...together!
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PostPosted: Tue Sep 16, 2008 3:14 pm 
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horizenjob wrote:
I was thinking along the lines of a rear radiator with cycle fenders on the rear wheels. THen try to get high pressure air from between the body and the rear wheels to flow into the radiator.

Not much room between the tank and radiator perhaps.


Like the sylva mojo, but ducted?
Image
http://www.sylva.co.uk/mojo.html

To my uneducated eyes, it looks like you could stuff a bike radiator just fine in there, and get the proper airflow. But I don't know what kind of airflow bike radiators need, and get. I just know I really love the look of the Mojo! A pity there isn't a US distributor.

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PostPosted: Tue Sep 16, 2008 5:08 pm 
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Talk about moving the radiator to the rear of the car and knowing that the nose cone of the Locost isn't really designed to be as efficient as it can be lead me to try to find the measurements of a proper nose cone.

(After taking a big breath with that explosion of words.)
As long as we're talking about streamlining the Locost nose cone, I thought let's see how aircraft designers do it. Admittedly aircraft go much faster and have more cooling air volume per unit of time to work with -but- the principles of reducing aerodynamic drag are the same.

Here are some links that give ideas of various ideas etc on aerodynamic drag, cooling etc.

Cooling your (aircraft) engine. With dimensions, angles for building a proper duct to the radiator for an airplane (your design WILL vary). This is partly why I say the Locost nose cone is not designed as well as it could be. My engine runs too cool! I need to block off the nose cone hole some.
http://www.ch601.org/resources/rad%20ducting.htm

Interesting article on liquid cooled aircraft engines.
http://sdsefi.com/air10.html

Aerodynamic automotive tips.
http://www.up22.com/Aerodynamics.htm

Ground affects and race cars.
http://www.ddavid.com/formula1/lotus79.htm

Nice article on race car aerodynamics. Particularly interesting is the comment about outboard front suspension in the last sentence of paragraph 7.
http://www.pitpass.com/fes_php/pitpass_ ... fes_page=2

Nose cone duct. Notice the drawing of the Supra duct work.
http://www.max-boost.co.uk/max-boost/in ... 2JZGTE.htm

OK, that ought to keep everyone busy for a bit. :)
The test will be on Thursday.

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PostPosted: Tue Sep 16, 2008 6:36 pm 
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The voice of reason
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Quote:
Nice article on race car aerodynamics. Particularly interesting is the comment about outboard front suspension in the last sentence of paragraph 7.


Not sure this applies to us. At the time being mentioned F1 cars had transitioned from "streamlining is everything" to let's shovel a few hundred HP into downforce. In that context drag was much less of an issue.

But you look at modern low horsepower formula cars and it seem important. In addition considering the length of the arms, outboard is actually difficult to do.

Also on cars that had the ground effects tunnels in the sidepods...

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PostPosted: Tue Sep 16, 2008 7:18 pm 
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Oh, and thanks for posting the links Rowdy, I'll read them all.

And for those of you with powerful motors, inboard really won't help with performance...

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PostPosted: Tue Sep 16, 2008 9:38 pm 
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OK, I finally found an article that gives the dimensions I vaguely remembered reading years ago. Tomorrow I'll measure my car but I'm sure the radiator is taller than dimension "L" in the drawing. :-(

But at least I'll have a hint of how much I can reduce the of the intake area of the nose cone (if I was flying at 200+ MPH). :drool:

http://www.ch601.org/resources/cooling_systems2.htm

Forget the aircraft part of the drawing. Just imagine that the duct work to the left of the radiator is the complete nose cone of the car. The idea is to have the minimum intake hole size while shaping the interior of the nose cone to maximize the pressure on the left side of the radiator.

The large opening we have now allows the air pressure to build up -but- the excess air spills around (and perhaps out of) the nose cone and causes turbulence. If the opening is the correct size, only the amount of air needed (at max cooling) is passed through the opening and the excess air is (more) smoothly diverted around the nose cone.

Your Locost may end up looking like an anteater if you also minimize the outside of the duct work, but that's the price of progress. :roll:

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PostPosted: Tue Sep 16, 2008 11:38 pm 
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olrowdy_01 wrote:
But at least I'll have a hint of how much I can reduce the of the intake area of the nose cone (if I was flying at 200+ MPH). :drool:



If you can't then you need to think turbo!

Those articles were interesting. I wonder how our cars would with a properly designed radiator ducting and evaporator coils. It would certainly help in the cheap and light aspect.


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PostPosted: Wed Sep 17, 2008 11:48 am 
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carguy123 wrote:
olrowdy_01 wrote:
But at least I'll have a hint of how much I can reduce the of the intake area of the nose cone (if I was flying at 200+ MPH). :drool:

If you can't then you need to think turbo!

Those articles were interesting. I wonder how our cars would with a properly designed radiator ducting and evaporator coils. It would certainly help in the cheap and light aspect.
If you were asking what the car would look like .............. maybe something like this? i.e. if that car were sectioned so the body was the same height as a Locost.

http://www.hotrod.com/featuredvehicles/ ... index.html

I seem to remember a picture of an old '32 roadster lakes car that had an anteater looking nose. The height of the radiator was still prominent under the nose cone but the intake was rather low and stuck out in front of the car quite a bit. It didn't look all that good but I guess it got the job done.

So as far as streamlining goes, up to the windshield we're doing sort of OK, but from there back .... ugh. But hey, we have "replica" cars and that's the way they were built and looked back then.

I probably have this quote all wrong, but I think I read that Ferrari said, "Aerodynamics is for those who fail to produce HORSEPOWER!"

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PostPosted: Wed Sep 17, 2008 4:12 pm 
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Lots of posts here. Note sure if we can take another, but I never chime in, and this is something Ive given some thought to, so heres my personal take on the aero issue. Starting with my design criteria for Areo modifications 1. I like the classic design of the Lotus 7 and don't want to mess with it too much. 2. My car is a book chassis, BEC, so I have some advantages. 3. My car is a road car, not a racer, so my primary aero requirements are for less wind buffeting, and a more pleasant driving experience up to about 65mph. Mostly this car is for going around 25mph curves at 40 on sundays. So Here's what I've done and have planned.

I created a custom nosecone of my own design, very similar to the classic (original) Lotus 7 nose, but only 24" (or is it 22"?) high from top to bottom. This is about 2 inches shorter than most modern locost nosecones made to acommodate automobile engines. It looks good, shark-like and purpousful. I've carried this 2" savings back across the hood and through the scuttle, so while the taper of the hood looks completely normal, the whole line is 2" shorter than most locost front ends.
Next, I have plans to build a complete, flat bellypan from the nose to the firewall. The BEC design doesn't require a large transmission tunnel, only a channel about a 4" wide for the two piece driveshaft to go through, so the bottom of the car will be completly enclosed and completly flat.
I have a double windscreen set up, with a somewhat conventional looking Locost windcsreen 10" in height, but it uses a design borrowed from the Morgan roadster. It folds forward, to lay flat over the hood(paralell with the ground). Behind this "normal" screen is a set of small tilt adjustable his and hers Brooklands half moon windscreens. If you are familiar with the way old WWII jeep windshields fold forward over the hood, you have the idea. This takes a huge chunk of the frontal area away, and smooths flow in and around the cockpit. The car will have a full Tonneau cover, which can be left in place while driving, with just the drivers side opened. The boot area will also have a fitted nylon tonneau that snaps over the opening. The hood has no holes vents or bump outs. This is the way I like it. However I do have plenty of room under the hood and behind the radiator to put a snow shovel-like air dam inside the engine bay, that could be made to channel air out of the engine bay, if I think it is benificial to do so. Undecided on that. (sidebar thought- rather than a snowshovel, the airdam could resemble the cow-catcher on the front of a train, and "plow" air out both sides. Formula 1 cars use side pod radiators, and exit air to advantage flow charicteristics, so it may be possible to use the heated air to provide some direction/order to the turbulent air swirling around uselessly behind the front wheel/suspension?
I'll have to think about that.
I also plan to modify my nosecone, and mimic the side wingletts on the current iteration of the Caterham nosecone, to deflect airflow around the a-arm bolts/hardware. I'm torn about the front fenders, I have a cycle style front fender from a Deman-Motorsports BEC, and it fits beautifully tight over the tire, and looks great. I may get the companion to it and call it a day, but there is a part of me that is drawn to the classic clam shell fenders, and I may go that route. I havn't decided yet. This will be an asthetic decision, and have nothing to to with aero considerations. Like I said in the beginning, I like the purist design of the original seven, and that is way more important to me than top speed.

Last, I will have a Bikini top that extends from the the top of the winscreen over a purpose built "rib" over my head, and over the roll bar and down to the back. I have no idea how it will behave at 60MPH, but it will be there to keep the sun off me on long drives. In the end, I hope the lower profile, enclosed flush belly, fold-down screens/brooklands screens will yeild a pleasant, and fairly smooth and comfortable environment for sunday driving, in the 40-70MPH range. That's the plan anyway. The Tonneau will be used when it's cold, and the Bikini top, when the heat is too much, otherwise these will be stowed. So for me Aero is about comfort, less buffeting, perhaps less wind noise, and an enjoyable place to do some spirited motoring on winding two-lanes without excessive fatigue from getting blown around.


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PostPosted: Wed Sep 17, 2008 4:24 pm 
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I'd like to see some pics of your "chopped" book Locost. You can upload them to the thread here if you like using the board software. (look below the field where you type the text of your post)

Oh and welcome!

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PostPosted: Wed Sep 17, 2008 4:55 pm 
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Jack at Kinetic sells a low nose which I'm using in my new design. In fact I've already implemented most of the ideas posted by Baldguy above - plus a few more :wink:
Image

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PostPosted: Wed Sep 17, 2008 9:41 pm 
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baldguy8 wrote:
snip]
3. My car is a road car, not a racer, so my primary aero requirements are for less wind buffeting, and a more pleasant driving experience up to about 65mph. Mostly this car is for going around 25mph curves at 40 on sundays. So Here's what I've done and have planned.
[snip]

Next, I have plans to build a complete, flat bellypan from the nose to the firewall. The BEC design doesn't require a large transmission tunnel, only a channel about a 4" wide for the two piece driveshaft to go through,

Welcome to the group.

The tunnel does add some rigidity to the chassis. Narrow tunnels give less strength. You might be able to use that fan drive shaft idea to pull air through the tunnel. I think on most cars the fan wouldn't be able to be very large in dia. because of the tunnel size.


so the bottom of the car will be completly enclosed and completly flat.

My tunnel is set up with the top held on with machine screws into threaded holes in the upper tubes. Being able to remove the top cover has come in handy a few times already when I was working on the rear end etc. The bottom of the tunnel is open.
[snip]

The hood has no holes vents or bump outs. This is the way I like it. However I do have plenty of room under the hood and behind the radiator to put a snow shovel-like air dam inside the engine bay, that could be made to channel air out of the engine bay, if I think it is benificial to do so. Undecided on that. (sidebar thought- rather than a snowshovel, the airdam could resemble the cow-catcher on the front of a train, and "plow" air out both sides.

Unless you have a sealed duct that directly guides the air from behind the radiator to an outside vent it probably won't matter too much if you have an inside shovel thing or not. And if the you do use a sealed duct I would imagine that the heat from the exhaust could get things very hot inside the otherwise sealed engine compartment.

I would be concerned about how the warm air from the radiator is going to escape at low speeds or sitting at stop lights. I'm using the original motorcycle fan and it really doesn't move a lot of air. But it has never come on either. :-)

The very hot headers got my hood so hot above the pipes that I couldn't keep my hand on the hood above them even with the vented area around the air scoop. I put an internal head shield above the pipes and now the hood temperature is bearable.


Formula 1 cars use side pod radiators, and exit air to advantage flow charicteristics, so it may be possible to use the heated air to provide some direction/order to the turbulent air swirling around uselessly behind the front wheel/suspension?
I'll have to think about that.

At least one Locost has a single protruding vertical vent on each side of the car near the windshield to allow air to escape from under the hood. But I'd want to check and see if it's a low pressure area first. If you don't plan on driving that fast you may not develop enough pressure differential where you need to worry about the exact placement.
[snip]

Last, I will have a Bikini top that extends from the the top of the winscreen over a purpose built "rib" over my head, and over the roll bar and down to the back. I have no idea how it will behave at 60MPH, but it will be there to keep the sun off me on long drives.

I have a similar top on my beach buggy. It bulges alarmingly upwards in the middle at high speeds. Enough so that at 90 MPH it actually would pull the windshield back a few inches!! The rear and sides of the top are completely open.

The windshield is much taller than a Locost windshield. When I am at the front of the line at a stop light I can't -see- the light. I have to stick my head out the side to see what's going on. If you use a 4 or 5 point harness in the Locost you won't be able to move around that much. I can't even lean forward enough to adjust the right side mirror (and barely enough to reach the left side mirror).


In the end, I hope the lower profile, enclosed flush belly, fold-down screens/brooklands screens will yeild a pleasant, and fairly smooth and comfortable environment for sunday driving, in the 40-70MPH range. That's the plan anyway. The Tonneau will be used when it's cold, and the Bikini top, when the heat is too much, otherwise these will be stowed. So for me Aero is about comfort, less buffeting, perhaps less wind noise, and an enjoyable place to do some spirited motoring on winding two-lanes without excessive fatigue from getting blown around.


All your ideas sound good. I've noticed that most of the air buffeting I get is from around the side of the windshield. My windshield glass is only 9" high inside the frame. I really don't feel that much buffeting from over the top of the windscreen since the air is thrown upwards.

I think when you put the wind shield down you may find that there is just way too much wind buffeting with the Brookland screens unless you are wearing a helmet. But they will look great even if you don't use them.

Keep us posted on your plans/build.

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PostPosted: Wed Sep 17, 2008 10:40 pm 
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so how do we test for high pressure and low pressure zones on a car?

i under stand the theory very well, just don't know how to test it in the real world term

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PostPosted: Thu Sep 18, 2008 2:18 am 
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I think the easiest thing to do is tape tufts of yarn all over the body, and then drive around and observe what the yarn does. You would have to do this on a calm wind day, of course. I think generally the low pressure areas will have the yarn standing up or twirling whereas the high pressure areas the yarn will tend to lay flat.


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PostPosted: Thu Sep 18, 2008 8:30 am 
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Yarn has absolutely nothing to do with pressure. It only tells you whether the airflow is turbulent or not. Smooth airflow can still be either high or low pressure. You need some sort of pressure gauge to take readings. The most cost effective means I know of would be to build yourself a water-manometer, although I imagine that would be somewhat difficult (but not impossible) to setup for this type of experiment.

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PostPosted: Thu Sep 18, 2008 9:11 am 
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Driven5 wrote:
Yarn has absolutely nothing to do with pressure. It only tells you whether the airflow is turbulent or not.

There's usually more than enough flow to also have the yarn indicate flow direction.

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