Author Topic: Rotus Project Build  (Read 10019 times)

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Re: Rotus Project Build
« Reply #570 on: July 12, 2019, 08:54:15 PM »
Goes quiet now and then..
Nice floor bud! I did have a nice diffuser on the westy til it fell off lo.

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Offline Jamie R

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Re: Rotus Project Build
« Reply #571 on: July 12, 2019, 09:48:21 PM »
Good to see more  Rotus action  :great:

Just an observation as im no aero expert, but with the flat floor you have built, I think for stability you will  a rear diffuser.

Also don't  cover your gear box an diff from air flow as I know somebody who did this with his FD and had sensors fitted and found he was frying both units.

Hope this helps.   

Evening Clive,

Yes diffuser already designed and is in the list of things to build.

Point taken on the gearbox and diff, NACA ducts are easy to fabricate, so can strategically position some of them.

Does the rx8 box and diff have sensors fitted? ? ?
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Re: Rotus Project Build
« Reply #572 on: July 12, 2019, 09:49:10 PM »
Goes quiet now and then..
Nice floor bud! I did have a nice diffuser on the westy til it fell off lo.

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Thanks Jon,

It's getting there, what do you mean it fell off? ? Lol
Its just Rotors and GRP

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Re: Rotus Project Build
« Reply #573 on: July 12, 2019, 10:52:38 PM »
100 mph...
Wind down the tunnel...turned the back off the car into a parachute blew it off, broke the rivets off. The air going down the tunnel needs an exit path at rear of car. Mind didnt have it.
On the gearbox there is a neutral switch and a reverse switch. The loom is on the end of the engine loom. This also has the rear 02 sensor on it.
Rear 02 and reverse switch if you dont want reverse lights can be done away. Neutral switch can be done away with but may be cause idle to hunt. Easy way is to map an 1100 rpm idle which sorts the hunt and also brings up idle oil pressure which at 850 rpm is naff all...i had about 10 psi of oil pressure @ 100deg C oil temp idling in pits, 1100 rpm good 20psi plus.

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Offline Jamie R

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Re: Rotus Project Build
« Reply #574 on: July 13, 2019, 06:16:28 AM »
Thanks Jon, font of knowledge as always.

Just going back to the diffuser topic.. I'm certainly far from an expert but doing a lot of research lately , the stability from the diffuser is offered by the downforce it produces

When a flat floor transitions into the diffuser, it's as that point where  the most downforce is produced. Race car builders will want to start the transition as close to the middle of the car as possible. So a percentage of the downforce will have an effect to the front suspension as well as the rear.

But rear suspension positioning and the droop of the suspension on the inside of the car when turning on a bend will clout the diffuser, so clever car design benefits.
Formula 1 is a great example of popular misconception that if teams build aero such a way, it must be right. Wrong. Teams are faced with different rules and regulations season after season, and what they build is the best they can achieve without breaking the rules, doesn't mean necessarily it's the most optimum design. Us mere home brew car builders only have 2 restrictions, lack of resource and lack of knowledge and experience lol

The transition from the flat floor to the diffuser needs to be smooth with an optimum angle of 7 degrees. The main purpose is to allow high velocity low pressure air to gradually go back to low velocity high pressure air when it meets the air flowing over the top of the car.

If the angle of the diffuser is too steep or the transition is too abrupt you will get air separation which creates turbulence and a partial vacuum. The best way to envisage  air separation it go to your kitchen sink, turn on the tap and hold a spoon under the flow of water. The bottom underside rounded end of the spoon needs to be in the flow of the water.

The flow of the water from the tap is the air travelling underneath the car, the rounded bottom of the spoon is the diffuser. Let the tap run and you'll get a constant stream of water in a straight line, then when holding the handle vertically down almost parallel with the water offer up the rounded bottom of the spoon into the stream of water.

The water clings to the contour of the spoon, changing direction of the water as it creates a boundary layer with the spoon. The air under the car does exactly the same. You can change angle in which the rounded bottom is presented in the flow of water and if it gets too steep, the water can't cling to the surface of the spoon and the water goes all crappy and broken up, that's exactly the same as air separation which is bad on cars.

Ideally the air on the underside needs to flow into the air from the top of the car and meet nicely at the rear without creating a vacuum.

Transit van on the m5 doing 100 mph, the air flow from underneath, over the top, down the sides of the van will very rarely get anywhere near the rear van doors, you'll get a vortex behind the van and some air will spill into that void. But by n large that void is a vacuum which actually slows the vehicle and tries to pull the vehicle backwards so the air from the flow can fill that void. Not good.

Lastly, ( as I need to get up n go in the shed, insomnia ruined my night ) another misconception about diffusers........ The vertical strakes that you often see dangling from the diffuser is not to channel air and keep it in a straight line.

Imagine a diffuser with no strakes at all, one big channel of air from under the car flowing nicely out the back. Soon to be disrupted by the turbulent air that's coming around the rear wheels as it spills into the area of the diffuser. It's called tyre squiffing or something like that I can't remember the name, anyway, the turbulent air, enters the diffuser and disrupts your nice air flow and negates all your hard efforts in producing downforce.

Add in some verical strakes, say 2, so the diffuser now effectively has 3 chambers LH, centre and RH. At the bottom edge of each strake, you will get a vortex, it always occurs to the side of the strake but adjacent to the bottom edge. This vortex helps to prevent the turbulent air from the rear tyres entering the next chamber along, so the LH and RH chamber will have a partial disruption from the tyres, leaving clean flowing air in the centre chamber from the underside of the car to create the downforce at the transition from the flat floor to the diffuser.

Add more strakes ( with a trade off of more weight) and you'll have more chambers in the centre of the diffuser that are uninterrupted by turbulent air.

Put a 90 degree bend at the bottom of the strake like an L with the bend pointing from the centre outwards and you can move the vortex closer to the ground without reducing ground clearance  which is even more beneficial.

Right I got pins n needles in my left arm from holding my iPad in bed. Getting up.

I'm not an expert on this, and sorry for "ladybird booking" what I've learnt so far.

Just hope all these theories I've learnt work, I really don't want to upset the classic lines of the Rotus by putting a spoiler over the boot.


« Last Edit: July 13, 2019, 06:32:46 AM by Jamie R »
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Re: Rotus Project Build
« Reply #575 on: July 13, 2019, 06:42:44 AM »
Whats the car? Volvo 1800 the saint looking?

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Saw one of these in white  yesterday and thought about your comment Jon lol

It's a very very pretty car, unlike my Frankenstein secret bastard love child lol
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Re: Rotus Project Build
« Reply #576 on: July 13, 2019, 08:01:17 AM »
A link to the basics which will explain it better than i ever could.

https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/

And a couple of pics showing my spoon method to support my crappy explanation. You can see the water tracking the back of the spoon and the flow of water changing direction from its original path from the tap.

Excuse my grimey sink, Im in the shed not the house lol.

« Last Edit: July 13, 2019, 08:03:09 AM by Jamie R »
Its just Rotors and GRP

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Re: Rotus Project Build
« Reply #577 on: July 13, 2019, 02:40:31 PM »
Thats that job jobbed.

Just some NACA ducts to install
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Re: Rotus Project Build
« Reply #578 on: July 13, 2019, 02:47:29 PM »
I have absolutely no expertise on aero, so admire the research you've been doing and the neat underfloor sections you've produced  :icon_thumleft:
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Re: Rotus Project Build
« Reply #579 on: July 13, 2019, 02:55:35 PM »
I could comb my hair in that floor Malcolm................if I had any !
Its just Rotors and GRP

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Re: Rotus Project Build
« Reply #580 on: July 13, 2019, 03:15:24 PM »
Ill read that later just got up from nights...
Coffee...

The air that enter under bonnet area via rad etc...then travels down transmission tunnel cooling gearbox and exits where? You need a vent at end of tunnel.
Rx8s and Rx7 get hot gearboxes and there open to the air under the car.
I think you need a vent in the back of the car above the flat floor.


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Re: Rotus Project Build
« Reply #581 on: July 13, 2019, 03:29:32 PM »
The radiator will have ducts that will transfer air from the back of the rad and out the bonnet. No warm air should enter the bay from the rad.

There will be some extra ducts in the bonnet to help push any exhaust heat out.

There will also be a duct feeding cool air into the exhaust tunnel and will be vented at the back.

I plan on putting some ducting on the flat floor to cool the gearbox and through the tunnel to the diff.

Should be able to mount a vent at the back of the chassis and direct away from the car.

Cheers Big ears  :icon_thumleft:
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Re: Rotus Project Build
« Reply #582 on: July 13, 2019, 04:10:16 PM »
Just had a light bulb moment.

If I redesigned the diffuser to an 80's / 90's formula 1 style diffuser  like in the below diagram..........

Where it says "Gearbox" I could route my exhaust out that point and any air that goes down the tunnel that cools the gearbox and the diff can be vented out the back as it passes the silencer.

Sorted! Im happy with that concept
Its just Rotors and GRP

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Re: Rotus Project Build
« Reply #583 on: July 13, 2019, 04:57:42 PM »
Yep and no parachute effect..and no gearbox sychro issues when gb oil turns to water when overheating.
Thats what you need.

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Re: Rotus Project Build
« Reply #584 on: July 14, 2019, 04:25:02 PM »
Emmas new shoes coming on a treat!

I should touch up the grass while i got the green spray out
Its just Rotors and GRP