LocostUSA.com

I have been looking at some of the parts available for my haynes roadster and came across the rear diffuser available from Gillham in the uk.

http://gillhamonline.co.uk/shop/article_118/Haynes-Roadster-GRP-Rear-Diffuser.html?sessid=h6OvR60qCfnz3sShR74YGxggSLXatfAnXLzV295Kgtkc6veKVLceUEu2hXHRiuxM&shop_param=cid%3D15%26aid%3D118%26



Has anyone here used it?

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Chris
"Start by doing what’s necessary; then do what’s possible; and suddenly you are doing the impossible." - St. Francis of Assisi
Building Miata Based +221 Sevenesque Roadster

Did you notice the 30kg or 66lb shipping weight,seems too heavy for that part.Its a very easy peice to make using aluminum.

It looks really cool, but will it have any real benefit? I'm not saying it won't, just wondering if anyone has looked at it from an engineering point of view and measured some improvement.

But, if you just like it, OK, that's fine too.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

to make a diffuser of any kind work, let alone that one you need a flat floor leading up to it with the proper rake. Most locosts I see around here don't incorporate a flat floor.

I'd guess they quoted that insane weight to account for the dimensional shipping rates - it is probably pretty reasonably weighted although I think some cut alumium would be a lot lighter/cheaper.

I'm planning on a functionally similar design - 7' rake - full width across the rear between the tires and 24" expanding area to meet my class rules. I'm planning on using a piano hinge on the leading edge to allow for some adjustment range for tuning.

It's a very safe design - not too aggressive. again, as long as you have a flat floor you should be able to see some benefit from something like this at speeds above 55mph.

If anyone is considering something like this i'd be happy to have my laser cutting quote redone to include more copies to ship to people as flat packs or weld them up - should be about half the price of the fiberglass option.

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My Build thread: F20C powered Autox & track toy

Buy my car! - F20C Race car

I think diffusers suck.

10 cents for the subtle pun, Cheap.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

diffusers have to be designed for the car they are going to go in .
if they are not done on a aerodynamics design program the chance it's going to work is very slim .
this FB and diffuser I designed on a aero program to give the most down force with the least amount of drag .
things like ride height cars balance to aero balance all have to be designed into the hole package .
they can be built out of many things and all have good and bad about them .
carbon is great but the cost of carbon is the down side .
fiberglass is also good the weight is not much more the carbon but like carbon if it's damaged you have to replace or repair it at a higher cost .
aluminum is good it's cost is low and if they are built modular you have a low repair cost as you only have to replace the section that is damaged .

getting rear down force on a car is very ez to do it's front down force that is the hard part .
if you add a rear diffuser and you add the wrong or no spoiler, splitter, wing to the front of the car the aero balance will be totally screwed up . that's if the rear diffuser is really doing it's job .

another car that i designed on a aerodynamics program .
the sides of the car were lowered 3 inches , the bottom of the car was smoothed and angled at the proper degree . the diffuser was designed and built to work all being built out of fiberglass .
the front behind the wheels was rolled to remove the higher air pressure in the wheel house .
a roof scoop was added to get cool air into the motors intake with the back edge of the scoop extended for better air flow .

locosts in general suffer from poor aero all over the body, especially without a roof.

there are no benefits to using a rear defuser without a complete aero package unless its for cosmetic reasons like looking "cool" but when someone who knows what they are looking at see it they will laugh at it and you.

the basic lotus 7 design has a front lifting problem with air, just as the nose is pointed compared to a full bodied car with air passing down the sides, the top and bottom are the same shape as the sides so it goes that the same air is passing over and under the car at the same rate flat floor or not but a chin spoiler is not easy to design because there is only a narrow front, this is the area that needs something, not under the back

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this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

I know the outfit that made the Haynes diffuser and can reassure you it has no science attached to it, it is purely for show. Donkervort have messed with sevenish aero packages with quite good results.

Bob

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Build Log viewtopic.php?f=35&t=16640&p=187700#p187700

Mancave http://s1116.photobucket.com/user/mypic ... ow/mancave

in my program I have the lotus 7 what you stated is 100% true !
much of the nose lifting dos come from the front fender design but even with them removed there is still way to much aero nose lift that is coming from like you stated the body shape .

the lower yellow and blue car is really no longer a 7 it has been turned into a sports racer .

you could do a formula car style front wing but if you want to change the looks of the car with wings and splitters then why would you buy or build a 7 to begin with you could just start with a design that offers good aero from the start .

if you look at the silver car in Bobs post, you will notice that there are two bumps hanging down under the car, these, i think are side skirts, at least an attempt at side skirts to try and direct the air under the car to the defuser where it is made to work and also to prevent air at the sides being sucked under the car.

on my car i did not roll the sides under like a book car but left them square to the body in the hope that the air passing the sides would suck under body air out.

also, my floor is completely flat except for the pan sticking out about 1-1/2" and a 10 degree flick up under the rear after the axle, i even tried winglets on the rear lower control arms to generate negative lift but noticed no difference at all.

i am considering some type of scoop in my front bumper to pull the nose down at speed but that is another story and any aero will mess with the spring rates if it truly works.

one thing i did try is to space my rear fenders away from the body to let the side air pass through the gap and out the back, when at speed, you can put you're hand there an feel the suck, in most locost, this area is an extreme high pressure area.

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this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

John, your front guards are probably as bad as you can get for lift, in fact if I wanted lift that's how I would design them.

You have the choice of doing a wrap till the front edge is considerably below the axle line or venting them so the air has somewhere to flow through, not ideal but at least you retain the looks. Remember some mesh to stop stones coming thru and the first vent needs to start before the vertical axle line.

One considerable amount of front lift comes from people's heads and the rollbar, you have no rollbar and a windscreen so you are ahead there.

Kick up "diffusers" are pretty well ineffective, they don't hurt but the flat plate surface has no hope of retaining a laminar flow especially short angles over around 6 - 7 degrees and with all the disturbances you have forward of it and from the sides. The effort and cleanliness of your bottom( ) is certainly worth some speed and fuel efficiency though.

not seeing the under side of the car I have no idea what the parts are they could be side skirts to make the center part of the into a tunnel .

as a car travels down the road it moves up and down as the suspension compresses and rebounds .
this changes the air pressure under the car .
depending on the cars speed air will get push out and sucked back in under the car .
AGAIN DEPENDS ON AT WHAT SPEED .
most wide cars with short wheel bases tend to get to much usable air under them were long thin cars tend not to get enough air under them .
moving air as we know is the tool that aids in down force .

with the 7 most noses from what I see tend to roll up on the underside at the front of the car .
this is were the car is getting allot of it's nose lift from .
this is also were it was coming from when I run the sim of the lotus 7 .

there are things you have to look at if you do build a FB for the 7's . the 1st is were to exhaust the air coming into the front of the car thru the radiator .
exhausting the air out the sides of the car tends to work best as it does not disrupt the air flow over the car as much .

there is also the angle of the FB you have to design into the aero of the car and the diffuser it's self .
if the bottom is totally flat from front to back then just transitions into a diffuser may not do any thing but create more drag with little or no rear down force from a diffuser .

my guess with out running any simulations would be a formula style front wing would be best for the 7's ? but this is just a guess !
then what design would or should it be ? again just guessing but the mid 1980's style F1 wing would work best . as they are a easer design to build and offer good front down force for the 7's body design .

because there are so many different designs of the 7's now a aero package for one will not cross over to the others .
so looking at one design that may work for that car may not work at all for your 7 .