Fatal Floor?

[RacerX]

Can anyone answer this?

We're doing some work on a Formula Ford. It's got
aluminium flooring at the minute, which will probably be replaced by steel.

Is this going to affect the balance/handling and
if so for better or for worse?

Presumably there's a degree of flex at the moment,
which will be illiminated, but is that good or bad. Will any good/bad characteristics of the car be exagerated?

Tips/advice anyone?

[Adam43]

No experience of FFord, but presumably (?) the steel is heavier than the aluminium. If this was high up it could make the handling worse, but seeing as it's the floor. It should be OK. Could make the handling better (less roll), but the performance worse (more weight).

Flex. Hmmmm. As the floor is presumably not a structural part of the car the decreased flexing shouldn't help (or hinder) the handling. Maybe there is some aerodynamic advantages to the flexing (like in F1)

This is all just "thinking aloud"

What gauge steel will you use? Thinking of the weight here.
Where are you going to race it?

[THR]

um y the hell would u want to replace it with steel!?

i cant remember if the floor on a FF goes from gearbox to nose, or just drivers ass to nose. but it might move the weight distribution forward slightly.

it should make the tub stiffer tho, as steel is stronger than aly, and will flex less. this assuming its the same or a bit thinner thickness.

stiffer is best, as it makes the suspension work, not the tub.

if ya gunna fix it with aly pop rivets tho. i think these are the weak point! but id hope you would glue the floor to the tub too.

[RacerX]

Hi,

Thanks for the posts.

Currently Alu, bonded with glue and rivetted. The Alu tends to bend/buckle pretty easy, and wears into holes, so the suggestion is to go with same thickness or slightly thinner steel. This is supposedly what most of the guys are running.

The flooring runs up to the box casing, and as the car is generally under weight with the Alu, we have ballast up the front, and normally top it up with fuel so that it's the right weight at the end of the race.

Therefore, am I right in thinking we're not really affected by overall weight, as it always has to ba a minimum anyway?

Cutting to the chase - good or bad idea then? Stick with what we have, or even go slightly thicker Alu?

[enzo]

The steel pan, in the weight scenario you give, will definetely be of help. There is no such thing as a too stiff frame!

However, the extra stiffness of the steel pan may give you problems as pertains to the life length of the bonding. The extra stiffness of the steel pan will increase the unit stresses on the bonds, and will most likely decrease it's integrity much faster.

The way to combat this is to increase the bonding area by welding in 1 inch wide strips of 18 gauge sheet to the inside edges of all of the frame rails, thereby doubling the shear area. Hard rivit the pan to those strips.

I've also noticed that the British manufacturers have a bad habit of riviting the pan down using just a single row of rivits in each rail. This may be cheaper for them labor-wise, but it is not good. Rivits should be installed in 2 alternating rows, about 2 inches apart in each row ( giving you a rivit spaced every inch).

Both the pan and the rails should be scuffed with a 36 grit disk, not left smooth, in order to give the surfaces some "tooth", and therefore increased bonding area.

When riviting the pan down, use blocks and c-clamps to squeeze the pan down to the rail - dont rely on the rivits squeeze action to squeeze it enough. Use 5/32" flat head alu rivits ( Avdel or Cherry are the best brands if you can get them over there) with steel mandrels.

Also, if the frame is stripped down enough, stick the whole thing in a 200 degree oven when done (if you can find a big enough oven!). Most epoxies will double their shear strength if baked at 200 degrees while curing.

Expect the car to be slightly loose when you first get it back out on the track.

Have fun!

[alfasud]

Specifit weight of aluminium is about three times less than steel.

aluminium 2.7g/cm3
mild steel 7.8g/cm3

http://www.bianchi.it/eng/tecnologia/mat_alluminio.htm

So if your floor is 2.0m x 0.5m x 1.6mm thick, then that's 200x50x0.16cm3 = 1600cm3. (someone check my maths please).

1600x2.7 = 4320gm = 4.3kg in aluminium.
1600x7.8 = 124800gm = 12.5kg in steel.

So can you stand an extra 8.2kg (depending on the size of the floor)? If space is not an issue, another option is a thicker gauge of aluminium or as has been mentioned, extra strips of aluminiun or steel.

[RacerX]

Amazing lot of information here guys. So basically, if we're going with steel, or thin steel, I need to be able to lose several kg from somewhere else (which we could by dropping the balast in the nose).

However, this is going to affect the overal balance, at a guess giving understeer ("push" right enzo?)? Unless of course the extra weight at the base of the car is going to give a different centre of gravity, and change the thing completely.

So assuming I can get the weight out, is this a good or bad idea?

Yours,
The Confused one.....

[boyracer]

Sorry, not going to provide definitive answer here.
But then who can ? Situation different for each car.
But in terms of weight and racing, the two just don't mix.
The weight even though it's in the floor is still going to add to the roll moment of the car, in other words it will roll more into corners producing understeer. You may be able to tune this out with springs and anti-rollbars, but still you are left with the penalty of accelerating and decelerating that extra weight, which from a previous post is somewhere around 8kgs.
The fact that the floor extends over most of the tub, the weight distribution should be fairly even, front to rear, so removing ballast from the front of the car is probably not going to help.
If the floor is more front biased than I am thinking it is possible you could remove some front ballast, but of course you've still added weight to the rear at the same time, so I would think the actual amount would be negligble.
You claim the aluminium is bending, is this due to the tub lacking torsional stiffness ? or is there another force at work. You also said holes were appearing ? unless the car is bottoming at speed or bouncing over ripple strips I can't see how this can happen.
If the rivets are pulling through the aluminium I definitely agree with enzo on staggering the rivets. The greater distance between the rivets will increase the shear area of the aluminium, which has to help, even if only to delay fatigue.
The best bet in my opinion would be to go for a thicker aluminium pan, as long as you don't compromise on ground clearance. This is still going to add weight to the car, but you may be able to 'pocket' mill some of the aluminum away. This would have to involve a bit of planning. By milling away the aluminium you are going to lose some strength, the concept is by keeping the section modulus reasonably high you can lose a large percentage of weight whilst losing only a small percentage of strength.
I've probably confused you more, if so I apologise. But thats the best I've got.

[RacerX]

Well, in slow corners it has understeer anyway,
unless it's forced into oversteer so this all sounds like it's going to make it even worse.

The holes are indeed from kerb hopping/bottoming but it's not taking much of that to wear it through.

Is everyone agreed that steel is not the way to go and that if anything, thicker Alu?

Or just stick to what we have and replace the floor now and again as the alternative?

It has to be said that in current form the car is fast (unless it's the man behind the wheel) and we're just trying to stop it falling (slowly) apart... so in the interest of being competitive just live with the 'character' for now?

[enzo]

The understeering can come from a variety of setup problems, not just weight distribution. Most Brit teams seem to still use the "soft spring and stiff shock" philosophy, which is 100% wrong, especially on small bore formula cars.

One easy way to tell if you are undersprung is if the car responds well to increasing the rebound.

Shocks are there to control the wheels, springs to control the chassis, not visa-versa. If you ever put the car on a shaker rig - with operators that know what they are doing - you'd be surprised at just how little damping is needed.

Driver style also coms into play. Does he try to finess the steering wheel in slow corners, or does he try to agressively rotate the car? If he is trying the finess route, then he will always get understeer.

What the ackermann on that car? Anything less than 100% is going to aggravate slow corner understeer.

Does the car have a tendancy to go loose at the corner exit? If so, then you have a basic understeer problem that needs to be addressed, probably by increasing the rear springs.

There are a million scenarios for your problem, but putting on a stiffer pan, even if it adds a few pounds extra, is very rarely a bad thing!

[JR Ewing]

Hello??
What sort of FF?
Van Diemen factory do run alu floors but this is a special hardened, anodised alu which is bloody pricey!
Cheap alu would be no good - too soft.
This is structural and most clubmen run steel.
If you haven't got it off yet, are you 100% certain it is alu, as most steel floors do look like alu anyway.
Whatever you do, make sure you do glue it on (Sicaflex).
Don't do what one dimbo I met did and fit a stell floor and use alu rivets. He wondered why his floor fell of at the second race!
It was very funny though.
Finally, countersinking the rivets into a steel floor is not the work of an hour or two - be warned.....

[RacerX]

It's a Van Diemen.... last time it was refloored it was done with Alu so pretty sure, but was hardened Alu.

[jamesb]

Why not insist the drive sits on the alu floor istead of his comfy seat? Make the excuse of a lower centre of gravity. A few laps hopping the kerbs and I guarantee you will not have this problem again. It may be a case of find the cause not the cure. The floor on my car is alu, and I have no wear problems at all. We have a glass fibre undertray which takes the brunt. Why not use tempered alum from the aircraft industry? I would advise against a steel floor, although a muppet I know bonded a steel floor to his alu floor. Not saying more than that as I'm sure you are thinking the same as me.

In all seriousness, contact British Aerospace and aske them, they may have some flat alu they can hardern for you cheaply.

Ps. I was under the impression that all ffords understeer. The rear has to be really soft for traction, so you are fighting a loosing battle. Turn in oversteer worked for me, you just trailbrake it in, or unsettle it by lifting at the apex. This pivots the car. Your driver probably knows this, but we all hate understeer and we all moan about it.

[enzo]

"Tempered" alu is available from any metals supplier, not just the aerospace industry. Some alloys are more common than others - 6061 and 3003 are more readily available than 7075 or 2024 - but it should be no big deal getting any of them as they are used throughout the fabrication industry all the time.

The least expensive, and most commonly used for floorpans, is 6061-T6. Some people use 2024-T3 or 7075-T6, but they are a lot more expensive, and only buy you more strength and dent resistance, but no more stiffness (Young's Modulus is the same for all alu alloys, regardless of temper).

Regardless of what you use for alloy, roughen the bonding area with a 37 - 60 grit sanding disk (NOT of aluminium oxide composition!) and anodize it (clear or color - your choice). Once anodized, dull the anodized finish in the bonding using Scotchbrite - epoxies dond't like to bond really well to bright, shiny surfaces. Then bond and rivit properly (I could easily write a whole page on the proper proceedure, but it has been thoroughly explored on many FF forums, including 2 here Stateside - The Formula Ford Underground, and Formula Continental.)

Fords need not be pushy, IF you set them up correctly. Most British cars seem to adhere to an obsolete setup philosophy (stiff shock and soft springs), which, if they would ever get away from and catch up with modern technology, they would find that that philosophy is counterproductive to getting the car to really handle correctly.

On your Zetec FF's, weight distribution (way too much at the rear) is a real problem, but some creative whittling on parts can help overcome that problem.

[jamesb]

Thanks Enzo. My suggestion of the aero industry was just from my experience, I asked them and they gave me some for free, so maybe it's still worth asking.

You think our suspension philosophy is obsolete Enzo? That exact combination of stiff shocks and soft springs is what I have at the moment.

My car is an outboard suspension single seater (Jedi)about 600lbs empty, 800lbs all up (yes, I'm a fatty) with no anti roll bars. I have 270lbs springs at the rear, and 550lbs at the front. Dampers are adjustable in one direction only (I always mix up bound and rebound terms so you will know which as one will make sense one won't)

The next circuit we visit has some very fast corners, and I felt the car rolls too much. I was planning to go to 800lbs front and 300lbs rear springs. What would you suggest? I tend not to touch dampers too much once I've found a nice setting. I know you are operating on limited info, but you made a very bold blanket statement about british philosophy so you clearly have a lot of confidence. Any suggestions you have will be treated seriously and may make it onto the car in 2 weeks for this race if they work.

[RWC]

Enzo had come good advice on fixing it to the frame right.
Basically you will be moving the COG back slightly and down slightly.YOU CAN TEST THIS BEFORE YOU COMMIT! Just work out the amount of mass being transfered(when you take out the nose weights and replace the floor)and make up some weights to that amount bolted to somewhere where the imitate the change.Simple.Now just to be sure of whats happening you may want to add LOTS of weight at floor level to REALLY get a feel for what happens when you do it in smaller amounts.No i'm not joking,it helps sometimes if you can't quite tell if a change is working or not when done in small amounts.By the way,what enzo said about 'more stiffness in a chassis is allways better'is not true.It all depends what gives you the most amount of grip.tyres have varying characteristics.To be simple-sometimes a flexy frame helps all the mass to 'dump' onto the outside tyres at just the right point in the corner for best handling.There are alot of variables,But to be fair a stiffer chassis has better feel(even if you dont like the feel!lol)and is NEEDED if you really want to get in and reduce the variables and fully control everything.

[avsfan733]

the stiffness factor is a serious one. My experience with riveted floors (granted on a kart) is that any change in material thickness is going to produce a significant change in handling. i actually carry 4 pans for my enduro in the trailer. the weight is higher but being that it is low in the chassis and shouldn't change the balance because it is the same shape and the density is consistent, don't worry just take off some ballast