Ideal Floor Pan design

[Gary Slahor]

In the conversion of my RF98 to Novak F1000 kit, I am doing a frame up rebuild, and have an opportunity to optimize my new floor pan design. I sent a private email to Coop, as he has the same car as me, but thought maybe the rest of the FB community might also have some good ideas on floor pan strategy.

I have a 4'x12' sheet of 7075 T6 Aluminum, so that is my only constraint.

So how about:

Making the pan one piece from the front bulkhead all the way to the start of the diffuser ? Also bonded to the Novak subframe ?

Extending the pan out past the side pods ...under the side pod floors ?

Extending the pan out in front of the pods like the new Phoenix (I believe) ?

Give me some good ideas....

Thanks in advance.................Gary

[Purple Frog]

My 2 cents. Extending out the sides under the sidepods could be problematic if you have any sidepod crash damage. Changing a sidepod floor is easier than chaging the whole floor.

Going under the subframe in the rear seems like a good idea in terms of stiffening the chassis.

[Wright D]

The new Phoenix does have a splitter that jets out in front, but it is made form glass, and has jab rock rub strips for ware. The aluminum floor that is boned on the chassis does not extend out past the chassis more than 1/2 inch. The lip created by the aluminum floor helps hold up the edge of the diffuser, side pods, and front splitter.

The design mantra for the new Phoenix Race Works F1k.09 was low cost and serviceability. We wanted to have pieces that are easy and inexpensive to replace if damaged by off track excursions. If the riveted and bonded on aluminum floor stuck far out from the chassis it could easily be damaged, and it would be difficult to repair and or replace, especially at the track.

Also; a 1/4 thick lay up (4 layers of 5oz. glass 3/16 core, and 4 more layers of glass) is typically lighter and way stiffer in bending then the thin aluminum sheet metal. The composite floor then can be used to hold up things like the oil cooler and radiator with less deflection.

1/4" thick plywood also works perfectly fine for making floors. It can be bit heavier then sheet metal, but is CHEEP, and is also stiffer then the aluminum. A plywood floor is probably way faster to make too.

Use the aluminum on the chassis bottom, extend it out 1/2", and rest the wood on that. Add a few floor stays, and you are good to go. The same could be done with a composite floor.

How thick is your 7075 sheet, just curious?

[Gary Slahor]

The 7075 sheet is .063"...to meet GCR requirements.

7075 is incredibly strong and stiff (70,000 psi yield) but the point about serviceability is a good one. Maybe I could make it out of several pieces, in the event one gets damaged. I was trying to keep the underside perfectly smooth though, so joint design would be important.

Thanks for the thoughts

Gary

[rickb99]

I need my heart medication!!

Just priced a sheet of 7075 versus 6061. Ohhh MY!

I did find this comparing the 2's physical properties:

http://edge.rit.edu/content/P08456/p...0vs%207075.xls

Found other comments about 7075 being more brittle then 6061 and 7075 not being a good alloy for welding. And on info on the weight per sq. ft. between the two. But I'd expect the 7075 to be slightly heavier.

[Gary Slahor]

Using AircraftSpruce's pricing (you can get it cheaper from a supply house)....7075 is about 58% more expensive than 6061 ...BUT it's almost 70% stronger in yield strength....so you do get value for your money.


edited 7:45PM
Just checked the reference above and they quote 82% stronger for 7075

[R. Pare]

7075 is only marginally heavier than 6061 - less than 1%, and no stiffer.

Don't stick the pan out past the sides of the frame. Use rivited-on aluminium angle instead. If you hook the angle on a curb, so what - you rivit on another one. If you hook the pan on a curb, you go home and spent many hours replacing it!

Look up the paper that Tom Johnson wrote about riviting and bonding. A real must is to add in the 20 gauge strips to increase the bonding area - you will be very disappointed with how fast you break the bond if you don't add them in.

Also, anodizing the panel as described is a must, especially with 7075 as it corrodes much faster than 6061.

[Gary Slahor]

I have Tom's article, and agree about the corner gussets. The 7075 is what they call ALCLAD with a clad coating for corrosion protection. I'm not sure how a clad material would take to anodizing. I was going to try a conversion coating to aid adesion though. West epoxy systems sells one they claim works well.


Is Hysol E-120HP the prefered adhesive ?

[rickb99]

Yes, that Hysol is (has become) the popular thing lately. But, some 3M products used to be the weapon of choice. See this:

http://www.apexspeed.com/forums/show...ht=pan+bonding

[Jnovak]

Gary, do not extend the floor pan as one piece onto the Nova rear sub frame. Yes, put a floor pan under the rear subframe but make it a separate part so that you can remover the subframe if needed.

Thanks ... Jay Novak

[sidney]

Since I'm getting ready to bond the floor, anybody care to share the article? TIA

[Mike B]

http://www.apexspeed.com/features/bellypan/

[R. Pare]

I have Tom's article, and agree about the corner gussets. The 7075 is what they call ALCLAD with a clad coating for corrosion protection. I'm not sure how a clad material would take to anodizing. I was going to try a conversion coating to aid adesion though. West epoxy systems sells one they claim works well.

Got to admit that I've never tried anodizing a clad material, but you still need it to be anodized somehow. All aluminium will form a skin of oxide immediately after grinding, sanding, etc, and that oxide will continue to grow in thickness after bonding, weakening the bond strength significantly. You will need to consult with the anodizer to see what process they will need to use.

The strips I'm talking about run the full perimeter of the lower rails, not just the corners. Big difference in the final strength and stiffness.

[tinkeringIdiot]

Anodizing usually starts with an acid bath to clean coatings off the metal. I've had 7075 Alclad anodized before without any extra prep on my part. Edit: Also, Hysol 9394 is my favorite adhesive for bellypans. It's a little different that most epoxies in that it is a two part paste rather than a liquid (feels like stiff silly putty), but it was originally designed to hold the skin onto the ribs of an aircraft wing. Good stuff.

[reidhazelton]

Sorry to hi-jack, but how come it seems everyone uses aluminum instead of stainless? If you need to add weight, there really isn't any lower place to put it that the weight of the floor pan. So, why not stainless, other than the cost and weight. Seems stainless would last much longer, what am I missing?

Reid

[Scott Hanba]

Stainless is harder on the cutting tools and drills. I did stainless on mine, have been happy with it.

[rickb99]

Reid,

Going by the minimum required:

18 gauge stainless at 2.016 Lbs per sq. ft.

0.064 T6061 at 0.9 Lbs per sq. ft.

On our '89 Reynard that would add about 14 pounds going to steel and we are already over weight by 53 Lbs with our existing aluminum and a 185 pound driver.

I think we'll compromise and use 0.080 aluminum as recommended by a prominent Forum member for additional stiffness with just a touch of added weight.

I don't know what the min. FC weight was in '89 but I'm guessing the assumption was a 155 or 165 Lbs driver back then. Cockpit also assumed drivers around 5' 10" to 5' 11". Not the 6' 2" young guys of this generation.

[reidhazelton]

Thanks guys, much appreciated! I actually need weight, I have about 85lbs on lead resting on the floor pan of my iron head FF, so to use some of that up in the pan itself will be nice, provided I get ambitious over the winter!

Any suggestions on how to break the hysol bond??

Thanks!!!!!

[Gary Slahor]

Some great info. Thanks guys.

Richard (Pare): Please tell me more about the perimeter strips. Are they on the outer perimeter of the lower frame rails (sticking slightly out past the frame rails) or inner perimeter of each boxed in section ? Typically what size are they (thickness and width) ? I guess they could be welded in, if on the outer perimeter, but wouldn't they have to be brqzed to the inner perimeter, as you would be getting into the existing brazing in the corners and I know welding and brazing don't mix ?

TIA ..........Gary

[racer27]

Any suggestions on how to break the hysol bond??

Thanks!!!!!

We used a sharp chiesl between the Pan and the frame. Once you peel a corner it goes quickly.

[racer27]

The strips I'm talking about run the full perimeter of the lower rails, not just the corners. Big difference in the final strength and stiffness.

New floor is in the cards for us as well. If time allows, we plan on adding the Parameter strips where possible to increase bonding surface area.

Richard -- At one point you suggested a 2 layer floor.... Out of what material & thinkness? Bonding between sheets? I also assume you want us repeating the zig-zagging pattern, using countersunk rivits exclusively.

[rickb99]

Thanks guys, much appreciated! I actually need weight, I have about 85lbs on lead resting on the floor pan of my iron head FF

As I stated, the 18 gauge stainless is the MIN thickness. Get rid of more ballist by going thicker. Two advantages. Better protection and gets that ballist weight lower.

[stephen wilson]

Don't just lay the lead on the floor-pan, a friend did that and the weight starting pulling the pan off!

[R. Pare]

Richard (Pare): Please tell me more about the perimeter strips.

The strips are welded (TIG) to the inner side in each bay. We use 1" wide 18 Ga. drilled for 1/8" rivits in 2 rows 1/2" apart. Rivits in each row are on 2" centers. We like dome head hard rivits (dome inside the cockpit) upset into a countersunk hole in the bottom face of the pan. You need a decent pneumatic rivit bucking gun to do the job well.

Using these strip will more than double the shear area of the bonding, leading to multi-year use of the car before reworking.

Ambrose: I sorta remember that post, but not the background of the recommendation. Was it to reinforce an already-existing pan?

[racer27]

Ambrose: I sorta remember that post, but not the background of the recommendation. Was it to reinforce an already-existing pan?

Thanks for the reply...

I can't find the post, but I believe it was in the context of someone asking as to best material and recommended thickness. No, intent is not to reinforce existing pan, just installing a plan with good durability, safety and performance (Adding to chassis rigidity).

I doubt we'd go with 2 layers, but may go marginally thicker as to keep pan from bowing under my fat rear.

[rickb99]

I doubt we'd go with 2 layers, but may go marginally thicker as to keep pan from bowing under my fat rear.

Ours currently has an extra 1/8" aluminum plate riveted to the belly pan inside the cockpit under the drivers seat. I'm pondering welding some 1/8" thick bar stock as cross runners under the driver seat. this will add some stiffness, give additional rivet points for the belly pan and give a perch for a thinner steel plate using screws to retain it under the driver.

[Gary Slahor]

[quote=R. Pare;190194]The strips are welded (TIG) to the inner side in each bay. We use 1" wide 18 Ga. drilled for 1/8" rivits in 2 rows 1/2" apart.

Richard: Do you stitch weld the strips in ? ...staying away from the existing braze material ?

[R. Pare]

Yes - stitch welding is necessary to keep warpage down. Braze where necessary.

[stephen wilson]

I'm still curious about spot welding a SS pan on, it could certainly be done without warpage, and would never need rebonding. The only BIG downside would be that getting the pan off for any reason would be damn difficult without ruining the frame rail.
Steve

[rickb99]

Hey,

For you guys (like us) who are doing belly pans on older cars, you might want to put a caliper or micrometer on some other metal parts while you're stripped down that far. Read and check while you're there:

http://www.apexspeed.com/forums/showthread.php?t=30159

That 'extra' material from the 4 x 8 (or 12) sheet might be useful.

[Joefisherff]

Of the aluminum materials mentioned which of them can be easily bent (if any) so that you could use them for fuel cell surrounds etc.. The reason I ask is that I was told that 6061-T6 is very strong but very difficult to bend. Thanks and great advice!

[R. Pare]

Any will bend readily, but the results will depend on the radius. 6061-T6 bends easily enough, but you need to use a large enough radius to keep it from cracking. Softer heat treat can use smaller radiuses. A T4 or T3 spec will suffice for fuel cell enclosures.

[Joefisherff]

Thank you Richard. Do you prefer 6061 or ?

[R. Pare]

6061-T6 or even T4/T3 is plenty for these non-structural applications. We've use both on our old-style fuel cell enclosures in the past. The later cars with the revamped enclosure all used T6. 7075-T6 is exellent for floor pans, but all you are really gaining is the extra strength, not extra stiffness.

[sidney]

Does anybody have experience with Zinc Chromte instead of Annodizing? There's nobody in the Denver area that can do the annodizing of the floorpan (too long), but Zinc Chromte is an option. I was just wondering how this would impact the boding of the floor. The color is also less than ideal (poopy brown/gold color), but if it works, it may be our only option.

[DanW]

Ian,

Try a search on Alodine. Some good answers by knowledable people.

[rickb99]

Does anybody have experience with Zinc Chromte instead of Annodizing?

First hand experience with Zinc Chromate? You bet-cha. All aluminum superstructure and any other aluminum parts are primered with Zinc Chromate in the U.S. NAVY! Hoo-rah!

It does an excellent job of protecting aluminum from corrosion in salt spray environments. But it doesn't go on real smooth or nice looking. Unless things have changed with Zinc Chromate you would want to paint over the primer.

You said "Poopy brown/gold color"? Hmm I used to consider it puke yellow?

Actually as mentioned above, you could alodine the parts too. Although better with dip method, you can purchase a 'brush on' alodine material (does a poor job). Even with dip, the finish will show any blemish's in the aluminum (and exaggerates them) right through the alodine (blotchy uneven color) depending upon the quality of the surface finish. A clear (or colored) anodize does not have this effect.

But of more importance to preventing galvanic corrosion of the aluminum, alodine is a conductor so eddy currents will pass right through it. Anodize on the other hand is a NON conductor (i.e. acts like an insulator).

If you cannot anodize, Zinc Chromate primer and a good paint is probably a better choice.

[sidney]

O.K. now another stupid question. Why would I paint it other than to cover the poopy brown/puke yellow color? Is the paint only for cosmetics? We use zinc chromate on fittings for hydraulic components and they generally do not get painted. Thanks for the advice folks.

[rickb99]

Only reason to paint is if you don't like the poopy puke.

[R. Pare]

Zinc Chromate IS NOT a good method for this sort of high-stress application. Think about it for a second - just how strong is both the adhesion strength and tensile/shear strength of that paint compared to the same strengths of a layer of anodizing, with both compared to the level of stresses imposed?

Not very favorable, I believe!

While the military will use it for corrosion protection - for which it is very good - and even possibly use it in some stressed-joint applications, the safety factors they use are probably 10x that of a race car (race car things are typically designed to be stressed to just under the yield point, rather than 5-10 times under).

I have no idea where alodine falls in this regard.