Designing a modern 275..... - Page 7 - Ferrari Life
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post #121 of 316 Old 12-16-2011, 11:57 AM
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Mark, is there any chance you can show us some of the initial drawings, even if not the current ones?
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post #122 of 316 Old 12-16-2011, 01:43 PM Thread Starter
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Mark, is there any chance you can show us some of the initial drawings, even if not the current ones?
I'm not supposed to because Mike doesn't feel that the drawings are presentation to the public quality. I think what he's done is pretty good and just needs a touch more aggression to be perfect, but when they get posted is up to Mike.....I'll ask again though.

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post #123 of 316 Old 12-16-2011, 01:48 PM Thread Starter
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Originally Posted by Brian.G View Post
Mark, how do you intend bonding/fixing the CF to the spaceframe?

With adhesives?
With mech fixings?

I thought about this along time ago, using fixings is tricky, as one stress/flex concentration on a fixer, will loosen that fixer where it is through the CF.

Are you depending on the CF for rigidity at all?

Brian,
The basic plan is that the CF will be the actual frame but there will be steel buried and bonded inside as a just in case kind of thing....just to be safe.
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post #124 of 316 Old 12-16-2011, 03:44 PM Thread Starter
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I'm not supposed to because Mike doesn't feel that the drawings are presentation to the public quality. I think what he's done is pretty good and just needs a touch more aggression to be perfect, but when they get posted is up to Mike.....I'll ask again though.

I think I got Mike to cave a bit and share some of the concept sketches this weekend. Please understand they are called concept sketches because they are...well....sketches. Really good sketches IMO but not the finished drawing perfect is every detail quality Mike usually like to present.
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post #125 of 316 Old 12-17-2011, 04:31 PM
 
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The basic plan is that the CF will be the actual frame but there will be steel buried and bonded inside as a just in case kind of thing....just to be safe.
Interesting.

Ive done a lot of research into just this over the last few years. I intend spending the next 5-10yrs building an open wheel racer also built with a fully built(all)engine.

The main issues with a CF whatever you want to call it part of the chassis is testing.
One chassis could display different different torsional rigidity to another(if your making more than one)and safety aspect. This depends on so many things as its nearly Impossible to replicate exactly from one to the next without an F1 house, or aerospace composite department to hand.
But, that wont matter if your fixing the suspension points to a metal spaceframe as the CF can only help stiffness.
The spaceframe too will have some degree of torsional flex. If you run it all in autocad and apply loads, or make a wire frame, no matter what you do, you wont spread the loads evenly over every member and end up with a practical light design(In my opinion). So, if your bonding into a CF monocoque I think maybe you need to figure out what it is you want the carbon to do for you.
Be it to provide extra torsional resistance(careful of load concentrations between the two materials)
Or to provide the cabin, and also provide you with panels that slow down sharp objects that would otherwise pass through the spaceframe easily. (They use approx 20 layers of Zylon in an F1 tub for this)

Ive thought long and hard about all the above as its very much on my mind for my racer. Its a real tough one.

There is a few ways I think to go about it, that is manufacturing for someone that is handy with their hands.
It moreso applies to an open wheel racer in my case, as the geometry is a little simpler than what maybe you have in mind but Ill state what Im thinking anyway, sure why not.

Sadly the main brain bending issues Im having is that of the Carbonfibre construction, and if it would be good enough off the drawings - without crash/impact testing/torsional test.

For the 'total' CF build I was thinking of a two piece mould, striked off a foam core. Moulds would comprise of a top and bottom section(top side of tub, and bottom side)
Part line may not be straight, and would follow along the 0 deg draft point along the side of the tub.

The tub would be made in two parts, top and bottom, and then bonded together.

Layup into both independent moulds first with x amount of layers. Given that I have not, and no chance of access to an autoclave, it would have to be a wetlayup. Layers would be vacuumed to mould.
Then, as soon as the resin allowed, bond in precut(s) sections of foam filled honey comb such as nida-core polyurethane foam. The foam would add to stiffness, and also stop the cells from filling with resin(more weight) when laying up the rest of the layers. Doing this as soon as the first vac'd layers allowed would ensure both mechanical and chemical bonding between the honeycomb and the first layers since crosslinking would not yet have ceased.
Once I had a 'certain' amount of layers done onto the H.comb, both top and bottom would be bonded to eachother.
Before this was done, Id bond in any bulkheads needed for suspension points, etc. Im not sure if you could have these anodized and primed alloy parts lay onto the last layers applied, since they would be isolated from the first outer skin due to the honeycomb interlayer.
Any suspension cornering forces or other would then be transmitted to just the internal tub skin. Im not sure if this would be ok. Also, in a shear situation, I wouldn't want the suspension fixture bulkheads moving sideways, and shearing off my legs. So maybe a weak point in the wishbones would be needed.
Same goes for the engine mounting points, whether to use flat bonded in ferruled/bolted through plates, or to bond in alloy tubes the length of the car between layers. These would have solid tapped sections at the ends for engine fixture points.
Same applies to these as the bulkheads, to bond the to interior layer, or exterior layer(honeycomb separating them), or omit honeycomb in those areas and bond to both?
Another way to do it, is to use piano wire, bent at 90 deg at the end, spun in a drill, to clear out some of the honeycomb. This internal space is then filled with a chopped strand mix, and when dry, bored out to accept the bolt/ferrule.
Once the top and bottom were bonded(honeycomb longer at edges in bottom part, sliding into a section in the top part like a mortise and tenon), I was then thinking of filleting around the bulkheads at the bond line with sphere filled epoxy mix. This would allow a smooth low energy transition between the two. Another set of layers could be applied over the bulkheads, and engine tubes bonding them further to the interior tub layers. These could be vac'd on, or via an inflatable bladder arrangement.
Where both meet at the outsides of tub, the moulds would have been shaped in such a way(may require removable parts for mould release) that there would be say a 100mm high, 1mm depression, or low zone all along the join line, where I could vac on CF strips to complete external join(Inside could be done the same, no need for 1mm depression.

Whew.... thats what I was thinking for the CF tub construction.

The spaceframe tub is a little simpler, just slightly...

Make it in steel tube as we have all seen.
Bonding/fixing CF to steel tube is not easy if you want to work in flat CF sheets. You will also have to form each section which you will see when viewing the car from the outside.
Bonding these sections to a spaceframe will require them to have two geometry's. One for the outer aesthetic layer, and another rear edge layer/profile fitting the spaceframe tube geometries perfectly for bonding.
How you make the moulds for these panels is a big job.
If you change to square tube spaceframe things get a little easier, but of course square/rect sections are not as torsionally stiff as round ones.
You could concentrate on just bonding flat CF panels to the interior of frame, adding a lot of stiffness. You could also vac on CF to the joins and maybe get an ok looking interior pan and sides.
The outer mammoth shell may then only be required for aesthetics.

I dont know how carbon bonds to steel tube, or how you would prep it, Ive never studied it.
Still having said that, Id be more confident with bonding to aluminium since Ive studied, once its anodized, primed, and isolated from the CF with a layer of glass.
Aluminium has a finite life though, and is a bit more choosy to weld.

One last possibly way is cutting(compound shapes) Foam to go into all the spaces between the tubes or box sections. You could then apply CF over the lot, Internally and externally. But, In your case Mark, you would still need an aesthetic skin on the outside.
Doing it this way, would I feel provide nothing more than intrusion protection, since its only really touching a bare tangent of the tubes and would not offer much to torsional rigidity.

You could too I suppose encase the tubes with the carbon monocoque. Gluing both internal, and external skins together, and then filling the internal void around the tubes with an expanding foam of sorts.


With all the above in mind I traveled over to Horacio Pagani last month to ask him about the construction of his cars Since he uses a CF monocoque, I also wanted to see the construction up close, Ill put all that in another post as this one has run way too long as is.

A lot to think about for sure. The main points that I feel need to be closely addressed, is if you are intending the carbon to add rigidity, If not thought out correctly, all it may add is extra weight.

I really mean it when I say I cannot wait to hear your thoughts Mark, on how your going to go about it all.


Brian,

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Last edited by Brian.G; 12-17-2011 at 04:40 PM.
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post #126 of 316 Old 12-18-2011, 05:11 PM
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599 rear glass for windshield

Probably not feasible for any number of reasons like defroster wires but its shape is very Thomassima III.
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post #127 of 316 Old 12-20-2011, 07:59 AM Thread Starter
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You covered a whole lot of ground it that post!

Iím not planning to use a space frame of any kind at the moment, just a safety cage that I want to try to make SCCA competition legal. I donít see anything being attachť to the cage except the seats and harnessesÖ..but Iíll know more once I get into the actual design work.

The manufacture of the CF will be much along the lines youíre thinking with a mix of solid, foam and honeycomb filled. It will be done in fiberglass molds made from CNCíd foam plugs. Iíll be using room temp cure epoxy, vacuum bags and laying things up in stages which will lead to a heavier that optimal construction but it the only practical way it can be done I think.

Hard points for engine and suspension mounting can be tough but I have a few ideas about how I want to proceed there, again with strength and safely over ruling weight considerations. The ideas involve things like putting the suspension rubber/ urethane mounts directly into the CF chassis rather than in the A-arm to better distribute the load and guarantee there are no stress risers generated. Weíll see when I get there.

Iím not real concerned about debris penetrating the body, but I am thinking of either using so Kevlar in the middle layers and maybe Kevlar reinforced CF throughout to prevent anything from disintegrating in an impact and that would also help with the debris penetration your thinking about.
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post #128 of 316 Old 12-20-2011, 08:10 AM Thread Starter
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Probably not feasible for any number of reasons like defroster wires but its shape is very Thomassima III.
I think it's just plain too big to use Reg.
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post #129 of 316 Old 12-20-2011, 09:30 AM
 
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You covered a whole lot of ground it that post!

Iím not planning to use a space frame of any kind at the moment, just a safety cage that I want to try to make SCCA competition legal. I donít see anything being attachť to the cage except the seats and harnessesÖ..but Iíll know more once I get into the actual design work.

The manufacture of the CF will be much along the lines youíre thinking with a mix of solid, foam and honeycomb filled. It will be done in fiberglass molds made from CNCíd foam plugs. Iíll be using room temp cure epoxy, vacuum bags and laying things up in stages which will lead to a heavier that optimal construction but it the only practical way it can be done I think.

Hard points for engine and suspension mounting can be tough but I have a few ideas about how I want to proceed there, again with strength and safely over ruling weight considerations. The ideas involve things like putting the suspension rubber/ urethane mounts directly into the CF chassis rather than in the A-arm to better distribute the load and guarantee there are no stress risers generated. Weíll see when I get there.

Iím not real concerned about debris penetrating the body, but I am thinking of either using so Kevlar in the middle layers and maybe Kevlar reinforced CF throughout to prevent anything from disintegrating in an impact and that would also help with the debris penetration your thinking about.
I just typed as it came out of my head really

As long as you weight the cloth, and resin, and make sure they weigh the same you wont go too far wrong with over resining.

If I think of more stuff Ill note it down, lots to think about,

Brian,

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post #130 of 316 Old 12-20-2011, 10:48 AM
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...The ideas involve things like putting the suspension rubber/ urethane mounts directly into the CF chassis rather than in the A-arm to better distribute the load and guarantee there are no stress risers generated. We’ll see when I get there...
Didn't Gordon Murray do something along those lines with the McLaren F1? I seem to remember that's how he got the steering precise enough while still retaining good road manners in a street car.
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post #131 of 316 Old 12-21-2011, 07:58 AM
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Originally Posted by Brian.G View Post
Interesting.

Ive done a lot of research into just this over the last few years. I intend spending the next 5-10yrs building an open wheel racer also built with a fully built(all)engine.

The main issues with a CF whatever you want to call it part of the chassis is testing.
One chassis could display different different torsional rigidity to another(if your making more than one)and safety aspect. This depends on so many things as its nearly Impossible to replicate exactly from one to the next without an F1 house, or aerospace composite department to hand.
But, that wont matter if your fixing the suspension points to a metal spaceframe as the CF can only help stiffness.
The spaceframe too will have some degree of torsional flex. If you run it all in autocad and apply loads, or make a wire frame, no matter what you do, you wont spread the loads evenly over every member and end up with a practical light design(In my opinion). So, if your bonding into a CF monocoque I think maybe you need to figure out what it is you want the carbon to do for you.
Be it to provide extra torsional resistance(careful of load concentrations between the two materials)
Or to provide the cabin, and also provide you with panels that slow down sharp objects that would otherwise pass through the spaceframe easily. (They use approx 20 layers of Zylon in an F1 tub for this)

Ive thought long and hard about all the above as its very much on my mind for my racer. Its a real tough one.

There is a few ways I think to go about it, that is manufacturing for someone that is handy with their hands.
It moreso applies to an open wheel racer in my case, as the geometry is a little simpler than what maybe you have in mind but Ill state what Im thinking anyway, sure why not.

Sadly the main brain bending issues Im having is that of the Carbonfibre construction, and if it would be good enough off the drawings - without crash/impact testing/torsional test.

For the 'total' CF build I was thinking of a two piece mould, striked off a foam core. Moulds would comprise of a top and bottom section(top side of tub, and bottom side)
Part line may not be straight, and would follow along the 0 deg draft point along the side of the tub.

The tub would be made in two parts, top and bottom, and then bonded together.

Layup into both independent moulds first with x amount of layers. Given that I have not, and no chance of access to an autoclave, it would have to be a wetlayup. Layers would be vacuumed to mould.
Then, as soon as the resin allowed, bond in precut(s) sections of foam filled honey comb such as nida-core polyurethane foam. The foam would add to stiffness, and also stop the cells from filling with resin(more weight) when laying up the rest of the layers. Doing this as soon as the first vac'd layers allowed would ensure both mechanical and chemical bonding between the honeycomb and the first layers since crosslinking would not yet have ceased.
Once I had a 'certain' amount of layers done onto the H.comb, both top and bottom would be bonded to eachother.
Before this was done, Id bond in any bulkheads needed for suspension points, etc. Im not sure if you could have these anodized and primed alloy parts lay onto the last layers applied, since they would be isolated from the first outer skin due to the honeycomb interlayer.
Any suspension cornering forces or other would then be transmitted to just the internal tub skin. Im not sure if this would be ok. Also, in a shear situation, I wouldn't want the suspension fixture bulkheads moving sideways, and shearing off my legs. So maybe a weak point in the wishbones would be needed.
Same goes for the engine mounting points, whether to use flat bonded in ferruled/bolted through plates, or to bond in alloy tubes the length of the car between layers. These would have solid tapped sections at the ends for engine fixture points.
Same applies to these as the bulkheads, to bond the to interior layer, or exterior layer(honeycomb separating them), or omit honeycomb in those areas and bond to both?
Another way to do it, is to use piano wire, bent at 90 deg at the end, spun in a drill, to clear out some of the honeycomb. This internal space is then filled with a chopped strand mix, and when dry, bored out to accept the bolt/ferrule.
Once the top and bottom were bonded(honeycomb longer at edges in bottom part, sliding into a section in the top part like a mortise and tenon), I was then thinking of filleting around the bulkheads at the bond line with sphere filled epoxy mix. This would allow a smooth low energy transition between the two. Another set of layers could be applied over the bulkheads, and engine tubes bonding them further to the interior tub layers. These could be vac'd on, or via an inflatable bladder arrangement.
Where both meet at the outsides of tub, the moulds would have been shaped in such a way(may require removable parts for mould release) that there would be say a 100mm high, 1mm depression, or low zone all along the join line, where I could vac on CF strips to complete external join(Inside could be done the same, no need for 1mm depression.

Whew.... thats what I was thinking for the CF tub construction.

The spaceframe tub is a little simpler, just slightly...

Make it in steel tube as we have all seen.
Bonding/fixing CF to steel tube is not easy if you want to work in flat CF sheets. You will also have to form each section which you will see when viewing the car from the outside.
Bonding these sections to a spaceframe will require them to have two geometry's. One for the outer aesthetic layer, and another rear edge layer/profile fitting the spaceframe tube geometries perfectly for bonding.
How you make the moulds for these panels is a big job.
If you change to square tube spaceframe things get a little easier, but of course square/rect sections are not as torsionally stiff as round ones.
You could concentrate on just bonding flat CF panels to the interior of frame, adding a lot of stiffness. You could also vac on CF to the joins and maybe get an ok looking interior pan and sides.
The outer mammoth shell may then only be required for aesthetics.

I dont know how carbon bonds to steel tube, or how you would prep it, Ive never studied it.
Still having said that, Id be more confident with bonding to aluminium since Ive studied, once its anodized, primed, and isolated from the CF with a layer of glass.
Aluminium has a finite life though, and is a bit more choosy to weld.

One last possibly way is cutting(compound shapes) Foam to go into all the spaces between the tubes or box sections. You could then apply CF over the lot, Internally and externally. But, In your case Mark, you would still need an aesthetic skin on the outside.
Doing it this way, would I feel provide nothing more than intrusion protection, since its only really touching a bare tangent of the tubes and would not offer much to torsional rigidity.

You could too I suppose encase the tubes with the carbon monocoque. Gluing both internal, and external skins together, and then filling the internal void around the tubes with an expanding foam of sorts.


With all the above in mind I traveled over to Horacio Pagani last month to ask him about the construction of his cars Since he uses a CF monocoque, I also wanted to see the construction up close, Ill put all that in another post as this one has run way too long as is.

A lot to think about for sure. The main points that I feel need to be closely addressed, is if you are intending the carbon to add rigidity, If not thought out correctly, all it may add is extra weight.

I really mean it when I say I cannot wait to hear your thoughts Mark, on how your going to go about it all.


Brian,
I'm in planning stages of a similar build but it will be closed wheel with a bike engine for power (scca D-sport). I've done quite a bit of research over the last couple of years and found that square tube vs. round tube is a minor difference in rigidity given same diameter and thickness, though the square tube will weigh a bit more (as it takes more steel to make a square vs. round section), but if you're planning a CF stressed skin instead of full triangulation, square tube is MUCH easier to bond to. I was planning on a square tube steel space frame with minimal triangulation and then adding flat CF shear panels on both sides filled with either foam or honeycomb with possibly some Kevlar/Aramid layers around the driver for intrusion protection. Without an autoclave, a full CF monocoque would be next to impossible. The steel spaceframe/CF stressed skin (semi monocoque as they call it) is almost as light as a CF tub and almost as strong, but the main reason not to use it is that you will have to add body work covering it as you really can't 'shape' it for design or aero reasons being limited to flat sections. Not a big deal for me as CF bodywork for the size car I'm buidling would only weight 30-40lbs, but if I had a huge budget and/or tons of free time, a CF tub incorporating aero elements could potentially save me 100lbs (but at huge cost and time differential).

Regarding the 275 build, a steel perimeter spaceframe/CF sandwich stressed skin with overlaying CF bodywork would probably cut your time in 1/4 in terms of design and mold making and only cost 150lbs and little rigidity. It would also make hard mounting points very easy, not to mention cost savings as dealing with flat CF panels for the structure is much much easier than trying to build complex shaped monocoque (so a lot less scrap). Bodywork would be a wash as it won't really be structural so won't need the same degree of attention. I understand the allure of a no compromise CF tub, but after looking at what it would take I'd probably have to align myself with a university that has an autoclave and sell all of my other toys and pull out of my retirement to fund it.
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post #132 of 316 Old 12-21-2011, 08:51 AM
 
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Interesting points Bobz-thanks. Without pulling the thread too off topic, why do you think it would be impossible without a clave?
Ive have seen, tested(torsional. R) wet.L tubs and spoke with many of the oldtimer composite guys, and Im convinced that it can be done wetlay, with vac bags.

Having said all that, Im still not convinced its the right choice for me. If I whack a wheel, steel anchor points can be repaired, not so with CF.

But. It is hard to make a good looking car tub, by using shear/triangulation as you mention, without adding an outer show/aero skin/cloak.

I guess it wouldn't be that big of deal...maybe im just being greedy by trying to get it all in the one hit.

As for tube vs square, I hear ya, but you can make brackets a lot smaller for introducing loads into tube walls semi evenly, than with square stuff though.
Perhaps a mix of both, round wins over square for a lot more reasons than square over round - shear plate bonding being the only pro I can think of for square stuff.

Interesting stuff for sure Bobz.

Brian.

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post #133 of 316 Old 12-22-2011, 04:02 AM
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Interesting points Bobz-thanks. Without pulling the thread too off topic, why do you think it would be impossible without a clave?
Ive have seen, tested(torsional. R) wet.L tubs and spoke with many of the oldtimer composite guys, and Im convinced that it can be done wetlay, with vac bags.

Having said all that, Im still not convinced its the right choice for me. If I whack a wheel, steel anchor points can be repaired, not so with CF.

But. It is hard to make a good looking car tub, by using shear/triangulation as you mention, without adding an outer show/aero skin/cloak.

I guess it wouldn't be that big of deal...maybe im just being greedy by trying to get it all in the one hit.

As for tube vs square, I hear ya, but you can make brackets a lot smaller for introducing loads into tube walls semi evenly, than with square stuff though.
Perhaps a mix of both, round wins over square for a lot more reasons than square over round - shear plate bonding being the only pro I can think of for square stuff.

Interesting stuff for sure Bobz.

Brian.

From what I've seen, with the autoclave you can do the whole tub in one shot and then let it cure and end up with more consistent and structuraly sound layup with less air bubbles. For a small single seater (like a formula sae) I think you could do a whole tub using wet layup and vacuum bagging. To do something larger you'd have to do it in sections and then bond the sections together. Not impossible, but then you have to also carefuly plan where the joints are, hope that all of the joints are sound, make sure each individual piece is cured properly etc. Being realistic about it and my abilities, I don't think I can get it right in less than about 5 tries. If you are confident you can do it, I say go for it. I fully understand wanting it all, but for me I just don't have the time or money to make multiple attempts at a tub and hope one comes out ok. I'm looking at trying to make 1100lbs weight with driver and feel I can get close without a full CF tub and instead using CF sandwich shear panels in a spaceframe with an aero skin. There's also another big issue for me in that a CF tub would have to be crash tested to FIA standards to be raced, where a spaceframe doesn't, it just has to have certain sized bars in certain places. I guess impossible wasn't the right word, more impractical given realistic time and money goals (I don't want to be into the tub for $50k alone).

Good point on introducing loads through round tubing, it may make sense to do the cockpit in square and then front and rear sub frames in round.

Last edited by bobzdar; 12-22-2011 at 04:20 AM.
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post #134 of 316 Old 12-22-2011, 04:49 AM Thread Starter
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I did a pretty complex space frame for an FSAE car back in college. The entire chassis weighed 28lb and had a torsional stiffness of 3500 ft-lb/degree which was about 10 times the stiffness/weight ratio of common space frames of the day. The chassis had something like 80 individual tubes and took about 100 hours to build. It sits on display in the engineering building lobby these days I'm told.

I also worked up the design for another version of the frame that would be a 2 seat mid-engine 365 size car that was looking like 56 lb, 9000+ ft-lb/degree, safe to 600+hp,.....really nice if I do say so myself

The issue with both designs is getting in. To get those kind of stiffness numbers it has to be fully triangulate and by fully triangulated I mean FULLY triangulate include the engine bay and passenger compartment. The engine bay is easy enough to handle with a bolt-in member (reamed and pined holes of course) but the passenger compartment is tough. What I did was move the front roll hoop forward about 6-8" of the steering wheel and bring it up just above the top of the steering wheel which let me put 2 bars from the main roll hoop above the driver's shoulders that met in the center of the front roll hoop. Those 2 bars alone (about 1.5 lb of metal) increase the torsional stiffness by 400%. This works fine for an open top race car but is somewhat less than ideal for a street car....


I also worked up a 3rd design that was also mid-engine 356 size but used large rocker panels to carry the torsional loads but still let you have doors to get in and 56 lb goes to more like 250-300 lbs to get similar performance of the fully triangulated design and this is what's pushing me toward wanting to go to a CF monocoque design for this project....I want doors
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post #135 of 316 Old 12-22-2011, 11:22 AM
 
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Mark, Drivers do tend to get nervous if you start bolting stuff around them after they get belted in, which is a shame!

Your FSAE frame sounds impressive.

Brian,

Edit, Bobz, After a sleepless night lastnight(its eating my head inside now) due to me wanting to make a decision, and go with it, Im thinking spaceframe, shear panels, and aero skin.

This way mainly because Im sure Im better in the workshop, than I am on the track! Would hate to waste a good CF mono by whacking a wheel...
Perhaps Ill get to make a lot of the aero/parts from honeycomb sandwich, and some other parts too, nosecone and rear impact structures mainly.

One more point about round vs square, well, here anyway, tube is available in far more wall thicknesses than square, but that may be just around these parts.

I bought a bunch of f1 crash structures last week Im going to chop up and study.

I know Ill be sorry for not doing a CF tub, but I know I wont be sorry when I clip a wheel, or worse and rip out a bracket or something.

Another point re autoclaves, pagani bond together cured parts on a lot of their cars.

If you think you can't you wont, if you think you can, you will

Last edited by Brian.G; 12-22-2011 at 11:38 AM.
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post #136 of 316 Old 12-22-2011, 12:29 PM Thread Starter
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Mark, Drivers do tend to get nervous if you start bolting stuff around them after they get belted in, which is a shame!
That and we had a stupid you need to be able to get out in under 5 sec rule

....which our larger driver could do in under 3 sec even with the above should bars so that worked out fine.


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Originally Posted by Brian.G View Post
One more point about round vs square, well, here anyway, tube is available in far more wall thicknesses than square, but that may be just around these parts.

.
Tubing come in thinner walls than the 0.028" that I use for EVERTHING?
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post #137 of 316 Old 12-24-2011, 03:04 PM
 
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Some interesting reading should tomorrow get boring,



http://www.firearmz.com/user/SAE_983055.pdf


Brian,

If you think you can't you wont, if you think you can, you will
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post #138 of 316 Old 12-29-2011, 09:36 AM Thread Starter
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Originally Posted by Brian.G View Post
Some interesting reading should tomorrow get boring,



http://www.firearmz.com/user/SAE_983055.pdf


Brian,
Interesting.

You know, since bobzdar first posted his shear plate I've been ponding why exactly I would want shear plates in a space frame and I honestly for the life of me can't come up with than answer.

It takes about 15-20 minutes to cut, fit, weld in a diagonal and I know exactly what it's strength is. Adding a shear plate instead seems to me to be much more difficult and uncertain and I'm not sure it's even any lighter.

I'm just not understanding the advantage to the shear plate design?
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post #139 of 316 Old 12-29-2011, 08:25 PM
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Originally Posted by mk e View Post
Interesting.

You know, since bobzdar first posted his shear plate I've been ponding why exactly I would want shear plates in a space frame and I honestly for the life of me can't come up with than answer.

It takes about 15-20 minutes to cut, fit, weld in a diagonal and I know exactly what it's strength is. Adding a shear plate instead seems to me to be much more difficult and uncertain and I'm not sure it's even any lighter.

I'm just not understanding the advantage to the shear plate design?
Well, what I'm describing is not what is shown in that paper. They use round tube and shear plates on one side of the tube. You can see some of the difficulty they had getting a good bond of the shear plates to the round tube - they had to weld sheet metal strips to the tube which would negate any weight benefit the round tube would provide. Also, by bonding to both sides of the tube and filling with honeycomb or foam, the resulting shear plate is over twice as thick as those tested - for the setup in the paper they used 10mm shear panels on a 1" tube, the setup I'm talking about would result in roughly 35mm shear panels on the same 1" tube, which would be close to an order of magnitude stronger with just the weight penalty of the foam or honeycomb center. I plan to build a few test panels using different sandwich materials to compare and could easily compare to a similar round tube triangulated frame/panel.
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post #140 of 316 Old 12-30-2011, 04:40 AM Thread Starter
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Well, what I'm describing is not what is shown in that paper. They use round tube and shear plates on one side of the tube. You can see some of the difficulty they had getting a good bond of the shear plates to the round tube - they had to weld sheet metal strips to the tube which would negate any weight benefit the round tube would provide. Also, by bonding to both sides of the tube and filling with honeycomb or foam, the resulting shear plate is over twice as thick as those tested - for the setup in the paper they used 10mm shear panels on a 1" tube, the setup I'm talking about would result in roughly 35mm shear panels on the same 1" tube, which would be close to an order of magnitude stronger with just the weight penalty of the foam or honeycomb center. I plan to build a few test panels using different sandwich materials to compare and could easily compare to a similar round tube triangulated frame/panel.
I agree it would be a whole lot easier to bond to square tubes, but you're still bonding and that is where all the uncertain comes into the game. Also for competition use you still basically scarp the frame after a hit or you go back and know out all the panels and re-do them.

You're point about using foam or honeycomb isn't really correct I don't think. You are absolutely right that adding fill will improve the bending strength (which is a function of thickness cubed) but I'm not sure that will help an awful lot in a shear load.....it will reduce any tenancy for the panel to buckle so you can count on it for compressive load not just tensile but there should be very little of either in a shear plate which should be in shear.

The 3rd dimension you are adding to the shear panels does give you the ability to make panels that are not flat if you chose so I think what you're envisioning is a monocoque design that you construct in a modular way with a steel safety cage buried inside. You and I are actually talking about very similar designs, your just uses more steel than I was thinking.
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