Moncoque versus Spaceframe

[JD232]

What do you guys think of monocoque designing.. very surprisingly very few teams are using it. Is it just the complexity? or some other factors?

[JD232]

What do you guys think of monocoque designing.. very surprisingly very few teams are using it. Is it just the complexity? or some other factors?

[kmrobinson]

Complexity, cost, materials avalibility, facilities avalibility, and technical knowledge are all factors when designing a composite monocoque chassis. We've done very well with space frame chassis in the past and don't anticipate changing due to many of the factors above.

[A Richards]

People could go on about this all day, really just depends what you know and have experience with. Having just finished building a monocoque i cant really say that it is all that difficult but it is a big commitment, especially since it will be your first. If you have your heart set on making one I would suggest doing a wet layup, you wont require much in the way of facilities. If your having trouble affording it work on finding more money. Come race day there are so many factors that will effect your performance and unless your commited to getting them all right what your chassis is made out of really isn't going to make any difference.

[MalcolmG]

Monocoques are a LOT of work. I wasn't around back when our team did a space frame, but it's difficult for me to compare the relative time and difficulty, but a monocoque requires a significant amount of time and effort to produce. Here's some things AGAINST monocoques:

- monocoques are not easy to change if you forget about something. This means you need to have design of most of the subsystems close to complete before you can be happy with begining manufacture of your monocoque.

- an easy thing to overlook is just how much work there can be in producing moulds. In 2005 our team had female moulds machined from foam, laid some glass into them, then had them re-machined. This was a big nightmare. This year, we planned to do something similar but on male plugs, but due to machinists not being able to meet our required deadlines we had to machine the plug from slices of MDF, then glue them all together. Once you have the plugs, you then have to go through the process of making moulds. All up I think it took us between 2 and 3 months to go from CAD model to finished moulds

- If you do a wet laminate, you will probably have to do it in many stages.

- If you infuse the part, then you'd better hope you have some game when it comes to infusions, because if you pop a bag, close out an area of the laminate, or get some laminate bridging in the wrong spot, you could end up with a very expensive, and not particularly effective, paperweight.

- If you are doing pre-preg, you'll either need access to an autoclave, or will need to invent something similar (i believe UWA use/have used compressed air in a sandwich bag around the vacuum bag to pressurise their parts, but it would be difficult to control temperatures to a suitable level of accuracy). Autoclave moulds require high-temp resins, which will often require post-curing before they can be used too.

- Hardpoints. Anywhere you want to mount something to the monocoque, you will need a hardpoint. This means measuring out the placement of them all at layup time, and making sure you get it right! Low-stressed points can be retro-fitted using epoxy and carbon tube, but if you get a suspension pickup hardpoint in the wrong spot, it could be fairly disasterous.

- Structural equivalency. It's not so bad once you get a template sorted, but your first structural equivalency will be a big old nightmare. Don't underestimate the time it will take to do this.

- Cost. Yes, it costs a lot to build a monocoque. We get all our autoclave time for free, but the materials add up pretty quickly. There's also quite a bit of cost in consumables, such as bag, tacky tape, airtack, peel ply, breather etc.

- Finally, if you go through all the expense (financial and time) of building a monocoque, if the people designing/building it made errors in the wrong places, then the first time you try to drive the car you might get a massive delamination or failure of the laminate, and it's a lot harder to fix that on a monocoque than it is to replace a broken tube in a spaceframe!


Enough of the bad though, there's plenty of good about it:
- Once you have finished the part, you're ahead of someone who has just finished a space frame, as you have already done your body, floor closeout etc

- For stiffness vs weight, a well designed and manufactured monocoque should be superior to a spaceframe. I should note that this doesn't necessarily equal on-track performance, and it is certainly debatable whether it makes a difference in FSAE

- Composites, and composite part design, are becoming increasingly important in various industries, and most of us are here to learn skills that will make us better engineers - this is certainly a great opportunity to do so

I'm sure there's more too, but I have a test in 5 hours and need to get back to study.

I would suggest very carefully considering whether your resources, in terms of finance, equipment, experience, and manpower, are up to the task of building a monocoque before taking the plunge. While some believe there's no place for them in FSAE, and that you should be doing all you can to simply get a car on the road, it really comes down to what your team wants to do, and probably what your University sees as being a successful year - should you be learning as much as you can, and exposing yourself to as many different technologies as possible, or should you simply be trying to build the most basic car you can, so you can get it on the track early and optimise its performance?

[LU-Bolton]

Building composite parts takes experience. If no one on your team has ever done it before, then you will probably have some difficulty. Don't let MalcolmG scare you though, it's not as bad as it sounds.

The major downsides to monocoques in my eyes are:
analysis, steel tubes are a joke to analyze for most teams. monocoques are not. chances are you won't have anything close to an accurate analysis your first year unless you have graduate or faculty help.
AND
carbon fiber cost. about $50/yard dry fibers or more sometimes for pre-pregs. easily solved by calling hexcel or equivalent company. they'll give it to you for free. http://fsae.com/groupee_common/emoticons/icon_smile.gif try it.

Other miscellaneous
Don't do an infusion unless you have experience(most people probably don't even know what it is anyways).
I recommend wet lay up for beginners, it's easy and you will have a good success rate.
Dare I say it.... You DON'T need to autoclave pre-preg parts. Can't wait to see the people disagree with me on this one. A wing is being built at work, it's all pre-preg carbon. It's 140 feet long. Do you really think they make autoclaves that big? Answer: we bake it when it's bagged, no pressure.
Yes you can create hardpoints after it is built also, people just think it's sloppy... kind of like hacking tubes out of a space frame. http://fsae.com/groupee_common/emoticons/icon_smile.gif

These are one-off prototypes, built by students. You can build things quickly for cheap, you just have to be creative and smart. Sorry Malcolm, just playing devil's advocate.

Aaron Cassebeer

[MalcolmG]

I wasn't trying to scare anyone, just trying to give people an idea of what they're getting themselves in for if they decide to do a coque. http://fsae.com/groupee_common/emoticons/icon_smile.gif To be honest this year's monocoque build has been a long and stressful event for me, so perhaps I'm a little jaded http://fsae.com/groupee_common/emoticons/icon_wink.gif

We did have some guys doing a composites-related 4th year project this year, who were going to test some samples of prepreg cured at 1 bar (vacuum bag in atmosphere), and others in the autoclave (~3 bar) and test them to see what differences in mechanical properties you get with the increased pressure.

Anyway, no need to apologies Aaron, I'm just sharing what I've learned from my very limited composites experience http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Bertie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
- If you are doing pre-preg, you'll either need access to an autoclave, or will need to invent something similar (i believe UWA use/have used compressed air in a sandwich bag around the vacuum bag to pressurise their parts, but it would be difficult to control temperatures to a suitable level of accuracy).
</div></BLOCKQUOTE>

Incorrect but keep guessing.
We found that if you buy the right carbon prepregs you dont need an autoclave, simply an oven or a heat gun (for smaller parts) will do the trick. Many prepregs are specificaly designed for vacuum only oven cures. how do you think boeing and airbus do most of their parts??

I also dont like the crap people are spinning about repairing CF chassis being hard. gimme a stanly knife, some sand paper, wetlayup kit and some bog you'd never tell if i'd repaired a section of tub, and you would be supprised at what can be done in a night by yourself.

It really isnt that hard to make a CF monocoque chassis, you just need the full support and help from your team. If some ppl are against it and dont help with even the basics like sanding and sanding and sanding then your gunna struggle. Man power is the key to a good chassis.

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bertie:
We found that if you buy the right carbon prepregs you dont need an autoclave, simply an oven or a heat gun (for smaller parts) will do the trick. Many prepregs are specificaly designed for vacuum only oven cures. how do you think boeing and airbus do most of their parts?? </div></BLOCKQUOTE>

Boeing and Airbus do use HUUUGE autoclaves to manufacture their parts under strict FAA and JAA or military regulations. There are marine specific composite pre-preg's that boat makers use to manufacture their hulls that have "out-of-autoclave" cure cycles. There are benefits and drawbacks to these composite pre-preg's, mainly they are good at handling moisture but they have a very low glass transition temperature (T_g).

[fade]

stressed panels on a steel frame. spacecoque

[MalcolmG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bertie:
Incorrect but keep guessing.
We found that if you buy the right carbon prepregs you dont need an autoclave, simply an oven or a heat gun (for smaller parts) will do the trick. Many prepregs are specificaly designed for vacuum only oven cures. how do you think boeing and airbus do most of their parts??

I also dont like the crap people are spinning about repairing CF chassis being hard. gimme a stanly knife, some sand paper, wetlayup kit and some bog you'd never tell if i'd repaired a section of tub, and you would be supprised at what can be done in a night by yourself.

It really isnt that hard to make a CF monocoque chassis, you just need the full support and help from your team. If some ppl are against it and dont help with even the basics like sanding and sanding and sanding then your gunna struggle. Man power is the key to a good chassis. </div></BLOCKQUOTE>

so you're saying that you believe you can build a monocoque out of pre-preg composites, simply by heating the monocoque if a large oven, and that this would be superior to a well made space-frame? While I fully agree that doing sidepods, ducting, or other non-structural pieces this way is perfectly acceptable, I wouldn't want to risk it on something as critical as a monocoque; but if you've done it before successfuly then I'm clearly overly cautious http://fsae.com/groupee_common/emoticons/icon_smile.gif

I didn't say that repairing damage to a small area of a monocoque is hard, but rather that if something wnet horribly wrong, eg someone didn't remove backing paper from a couple of big pieces of laminate (it does happen, many composite part manufacturers have a guy whose job it is to check this hasn't happened), then it's potentially going to be very dfficult to repair.

Bertie, I take it from your first comment that you're from UWA?

[RiNaZ]

I think in FSAE, much of the rules in composites can be simplified, and that includes not using autoclave for your parts.

When you take autoclave out of the equation, you're probably gambling your parts with unsupervised heat and pressure management. And if it's bad enough, can lead to 'surface pitting' which can greatly reduce your tensile strength and more importantly, can lead to delamination.

Having said that, yes, i do think you can do a full monocoque w/out autoclave and still be superior to a well made spaceframe. Ive done structural parts w/out an autoclave, and so far hasnt been any complain yet. I also did HANS device worn by John Force ... and so far no complains yet. I havent done any test on parts with and w/out autoclave but it should be very obvious on how well your part is with an autoclave.

In composite, you can do great parts with less tools if you have the TIME. Experience helps too. So if you have the time to be very detail in making your monocoque, then it shouldnt be a problem. As long as you can make your chassis not delaminate, then you guys should be good.

p/s: as a good rule of thumb, always refer to your fabric manufacturer for details. Info from others are good, but you cant beat the ppl who produced it.

[Bertie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
so you're saying that you believe you can build a monocoque out of pre-preg composites, simply by heating the monocoque if a large oven, and that this would be superior to a well made space-frame? While I fully agree that doing sidepods, ducting, or other non-structural pieces this way is perfectly acceptable, I wouldn't want to risk it on something as critical as a monocoque; but if you've done it before successfuly then I'm clearly overly cautious http://fsae.com/groupee_common/emoticons/icon_smile.gif

I didn't say that repairing damage to a small area of a monocoque is hard, but rather that if something wnet horribly wrong, eg someone didn't remove backing paper from a couple of big pieces of laminate (it does happen, many composite part manufacturers have a guy whose job it is to check this hasn't happened), then it's potentially going to be very dfficult to repair.

Bertie, I take it from your first comment that you're from UWA? </div></BLOCKQUOTE>

Yes Malcom your powers of deduction are strong it seems. I am from UWA and was "The" chassis guy last year.
Well fuk me if i'm wrong but if i recall correctly our 06 chassis was the stiffest SAE car ever seen on goodyear's SPMM rig, being stiffer than cornell who run a space frame. Clearly your team (after speaking to some of your 3rd years at the Oz comp after party last year) get all its high temp prepreg for free and free autoclave time. In western australia we dont have an autoclave big enough to make a chassis let alone a side pod, and we have to pay for materials.
Oh and when was it that Auckland last beat UWAM???? i forget.
I hope it doesn't scare you too much but all of our cars have used maring grage composites, coz we have to pay for them. However if you relised the maount of testing and number of theses done on composites for our cars we have been cautious and satisfied any fears beyond any doubt.

Nah big repairs like that aren't much harder. you just need to have the skills to pay the bills http://fsae.com/groupee_common/emoticons/icon_smile.gif Plus i do know about plastic backing being left behind. i had to repair our car 2 days b4 comp last year. took me about 6hrs to replace the insert that failed coz a 20cent piece of backing was left on, but it was in the most critical and heavily loaded spot on the whole car. The next person to do so cops a pineapple. with no lube. so it aint gunna happen again.

Ok TG you got me there. Many parts are made with the autoclave at boeing and airbus, but many parts nowdays are moving towards resin sytems that can be ovencured, particularly for the new 787 and the new A3?? cant recall the number. I should know coz i was working for a company with strong links to EADS, the guys who own airbus and eurocopter.
Having a lower Tg just means you have to design to avoid heat build up inside rear cowlings, and to use appropriate insulation.

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bertie:
Many parts are made with the autoclave at boeing and airbus, but many parts nowdays are moving towards resin sytems that can be ovencured, particularly for the new 787 and the new A3?? cant recall the number. I should know coz i was working for a company with strong links to EADS, the guys who own airbus and eurocopter.
Having a lower Tg just means you have to design to avoid heat build up inside rear cowlings, and to use appropriate insulation. </div></BLOCKQUOTE>

They might be switching over for non-critical parts, like those in the cabin. But for structural parts, I think aerospace composites will always be made in the autoclave, considering the cost of having any extra weight in the structure per mile flown. I know that some of the worlds largest autoclaves were constructed to produce the body and wings of the 787. Airbus is moving towards the use of thermoplastic reinforced glass in their structures and I am unaware of a structural thermoplastic (PEEK, PPS, etc.) that does not need an autoclave to process.

insulation = weight... I'd use a high temp composite around high temperature parts and lower temp elsewhere. For example, I noticed that the UWA uses some pretty heavy insulation on the a-arms around the exhaust. Those parts aren't all that large, I don't see why you guys don't go ahead and use high temp pre-preg for those at least and get rid of the insulation.

[PaulR]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by TG:
]

insulation = weight... I'd use a high temp composite around high temperature parts and lower temp elsewhere. For example, I noticed that the UWA uses some pretty heavy insulation on the a-arms around the exhaust. Those parts aren't all that large, I don't see why you guys don't go ahead and use high temp pre-preg for those at least and get rid of the insulation. </div></BLOCKQUOTE>

Well spotted TG. our 05 car used some petty bulky insulation. 06 used partial chromoly wishbones near the exhaust and just some gold reflective tape on the opposite side. High temp resins are high on the list of options for 07.

[repeatoffender]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bertie:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
so you're saying that you believe you can build a monocoque out of pre-preg composites, simply by heating the monocoque if a large oven, and that this would be superior to a well made space-frame? While I fully agree that doing sidepods, ducting, or other non-structural pieces this way is perfectly acceptable, I wouldn't want to risk it on something as critical as a monocoque; but if you've done it before successfuly then I'm clearly overly cautious http://fsae.com/groupee_common/emoticons/icon_smile.gif

I didn't say that repairing damage to a small area of a monocoque is hard, but rather that if something wnet horribly wrong, eg someone didn't remove backing paper from a couple of big pieces of laminate (it does happen, many composite part manufacturers have a guy whose job it is to check this hasn't happened), then it's potentially going to be very dfficult to repair.

Bertie, I take it from your first comment that you're from UWA? </div></BLOCKQUOTE>

Yes Malcom your powers of deduction are strong it seems. I am from UWA and was "The" chassis guy last year.
Well fuk me if i'm wrong but if i recall correctly our 06 chassis was the stiffest SAE car ever seen on goodyear's SPMM rig, being stiffer than cornell who run a space frame. Clearly your team (after speaking to some of your 3rd years at the Oz comp after party last year) get all its high temp prepreg for free and free autoclave time. In western australia we dont have an autoclave big enough to make a chassis let alone a side pod, and we have to pay for materials.
Oh and when was it that Auckland last beat UWAM???? i forget.
I hope it doesn't scare you too much but all of our cars have used maring grage composites, coz we have to pay for them. However if you relised the maount of testing and number of theses done on composites for our cars we have been cautious and satisfied any fears beyond any doubt.

Nah big repairs like that aren't much harder. you just need to have the skills to pay the bills http://fsae.com/groupee_common/emoticons/icon_smile.gif Plus i do know about plastic backing being left behind. i had to repair our car 2 days b4 comp last year. took me about 6hrs to replace the insert that failed coz a 20cent piece of backing was left on, but it was in the most critical and heavily loaded spot on the whole car. The next person to do so cops a pineapple. with no lube. so it aint gunna happen again.

Ok TG you got me there. Many parts are made with the autoclave at boeing and airbus, but many parts nowdays are moving towards resin sytems that can be ovencured, particularly for the new 787 and the new A3?? cant recall the number. I should know coz i was working for a company with strong links to EADS, the guys who own airbus and eurocopter.
Having a lower Tg just means you have to design to avoid heat build up inside rear cowlings, and to use appropriate insulation. </div></BLOCKQUOTE>

Wow what hospitality from a member of UWA! Why does that not suprise me!

If i was your team manager i would be giving you the first pineapple with no lube treatment right now considering the utterly discusting representation of such a 'professional' team. I know you guys pride yourselves on such a reputation.

Lastly seeing as your throwing punches for no reason, or are you upset because someone has released 'private' information, why would you guys consider comparing your yellow submarine with cornell's car? I could be mistaken, so please correct me if im wrong, but you have never won a detroit competition have you? Im sure they dont go round claiming they have the STIFFEST 'coque,' excuse me, 'spaceframe' now do they!

[MalcolmG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bertie:

Yes Malcom your powers of deduction are strong it seems. I am from UWA and was "The" chassis guy last year.
Well fuk me if i'm wrong but if i recall correctly our 06 chassis was the stiffest SAE car ever seen on goodyear's SPMM rig, being stiffer than cornell who run a space frame. Clearly your team (after speaking to some of your 3rd years at the Oz comp after party last year) get all its high temp prepreg for free and free autoclave time. In western australia we dont have an autoclave big enough to make a chassis let alone a side pod, and we have to pay for materials.
Oh and when was it that Auckland last beat UWAM???? i forget.
I hope it doesn't scare you too much but all of our cars have used maring grage composites, coz we have to pay for them. However if you relised the maount of testing and number of theses done on composites for our cars we have been cautious and satisfied any fears beyond any doubt.

Nah big repairs like that aren't much harder. you just need to have the skills to pay the bills http://fsae.com/groupee_common/emoticons/icon_smile.gif Plus i do know about plastic backing being left behind. i had to repair our car 2 days b4 comp last year. took me about 6hrs to replace the insert that failed coz a 20cent piece of backing was left on, but it was in the most critical and heavily loaded spot on the whole car. The next person to do so cops a pineapple. with no lube. so it aint gunna happen again.
</div></BLOCKQUOTE>

I didn't come onto this forum to have pissing contests with other teams, I came to learn from the experience of others, and help where I can by offering the experience that I have. I wasn't attempting to bad mouth your team or your car, and if you took it that way then I'm sorry, but as has already been said, your response reflects poorly on your team, and if anyone from UoA made a post like yours they would be in for an earful from myself for damaging the reputation of our team.

For what it's worth, we certainly do not receive our composites materials for free, and never have done. We pay trade prices for all our fibres and pre-preg, the only thing we get for free is autoclave time. Whoever told you that we get free materials was obviously mistaken - in fact nearly a quarter of our budget for car development this year is allocated to composites. Interestingly it was someone on your team that told our old composites guy about using compressed air to apply pressure to pre-preg parts as I had mentioned in my first post - goes to show that you can't necessarily believe everything your hear from teams.

[Moke]

Wow Bertie, that's really uncalled for. But I'm guessing that you were kinda angry by the spelling mistakes.

Malcolm didn't say that we are better than you; he just stated a reasonably well accepted fact that autoclaved composites exhibit better mechanical properties. We too have undertaken research that supports these claims. And as a team we will manufacture accordingly. So in just our 3rd year of coque design (you're in what year?) we will go with what we know.

I guess that we are just luckily that in a country, 9.8 times smaller your state, we have many autoclaves, I can name 6 in Auckland alone. But with no aerospace industry, why so many you ask? Marine industry is big, so maybe someone in Western Australia makes masts and might have an autoclave.

For any other UWA members out there:

The really sad thing is every time someone convinces me to give you UWA guys the benefit of the doubt, one of you gives me a better reason not too. I really don't want to tar you all with the same brush. I admit you guys are good but you don't need to be cocks about it.

[Gurkaran]

Malcolm,

This thread really has gotten out of hand. Bertie was the 06 chassis man, he is a composite genius...but a communication nightmare. He has a very colorful style as can be attested by our team. I think he was just defending his work on our car and what UWA believes about working with composites. Our team members are rightfully passionate about our cars, but occasionally it goes a bit far. I do apologize for any offense caused by the comments.

Obviously there are some people who look for a reason to go UWAM bashing, and we have to cop that, but people have to remember that the students come and go, and we aren't as arrogant as our reputation suggests. I hope when we meet at comp there won't be an ill feeling between our teams, because there certainly won't be from us.

Consider the pineapple applied.

Cheers,

Gurkaran

[MalcolmG]

No hard feelings at all mate, maybe after the comp this year we can put our monocoques into a ring together and let them battle it out to find out whose is best http://fsae.com/groupee_common/emoticons/icon_wink.gif