Chassis design using honeycomb core

Hi everyone,

I've been designing a chassis for a project I've got on my hands. The car, when finished, will be a summer daily driver. Until recently, I was convinced that the only practical alternative for the project was a space frame. I came across some information on honeycomb that has really piqued my interest. The material seems perfect for the type of vehicle I'm working on, but I have a few questions I can't find answers to. With all the varied and knowledgeable forum members, I figure someone has the answers.

First, how durable are chassis using honeycomb panels and epoxy? I'm looking for the chassis design to last atleast ten years of 'normal' driving. Can I depend on the (properly created) epoxied joints to stand up for this length of time? I know riveted structures tend to loosen some over time. Does the same happen for epoxy joints?

My present thoughts are to have front and rear space frames for the suspension/engine to attach to, that simply bolt up to the honeycomb chassis. This seems like a more durable setup. Am I just as well off going full honeycomb?

Any references out there that talk more about all the ins and outs of chassis construction with honeycomb? I've looked a fair amount, but have found little in the way of details. I've run across one reference that talks about proper reinforcement of epoxied seams and dealing with 'point' loads applied to the chassis (Tony Pashley). It would be nice to have corroborating info.

I'll keep combing the 'net for info, but any help would be greatly appreciated.

Aaron
 
Hi Aaron,

My intial thoughts had been to go down this route as well and I came to the same conclusion as yourself below too...

My present thoughts are to have front and rear space frames for the suspension/engine to attach to, that simply bolt up to the honeycomb chassis. This seems like a more durable setup.
Aaron

What stopped me in the end was trying to get hold of decent reference engineering information. It seems to me the people who know how to do this don't seem too keen on sharing the hard learned knowledge. Which I can understand to a certain extent. There really doesn't seem to be any good books that I could find on the subject either.

I think the best advice is to find a manfacturer of the material who's got good tech support to work with you on how to do things with it.

The other thing is that tube frames are rarely really just a tube frame and properly attached panelling make the things semi-monocoque anyway.

Neil from Race magazine was taking this hybrid approach using sandwich and steel with his project he's gone a bit quiet lately, I hope he's carrying on with it.
 
Aaron, there's obviously a lot of skill and technology behind the use of honeycomb panels - the renouned experts are companies like Boeing and Lockheed who have used this material (both the aluminum skinned and now carbon skinned) extensively in the past. Doug is right - it doesn't seem like these Boeing engineers have written any kind of how to manual unfortunately. I've spent some time with Boeing over the years and have learned a little on this topic and I'll share what little I know.

Basically, the typical aluminum skin honeycomb panel is good only in certain situations. It's great as a bulkhead and can take significant loads on edge (forces applied in the same plane as the panel face) but can't take as much of a load 90 degrees to that - that's why it's great as a bulkhead. The panels are fairly resistent to weather although they are not designed to be "outdoor" panels, meaning, the bonding between the honeycomb and the aluminum skin is very strong and water resistent, but it's not water proof. If you were to use these panels in a chassis you would need an effective way to keep road water and salts off the panels and joints.

I think the most significant point in this whole discussion regarding using these panels is that they need to be properly affixed. To be specific, you need to attach the panels in particular ways that reflect the panels physical properties. What this means is that you simply cannot rivet or screw the panels together and apply a little epoxy and expect it to stay together - it won't. The aluminum skin is too thin for rivets or screws to bite and you can't bolt through the panel - it will simply crush it. If you bond with epoxy the point load on the skin has to be quite low as the skin will tear away from the honey comb.

Boeing has used these panels in the manner in which you are describing by utilizing complex filleting - either add'l layers of aluminum bonded to the joints (so the load is spread across a larger area) or machining a fillet out of aluminum into which the panel fits and then bonding and through bolting (the panel won't crush because the machined fillet takes the load). However, with all the filleting calculated into the total weight you're only saving a modest amount of weight over spot welded steel panels frankly.

Back in the 60s Ford commissioned an aerospace manufacturer to do exactly what you're thinking about doing - build a honeycomb paneled GT40 chassis. It wasn't very successful over the long haul because of problems with the joints.

You certainly wouldn't want to try to bolt suspension pieces up to a honeycomb panel, even with add'l reinforcing - you're asking for catastrophic failure at speed.

Boeing is now using honeycomb panels with carbon skins. These are used in limited applications such as exterior panels for flight surfaces and such - they are made in the shape of the flight surface and bonded in a complex manner to the underlying structure - this is beyond the skill of the average DIY guy.

I hope the above is helpful. I realize it may not be that encouraging however.
 
I may not have the whole story correctly in memory but didn't Ken Miles perish in the crash of one of the experimental honeycomb chassised J-cars? Was it that the car came apart in the crash or was it because the structure failed that it crashed in the first place?
Either way,something to think about as you're cruising along at 160mph or so. A.J.
 
"Boeing is now using honeycomb panels with carbon skins. These are used in limited applications such as exterior panels for flight surfaces and such"

Cliff,

I respectfully beg to differ, the 787 will be 50% advanced composites.

The Dassault Falcon 7X will also feature them;
Hexcel.com - Press Release

Ask me how I know...;)


..................................

Aaron,

I see by your profile you are a mech engineer.

Advanced composites are the future.

Take a look at the McLaren F1 or more recently the Porsche Carrera GT.

A great article follows;

Carbon fiber race car technology hits the streets: COMPOSITESWORLD.COM

You will not find much accurate advanced composites tech on this forum, yet.

Advanced composites certainly are not chopper gun fiberglass.

TSC currently has a C/F monocoque chassis under development.

Call me for a chat sometime and we can discuss your build options / how you wish design it.

Best regards,

Scott Calabro
 
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I wrote an article incorporating attaching panels for the GTD40 Car Club. It included rivets and epoxies. Not real heavy in engineering though. It might be here on the forum somewhere. I am no engineer and do my best work in the operating room. In my research I found that epoxies are used by the trucking industry in the assembly of the trailers along with rivits(solid). If you do a search on the web on epoxies I am sure you will find a wealth of information today. My article was written a year or so ago and I am sure there is more out there.

Bill
 
"Boeing is now using honeycomb panels with carbon skins. These are used in limited applications such as exterior panels for flight surfaces and such"

Cliff,

I respectfully beg to differ, the 787 will be 50% advanced composites.

The Dassault Falcon 7X will also feature them;
Hexcel.com - Press Release

Ask me how I know...;)


..................................

Aaron,

I see by your profile you are a mech engineer.

Advanced composites are the future.

Take a look at the McLaren F1 or more recently the Porsche Carrera GT.

A great article follows;

Carbon fiber race car technology hits the streets: COMPOSITESWORLD.COM

You will not find much accurate advanced composites tech on this forum, yet.

Advanced composites certainly are not chopper gun fiberglass.

TSC currently has a C/F monocoque chassis under development.

Call me for a chat sometime and we can discuss your build options / how you wish design it.

Best regards,

Scott Calabro

Hi Scott,

I didn't make any reference to the 787 - you did. I merely indicated that "Boeing is now using honeycomb panels with carbon skins. These are used in limited applications."

Here's how I know: my company makes an advanced inspection system for Boeing to test the structural integrity of these very panels.
 
One of the first, if it wasn't the first roadcar, with Carbonfiber chassis, is the BMW Z-1 and as far as I know they also had Honeycomb in it.
Maybe worthwhile to find out how they did it.
 
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Arking..log on to www. ferron.nl...click English ..then click news..I,ve been following this for some time a little slow but the results look very impressive.
 
Thanks for the replies everyone. I appreciate your input.

There are references, like Carol Smith, who really don't like the idea of using this material. He specifically mentions the GT40 Mark IV as being a very difficult chassis to work with.

The only informative book I've been able to find is Tony Pashley's "How to Build Motorcycle-engined Racing Cars." In it, he talks about adding fillets and other reinforcements, though no real numbers to back up anything.

It's a tough call on whether to use the material or not. I suspect I'll simply have to start working with the stuff some and get some experience with it. The link Eddie included shows a chassis pretty much like I envisioned.
 
Hi Aaron, you might want to give the fellas at either RCR or CAV a call as I believe they are both utilizing composites/carbon fiber in lightweight versions of their standard chassis. They've been at it a while so I suspect they can give you very accurate technical information for advanced composites. Their service and collegiality is second to none. Good luck with the project and post some pics! There are a lot of highly talented builders on the forum who undoubtedly have some excellent hands on knowledge of the material and will chime in.
 
Aaron, You might find you will have to make your own honeycomb panels your self. To do it correctly, you have to design in all the locations of inserts and edge treatments. Doing it after take different techniques. I found this out back in the sixties and seventies. In the sixties I was in the USAF and went to the tech. school for composite repair. I believe I was the first to male a honeycomb racing rowing shell in 1975. I used Hexel HRH-78 over expanded arimid paper honeycomb with the thinest woven carbon and Kevlar I could get. It all had to be vac. bagged. Now this type of construction seems to be the standard. It ain't cheap !!
 
Current Lotus chassis are aluminium monocoques where the panels are glued together. Don't know what type of glue is used, but it is orange in colour - I had an Exige and you could see where it had oozed out of the joints. Panels are aluminium sheet and not honeycomp, however. The chassis do seem to hold together indefinitely.

Chris
 
The Mosler MT900 and the DP1 are examples of vehicles that use bonded honeycomb panels for their main chassis construction. The Mosler is currently for sale as a production car and the DP1 is gearing up for production. Interestingly enough they both started out as hobby type "toys" for their makers and turned into a business...

http://www.teklam.com This is the manufacturer of the honeycomb panels used in both the Mosler MT900 and the DP1. I have personally talked to an engineer at the facility in regards to the panels for the same use you are looking into...

Mosler Automotive Have a look around, the chassis for this car is made of bonded sandwich panels (honeycomb core w/graphite faces)

Trenne Technologies - TrenTeck Chassis This is the homepage of the designer of the Mosler MT900, he is a former Corvette engineer

dp vehicle home Click on the DP1 page, go to page 10, scroll to the bottom for a view (this pertains to the use you specified - but really his whole page is worth perving...gearhead porn :D )
 
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From the TrenTek site:

The TrenTek chassis is the world’s stiffest, lightest and most cost efficient car chassis. Made of composite honey comb panels, the TrenTek chassis for the MT900 weighed in under 90lbs, and could be put together, by hand, in approximately 20 minutes, eliminating the need for an expensive assembly line. This chassis is offered exclusively through Trenne Technologies, Inc. and Teklam Corporation.


This highlights the allure of these panels for me. The material is stiff, light, and seem relatively easy to work with. You can cut the chassis components from the large panels it comes in with a (CNC) router and glue everything together. I can TIG weld, but I know I'll get distortions if I make a space frame. The use of honeycomb would get rid of this issue all together. The only downside appears to be cost. This is why I posted the question to begin this thread...I feel like I must be missing something---this stuff seems too good to be true. What's the catch here?

I did look at the Exige chassis. I didn't realize the extent to which they glued that chassis together. This makes me feel a bit better about glued joints.
 

Chris Duncan

Supporter
I've been designing a chassis for a project I've got...

There are references, like Carol Smith, who really don't like the idea of using this material. He specifically mentions the GT40 Mark IV as being a very difficult chassis to work with.

The only informative book I've been able to find.....


Race Car Chassis, Design and Construction by Forbes Aird has several pages on sandwich and composites. The consensus I get from it, difficult and expensive.

You have seen this thread?

http://www.gt40s.com/forum/gt40-build-logs/24086-carbon-gt-mono.html

It's hard to get more specific with what little info you've given about exactly what type of project you're designing.

The GT40 was originally a monocoque and when you copy that shape with tubing it's pretty hard to get torsional rigidity, you need a ground up re-design, just look at the factory 5 supercar. The same would apply with a honeycomb. It would need a re-design.
 
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Hi Kalun,

Yes, a C/F sandwich chassis will look different!

The advantages of one will far out weigh the fact that it would not resemble an almost 50 year old design.

I say it has a certain beauty all its own.

Cheers,
Scott
 
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You could build your own panels. You could vac or press your aluminum face sheets onto aluminum honeycomb. The bond could either be bone with film adhesive or paste adhesive in an oven. Several compaines sell structual closeouts that would allow you to fasten the panels together. If you can design in CAD you could have the honeycomb panels CNC cut with waterjet or a router. Understanding load paths, will drive your design, that will determine core desitiy, thickness and facesheet thickness.

Check out Hexcel and Plascore for your honeycomb. Film adhesive can be purchase in small quantities from companies that specialize in selling hot bonding equipment to the aviation industry. Aircraft Spruce and Speciality has everything you need to start experimenting.
 
I suggest you should think long and hard about using aluminium honeycomb, I decide to have a go at building a GT40 using a honeycomb chassis similar in concept to the Mk4, but with a Mk1 body. That was some time ago and although I am making progress, it is very slow and I keep encountering problems I had never even considered. It is possible, as I know of one that has been built and is use in the UK, but do not underestimate the problems you are going to meet.

Hopefully, one day I will finish the project – but if I were to bend it I have no idea how it could be repaired!
 

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