Large Model Association Forum

Hi,

I have a small idea I am testing out, in theory it should work, a Carbon fiber composite crankcase to save weight on a brick of a 3W 240, the DA 200ML has shown that magnesium is too soft for the job.

Does anyone know a good UK sourse of high temp epoxy? I think I need something that is OK to about 500°F rather than one of the crazy expensive 700° versions that F1 teams use. I can't see a crankcase on a big petrol plane passing that temperature, it would most likely stop working first from overheating. Normal max temp is around 300° F which is way too borderline for normal epoxies.

Preferably one of the newer polymer epoxies that cure at slightly lower temperatures as I will be using my oven as an autoclave.

Also any advise or experience on using or moulding carbon for high temp applications would be appreciated.

cheers

Kate

JB Weld is rated at 550degF

John Rickett wrote:JB Weld is rated at 550degF

cheers, but not what I am after. Normal epoxy resin has a much lower continious heat rating.

I was after a laminating resin, you know, the kind of thing you put under pressure and cure at high temperatures, I doubt a JB Weld crankcase would last long enough to even machine the bearing seats or be lighter than the original.

Hi Kate, I think that an advanced aerospace resin may be the answer.
Lots of good knowhow here.
http://www.shadowaero.com/TECHNICAL.htm

Tony.

i have a lot of experiance in machining carbon fibre for F1, we deal with a company called Tricast Composites, in rochdale, they have all the facilities for making whatever carbon lump you require, if you wish, i will talk to them, or you can ring up, ask for Steve, and tell Steve its through Alan Cantwell from Dawson Presicion, they could welll advise you as to what you need, carbon, or some sort of resin,

just a thought, how will you put inserts into the block to take bolts to take the assembly screws, they have to be cast in place at the outset of the molding, carbon, or resin does not tap, also, not knowing of your skills, but you sound ok, have you machined carbon or resin before? we use cast iron tips, and diamond tips to machine the stuff, its quite a high attrition rate, then there is the inhalation of swarf and dust, my CNC is enclosed, om some of the stuff for F1, i cannot use coolant, and actually have to wait 5 mins for the dust to settle before opening the doors!! even then, i wear a suitable mask,

Thanks, Tony and Alan,

Great help, I will check out those sources out.

I had assumed that I would have to make a mold that would act as a jig for the thread inserts. As for machining, whle i have access to a home made CNC and a small hobby lathe that will do to make a prototype or 2 ( or 5), the final item would probably have to be subcontracted.

I have had this idea for a while, but was more concerned with the heat disipation and getting around the galvanic corrosion issues.

Kate

i know nothing about the last bit, i am only a machinist, but about the inserts, i doubt if they will stay in place to be drilled and tapped in situ, i think they would be better done first, and set into the molded unit, perhaps tricast could advise in this, one thing though, this carbon making stuff aint cheap, the forumla 1 parts i do are multi weave units, and cost a few hundred quid a time, would it not be feasable to just machine what you have and make it lighter? reduce wall thicknesses, shave some off the heads, i know that my 3Ws are lumps, and have looked at ways of reducing one of them, but, its weight in the right place, up front!!

3W engine casings are not heavy, it's the crank & other parts that are the heavy items because of the dynamic balancing that the engine has to reduce vibration. Should you start shaving off weight from those parts then the balancing will have to be reviewed.
Cary

The engine is for an aerobatic plane, so all weight loss is important. if it was a warbird I wouldn't care. I can't afford to buy a 3W 275CS so I am stuck with using this. I bought a 240cc 3W because at the time I lived in a country with a 25 kilo and 250cc limit before needing an exemption certificate. I can lighten the cylinders to remove some weight, but I need to lose more really. It is a total brick.

I also have a DA200 ML sat here that still needs a new crank, Don't they all? that may make a better test subject due to the way the case is split and the parts being much smaller and simpler in shape. They charge a fortune for them and sell them with zero warranty because the magnesium case is just too soft. Every 200 ML sold in France has damaged its crank, some 2 or 3 times, yet there are plenty of aluminium cased ones still running. The case replaced in carbon composite would be many times stiffer, though probably no lighter than the magnesium ones.

As for the resin, I know the resin F1 teams use has an insane cost, 300£ a lb or something bonkers like it. But it is way over spec for my needs.

I admit to having never taken anything more than the carb intake casting off my 3W, but even replacing a simple piece like that could save quite some weight. it is way way heavier and stronger than it needs to be.

Hello Kate. I am currently building a carbon-fibre based racing sportscar (own design). We use machined dural 'bobbins' to accept the various threads in the chassis. These are bonded into the carbon panels using a high-specification adhesive. Where high temp's are involved, it's best to source the carbon and the adhesives from the same supplier group as the right chemical mix is crucial. I use Technical Resin Bonders /Amber Composites based near Cambridge. For the curing process(es) at Airbus, we used ovens with closely controlled ramp-up and down times. Your supplier should be able to give you temperature graphs and you may have to adjust accordingly by hand on your oven. Another tip is to wind strands of Kevlar (Aramid) around the bobbins before inserting them. This gives extra shear strength and should help to prevent them unwinding in use.

Hope this helps !
Dave