tschmidt

My Feedback: (1)

What materials are you all using when molding fuselages to obtain best weight and strength? I know this will vary depending on the application. I did this lay up this past weekend and am kind of dissapointed in the overall weight. This fuselage is for my 2M pattern ship which can weigh no more than 11 pounds ready to fly. This fuselage came out 32oz and really should be around 27 or 28 max.

Here's what the layup consists of:

Main Fuselage
1st layer: 3.1oz crows foot cloth
2nd layer: 1.7oz kevlar form center to tail post
3.5oz carbon cloth from center to nose ring
3rd layer: 2oz cloth over the carbon area
1/8" thick 3/4 pound foam covered with .75oz glass cloth

Canopy hatch and chin cowl,
1st layer: 3.1oz crows foot glass cloth
2nd layer 3.5oz carbon cloth

Any suggestions would be greatly appreciated. One area I thought of would be to reduce the 3.1oz crowsfoot to 2oz cloth. Any idea how much weight that would save?

Thanks,
Todd

soarrich

My Feedback: (98)

First, nice fuse.

You have to lose 5 oz., what jumps out at me is do you really need so much in the canopy? is it structural? If not 3/4 oz and 2 oz might save some there. The chin cowl same thing.

>Canopy hatch and chin cowl,
>1st layer: 3.1oz crows foot glass cloth
>2nd layer 3.5oz carbon cloth


Is from the firewall forward is cosmetic? Or is the motor mounted to the nose ring?

Do you need the carbon from top to bottom back to the main wing tube, maybe a triangle of CF from the firewall back to the wing tube.

>1/8!QUOT! thick 3/4 pound foam covered with .75oz glass cloth

Is this for sound deadening or for strength?

I don't like to mix fibers, the carbon is going to be carrying the load, the glass seems to be just along for the ride. Why not 3/4 oz glass for pinholes, then use a layer of 3.5 oz CF, with extra layers where needed?

ptxman

My Feedback: (2)

Your layup schedule doesnt sound much different than what I ended up using towards the end on a similar application. My memory is getting very foggy but I do recall 9.3 pound models back in the YS-140 days & probably with a big area wing by todays standards. I suspect the rules are still 5.0 kg max? Anyway my first layups were 3 oz s/w with 6oz on the main fuse. The canopy & bellypan were both 3 + 4 because they are just going along for teh ride. (I kept on using 3 oz only because I realy liked the cloth & had a roll to use up. They layup components were not pre-painted but were pinhole free, pretty good overall but I wanted more rigidity for the 4-banger washing machines so I went to 3 oz glass + 4 oz CF on the fuse with either foam or balsa sandwich in the aft similar to what you are doing.

Basically you have better materials going for you now than what I was doing. It could be that the devil is in the details, meaning resin use. Its amazing how even a dry looking layup can get some more resin coaxed out of it by careful squeegee action. Fillets especially are a weight culprit & should be neat & minimal, say 1/16" radius on 90 deg corners. Better yet, CF tow. I cant see much resin getting into your foam assuming its polystyrene? Rohacell & other urethanes are a bit more resin hungry but not that bad relative to balsa. Its a good idea to chamfer the edge so teh inner cloth transitions over the edge without void whih can potentially fill with resin along the edge.

That said, it took me some learning & practice to get the hand layup technique down, but these days I would not consider anythng other than vac bagging with peel ply. Its mindless, you resin the cloth, apply the peel ply (=light weave like 2 oz max) & wick, clos eteh bag & turn on the pump & it does all the work for you consistently & faithfully every layup. All that extra resin is evident in the disposed wick layer. Its truly amazing evenwhen you think you've pulled out too much resin already. Any of the high performance (we're talking gram shaving) performance models like F5B & F5D are done this way. If you havent played with bagging yet, I encourage you to. It is the final step of the Jeti Knight Composites Master I can send you some good links if you are interested.

esamart

Kevlar on rear fuselage does not give much stiffness weight wise even with glassfiber. Full fuse lenght of 3,5 Carbon gives enough strenght for these rather thick F3A fuselages to withstand manouvers. But vibration of combustion engines was and still is a designing criteria and many places needed some sort of strenghtening. Canopy area and wing tube? So what power is this for? Groundhandling in another. If you make yourself or for sale. Foam sandwich is really good for thick fuselages on all aspects.

Please install this fuselage 90 decrees thru wing tube and start putting plastic bags filled with sand above and measure how it bends and perhaps where it breaks.

Edited: Of course formers inside should be there. And why wing tube is that on snaproll there is most G forces.

Magne

Hello.
A rough rule of thumb regarding resin consumption.
This is based on product catalog from R&G in Germany:

Glass: 0.8 parts epoxy to 1 part cloth,
Carbon: 1.15 parts epoxy to 1 part cloth,
Kevlar: 1.4 parts epoxy to 1 part cloth, all by weight, for hand laminates with 35 % fibre content by volume.

In my own (fairly limited) experience, these "targets" may be somewhat difficult to achieve unless you use vacuum and go very carefully on the epoxy.

My own modified rule of thumb is:

Glass: 1 part epoxy to 1 part cloth, (i.e. 1 sq. yd. of cloth weighing 3,2 oz would require 3,2 oz of epoxy.
Carbon: 1.4 parts epoxy to 1 part cloth,
Kevlar: 1.8 parts epoxy to 1 part cloth.

By making some very rough estimates of your cloth consumption, I believe that your resin consumption has been a little too high. I would therefore focus on this, rather than try to reduce the cloth thicknesses.
Do you know how much resin you actually used? (I sometimes note down the total weight of the mixed epoxy, and then I weigh the left-overs after the job is done. Gives an indication of what actually went into the molding.)

(I may be wrong.)

Magne

Marco Vergara

Ptxman, I would like to see those links, I have used the vacuum bagging technique in hollow core wings but I want to try the technique in composite fuselages.

Marco

ptxman

My Feedback: (2)

some related links
http://www.rcgroups.com/forums/showthread.php?t=229462
http://www.rcgroups.com/forums/showthread.php?t=141255
http://www.rcgroups.com/forums/showt...highlight=jibe

which originally I mentioned here in post #6
http://www.rcuniverse.com/forum/m_40...tm.htm#4093308


Here is another link to a short video which is very interesting. It pertains to wings, but not too much difference in technique to fuses. Somewhere in there one of the guys is offering a burned dvd of teh movie clip for very reasonable cost (because it’s a big video in terms of posting on a group) & I think there was some discussion for a followup on fuses.

http://www.rcgroups.com/forums/showthread.php?t=392045

tschmidt

My Feedback: (1)

Thanks everyone for your information its greatly appreciated. As mentioned and I agree, one area is to reduce the amount of carbon fiber in the nose. I'm going to reduce the cloth weight from 3.5 to 2.9oz. and not cover as much area. I feel some is needed because I'm using a YS160dz with a nose ring mount and the vibration can really take its toll. I'm also going to reduce the first layer of glass from 3.1 crowsfoot weave to 2.0 regular weave glass and carry the foam into the top deck of the fuselage. It's really amazing how stiff the foam covered areas are. The foam also seems to help with vibration too.

Chin cowls on these pattern ships take a beating, especially when using a soft mounted 4 stroke (I think kit producers should include two with every kit) so it needs to be strong. The chin cowl I layed up only weights 2oz and is pretty strong, so I'll probably leave it as is.

Vacuum bagging is something I'd like to learn more about, I've tried before but was not able to get good results and gave up. I need to take the time and do more research, so I really appreciate the links given on this thread ptxman.

I'll let you all know how the next fuselage turns out.

Thanks again everyone!

Todd Schmidt

Magne

Todd.
Because of the special shape of your fuselage, I think you will have some difficulty continuing the foam into the top deck of the fuselage, at least in one piece.
(Assuming you are not using vacuum to hold everything in place, but even then, laying up would be a challenge. I would suggest making the foam in two pieces for each fuselage half, one piece similar to what you have now, and one separate piece for the top deck. The area with the longitudinal "ridge" will be stiff enough anyway, without the foam sandwich.
Do you think that the top deck is too soft now, without the sandwich?
Regards,
Magne

tschmidt

My Feedback: (1)

Hi Magne,

The fuselage shape didn't help as much as I thought it would. I wish I would have gone all the way up because its a little more flexible than I'd like. Not bad, but If I'm going to use a lighter cloth I think maybe it would be good to up on the foam. I have a vacuum bagging system and will use it to hold the foam down. Hopefully it all works out okay!

Todd

ptxman

My Feedback: (2)

some discussion on vac pumps & methods here

http://www.rcgroups.com/forums/showthread.php?t=445343

SCALECRAFT

My Feedback: (13)

In my layups I have noticed that ambient temperture affects my layup weights. Cold days yeild a heavier part. Cold epoxy thick like honey. Warm days thin easy to work epoxy needs less. . Composites wet out faster.

Of course, the other side of the spectrum if epoxy is warmer, less work time.

Just something to consider.

Steve