Glass vs. build up
 

how much weight could I save if I made a fuse of fiberglass as opposed to built up. I know the work is tremendously tedious, but what I'm looking for is finished performance. The model is a scratch built F4 phantom. roughly 58 inches long with about 45 inch ws. (measurements are rough because I may make some adjustments.) I am going to make ducting for DF version, and an interchangeable nosecone as the plane will be a propjet to start. when my thumbskill is adequate I'll convert it to DF.
the ducting in place will act as a cooling tunnel for batts and so forth. I have drawings that are fairly close to scale.

Glass vs. build up
 

In my opinion, the weight savings isn't huge, but you'll definatly have a nicer surface with glass. You'll either use a little more glass to get the rigidity, or you'll use light glass, but with a handfull of formers to get the same rigidity. Either way, unless you're a pro at composites, the weight difference will be negligable.

So what are the specs on the plane? What size engine are you putting on/in it? I'd go right for the DF and forget about the prop. But that's only if you've got some experience flying. By the way, if you have a lot of things in the ducting (i.e. batteries, etc...), you could be inducing a lot of drag.

Just my $.02 worth


Russ
Oakdale Aircraft

Glass vs. build up
 

The only thing Im planning to put in the ducting is the batt. The length is between 58 and 60" and the WS is probably gonna be around 45". I'm shooting for an AUW of 10-11 lbs. Wings will be sheeted foam. don't know if Ill use mechanical or pnuematic retracts. As far as the engine goes, Im gonna try the prop first. in the design, I'll lay up 2 nose cones. One for the prop engine, and one for the DF conversion. when Im ready to upgrade I should be able to dismantle the prop engine and install the nose cone with the batt tray and reciver tray in it. then Ill pop the hatch and insall the fan and motor. It will probably be alot of work, but Ill only need to lay up one fuse. I may experiment with different size wings also. But, Its in the thought phase now. I am deffinitely gonna start the plug in the next couple of weeks.


BTW the prop engine Im looking at is the G-90, and the DF is OS 91 with Dynamax fan. Dunno which pipe yet or which version of .91 Ill use.

Glass vs. build up
 

Well, if it were a normal "box" fuselage I'd say it's not worth the effort to make a glass fuse.

But with the curves on the F4 you'd have to either cut a lot of round formers and bend sheeting around it or use thick wood and big sticks for corners to get the shape.

My opinion is buy a kit. :D

Glass vs. build up
 

no fun in buying a kit. I am looking for a long project with different aspects, so I can learn more. cutting formers and the like is failry simple, so what I am debating on is whether to use balsa block or foam between them.

Glass vs. build up
 

I will add: balsa if quieter in flight, balsa dampens vibration better than glass, and balsa is easier to repair. All IMHO :)

Glass vs. build up
 

I understand the tensile differences between the two. My question is this, how much WEIGHT would I save in the process. I do plan to build a few of these for personal reasons.

Glass vs. build up
 

Octane,
I dont believe anyone can give you any real info on possible weight savings because no one has any idea about your skills.

If you build it up it can get real heavy unless you can keep the former count low and minimize the use of ply except in the high stress areas. You have to be smart about where the wood is going. Example; a top quality aircraft grade 5-ply 1/8 thick is usually stronger and lighter than a cheap grade 3-ply 1/4 thick that is commonly found on the LHS rack.

As for laying one up I have to agree with Russ's comments. But if your really good you may be able to save 4-8 oz by using fiber-glass. From what I have experienced, generally the larger the model the greater the possibilty to save weight by using composites.


Since you plan on building more than one, why not build one up and lay up another. For the glass fuse you might consider the lost-mold-method aka investment casting. Make a mold from foam and lay the glass over that. Then cut and melt the foam out.

Cheers.
James

Glass vs. build up
 

Glass covered hollowed out blue foam might be an option to consider. One of my buddies built a C130 with 6' wingspan, powered it on those little GSW motors swinging a 4 blade prop.
It sands nice, take glass with some Zpoxy. You leave a 1/2" - 3/8" wall thickness with an oz of glass over it, paint it with acrylic and you'd be there.

Glass vs. build up
 

Make your mold out of pink or blue foam and sand it smooth. Then try glassing scrap pieces of foam using 1.8 or 3.6oz/SQ Yd E or S glass cloth,experiment with both using small pieces. Once you decide on the cloth, you want to use you could do one of two things . 1. cut the mold in half and then coat it with expoy resin and then mold release to made two matching halfs and then be able to make more fuse's. 2. coat the mold with a light coat of expoy resin then lay some glass and add another coat once it dries and add more till it feels strong enough, then just use acetone to melt the foam inside your fuselage, you end up with a hollow fuse.


Hope this helps, you may want to look at Ezone for more tips in the foam section under Electrics.


Mike

Yep
 

I agree that you won't typically save much weight over a built-up structure. (The percentage, or even an accurate estimate of what you would save, is impossible for us to predict... It really depends on too many variables in the way you build.)

The main thing that makes glass work worth it to me is repeatability. Once you've made molds, damage and crashes become much less heartbreaking.... More of an inconvenience. Especially true if you've done panel lines, rivets, and all the other stuff that can go on a glass part.

Keep us informed, if you proceed with your F-4. Good luck.