Piaggio P180 Avanti scratch build previously "Foam choice for a scratch build...

[Wingnutz]

About to start a scratch build from a 3-view...if there are plans out there, I can't find them!
Want to build a foam fuse with glass skin and I'm not sure what kind of foam to use. (I lent my copy of Keith Sparks' book on building foam model airplanes to Andre and he's still in Trinidad)
Formers will be balsa and I'm planning 3or 6" EPS foam wafers between...
Recommendations gladly received!

[Ededge2002]

Styrofoam is light, sands poorly,  cuts poorly and shatters easily.
Styrofoam SM (the pink stuff)  is heavier, tough to sand lightly but removing large amounts seems easier to me,  and is tough as heck.

If your hot wire cutting the pieces than I have no input as ive never done that.

sorry that's all ive got but looking forward to some of the other answers!

[Wingnutz]

Cut some balsa formers and EPS wafers...3" to try the materials and assembly procedure. Glued using canopy glue as recommended by Dave Henry at Pinnacle. Seems to hold, shape and sand okay...suggestions from experienced types appreciated.
Formers are 3/32" balsa sheet and I'm using my magnetic building table so I can keep pressure on the developing fuse while the joints set up. So far I've rough cut the foam with a hand saw which isn't as accurate as I'd like ...I'll probably have to add the cost of a band saw to the cost of this model...will a bandsaw cut 3" foam fairly cleanly or does it just shred the foam?
There's foam snow all over the work area floor already! Have to quit for now, I'm out of balsa.

[Papa]

The band saw will cut very cleanly with an 18TPI blade.

Jack.

[Wingnutz]

Thanks Jack. Are we starting scratch build classes next week?

[Wingnutz]

A few more wafers with Ed's size gauge (Lost the betcha can't have only one bet!) including the first obvious mistake that I've caught.
Used a cut edge for the surface that goes on the plan for wafer#4. It wasn't as flat as I thought and it doesn't sit flush with the table top. I'm going to  leave it for now, try to fill it later and look for a bandsaw so I can cut usable edges.

[Papa]

Can't start the scratch build until the wood kit is available.

Jack.

[Skyking]

I even cut foam with a 3TPI blade.
You will still have dust Bill but it will all be under the bandsaw.

The bandsaw will be useful for other things as well.  (Slicing meat for sandwiches, trimming your fingernails and toenails,
cutting off your ring like Simon had to do, Resizing your cat etc) You will wonder how you ever got along without it.

Do not cut carbon fibre or your blade will immediately be dulled.

Ken

[Andy Hoffer]

Why not use a simple hot wire?  It's a LOT less messy.  I use SIG nichrome wire (http://www.greathobbies.com/productinfo/?prod_id=SIGSH135) hung from the ceiling next to my work bench.  It acts like a bandsaw - with NO dust.  If I recall, 12 volts across a 24-inch length works perfectly for cutting blue foam.  I think Rob Pike is pretty knowledgeable on this subject.

Andy

[piker]

I started building a 1/7 scale Mig-3 many years ago using a method very much like you're doing there.  My goal was to experiment with balsa forming around compound surfaces.  I started with a built-up framework which was to be the internal skeleton of the fuselage.  I then covered it with blocks of blue foam, between the formers and carved and sanded to the final outside shape I wanted.  I then soaked sheets of balsa in water and ammonia until their cellular structure weakened and I was able to form them reasonably well over the fuselage form.  I then wrapped the assembly with lots of rubber bands and tape to hold the balsa in place until the wood dried out.  After the sheet wood was removed, it held the compound curves quite well.  I then removed all the foam from the wooden framework and the next step was to glue the sheeting to the structure... but that's where I stopped.  I still have the 80% framed up Mig-3 waiting for my attention, in that state.  Even the wings are almost finished with four segment flaps and retracts.  Maybe I'll get back to it one of these days.

Anyway, yes, foam cutting it easy and quite fun once you get a cutter set up.  I need to do that myself so I can cut some racer wings.  It's been a long time since I've done any foam cutting (6 years).  However, I wouldn't use a hot wire cutter directly over your final shape formers as the final foam form would be a straight line approximation of your curved shape (when I cut the Sandringham fuselage segments, I made the templates slightly larger than final shape knowing that I would be sanding the high points off after assembly), PLUS, the foam usually sinks in from the templates slightly as it melts away from the wire.  I would simply use a Home Depot utility knife with the snap off blades that are about 3/4" wide.  I use those knives a lot for reno work and they are sharp and can be extended out about 3".  Just slice away until your shape is very close then sand lightly to final shape.  Blue or pink foam is easier to work with but is, as I recall, more than double the weight of white foam.  Even regular white foam is heavier than Sig aircraft foam (if that's still available).  I used the Sig stuff in the wings of my Sandringham.

Your progress so far looks great!  It's nice to see some building technique experimenting!

[Wingnutz]

Thanks for the suggestions, humorous and serious! They're all appreciated.
I have a foam cutter which I'm planning to use to cut wing blanks to be balsa sheeted. I'm gonna need some serious suggestions about which airfoil to use as the 3-view is no help at all on that one.
The foam cutting problem I'm trying to solve is how to cut perfectly straight cuts with a face perpendicular to the factory cut top and bottom of the 3" sheet.
Think I'm going to try a fine tooth blade and rip fence on the table saw first. I need lots of straight flat edge for the gluing surface of each half.

[Wingnutz]

Today's progress...we're up to 11oz...I'd hoped for less. The structure is just over 36" long...diet time! Both of us! Rough sanded, a little filling on the low spots where my utility knife went overboard.

[battlestu]

looking good Bill... not sure what it will be but i do know it likes beer. So something Canadian I'm guessing

[piker]

Now that I DO know what the model subject is, I'm more excited to see the build progress.  However, I'm not sure about the Canadian content.

[Wingnutz]

I'm ensuring "Canadian" content with the beer...alas, the aircraft is again Italian. It's going to be a Piaggio P180 Avanti...now semi-scale. The fuselage moved about 1/4" part way through the process of adding foam wafers (maybe too much Canadian content) so it's now about 1/4" longer than my 3-view thinks it should be. Luckily the mistake occurred in the centre section where the fuse is a cylinder, not where it tapers so I will have a "stretched" Avanti. Picture of a standard Avanti below. As long as I can make the same mistake on the other side I think it should be okay.
While we're on the topic of cool Italian airplanes, Bruce Weaver is building a Savoia Marchetti S55x which is a really nifty waterplane, so support me in pestering Bruce to post his build! Should be an interesting model!
Started putting the Avanti half fuse on a diet by hollowing it out...foam definitely makes my short list of messy materials now...I've got foam snowflakes everywhere in my house including on my clothes and even found some...well, I'll leave that to your imagination. This morning I started using coveralls and an old pair of shoes which will stay in the work area but a bit of too little, too late. Goggles and I'll look like a hazmat dude!
I think I'll try building the second half pre-hollowed!