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Oct 04, 2019, 08:52 AM
Build Fly Crash - Start Again!
onewonders's Avatar
Thread OP
Question

Balsa Formers with Foam Instead of stringers


I've been kicking this around for months, trying to decide how best to proceed. After searching and searching the forum I could not find an answer on how to proceed.

The plans show blocks of polystyrene foam in between balsa formers. see pic #1 and #2

The foam will be cut to match the inside curves of the formers. see pic #3

So I have pink insulation sheets left over from a reno. I also have some white EPS foam insulation.

Which is preferred?

I would start by cutting the foam into similar rectangles to create a jig so to speak, but should the glue seam go along the length of the fuselage or across the length of the fuselage?

I would like to know can I glue the blocks together then use a hot knife to hollow out the foam to match the formers? And what would be the best glue that can be cut with a hot knife?

FYI the plane is a DeHavilland DH100 Vampire the plans are from Aviation Modeler a very old defunct magazine. WS 1500mm or 60"

Thanks in advance
Doug
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Oct 04, 2019, 09:09 AM
treefinder
springer's Avatar
Pink foam (xps, extruded versus expanded bead foam) will be easier to work with, though both will work. Most folk don't bother with the formers, but use them as templates for hot wire cutting the foam "donuts" that get glued together on a mandrel. Check out Sparks current thread about his Connie build. He uses this technique, lots of pics.
For glue, I'd use Gorilla glue white, with tape or clamps to manage the foaming and keep everything in place while curing.

Edit: Have to correct myself, Sparks doesn't glue the foam discs together in that build, but uses them as formers and adds stringers and skin. Have to do some searching for the other planes that are built with glued up discs. The Connie thread is here, though: https://www.rcgroups.com/forums/show...-Constellation
Last edited by springer; Oct 04, 2019 at 09:15 AM.
Oct 04, 2019, 09:26 AM
An itch?. Scratch build.
eflightray's Avatar
Have a look a Lockey's thread ---

de Havilland Vampire

.
Oct 04, 2019, 10:26 AM
Registered User
Zipman's Avatar
Doug,
Here is a good example of what you are looking for. This member has done several models this way. He goes beyond what you want and uses the foam shaped fuselage as a male mold to create a formed foam and glass fuse shell. you can use his technique to just create the foam mold then hollow it out as a completed fuselage. Others have done similar molds and shells using formed balsa sheet over the foam molds.

https://www.rcgroups.com/forums/show...-an-invitation
Oct 04, 2019, 10:33 AM
Registered User
Zipman's Avatar
Here is another amazing foam builder. Look thru his blog. He uses multiple ways to form foam models. Big ones too.
https://www.rcgroups.com/forums/member.php?u=3728
Oct 04, 2019, 11:56 AM
Build Fly Crash - Start Again!
onewonders's Avatar
Thread OP
Thanks Springer, eflightray and zipman much appreciated.

Those are absolutely amazing builds WOW.

So there is life after Balsa

I've got some ideas now on how to proceed; when I get started I will post so everyone can have a good chuckle LOL.

I've got all the parts ready, three sets of plans just in case I need to cut one for templates, two shortkits (long story - do a search you might find the story) - I'll get this on the building board once I finish wing of my Harvard.
Doug
Oct 04, 2019, 10:52 PM
flyin' fool
goldguy's Avatar
Pay for the shipping and you can have this kit for free!! From here to TO shouldn't cost a fortune.

https://www.rcgroups.com/forums/show...94&postcount=1

It's a barn find with a few water stains.
Oct 05, 2019, 06:29 AM
Build Fly Crash - Start Again!
onewonders's Avatar
Thread OP
Quote:
Originally Posted by goldguy
Pay for the shipping and you can have this kit for free!! From here to TO shouldn't cost a fortune.

https://www.rcgroups.com/forums/show...94&postcount=1

It's a barn find with a few water stains.
Interesting offer. I am visiting / maybe moving to Langford early next year. If it still available then I'll take it off your hands.
In the meantime I have two short kits to put together!
Or my father-in-law lives in Langford, an ol' rc builder flyer himself from the Victoria club, he could always come by and take it off your hands and ship it.
Let me know and thanks for the offer.
Doug
Oct 05, 2019, 07:10 AM
flyin' fool
goldguy's Avatar
I just sold my house and am moving in a few weeks. Get you relative to call me at contact in PM. I fly with guys from Victoria at a site near Duncan. Should be easy to find a way to get it to you.
Oct 05, 2019, 07:29 AM
treefinder
springer's Avatar
"So there is life after Balsa†"
You wont believe how good life is after balsa!

If you do the stacked donuts method, be sure to use a mandrel to keep everything straight. Especially if you use gorilla glue. When it foams, parts move unless constrained/ clamped.

Welcome to the foam side!
Oct 05, 2019, 07:36 AM
flyin' fool
goldguy's Avatar
If you don't like those hot humid summer days and freezing cold snow filled winter ones, then this is the place be. Oh, and we get half the rain the Vancouver gets.

We have flown our float planes 'every Monday of the year' for over 35 years and only missed a handful of days because of the weather. The winter months are usually great if your into slope soaring.

Langford is over to the very left off in the distance. This shot is from a slope site over on Salt Spring Island.
Oct 05, 2019, 09:42 AM
Build Fly Crash - Start Again!
onewonders's Avatar
Thread OP
Born and bred in Victoria/Powell River. Going home! beautiful views...Thanks will PM you
Oct 06, 2019, 01:09 PM
Build Fly Crash - Start Again!
onewonders's Avatar
Thread OP
Quote:
Originally Posted by springer
"So there is life after Balsa†"
You wont believe how good life is after balsa!

If you do the stacked donuts method, be sure to use a mandrel to keep everything straight. Especially if you use gorilla glue. When it foams, parts move unless constrained/ clamped.

Welcome to the foam side!
You mean the dark side LOL.
I really enjoyed all of the links. Time to get the book building with foam.
I have a lot of balsa planes to build first as I have lots of balsa to use up. But Iíll definitely tinker with foam.
Oct 07, 2019, 03:25 PM
Registered User
ErcoupeEd's Avatar
Quote:
Originally Posted by onewonders
You mean the dark side LOL.
I really enjoyed all of the links. Time to get the book building with foam.
I have a lot of balsa planes to build first as I have lots of balsa to use up. But I’ll definitely tinker with foam.
onewonders,

You will enjoy the book, building with foam.
I started out with Sparky's original book and now also have the revised book.
I have been browsing this thread and have learned a lot .
I will apply it along with Keith Sparks methods.

I have two sets of plans for the Wendell Hostetler plans of the 102 inch wingspan
Sirius.
Plan on making patterns from one set and build on the other.
I love the older vintage aircraft.
I own and fly a full scale 1946 Ercouupe myself

I belong to the EAA and the VAA at OIshkoish Wisconsin and do volunteer work in the VAA division every year for the past 25 years.
I have been flying full scale since 1994 and and models since age 6, or 62 years ago!

Blue Skies,
Ed
Oct 07, 2019, 03:46 PM
Build it, don't buy it
foamnpacktape's Avatar
Quote:
Originally Posted by springer
For glue, I'd use Gorilla glue white, with tape or clamps to manage the foaming and keep everything in place while curing.
I have not used Gorilla white glue before, but I am skeptical, can it be cut with a hot wire or knife as the OP requested?

The only glue I have found that works well in such situations is Super 77. It is a contact adhesive and a hot wire glides right through it, unnoticeable.

As for general gluing, I use regular white glue almost exclusively, it sticks well to EPS foams, dries clear, is sandable, and easy cleanup. I do use gorilla glues if there is some gap filling needed, but the stuff is messy to work with. I haven't tried their white glues though.

Although with the extruded EPS sanding and finishing is easier, and it is slightly stiffer, there is a significant weight penalty associated with it over expanded EPS, and it is more expensive. On the whole, for my builds I stick to regular expanded polystyrene, but I am cheap and anytime I can save a gram, I do so, those grams add up quickly.

Here is an example of my latest project, https://www.rcgroups.com/forums/show...rrow-the-third


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