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  1. #1

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    Cutting and Prepping Lightweight Foam Cores

    I started this thread to expand discussion from my previous "1.4 oz vs .75 oz Fiberglass Cloth For Balsa Finishing" thread that morphed into other building discussions. Great ideas there but many of follow up questions were off topic.

    I like scratch building but have been
    severely limited by time the last several years. Retirement is approaching and I want to start again. So I want to pick the brains of you builders that use composite materials that I want to use.

    Specifically for this thread the techniques for cutting and prepping foam cores for large 100" plus aircraft.

    What type of foam do you prefer and where do you get it and what it costs?

    What type of foam cutter do you use for large cores? Many online ideas show glider wings with short chords. What works well with chords of 24" and larger and thick airfoils? Hand bow, suspended bow, double wire, swing arm,etc. Photos would be great.

    How you cut channels for wing spar tubes, wood spar channels, wire channels, etc?

    How you make lightening holes, servo well, gear well, etc in the foam cores.

    Bob (Sensei), if you are there, how do you make your panel templates for cutting the lightening holes? Do you jig saw, router, etc the templates. Do you have a photo of one of your template sets in use? I see in your gallery a foam core with lines on it for the lightening holes. I assume you would have to reapply the template to top and bottom to make the foam cuts. Do you have a photo of your foam cutter for the lightening holes? Bow, hand held wire, etc.

    Surface prep of foam before glue, sanding, sealing, etc.?

    Materials other than balsa for skinning the foam.

    What type glues

    Looking forward to collecting all your ideas.

    Gary

  2. #2
    sensei's Avatar
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    Quote Originally Posted by Viper1GJ View Post
    I started this thread to expand discussion from my previous "1.4 oz vs .75 oz Fiberglass Cloth For Balsa Finishing" thread that morphed into other building discussions. Great ideas there but many of follow up questions were off topic.

    I like scratch building but have been
    severely limited by time the last several years. Retirement is approaching and I want to start again. So I want to pick the brains of you builders that use composite materials that I want to use.

    Specifically for this thread the techniques for cutting and prepping foam cores for large 100" plus aircraft.

    What type of foam do you prefer and where do you get it and what it costs?

    What type of foam cutter do you use for large cores? Many online ideas show glider wings with short chords. What works well with chords of 24" and larger and thick airfoils? Hand bow, suspended bow, double wire, swing arm,etc. Photos would be great.

    How you cut channels for wing spar tubes, wood spar channels, wire channels, etc?

    How you make lightening holes, servo well, gear well, etc in the foam cores.

    Bob (Sensei), if you are there, how do you make your panel templates for cutting the lightening holes? Do you jig saw, router, etc the templates. Do you have a photo of one of your template sets in use? I see in your gallery a foam core with lines on it for the lightening holes. I assume you would have to reapply the template to top and bottom to make the foam cuts. Do you have a photo of your foam cutter for the lightening holes? Bow, hand held wire, etc.

    Surface prep of foam before glue, sanding, sealing, etc.?

    Materials other than balsa for skinning the foam.

    What type glues

    Looking forward to collecting all your ideas.

    Gary
    I make my templates by laying them out, cutting the out close to the line with a jig saw, and sanding to the line with an oscillating spindle sander. this sander can be purchased from Harbor Freight for around $100.00. I don,t have any pictures of templates or my bows. You are correct, I apply a template to both sides of the core, use a soldering iron and burn through the center of each opening of the template, string my wire through and reconnect to the bow, make my cut, disconnect and remove core plug. I repeat over and over until my core is finished.
    Fly It Like You Stole It!!!

  3. #3

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    Hi Bob,

    Thanks for your reply.

    Do you use a bow for cutting the holes or do you just string a hand held wire and freehand inside the template hole?

    What is the density of the foam you use and your source?

    I am looking at driving to Peachtree City, Ga to Aircraft Spruce East to get plywood. I can stuff 4x8 sheets of basswood and lite ply in our minivan if they will flex a bit. It will cost less than shipping and would be a short getaway with the wife later this fall.

    Enjoyed looking at your gallery. Got lots of ideas there. Was your 33% Giles an old Aeroworks kit? I built several of their old kits when I lived in Denver. Still flying the Giles wing on my AcroJet pictured in the other thread.

    Gary

  4. #4
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    Quote Originally Posted by Viper1GJ View Post
    Hi Bob,

    Thanks for your reply.

    Do you use a bow for cutting the holes or do you just string a hand held wire and freehand inside the template hole?

    What is the density of the foam you use and your source?

    I am looking at driving to Peachtree City, Ga to Aircraft Spruce East to get plywood. I can stuff 4x8 sheets of basswood and lite ply in our minivan if they will flex a bit. It will cost less than shipping and would be a short getaway with the wife later this fall.

    Enjoyed looking at your gallery. Got lots of ideas there. Was your 33% Giles an old Aeroworks kit? I built several of their old kits when I lived in Denver. Still flying the Giles wing on my AcroJet pictured in the other thread.

    Gary
    I use a bow for most stuff, but if the cut is really deep then I sometimes use two handles with the wire attached and alligator clip the juice to the wire. My giles was actually an old Lanier kit, I built two of them back in the day. The only Aeroworks kit I ever built was my 40% Edge 540 with the Obsession Name on the wings in my gallery. Now that dates back aways as well...

    Bob
    Fly It Like You Stole It!!!

  5. #5
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    For the past year or so I have been cutting my templates from 3/32 ply and then gluing .020 music wire on the edge. The stainless wire I use on the bow glides over the templates really well. I have not gotten into lightening the foam as much as Bob. As far as cut outs for servo mounts and such I use my dremel router with a dry wall bit. before sheeting I sand the cores with 320 and vacuum clean. They really need to be as dust free as you can get them. Any flaws can be filled with light weight spackle. For attaching the skins I use epoxy with a touch of cabosil added and vacuum bag them. if added strength is needed in some areas, a strip of 2 oz cloth between the sheeting and foam does the job.

  6. #6

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    Speedracerntrixie,

    Thanks for the ideas.

    I have been thinking of the wire on plywood templates to make the bow go smooth. I have had a hard time making formica templates in the past. What type of glue do you use to attach the wire. I just got the router base for my dremel so I will give it a try. Do you just freehand it or do you make a cutting template ?

  7. #7
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    I just use thick CA to glue the wire after cleaning with acetone, sanding and cleaning again. I usually freehand with the dremel but the next set of cores will need a template of some sort. Building a couple pylon airplanes and will have to do spars in them so I want a strait rout that will be a tight fit on the spars. There are so many ways foam wings can be done. This particular project will have 1/4" sq routs in the foam that will be covered with a 2" strip of 2 oz cloth then the 1/4" sq balsa spar will be set on the glass then pushed into the slot. I will cap the balsa with another 2" strip of cloth full span and then a 3" strip of 3K unidirectional CF 1/2 span and lastly bag the skins on. All this will be done in one shot. The wing joiner will be 1/4" vertical brained balsa that has been sandwiched with 5.7 oz CF at a 45 degree bias. The goal is a light super stiff wing.

  8. #8
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    I use sticky backed copper tape on the edges of my templates. It can be purchased from hobby supply places that sell supplies for stained glass makers

  9. #9

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    Seaplane,
    Thats a great idea. What is the copper tape used for in stain glass work. Would Michaels or AC Moore have it?

    How wide is the tape?

    Gary

  10. #10

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    i used Birch veneer (.023") from Woodcraft to sheet the wing of a fairly large profile plane with EXCELLANT results. Used 3M Polystyrene foam adhesive (#78) to attach the veneer to the foam. *I used NO reinforcing spars, not even the leading edge, just at the rear to hold the hinges. *I used two 2" sheet of white foam to get a blank of 4". *At the wing root the wing is 3 5/8" thick. *With using two pieces of foam, you can rout your wing joiner tube in the foam before gluing. *Servo pockets were routed AFTER sheeting with a small router. You can use Gorilla glue to join the two sheet together, but for a large wing, I would cut lightening channels in the foam, that way you won't use as much glue as i did (Gorilla glue is fairly heavy). Flew the pants off this plane this summer and the wings held up very well. Trying to bore the wing tube channel from a solid block, while can be done, seems iffy.
    Last edited by jp1961; 09-30-2013 at 05:09 PM.

  11. #11

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    jp1961,

    Do you have any photos of this wing or plane. Would love to see it. What is your wing joiner tube. Is it large or small? How did you rout the wing joiner tube and what bit did you use? Also can you explain more how you mated the top and bottom sheets and your suggestion for lightening channels.

    Thanks
    Gary

  12. #12
    seaplane's Avatar
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    I don't know what the copper tape is used for in stained glass, but the idea just popped into my head one day and I did a search on-line and found it in many places. I don't remember which one I purchased it from. It's MasterFoil Plus from Venture Tape. The roll I purchased is 3/8" wide by 36 yds long. I also don't know if Michaels carries it. The glue on the back of the tape is heat resistant so it is perfect for this use.\
    Ralph

  13. #13

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    Seaplane,

    Thanks, I will look for it. Sounds like a great idea to get plywood templates for large wings smooth with min work.

    Gary

  14. #14
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    JP1961,
    I've made over 1200 foam core floats using 3M 78 and I think it is the best glue around. I laminate layers of foam with it and I glue balsa sheeting with it. It has become expensive over the years, probably around $17 per can if you can find it. I buy a case at a time so I get it a little cheaper. I also use Gorilla Glue to glue in backbones and anchoring dowels.
    Ralph

  15. #15

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    I shape all my foam templates in plywood first. I then use the plywood shape and a router/template bit to cut them in counter-top laminate material using the process that similar to the below video.

    https://vimeo.com/1636764

  16. #16

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    Gary,

    I used a standard 1.25" aluminum tube you'd find at a hardware store or Home Depot. *Since I couldn't find a cardboard tube to snugly fit over it, I made a tube out of fiberglass and West System epoxy. I used a standard half round router bit to cut the channel for the fiberglass tube in the foam, if you can't find the exact size you just have to make multiple passes to make the channel in the foam big enough. *The fiberglass tube was glued in when i glued the two blocks of foam together. I'm having a lot of problems uploading pictures since RC Universe switched the forum around, you can send me a personal message, and i'll forward you all the pics i have of this airplane.

    Jeff*

  17. #17

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    Here is a pic of the wing and finished airplane

    Jeff
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  18. #18

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    This plane came out at 14.5 lbs. *It is*underpowered with a Homelite 25cc but it does fly. *I could have shaved 2 possible even 3 pounds if I did away with the wing tube, used a solid block of 4" foam (instead of laminating) and used thinner plywood for the sides of the profile fuselage (I used 4mm marine ply simply because it's what i had at home). It has better flight qualities than any kit I've built and I've built nearly a dozen kits. *Make sure when you cut your cores you put in a small amount of wingtip washout. *Give the Birch veneer a try, you won't be*disappointed.

  19. #19

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    I forgot to mention a Homelite 25 cc weighs 4.5 pounds with prop and spinner so some of that 14.5 pounds is engine.

  20. #20
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    Quote Originally Posted by jp1961 View Post
    Here is a pic of the wing and finished airplane

    Jeff
    Nice looking airplane, what is the wingspan and wing area if I may ask?

    Bob
    Fly It Like You Stole It!!!

  21. #21

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    Jeff,

    I checked Woodcraft online for the birch veneer. I could not find any large sheets. What size sheets did you use to cover the foam?

    Gary

  22. #22

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    The wingspan is 63", wing area 1080 sq inches. Woodcraft sells Birch veneer in 4' x 8' sheets rolled into a tube and they will ship to your house. *When I glued the veneer on, as I rolled the foam core onto the birch i pulled very hard, something you wouldn't be able to do if you used balsa sheeting edge glued together.

    Jeff

  23. #23
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    Quote Originally Posted by Viper1GJ View Post
    I started this thread to expand discussion from my previous "1.4 oz vs .75 oz Fiberglass Cloth For Balsa Finishing" thread that morphed into other building discussions. Great ideas there but many of follow up questions were off topic.

    I like scratch building but have been
    severely limited by time the last several years. Retirement is approaching and I want to start again. So I want to pick the brains of you builders that use composite materials that I want to use.

    Specifically for this thread the techniques for cutting and prepping foam cores for large 100" plus aircraft.

    What type of foam do you prefer and where do you get it and what it costs?

    What type of foam cutter do you use for large cores? Many online ideas show glider wings with short chords. What works well with chords of 24" and larger and thick airfoils? Hand bow, suspended bow, double wire, swing arm,etc. Photos would be great.

    How you cut channels for wing spar tubes, wood spar channels, wire channels, etc?

    How you make lightening holes, servo well, gear well, etc in the foam cores.

    Bob (Sensei), if you are there, how do you make your panel templates for cutting the lightening holes? Do you jig saw, router, etc the templates. Do you have a photo of one of your template sets in use? I see in your gallery a foam core with lines on it for the lightening holes. I assume you would have to reapply the template to top and bottom to make the foam cuts. Do you have a photo of your foam cutter for the lightening holes? Bow, hand held wire, etc.

    Surface prep of foam before glue, sanding, sealing, etc.?

    Materials other than balsa for skinning the foam.

    What type glues

    Looking forward to collecting all your ideas.

    Gary
    Gary, I stumbled on your thread and you ask some good questions. My answers may have been covered by others, I don't know, I didn't read most of it.

    I use a bow to cut foam. It is a simple fiberglass reflector post from Home Depot, about 3/8" in diameter and about 45" long, and flexes just right for applying tension on the cutting wire. The posts are about 6 feet long, The extra material is used as the ends of the bow, glued at about 110 degree angle and reinforced with some scrap 1/16 ply

    I suspend my bow from a shelf to counterbalance its weight. I use the gravity technique with pull strings for moving the bow through the foam

    My power supply is the Burt Rutan Special from Aircraft Spruce. Simple and inexpensive to make....Works fine. Search under Foam Cutting Supplies.

    My templates used to be rather elaborate polished phenolic. What a pita to make those......Well there had to be a simpler way. Now I use simple plywood templates. The edges are lined with teflon adhesive backed tape. Nothing is slipperier than teflon so this works better than anything else I've tried regards to templates. Of couse a CNC cutter uses no templates and is likely more accurate but I'm not about to spend a few 000's for a foam CNC cutter.

    Regarding glues, for the past 25 years I've used laminating epoxy. Since I vacuum bag all my panels, very little is required. I use epoxy with about 90 min pot life which gives me plenty of working time. Gorilla glue is also used by many, except, you have got to work fast or it kicks off right before your eyes.

    On skinning, I've used regular cardboard stock from Staples years ago. It builds rather heavy tho. Many moons ago I used 1/64 birch ply veneer from Aircraft Spruce, but used it only once. Sure wings were bullet proof but they were also far too heavy.

    Nothing but 1/16" contest grade balsa since. It also allows taper sanding the balsa for further reduction in weight. But if you like to paint stuiff as I do, finishing balsa can be a pita. Time honored nitrate and Esaki tissue over balsa simplifies things and keeps things light, but it's an awful lot of work, work that I do willingly on all my competition models where lightness and weight specs count the most

    Lately I've been experimenting with casting fiberglass onto plate glass first to form and cure the stock sheets, vacuum bagging that to the smooth finish of the plate glass. Then epoxying that onto foam directly. G10 sheets are similar, except I control where to place the strength and control its weight. The glass smooth finish is hard to beat and it is done with almost no effort. I haven't worked an optimal glass weight versus strength yet, but it's coming. It isn't lighter than balsa but does offer considerable ding resistance and much less work in the long run.....
    Regards,
    MattK
    (Rcmaster199@aol.com)

  24. #24

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    An*excellent*book on the topic of making foam core wings is "Radio Control Foam Modelling" by David Thomas. *Shows all sorts of tips and*techniques, paperback. I don't think foam core wings will ever be as light as built up wings, with the possible exception of vacuum bagging carbon fiber cloth over foam, but that would be an expensive proposition. *Each method of building has it's advantages and*disadvantages. *
    Jeff
    Last edited by jp1961; 10-03-2013 at 04:03 PM.

  25. #25

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    One item I use for making cutouts for landing gear, servos, etc. in the foam wings is to make wire forms from 12 AWG household copper wiring and install these in my Weller soldering gun. With various shapes and sizes, I can cut out stepped down cutouts easily and quickly. The nice part about this method is that the edges of the cutouts are sealed off from the heat of the wire and there is no foam dust to vacuum and mess with.


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