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Old 11-06-2011, 09:35 PM   #1
payne9999
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Default Carving and finishing "Blue" foam

Ok, so I have never used any foam of any kind in a project. However, this Cessna 310 requires a significant amount of fill material on the nose, over the cabin and at the tail (fairing).

I have searched and found a lot of info on building whole airplanes from foam but not much on using it as fill.

So, what is this stuff, is it blue foam sheeting like is sold at Home Depot?
This is a picture from Pat's build thread:


Also, once the foam is identified how do you:

1. Shape it (I am assuming sandpaper)
2. Fill it so the pores don't show (maybe the light spackle stuff)
3. Seal it
4. Paint it

Thanks,

Dave
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Old 11-06-2011, 10:06 PM   #2
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Great mind think alike been wondering the very same thing. Years ago I used urethane foam (marine industry), which would be ideal for this purpose,but I have no idea where to get it.
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Old 11-06-2011, 11:07 PM   #3
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Sand it with sand paper 60 grit to start… then to finer grits

Paint should be acrylic enamel or non petroleum based (some solvents within the paint can attack the foam)
Also…
Bondo and other types of body fillers can possibly attack the foam

Remember to do all this sanding at your best friends house on there dinner table with the ceiling fan on while drinking a malty beverage


One other quick note… if you paint the foam firstyou may apply the body filler onto the paint without the risk of the foam being attacked

Have fun
Cheers,
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Old 11-06-2011, 11:57 PM   #4
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Originally Posted by HO-229 View Post
Sand it with sand paper 60 grit to start… then to finer grits

Paint should be acrylic enamel or non petroleum based (some solvents within the paint can attack the foam)
Also…
Bondo and other types of body fillers can possibly attack the foam

Remember to do all this sanding at your best friends house on there dinner table with the ceiling fan on while drinking a malty beverage


One other quick note… if you paint to the foam firstyou may apply the body filler onto the paint without the risk of the foam being attacked

Have fun
Cheers,
Dave
What type of raw material is it though?

Dave
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Old 11-07-2011, 12:10 AM   #5
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Expanded Polystyrene Foam
Expanded polystyrene foam (EPS) is the cheapest and least used foam board product on the market. This product typically has an R value of 3.6 to 4.0 per inch of thickness. Expanded polystyrene insulation is similar to the foam used for packing “peanuts” and it’s typically used for insulated concrete forms also knows as ICF’s. It is also sometimes used on commercial buildings for roof and wall panel insulation which is typically sandwiched between light gauge metal.

Extruded Polystyrene Foam

Extruded polystyrene foam (XPS) also known as blue board or pink board comes in many different thicknesses and edge profiles. This insulation board is probably one of the most widely used foam board insulation products in the residential construction industry. XPS has an R value of 4.5 to 5.0 per inch of thickness.
Polyisocyanurate and Polyurethane
Polyisocyanurate also known as polyiso is seen in all kinds of commercial building applications and more recently with residential building projects. Polyiso is typically used with a foil facing and it has an R value of 7.0 to 8.0 per inch of thickness. The reflective foil facing makes it an excellent insulation board when radiant heat is involved. The foil facing also makes it very easy to seal with good quality foil faced tapes.

Some data, mostly useless for RC


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Old 11-07-2011, 12:28 AM   #6
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Originally Posted by HO-229 View Post
Extruded Polystyrene Foam
Extruded polystyrene foam (XPS) also known as blue board or pink board comes in many different thicknesses and edge profiles. This insulation board is probably one of the most widely used foam board insulation products in the residential construction industry. XPS has an R value of 4.5 to 5.0 per inch of thickness.
Polyisocyanurate and Polyurethane
Polyisocyanurate also known as polyiso is seen in all kinds of commercial building applications and more recently with residential building projects. Polyiso is typically used with a foil facing and it has an R value of 7.0 to 8.0 per inch of thickness. The reflective foil facing makes it an excellent insulation board when radiant heat is involved. The foil facing also makes it very easy to seal with good quality foil faced tapes.

Some data, mostly useless for RC
Do you think the blue XPS is the stuff used in the build picture?

Thanks,

Dave
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Old 11-07-2011, 12:44 AM   #7
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Most likely XPS... very common EPS is often used for wing cores
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Old 11-07-2011, 01:50 AM   #8
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I recognize the foil backed stuff by its creamy yellow color. Very similar the the stuff we used as core material on boats 40 years ago. If it is indeed the same polyurethane foam, it is very easy to shape, sands easier than balsa. Now, to find it, and then, will the foil come off cleanly? I'll have to stop by the lumber yard and check it out.
Thanks for the info Ho-229
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Old 11-07-2011, 06:10 AM   #9
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When you find something that works really well, you stick with it. I use 60 and 80 grit belt sander belts, for everything in foam shaping. The 60 is for sculpting, and 80 for finishing. The beauty of it is, that you can get everything from perfect compound curves, to flat surfaces, depending on how you hold and work the belt in your hand. The are stiff enough to hold and use as a block, while they can also be curved and held to shape, to sculpt perfect curved surfaces.
All of these fuses below were shaped with the 2 belts only.

With the foam you are using, I would just cover directly over it, with as low heat as possible. I've never bothered with surface prep other than filler for really bad areas, if it is to be covered. The stuff will sand to a harder finish with less pits than bead foam. With a lightweight covering, it is really easy, if you're not heavy handed with the iron, and avoid the obvious such as digging the edge of the iron into it.


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Old 11-07-2011, 11:18 AM   #10
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Beautiful craftsmanship Bill. . Thanks for the help.
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Old 11-09-2011, 05:44 AM   #11
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Got some of the pink stuff from Home Dee pot. The sheets come 4X8 feet. Enough foam for a long time!

Works great for sawing, shaping, attaching and sanding. I have not finished it yet but I imagine the water based polys will work fine.

I filled any dings with the lightweight spackling compound.

Dave
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Old 11-09-2011, 10:50 PM   #12
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That's good news, got a HD just down the street. I picked up some blue stuff laying along side the road on the way home from work today. Must be some kind of insulation board because it has tongue and groove edges. It's about 5/8" thick. Kinda hard to tell exactly with all the dings and tire tracks all over it . I snapped off a chunk to see how it takes to sandpaper.
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Old 11-10-2011, 03:29 AM   #13
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The stuff I have is tongue and groove as well. The folks at HD said the pink and the blue stuff are the same base material.
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Old 11-10-2011, 07:28 AM   #14
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Is the best adhesive going to be foam safe CA, epoxy, Gorilla?

Thanks,

Dave
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Old 11-10-2011, 07:22 PM   #15
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Originally Posted by mararra View Post
I recognize the foil backed stuff by its creamy yellow color. Very similar the the stuff we used as core material on boats 40 years ago. If it is indeed the same polyurethane foam, it is very easy to shape, sands easier than balsa. Now, to find it, and then, will the foil come off cleanly? I'll have to stop by the lumber yard and check it out.
Thanks for the info Ho-229
M
Foil faced Polyisocyanurate foam should never be hotwire cut. Very toxic fumes. Hotwire cutting EPS and XPS releases nasty fumes too. I wear a respirator and work with the garage doors open.

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Old 11-11-2011, 10:03 AM   #16
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Originally Posted by payne9999 View Post
Is the best adhesive going to be foam safe CA, epoxy, Gorilla?
All of those will work but Gorilla would be my preference. But in fact I mainly use UHU Por or aliphatic wood glue for sticking foam myself.

BTW I've always found the pink XPS foam to be slightly more brittle and less resilient than the Dow blue stuff....but there's not much difference, you just need to be a bit more careful with it.

Steve
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Old 11-11-2011, 02:08 PM   #17
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Originally Posted by payne9999 View Post
Is the best adhesive going to be foam safe CA, epoxy, Gorilla?

Thanks,

Dave
One of the major mags did testing with UhuPor, epoxy, CA, Gorilla, and several other glues. The epoxy was found to have the highest bond strength, not surprisingly. I use 5 and 15 minute epoxy, mostly due to lack of patience. Along that thought, every one of my sheeted balsa planes was sheeted using BSI thick CA. You have to really move, but there is no waiting time.
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Old 11-11-2011, 03:58 PM   #18
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Default Glue, Tape, or ...

Originally Posted by payne9999 View Post
Is the best adhesive going to be foam safe CA, epoxy, Gorilla? Thanks, Dave
I am sure you will discover each type of glue has advantages, depending on your working speed and the type of joint you need to make. Epoxy is an old standby that tends to be a little expensive compared to other options and can be applied too heavy when the objective is to keep the glue weight to a minimum. Even so, it is still one of the best for motor mounts if used sparingly and remains flexible. Some brands of epoxy tend to age badly and get brittle. Foam safe CA is a favorite of people always in a hurry to get the model built and flying, but there are risks to health, other than glueing your fingers together, or to the model. Gorilla glue is an art to apply and cure properly, but if you remember it needs a water misting on the other side of the joint and a very light, thin application to keep the foaming action controlled, a patient person will love the bond with foam and wood. The key is learning a very small amount of glue will do the trick since it is the foaming characteristic under lite clamping pressure that makes the bond so strong.

The common wood glues often do a good job also, but they do need lite pressure and access to air to cure/dry properly. Otherwise each joint may need a day or two to set. The deal is foam tends to be less porous than wood and the glue has a lot of water in it that needs to escape. Which brand that is used makes a big different on how brittle the bond is and becomes with age. Since most builders want to get things done without excessive delay, the hot glues (low temperature types for foam) have become very popular, but it is easy to add a lot of glue weight. One trick that makes the common crafting hot glue useful with foam is learning how to apply a small, thin, lite bead in the joint and follow up with a small heat, or sealing iron commonly used with the thin plastic sheets for RC aircraft models. Hot glue tends to make a good, flexible bonding agent and it can be reheated many times before it become less flexible. If the temperature of the heating iron isn't too high, you can reheat the thin hot glue bead to spread the glue even thinner without harming the foam and keep it hot enough to press the joint. But, be aware alcohol can cause the hot glue bond to let go, just as heat inside a hot car during the summer in various parts of the world can soften the glue enough to defeat the bond.

There are many other types of glue for foam I haven't addressed, but let me press on to an adhesive few use for their foam model aircraft. Have you considered using carpet tape? The adhesive on the double sided tape is very strong and you can get less expensive brands that make a bond so strong you will damage the foam trying to defeat the bond between two pieces of foam. The key is how fast can you cut the tape and put it in place? The process is like using contact cement, but there is no waiting to make the joint. For long joints where hot glue and other glues tend to set up too fast to bond properly, carpet tape will wait on you to make the joint and apply a small amount of pressure. The only precausion is to make sure the alignment is correct the first time, since there is normally no second chance, nor an adjustment period. At least with most contact cements that are foam safe you can make the joint a little early and have a short adjustment period. Instant glues are the same way; you have a very limited ajustment period, if any.

So, no matter what type of adhesive you use, it often comes down to the joint type and the bond strength that is required. In time each builder tends to pick favorites and one of mine is epoxy when bonding a wood firewall to foam. I also like epoxy for fiber glass cloth, especially if I am making a repair, but since I don't normally use fiber glass cloth to make a tough skin on foam, I select the adhesive to the joint type and how long of an adjustment period I am likely to need. What I have learned over the years is carpet tape has no smell I can detect easily, it cuts well, and if I use thin strips, one roll can last a long time. You can also keep the weight of the adhesive down if you buy the lightweight rolls. There are other rolls of double sided tape used for all sorts of things, to include mounting photographs in a book, but they are for light duty tasks and often not adequate in our hobby. Most of us tend to over bond a joint and add excess weight to a model that needs to be as lightweight as possible for the best flight characteristics. Instead, we have the option to learn what works better and make test joints to learn the advantages and disadvantages of each adhesive option. Best of luck.
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Old 11-11-2011, 06:58 PM   #19
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I dont like to play with foam on my balsa builds cause i just dont know how to finish it either . The nose and upper cabin area on my solent is balsa blocks glued together then tacked in place.I then carved and sanded them to shape and took back off and grinded out the insides to save wieght. I dont like to try to cover two different types of materials on the same plane i would melt something for shure. It is a new state law here in IL to use that dow 2 inch foam from the bottom of the footiing to the top of the concrete walls on the whole foundations . I grabbed a couple scraps to build cradles to hold planes but never thought about using it to build them. I cut a chunk up to stick all my screwdrivers in on my work bench also. I read a thread where a guy used foam for the necells on the wing and then glassed them but when he took it out in the sun it bubbled up so he went back to planking them with balsa. joe
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Old 11-11-2011, 09:11 PM   #20
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Originally Posted by road king 97 View Post
I dont like to play with foam on my balsa builds cause i just dont know how to finish it either . The nose and upper cabin area on my solent is balsa blocks glued together then tacked in place.I then carved and sanded them to shape and took back off and grinded out the insides to save wieght. I dont like to try to cover two different types of materials on the same plane i would melt something for shure. It is a new state law here in IL to use that dow 2 inch foam from the bottom of the footiing to the top of the concrete walls on the whole foundations . I grabbed a couple scraps to build cradles to hold planes but never thought about using it to build them. I cut a chunk up to stick all my screwdrivers in on my work bench also. I read a thread where a guy used foam for the necells on the wing and then glassed them but when he took it out in the sun it bubbled up so he went back to planking them with balsa. joe
Joe,

I am using Poly U water based clear with some talcum powder in it to fill and seal the foam. I will not cover it but paint it to match the plane. The glue issue was the main thing I needed to figure out. After working with balsa blocks I decided to switch to foam for nose blocks fairings etc. because it is so light, easy to shape and readily available. One sheet could last for years.

My P-51 (mountain Models) had a vacuum formed radiator scoop under the wing. Because it was not truly flat and it was slippery plastic it kept falling off in flight. Also, because of all the curved edges it didn't blend into the fuselage shape and fit nicely. I carved on from pink foam in about 15 minutes that had a better shape, fit better and was also very light. I sealed it with Poly and painted it aluminum and it looks great and stays put.

I think I am going to experiment some more but the carved foam on the nose, cabin and tail fairing are coming out pretty nice on the Tritle Cessna 310.

I would like to be able to carve and cover a fuselage in light silk someday to make a psuedo-glassed plane at some point because a lot of warbirds have complex curves in them. Many warbirds are far to heavy and I am wondering if someone could get to 50" or so with out going over about 2-1/2 pounds. Every warbird I look at in that size is either flying packing material (expanded foam...YUK!) or 5 lbs or more of built up airplane that requires a .40 size equivalent motor.

Someday I want a parkflyer warbird that is more than 36" and not a brick. My MM P-51 is a little small and twitchy even though I really like it and fly it a lot.

Dave
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Old 11-11-2011, 10:49 PM   #21
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I like a product called Foam-Tac by Beacon. It is a contact glue that you apply sparingly to each part. Let each piece air dry for about 10 - 20 minutes and fit together carefully.

It also seems to work fairly well by glueing the parts and putting them together without waitin for the air dry process.

I have made a number of repairs, successfully glueing a broken wing on my HZ Champ. The only draw back is you should give it a couple hours to cure - the label says 24 hours.
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Old 11-11-2011, 10:57 PM   #22
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Originally Posted by payne9999 View Post
Joe,

I am using Poly U water based clear with some talcum powder in it to fill and seal the foam. I will not cover it but paint it to match the plane. The glue issue was the main thing I needed to figure out. After working with balsa blocks I decided to switch to foam for nose blocks fairings etc. because it is so light, easy to shape and readily available. One sheet could last for years.

My P-51 (mountain Models) had a vacuum formed radiator scoop under the wing. Because it was not truly flat and it was slippery plastic it kept falling off in flight. Also, because of all the curved edges it didn't blend into the fuselage shape and fit nicely. I carved on from pink foam in about 15 minutes that had a better shape, fit better and was also very light. I sealed it with Poly and painted it aluminum and it looks great and stays put.

I think I am going to experiment some more but the carved foam on the nose, cabin and tail fairing are coming out pretty nice on the Tritle Cessna 310.

I would like to be able to carve and cover a fuselage in light silk someday to make a psuedo-glassed plane at some point because a lot of warbirds have complex curves in them. Many warbirds are far to heavy and I am wondering if someone could get to 50" or so with out going over about 2-1/2 pounds. Every warbird I look at in that size is either flying packing material (expanded foam...YUK!) or 5 lbs or more of built up airplane that requires a .40 size equivalent motor.

Someday I want a parkflyer warbird that is more than 36" and not a brick. My MM P-51 is a little small and twitchy even though I really like it and fly it a lot.

Dave
The weight issue is why so many guys are building from ivans plans ,including me. Its like stick building a 100 inch wing span plane but building it like a free flight model of the 40s . I just ordered his twin otter plan and it will be very light but have a 84 inch wing span. He has one or two warbirds but none that iam interested in . I used wpu on my solents cowls and painted them cause they were balsa and round and i could not cover them with any plastic film without a ton of wrinkles . I have seen you build a couple other planes and they always impress me how light they are . I hope you start a build thread and let us peak. Oh ! i have been using stick and seal from locktight for foam and gluing my windshields on. http://www.acehardware.com/product/i...ductId=1793239 Works great on plastic and no runs its a gell. joe
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Old 11-12-2011, 12:18 AM   #23
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Default Foam vs Balsa

Originally Posted by road king 97 View Post
I dont like to play with foam on my balsa builds ... I read a thread where a guy used foam for the necells on the wing and then glassed them but when he took it out in the sun it bubbled up so he went back to planking them with balsa. joe
I can understand a reluctance to try foam products after working with balsa for a few years or longer. If you don’t mind the expense of balsa you might as well continue to work with it. If on the other hand your objective is to make larger, less expensive flyers, you will want to switch to foam. Of course there are more than one kind of foam to play with, but you might as well start with the cheaper ones in the beginning. You can always switch to the more expensive foam types if you later decide it is a good idea. I love the fact I can buy a large ˝” thick insulation foam board for $10-$12 and have a 4’x8’ sheet to whack at. I can make park sized flyers and do a bit of sanding/carving, or get into the 40” or larger wing spans and still use the cheaper electric motors if I keep the project simple and lightweight. The foam board is very lightweight, but it is easy to use excessive amounts of glue and hardware and end up with an extra pound or two that isn’t needed. If I want to put some effort into the construction and finishing process, I can end up with a model that is not only more than half the weight of the same size on the commercial market, but much better in many ways. It does come down to skill and experience, but we all must start somewhere.


The fact is many who use to build only with balsa and plywood have dived into foam crafting and learning what the various types are best for due to lower cost and what many famous people have done already. Does the name Burt Ryan ring a bell? Many of the RC model magazines demonstrate a steady increase in the use of foam, and a decline in all balsa and plywood examples. I do realize many kit makers are still doing the thin plywood and plastic sheet covered models, yet many more are switching over to all foam models because they are lightweight and the shipping cost is less. Once you get use to the idea of lightweight flyers, it is hard to go back and spend more to do the same things in the RC hobby. Keith Sparks is a good example of a guy who started his RC hobby life back when balsa and plywood were popular construction materials and foam was not yet an option. He has since made the switch and has built over 200 models. He also makes short kits for those who need parts. To share his knowledge he published a book - Building with Foam that demonstrates the many ways foam types are used and what is possible. Not a very expensive book to have in a personal library, but it is full of information about methods and tricks he and others use. Of course his book cannot have every trick and method possible with foam, and that is why there are Internet sites to share.

His web site is called ParkFlyer Plastics, and you might want to check it out and purchase the book. I did, even though I am not new to making foam flyers. As to finishing foam, there are a lot of options and most of them are cheap ways to get a really nice finish that looks like an expensive method. I can share more on various ways to finish and protect soft foam later, but for now be aware the products are easy to find in craft stores like Hobby Lobby (not the RC Hobby Lobby) and hardware stores. Once you get the foam ready for electronics, then you will want to get parts from an RC provider/supplier. People do makes basic, or simple mistakes when selecting finishing products, but there are many more who don’t, so those are the folks you want to learn from. At the moment I am making a 30” Delta Wing flyer using only two sheets of Readi-Board foam core and some scraps. Each sheet cost $1 plus tax and is 20”x30” in size. Think about that for a bit and ponder what two sheets of 20”x30” balsa around 1/8” thick would cost. Of course I will want to put a finish on the soft foam since the RB foam core is one of the softest available and also one of the cheapest. On the other hand, I like to use the ˝”x4’x8’ insulation foam boards when I do something bigger than a park size flyer. Many are using the larger foam boards to make scale models up to 1/3 scale of everything from WW1 fighters to modern jets with turbine motors. That is a bit out of my league for now, but who knows what I might do later. The foam versions of the same thing in the same size tends to be at least 40% lighter, but you can also build to be 65% lighter and use all electric components already available and growing in choices. The battery packs are still growing in types, and it does seem the next generation can pack more energy into yet another smaller package that is lighter in weight. It is amazing what has happened in the last ten years with just the battery packs, let alone the other parts.
There is so much more that can be said, but this is starting to get a bit long. Until next time.
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Old 11-12-2011, 01:43 AM   #24
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Keith Sparks is a good example of a guy who started his RC hobby life back when balsa and plywood were popular construction materials and foam was not yet an option. He has since made the switch and has built over 200 models. He also makes short kits for those who need parts. To share his knowledge he published a book - Building with Foam that demonstrates the many ways foam types are used and what is possible. Not a very expensive book to have in a personal library, but it is full of information about methods and tricks he and others use. Of course his book cannot have every trick and method possible with foam, and that is why there are Internet sites to share.

His web site is called ParkFlyer Plastics, and you might want to check it out and purchase the book. I did, even though I am not new to making foam flyers. As to finishing foam, there are a lot of options and most of them are cheap ways to get a really nice finish that looks like an expensive method. I can share more on various ways to finish and protect soft foam later, but for now be aware the products are easy to find in craft stores like Hobby Lobby (not the RC Hobby Lobby) and hardware stores. Once you get the foam ready for electronics, then you will want to get parts from an RC provider/supplier. People do makes basic, or simple mistakes when selecting finishing products, but there are many more who don’t, so those are the folks you want to learn from. At the moment I am making a 30” Delta Wing flyer using only two sheets of Readi-Board foam core and some scraps. Each sheet cost $1 plus tax and is 20”x30” in size. Think about that for a bit and ponder what two sheets of 20”x30” balsa around 1/8” thick would cost. Of course I will want to put a finish on the soft foam since the RB foam core is one of the softest available and also one of the cheapest. On the other hand, I like to use the ˝”x4’x8’ insulation foam boards when I do something bigger than a park size flyer. Many are using the larger foam boards to make scale models up to 1/3 scale of everything from WW1 fighters to modern jets with turbine motors. That is a bit out of my league for now, but who knows what I might do later. The foam versions of the same thing in the same size tends to be at least 40% lighter, but you can also build to be 65% lighter and use all electric components already available and growing in choices. The battery packs are still growing in types, and it does seem the next generation can pack more energy into yet another smaller package that is lighter in weight. It is amazing what has happened in the last ten years with just the battery packs, let alone the other parts.
There is so much more that can be said, but this is starting to get a bit long. Until next time.[/QUOTE]

I just ordered a kit of plastic parts from Keith (Sparky) today! I didn't realize he had a book about foam. I will have to order it.

Also, I have to say that Keith was very prompt in answering my questions and shipping the order. He makes all the plastic parts for Dare and Pat Tritle (for his short kits) and the quality is exceptional.

I don't like all foam planes that are not covered or lightly glassed but I have to admit for RTF and ARF flyers that don't have time to build it has been great for them and it has changed the industry a lot.

Dave
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Old 11-13-2011, 07:31 AM   #25
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Given your level of building skill David, I would consider sculpting the parts from light solid balsa. You won't have to worry about covering iron marks as much. I hog out the finished parts as much as possible, making them possibly as light as they would be from foam.

I'm assuming that you are like me, in that you like a good finish. I cover foam planes that I have, as I don't care for the bead look. I almost reached a point at one time where I was building exclusively from foam. The reason is likely the same as most: I didn't think that I had it in me, to frame and sheet complex shapes and get the same results, when building planes with complex shapes. Ironically, I look at it the opposite now. I can't get the same degree of precision with foam that I can from balsa. I think most people have a lot more ability to frame than they think, if they pushed the envelope a bit.
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