Design with Foam

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Foam construction

Foam has become my friend when building a plane. It is easy to work with, light and strong perfect for building plane with. What I like most is the ability to build a simple plane and flying it almost as soon as I finish it. A plane made from foam will out last any other type of structure when it encounters a crash. Therefore more flying time is enjoyed. I recall all of my best flying was done with foam planes, mainly because, I was learning to fly, care free, still am by the way... :)

There are several types of foam to build with. Each has its own characteristic for different purposes. I will try to list them out for you.

I will start with those I am most familiar with, and I welcome any input on the subject since I am still looking for the perfect material for my projects.

The tools needed are basic and some are special, like the hotwire cutter. I will help you out with some ideas.

So I did more research and found out that people been making planes with EPS and EPP. From all the reading I have done, looks like EPP is a better foam and will take more abuse then EPS or Styrofoam.

POLYPROPYLENE FOAM (EPP)

Flexible expanded polypropylene foams, ideal for shock protecting

This is the latest foam on the modelling scene. It comes under the brand name of Eperan 2, the bead precursor for the foam (Neopolen P) is made by BASF and is expanded in a low pressure steam chamber without using blowing agents. In the jargon it's called a closed-cell thermoplastic olefinic foam material. Nowadays it's used for wings and fuselages for Combat flying although was originally developed for use by the car (automotive) industry for impact absorption (i.e. bumpers, dashes, etc). EPP is a beaded foam which has a memory; that is to say that it returns to its shape after being distorted. It is a white colored foam with a waxy feel and appearance and really needs to be sprayed with 3M adhesive before applying fiberglass reinforced tape and/or plastic film. It can be cut with a hot wire, though not as well as PS foams. I hear tell some cut it with a flexible wire saw too. As far as I know it comes in two standard grades, 1.3 lb and 1.9 lb per cubic foot. The lighter version is generally used for models.

POLYSTYRENE FOAM (BLUE FOAM)

Extruded polystyrene (in blue, green, gray, pink or purple smooth plates, depending on the manufacturer)

Blue foam is a lay term for the family of expanded polystyrene foams sold at building supply stores for use as exterior insulation. Depending on the manufacturer it may be either blue or pink.
The foam comes in an number of densities, of which the pink colored foam has the lowest density. In most cases the higher density blue material is easier to work with but it may not always be available.

Blue foam is a good material to use when you need to make sculptural forms or models that need to be solid. The material is easy to cut and shape with hand tools and is fairly inexpensive.

Su-27 Flanker a very good example by Tom Nelson

EXPANDED POLYSTYRENE (EPS)

Expanded polystyrene (blocks of expanded white balls)

DEPRON

Polyethylene foams, flexible and tear resistant

Quickly growing recognition of this perfect unique material for airplanes modelers, certainly has become the preference for 3D planes.

A stiff lightweight foam material best known in the shape of a serving trays used by catering services and food container for burgers used by fast food restaurants.
Depron is quite resilient to damage. It can be bought in sheets from 1mm up to 6mm thick. The molecular structure is made up of dense air bubbles with a smooth surface skin on each side resistant to scoring. This make for a very light and strong material, a good candidate to build model planes with.

This product is hard to find in North America as a building material in sheet form. In Europe it is widely used as a sub-flooring insulator and easily obtainable.

WORKING WITH DEPRON

Depron foam is quite easy to work with, no special cutting tools are required. A common sharp blade is all you need. It cuts nicely, but to ensure straight cuts use a long metal edge. It can be sanded on the edges or on one side to thin it out to join.

TO FOLD THE FOAM, a line drawn by a ball point pen on one side will provides a the necessary guide for the fold to act on. It basically compresses the foam allowing it to fold easier. Some cases multiple lines will help achieve larger rounding effects like a leading edge of a wing. To prevent cracking of the thin skin surface, packing tape the cheap kind makes for an added precaution when applied.

A good demonstration dome by my friend Yann with another material similar to DEPRON called ZEPRON

Because of its outer skin layer, it can be crushed into shape. This done by compressing the foam using a rolling pin or similar. You can also do this by hand, by pressing down in the areas where the shape is desired.

HEAT TO SHAPE, if heated too much it will loose the original shape by shrinking or expanding caused by heated gas trapped inside the tiny air bubbles. It also becomes brittle when cooled after being heated, but there are measures that can be taken to shape the DEPRON into something desirable.

MOLDIND DEPRON

Yes, DEPRON can be molded into shape using an electric kitchen oven.

a mould out of wood, of the shape, is first made
pre-heat your wooden mould of the shape in an electric oven for 20-30 min at 80-90 deg.C (176-194deg.F)
form the piece of Depron onto the heated mould by first carefully cold-crushing it without cracking it.
wrap packing tape tightly around the whole outside and seal the edges. This prevents the gases to expand and forces the depron foam to follow the shape of the mould.
place it in the oven for 15 minutes at 80-90 deg.C (176-194deg.F)
remove from oven and let cool for 1 hour. The depron will fix to the shape of the mould and retain its strength too.
Carefully remove the tape. Sometimes the thin skin is compromised, but the shape is achieved.

GLUING DEPRON can be glued with odorless cyanoacrylate (the normal CA melts polystyrene), and various other non-solvent based glues and cements. Other ones that work more or less are , yellow carpenter's glue Titebond. Epoxy is your last gasp -- heavy!!!!

A preferred glue is UHU glue for foam. The widely used polyurethane glue like the Gorilla Glue, not instant, but it foams up when in contact with moisture to fill gaps and becomes light when dry. It is VERY strong, and sticks best. I mix it with a drop of water in a separate container, and apply it with a pallet. After about 30-60 minutes, you can wipe off the expanded residue. If you wait a couple of hours, you can slice off the excess with an exacto blade. Overnight it becomes hard as epoxy, but much lighter. Other good alternative polyurethane glues in picture ---------------------------------->

A low temp hot glue gun works for fast jobs, a little heavier but works well and will dry fast!

BLENDERM a double-sided tape. BLENDERM is a really cool adhesive tape made by 3M for the health care industry. It can be found in some pharmacy or ordered online. If you feel like buying the stuff in boxes of 16 rolls, you can order from medical supply stores (like MVAP Medical Supplies), but if you want more reasonable quantities, you can order from Air Dynamics

PACKING TAPE is also an alternative to gluing. It also acts as a protective coat and strengthen the structure.

UV-Resistant Tape By Lee Valley, made from UV-resistant plastic and UV-resistant acrylic adhesive, it won't break down in the sunlight and is perfect for hinges

Foam wing construction using 1mm DEPRON as the Skin

Hot wire the foam into airfoil shape, with the 1mm DEPRON I covered it giving me my finishing along with the resistance to damaging, thereby complete the structure. It is in the glue; polyurethane acts as filler and dries light and hard, acting as a stiffener. A great combination, the end result is a light stiff wing. For smaller wings this works, I would use some stiffeners like spars for lager wings.

Samples of work done by others with DEPRON

I could have put together some samples, but I thought this was already done nicely by others. It also demonstrates this can be done by anyone and having fun with it. My Ductlings are built with DEPRON
Building a simple foam wing ribbed folded and taped with control surfaces.

Molding Depron where I learned about it, nicely explained, nice project too a Learjet.

DEPRON Avero Arrow a electric model plane plan available

DEPRON F-15 electric model plane

What is DEPRON? Nicely explained

Yann's planes Interesting concepts and designs, demonstrates how fun working with DEPRON can be.

FOAM CUTER

There are several way to cut foam. Hot wire cutters are popular because they generate the best results. Some concerns is the power supply for the cutters

Here is a very good site with detailed instructions no how to build and use the different cutters

UTAH FLYERS Foam Cutter Plans