Foam Wings
02-23-2006, 08:44 PM
#1
Thread Starter
Foam Wings
Here are some photos of a Giles 300 I built last year from Procraft plans, the original design was built up construction but foam is faster and easier. The photos are of the stabilizer however the same process was used for the wings, I got the digital camera after the wings were cut but not sheeted.
The foam block is first cut to the exact outline of the flying surface allowing for 1/2 balsa leading edge, the trailing edge is foam so the cores taper to almost nothing, I left about 1/32" of foam at the trailing edge to allow for melting as the wire pasts. 1/64" plywood strip about 3/4" wide is laminated under the balsa skin to provide a stiff trailing edge.
The second photo is showing the templates used to cut the access hole to cut the wing tube.
The foam block is first cut to the exact outline of the flying surface allowing for 1/2 balsa leading edge, the trailing edge is foam so the cores taper to almost nothing, I left about 1/32" of foam at the trailing edge to allow for melting as the wire pasts. 1/64" plywood strip about 3/4" wide is laminated under the balsa skin to provide a stiff trailing edge.
The second photo is showing the templates used to cut the access hole to cut the wing tube.
02-23-2006, 08:47 PM
#2
Thread Starter
RE: Foam Wings
The homemade hotwire bow is ready to cut the access holes, there are templates on both sides of the foam block, the templates are held in place with aluminum siding nails. I heat a steel rod with a propane torch and use it to pierce the block to insert the wire, string the bow with wire through the hole and cut to the templates.
The second photo shows the tube and sockets.
The second photo shows the tube and sockets.
02-23-2006, 09:21 PM
#3
Thread Starter
RE: Foam Wings
The wing tube centerline is drawn on the bench, I laid down a strip of marking tape and drawn the centerline on it so I can easily see it. Templates are made from 1/8 plywood, both hole are the same height above the work bench. I use a hole saw to cut the templates and sand the id for smooth surface, there's also a saw cut from the top of the template down to the hole for wire to past. I don't waste to much time on templates since the hole surface isn't a big deal, maybe sand with 220 grit. Templates are aligned and screwed down to the working surface, the straight edge is clamped down to the bench that aligns the foam cores. The holes will be cut in both cores simultaneously so the everything lines up. Notice the filler pieces sticking out of the foam blocks, these will be installed in the blocks while cutting the airfoil shape, I will be vacuum bagging the wing so all holes must be filled. The small section will be glued in after the outer wing socket plates and sockets are installed.
The blocks are positioned and weighted down to ensure a straight wing. Please be sure to use 1 pound virgin Expanded Bead Polystyrene for your cores. Typical insulation grade foam may contain regound beads which is difficult to cut with the hotwire and achieve acceptable results. I order my foam from the local foam manufacturer, it's blown to order.
I make a small bow that fits on the outside of the templates, heat the bow, cut through the saw cuts down to the bottom of the template, work the bow around the template using caution when it's near the saw cut. I find it easier to remove the first half moon pieces before cutting the other side, once it's loose, it just gets in the way. Be careful not to move the blocks at this point.
The blocks are positioned and weighted down to ensure a straight wing. Please be sure to use 1 pound virgin Expanded Bead Polystyrene for your cores. Typical insulation grade foam may contain regound beads which is difficult to cut with the hotwire and achieve acceptable results. I order my foam from the local foam manufacturer, it's blown to order.
I make a small bow that fits on the outside of the templates, heat the bow, cut through the saw cuts down to the bottom of the template, work the bow around the template using caution when it's near the saw cut. I find it easier to remove the first half moon pieces before cutting the other side, once it's loose, it just gets in the way. Be careful not to move the blocks at this point.
02-23-2006, 09:44 PM
#5
Thread Starter
RE: Foam Wings
Here the template is installed for the top of the airfoil, since this is a small wing I can cut it myself and control the wire speed so the wire enters and exists the foam at same time. On larger wings I use station numbers, maybe 30 equally spaced on each template, I control the cutting speed on the root, my wife follows on the tip as I call the numbers. Be sure to press down on the template as cutting progresses, pull the wire smoothly through the foam and let the wire cut, maybe 2 pound pull on each side. Notice the the paper clip on the trailing edge, this stops the wire as it exits, the wire will bow as it cuts through the foam, it will exit at templates before the center of the wing.
The second photo shows the opposite side, a small wood strip to prevent the block from moving once cutting begins, and weights keeping the block straight on the workbench.
The second photo shows the opposite side, a small wood strip to prevent the block from moving once cutting begins, and weights keeping the block straight on the workbench.
02-23-2006, 09:57 PM
#7
Thread Starter
RE: Foam Wings
Finshed cores trial fit together. Time to install the wing tube sockets.
The sockets are fitted with 1/8" lite ply stops to prevent the tube from entering the foam. The socket is supported on the outer end with 1/8" lite ply plate glued into the access hole. The inner portion of the socket is supported by the root plate, I used aircraft ply since a tab will be located on the bottom of the wing to retain the stabilizer. The filler pieces are sanded down and fit in, everthing is glued with Probond poly glue.
The sockets are fitted with 1/8" lite ply stops to prevent the tube from entering the foam. The socket is supported on the outer end with 1/8" lite ply plate glued into the access hole. The inner portion of the socket is supported by the root plate, I used aircraft ply since a tab will be located on the bottom of the wing to retain the stabilizer. The filler pieces are sanded down and fit in, everthing is glued with Probond poly glue.
02-23-2006, 10:18 PM
#9
Thread Starter
RE: Foam Wings
When cutting high taper sections such as rudders the one end of the bow is fastened to workbench at the point where the leading and trailing edges intersect. I still use templates on both ends when making these cuts.
02-23-2006, 10:28 PM
#10
Thread Starter
RE: Foam Wings
Wood dowels will be used for mounting the control horns, the position is laid out and 1/8" lite ply plates are inset to provide additional support for the dowel on the top and bottom of the core. I made a jig for the Dremel router for this purpose, the plates are glued during vacuum bagging. The hole is drill after the skins are glued on. I got his idea for Mike Hurley's project Extra 300 in Model Aviation.
02-23-2006, 10:35 PM
#11
Thread Starter
RE: Foam Wings
Since the stabilizer is not thick enough to surface mount the servo, I installed them on the side through the root plate, the servo mount plate is fitted into the foam before skinning. Root plate is also installed.
02-23-2006, 10:41 PM
#12
Thread Starter
RE: Foam Wings
Here is the 1/64" plywood reinforcement strip for the trailing edge, this is coated with Tite Bond poly glue and installed when vacuum bagging. Also installed a 1/64" plywood strip where servo horn will exit wing near root plate. Getting close.
I install the 3/32" balsa tip plates prior to skinning.
I install the 3/32" balsa tip plates prior to skinning.
02-23-2006, 10:52 PM
#14
Thread Starter
RE: Foam Wings
Time to vacuum bag. No more than 5" of mercury vacuum, I use Tite Bond poly glue for skinning since it sets up faster than the other brands I have tried. It starts foaming while spreading the glue on the skin, about 3 hours under vacuum, the glue is set.
02-26-2006, 11:43 PM
#17
Thread Starter
RE: Foam Wings
First I layout the cut lines, then cut through the skin with an Exacto knife. The cut the foam I use a Zona saw with the reinforcement bar removed, the knife cuts guide the saw blade. Work slowly as it's easy to saw blade to wonder off course. The blade is very thin so not much material is lost.
02-26-2006, 11:51 PM
#19
Thread Starter
RE: Foam Wings
Glue the trailing edge on. I use foam blocks cut to fit the wing to hold it, nothing fancy just scape blocks with the airfoil shape cut on a blade saw. I use weights while gluing the leading edge on the the ailerons. Carve and sand to shape.
Tony Hallo
Tony Hallo
02-27-2006, 04:55 PM
#21
Thread Starter
RE: Foam Wings
I just sand lightly with a long sanding bar to knock the high spots down so the balsa has good contact, I use poly glue when expands and fills voids where foam is lost.
10-11-2007, 01:27 PM
#23
Thread Starter
RE: Foam Wings
I use the cheapest plastic drop cloths available and cheap latex chaulking for sealing the edge, five bucks of material does one plane, don't reuse anything, just throw the bag away after the glue sets.
You are correct as all my foam cutting and vacuum bagging equipment are home brewed, not much invested but the results are good enough for me.
Here's a 96" one piece Cessna wing I did in the past.
You are correct as all my foam cutting and vacuum bagging equipment are home brewed, not much invested but the results are good enough for me.
Here's a 96" one piece Cessna wing I did in the past.
10-11-2007, 04:15 PM
#25
Thread Starter
RE: Foam Wings
Check this post out, there's information I posted some time ago
http://www.rcuniverse.com/forum/m_39..._2/key_/tm.htm
On foam wings with tubes, I just stick the hose into the tube. My breather tube is a Sullivan Nirod outer tube (Blue) drilled with 1/16" holes every 1 1/2" or so, somewhat random, this is caputured inside a piece of rag material, nothing fancy. To be honest, I rarely use a tube, just try to locate the end of the vacuum hose on an area where a small indentation doesn't matter.
http://www.rcuniverse.com/forum/m_39..._2/key_/tm.htm
On foam wings with tubes, I just stick the hose into the tube. My breather tube is a Sullivan Nirod outer tube (Blue) drilled with 1/16" holes every 1 1/2" or so, somewhat random, this is caputured inside a piece of rag material, nothing fancy. To be honest, I rarely use a tube, just try to locate the end of the vacuum hose on an area where a small indentation doesn't matter.