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Scale Foam Scratch Build: Inspired by David, For teaching everyone

willsonman

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#1
IMG_8096.JPG IMG_8094.JPG IMG_8093.JPG IMG_8092.JPG Ok, so, I've wanted to build this subject for quite some time. I've had parts to do it but just never found the motivation. I love building. I love it more than flying. Since David is so fantastic in this area as well I figured I would do one... "For Him" per se but really its inspired by him. I also wanted to capture many details about building a scale plane from scratch for many who are new to the hobby but also new to building with foam. Many techniques I have picked up from others and a lot are improvised.

I will not reveal the subject but As it gets built I am sure it will be guessed. Info about it is... It is VERY RARELY built. Thats all you get for now. So first I got my 3-views from Google. Most will do fine but this one was actually for an RC plane and already had fuselage templates. So, I figured what size I wanted. We are looking at a 45" wingspan. The goal is to have very scale features for its size without going overboard. I will be scratch building it all so lets get into it

I started off with the center wing section. Wing will also have two outer wing sections with dihedral. The scale airfoil was selected for the root and tips of this section. See my tutorial on how to do this.Very simple cut but I messed up the first core I made. Foam is cheap so I made another in about 10 minutes.

Based on the plans I measured for the Landing gear placement. I centered up the servoless retract and pressed firmly to get a nice outline. I bored out the foam using a dremel with a slight incline using the TLAR (That Looks About Right) method. Once done I bonded hard points with hard balsa using gorilla glue. This will be the rails the retracts screw into. I drilled small holes through the rails and inserted carbon fiber rods with gorilla glue for strength. I also lined the insides of the bay with balsa for additional strength.

Back for more later.
 

willsonman

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#2
Making the horizontal stabilizer is quite easy. I printed out the profile from the 3-view and enlarged it the appropriate amount. I traced it onto $tree foam board making two complete copies. I peeled off paper from one side of each and applied super 77 spray sparingly at 18" distance. Once fairly dry and tacky I mated to two together and placed on my work bench to dry with weight on top to prevent curling. I then beveled the leading and trailing edges. The leading edge I beveled with my sanding block. The trailing edge I wanted more of a taper so I used my metal bastard file as it cuts quickly and the long file allows me to get the longer bevel I wanted for an overall airfoil shape. I then cut out the elevator profile from the printout and traced the cut onto the foam. Once done I did a final sanding on the corners and used the file again to create a nice taper to the rounded edges.

I then went on to install the spar. I used some carbon fiber rod for the spar and cut a grove in the foam just deep enough for the tip of my bit to make the groove. I inserted the spar with gorilla glue and allowed to set for an hour. Once dry, I picked out the foamed up parts and again used the dremel to cut away any residual hard glue that would not allow me to sand. I applied some lightweight DAP spackle to fill the gap and it will set overnight to dry.
 

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willsonman

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#4
So, once the spackle is dry gently knock off the major bumps loosely with your finger. Basically this prevents the dried chunks from marring up your foam when you go to sand. Then lightly start to sand eventually giving pressure to cut through the spackle cleanly. Once smooth cut out your control surfaces. Select some thin Balsa to give the joints some hardness. Cut the thickness of the balsa away from each surface you will glue wood to and apply the wood segments using Titebond II. Hold in place with tape until dry. In this case tomorrow.
 

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willsonman

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#6
You are quite welcome. I love to build and I love scale modeling. Its a dying breed for sure with all the easy foamies and ARFs out there.

So, the next steps here will not really involve too many pictures. The plan next is to rim up the balsa hard points and sand it all flush. Once that is done I'll install a couple hard points for the elevator hinges. The actual plane has them aft of the break line. A couple small blocks of balsa will go there and hinges will be installed after covering.

I can show pictures of what follows. The leading edge (LE) will be rounded on the elevator but the trailing edge (TE) of the horizontal stabilizer (H-stab) will remain square. The two elevators will be joined by the control rod and linkage will be internal. After joining the elevators I'll cover them and a small cut will be made in the H-stab and repaired for the hinge point of the control rod.
 

earthsciteach

Moderator
Moderator
#7
I had the idea of using Starbuck's coffee stirrers on on my hinge surfaces of the STOL plane I'm building as you have done above. However, the width is just a bit off. The doubling of the foam is the solution I needed! Can't wait to see more of what you are doing.
 

willsonman

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#10
In the lower left you can see the control horn construction. Its a simple bent coat hangar wire bent to shape. The white piece in the center is a piece of plastic from wire hold-downs that are tacked down. I removed the tack and trimmed the loop around. Once I get my positioning set I'll gorilla glue to the rod. The tubes over the wire will be embedded in the foam and act as a bearing.
 

willsonman

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#12
IMG_8107.JPG IMG_8108.JPG IMG_8109.JPG So, any guesses yet on what subject this is? Moving along... I had a fly-in to attend last weekend so I had to get all my planes ready to go for that. I'm back on the build now.

So, for the fuse templates you have to use reference lines to get them to align right. So, The vertical center line is easy to get from the former templates off the plans. The horizontal you have to measure from the top of the former to the datum line (thrust line basically). Once marked on the templates I spent about 1.5 hours prepping the templates with my aluminum ducting tape. Works wonders on the hot wire and WAY easier then cutting out formica or wood. So with all the templates ready I measured the distance between each fuse former and wrote it down on a list. Creating blocks of foam based on former distance(thick) and overall width and height (from the fuse formers to be used for each block) I made a single block at a time so I did not mix them up. Now, I'm using 2" thick pink foam. One of my formers was at 1.5" width and another at 2", another at 3.5". For the 1.5" I simply measured a line to cut around the perimeter and cut with the foam off that was not needed. I used this same technique with the block needed that was 3.5" thick. I simply bonded two blocks of foam together with a light coat of Super77 and held them in front of my fan for about 10 seconds to help the acetone evaporate. By then it was super tacky and I joined the two. Now you have a 4" block of foam that a hot wore will easily cut through.

I used my small bow (14") to cut the outside. It has a thicker wire that allows for smoother cutting. I used my vertical (think scoll saw type) for the inner cutting since it has a smaller diameter wire and I really do not care what it looks like. I got several cuts done before breaking for dinner.
 

willsonman

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#13
Ok, BIIIIIGGGG update. I was able to finally finish all the "donuts" for the fuselage. I left the center section where the wing cutout would go unsecured from the fore and aft sections. This allowed me to draw a line in reference to the datum line(also used for foam cutting the fuse) and draw a line for the main wing. From there it was as simple as taking the same templates used to cut the wing core and cut the sections out of the fuse with the hot wire. Once one cut was done the saddle was then cut separately for ease. This same reference line was drawn for the H-stab.

I got the V-stab cut out and put in balsa reinforcement. I started to cover it but I'll get more into that later when I go to cover the H-stab.

I couple areas I had to actually work... The aft angled area of the cockpit I had to carve out... again using reference lines to the datum from the 3-view...I just used a coarse bastard file then a fine metal file. Finished up with some 220 grit sand paper. an additional section for the V-stab mounting plane had to also be cut into a fore former just aa bit and I used that same method.

I also have carved out TWO pieces of foam for the pylons that conceal the landing gear. They are ready for glassing. More on that later.

Please keep in mind this is just a dry mock up:
The H an V-stabs need finishing before mounting.
The wing still needs a spar a outer sections
The fuselage sections are only tacked together with Super77 spray
The Pylons need to be glassed, trimmed, sectioned, and mounted. They will be cut into 3 sections

Still no guesses for what plane it is? Wow it really is obscure.
 

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willsonman

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#14
Ok, on to the H-stab covering. I do it this way because of several things. 1: Its fairly easy AND cheap. 2: it adds a bit of strength for the weight applied. 3: This will seal the foam so that you can use whatever paint you want. Acetone based or not you can spray, brush... whatever you want to this surface once its done. Even Acetone based rattle cans will not penetrate with a heavy hand. 4: DING RESISTANCE. I cannot tell you how many times I have gone to the field and cursed because of something dinging the foam in the back seat on the way. I'm a perfectionist that way. This adds quite a bit of resistance. 5: Waterproof. The bane of MD is humidity and this works for my humid climate.

General rules: More layers adds strength but adds more weight. I usually do one or two. Two for strength on weaker parts. I never wait for the first coat to dry but add the second right away. Don't expect to do this right the first time. Practice! WBPU can get sticky as it dries. Make sure you have something down while you work. I use wax paper. A warm summer garage will help this to cure faster.

1: cut out tissue paper large enough to cover an entire side.
2: Brush on WBPU. Not thin... not thick... enough to get the paper to stick but not entirely bleed through.
3: Apply your sheet of tissue to the wet side
4: Brush on a layer of WBPU pretty thin but enough to get the paper entirely wet. It will change color.
5: Brush the WBPU just past the edge of the surface and it will make the paper wet and then you can tear it away rather than cut it.
6: If you have torn away too much material simply patch it with craps from what you tear away. Do not be too worried about the "patchwork" look. More to come.
 

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willsonman

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#15
Doing some digging tonight after a trip to the field to get a few flights in I remembered a great source for plastic parts I wanted to share. Park Flyer Plastics. I have one of his cartoon P-40 kits and it was a breeze to build and totally looks dorky. Fun though. I have conceded and will forgo scratch building the cowl and bombs. At $6 for a cowl and another $6 for the cowl extension its hard to justify the time and headache of scratching a cowl. The bombs are $4 and I get 4... which is what I need. It will be a tight fit in the bay but that is what I was expecting. I highly advise you all to look there for various parts as they are all made in the good ole' US of A and are top shelf. I've also gotten a replacement cowl for my parkzone corsair and it too is a great piece. Thicker plastic and perfect fit.
 

Jaxx

Posted a thousand or more times
#18
This is incredible! I wish I had skills like this, but it looks like a very intimidating process. How long have you been doing this, and was it difficult to lean?
 

willsonman

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#20
Jaxx, I've been building with composites for a couple years now but honestly the learning curve is a lot better. Mostly because materials are cheap so if you mess up you rarely care! Try something new. Look at other building styles and try it! I'll also let you in on a little secret... I've never done a fuselage constructed this way! I took my wing core skills and they transferred over to the fuse sections easily.

Dauntless? Nah, already got one! Fish again!