Big Foamboard Spacewalker

(Comments and opinions written here are solely my own and are not intended to cause argument)

Throughout model aircraft history there has been a rather small, select group of designs which have proved to be so good, that they have become classics in our hobby.   To name just a few, there is the:

                                                                     Kadet Senior

                                                                           Ugly Stick

                                                                           Sky Raider

                              nearly all of the foam pusher props (Bixler, AXN, Cloud Surfer etc)

                                                most of the 40 to 60 size high wing trainers.  

                                                                          Telemaster

There are heaps of others but the list is far too long for this article but please feel free to add your own.  Now for a model to be listed above, whether it be a kit, scratch build or ARF it must do more than just fly nice.   It must be the complete package.  IMHO, this includes every facet of operation.   Ease of build/assembly.  Can it be built or modified to use gas, nitro or electric. Does it look nice both on the ground and in the air.  Can it be transported easily.  Ease of field assembly and if electric, access to the battery.   Then the flying including take off, flight, aeros, stability, landing and taxiing.

All of these facets contribute to the overall enjoyment.  Its not enough for a plane to merely fly well if it ground loops at the merest touch of throttle or if it stalls on [very] short finals or if you need hands the size of a 1 year old and the dexterity of a brain surgeon to install a battery.   I guess by now you get my drift.   All of the above mentioned aircraft are ones which I have had plenty of varied experience with over many years and which I consider to be brilliant in all of my criteria.

The subject of this article is another of my favourites and a favourite of many other RC modellers.   The Spacewalker is one of those old fashioned styled planes which thousands of people have flown and enjoyed over the years when they feel like just relaxing and stooging about.

Now there used to be quite a few balsa/ply ARF kits on the market.   The size ranged from around 1000mm (39 inch) to well over 2 metre (80+ inch).  The most common was in the .46 size, around 1500mm (60 inch).   They were nearly all red and yellow and no matter what brand, they nearly always flew great.    Well recently I had a hankering for another mid size Spacewalker but found they were very hard to get except for very expensive brands.   So in keeping with my usual thought processes, I decided to scratch build my own using what is now my favourite material;  foamboard (hereafter referred to as FB).

Its a funny thing when you start to design your scratch build as to what factors can dictate your build.  It may be what power unit you wish to use, or the physical size of the finished model or even the size of the plans you use.    I even once built a plane specially to suit a pilot figure I wanted to use.   In this case I wanted the plane to be around 1500mm (60 in) wingspan but most importantly was that I could build the fuselage without joining sheets of FB together.   So first off, on to the computer and Google images, typed in "RC Spacewalker aircraft plans" and found this:

I printed it out on A4 paper.   Then I measured the main fuselage sides which came out at 103mm (4.05 in). The FB I use measures 860x590 (33.8x23.2 in) so I played around with an on-line percentage calculator and came up with 780%.  This would give me a fuse length of 804mm (31.6 in) and a wingspan of 1480mm (58.2 in).   After this, I simply measured all the rest of the plans, did 780% conversions for all and then retired to the workshop and grabbed my ruler and pen.

The wing is very conventional for anyone who has watched a couple of the Flite Test build vids.  I simply drew the outline on the FB, added all the score marks and CG and spar position and got cutting.   I won't bore you with all the step by steps but here are a couple of piccies to give you an idea.

I always reinforce the leading edge fold and the ailerons with fibre tape and so I do this before I start glueing. I've also come up with a method of putting down the tape without wrinkles.   If you look closely at the above photo, you'll see that I have stuck the end of the tape to the desk.   This gives me stability while I put the tape down and you can pull the tape to keep it straight.

I also use a straight edge to push it down.  

I also built a few degrees of dihedral into the wing in the method that Flite Test use.   A small gap is drawn into the wing upper join and when the two halves are joined, a heap of glue is poured into the gap, particularly where the spar is and one wing tip is supported and left to dry/cool thoroughly.

So much for building the wing, you'll see it completed shortly.  And so onto the fuse.   The two sides were drawn and then cut out as well as three FB formers and a 5mm ply firewall.

Note the use of a square.  I made this one from FB because I wanted it small enough to get in tight spaces.   Don't ignore this step.  The squareness of your formers will determine the rest of the build and possibly effect the flying characteristics.

Some forward planning is needed here, make sure you cut holes in the formers to allow for pushrods.   Also, as I don't know at this stage where I'm going to mount servos, receiver, battery, ESC etc, you need to keep everything as open as possible.

Here is a very early mockup to see if everything "looks right".   Note the wing is finished.  And so onto the tail surfaces.   Same routine, draw on FB and cut out.  Then single bevel for rudder and elevator and check to see how they look.

After the fin and horizontal stab are glued in place its time to install servos and pushrods.

I chose to use the old wire and dowel pushrods for their lightness and stiffness.  If there's anyone who doesn't know how to make these, let me know and I'll write a how-to article.

The underside is sheeted.  Note things such as the large rectangular hole to allow cooling air to flow through the fuse.  Also the cut out area where I later glued in a 5mm ply plate to mount the tail wheel.  Also note the paddle pop stick used as reinforcement between the two elevator halves.     Next is the top turtle deck.  Flite Test normally use poster board for this but I find it flimsy and distorts easily so I try and use FB where ever possible.   Unlike the FB that Flite Test uses, my FB is very difficult to remove the paper covering.  So for curves like the turtle deck, you have to convince the FB to bend to your will as the following photos show.

I draw out the rough shape which is usually wider at the front and narrower at the tail.   Here I drew lines which were spaced 10mm at the front and 5mm at the tail.  These are then score cut and a sharpened popsicle stick used to open the cut.

The piece is then bent and shaped and the final measurements marked.  The excess is then cut off and the whole lot glued on in two steps.

First one side is glued on and allowed to dry.  (Note that the side edges have been cut with a slight bevel for a neat join).    Next glue is put on the formers and the fuse side and the turtle deck folded over and held in place.

And there it is.  Nice and solid and not a piece of sticky tape to be seen.  Next up, the forward fuse top.   I could have made a rounded top but for simplicity I decided to go with just a flat top.

I did however make the cockpit slightly 3D.   This would look much better later when painted.

The top plate is held on with two magnets.   Note the extra FB plates which sit neatly between the fuse sides and stop the top from moving around.   Also at the bottom of the photo, you can just see the end of the battery tray.   This model uses a 2700 to 4000 3S Zippy compact.  As you can see, putting battery packs in and out is very easy for even my big stumbling hands.

The main undercarriage is bent from 4mm spring steel rod.   I have used 3mm ply for the forward underside of the fuse.

And here she is all ready for motor and other gear.   Installing all of this is fairly basic so I won't bore you with it. The motor is a (now) rather old and very well used Turnigy G25 with an equally old and well used 50A Red Brick ESC.   Prop is a 13x6.

Before doing all the nice finishing touches I took it out for a maiden/test flight.   I will soon have a mobius camera and so will be able to join the "Hat Cam" brigade, but suffice to say she flew beautifully.   ROG was about 15ft and landing was about walking pace.   Stall was almost non existant, she just bobbled around a bit but never dropped a wing.   Once off the ground, the throttle sat on about half for the whole flight and she was rock steady in the air.

And so next was to do the finishing touches.   Flite Test suggest using Minwax to seal your FB but here in Gods Own (Australia) I have found that "Cabots Oil Based Polyurithane" works very well.   After two thin coats I just used el cheapo rattle cans to paint it.

 Just a couple of final points.   You'll see that the ESC is mounted in behind the firewall where it would get no cooling air.   So firstly I cut away some of the heat shrink covering from over the heat sink.  I also cut an air duct and covered it with an air scoop.   I make these from cutting up a plastic spoon.  Make sure you really scratch up the inside edge of the plastic so the glue has something to bite on to.   I was worried that air could still get in under the top fuse plate so I used a piece of BBQ scewer to hold it down.   The windscreen is cut from a Pepsi bottle.

So there you have it.   A .46 size model of a very popular, tried and trusted subject which was interesting to design, cheap and easy to build, looks different from all the other ARFs out there and flies every bit as good.   Oh and speaking of cheap, this only took about two and a half sheets of FB.   So it cost me about $20 Aud.   Everything else I already had.   Now if I had bought that ARF I mentioned at the start, it was around $250 for the kit and then postage on top of that.   There would not have been much change from $300.   I still would have used motor, ESC, servos etc from my own stock so using my on line percentage calculator again I see that I have saved......er......bloody heaps.   And whats even better, I have the pride of designing and building it all myself.    Gotta love scratch building.   

https://youtu.be/g4_kc7tD0M4