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Apr 12, 2020, 02:19 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
It took me quite some to time to come up with a neat way to attach the cowling.

1. 4x flanged screws standing off about 2mm.
2. Slots cut into cowling backing plate to allow the heads of the screws to slip behind it.
3 & 4. Fit cowl and push down to lock into place.
4. Retaining screw to prevent it from sliding back up.

It seems to work very well and is a snug fit.

After that the tail wheel was a breeze.

Next: Control horns, elevator link and battery hatch.
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Apr 12, 2020, 02:17 PM
Foam is my friend!!!
NewZee's Avatar
That's some slick engineering on the cowl attachment! if you can reach the heads of the flange screws with the cowl in place, (prop and spinner off), you could even tighten them down a bit, although your retaining screw should do the trick! Well Done!
Apr 14, 2020, 12:13 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
I must admit that installing control horns has always been a bit of an after thought for me and as a result it becomes an unnecessary source of frustration.
This time I decided to throw a few more little gray cells at the problem.
First off I enlarged the elevators by about 25% because I reckoned that the originals were a bit pewny. More importantly, they look nicer now.

1 & 2. The connecting wire is around 2.25mm and it is attached to 2.5mm ply plates with cotton thread doused in CA. Small notches were cut into the back side to allow the threads to sit flush.
I carved out recesses in the elevators so that whole assembly sits nice and flush. I used PU glue for this job due to its excellent binding properties on rough surfaces.
End result is a very rigid link between the elevators.
3. I think this the first time that I have installed control rods etc without having to put kinks and bends in them.
Last edited by brett.c; Apr 14, 2020 at 12:23 AM.
Apr 15, 2020, 12:04 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
The battery hatch.

1. A couple of old motor magnets are epoxied to a strip of ply. These magnets tend to be strong and are ideal for hatches etc.
2. For the other side I like to use these large size picture frame hangers. Just straighten one leg out and bend to suit.
3. The rest of the pieces are laid out here. I decided to use pilot Pete as the hatch handle. To do this I "inserted" a plastic plaster screw (don't worry he was sedated first) and a 5mm screw to hold him securely to the hatch.
4. This is the hatch complete but not glued. I will do this once painting is complete.

Next: The wings.
Apr 16, 2020, 03:46 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Hotwire cutting wings, my least favorite job.
Usually something goes wrong when I try this and it takes a few goes to get it right.
Luckily these ones came out none too shabby on the first attempt.
I upgraded the bow from 20lb to 60lb wire so that I could give it more tension. This seemed to help.

From the plan I deduced that the cord thickness was something like 18%. I wanted something a little thinner and more sporty (and easier to cut). Therefore, I went for the S-8035 14% symmetrical profile. Not that I'm all that much into the pros and cons of wing profiles , it's just that I liked the shape, and you really can't go too far wrong at this scale.

The first cut was a little ripply because I didn't have enough weight on the drop arm causing the speed to be a little slow. Nothing that a bit of sanding and filler won't fix. The rest came out ok.

Next: wingtips and ailerons.
Apr 16, 2020, 08:38 AM
Foam is my friend!!!
NewZee's Avatar
Brett, you are making excellent progress! thanks for sharing your techniques! I'd be more than happy to get results like yours!!
Apr 17, 2020, 12:13 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Thanks NZ.
This little project helps keep me sane while the rest of the world is getting crazier.

Today I finished off the wing tips. I borrowed their styling from the Space Walker.
I also cut the wing profile into the fuselage giving +1 deg of incidence as per the plans. This involved delving way back into my high school triganomtry days (a long, long time ago) which provided me with a 4.2mm delta on the leading edge.
Ailerons are marked out at 45x350mm which should give me plenty of roll authority without being too twitchy. The original has strip ailerons which are a bit too thin and floppy when done in foam, so the good old barn door type will suffice.

Now I'm trying to figure the best dihedral angle. Too much looks like a dorky trainer and too little looks like a plank. Plans call for 25mm at each tip but I'm thinking of going with 20mm purely for aesthetic reasons. My rule of thumbs is that if it looks right it will fly right.

I'm also pondering whether to fit the landing gear to the fuse or on the wings as per plan. Each has their pros and cons. Ether way I will make up some wheel pants in keeping with the overall streamliner theme.
Apr 17, 2020, 08:24 AM
Foam is my friend!!!
NewZee's Avatar
It looks "Fantastic"!!! can't wait to see it as you add color!! a few things to share (You may well know all this already), Here is a link to a great airfoil tool!! http://airfoiltools.com/ , it lets you search, plot, and scale any airfoil you like if you play with the airfoil plotter tool you can change cord, thickness, pitch etc. helps loads in making hotwire templates! I also have used balsa (see pics) for long thin ailerons on foam wings! (Solves the "floppiness" issue)! I think 20-25mm on dihedral would be just about right! the "Spacewalker" wingtips are perfect!!
Last edited by NewZee; Apr 17, 2020 at 08:32 AM.
Apr 17, 2020, 05:17 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
Nice foam and tape build there mate, I reckon it would be a hoot.
I did similar on this one https://www.rcgroups.com/forums/show...4-clone-cloned. It is the best flying plane I've ever built and beats anything I have bought.
I just don't have any balsa at hand and the "challenge" of this build is to use whatever is in my shed.
Came up with that airfoil by doing some research on this forum and from that site. It seems like a good all rounder if you'll excuse the pun.
http://airfoiltools.com/airfoil/deta...rfoil=s8035-il
Apr 17, 2020, 07:52 PM
Registered User
crash&fix612's Avatar
Nice build, and cool plane. But don't ya miss the days when RCM always had a picture of a pretty girl on the cover
Apr 20, 2020, 08:06 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
Wings are now complete and it's getting close to covering time.

To get the right dihedral angle meant drilling the hole for the spar at 1.9deg. The spar (and drill) is an 11x750mm CF tube.
I also drilled out holes for the servo leads.
With the alternative wing tips the span was increased to 1300mm, so I sliced 25mm from the center section of each wing to bring it back to 1250mm.
I've decided to go with a simple center mount off the wing for the landing gear. The struts will be 2mm aluminum with yet to be determined wheel pants.
The wing will be permanently attached to the fuselage because I see no need for the extra complexity and weight by making attachment points. Besides, I think it makes for a much stronger airframe.

All foam pieces have now been given the boiling water treatment which removes 90% of all construction dings and scratches. You can use straight boiling water as I doesn't cause issues like with EPO foam.

Next will be some filling with lightweight spackle, final sanding and a coat of PVA/Water prior to covering.
Apr 22, 2020, 02:15 PM
Foam is my friend!!!
NewZee's Avatar
Looks good! good call on the permanent wing!
Apr 23, 2020, 03:19 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Paper covering has started.

This is my 4th paper covering job and the first time that I've had issues with warpage.
I put this down to the type of glue I am using and the unusually warmish weather lately.
I use exterior grade Gorilla wood glue which is faster drying than normal PVA wood glues. This does help when doing curves and edges because the glue goes tacky rather quickly making it easier to fold over the paper and get it to stick. I guess everything has its price.
Fortunately a bit of steam and bending on the rounded edge of the kitchen bench brings everything back into alignment.
My main concern is with the wings, so I'll do them in the evening when its much cooler.

Prior to covering the bare airframe weighed in at just under 450grams. My estimation is the covering will add another 100grams to that and about 5 times to the overall strength and durability.
Apr 23, 2020, 07:16 AM
Foam is my friend!!!
NewZee's Avatar
just curious if or how much you dilute the glue? and do you really "soak" the paper in the glue, or just apply the glue to dry paper??? I've played with brown paper on foam, but have yet to "develop" my technique!!?? (I wish it was warm here!! I'm in western New York State, North East US, and winter just won't die!! temps are in the mid 40's F, I'm ready for Spring!!)
Apr 23, 2020, 05:50 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
Hi Zee, I generally follow the Hoppy method https://www.rcgroups.com/forums/show...ng-improvement
The paper I use is recycled rubbish and it cannot be soaked for too long without tearing. You also can't cut it once it is wet. I really need to find a source of decent virgin paper, and haven't found one of those in years.

I use between a 60-70/40 mix with the outdoor glue and 50/50 with ordinary PVA.
Prior to applying paper I coat the whole airframe with a glue water mix. Once dry I give it a light sand, clean with compressed air and a wipe down with isopropanol alcohol (IPA).
I cut out the shape and wet both sides of the paper using a foam brush. Then I wet down the foam. Once the paper goes dark I know it is fully soaked through and can begin applying it. I use a credit card to squeeze the excess glue and then squeegee it with a kitchen sponge. You can't play with this recycled stuff for too long because it begins to tear and gall up.
I prefer to fully wrap the part so that when the paper shrinks it applies even pressure to both sides. It also leaves a tight stressed skin which I believe gives it greater strength. Seams and joints should be done on the underside wherever possible and I prefer to align them with edges and rounded surfaces where feathering in hides them.

Tips. Pick a plane that has lots of flat surfaces and not too many compound curves. This makes the job a whole lot easier and far less frustrating. This is why I prefer the old slab sided balsa designs.
Your plane to going to end up on the heavy end of the scale but it will be extremely strong and rigid. Chose a design that has a large wing area for its size. This will help reduce the wing loading.

So far I have done 3 planes this way and all have turned out very successful. Although a bit heavy they seem to fly a lot smoother than my other foamies. They are also more responsive and once trimmed they stay trimmed, unlike a lot of foamies which always seem to need a click or two every time you fly them.
Last edited by brett.c; Apr 23, 2020 at 05:59 PM.


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