ewan

The builders kit consists of a quality painted lightweight fuselage (1003gms inc canopy) with the rudder already hinged. U/C legs, wing and tail tubes,ply battery tray and tube hard points are also included in the kit. The tail tube holes are already drilled. Wing and tail drawings are in PDF and Cad format with dimensions which were easy to transfer or print.
About 10 days into a wing and tail build, future posts will include lots of photos of progress.

Ewan & Hamish Galloway

ewan

Here are a few photos of the kit. Photo inside the lower rear fuselage shows the paper tube for the servo leads. Crutch is light and works well. Everything fits together really well. Canopy attachment is very secure.
Next postings I put on will be about building wings. It's been a long time since a lot of us have built a foam wing as we have all been buying ARF's.
Ewan

ewan

The Plans.
The plans come as PDF and DXF files. The dimensions are imperial and they transfer easily. I was brought up on imperial but run a metric workshop. A calculator and the digital vernier metric conversion helped. You really only need to print off the airfoil sections full size. These are drawn for hand cutting. I draw the working plans for foam wings on 200gsm poster card. They are usually coloured and it is rare for me to do a white set. A1 sheets are available from most book shops. Years ago I did them for cutting the foam blanks and they had no other information on them but these days they are the master plan and everything is on them. Dimensions of where the wing tube is, the servo and hardpoints are cut out which makes the transfer to the foamcore and ultimately knowing where these are after the wing id skinned.

ewan

Foam cutting.
There are 3 basic methods of foam cutting with a hot wire. Hand cutting, drop arm automatic cutters, and CNC.
The plans templates are drawn for the hand cutting method which most of you will be familiar with and in reality most of you will cut a one off this way. I read about it in a 1961? Model Airplane News and was on the other end of the bow in 1967 when I joined a club with some good F3a flyers in it at the end of the reed era.
The bow was the familiar "H" bow suspended on each end by pulleys and weights. When I started cutting in my own workshop I suspended it from 2 bungees and finally tried a single bungee tied off on the center bar and cable tied to the top tensioner. This bungee wants to be as long as possible and I have a chord with a dog clip passing through an eyelet in the ceiling that can be tied off on a wall hook. Run the power cable up the bungee to keep it out of the way..Put a couple of pieces of dowell on the wire to hang onto.
Templates from bench top formica, The old stuff was thicker than the current product, I often glue it back to back. A good smooth edge, and wax it with candle wax. I have seen aluminium templates used but they cool the wire near the edge of the cut.
Stick them on with double sided sellotape plus a few big pins.
Make a lining template from scrap 1/16 balsa that fits under the template for setting up. The errors can add up if you are lining to lines on foam and the template, photo shows the shaded area of the template.
Do the top cut first. Cut the panels as left and right. Symmetry is important on an aerobatic aircraft.

In 1999 I made a drop arm cutter which uses separate templates for the top an bottom cut, I have cut my wings on this cutter. Following posts will show the cutter in use. About this time I saw and built wings from a commercial CNC cutter, I was not convinced! In recent times I have worked with Rod and he has his CNC cutter sorted. I think he is now on version 3, 3.2 meter IMAC wings provoked the last rebuild.
Besides the CNC accuracy for airfoil reproduction the wire is run hotter and cuts with radiated heat without actually touching the foam so there is no wire drag, the extra melt around the wire is programmed in. That is why they can cut around leading edges so well.
Photos show the area shaded for 1/16 balsa template and the original "H" foambow from 1967, the underslung bow is from the drop arm automatic cutter table, the table below. More on that later

Ewan

Jason Arnold

Hi Ewan,

I love the candle wax trick on the templates.

Very much looking forward to seeing the rest of your build.

Cheers,
Jason.

rm

My Feedback: (27)

So if you want one of these you have to have a foam cutter and be able to find foam?

Portlandflyer

Or use a cutting service

http://www.matneymodels.com/wingcut.html

https://www.flyingfoam.com/

There are others

Jason Arnold

Something like that is an option or soon a built-up wing and stab kit will be available.

Cheers,
Jason.

ewan

The drop arm auto cutter.
This cutting system uses a weighted arm to pull the wire through the foam with a chord at each end of the core and pulleys (usually 3) so they run at the correct speed.
Instead of a template that is the shape of the airfoil it runs separate template top and bottom templates.
The bottom cut is always done first and the core drops down into the shuck, and then the top cut. The foam melts cancel each other as long as you don't change the cutting speed between the top and bottom cuts.
The foam bow is always sits on the templates and an underslung bow with its frame under the table can be used on wings but not very well on tailplanes, fins and rudders where the bow has to rotate a lot in the cut. The final result is almost exactly the difference between the top and bottom templates and it is possible to cut TE's consistantly 1mm thick.
Mine was the fourth one built around here (about 1999) and incorporated ideas from the ones before it. The templates are quick change and lock into the table. This machine has been used on production runs and at one stage I had my 18 year old niece running it. Only one bad afternoon when one of the templates didn't lock in properly on left wings for a 100 inch IMAC design.
I don't know who came up with this system, but he sure deserves credit.
Photo shows how the templates fit into the table.
So, three methods of cutting wings, they all work well with attention to detail.
The build is running 10 days ahead if the script. Next posting will be making the the top and bottom templates from the drawings.
Ewan

ewan

Cutting Templates.
The ready access of photocopiers has made life much easier for this task. Keep the original as a master and take a copy for sticking to the template stock (double sided sellotape). As this is a symmetrical airfoil you only need one cut for the top and bottom template so make an accurate one. Clean up the concave bottom one and sand the top convex one to fit it. Continue the trailing edge past the foam at the same angle as any lag in the wire will be pulled at the correct angle. I do the same with the LE too by habit (no good reason). Mark the LE core position on the template as the core is lined up from it during cutting.
Tape the templates together with masking tape. The final result is the difference between them, make no allowance for anything. Get the TE's right thickness as per the plan, check the chord length. Consistent 1mm thick TE's are possible. I bolt them together when I am happy as a reference. Trim the bottom to correct incidence and foam thickness. This cutter needs an extra 16mm for the clamp sections.Final decision is where the core will sit on the table, the root template needs to be up against the foam core. On the Allure the wing seats parallel ant the TE is straight both the root and tip sections will be the same distance from the front of the cutting table.
Changing templates in practice simply push the down and pull back against the stop.

Ewan

ewan

Wing build.
There are a few basics to building a foam wing with many slight variations on the way it is done.
The end of the tube is where the most local stress is in the wing. The plan shows a half rib for support, I use a full rib, usually liteply with large lightening holes because fitting is accurate and easy with one slice with a foam bow and glues in with aliphatic (no heavy bog).
The structural failure point us just outboard of the end of the tube, The plans show some carbon uni under the wing skins which is very normal practice, I will be notching the foam with the foam bow, carbon tow under a 1/8 x 1/4 balsa cap.
Boring an accurate hole for the tube sleeve is a must. Dihedral is 7mm on the C/L of the wing and must be as designed because it affects cross mixing. Boring holes with some form of cutting tube on a guide is common practice. I cut them with a foam bow using the root rib and the end of tube rib as the wire guide.

With the above in mind, the approach to the build will be.
1; Cut the core and lower scab off with the foam bow.
1; Notch the spar grove in with the foam bow.
3; Cut the core and lower scab off at the end of the tube for the rib.
4; Fit the root rib and the end of tube ribs or a master template copy and cut the tube hole.
5; Glue the lower scabs back together with aliphatic and the outer wing panels back on.
Photo shows the wing plan with the panel cuts , spar etc.
Ewan

ewan

Here is a photo frame of notching the spar into the foam.

Jason Arnold

Love the little dowels so you don't burn your fingers.

ewan

Ribs.
Photo shows that have been made as left and right pairs. This tail plane set are made from lite ply with suitable lightening, tube and coring holes.
They are made as inner and outer sets double sided taped together to make identical left and right pairs with tops marked so any errors in cutting the holes for the tubes cancel each other out.
The wing ribs can be made this way which is my normal system.
We have decided to make these as composite ribs which are not going to be smooth enough to cut the tube and lead holes so a pair of hoop pine masters have been made. Important to cut the root rib tube hole above the C/L to achieve the correct dihedral. This is 7mm over the panel length of 845mm, which is 2.1mm over the length of the tube sleeve. Mark the top of the panel and the top of the rib and don't make a mistake!
Photos show boring the pilot hole for foam bow and the foam bow cutting the tube hole.
Ewan

ewan

Wing fit.
Good time to mate the wing to the fuselage before going any further with the wing. This is a good time to sand the foam on the end of the core for a good fit as I will glue the root rib on before skinning the wing.
The root rib template is seen here against the wing fillet to mark the tube holes and the incidence pins. The tube installation in the fuselage could be done now but I have only cut the holes in the right place.
No fitting was required, a good sign everything is true. Ewan

ewan

Composite ribs.
Here are some photos of the composite ribs used in the wing. At 25gms for the pair they are a little lighter than liteply with lightening holes in them as I used in the tailplane. I weighed the template ribs that these were cut from (they were either hoop pine or birch) and they were 65gms for the pair.
The composite ribs were made from a layer of 90gm (3 ounce) carbon cloth either side of 3mm a rohacell 51 core which have been vac bagged with peelply and soak cloth to remove excess resin. The liteply hardpoint for the wing
tube and wing retaining blind nut can just be seen through the carbon cloth.
Blind nut for wing retaining bolt fitted before the rib is glued to the foam. It is hard to fit later.

Ewan

ewan

The wing tube sleeve is glass fiber reinforced with a fine tolerance on the tube (but OK). I made sure the sleeve with tube inside was a good slip fit through the wing ribs and foam core and glued it in with PU glue. It really only needs to be glued into the ribs for flight loads but I put a smear of glue on the foam near the ribs with the intention that it will expand and support the sleeve while taking the wings on and off. I left the tube in the sleeve while the glue hardened.
Important to bung the ends if the sleeve to stop the tube from damaging the foam. Drill a hole in at least one end to release the trapped air while taking the wings on and off and leave a track for the air to escape through the foam into the lead hole.

Ewan

brustyrc

Greetings Ewan (and Hamish), Just subscribed and following with great interest. Your skills just keep growing, Cheers, Barrie.

ewan

Hi Barrie,
You would enjoy flying one of these new generation F3a machines. They are great for us aging flyers as well as the younger generation(s)

Ewan

ewan

Spars.
3 tows of 12k strands of carbon are laid into the groove cut by the foam bow and a strip of medium balsa laid on top next to the wing skin.
Only one tow is full length, the others are staggered. I have used this system since seeing it in the English RCM&E mag in the early 90's. Wing failures are usually compression breaks and the carbon separated from the skin in this way actually goes under tension to prevent the skin creasing.
There foam cores are going to get a lot of lightening holes in them and foam does not take shear load very well at the best of times so I have cut in a 0.8mm (1/32) ply shear web outboard of the tube. It only weighs 2.2gms, we will get 40gms of foam out with lightening.
The top of the balsa spar cap was cut off with a razor plane and taped and the wings weighted in their shucks to keep them straight.
Ewan

serious power

Hi Ewan,
Are you going to film cover these - or what ??

Brian

ewan

Hi Brian,
I will use film as it is the lightest finish. Spraying (saturating) the balsa with budget hairspray and letting it dry completely before the final sand helps adhesion and will only add 2gms per wing.

Ewan

ewan

Servo boxes.
Cut the holes for the servo boxes and hardpoints for servo horns and incidence pins. These templates fit most F3a wings and I have a larger set for IMAC wings. The mini foambow wire is quick release on one end and has a switch mounted on it.
Ewan

serious power

Hi Ewan,
Thanks, it helps to understand the process.
Heard of using hairspray to reduce epoxy soak-age when glassing but not ,till now, as an aid to film adhesion - interesting.

Brian

ewan

Hi Brian,
It seems to act as a sticking agent rather than just a sealer. However it does make any ball point pen marks run, must try a different type of pen.
Dope is good for reducing epoxy seepage.
Ewan