Footy Sailboat model yacht build log: Part 2, Finishing the Boat - Ready for Maiden Voyage

Hard to believe that Part 1 of this series was 10 years ago! To say that many things happened during that time would be an understatement. The pandemic, lockdown, loved ones passing away, and many changes. A few weeks ago, I “found” the unfinished boat tucked away in a shoebox, where I'd put it aside. Its cute size and recent memories of taxiing my plane on water made me want to complete it. This would be my first time building and sailing a radio control boat. This one is based on the Papaya 3 Footy by Mario Stiller. Single chine, flat bottom. Before the delay, I had started to build it in 3mm Depron foam, instead of Stiller's balsa, glued together with Uhu Por. This post documents how I completed the model and tested it ready for the maiden. 

Keel and Bulb 

I do not fish, but 10y ago I’d also put aside a bag of 200g fishing weights. Small miracle that I found the bag; one of them would be the keel bulb. I found some material for the keel — a piece of knot-free pine. To join the two, I drilled and scraped a slot in the keel bulb, and shaped a tenon in the pine to fit. By this stage, the bulb weighed 185g. Obviously, it would not be sensible to glue it on to the keel wood at this stage because of all the other building work still to do. So I set it safely aside.

With wood glue, interior gunwhales (or ‘gunnels’) were added in balsa at the rear and thin obeche at the front, as it was flexible enough to follow the curve. These increase rigidity and create a gluing area, e.g. for the mast tube support plank and decking. Again a departure from Stiller’s original plan.

Next I cut a slot in the hull bottom for the keel. Very scary to do, but I tried to think very carefully about every step before cutting anything. I used part of the bulkhead as the anchor point for the keel which I cut a step and a slot on to.  

While epoxying the keel in position, I also put a fillet around the outside of the slot, just to be sure.

Once it had set, I reinforced the bulkhead with extra balsa timbers, also with epoxy.  

The nose piece was another problem. I tried a foam block which looked ugly and was difficult to shape. In the end I simply glued a triangular piece of balsa in the centre and placed blocks on each side of that. Then just carved and sanded it. It came out fine - there are photos of it later on in this blog post. 

First-time Float

At this point I decided to give it a float in the sink to check for leaks. A lot of fun, and it was leak-free! Depron sticks well with Uhu Por and the bond lasts well - at least 10y it seems. The epoxy around the keel slot was sound. 

Mast and Sails 

The pine mast support plank was placed athwart, glued to the inner gunnels. 

Underneath the plank on the floor was the mast footing, which was made as a sandwich of balsa, ply, a tiny square of thin stainless steel under a pine block with a hole in it. The steel was from an old floppy disk — the part that slides across to reveal the tape. The metal is necessary to prevent the mast drilling a hole in the bottom of the boat as it spins. 

Decided to put the mast tube at 66% of the overall boat length measured from the rear, as my research showed that this was a common place for una rigs and McRigs (more on McRigs below). This is different to Mario Stiller’s design, which shows a full Bermuda-style mainsail and jib. I toyed with the idea of adding further mast tubes and decided against it. Too much hassle, weight and surely I should be able to get at least one sail rig to work with a solo mast position? After playing around with alloy tubing in my stock, I picked a tube diameter that accepted a 3mm carbon tube, which will be the mast for one of my sails. I cut a smaller diameter alloy tube piece to insert into the mast tube. It makes a lining that allows a wire Z shape mast of a McRig to spin beautifully in the mast tube. This gives me at least 2 mast options. I took care to ensure that the bottom of each mast was slightly rounded so that it could spin well on the steel floppy disk piece under the footing.

Then I took a bit of time to make masts and sails and to my surprise found it quite enjoyable. I think they are easier to build than wings and you can be quite creative. A new purchase was an eyelet punch and I had to revise my knots. 

It was enjoyable to make bend wire attachments for lines and rigging. Unlike aircraft undercarriage, you’re working with thin wire so bending is easier and you can let creativity flow.  

In this post you will see photos of three sails. The blue one is about 65in2 in area. 

The white with orange trim is 105in2 and the largest, the McRig style, in white and purple is about 115 in2. 

These photos also show the simple stand that I made in a few minutes. You need one! I decided that I will use the white and orange sail first to see if I can get the hang of this RC yachting malarkey. 

The block attaching the boom to the mast is made of rosewood. Just a piece of scrap that I had lying around and I'm particularly pleased with the little footy logo on its front (photo of that later below). It's probably overbuilt but it does the job. 

Rigging, Servo Mounts and Controls

I prepared runs to allow the main sheet to pass through the deck; a short piece of aluminium tube set into a small disc of pine. These would be glued under the decking pieces. As I fitted the decking of 1.5mm balsa, I also glued in the sheet tubes. I tried to put these around 55 mm from the centre of the mast hole because in my tests this is the distance that seemed to work ok. 

I built the servo mountings as simply as possible - merely a ply u-shaped piece on a balsa block. These were assembled using waterproof white wood glue and then fixed in the boat using UHU Por. The mainsheet servo arm was bent out of a stiff piece of wire that I had lying around.

After umming and ahhing about mounting the battery and the receiver, I opted for the simplest idea, which was velcro that had been a UHU Por-ed in position. The rationale is that the battery being heavy can sit very close to the middle of the boat and hopefully provide the right balance. Antennae held in place with paper tubes, tips horizontal and perpendicular to each other, I did a range check and it was fine.  

The rudder that I had started to make in Part 1 seemed flimsy to me because of the flexible carbon tube. On reflection, I opted instead for a good hard piece of balsa attached to a ply control horn, pinned with gussets. The wired hinge would be stiffer under load. The rudder was then glassed with 25g per sq. m cloth, as was the exterior of the Depron hull and the balsa rear transom. This massively increased the rigidity of the whole boat without much weight penalty.

The rudder servo pushrod went through a large 5mm hole through the rear of the boat. I made the hull cutaway box as small as possible to allow the control horn of the rudder to pass. 

A piece of ear plug foam, with a hole drilled through the middle, is trimmed, rolled and pushed into the hole. The control rod goes through that. That is the waterproofing system and before you take it on the water, give the control rod a little bit of silicon grease. Initially, I set the rudder servo throw at 30° port and starboard. I don't have a photo of the rudder during construction, but here it is after fitting. 

One of the hardest issues was figuring out how best to attach the main sheet to the boom. To swap out sails, you need to be able to remove the sheet easily, and also adjust sheet length so that the servo moves the boom from close haul to fully open (just under 90° to the boat centreline). I tried hooks, fishing snap links, and cable ties but in the end what seemed to work best was a thin aluminium tube bound at 50 mm from the axis of the mast. The main sheet would pass through this and onto a bowsie which I made very easily out of an old credit card (later, this was replaced by a thicker piece of wood, as it’s easier to handle). What I really like about this is the snag-free nature of the main sheet to boom attachment, and the accuracy and ease of shortening or lengthening. With the throttle lever fully forward and the throttle trim centred, you set the sheet length using the bowsie. Thereafter, if you need to adjust trim, you have both the bowsie and the transmitter trimming feature. More than adequate and only one overhand knot to undo when you change sails. 

Finishing and Testing

The hull was painted by brush with two coats of primer and then two coats of paint. More details of the paints and finish used are in the specifications listed below. Finally some coats of exterior water-based clear varnish, at least 2 on the painted parts and many more on the stained deck. When I started painting the hull it weighed 69 g (including the unpainted keel and servo mounts). When I finished it weighed 71 g. 

After charging up the batteries I was quite keen to go and sail it on the open water. However, I decided to try it first in the bathtub and I am very glad I did! 

I used a couple of battery powered handheld fans to create wind across the bathtub! Immediately, it ran downwind well, but would not turn enough to tack upwind. I realised that the rudder-throw was just not enough. So I adjusted the rudder, which required widening the hole a tad, changing to a bigger servo arm and was able to increase the throw to 45° port and starboard. That made a big difference and I was now able to turn to tack upwind. Eventually, I was able to sail figure-of-eights up and down the bath with a few jogs here and there to stop it sticking to the side. Load of fun, but importantly, it gave me confidence that the boat was watertight and had some upwind ability. 

Here's the boat rearing to sail but land-locked!

And the side view. 

Next, the maiden voyage. 

Specifications 

AUW ready to sail: 340g.

Hull: 3mm Depron foam, exterior surface epoxy/fibreglass 25gsm.

Rudder: balsa and ply, exterior surface epoxy/fibreglass 25gsm.

Keel: Pine.

Keel bulb: Fishing weight 185g.

LOA (max): 303mm. This excludes the rudder and its hinge tube/support. Rudder projects 37mm aft of transom, hinge tube support is 5mm wide. 

Beam (max): 106mm.

Top of deck to bottom of keel bulb: 217mm.

Height of hull at front edge of keel: 63mm.

Height of hull at transom: 52mm.

Height of hull at bow: 54mm.

Finish: All water-based. Vallejo primer and premium model acrylic paint both in white; Deck stain WooDeeDoo interior wood stain dye, Dark Cherry. Rustins quick dry outdoor clear varnish.

Hatches: Acetate sheet held down with 3M Scotch Magic tape.

Rudder servo: Emax ES08AII analogue 9g.

Mainsheet servo: Tower Pro SG92R digital 9g.

Mainsheet: Braided Dacron, Climax Black Line 25daN kite line.

Sail clew, tack and head attachments: Linen thread.

Receiver: FrSky X4R.

Battery: NiMH 4 cell 400mAh, 30g including wire and plug.

Sails: 105in2 Bermuda (white and orange), 115 in2 McRig (white and purple), 65 in2 training or high wind Bermuda sails (blue and purple). All areas are best estimates and may have error up to 5%.

Flying off Water: Durafly Tundra with Floats

January 2024. With the deluge of rain in the UK, came the floods. Being on low ground next to the river, my club’s airstrip was submerged. Water was above the knee in places and swans, geese and ducks didn’t take long to splash in. Likewise, RC aviators donned floats on their planes and skated off the water. 

Having never done this before, I couldn’t resist giving it a go. After all, my Durafly Tundra v.2 came with floats and they had never been used. So, the first thing was to remove the wheels and fit the floats. The manual is very clear on this and there are also some useful videos on YouTube, as the Tundra is a popular model. This was straightforward and I won’t cover it here. However, none of that info tells you how to fly from water, and crucially, how best to set up your floats. With hindsight, that’s probably a good thing, as it makes lessons learned ‘sink in’. As we all know, overcoming problems is part of the fun. And fun it was! It’s very liberating to have a big flat open “plain” to taxi about on (mind t’ ducks!).  

In no particular order, here are things I’ve learned during this experience.

1. It’s loads of fun! I found myself taking off and really not being much bothered about flying as such. I was more interested in zooming about on the water, taking off and landing. For me, it was all about the water! In fact, the experience helped me to decide to finish off the boat I was building long ago...

2. The floats “stick” to the water. It’s a kind of suction that is hard to describe, but you can certainly feel it on the take off run as you feed in up elevator to get airborne. You also notice it on landings - the water almost grabs the plane as it touches down. I found it useful to have a tiny bit more speed on approach than I would with wheels to make the landing smooth. 

3. The plane is less agile in the air because of the extra weight and drag of the floats. The Tundra manual actually suggests using a lighter, lower capacity battery to compensate. 

4. Which brings me to my first major learning. I figured that the CG should be in its usual place on the wing, but it should also be about 1-2cm in front of the “step”. This is the right-angled transition on the bottom surface of the float. If the CG is too far forward, then more of the front portion of the floats stay in the water, making the forward tracking on taxi a bit unreliable - it can suddenly veer off to one side, and that happens seemingly at random. 

5. When taking off, if there is anything not right about the “ground” run, then abandon the take off! So, if you start veering off and can’t get it back promptly and easily, just power down and stop. Go round and try again. Likewise, if a duck swims into your runway!

6. On the ground run, I found it useful to feed a little bit of up elevator to get the plane on to the step as you accelerate to take-off speed. 

7. Whether it helps to toe-in the floats in a bit seems to be a point of discussion and debate. I’ve heard views both ways, and in the end, I haven’t tried it, but I think it is something I should try to see if it brings more stability to the ground run

8. Incidence. Tundra manual mentions using a bit of flap for take off. I tried it and it works, but I actually preferred the longer “ground” run fun with no flaps. I’m not really sure why, but I did.  

9. Water is such a beautifully level surface and you can approach directly into wind whatever the wind direction. This makes it ideal for practising fully held-off landings. Here is not one of them:

10. 
    
    
    

11. Super important to think about how you would retrieve a stricken plane, e.g. in the event of a radio malfunction or crash. One of our club members has waterproof waders and very helpfully made multiple trips to retrieve planes. However, not everyone has a “Darth Wader” to rely on. So, think model boats, wellie boots, even a full size kayak or inflatable boat. 

12. Have someone take photos and videos. With the reflections and ambience, it can be very scenic. 

I hope these tips are helpful. Have to admit that I’m partly hoping that we’ll get more chances to fly off water this winter. I leave you with my favourite photo of the sessions we had out there - Darth Wader in action!

Classic balsa RCM Trainer Junior electric: Build Log and Flight reports

This is my scratch-built electric version of an iconic 1970s i.c. trainer - the Radio Control Modeler magazine (RCM) Trainer Junior. The article on this 52” span model appeared in the June 1974 edition and opened with the remarks: "Another reliable, good flying 60 becomes a reliable, good flying 40. An aerodynamic design that makes for slow, stable flying when you want it but, will loop, roll, spin, fly inverted, or…[sic]."

Introduction

Designed by Joe Bridi and Don Dewey, the RCM Trainer Junior became the “Trainer 20”, kitted out by Great Planes. As far as I can see, the Great Planes kit version differed in having a split elevator instead of one continuous sheet and framework to hold the wing dowels instead of solid balsa block. Both plans are available from the Outerzone website. These trainer type designs were ubiquitous and became a staple. I suppose the modern equivalent would be foam trainers, like the Durafly Tundra, E-Flite Timber, FMS Kingfisher, Max-Thrust Riot, etc, although of course, they are tail-draggers, as opposed to tricycle undercarriage. 

I was curious to see how an old-timer balsa trainer would compare to the modern stuff. Also, this would be my first tricycle undercarriage RC plane. With photos, I’ll show you the build, the mods I made and describe the first few flights.

 

Building the RCM Trainer Junior

Rather than messing about with pdf files, I conveniently obtained 2 copies of the 1974 original plan from eBay seller “mrhobby” in Maryland, USA. I left one plan intact, and used the other one. Thanks to mrhobby for continuing to help the modelling community. While I'm at it, thanks to folks at 4-Max UK, DuBro in the USA for very helpful email correspondence, and Balsaworkbench.com for some inspiration. I cut the plan into sections to fit on my building board. Adhesives were primarily aliphatic resin (EvoStik exterior), epoxy (Devcon 5min and Araldite precision) e.g. for the fin-fuselage joint, and just a little CA, e.g. thin Zap for Great Planes CA hinges, and on a few bits and pieces where CA made sense.  

Tail Feathers 

The elevator was solid balsa, as per the plan. To try to keep the tail end light, I departed from the plan and constructed a built-up fin, rudder and stabiliser.

You can just see the thin ply ‘biscuit’ brace to strengthen the centre joint. Why did I bother with this? Well, many experienced RC modellers told me that i.c. engine aeroplane designs require lots of nose weight when you convert them to electric, because the i.c. motor and tank are heavy compared to a modern brushless electric motor and LiPo. 

Fuselage

Fuselage construction followed, and my next mods to the plan were to change the second bulkhead to an open frame and add a ply bulkhead for the electric motor ahead of the one for the nosewheel steering mount (DuBro nylon for 5/32” (~4mm) wire).

For access, there is the hatch above. Underneath, I made another hatch out of 1/16” ply, eventually painted white and held on by 4 screws. That needed an egg-shaped cutout to allow for movement of the sprung nosewheel steering arm.

It is important to have the nosewheel steering arm spring centered on the bottom edge of its bulkhead. It's simple physics of moments and indeed, it is shown on the plan. That said, I can't count the number of times I've seen that spring dangling way below a model!

Wing

I used the pinhole method to make templates: hold the plan over a piece of card, use a pin to prick holes around the desired outline, e.g. the wing rib, then join the dots on the card, and cut out a template. I ended up using thinner ribs outboard and thicker ones inboard, just because my balsa sheet stock was limited.

 

Spars were 6mm bass wood, rather than balsa. Another departure from the plan was to angle slightly the thick innermost ribs on each wing half and then sand them for the dihedral joint. To me, this was easier than the additional wedge shaped centre rib and dowels shown in the plan.

To glue on the LE and TE, I used this technique with pole elastic and clothes pegs. It worked very well.

Similarly for the pine blocks in the middle and pins for the tips.

As you can see, I also made wing servo mounts, for individual wing servos. I think this is more modern and easier than the torque rod single servo setup.

It means short control rods externally, but that itself is useful when it comes to setup and adjustment. Further, it gives me the option of programming differential or flaperon.

The plan specifies wing dihedral as 1 ¼” (32mm) under each tip rib. When joining the wings, I reduced this to 20mm and added short ply braces across the central joint. Generally, I had kept an eye on the weight of each wing half as I built it and chose materials to keep them balanced. This was very useful because at the end all I had to do was adjust my choice of sheeting balsa to even out the lateral wing balance - no balancing weights were required! As per the plan, after sheeting, I applied glass cloth over the centre joint.  

Undercarriage

In addition to the wire sprung nosewheel described above, I made the undercarriage legs out of aluminium sheet and longer than the plan, as I needed clearance for a 12” prop that suited the recommended electric motor (advice from 4-Max). Since it is not “Dural” and therefore prone to bending, I decided to also add suspension: a central binding eyelet, springs and wire connecting rods. 

Servo Mounts and Connections

I added the rudder snake outer at this stage, but here I made a mistake: I built all the fuselage servo mountings at this point - Rudder (snake), Elevator (pushrod) and Nosewheel (pushrod). This eagerness bit me later on, as I’ll explain below in the sections CG and Balancing, and Radio Installation. 

Covering

The obligatory naked model photo:

For the Oracover covering scheme, I deliberated for quite a while. My aims were to show off the framework in the tail feathers and wing, aid in visibility - distinguish underside from top and model heading forwards or backwards - and to look nice!

Underside is all white except for some red stripes (see photo in the Undercarriage section). I allowed myself a single stripe of black trim, and a couple of side panel stickers. I applied thin white foam around the inside of the motor bay to clean up the look and perhaps provide some sound damping. The hardest parts to cover were the front corners of the wing. I could not get them wrinkle free. It was awkward because I was using one sheet for the main bay and tip. I suppose I could cut off the film from the outside edge of the last rib to the tip, and try to stick on new smaller sections without wrinkles, but I’ll leave that as a rainy day task.

CG and Balancing

To my total irritation, it came out nose heavy. I guess the motor is pretty chunky and far forward. As I’d built the servo mounts, pushrods and fitted the snake already, I couldn’t easily move the battery back enough to balance it out. And even if I’d ripped out all the servo mounts and moved the battery back, it would have been very awkward in use as I’d need to take the wing off to change battery. So, having considered all the options, I moved the battery back as far as I could while still being able to access it from the main hatch and added tail weight. Generally, I prefer not to add tail weight, but here, the convenience won out. I fixed lead buttons (for curtains) inside the rear of the fuselage, which I reinforced. I also added a tail skid, which would save the elevator in an awkward tail-down landing.

Altogether, I added about 35g to the rear. So, I would have been ok building solid balsa tail feathers after all!

Radio Installation

Here are photos of the fuselage-mounted servos and receiver. First, a top plan view, looking right and finally looking left:

The best bits are the paper tubes that allow me to orient and fix the antennae tips at 90° to each other. They help to ensure that the working tip portions of the antennae are kept straight. As a reminder, in 2.4GHz kit, the strongest connection between transmitter and receiver antennae is when they are parallel to each other. I made the paper tube by rolling thin paper over a cocktail stick (using squared paper helps with alignment), and gluing the long edge with pva adhesive. Leave some paper over as a flap, to help with mounting. I mounted the tubes with paper masking tape, in case I need to reposition things after experimenting.

What’s it like to fly?

It was a lovely day for the maiden, sunshine and 7mph wind. With the CG at the forward end of the range on the plan, transmitter on low rates, I did all my checks. Nerves mounting, the take off was exciting and easy! I just moved the throttle open, picked up speed and lifted her off! She seemed nicely balanced fore-aft and laterally, just two clicks of down trim required. Changing the throttle setting, I was surprised that I didn't feel the need for any thrust line or balance changes. She glides really well, can fly slowly - so wing loading must be low - and there is loads of power available if I need it. A slightly bumpy landing - because I didn’t align for the cross wind very well and didn’t hold off properly. Plane was fine, except that the right undercarriage leg had straightened a bit, making the right side sit low. Decided to stop there, quit while I was ahead and return another day! The colours were magic for orientation and my wife said it looked great in the air. Very satisfying. 

At home, I removed the alloy undercarriage, straightened it and refixed it with a slightly longer and wider central spring anchor. I also changed the springs to much stronger ones. This may help to prevent it deforming on a heavy landing. I found myself wondering what she would fly like on mid rates!

A few weeks later, I flew again and discovered the answer: the plane feels fabulous on mid and high rates - simply brilliant. I tried some aerobatics: inside loops, Immelman turns, humpty bumps, rolls, reverse shark tooth, cuban eight. I could hold inverted too. I tried a spin, but wasn’t sure if what ensued was a spiral dive, although it looked pretty. I have not yet tried outside loops. It was so much fun to fly, and I nailed these landings, properly lining up and holding-off for a gentle touchdown.  

After just a few flights, I love this plane. It’s not as “flippy” as the modern foam trainers mentioned above. To explain further what I mean, consider the BMFA ‘figure of eight’ manoeuvre that is used in the A and B tests. This should be thought of as two level 360° circles, not a squashed 8. Compared to a modern foam trainer, the Trainer Jr was much easier to control during this - I found it easier to adjust the bank, turn radius and height. I’d imagine that the unmodified original, with its greater wing dihedral, would be even more stable. I’d describe the response of my version as immediate, smooth, predictable, and very rewarding. I also enjoy the tricycle undercarriage as it seems to steer well on the ground and lessen the influence of a crosswind after touchdown. 

Specifications

Span: 52”

AUW ready to fly: 1.56kg

Balance point: 81mm from LE

Motor: 4-Max Professional Brushless Outrunner 3547, 960kv 

Prop: APC Electric 12x6

ESC: 4-Max 40A 

Battery: Overlander Sport LiPo 2200mAh 3S 35C XT60 connector 

Receiver: FrSky Archer R6 ACCESS

Transmitter: Taranis QX7 ACCESS, Open Tx

Rudder servo: EMAX ES3104 - 19g

Nosewheel servo: EMAX ES3104 - 19g

Elevator servo: JX 1109MG - 9g

Aileron servos: EMAX ES08MAII - 12g

Conclusion 

A self-build model nearly always provides enjoyment during construction, but you never know whether you’ll enjoy the flying until you try. This one definitely ticked both boxes. Overall, the project has been hugely satisfying and worthwhile - it seems that the original designers’ opening remarks were correct! 

Build a field box for RC aeroplane flying - DIY project

Being organised on the flying field is important. It reduces the chance of accidents and makes your life easier. Recently, I acquired my first ever i.c. powered RC plane. Flying i.c. requires you to carry fuel bottles, fuel pump, battery, starter motor, glow starter, and other odds and ends, such as glow plug spanner, spray bottles and cloths for cleaning any residue off the plane. Searching online, field boxes seemed very expensive. I just wanted a basic one for i.c. that worked for me, so I built one out of bits and pieces that I had lying around. 

Materials were ply, dowel, a few bits of softwood and even some balsa spar - which I used to frame around the base of the battery, to make a tray. The battery is held down in the tray with the top ply plate and three screws - there's a pad of stiff foam on top of the battery. This arrangement is easy and keeps the battery in place.  

Unusual colours because I had leftover small sample tins of a water-based outdoor garden paint (Sadolin Superdec, Dark Dusty Rose internally, Gull Grey and Cloverleaf externally). The handle had 4 coats of a linseed/carnuba/beeswax and the other ply parts around the battery box and electrical panel were varnished.

Below is a close up of the panel. There are two safety features: 1) a physical barrier (wood) between the 4mm binding posts; and 2) a fuse (20A). I thought the triangle was a quirky design choice!

 

  

The battery is sealed lead acid 12V, 7Ah. I could also use it to charge LiPOs on the airfield. Below, side view, there is enough space to hold what I need.  

I didn't include space for transmitters as I have a separate alloy flight case for my radio gear. I particularly like the hand-operated fuel pump. It has a filter on one end of the fuel line that drops into the fuel bottle. The other end is attached to the filler nozzle on the plane. Cranking the handle pumps fuel into the model's tank. 

 All in all, this didn't cost me much, except time. I enjoyed designing and building it and am certain it will be useful. A great way to occupy days of unflyable weather!