Glens CAP232 30%

As a keen modeler, I have always been interested in sport scale aerobatic aircraft. While progressing through a variety of smaller aircraft (less than 57" wing) while learning to fly, I gained a passion for the CAP232.

The CAP232 was developed by the French aircraft company Avions Mudry back in the mid-1990's. It originates from the CAP stable of aerobatic aircraft that began with the CAP10B back in the late sixties. The aircraft has advanced considerably and has gained an unbeaten record in aerobatic competition.

The full-scale CAP232 is a single-seat monoplane constructed mainly out of timber and carbon fibre. The first prototype was flown in April 1996, powered by a single Textron Lycoming AEIO-540 horizontally opposed flat-six air-cooled engine rated at 300bhp. The aircraft has a maximum speed of 217 mph, an can pull +/- 10Gs.

My first model flying experience with this aircraft was with the Kyosho CAP 232 40. Displayed in the Breitling colour scheme, the aircraft was powered with an OS46FX engine and a 12x7 prop. It is a stable aircraft with little tendency for tip-stall. Downsides are a slight fish-tailing when flying downwind. Although the aircraft has served me well, the sight of larger scale CAPs at model air shows and on the web are an irresistible temptation. I decided that making one would be a good winter project.

Firstly, what scale CAP232 would be acceptable? There are many kits available at different levels of building ability. ARTF CAPs tend to max out at 72"; at this size it was not much bigger than the Kyosho model I had, thus would leave me wanting more. Fortunately, my building skills are above average and was prepared to put the work into building one of the bigger kits. After some investigation, I discovered that there was a number of kits that fall into the 1/4 and 1/3 scale category. This seemed large enough, third scale was reaching a wingspan of 88", a 1/3 bigger than my Kyosho model.

One manufacturer claiming to have a good reputation was Glens Models. They stocked a 1/3 scale CAP232 that was formed of pre-cut material. According to the manual, building this aircraft is a straight-forward process, no jigs are needed for the fuse or wings. At 374.00 pounds, it seemed a costly investment for a person who was used to spending a lot less on his aircraft. But naturally, scale aircraft at this size are not cheap.

November 2004:

After a bit of consideration, and rattling of the piggy-bank, I decided to wait for a second-hand aircraft to come my way. With good fortune, I discovered a local person offering a newly-built but uncovered airframe for sale. After a bit of negotiation, I came away with the airframe for 210.00 pounds. I would have liked to experienced building the airframe myself, but the likelihood of finding an unbuilt kit for sale was minute. So, still happy I decided this would be the best solution for now.

When I picked up the aircraft it suddenly hit me how large it was. Although I knew the measurements, it had not sank in until physically faced with the real thing. With the car backseat down, the aircraft barely fitted in the back of my Rover 400. What am I letting myself in for? Still not deterred, I whisked it home to my workshop.

Looking over the airframe briefly, it seemed to be in good condition. The builder had taken care to assemble and store it correctly.

While looking for an airframe, I had to take into account that I would need and engine. The recommended engine was in the region of 35-75cc that falls mainly into the petrol category. Having had a little bit of experience with petrol engines on power boats, I was familiar with the Zenoah range. After some further searching, I managed to locate a second-hand Zenoah 62cc with recoil starter, coincidently removed from another Glens CAP. The engine did not have a prop, so one was sourced from Just Engines, a wooden 24x10.

Things were starting to move forward. A plan of action was needed. What should I tackle first? Well, an indepth inspection of the airframe was made to ascertain if everything was built correctly. I noticed that some of the Tufnol hinges were missing for the ailerons. Moreover, the ailerons had been built-up; the veneer covering had been prematurely fitted before the hinges were in place. Pain! This means that I would have to strip back the veneer to fit the hinges. I decided that the amount of work required to undo this mistake was unacceptable (I could do more damage). However, replacing the Tufnol hinges with large plastic hinges seemed a feasible solution. This took two evenings of work, but the results were acceptable. Panic over. The airframe was sanded down then given a liberal coat of BalsaLoc ready for covering. I had decided to use Profilm for covering. Although I had never used Profilm (mainly Solarfilm and other brands), many people claim this was the best. So, wanting the best for my aircraft I decided to try it out.

Time to choosing a colour scheme for the covering. I was not keen on the conventional colours used by Glens Models (white, light and dark blue), so decided to experiment. I had decided a while ago that if I ever built a large scale model then the underwings would be covered in a checkered pattern. Decided on a red/white checker pattern for the underneath of the wings and horizontal tail, and the complete vertical tail. The upper wings, upper horizontal tail, and parts of the fuse would be covered in white. This gives me a blank canvas to overlay with trim patterns, or even paint. The rudder was covered in a semi-transparent blue covering. Contrast between aircraft top and bottom was good, making orientation easily distinguishable in the air.

Profilm was very impressive. When applied correctly it does not bubble, go transparent or peel off. Although it can be twice the cost of other coverings, for a professional finish it is worth every penny.

Fitting the engine into the fuse. Not too difficult as the firewall had been pre-drilled for a Zenoah 62. Four mounting bolts with captive nuts on the back of the firewall secured the engine. A 32oZ Dubro tank with petrol fittings was selected. Not sure at present if two or three tank lines are needed, so decided to play safe and fit all three. The existing box exhaust was not suitable to fit inside the cowling, so I invested in a Pitts style exhaust (very sexy!). The exhaust has a smoke connection, which I intend to take advantage of in the future. The throttle linkage sited on the side of the carb operated sideways making linkage back to the throttle servo difficult. This was resolved by adding a bellcrank (made from a servo arm). This was attached to the firewall using an aluminium bracket.

Servos. Each control surface has it's own servo, thus totaling five devices. I have used JR NES591 servos. Not the fastest servos in the world, but have a greater torque than the basic ones available. All linkages were fitted with 3mm ball links.

Covering the fuse. Large amount of surface area with big curves. Started at the top and bottom surfaces.

Tail wheel, rudder servo and pull-pull rudder fitted.

Start paneling the sides of the fuse.

Slowly getting there! All major surfaces are now covered with film.

December 2004:

Now to get on with the electrics. There are six servos to wire back to the receiver. Two aileron, two elevator, one rudder and one throttle. Decided to make the engine choke manual operation. Using a Futaba FP-R138DF PPM receiver. Two sets of 6V 2300mAh batteries are used to provide redundancy measures. Battery charger sockets are located at the base of the fuse where the undercarriage will be located. Batteries are combined through diode-'ANDing' circuit. This will provide isolation incase a battery pack fails. A Tower Pro 6V monitor is used to indicate battery status. Intend to upgrade the receiver to PCM later so for fail-safe features - this receiver will do for now for testing.

The battery packs have been mounted as far forward to aid the C of G, and are hidden under a false compartment mounted under the firewall next to the muffler.

Receiver antenna has been run on the underside of the fuse.

Fitting the upper and lower cowl. The cowl is split along the horizontal axis, aligned with the centre of the spinner. The split cowl allows for easy access to the engine without complete removal. The cowl is joined by ten 4mm plastic bolts, five per side. These screw into captive nuts epoxied onto the inner side of the lower cowling. GRP/fibre glass cowlings can be a pain to mount, and have a habit of fracturing due to engine vibration and normal wear-and-tear.

To give support to the side cheeks of the cowl, a wooden support was fitted to either side of the firewall. Also, a petrol refueling valve was mounted in-line with the fuel feed and mounted on the left cowl cheek. The wooden support provides resistance to pressure when attaching the fuel line to the valve, and minimises the likelyhood of the cowl being damaged when refueling.

Modified carb inlet flare. With the carb being side mounted, the flare protruded outside the cowl. I decided to shorten the inlet to keep it internal within the cowl. I intend to put an air filter over the inlet, this may reduce carb noise (if required - need to experiment).

The tail section of the fuse is covered by a GRP panel. This acts as a service hatch providing access to the horizontal tail screws.

Grille mesh is fitted into the cut-outs in the cowl. Picked some of this material up on Ebay, thought it would make a nice finishing touch. Grille is epoxied to the inside of the cowl.

January 2005:

I prefer to painting using an airbrush. Cowl and spinner are primed with several coats of zinc etch primer, rubbed down wet in between each coat with wet & dry paper (800,1200,1500). This is pain-taking work, but worth it for a good paint job.

A test coat was performed with the spinner to see how it took acrylic paints. So far so good...

Now for the final paintwork. Airbrush flame patterns onto the spinner. I shoot 1:1 acrylic paint and water mixture. Sometimes add IPA to aid the mixture. Paint job needs a few more coats of acrylic lacquer to finish it.

Onto decals. The Futaba logo decals are cut from Profilm using a set of card templates, printed on my computer.

More lacquer on the cowl, spinner and tail section panel. Looking good! May give it a bit of polish later. Lacquer is always a pain to spray. Ideally, the coat should be put on thick to minimise the 'orange peel' effect, but too much will generate runs. I use a heat gun to quickly cure each coat, minimising runs. However, the downside is airborne particles getting into the finish.

I have got into the habit (between coats) of lightly wet-sanding with wet&dry 2500 to remove runs and particles. This improves the finish considerably. However, do not be tempted to over-sand.

Today ordered a number of vinyl decals off Ebay to decorate the fuse and wings. Many are listed in the automobile section, search for vinyl (decal*, stickers*). Popular sponsor logos are available in different sizes and colours.

Vinyl cutters are available as computer peripherals but are quite expensive, around a thousand pounds, so it is quite fortunate that other people have invested in these devices and operate a cutting service. On request, many suppliers offer custom services.

Feburary 2005:

Vinyl decals arrived and attached to aircraft. They look quite good, typical sponsorship logos that would brighten any airframe. I tried to hand-cut corporate logos and brand-names from Profilm, but lost patience. Hence the cop-out buying the vinyl decals. There are a few more to attach.

Finally the canopy and horizontal tail are bolted to the aircraft. Notice the hi-tech C of G adjuster mounted on the horizontal tail...

Found a small amount of interference with the leading edge of the wings and engine cowl. Quick trim with the Dremel and everything fits OK.

Looking at the remaining items to do: make and fit fuse underside hatchcover; fit failsafe unit on the throttle. After that I think its time to take her outside and fire up the engine :)

If the engine performs OK, I will then correct the C of G ready for her maiden flight. Let's hope the weather picks up in the near future.

Jan 2006:

Well, it's been over a year since I last updated this webpage, and have done little with the CAP232 due to commitments. In late 2005, I noise tested the aircraft and found it failed miserably (87dBA peak). So, needed a plan of action. First decide what was mainly contributing to the noise (engine exhaust or propeller) and how to solve it.

Noise testing was an interesting experience. When holding the aircraft while it was running at full power, the propwash was so powerful that it put positive pressure across my lungs stopping me from breathing! You had to turn your head downwind to be able to beathe. The engine is amazingly powerful, greater than anything I had experienced with glow types.

Listening to the noise, the majority of sound was being produced by the exhaust. So, decided to fit some secondary exhausts to reduce the level.

I've not seem many companies or importers dealing with secondary silencers / canisters for large petrol engines, and the ones I've seen in the USA were quite expensive. Right, time for experimentation. Decided to have a go at designing my own.

I had access to 38m OD steel tubing, about 1mm wall. Cut two lengths about 300mm. Machined two ends for the tube: exhaust entry end OD was about 20mm, exit end 15mm. Made a seven section baffle stage out of discs cut from aluminium, perforated with 2mm holes, and a centre hole for a section of steel stud bar that is used to space and holds the discs apart. Simple, little science, but this was an experiement.

Welded some supports onto the tubes and attached them to the underside of the fuse near the engine. The exhausts were coupled to the original engine exhaust using high temp silicon rubber tubing and jubilee clips.

Initial tests were exceptionally promising. Noise had dropped to around 82 dBA and under. Had a problem with the silicon tube kinking so looked for a suitable replacement. Found some Eberspacher stainless steel exhaust tubing that is used on vehicles. About 24mm ID and a flexible, thin wall. Expensive at about 15 pounds per metre, but ideal for the job.

April 2006:

Weather has been aweful over the last four months, excessive wind, rain and a bit of snow. Flying at the club has been limited by this, novices grounded. Virtually impossible to noise test the aircraft as the wind inflates the noise figures. Finally a break in the weather in late April, back to testing. With the new exhaust pipe coupling, I changed the prop from 22x10 two-blade wood to 24x12 three-blade carbon fibre. Noise dropped to an average of 77 dBA! Major improvement.

There is a noticable decrease in power with these changes, but overall the performance is acceptable. As this is my first petrol and large scale aircraft, prop hanging the beast was not high on my agenda.

Had the aircraft structrally checked. One recommendation was to change the flimbsy aileron hinges fitted. Replaced them with Robart large knuckle hinges, mountedinto hardwood blocks (rather then straight into balsa) in the wing.

Noticed that the engine mount's rubber had started to tear. Upgraded the hardness and size of the mounts. Vibration at very low RPM is noticable and part of the problem.

Wednesday 26th April 2006:

Initial test flight.

Well, the moment of truth has come. The aircraft is cleared to fly, noise tested and structurally approved. Was off work Wednesday on a holiday break, so had the day to make final adjustments. Centre of Gravity was checked and it felt a bit neutral to tail heavy. Probably due to the additional exhaust weight under the wing. Not the ideal condition for an initial flight, but as it was not excessive we decided to continue.

Radio range check OK, fuelled up, choke on, full throttle, wound the prop recoil starter back and primed her. Choke off and throttle low, recoiled the prop and started her.

Final checks on the runway, powered up, tracked her with rudder and elevator as she teared off down the runway. As she lifted into the air she started to nose up. Noticed that the elevator was very sensitive, although the control surface throws had been set low. Must be the CofG issue raising its head.

Got to a safe height and took it around for a few circuits. So far so good. Tried a stall test - engine to idle, gently pulled back on the elevator. Stall speed was very low, dropped a wing to the left. This was repeatable. The difference between this aircraft and my smaller glow models was significant. This was a large and graceful machine, cruising low passes was a thrill. The Zenoah sounded beautiful. Now started to think about landing. A few more low passes to get a feel of the approach and gauge my landing speed. The landing was a bit heavy but no damage. Well, thoroughly enjoyed the first flight, although I had been dreading it. Twenty pounds of deadweight material dropping out of the sky was my biggest fear. Decided to do the necessary trimming changes another day, also give my nerves a deserved rest.

Back in the sky on the weekend. CofG changed to slightly nose heavy, batteries and fuel tank moved forward to the firewall. Second flight was more eventful. CofG correction removed the elevator sensitivity. Tried my first bit of aerobatics - square loop - no problem. The aircraft went vertical and climbed steady, looked like it could go vertical forever. Squared the sides, throttle lowered on the downward side. There was no tendancy to roll out of the loop, etc. Felt very comfortable. Onto a few more low passes. Noticed a slight fishtail on crosswind, may a characteristic? Then more fishtailing on downwind, engine sounding louder. Problem! emergency landing. Got her onto the runway and back to the pits. Thought the fishtailing may had been interference, then noticed that the exhaust had come loose and that one of the secondary exhaust brackets had sheared. Maybe metal-metal radio interference? Back to the workshop to beef these parts up.

Guys at the field had taken some pictures of her flying, will publish when I get my hands on them.

(Wait for the next thrilling installment)

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