Cermark Pitts Special refurbishment.

[Mike.K 60]

Only recently did I discover how difficult it was to source a ply and balsa 60" span RC Pitts Special kit either as a self build wood kit or as a pre-covered ARTF. I`m not interested in small cheap, budget disposable junk models. I`m a long term true aero modeller rather than a short lived plastic toy plane operator. Hobby King or FMS foamies are not for me.

Although Blackhorse show their Pitts Special BH85A ARTF kit on their Vietnamese site, not one UK agent has one in stock. The same situation at European outlets. Priced at a whopping £588, this airframe only Pitts kit certainly isn`t aligned with typical Seagull offerings which are more towards the £360 new price point. (As at 04/10/2021, £1 equals $1.36USD)

Seagull do make and market the similar wood ARTF Steen Skybolt at around £360, but I already have one and I wanted a Pitts to convert and re-cover to dipict an aircraft of the Rothmans Aerobatic Team of the 1970`s. I used to watch the four ship Team display at the wonderful Biggin Hill Airshows as a teenager. Now in my sixties, I desparately wanted to step back to my youth and produce a RATs Pitts Special. Short of scratch building from plans or using unsatisfactory short kits of dubious quality, my options were strictly limited.

Hanger 9 offer a rather larger and significantly heavier airframe wood ARTF but in that case, a £900 kit price tag puts that kit totally outside my budget. That said, their kit is far too heavy to be flown by me within UK Flight Restriction Zones adjacent to operational UK airfields. My model flying takes place within the M25 orbital motorway around London and most of the contained flying sites operate very near to provincial airfields. Biggin Hill, our immediate airport is one such example of an airfield that only allows nearby model flying under those FRZ Regulations. A weight limit of 7.5Kg/15.7Lbs maximum take off weight dictates what we may or may not fly in such locations under EASA Regulations and Article 16 legislation. A maximum flight altitude of 300ft and a distance rule of 5km or 3.1 miles from those active, full size aircraft operational bases also applies. So no large, heavy models for me unless I travel out of area. Models weighing much more than 13Lb also cause me a problem. I`ve a severly damaged lower back with attendant sciatic nerve issues. I find models weighing much more than 13Lb cause me pain and distress so I have to look carefully at what models I build and operate.

This summer I started to look for a pre-used Blackhorse Pitts. The internet produced nothing, then quite by chance I found a pre-owned American Cermark Pitts on eBay. Research and You Tube videos indicated this ARTF model flew well and might make an ideal canvass on which to start to build up a model of my beloved Rothmans Pitts. A trip to Bristol, some 130 miles distant found me an unflown vintage airframe complete with servos AND a very low time ASP180FS nitro motor for a bargain £240 paid to the seller in cash. I was well pleased with the purchase and found myself with something that would easily convert to single seater spec with my own personal choice of livery. Shortly after returning home, this model went under my knife and all the old, embrittled covering went straight into the rubbish collection bin! The airframe was totally undamaged and was not soggy with fuel oil residue. I was a very happy guy having sourced just what I needed and at a very acceptable price. I never walk away from a used model without looking behind the accumulated dust of long term storage. Believe me, there are some real gems to be found hidden under the rubbish. Buy sensibly and realistically cost out a potential referbishment project in terms expected cash outlay together with time required to bring a used model back to prime condition. Be realistic, buy the good stuff and walk away from the junk.

Having cleared the model of covering detrietus, I began modification of the airframe. I covered over the front cockpit with 1.5mm balsa sheet, added  longitudinal stringers to fuselage sides, and removed a cheap and nasty tail wheel unit. A rather more suitable and robust alternative was sourced from my wrecked Seagull Funky Cub that I flew too slowly and spun into the ground! I never really liked that model and found myself being quite joyful with the quantity of useful salvagable parts that then found their way into some of my other models. Unexpectedly gaining eight usable servos, a good four stroke motor, battery and receiver in one hit is like winning the jackpot!! Anyone want a broken (very, very broken) Funky Cub suitable only for firewood? I`ve not shed any tears for that Cub..........

Three weeks after the Pitts went under my knife, it has seen the rudder servo moved to the tail adjacent its brother elevator servos. This arrangement gives a slop free push rod installation for rudder and elevator control surfaces. A quick weight and balance review saw a new 2600NiMh Rx and servo power battery installed just forward of the tail plane to achieve what has since proved to be the right place to install that battery. This is counter-balanced by the huge lump of metal ASP180 FS on the front bulkhead. I`ve added a flexi exhaust from Just Engines which gets the engine muffler outside of the engine cowl with its location being between the ali landing gear. The muffler points slightly downwards allowing exhaust residue to be directed away from the underside of the fuselage. Modification of the fuel tank floor complete with a new 20oz Dubro fuel tank sees the fuel pipe to the carburettor sitting at the same height and the carb spray bar. Carb flooding due to syphonic action is not expected.

The core colour of the new Hobby King covering is white. Dark blue HK covering provides the trim detail. The undersides of all four wings are covered in light blue Solarfilm. No other manufacturer produced any film even close in shade to that required. My Solarfilm supply came from a local model shop as redundent stock. It is such a shame Solarfilm closed their factory two years ago due to the influx of cheap Chinese covering materials onto the Worlds markets....now I find myself predominently using the Chinese products as the alternative Oracover products are so incredibly expensive. Like most modellers, I`m not imune from making financial savings where I can. I`m undeneighably a part of the cause, the issue and the outcome!

The glass fibre engine cowl and wheel spats have been wet flatted with abrassive paper to remove the previous Cermark colour scheme. Repairs were not required so I sprayed grey primer on the parts before again wet flatting and spray painting all parts with two pack, fuel proof white paint. I shall leave the painted parts to harden for a few days before masking up and adding dark blue two pack spray to match with the fuselage. Letting the white paint harden before over painting with the dark blue is worth doing. If you rush the job, finger prints are likely to appear in the white base coat and the job will not be a good as it could be. I can wait. I`m not in a rush, prefering a tight looking result rather than one that looks like a dashed bodge. (Lashup!)

I`m fortunate that our Emma within our model flying club owns a sticky vynal cutting machine and is able to produce model registration letters, logo`s and trim to my own sizes and specification. Results of Emma`s wonderful efforts can be seen in the images below. Without those prized graphics being available, my model building would be made so much harder. Nice work, Em. Thanks. Contact Emma directly if you have any sign writing requirements.

My finished maximum weight looks like completing at just over 12Lb without fuel. To my astonishment, reading some of the internet forums indicate that some examples of this model are flying with a weight that exceeds 14Lb! One example seen used a massive Hacker electric out drive with a monster 10S power pack. A weight of 13Lb doesn`t seem uncommon. I`m pleased to have created an example of such a low weight. That is very encouraging. I`ll have no difficulty placing the Centre of Gravity at 1/4" in front of the LEADING EDGE of the LOWER WING as suggested in the user manual as a good starting point for initial test flights.

So I still have alittle more to do before the model goes the field. I must make a new cockpit wind shield, add some flying rigging for aesthetic perposes, finish the cowl and spat paint jobs, check the CofG, sort rates, expo, end points and ensure the motor runs and idles reliably. Those jobs complete, the model will be good to go.

I`ll add more images here as the model completes.

Mike

 

[Mike.K 60]

Two days after I started this thread, further work has been done to the Pitts.

Rigging hard point plates have laboriously been cut and fettled from 0.5mm ali sheet. Eight are required in order that the model will look the part. A Pitts without rigging would appear to be missing a vital part of its character. Making these parts is certainly tedious but vital to achieve the right effect. My last work action this evening was to bolt the hardpoint mounting points onto the model. Rigging wire fitting begins tomorrow.

The cowl, ali spinner and wheel spats have been sprayed and the masking removed. Painted in a base white two pack finish, the high contrast dark blue overpainting took time and concentration to achieve the result shown in the attached images. Frustratingly, a masking tape glue residue appeared to remain on the base white paint. Further investigation revealed that the glue had damaged my lovely white paint finish so I had no choice but to wet flat the damage out with P2000 wet and dry production paper. The positive side of this action was that after buffing up the paint with rubbing compound, I had an even better finish that I`d managed to achieve straight from the aerosol paint can. Such flatting work is common in the refinishing trade as it levels the paint and promotes a higher lustra. In truth, I should have confined the green masking tape solely to the fine line tape border and completed the bulk of the mask in brown parcel wrapping sheet or plastic bag material. So a little extra work was caused by my minor error of technique.

Tonight the cowl rests quietly as the paint hardens. The paint will be fully cured in about a week. In the meantime although dry to touch, finger marks are easy to press into the relatively soft finish meaning that for the time being the paintwork requires very careful handling. Two pack paint in aerosol cans, masking materials and general consumables came from L E Went on the Selhurst Industrial Estate. If you take a sample of your covering material to them, they will paint match using an electronic spectrometer and mix the appropriate paint brew for you whilst you wait. Expect to pay around £65 for a couple of aerosol two pack cans, some aerosol primer, masking materials and consumables. Paintwork materials are not cheap!

The fitted motor is an ASP/SC 180FS with an ali prop spinner. I`ve had to address the common prop lock nut and usual ticklish issue of spinner fixing. It isn`t always easy. Fortunately the operator of Just Engines, Andrew White, has solved all my previous internal combustion engine issues without drama or fuss. Without his advice and parts supply brilliance, I`d probably find IC engine operation to be a most frustrating thing. With Andrew`s help I can keep my model fleet working dispite frequent commisioning, running or maintenance issues. Andew will shift Heaven and Earth to come up with parts and solutions and I`m indeed grateful to be able to contact him by phone to discuss any engine problem I may have. If you operate model IC engines, then I strongly suggest you use his services. You won`t be disappointed. His latest part suplied to help with locking nut issues is the supply of a large, weighty, 40mm diameter over-nut cover. This gives me a liitle extra required nose weight as well as having a tapped 4mm thread to allow fitting of a 75mm ali spinner.

That`s it for tonight. Enjoy the images. I`ll be back with more over the next couple of days.

Mike

 

[Mike.K 60]

The Pitts is now 99% complete. Just the windshield to screw into place tomorrow once its surround paint has dried.

Today saw the rigging wires fitted and tensioned...an ongoing job as rigging wire has a horrible propensity to slacken until it stretches out after several retension sessions. The most tedious part of this job was laboriously painting those flying wires with white fuel proof Guild paint using a small paint brush. The effort was well worth expending as the painted flying wires add a degree of interest and gravitas to the model. Left in the supplied bare stain less steel configuration, the wires just looked like simplistic "add ons" with the model looking quite unfinished.

On the electronic weighing hook, the weight increased by a pound since I last weighed the model. Where did that come from and why does that always happen during the last few hours of completing a model?......... So now at 13.3Lbs but certainly not the heaviest example by a long chalk. I`d certainly expect this model to have a highish landing speed so that will keep me on my toes.

So little to do now exept wait a week or so to let the paint fully harden and set up before subjecting it to the potentially vicious effects of methanol and nitro methane contact. Both these chemicals can do untold damage to fresh paint, non fuel proof paint and even two pack paint if the cure process is not fully complete. Once again, I`m watching paint dry!

You will perhaps note the colours applied to the prop spinner. Even though I used acid etch primer in an attempt to help the top coats adhere to anything made from aluminium, I concider the use of an electric starter on this particular spinner to be undesirable. I can`t see the white and blue paint job lasting five seconds when subjected to the torque, generated frictional heat and the inevitable poly-propolene starter cone slippage when using an electric starter. What you see in the images will be used as a display spinner only. A second polished ali spinner will be fitted for flying perposes. At least the crud from the starter motor cone removes faily easily.

The CofG is spot on being located a quarter of an inch forward of the bottom wing leading edge. I`ve extended a line upwards to place it immediately in front of the rear canane strut which supports the top wing. No additional balast has needed to be added to the front end of the model. The location of the 2600NiMh Rx and servo battery in front of the tail mounted servos appears to be perfect. It nice to get something right occasionally!

So this referbishment is now done and dusted. Its very different now to the lack lustra forty odd year old basic Cermark Pitts that I collected from Clevedon near Weston super Mare just a couple of months ago. The model has been a cost effective excercise landing me with a model that I dispaired of ever owning. The result is more than just pleasing.

Special thanks for help with this model must go to Rob Newman at Avicraft in Bromley. He supplied many components for the model as well as giving a huge amount advice. Emma Chase has been a star cutting the graphics for the model. Her work is top class and really helps the model to"ping" visually. Andrew White at Just Engines continued to find me the parts needed for the exhaust and propeller locking systems. He is great guy to deal with providing fast service and wide ranging engine based assistance. Finally, L E Went in Croydon deserve a nod for supplying top quality paint and production materials. All mentioned here have my thanks and gratitude for making this and many of my other models come to life on a predictable and planned basis. Thank you all so much.

Now to the images. Please enjoy them.

I`ll return to this thread once I have this model flying.

Mike

[Mike.K 60]

For those wishing to see my plan for getting myself up to speed for flying this gem of a Pitts, they should visit my thread in the Scale Section entitled " Ramair 50" Ultimate Bipe........the lead up to flying my Pitts Special". The thread describes the aquisition of the Ultimate airframe shown in the image below together with its strip down, modification and rebuild to afford me suitable fast bi-plane flying experience.

Plenty of large images support the story.

Mike