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Building, flying and displaying a Pitts Model 12: Part One

PUBLISHED: 17:21 19 June 2019 | UPDATED: 17:21 19 June 2019

Little and large model 12 with Mark O'leary's S1

Little and large model 12 with Mark O'leary's S1

Peter Borchert

Part One of the story of one man's quest to build, test-fly and display the 400hp Model 12 'monster Pitts' | Words and photos: Peter Borchert

This is my story about building, test-flying and displaying a Pitts Special. A rather special Pitts, as it happens.

The ultimate iteration of a series of aerobatic biplanes that started in 1946, designed and built by Curtis Pitts. The Model 12 was the last he designed, built, and test flew himself in 1992−on his eightieth birthday! An inspirational man, he has left an enormous legacy from his passionate and talented life's work.

But why build an aeroplane? Firstly, my interest includes the technical−the engineering of aircraft. My thirty years of flying followed an interest in generally anything with an internal combustion engine: as a schoolboy, the excitement of mastering the controls of a (terrifying) petrol-powered lawn mower; later, growing up on a farm, driving a tractor.

These early experiences inspired my life of relationships with machines: motorbikes, cars and then aeroplanes. For me, to become a pilot and master a flying machine was, and remains the ultimate relationship you can have with a machine.

Photo from Nick JenningsPhoto from Nick Jennings

Everyone who drives understands the intimacy you can have with a car; pilots can have this with aeroplanes. The challenges of aerobatics or perhaps just a long cross country or greasing a landing have us feeling at one with our machine.

Now imagine the intimacy if you had built the machine. If you understood everything about it, knew every circuit, diode, resistor and relay, every nut, bolt and bearing−because you had built it! That was my dream.

In 1989 I met a pilot called Nick Grace. An impressive man−not least because he was a display pilot and flew a T9 Spitfire−but because of what he had achieved in the rebuild of his aircraft. Quite unexpectedly this extraordinary man offered to take me−a Piper Cub pilot−for a flight in his two-seat Spitfire.

I was of course spellbound, not only by the flight but the epic project he'd undertaken to get this very special aircraft flying. I can trace my plans to build an aeroplane back to this chance meeting. Tragically Nick was killed in a car accident before I could meet him again, but what he had achieved left many people like me inspired. I was going to build an aircraft, a special aircraft. Oh, and I was going to become a display pilot.

Finished Pitts Old SarumFinished Pitts Old Sarum

My flying developed from taking up club instructional types to owning aircraft that fascinated me most. First a baptism of tailwheel with a Piper Cub, followed by a Tiger Moth, then the Yak-50. Skill levels had to keep pace with the challenges of each machine.

By the late 1990s I had taken up display flying in the Yak-50 with the Yakovlevs formation display team. I loved to fly the aircraft, then fate intervened. A pilot friend was killed flying low level aerobatics in my Yak.

It had a profound effect on me. I didn't fly for months. Ultimately my flying passion resurfaced and I returned to flying−with a plan. I knew that if I was going to survive as a display pilot there were things, in my control, that could reduce the dangers. Top survival measure was to get more training−a lot more.

Raising my game

My aerobatic training looked rather shallow compared to the fast jet pilots I was flying with in the Yakovlevs.

But where to go? In my search for the best teacher to develop my aerobatic skills one name kept cropping up: Alan Cassidy, four-time British Aerobatic Champion. Alan instructed with an S-2A Pitts Special and this was my introduction to the type.

Adaptable garage extension with removable wallAdaptable garage extension with removable wall

At first Alan's intellectual approach to coaching challenged just about everything I'd learned about flying, including the way I'd been trained. The demanding sessions were bewildering but his outstanding book Better Aerobatics was (and is) an excellent training manual for me, offering an intelligent understanding of aerobatics for every level.

What was too difficult for me to comprehend in our training sessions I could learn at my own pace with this brilliant book−and become a confident, safer aerobatic pilot. What's more, I'd grown to like the Pitts Special so I bought a Pitts (an S-2B) and my display flying turned to solo aerobatics.

In October 1999 I read a Pilot magazine article on Curtis Pitts' Model 12 - a Pitts Special powered by the radial engine from Yaks and Sukhois. It combined this charismatic engine with the brilliant airframe of the Pitts Special−a combination of the two aircraft I came to admire the most.

There were plans to make it available as a kit, and I knew this was the aircraft I would build. But there was a problem. The PFA (now LAA) had a restriction on the maximum engine size of homebuilt aircraft of 260hp. It was several years before the limit was raised to accommodate the 360-450hp of the Model 12, so one could be built in the UK.

The Pitts Special ShedThe Pitts Special Shed

When the first (American-built) aircraft was registered and approved to fly here I began to dream again about building my own. In 2013 I placed an order for the Model 12 kit offered by the Jim Kimbal company.

Jim is known, amongst other things, for the replica of the Granville Brothers' Gee Bee model Z racer that is now owned and flown by Kermit Weeks. Jim and his son Kevin worked with Curtis Pitts on a development of the Model 12. With airshow pilot Steve Wolf they developed it into the HP (High Performance) version with clipped wings, larger ailerons, and shortened fuselage that became the basis of the Jim Kimbal kits.

No one had built a Model 12 Pitts in this country when I started to plan my build, and before I committed to the project I needed some reassurance that it would get approval. Competition aerobatic pilots Rob Haworth and Alan Cassidy were the first to bring an American-built Pitts 12 to the UK and to get the type approved by the LAA. That meant I could avoid the daunting approval process.

And when I contacted Francis Donaldson, Chief Engineer at the LAA, he had a real enthusiasm for the Model 12−he'd been involved with the approval of Alan and Rob's aircraft. My discussions with him were encouraging and left me with things to do but no doubts. I placed my order with Jim Kimbal.

Rob Millinship mentor and skill teacherRob Millinship mentor and skill teacher

Next I needed an LAA inspector. Similar to my aerobatic training research leading to Alan Cassidy, all roads led me to one man who stood above all others as the specialist for the Pitts Special: Rob Millinship. I knew Rob from the display circuit as a pilot at the Shuttleworth Collection.

He has the distinction of flying Shuttleworth's rotary-engined aircraft and also displays their rather wonderful Gloster Gladiator. More importantly to me, he is Mr Pitts Special.

It became obvious to me that, while my local LAA inspectors might have the generic knowledge about wooden wings and fabric etc, an expert on the Pitts would bring much more to my project. And so it was to be. Rob would become my reference for all things I didn't understand. He trained me in skills I didn't have and was a mentor on the end of a phone. His extraordinary knowledge and exact approach became an inspiration for the quality of my build.

A labour of love

The build took almost exactly five years. At an average of three hours each day I estimate over 5,000 hours.

What I didn't expect at the outset was the extent of what I had to do. I had naïvely expected that a 'kit' would mean parts that would require unpacking and assembly. Unlike a car, handmade airframe components are rarely interchangeable without adaptation, and everything takes a lot of skill and effort to assemble.

Wing rib productionWing rib production

The drawings Curtis had sold for others to build his series of Pitts Specials were drawn by hand by a draughtsman−not in CAD−and so too were the drawings for the Model 12.

I went from being slightly disappointed by the lack of CAD and efficient streamed updates to enjoying the challenging methods required to create a hand-built aircraft. When there were gaps in the information I got from the Kimbal company I would refer to Rob.

When the wing 'kit' arrived it was three boxes of wood−not the kit you might expect but the raw materials to build the wings. The spars were machined to shape and the leading edge ply formed to shape−but that was it. The kit did include jigs to form the profile of the ribs, which was a great help. Wing construction, from wood work to fabric covering and painting, took a large part of the project−nearly two years.

With Rob's regular visits and contact by phone progress was steady. Each day a bit more, and I never lacked motivation, looking forward to my evenings in the workshop, encouraged that I was adding each day to the finished project.

Bottom wing assemblyBottom wing assembly

Highlights were the completion of a particular assembly: the all-wood construction for the first wing, then the top wing, the start and finish of the fabric covering, and the move to the fuselage frame and metal parts and so on.

The satisfaction lay in completing each bit and making a good attempt at perfection−every part becoming a thing of beauty. Slowly, year-on-year I was converting the kit into a collection of recognisable components of an aeroplane.

The Kimbal 'kit' is not a complete set of parts like the superb Van's RV aircraft kits. A long list of parts has to be sourced to complete the aircraft, including major items like the engine, oil tank (from a Yak or Sukhoi), engine instruments, avionics, fabric/paint, hardware, hoses and metal tubing.

First complete assemblies - bottom wingsFirst complete assemblies - bottom wings

All-important engine

I couldn't wait to source the engine! Richard Goode had sold me my first Yak and has long supplied engines to the Yakovlevs team. I've always enjoyed a good working relationship with him.

Richard, you may know, had a notable career in competition aerobatics (flying for the British team in the World championship) as well as display flying, during which time he came across and admired the aerobatic machinery produced by the Russians. After Glasnost he led the import of Yaks and Sukhois.

Today he operates as a supplier of Russian aerobatic aircraft and engines. I would describe him as having a deep rooted empathy for his customers.

Fitting of engineFitting of engine

He trades as agent for the Hungarian-based company Aerometal. Based in Budapest they are a large organisation overhauling, amongst other engines, the Vedeneyev M14P series of engines. Curtis Pitts designed the Model 12 around this engine with up to 450hp, the maximum output of the M14P.

The standard version, fitted to the Yak 52, develops 360hp. A subsequent Russian development of the engine, the PF version is a simple re-gearing of the supercharger to run at higher rpm and produces an increase in power from 360hp to a nominal 400hp.

It comes without any weight increase and was an obvious choice for me. The M14P is no longer in production but they made them in the thousands and there are many source engines to be the basis of a zero-time rebuild.

My engine was on its first rebuild, having had a short (187 hour) life in a Yak-18. It suffered a hydraulic lock in one of its bottom cylinders. This occurred after its pilot neglected to pull the engine through before start-up.

Outside the house for trip to airfieldOutside the house for trip to airfield

Typical of all radial engines, the lower cylinders are upside down and care must be taken before start up. During the cooling process after the previous flight, oil can seep from the crankcase past the rings of the bottom cylinders. The flow of oil is assisted by the contracting cooling air in the combustion chambers.

The effect this can have can be catastrophic if the engine is started. The upper cylinders will start to operate whilst those with incompressible oil in them will cause a failure−usually no more than a bent connecting rod, but requiring a full engine rebuild.

These consequences are avoided provided the pilot pulls the prop through sufficiently for each of the cylinders to run through a complete cycle so that any oil escapes through the exhaust valves before start up. If neglected the consequence is costly. But for me it provided a low time engine as the basis of a rebuild.

An invitation from Richard to go the factory in Budapest to see my engine run on a dynamometer following its rebuild was really worthwhile. I learned a great deal about the engine and its installation in the airframe from the people at Aerometal, and it was a joy to see it run.

It arrived well in advance of the airframe being ready to receive it, but was a great boost to the project when it arrived. It sat in the hall outside my office as an inspiration until I was ready to fit it.

The most significant part of the kit was the fuselage space frame. This was jig-welded to impressive accuracy in America. Some choose to construct their own fuselage frame from plans, but this complex piece of engineering seems to add years to build projects, and whilst it is costly it was to get me flying sooner.

When it arrived and I started work assembling the attachments, it became obvious how well engineered it is. Details like the bearing housings were precisely machined, and the assembly of the control system was more like the kit build where everything fits that I had been expecting.

First fabric on the smaller areas of the empennageFirst fabric on the smaller areas of the empennage

Panel and avionics

Most aircraft kits will leave the builder to design the panel and avionics fit. The Kimbal kit includes a blank panel for you to make your own choices and design. Of course I looked at other examples of Model 12s to see what others had done. Electronic flight and engine management with digital displays are popular.

I also studied the instrument panels of historic aircraft. These can be quite beautiful, particularly military aircraft. Complex displays of information with shielded toggle switches and, of course, analogue dials. For me, for a biplane, an historic form of aircraft, analogue dials seemed the obvious choice. My instruments would be analogue though electronic, with wires linked to senders.

In the motoring world the design of the position of switches, and the readability of instruments and access to controls−the ergonomics−are precise and carefully considered. It has always surprised me how haphazard this is with aircraft - often dangerously so. Here I had the chance to design a panel and switch/control layout that was a coherent design.

Panel design and assemblyPanel design and assembly

I started with a cardboard panel and sourced the dials and avionics that could work. They had to be small to get onto the relatively small panel size. I found an American company UMA who made 1¼ inch diameter dials. They really couldn't have been more helpful.

I researched the engine parameters and they calibrated my gauges with the operating bands coloured green/red etc. I even got to choose the units. I have flown aircraft with airspeed indicators in mph, knots and kph. I decided on airspeed in knots, pressure in psi and fuel flow in litres to suit the cocktail of metric and imperial units that we fly with today.

With painting finished I started the very satisfying process of assembly. This really is the best part of the build. Components that have been in the making for a number of years, now beautifully painted, are assembled to form recognisable parts of an aeroplane. I had looked forward to working on the oily bits, and installing the pristine engine was a joy.

Before the fuselage could be completed I would have to design the wiring layout and assemble the loom. It seemed like it was going to be simple, but with the systems that come with the engine, including a compressed air starter, and the general complexity of the avionics and charging systems… well, I was out of my depth and needed help.

After some research amongst the local community of aircraft builders I came across Jon Woodward. Jon has a motor industry background and is a keen pilot. When I first met him he was planning a quiet retirement enjoying his flying, but he had started to take on wiring work on LAA permit types.

Jon guided me through the wiring design, circuit protection, wire gauge selection, and the separation of power from data and avionics wiring. Guidance that set me up to form the wiring loom.

All the grahics were designed on CAD and painted on with cut vinyl masksAll the grahics were designed on CAD and painted on with cut vinyl masks

I didn't want to leave the first engine start until the aircraft had moved to an airfield; I imagined complications and being near my workshop seemed sensible. So I planned the first start-up at home outside my workshop, of course before the wings were attached.

I tied down the tail to bolts in the concrete floor of my yard and fitted the propeller. On Richard Goode's advice, I got his expert Russian engineer Gena Pervendentsev to look over my installation of wiring and pipework.

Gena spent the morning going through the systems and was left with the task of modifying the airstart distributor to accept the American rpm drive (to the rpm gauge). It was late afternoon and dark before we were ready.

Now, a 400 horsepower radial with a 2.6m diameter prop is a serious piece of machinery, and starting it in the dark in the confined space of my yard was a little bit terrifying. But in the end all was well. It ran with good oil pressure and my neighbours, far from complaining, said it made a glorious noise.

Moving the aircraft to the airfield involved a flatbed lorry for the fuselage on its wheels, and a furniture removal lorry for the wings. At the airfield (Old Sarum) I was given a corner in the museum's hangar (Boscombe Down Aviation Collection).

Here my very helpful host let me construct scaffolding, to raise the top wing and lower it onto the fuselage. It took a month of dark winter evenings setting up the rigging of the flying wires and getting ready for Rob Millenship's final inspection. Rob came with scales to check its weight and centre of gravity. All was well and, with paperwork submitted to the LAA, I waited for the permit to test.

Carbon seats provided space for breakers and switchesCarbon seats provided space for breakers and switches

Preparing for the test flight

The LAA generally provides a test pilot to undertake the first flight and carry out the test schedule. This is a test pilot with the appropriate experience in comparable types.

With some encouragement from Rob, I applied to the LAA to undertake the test flying myself. I had a few hundred hours on both the Pitts and aircraft with the same type of engine. I was keen to see if the LAA would accept me undertaking the test-flying.

They wanted full details of my log book and ratings plus the details of pilots who knew my flying. The first flight of an aircraft carries higher risks than a normal flight and you can appreciate there are checks they have to make to be satisfied that a pilot is suitable to carry out the testing. Not least that you won't kill yourself or a member of the public.

Final assembly in WWI hangar Old SarumFinal assembly in WWI hangar Old Sarum

In preparation I got some time flying circuits and aeros in the only Pitts 12 on the UK register, an American-built aircraft belonging to Will Wright.

I filled my boots and got very comfortable flying the Model 12. Landing an aircraft becomes a preoccupation on learning to fly a new type. After flying Will's aircraft it occurred to me that it was rather flattering to land, quite unlike any Pitts I had flown.

The takeoffs required some care, to resist using full power from the start of the takeoff roll, but I was relieved that I wouldn't be anxious about landing on my first flight.

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