SPRITE

My project journey started in April 2015, an email from a friend pointing out an interesting looking aircraft for sale on a popular aviation website. We had been considering changing our aircraft and this, unknown to me, all-metal twoseater, operating on a Permit to Fly, looked rather intriguing. Some online research revealed a degree of information about this Practavia Sprite, and I made an impromptu trip to see it the next day. A picture of course, can certainly flatter to deceive and on inspection this aircraft certainly had rather a lot of warts.

Having stood outside for many years with no covers, the

British weather and very few hours had left their scars. It certainly needed a respray, possibly an engine overhaul, a Above Looking rather unloved and forlorn on our first visit to take a look. new canopy and plenty of TLC. However, there was something compelling about it and, after a good look around and a chat over a few mugs of coffee, I decided that it was a viable project. She had a current Permit to Fly and had been regularly ground run, but not flown, which is not always a good thing I know. So, there and then, on the basis of ‘subject to my Inspector’s approval of its airworthiness’, a deal was struck.

The ensuing inspection drew strange mutterings from my own Inspector. I could hear phrases like ‘money pit’, ‘what a travesty’ with lots of head shaking and tut tutting, so I felt a certain sense of foreboding. Finally, I mustered up the courage to ask, “So what do you think then?”.

The response was along the lines of ‘...well I wouldn’t buy it’, followed by a long list of problems, issues, snags, likely unknowns and not least, costs.

However, there was also begrudging acknowledgement that it was robustly built, so was likely a solid base upon which to start a rebuild. He followed this up with the news that he was intending to retire from inspection at the end of the year – but he is my father-in-law so perhaps he just thought this project would be a blight on our relationship! I did some research to find out more about the origins of the marque, and the history of this particular example. The project started in 1968 as a design competition by Pilot magazine and was won by an all-metal design from a team at Loughborough University. The prototype was known as the Pilot Sprite, subsequent examples being known as the Practavia Sprite, after the company took over the type and marketed the plans. Only about a half dozen were ever completed, only two currently being airworthy. G-BCVF first took the air on 18 July 1978 from Elstree Aerodrome, according to an article I have with the documentation, although the logbook shows first flight as 26 June 1980. There are some lovely handwritten notes giving details of the flight tests, and in one of the early logbook entries a note to say that it was flown by Wing Cmdr Roly Beamont, well-known WWII fighter pilot and test pilot on such aircraft as the Typhoon and EE Lightning, and one time President of the LAA.

I went through the aircraft’s paperwork, followed by several visits to the airfield for further inspections with all covers off, and found nothing to suggest that it wouldn’t fly. We carried out ground runs and the only minor concern was a lowish static rpm. All pipes and filters were checked and while incredibly sad looking, it gave every impression that it would survive a ferry flight of an hour. We did some slow and fast taxying and although I still felt a little uneasy, there was little left but to fly it.

One sunny and breezy Sunday, after uplifting fresh fuel and oil, I strapped myself in, paying close attention to the tightness of the belts, the wind and of course having memorised the straight-ahead landing area. Suffice to say, my earlier uneasiness was trying to tell me something as the flight home resulted in a precautionary landing and the aircraft had to be ferried by road to our maintenance base so the rebuild could get underway. I lived about 50 miles away so trips to the airfield would be infrequent and juggled around work and family commitments. Various small jobs could be carried out by me and my two boys, but I left most of the clever stuff to my Inspector, Carl Tyers and his team at Windmill Aviation, Spanhoe. As my time, ability and knowledge is limited, I would be sticking to manual labour and the ‘easy’ bits, making tea and coffee, encouraging people and telling Carl what an excellent engineer he was, hoping it might reduce the size of the bill!

So, where to start? My plan had always been a respray, an engine rebuild or replacement – I had not really budgeted for a new engine but accepted that it may be a necessity. Also, the firewall and engine mount would be checked and resprayed, and a new panel and internal upholstery fitted. As always with these things however, the list starts small and grows according to your own standards or wallet. This ‘lady’ would turn out to be no different.

I spent several weeks getting prices together, speaking Above Sitting sadly on her tail after the engine was removed.

Below left Number two son helping by removing the copious paint from the cowlings.

Below right The ‘new old stock’ canopy with most of the protective grease removed. to LAA Engineering, and generally ferrying bits around. An entire network of people started to come together to help me with the things I would be unable to do myself. This meant I had to find fibreglass people, engine people, airframe people and painters. I relied heavily on Carl, whose years of experience in the business and enthusiasm for the project were to prove invaluable. I quickly made contact with the owner of the other flying example, thanks to LAA HQ, and it was located only 50 minutes driving time away, so a visit was promptly arranged. It never fails to amaze me the comradeship and kindness shown by the members when it comes to helping with advice, or indeed anything aviation. Alan and his wife met us at the airfield and answered no end of questions, while giving me a free roam around their aircraft, G-BCWH, taking it all in.

It was clear that this one had been much more cared for than mine, it had always been hangared and was in lovely condition. It was noteworthy that the undercarriage was quite different – as was the panel – an indication of the flexibility the Permit scheme affords builders in making their own choices. I took copious photographs, some of which were to prove useful later down the line. I also took away ideas and thoughts, and a promise that we must get them together at the LAA Rally one day.

Next, I needed to find out the cause of the high temperature and CO fumes picked up by a portable sensor that caused the cessation of the ferry flight. I needed to know if the engine was worth salvaging, so off it went to Deltair near Southampton.

I was hoping for good news, but I think in retrospect I

was somewhat deluded, given the state of the engine, and in fact a replacement was always a more sensible option. The existing engine was a Continental C125-2, a forerunner of the Continental O-300 engine which graced many C172s.

In due course news came that there was a crack in the engine’s crankcase which financially made more sense to replace it with an O-300. Luck was with me, LAA authorised the engine change quickly and I found a good engine complete with starter, magnetos and its electrical system for a sensible price. It would need a top end overhaul, but it came from a parked aircraft that was hit by another, its front end being completely undamaged, plus it had a full history, which provided a lot of confidence.

The replacement engine provided more ‘modern’ accessories, an extra 20hp, a key based starter rather than pull and was generally much smarter. And the weight penalty, according to book figures, was only 11lb.

Although the Lycoming O-320 would have been a more modern alternative again, and indeed a third example of the Sprite is currently nearing first flight fitted with an O-320, Carl and I could not justify the additional work of making a new engine mount etc. The O-300 is pretty well a straight swap for the C125.

The fibreglass cowling was in a sorry state, and its two inspection doors looked like they could possibly have been cut out by a blindfolded man with a bread knife. I started by removing these inspection hatches, as well as the badly rusted Dzus fasteners. I also enlisted son ‘number two’ to help with the sanding down. Once the two different paint coats had been removed there were several fibreglass repairs to take care of.

We were not really sure why there were two inspection hatches, one each side. The one for the oil filler and dipstick made sense, but the other we decided was probably for an O-240 engine the aircraft was fitted with prior to the C-125 it had when I bought it. There was also a ram air duct which was not used, so I decided that both these could be removed with a bit of additional GRP work and the main inspection hatch was recut with a much-improved finish. I was not a complete novice with GRP but certainly no expert, but I was happy with the end result.

Carl was making progress with the canopy, which needed a lot of work including new Perspex. The runners needed replacing and there were also alignment issues that needed addressing. The original Sprite cockpit design called for an early unpressurised Jet Provost canopy ‘bubble’, and Carl managed to source one! It was ‘new old stock’ and caked in hardened grease, and I made countless trips to the airfield to remove it in order to arrive at a nice transparent canopy. Windmill staff also spent a lot of time on it, for which I was very grateful. The grease had been there for nigh on 50 years. Below The new propeller spacer made by Windmill Aviation.

Late 2015, and it was time to send the aircraft off to the paint shop piecemeal. I wouldn’t see it again for a few months, when hopefully it would return in dark blue rather than the patchy battleship grey it was at the time.

While she was away there wasn’t much to do except planning and research. I spent the time looking at radios, decals, weight and balance diagrams, battery technology and generally looking for weight savings. I also started thinking I was mad…

When she came back from the paint shop, I knew we had selected the right colour, a dark blue which everyone at the airfield thought looked great. More good news accompanied her – there was very little corrosion and what there was had been treated. It felt like real progress.

As work progressed on reassembly, we found more and more oddities which needed addressing. For example, non-aviation grade hardware, discrepancies between units within the documentation package, non-conformant fuel pipes, frayed bungee cables, slack cables, less than perfect brake discs, rusted bolt-on components… the list goes on. However, there were no major difficulties that I was unable to help with. Being able to remove and replace or remove and renovate items kept much of the work within my own capabilities, so it was a case of rolling up my sleeves and taking it on the chin. I left the difficult and critical items to Carl, which included top overhauling the replacement engine, installing and testing it, removing and refitting all the control surfaces (with appropriate duplicate inspections) and any jobs that required remanufacturing or critical control systems.

The engine mount was dye penetrant tested for cracks, a small weld repair carried out and then it was resprayed. The engine was mounted and plumbed in, which meant she finally sat upright rather than on her tail, so could be moved around more easily. The engine baffles were all cleaned and resprayed, or remade as necessary. The tailplane struts had to be remade due to excess corrosion, a new fuel pump was fitted, new fuel pipes manufactured, new hoses installed, manifold damage repaired, the firewall cleaned, the fuel tank selector changed and the gascolator cleaned and tested. In fact, the whole fuel system was replaced or refurbished. I had the airbox sandblasted and resprayed and the air filter was upgraded to a new one rather than the oil-soaked offering that was left from before.

Because the engine had changed, the propeller was no longer suitable. An additional problem is that the 0-300 flange has eight bolts whereas the C125 has six and there was also a prop extender in place to increase the forward moment. We could have looked to remove it, but it would have meant reworking the cowlings. So, it would have to be replaced as well, and a new bolt kit procured.

Luckily, Windmill Aviation was able to manufacture a lovely new prop extender which was duly fitted. It had been made to the same length as the previous one, but when fitted it looked to stick out from the cowling too much. Most likely no one would have noticed such imperfections on the old girl previously, what with all its other warts, but now on a much smarter airframe it stuck out like a sore thumb. It had to go back to the workshop to be shaved back a bit. The end result looks great, but I came to realise that propeller bolts are probably made from gold!

A new McCauley prop for this engine would have been several thousand pounds but, by a quirk of fate, I had met a parts broker at Earls Colne when he had come to inspect a damaged aircraft. Little was I to know that I would end up with the engine from the wreckage he purchased from the insurance company. It turned out he had sold the propeller but had another one that would work, although in order to retain the correct diameter it would have to be clipped by 1.5 inches. This would get me going until I could replace it with a new wooden one. Under the watchful eye of Carl, I rubbed the prop down and left him to work his magic with the hacksaw and spray gun. It came out looking like new.

Around February 2016 the weather was good enough to try to run the engine. I wasn’t there but Carl reported it started easily and ran nicely, with just the tachometer not working. The problem was quickly found and rectified. Our next job was to refit the cowling. Many hours had been spent fixing, glassing, filling and sanding but the fit was never going to be perfect. You can’t make a silk purse out of a sow’s ear but I did want it to look respectable. The cowling is probably the area that people notice most so even more hours were spent fitting, altering, adapting, trimming and finally, riveting on the new fasteners.

The cockpit interior was ragged so the horrendous 40-year-old fabric panels were removed, along with plenty of grotty material. I repainted the black interior finish and Bex Aviation, also at Spanhoe, did a very nice job of remaking the leather side panels. The tired seat Above Back from the paint shop and looking resplendent in her new blue coat.

Below left Trial fitting the repaired cowlings.

Below right The canopy with its greatly improved rear skirt. covers, although looking jaded, actually cleaned up well with some fabric cleaner and a lot of elbow grease.

At the end of the rebuild Bex covered the coaming with a black anti-glare faux leather, which set off the cockpit nicely. Final touches to the canopy involved fitting a new classic car style handle and replacing the rear ‘skirt’ which had previously been made from fibreglass and looked awful. Carl had a new one formed out of aluminium, we had it sprayed and it was a considerable improvement.

After looking at radio options I decided on the 8.33 Dittel KRT2, which I think has a more visible interface than its competitors in the same price band, and also had some decent reviews

The panel was fairly well kitted out, however the instruments were positioned using the scattergun approach. It also transpired that some of them did not work, so I had to replace a few. For relatively small amounts of money, I collected various things from flea markets and websites and a bit of manoeuvring saw us back with something resembling the standard ‘T’. The previous installation had relied on a venturi to drive the gyros, but I had found a used engine driven air pump and regulator. I decided not to add anything else too fancy, but went with a tablet running SkyDemon, a great piece of software that does everything most VFR pilots ever need.

Throughout 2016 and 2017 a myriad of small jobs followed. In no particular order these were, rudder bungee replacement, instrument checks, taxi and steering checks, brake checks, placarding, compass swing, wing walk material replacement, decals, fasteners, canopy latches, engine fuel flow checks and a host of adjustments. We found some minor issues, but these were all generally easily rectified. I could do most of them myself, which was nice as it satisfied the ‘frustrated engineer’ inside me and made me feel like I was doing some of the real work. Finally, it was starting to look like a flying machine! l In Part two next month, the aircraft flies… but CoG and max weight problems have to be resolved. ■