Corby Starlet

This is my current aircraft.

After re-fuelling at Caernarfon airport. One of my favourie destinations!
Ready to fly off over Snowdon.

The Corby Starlet is a single seat, wood and fabric aircraft for amateur construction. It is not available factory built, nor even as a partly built kit. If you want one, you have to buy the plans and build it from those, buying spruce, glue, fabric, dope, an engine, propellor, instruments, wheels, and so on. It was designed by John Corby in Australia in the 1960s. Many have since been made to his plans, and many have been modified to suit their owners. There are 7 in the UK register, but only 4 are presently airworthy. Many others exist around the world.

In the UK, the build has to be done under the auspices of the Light Aircraft Association (LAA). Once constructed and in flying condition, the owner can maintain it with the guidance of an LAA inspector. Every year, a formal inspection is carried out, and is verified by an LAA inspector, and a test pilot (who can be the owner) flies it in a way that will discover any unusual flight characteristics. Once theseare satisfactory, the LAA will authorise a Permit to Fly which means the aircraft is considered fit to fly for another year.

History of this aircraft

Built by Ian Aikman, G-CCXO flew for the first time in 2004. Ian subsequently sold it to Nigel Robbins, who sold it to me in 2009. It had only done 87 hours of flying at that time.

I was planning to build a Starlet from scratch, but was having difficulty in getting enough aircraft grade spruce to make it. Then CCXO came up for sale. It hadn’t been finished the way I wanted mine to be, but it seemed to be 80% of the way there. This is how it looked then:

Awaiting a new owner at Knockin airfield

What’s wrong with that cutie, then? This is how it was originally designed by Australian aircraft engineer John Corby in the 1960s – open cockpit and simple.

To me, the first problem was that open cockpit. It was very cold in the winter! I only had a couple of flights in it like that. I clearly recall looking at those small wings thinking, “I’m flying on those little things!”. But also, “I’m cold!!” And also, “It doesn’t go very fast”. Flat out it was doing about 85 mph straight and level , cruising was 60-70 mph, and stall was somewhere in the 32-38 mph region (the ASI is inaccurate at a high angle of attack needed to fly close to the stall speed). This was due to the drag of the open cockpit and poor aerodynamics of the cowl, landing gear and fairing. Adding a full canopy would keep me warmer for longer flights and increase its speed. Starlet G-ILSE can exceed 130 knots on a similar VW engine with only about 10HP more.

Steve Stride’s lovely Starlet G-ILSE

So when its Permit to Fly ran out (see http://www.lightaircraftassociation.co.uk/ for details of the UK Permit scheme) I started to modify it. The wing came off and the fuselage went home for the transformation of a new cowl, new cockpit canopy, faired landing gear and wheel pants, complete re-wire, new instruments, new carburettor, induction and heat system, new colour scheme and many minor improvements to fairings and cockpit ergonomics. I thought it would be done in 6 months. Unfortunately, it took me 2 years. Here it was in my workshop (aka my garage) in 2010, approaching completion:

The canopy was made by a New Zealand company Composites International (see http://www.compositesinternational.co.nz/). They made me 3 kits and shipped them to me. Two went to other builders (which have not appeared into the flying fleet yet)

Unfortunately a problem appeared when first running the engine at Sleap which initially looked like a fault in one of the twin Leburg ignition units. I had accidentally damaged one during my refurbishment work, but thought I’d resolved it by replacing a timing sensor. However whilst the static timing looked OK, it ran really badly on the “damaged” ignition. This meant a delay until Stormamps, the company then supporting Leburg units, could check it out. However they found it was OK. I went round in circles looking for the problem, but my helpful inspector came to my rescue and found the problem in some faulty (brand new) spark plugs and a badly mal-adjusted carburettor. The original carburettor had been exchanged with a similar one from my previous inspector, but it turned out to be a poor one. Apart from the initial poor adjustment, it was also badly worn and caused a number of problems which could have caused a forced landing. So it was scrapped and a new one obtained a couple of years later from the ever-helpful Barry Smith (https://www.acro.co.uk/).

Initial taxi trials found the handbrake was quite ineffective, and tightening it caused the parking brake to fail to release. The handbrake wasn’t allowing the master cylinder to fully release and vent the fluid, so a new actuator with longer throw was needed.

I received the Permit to Test Fly in July 2011. The requirement was to do 5 hours to prove the engine reliability, and I hoped to be able to fly it to Sywell that year. I then found it was directionally unstable when the tail wheel was down despite all efforts to learn how to control it. However I was convinced it was my ham-fisted control as that was the only explanation that others could offer, so I progressed and got a Permit to Test Fly from 15/7/11.

Alas it all went pear-shaped on 25th July 2011.

I still was finding that it was difficult to control on hard surfaces. This was said to be normal for the type, and I had taken advice from several pilots who are very experienced in the type on how to deal with this. No-one could see any issues with the mechanical arrangement, although that turned out to be completely wrong.

On the day of the accident I decided to do more taxi trials and to leave the first flight to the following day. I entered runway 36 which was the active. I found the same behaviour as previously, and decided to try the grass runway next to runway 23 as one of the other pilots had advised me that it would be easier to control on grass. I found that this was the case, and I ran the length of the grass runway about 10 to 15 times. These runs had taken the speed from nil to about 40 kts on several occasions, when the tail had lifted and the aircraft had probably risen a few inches into the air. However as engine temperatures were building up due to the low airspeed, and it was getting into late afternoon, I decided it was correct to delay the first flight until the following day.

I returned to runway 23 (hard) to taxi back to the hangar. After about 100m the aircraft swung to the left. I was mindful of the advice I had been given, which was to “correct gently”, and did so, and at the same time reduced the power to idle. This had happened a few times before, leading to oscillations but eventual return to control or stopping. Unfortunately this time the swing built up very quickly and the aircraft turned 90° to the left. The speed was probably only 10-15 knots, and the engine was idling. It was enough to make the aircraft roll right and the starboard wing tip touched the ground. After a few seconds the starboard undercarriage leg (the undercarriage is in 2 parts with a separate leg on each side) failed and folded backwards. The movement caused the aircraft to pitch onto its nose. This caused the propeller to break. Here you can see photos of the aircraft after we dragged it off the hard runway onto the grass runway. This caused the undercarraige leg to fold forwards.

That was the end of flying aspirations for the Starlet for a couple of years – repairs can take a surprising amount of time, as I’d previously discovered.

Repairing the Starlet wasn’t straightforward. I was very disheartened, My inspector said that he could repair the damage for me. Eventually, helped by a generous insurance pay-out, we agreed that he would repair the damaged woodwork and check the engine for crankshaft damage, and I’d to the rest. Bob did a great job of his side of the deal, and I got the aircraft back in early 2012.

I replaced the broken prop with a Hercules one which has been very successful. The cowl and wheel pant were repaired, differential heel brakes were added in the anticipation of more directional stability problems, and all minor damage made good.

An important factor of course was understanding the cause of the directional instability. To cut a long story short, I realised that the problem was simply the tail springs, ie the springs which connect the horns on the elevator to the horns on the tailwheel carrier. Previously the springs (as fitted when I’d bought it) had been too weak and had not been pre-tensioned. It’s quite possible that when I replaced the rudder after my initial phase of refurbishment work before the accident I had failed to replace it exactly as it had been when I bought it, as its previous owner (a very experience tailwheel pilot) had reported no problems. However I’d found it a problem even before I took it apart for refurbishment, so I had blamed my problems after the refurbishment on my own inexperience rather than on a physical problem with the aircraft. Well my inexperience was undoubtedly contributory, but the change in the aircraft’s ground handling after a further modification was amazing.

The airfraft had originally been fitted with a tiny tail wheel from (I think) a child’s scooter. It was only about 3” diameter. In  2012, my wife and I went on holiday to New Zealand, where I met Starlet owners Don and Dave Wilkinson, who each have a Starlet.

Don starting his aircraft with Don in the cockpit
Dave flying beside me near Auckland (I’d been given a ride in Garry’s Hawk)
Garry and his Hawk
Both Starlets approaching Auckland harbour.

These Starlets have flown literally thousands of hours without a major incident. They also use VW engines. The difference in their tailwheels compared to mine was very clear, and so when I got home I bought the same tailwheel as they have, sourced some springs with the correct characteristics to give the correct tension, and made a new wheel holder with steering horns –

This remaining work took a long time as I suffered a major illness in 2013, and eventually it flew again in May 2014, which was its first flight in its new guise.

What a transformation! The aircraft now handles wonderfully. It took me a while to build confidence, and initially I only flew it off grass. Whilst it is slightly more lively on tarmac, it’s not a problem, and in fact it’s the nicest aircraft to handle on the ground (and in the air!) that I’ve ever flown. Thanks, guys, I owe you!

Also in North Island, I met Clive Whitfield, manager at the company who made my super sliding canopy. He took me to Ardmore airfied, which is home to a very active restoration centre. There were various warbirds under reconstruction, including a Spitfire and my favourite aircraft, the de Havilland Mosquito. They even have a road where I couldn’t miss a self-protrait –

Photo by Susan Ord

I’ve now (January 2020) flown 190 hours in CCXO.

It hasn’t all been plain sailing, the two worst problems having been the carburettor and the crankshaft oil seal.

Carburettor

Initially the aircraft had a fixed jet Stromberg CD150 carb on it, My previous inspector at the time recommended an adjustable jet one to make it easier to get the mixture exactly correct. He swapped the existing one for one from a Tipsy Nipper he was working on. Alas it had many problems, starting with an overflowing float chamber (found to be due to the float chamber not being vented). This was repaired before the engine could run, but later problems developed with the mixture going rich due to the adjuster slipping, and engine stoppages (fortunately all on the ground) due to the general poor condition of the carb (even though I had replaced the diaphragm, fuel valve, and float).

Eventually I gave up trying to correct it and fortunately Barry Smith, a guru in VW engines, was able to sell me an unused Solex CD150, which worked perfectly after I calibrated its needle.

Crankshaft oil seal

The engine is a Great Planes VW conversion (1834cc) and has their “Force 1” bearing and crankcase oil seal on what was originally not the power take-off end of the engine. This is a normal arrangement for aircraft conversions. However when flying to Llanbedr in North Wales in November 2014, the windscreen started to collect liquid droplets, and soon I could hardly see forwards. Fortunately I was only 10 miles from Llanbedr and made a priority landing.

The front bearing has 2 oil seals, one of which can only be changed by removing the engine and separating its two crankcase halves. That would have meant trailering the aircraft home. So a second solution, to replace only the outer seal, was tried. This only required pulling off the prop driver. To give it a chance, the root cause had to be found, as it’s rare for these seals to fail. The most likely cause was excessive crankcase pressure. I had run a vent line from the oil breather to below the aircraft, and my inspector suspected that it might have been the problem. So the line was temporarily removed for the flight home. This went well, and the seal hasn’t leaked at all since. The breather tube was replaced with a shorter, larger diameter one, going to a collection bottle, and it keeps any vented oil mist from oiling the engine bay in general.

Performance

Was it worth all the effort?

Most definitely, yes. Everyone who flies a Corby Starlet is full of praise for the little machine. It only has room for my 80kg 1.75 m frame and full fuel and 5kg of luggage, and its range is only about 2 to 2.5 hours on its 30 litre fuel tank, but what a delight it is.

Photo by Steve Grimshaw
Photo by Steve Grimshaw
Photo by Bob Fletcher

With its new Hercules propellor, performance figures are now:

RPMKnotsComments
Idle38Stalls
220060
250070
270085
2900100
3200115
3300124 Maximum speed, straight and level
----138VNE (never exceed speed), only attainable in a dive

A modification I made a couple of years ago was to provide an elevator trim. Not all Starlets have one, and the type which the LAA agreed to let me fit was a bungee attached to the control stick to put a variable force to pull the elevator down. This was done using some spare tailwheel springs acting on the control stick via a pulley. The tension is varied using a lever on a castellated semi-circular piece of wood.

The components of the elevator trim system
The trim system in place. The return pulley is hidden by the seat.

In use, take-off and landing are done with the lever fully back. Once climb is established, I increment the trim to a suitable position according to the speed I want to fly at, then it flies with no force on the stick to keep the aircraft level. I discovered that quite by change, the castellations represent about 5 kt increments in trimmed speed, which is really handy.

Other performance figures

CharacteristicValueComments
Climb rate~800 fpm (4.1 m/s) at 70 kts, still air, 1013 mbar, 20°CChanges little between 60 and 90 kts
Take-off roll~200mTarmac, still air. About 300m off short grass.
Landing roll~200mTarmac, still air. About 100m on grass.
Fuel consumption12 litres/hr at 90 ktsCan be as low as 10 litres/hr at 70 kts. Uses super unleaded fuel normally. Avgas is OK provided the oil is changed at shorter intervals.
Duration2 hrs with 30 minutes reserveFuel tank is only 30 litres. Longest flight to date was 2 hrs 15 minutes.
Oil change50 hrs if essentially fuelled by mogas, 25 hrs if on avgas 100LL.Should be low ethanol, but it's hard to find now. All pipes etc are OK with ethanol, but cavitation is a risk in hot weather. No problems ever experienced.
Carb heaterCan achieve a throat temperature rise of up to 30 degC.And it slows the engine a lot! Temperature is displayed on the panel GT-50 instrument.

Instruments

The instrument panel isn’t large, so if you want to pretend to be a “big” aeroplane, some shoe-horning and careful design is needed. Multi-function instruments help a lot. So I now have lots of cockpit toys!

FunctionInstrumentComments
AltimeterWinter 0-4000ft, single dialI replaced my original dual dial gauge which failed. This style is well suited to a light aircraft which rarely goes over 4000ft
Air speed indicator
Engine monitorMGL Avionics G-3 (Stratomaster Velocity)3.125" version. I initially installed a 2.25" version. Unfortunately this monochrome instrument is no longer manufactured. It gives a display of RPM, 2xCHT, 2xEGT, oil pressure, oil temperature. Excellent instrument with alarms and bargraph displays as well as figures.
Secondary sensorFlight Data Systems GT-50Provides g-meter, voltmeter, carb throat temperature, Hobbs meter, flight timer
Magnetic compassHamilton style vertical cardBought to replace the standard compass that swings wildly in turns. Alas, this one does too despite the manufacturer's claims that it doesn't
Turn co-ordinatorElectric typeHas unbuilt turn and slip indicator.
Vertical speed indicator± 0-2000 ft/minAnalogue instrument.
Ignition controlLeburg ignition controller / monitorDisplays an indication of the ignition status (off, ready to start, running, fault)
Battery monitors2 x car multi-colour displaysThe Leburg system uses 2 batteries, a main and a backup in case the alternator fails.
Flight timerASA timerProvides a range of timers, count up and count down.
GPSSmartphone using Sky Demon software
ConspicuityPilot AwareShows the position of detected traffic on the Sky Demon display.
Fuel pressureRaceTech car gauge, 0-15 psiNormal flying pressure is 2 psi (1 pump running) to 4 psi (both pumps running), 5 psi with engine stopped. (2 x Facet pumps)
ConspicuityTrig TT21 Mode S transponderIt added over 10% to the value of the aircraft!
CommunicationYaesu FTA 550 transceiverHas a great memory function to reduce pilot workload
CommunicationLightspeed Sierra headsetGood performance and good value ANR headset. Allows connection of music, but I prefer the sound of the engine!
Photo by Kerry Hodson
Photo by Kerry Hodson

Acknowledgements

Thanks to all those who have sent me pictures of XO when I’m in the driving seat!

Thanks to Trevor Pugh for hangarage and friendship when I was hangared at Breidden (the above 2 pictures were taken at that very pretty strip).

Thanks to Shropshire Aero Club and Sleap Aerodrome where XO is currently kept.

Thanks to Ian Aikman who build the aircraft originally.

Thanks to Nigel Robbins who was the second owner and sold it to me.

Thanks to the excellent LAA (Light Aircraft Association (http://www.lightaircraftassociation.co.uk/), who keep the skies open to amateur and future professional pilots in the UK and protect us against over-zealous CAA and EASA restrictions. We recreational pilots owe their Office and Engineering departments many thanks.

Thanks to Don and Dave Wilkinson for help and encouragement, and for welcoming me to the very aircraft-friendly side of New Zealand. Also to Clive Whitfield there, who made my canopy.

And most of all, thanks to John Corby for a great aircraft design, and to my inspector Bob Hallam for all your help and support in getting it flying! John was presented with the Order of Australia Medal for services to aviation in 2019 (see https://www.australianflying.com.au/latest/six-aviators-in-queen-s-birthday-honours-list) – well done, John.

© Stuart Ord, 2010