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The following article was written for New Zealands Sport Flying Magazine, published April 2011

Flying the Tiny French Twin

Cruising at 100 kts with the Taranaki Coastline visible. Note the voltmeter on the right, ignition switches on the left, strobes switch label obscured

When  Cricri aircraft were first presented on the international stage at Oshkosh in 1981 they were the talk of the show for that year. A pair of aircraft from France with highly competent pilots performed back to back aerobatic manoeuvres that were impressive for an aircraft weighing 190 lbs (90kg) and with wingspan less than 16 ft (4.9m). For me, as a builder planning to conduct the first flight and test flights thereafter, I was impressed with the paucity of information on what to expect. Most of the flying aircraft are in France – with few published flight reports (at least in English!). It isn’t even practical to get a formal rating in the aircraft type – so with some basic airspeed details from the published flight manual, and some personal tips from the only other NZ Cricri owner -Nev Hay- the first flight took place. Now, two years on – the lessons learned can be passed on hopefully in a format that would better equip any reasonable 600 hr pilot to conduct a safe flight in the Cricri should he/she be offered this rare privilege.

Personal Stuff

Flying this aircraft is not going to be for you if you exceed 180cm (5 ft 11), unless you are particularly short-waisted. You won’t fit under the canopy. Likewise, a weight of 90 kg or more will put you over the MAUW (170Kg) without any fuel. Oh well- back to the diet. Me – I weigh in at 72kg and span 180cm toe to vertex, have 650 hours flight time and half a dozen type ratings.




Climbing in.

The Cricri is so small that you climb down into it. Sort of like getting into a go-kart. The canopy does hinge sufficiently clear of the fuselage for the pilot to stand on the seat, hands on each side of the fuselage – and slide your legs down over the fuel tank towards the rudder pedals – which you feel rather than see. The pedal tray is adjustable on rails so can be slid away or towards you for comfort. The seat is fixed and is cushioned with a single 12mm covered foam squab on a minimally shaped aluminium seat pan. With a small cushion behind your back its snug and comfortable. The harness is a light five piece unit but before you strap up – give some thought to starting the engines. For this flight the kindly instructor has offered to start your engines for you today, so stay in your seat.

Pitch trim on the right, Flaps on the left, fuel pressure bulb on the seat

Get familiar with the controls.  The stick and rudders are comfortable and light. The stick forces are set with firm elastic bands.  There is a trim adjust for ailerons on the stick, and pitch trim is a lever on the right wall of the fuselage that simply adjusts the centre of balanced elastic bands that preload the controls. Ailerons and pitch surfaces are all dynamically balanced so the  control input forces are set by the tension in the elastic bands. The forces seem quite stiff on the ground, but the same control force in the air seems very light. They can be set to your preference. I prefer light controls. One unusual item is the brake, which is a single hydraulic bicycle lever mounted vertically on the control stick. Excursion is almost right to the stick to lock the wheels, but the brake can easily hold a full power ground run up.

Finally – the flaps deploy lever is on the left, opposite the trim lever. It has three detents: 27 degrees, 12 degrees and -3 degrees for cruise. The lever is a little difficult to reach because your elbow won’t fit past the upright of the seat back. If you have long arms  you need to hook the control with your little finger to change flap settings. Make sure you are comfortable with this  on the ground. A flapless landing is quite  demanding as the Cricri is extremely slippery in flight.

All the switches, radio, and instruments and logically laid out on the small panel. Apart from an ASI you will be flying by glass for this flight.

Engine start

These little German made engines weigh less than 15 lbs and produce 22HP at 7000 RPM. The alternator is a home designed extra – fitted to the LH engine only


Unlike most Cricri’s, which are powered by French JPX engines of 18HP, my CRI has German made  engines (3W 240cc ib2’s) which herald from the model aircraft stable and have dual electronic ignition and plugs producing 22HP. They usually start easily by hand if you get the mixture correct from the outset. Pressurise the fuel tank with a few puffs of the blood pressure bulb attached to the fuel tank vent hose. Brakes and ignition checks, throttle set and a few flicks has both engines burbling at a healthy 1800 RPM. When the LH engine comes to  life the voltmeter should jump from battery voltage to charging voltage (14.5 volts) Battery life is perhaps 25 minutes if the alternator fails. Both engines stop abruptly when the battery depletes below 10 volts- so keep an eye on main bus voltage. That’s why the crammed panel has a space for a two inch voltmeter.

Climbing out

Taxiing is straightforward with no vices. Again – it feels like a go-kart. You may need the radio volume louder than usual because of the loud bark from the tuned engine exhausts that liberate their spent pulses of exhaust energy just 30 cm from each ear.  Assuming checks all performed, radio calls in hand and you are now lined up – ready to roll. Full power delivers a nice little kick. There is no yaw as the engines have opposite directions of rotation. Roll is around 100 metres and take off is intuitive. One point to watch on climb out is airspeed.  Don’t exceed 70 kts with flaps out, but this  requires a steep angle of climb on full power. With both engines performing well and ¾ fuel the climb rate is 1300 ft/min. At 300 ft into the climb you now have to manoeuvre your left arm to retract the unwanted flap, using the little finger to slip the flap lever forward to its -3 degree cruise detent.  As you throttle back the next distinctive Cricri issue presents itself – what I call “thrubbing”  from asymmetrical engine RPM. Choose the RH engine to adjust as it’s the closest throttle lever. Trial and error will soon establish which engine is fast, or you can simply check the tachometers. They are sufficiently accurate to  pick appropriate corrective throttle action.

Turns, Stalls and single engine.

Establish a 90 kt cruise, straight and level at your selected altitude. By now the engine RPMs should be balanced and you are just beginning to feel comfortable and in control. Re-trim for hands off flight. The first thing you are immediately aware of is the fabulous unimpeded view. The wings look tiny – but they are just over 2 metres reach out from the fuselage. You have this go-kart feeling again – light and very nimble in all directions. There is little lateral momentum so abrupt rolls and roll stops are straightforward.  Pitch control is sensitive and may take a few trials to maintain a balanced turn without altitude gain. Yaw is not easy to detect so a yaw string – glider style – is taped to the canopy. It is a little too sensitive so you will have to tolerate small amounts of unplanned yaw.

It’s time to climb for stalls – and here you will encounter another Cricri feature that justifies a briefing. The stalls fall right on the book numbers: 39 kts, 44 kts and 49 kts with progressively less flap. However there is no buffet whatsoever – no warning - and the stalls at each configuration are abrupt and symmetrical – even with power applied. Once again, the opposite turning engines cancel the effect of torque completely. Recovery from the stalls is standard – but the relevance of a missing buffet is to avoid stalling the aircraft on to the ground at landing. On several approaches I have encountered a rapid loss of height as the airspeed washed off just a meter above the ground – particularly with full flap. 

Single engine performance will only just sustain a gentle climb with around 1/3 rudder at 70 kts. I have had one engine failure – at 800 ft on take-off. The circuit was easily completed and a conventional landing was achieved without difficulty, but not without displacing a scheduled airline for a go around!

Landing

Landing at Raglan, one notch of flap deployed (Photo D Gwilliam)

As you approach for downwind you need circuit planning more typical for a high performance aircraft than a 400 lb Microlight. The Cricri is streamlined. The engines don’t like to idle. So begin to slow down early. Deploying flaps at 70 kts brings a minor pitch change but a major change in drag , so the descent on finals will be as steep as for a Cessna 152 with full flap. At low power some RPM settings are accompanied by unpleasant engine resonance and vibration, so the range of power settings will be less than you may be used to with normal aircraft engine.


At touchdown the suspension is very forgiving, but beware of the unexpected stall as you hold off. I suggest flying onto the ground a few knots above the stall speed. Use brakes as required. They hold straight and true. Return to the hanger for shutdown, debriefing, and a huge sigh.

                                                            Raglan                   (Photo D Gwilliam)

Wayne Butt

Taranaki Chapter

butt5@xtra.co.nz













First Flight
Preparing for the first flight


Maiden flight of CHARLIE ROMEO INDIA took place on Dec 26th 2008. The evening was a warm summer one withn QNH rising through 1020. My daughter, Christina, was there with her camera, and Matthew, my flight advisor. All systems thoroughly checked  again for the 25th time. As planned I performed two more full runway length hops to about 3 metres then taxi backtracked to the extreme threshold of runway 23 at New Plymouths regional airport. Tower had closed for the day (it was 8.30 pm - asmost dusk). The unattended radio frequency was 124.7.

Full power and takeoff were uneventful, but more noise than I expected, and a much more rapid rate of climb (arround 1100ft/min by recollection). Retracting the flaps without looking down for the lever wasn't as easy as expected, with some nimble elbow work required to reach the flaps lever. I soon got used to this and now find it straightforward.

The plan was to carry out one large circuit then land - a plan to  which I adhered. Slowing down to  flaps deploy speed (70 kts) took forever and required a lengthened downwind segment but once the flaps were deployed the aircraft slowed rapidly. The aircraft  remained symetrical and easy to control with flaps fully deployed, which was a relief as the flap excursion had around 1mm difference which I couldn't correct.

On selecting the full flap detent at 300 ft the flap lever slipped out of dentent to no flaps position with a "bang". Gave me a bit of a start, but was soon rectified and full flaps more carefully selected. This time I had sufficient confidence to glimpse down and check correct lever position.
Touchdown was impeccable.
Rolled out and cleared the runway to awaiting smiles and camera shoots after a sucessfully executed first flight.It was a once in a lifetime proud day.


Downwind leg of LH circuit for Runway 23,  Waitara township visible in the distance
Image

Photo2 - returning to the hanger after first flight
Image


High Speed Taxi and Hop


You Tube URL (allows full screen view)



First Flight - Take Off

You Tube URL of first flight

First Flight - Landing phase

Or check the You Tube URL
Random Stuff I have been thinking about.

Here is another challenge for another year.
Image
 It really has flown. A little more information at http://www.jp-petit.org/nouv_f/avion_electrique/avion_electrique.htm

August 2010 Update:

Just back from a fantastic week at Oshkosh where Cricri were mostly abscent except for one mounted from the roof in the wearhouse store. Forums on electric powered flight were extremely popular, and many questions asked about the carbon fibre electric cricri being build by Airbus Industries as their "green" project. At present battery energy density the maximun flight time for an electric cricri is - by my calculations, 20 minutes, When the batteries store 350 watts/ Kg I will have an electric conversion on my drawing board.

Another short seamless flight today. I am slowly learning the intriguing flight characteristics of this little craft.

 Just recently aviation photographer guru (John King) arrived 
to take some in flight photos of CRI for a forthcoming magazine publication. I have contributed a short piece on "building light". The photo shoot was just after dawn on a frosty morning from a Cessna 172 with the door off. He froze. I froze - but the in flight photos are supurb +++. To keep you checking this site I'll feed them in as the lead image - a fresh one every few weeks. You will not see better in flight photos of a Cricri. To see more - follow the 'Photos' tab above to 'John Kings Professional Photo


Update Jan 2010


 My last flight surprised me with an engine failure at 800 ft after takeoff, still on takeoff heading and without warning. After a request for immediate landing a commercial aircraft on finals performed a go around. My progress from there was straightforward - with continued climb to circuit altitude then a short approach and single engine landing into wind. No dramas there.

The engine It turns out the front cylinder big end needle bearing had collapsed and the engine seized causing considerable internal engine damage - but under repair now.
Philosophy.  I guess this is the risk of experimental flying. I am grateful for two engines and a helpful tower. I see this as an illustration of the drawback of using high power 2 stroke engines in aircraft. Even Mr Colomban warned me personally to be ready for an engine failure - as it will certainly occur if you fly enough. I just didn't expect it so soon.

More again when the new crankshaft, bearings, piston, con rod, prop hub, prop and spinner have been fitted.

Engine now repaired and reinstalled. CRI should be back in the air soon. (Feb 16th 2010)

Log March 19th 2010
Repaired engine installed. Since I had the cricri home in the garaghe i decided to continue the work with a buch of other small mods - just for fun. Shows the mindset of a builder compared with pilot. Changed wheel pants to single piece and simplified the attachment system. Strengthened the instrument panel hinge points that were beginning to sag under the weight of the panel. Painted slightly crazed area on rear of turtledeck.
Now ready for flight again!



Update Oct 09
Every flight gives the opportunity to learn new characteristics of this aircraft. After flying alongside Nev Hays 6 yr old Cricri this weekend and taxying his very tidy LBW on the ground I can draw some comparisons between the JPX and 3W powered versions of the Cricri. I was quite surprised at how much more mild vibration the 3W has on the ground - and a much noisier exhaust sound. However the 3Ws give considerably brisker performance and is simpler to start (handflick instead of pull cord). The hydraulic brakes and push pull throttle on CRI are excellent mods but Nevs JPX sipped fuel at a slower rate than my thirsty beasts (3 litres compared with 5 litres in 30 minutes). I still have rich settings so this may improve with more fiddling.
Watch this space.





Update July 2009
Just back from a holiday in France - 3 wks. Unfortunately I didn't see a single cricri - but did talk briefly to Monsieur Colomban at his home - and thanked him for this remarkable project he has made available to some in the aviation community. I did ask him about succession re plans as I have the feeling his other aircraft hold more interest for him than the Cricri does now. He is going to write a reply to a letter I wrote earlier, asking if there are any conditions for which he might appoint an agent for the sale of plans.

Wait and see!

I now see that it will take the best part of a year to iron out the minor issues with CRI. New props are on their way, this time via UAV Products who now hold the agency for Bolly Props. The cost for a pair of matched RH & LH wooded 28 x 26 in props is $275 (US).

New spinners also purchased and fitted to a standard backing plate - fabricated in fibreglass with 8-32 nutplates. Should be ready to  fly next weekend.

Gradually - by small increment I begin to feel less vulnerable in the Cricri. The controls feel dependable and precise. the engines hiccup from time to time - but they seem to keep running. The fine tuning can wait - for now they just run a bit rich.
The loudness of the engines is one of the features - attracts an audience and is very distinctive. It takes high grade earmuffs over an earpiece headset to really get good noise damping in the cockpit.

Flight Test Progress as at April 2009
Now three flights into the programme and first impressions: it is tight in the cockpit but the essential movements are straightforward. The throttles lie conventiently, and the stick is perfectly situated. The flaperon handle is a bit of a mission to operate because the elbow has to extend beside and benind the seat. On an early flight I failed to engage the detent accurately and the flap handle slipped forward a notch but I now know to  check the position before releasing.



On apporach the flaperons are remarkable effective - 1500 ft/min descent at 70 kts and a very steep approach - with 27 degrees flap. Working the flap lever is a bit of a mission because the elbow has to extend behind the seat. These are contortions you have to get used to in a tiny cockpit.

However, in such a quirky aircraft it still feels like each flight defies death and so it takes me considerable courage to climb back in the cockpit for each takeoff. There are just so many things that could go wrong. So far I have had only minor upsets  - but one major - like an engine failure - might dampen my enthusiasm for flight in the cricri considerably.

I should be elated. This creation seems to do all I desired and the 3W powerplants have been a huge success. They start within 3 flicks every time

more later....

May 2009 entry:
Flying the Cricri remains an exhilarating adventure every time. I particularly enjoy the phase when lined up and tower gives clearance for takeoff. Climb out is just fantastic. Its brisk, noisy,steep, and fun. Ease of lift off seems to depend on the loading on the nose wheel ( and therefore attitude of wing) on takeoff roll. A little more tension on the bungee for the nose leg would give unassisted takeoff at around 50 kts, but as is I need a little up elevator to instigate the break. I have not experienced the "zoom" that some pilots describe.
One thing that takes some getting used to is the view of the engines, which are standing out on their pods like naked ladies. All the components are there for you to check in flight. I can see the occasional air bubble in the fuel lines, the spinners deform slightly with high engine RPM, and the  vibrations of the engines absorbed by the Lord engine mounts. The controls are light and well balanced. The tiny size of the aircraft is the one overwhelming impression - supplemented by the view - the likes of which I have never experienced in an aircraft before.
With the extreme noise of the engines just inches from your earholes one is very conscious of engine synch. I find myself juggling the throttle regularly to abate the out of synch hum that develops. Which engine is fast is just a guess, The tachos aren't that sensitive.
Next phase of flying is to check best rate of climb speed, stalls, and single engine performance.

I'm off on a 3 week trip to the country that started it all - France. A week from Carcassonne on canal du midi and a few days in Paris. I have never met M. Colomban - should I phone him? It would be such a privilege.
 


Update April 2011


Comfotable cruise. Good view of Dynon screen. The VSI is difficult to read. Be nice to have a dial VSI!





Downwind for runway 14, home airfield. Completion of a 20 minute flight. Fun!