Cricri aerobatic aircraft and other complex projects Page Home
Welcome - This Cricri took 6 1/2 years to build from the day plans arrived to the first awesome flight. Read on - and share the journey with me.
Wayne, August 2017
Various photos by John King and Don Gwilliam
Cruising along at 100 kts (116 mph) - comfortable. The panel worked out well although it was a bit of an experiment - flying with a "glass panel" for the first time. I put a Hobbs meter in later because I am always forgetting to record the flight start time. The Hobbs is connected to the strobe light circuit.
Getting in - you climb down into the seat! Get an idea of the layout. Not much room for elbows. Red line on the fuel tank at 15 litres - max fuel for aerobatics.
Below, the newly fitted transponder. They wont let me fly in local airspace without it now.
Pressure bulb for pre-pressurising the fuel tank before start up
Video of first landing, rolling out, very happy smile. Dec 2008
(Jan 2015) The Cricri hasn't flown for some time because of a second engine seize. This has been a definite setback. Fortunately the failure occurred during ground running but the cause is unknown. The big end bearing failed. I am in the process of gaining CRI's annual maintanance release. Also, one of the four ignition modules has failed and I have arranged a replacement from a supplier in the US. I am going to try an aftermarket CDI as the 3W ones are expensive and 2 have delevoped faults so far. Hopefully I will be back in the air within the next few months.
(June 2012)One intriuging thing about the Cricri is the crowd that gathers around when I start up the engines. It is therefore essential to have a fail-safe starting sequence. This has eluded me so far and I have have several embarressing moments of an engine not lighting up.
I have learned that two stroke engines are extremely fickle when it comes to mixture, To obtain smooth running across the RPM range both high and low speed jets must be exactly right. I have now nearly reached that Nirvana point with both engines.
For me, the best way to start (after much experience) is to:
Pressurise the fuel tank with air pressure bulb - to about 0.5 PSI.
Depress the needle valve in the Carburetor pump as show elsewhere. Allows fuel to flow up to the carburettor.
Set throttle at 1/3 open.
Squirt 3mls of fresh petrol into the Carburettor throat via a nozzle fuel bottle and hypodermic syringe.
Hold choke closed with left hand and flick propellor (right hand) from behind the engine, with igntion on.
After 3 or 4 flicks the mixture will be appropriate for a clean start. This process has worked better than all the other sequences I have tried.
Am ready to go flying tomorrow.
A typical Flight:
To outline a typical flight, after the aircraft is fueled to around 18
litres ( of 23 for a full tank) the aircraft is gentled pushed out of
the hanger onto to grass berm. This gives a AUW of 370 lbs - close to
MAUW of 375 lbs. Preflight, I pay particular attention to tyre pressures, all visible fasteners, security of nose cone, and double check of wing pins and aileron attachments. I carefully check the canopy attachments, seat attachments and seat belt attachments. All these items are as light as could be - and any of these could fail with catastrophic consequences.
The fuel tank is then pressurised with a small sphygnomanometer bulb - to about 0.5 PSI. The carbs are tickled with my unpatented lever which opens the fuel valve, and pressurised fuel flows directly into the carburettor throat - for 7 seconds.
Ignition on - RH engine first. It is started from the front and turns counterintuitively. This is, of course, after brakes have been secured (velcro wrap around brake lever). Two flicks usually suffices. Then the same treatment to the right turning LH engine, but I start this engine from behind - to be well clear of the other prop.
With both engines idling at 1700RPM I climb in - easily performed single handed - 5 point harness secured, clarity aloft headset in place and earmuffs over top of them. Radio on and tune to ATIS as I taxi to the holding point for run up and take off checks.
Lined up, takeoff approved, full throttle. The response is very brisk and within 7 seconds and 250 ft CRI has departed the ground, climbing at 1200 ft/ min at 70 kts. The flap handle can be relocated into the "flaps up" detent with the little finger. Throttle back to 4800 to continue a gentle climb and conserve fuel. With 3W engines it has been possible to go through 15 litres/ hr with lots of full power climb (at 1300 ft/min). 8 l/hr is the desired rate of fuel consumption, but achieving this economy requires conservation of power. The noise level is high and the out of synch thrubbing can be annoying, but easily corrected with gentle nudge of the throttle. The panaromic view and responsiveness to the controls make each flight pure adrenaline surging pleasure.
For me - I wouldn't even think of aeros and high G manouvres at this early stage of flight testing. Arriving safely on the ground after each flight gives satisfaction in gobs.
Recorded Flight Characteristics: -climb out at 70 kts at 1300 ft/ min - max speed of 115 kts (VNE 140 kts) - comfortable cruise of 90 - 100 kts - fuel consumption 8 - 15 litres/hr- to be refined. - single engine climb at 2500ft, 70 kts is 150 ft/min. - stalls at book numbers - 39 kts with flap, 49 kts without. - noise level - very high - like a sawmill - fun - unbeatable
Stall is gentle but no warning - around 49 kts without flaps. Maintaining 49 kts gives a high rate of descent (600 ft/min) without the nose dropping. Applying more elevator produces a typical stall - straight ahead - no surprises. This is reassuring verification of effective washout (difference in incidence between wing roots and wing tips), where the wingtips continue to maintain lift after the wing roots have stalled.
Little rudder is needed for balanced medium turns. The stick is sensitive so don't bump it inadvertantly with your knee while taking a photo! Orientation changes very rapidly indeed. Easy to trim for hands off flying (but only lasts a few seconds).
A few changes made since the maiden flight.
Above: The wheel pant has been converted to a single piece, with carbon fibre cover on the inside. A single internally threaded socket screw to secure. Easy to remove. Bungees for trip and control resistance.Pressure bulb for pre start pressurising of tank. Support cradle for exhaust.
The extended stinger includes two baffles diverting airflow from one side to the other - for a vast reduction in noise and only 5% power loss
Covers fabricated in Carbon Fibre - for weight reduction. Cover behind propeller on LH engine is just to mimick the cover for the alternator on the RH engine.
Battery weight halved now that I am confident with the alternator on the LH engine. Instead of two 12v batteries - down to just one (saved 750 gm).
The trailer is set low on springs so cricri can be loaded and unloaded without detaching the cover. Setup time from parking car is around 12 minutes.
Total cost of project- roughly US$26,000 (with trailer)
Trailer The trailer is wide enough to fit the Cricri with installed tailplane, whereas the Colomban version is narrower than the tailplane so a flared upper piece is needed to protect the tail. The slight drawback is a larger and heavier trailer.
Points of Interest:
Note the red self aligning electrical plug where front of wing attaches to fuselage. This is the connection for the wing tip strobes - earth and two cores. Works well. No wires to connect. The unit floats on small springs, so self centres. Available from specialist electrical stores.
With a lot of fiddling the throttles are now light and synchronous. The icing on the cake is the extra link with spring loading on the "pull to close" side. This puts the circuit in constant tension so little chance of the throttle wire disengaging from the pulley.
The Cricri is a remarkable single seat aerobatic ultralight aircraft aircraft designed by French aeronautical engineer Michel Colomban. Plans for construction can still be purchased from M Colomban for approx $600US, but he will not sell to residents in North America. All the information to purchase plans is on Petr Philips web site. The saga behind the refusal to supply North Americans stems from a kit version of the aircraft that was available several decades ago with some unfortunate consequences. If interested, scroll the relevant threads of the Yahoo cricri group forum where the issue has been well explained by the moderator. (CriCri@yahoogroups.com)
3W 240 iB2 engine, with alternator
History of the Cricri
If you have found this site you will already know that the Cricri was designed by Frenchman Michel Colomban soon after he completed his training in aeronautical design. ( If you don't have the info go to http://www.flight.cz/cricri/english/index.php ).
The achieved brief was to create the lightest comprehensive powered aircraft possible with the materials available in the 1960's. Two engines were selected to achieve satisfactory power to weight at engine RPMs without reduction drive (requiring small diameter propellers). Inverted and aerobatic capability was built into the design from the outset. First flown in France in 1973 this aircraft has some standout features - with only minor subsequent changes to the original design and concept.
Apart from the Cricri's extraordinary size for a piloted aircraft, it is a fascinating quirky aircraft with a host of remarkable features:
(1) 34 years since its first flight it is still the worlds smallest twin engined piloted aircraft. (2) A respectable cruise of 95 - 100 kts (3) Empty weight of 80 - 85 Kg (180lbs) (4) Dynamically balanced controls. (5) Flaps (6) Brakes (7) Adjustable rudder pedals (8) Easily trailered, assembled in minutes (9) Aerobatic with sustained inverted capability
10 BUILDING TIPS AND SHORTCUTS
1. Cutting Out A vast number of parts need to be cut accurately to size. Two good techniques for this: photocopy plans to paper, cut to the line then glue to aluminum with glue stick. Cut to the line on your band saw, using magnifying safety glasses. Alternative, purchase excess 1mm (0.040in) polycarbonate ( used for turtledeck), lay over plans and trace outline onto the clear with marker pen. Cut to size and use as a stensil. Good for multiple parts. Also a good way to counter-transfer holes (ie where can't access guide hole to transfer location).
2. Klegecell alignment holes Alignment holes in Klegecell ribs - use a short length of brass tube of correct outside diameter (say 4mm). Taper the outside edge to a sharp profile with sandpaper, while rotating in drill press. Then file an exit port about 5mm from the cutting end, as for a hole punch. Rotate in drill press to cut a clean hole of perfect diameter for guide screws and wires prior to machining the outside profile of the ribs.
3. Instrument panel Consider a Dynon 10A EFIS (http://www.dynonavionics.com/) for main instrument. Weighs much less than conventional instruments and includes G metre, VSI and compass. Also has transponder feed - if you need one of these in your airspace.
4. Instrument panel fabrication The instrument panel is hard to flange around the outside edge. Consider a fibreglass mold with raised segment for instrument groupings. This is an idea I saw in an aviation magazine. Fabricate a female panel mold and vacuum 4 layers of fine weave cloth/epoxy. Vacuum bag as for the Cricri flying surfaces. Best with releasing agent and gelcoat which you can get from any fibreglass and epoxy supplier.
5. Paint colour If you don't want grey or yellow primer you can tint with pigment from other paint with similar chemistry. Experiment first. I have used Altex 2 pot epoxy primer tinted with Altex Tasman Blue Polyurethane (colour only - no hardner), and other colours. Only for surface protection - not bonded surfaces! Just makes it pretty.
6. Maintanence: Access to rudder and noseleg bungees, fuel lines, steering cables, battery and wiring through the front fuselage is poor in the cricri. Forget the looks - I am putting an access hole with nutplates in the front fuselage skin. Also running fuel hose and electrical wire thru automotive split conduit. This way you can replace and service the items. In my humble opinion it adds functionality without much compromise.
7. Brakes I have seen comments about poor braking from the plans proposal for drum brakes. So I am using Shimano Deore hydraulic bike brakes with 160mm rotors. The tricky bit is designing the rotor and caliper mounts, and machining the "t" hose splitter. Will tell you if it works - later!!
Yah - it does. Just finished bleeding and assembly tonight. Takes nearly full excursion of the lever but the assembly is smooth, light, and powerful (Sept 24th 2007). Note the filler site with cap head screw!
8. Canopy Mod I'm 5 ft 11 inches. Had to add 50mm (2 inches) to the rear canopy to fit comfortably with headset on. As a retro change this cost approx 20 hours. Advise consider from the start if you are over 5ft 8 - as outlined as an option by M Colomban.
9. Finish Polishing the finished Aluminium is an excellent way to save weight if you find your Cricri is heavy, and is indeed recommended in the plans. But to do this you have to take great care to avoid scratches and dents during the construction process. Only very small scratches can be polished our with the Cyclo polisher and Nuvite wax (gold standard for polishing Ali)
10. Bushes for wheel pant screws Fibreglass wheel pants are extremely thin to remain light and the securing screws soon tear through. To resolve, install small shouldered washers/ bushes (aluminium - simple to turn on the lathe ) and epoxy into the hole so the screw is only in contact with the shouldered washer and the nutplate into which it is driven.The wheel pants can now be removed regularly - and no ovalled holes.