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.
Current Progress:
(July 2019) The Cricri hasn’t flown for some time. The free web site that was hosting my work folded, so I am in the process of rebuilding. I have kept CRI licensed and certified and ready to fly – but just on hold until I complete some other chores and tasks. Hopefully will be in the air again soon.
Some Cricri observations
One intriguing 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 embarrassing 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.
W
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 sync thrubbing can be annoying, but easily corrected with gentle nudge of the throttle. The panoramic 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.
More later
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 inadvertently 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).