Cricri aerobatic aircraft and other complex projects Page
Engines / Alternator/ Fuselage
Irrelevant but favourite photo of our local Mt Taranaki (8260 ft) from my Zociac CH601, 20 mins flying time for our local airstrip.
Club RPM outputs requested by M Colomban for measuring HP output of non standard engines
Measured HP 21.5 @ 5500RPM
3W 240i2B Engines
Both engines (right & left turning) received June 04 from HDModelmottoren at total cost of NZ $4113 each.
First Engine Run Dec 04
An old outboard motor stand was modified to take the 3W. Electrics wired up. Tachometer tested and circuitry checked. Tachometer needs calibrating to known RPM, so hand held laser tacho purchased from AS&S for $75. Right hand motor was successfully run Dec 04 with Matt Connors help. Impressively smooth and easy to start.
Both exhausts returned to Shaun Raven for addition of mufflers, beautifully fabricated and received April 27th 2005.
(Total cost of exhausts- $1900) Fabricated from 0.8mm titanium, cut to pattern of my design based on info on the internet at various sites. Have used a reasonably standard 7 degree divergent cone and 11 degree convergent cone. The information for design of 2 stroke exhausts is available on the internet. Shaun fabricates motorcycle exhausts in titatiun for a living. He Tig welds while rotating the work in a custom jig. No grinding at all!. One of the beauties of a project like this is the super skilled craftsmen you come across.
Further work on alternator, with at least 5 hours to fabricate the mounting blocks from billet round bar machineable 100mm aluminium stock. Alternator stator cut into two pieces to mount in horseshoe fashion around engine crankcase. Divided wires soldered and join by electrical 3 pin plug. Two clamp screws 4mm vanadium and 1 hoseclip to secure. Produces 14.5v from idle to 5000rpm. ( Note the clever flywheel balancing system.)The alternator was constructed from a Yamaha Big Bear ATV. Much machining to lighten the components from 3kg.
More on alternator
Two voltage converters with 6 v and 1800 mA output purchased from Dick Smith for $39. After having a friend check the quality of the units I removed them from this plastic surround and set them in an epoxy box.
Seems to operated perfectly, running both ignition units (which have max current draw of 1500mA. The quest for a reliable voltage supply has taken much thought and generated an evening discussion at an SAA meeting. After considering expenditure batteries, solar cells, fuel cells etc—I have elected to try constructing an alternator from a Yamaha Big Bear ATV. Much machining to lighten the components from 3kg and to fit over crankcase behind the spinner. A ground rig for engine running is designed and built– completed 20th Dec 2004. First run when Matthew Connor comes round on Wednesday.
First noticed the carby was ‘spitting’ fuel vapour up to 2500rpm and the engine revs increased if exhaust removed. At first I thought th exhausts would need further tuning until I noticed that over 3500 RPM the tables turn and HP output increases with the turned pipes installed. By chance the design hass worked with optimum performance cutting in at relatively low RPM (3500) as hoped. No modification of exhausts needed.
Fuselage August 05
Rear Fuse: As with other parts, all sheet cut out accurately. Scoured and prepped with EC 3901. Plastic protection left intact on external surface but peeled back along rivet lines. Frames 11, 12 & 13 folded on my folder. Frame 12 hole surrounds flared with jig, successfully. Rear sides folded on Chubbs 8 ft folder for a $20 donation. Vertical tail main spar fits snuggly. Bonded surfaces all glued first then rivetted when dry. Interior painted with Altex epoxy primer along with cover exterior where tail sits. Internal klegecell bracing fitted to 3 sides, then to last skin before fitting belly skin to fuse. A reasonable finished product, but pity about the twisted frames and rear deck slope. Vertical tail fitted and squared using a laser level to ensure vertical cf belly skin. Holes drill but tail not fitted.
Rear Fuse finished Oct 05. Time off: Oct 10 to Dec 05 for revamp of Albatross boat. All Cricri parts moved to loft. Will resume after Christmas.
The vertical tail fits firm and flush to its attachment and the whole structure is rigid. Following assembly but prior to installing the deck all internal structures were sprayed wth Altex 2 pot epoxy primer (grey) - in addition to the EC 3901 already applied to all surfaces.
Next ..... Diary 3