checking out the fit in Chris Willis' cricri easter 06
Construction Details from May 2003 - May 2008 !!!Intro:
Building a Cricri has been a distant thought since about 1982 when such flights of fancy began to enter my thinking – as I obtained my PPL in Hamilton in 1981.
Mere dreams became passion in Dec 2002 when Nev Hays Cricri made its maiden flight and his saga was published in Sport Flying, cemented when I met Nev at Pine Park and sat in his Cricri in Jan 2003.
With some contacts and ideas from Nev I purchased my plans from Michel Colomban in France (cost $1007 with postage) . They arrived on April fools day 2003; the manuals and booklets a week later, and the project began.Equipment:
Whatever the plans say you need a host of equipment to built an aircraft from plans. Helps to have a bandsaw and bench sander, compressor, air riveter, spray gun, a bending brake and a small lathe is invaluable to machine many small parts. Good sheet metal shears are a must.Supplies:
The inventory of parts required to build a Cricri is huge. Initially I hoped the listed French supply company ULM Technologie would have a complete ‘kit’ of parts, but no such luck. They have provided only a few metric bolts and the crucial SKF spherical metal bearings. Almost everything else has come from New Zealand suppliers: sheet metal from Flightline and Pacific Aerospace, rivets and clecos, wheels and strobes, wing angle and many other fittings from the endlessly helpful Lyndon Knowles of Aeroware.
The upstairs in the garage is beginning to look like a warehouse - but acquiring most of the stuff first is the way I like to do big projects. Acquisition is exhausting and non availability can sap your spirits at crucial stages.Beginnings:
As with any new project the starting point is homework and preparation. Graham Smith from the composites shop at Air NZ responded helpfully to dozens of my queries regarding appropriate metal preparation techniques and products, and an adhesive. I have selected 3Ms EC 3019
as an air cured watery chemical bonded and corrosion resistant agent (500mls purchased through Hardy Packaging for $180) and EC 2216
grey for adhesive. Later, I have added grey Altex epoxy primer for non bonded parts, for additional corrosion resistance.
Then came fabrication trials of heat tempered ribs, rivet tests, Klegecell shaping, and reaming holes for 14mm bearings. Elevator and Rudder:
The tailplane came together remarkably quickly, but with the sort of obsessional passion invested in these components—no wonder. According to Graham Allen, who visited to collect the wing tips I ordered from France, a few of my rivets were ‘smilers’. One in ten is permissable. A few redone on his advice - until acceptable standard acheived. Details, Elevator & Rudder:
Web and caps prepped thoroughly with MEK, scotchbrite and Ajax, then with EC3901. Small parts like bearing holders also spraying with Altex 2 pot primer. The wingtips were epoxied to false ribs bonded to the outside rib. One mod on the rudder was to place spherical bearings for both upper and lower rudder pins to run in. The spherical bearings were all glued (EC 2216) and stamped in the reamed hole.
The elevator skins had to be slightly ‘dented’ ajacent to the pivot bearings and the heads of the two pop rivets filed flush to clear the vertial longerons when the tailplane is installed. There isn’t much room for movement of the elevator on the rudder! Nev Hay had to flatten these rivets as well - to get clearance. Wonder why it isn't in the plans! All the finished parts wrapped and stored in the attic—just brought out to show visitors.
Spar webs and caps: Webs cut to shape, with doublers. I shaped the caps by cutting on the little bandsaw, accurately for the 15mm side, roughly for the tapered side. Then cut grooves with the hacksaw to measured depth, then using coarse grit belt sander to pare away aluminium until the cut slot disappeared. This worked well for an accurate and obvious critical depth guide for a complex taper. Very little additional fine sanding required. No file used at all. Eight caps, one at a time.
Nev Hay's spar cap bender worked fine ( kindly loaned for the purpose), after minimal experimentation. All caps bent using 7 degree and 4 degree settings in the bender. A little fine tuning done in the vice and this was repeated throughout the construction as the bends alter with riveting and bonding.
Wing on its jig, ribs bonded, ready for skin to be bonded and vacuumed on. The washout is achieved by twisting the jig in the correct direction!!)
Webs, doublers, caps and stiffeners were prepared and treated with EC3901. I decided to bond all the caps to the webs prior to riveting– which actually made riveting easier. Had to debond the left wing to correct for span greater than 103mm in places near the bend.
No photos of the main pin drilling jig, but using an idea from Ian Griffin, I set up the drill horizontal and moved it on a guided frame into the hole with the wing splice firmly clamped in place and the dihedral exactly symetrical, with spar assembled on a strong aluminium square section. Went to huge care to keep the hole perpendicular and true, then reamed to 5/8 inch to accept the 4130 5/8 locking pins. Sept 04 Completing the main spars
With thin mirante ply to even out the upper and lower splice section of the main spars, with final sanding to 103.9mm, giving an even and firm fit together. Both spars then prepared and primed. Note : the stiffeners adjacent to the wood spacers had blind rivets to secure. No way to set solid rivets in this location.Oct 04
The dihedral was set using a long plastic tube and fliud levels at each tip before clamping and drilling of guide holes for the main wing pins (5/8inch to use the 5/8 chrome moly tube already stocked)Frame 4:
All components for frame 4 cut and prepared. Two difficulties arose— remaking parts of frame 4 slightly larger to accommodate my spar junction (103.9mm x 49.0mm). Also, with protection from gluing using a single layer of glad wrap, it was difficult to separate the parts. Vasceline liberally applied for subsequent fits—which proved perfect. Frame 4 was prepared with EC3901 then spayed before and after assembly with altex primer. Holes drilled and reamed to 5/8 inch so as to use the easily available 5/8 tube for the pins.
Completed Frame 4 & Wing spars
The jubilation of a completed set of components. Sunday Oct 17th 2004. Frame 4 and wing spars.
Completion of wings.
Ribs bonded onto the spar as outlined in plans; rear ribs spaced to fit jig using spacing guides with the same cuts. Very little overhang from the front ribs, but small pieces of Klegecell glued to the spar seemed to give a smooth finish, as per plans. Both wings completed and skins cut and bent before proceeding to fitting skins. Neville Hay had kindly given me the jig for bending the concave in the skin undersurface. The rear fold was done on the construction table, with a long aluminium bar set 15mm from the rear edge, then the edge was just tapped down to the 21 degree angle. Wingtips and Strobes
Similar to horiz. tail, with hollowed out false ribs to bond French sourced fibreglass tips. See photo for clever strobe installation. Unit protrudes thru carefully shaped hole, secured by a vanadium screw.
The strobe can be removed through the hole by removing the rubber seal.
Made in a jig as 1m lengths, then two halves screwed together. 1.5 degree twist to each of the 4 flaperon components - as per plans. Check and recheck, then check again - that the 'washout' is in the correct direction. All parts rivetted and bonded as per plans. Wings, cont
Wing spars and fittings touched up with Altex two pot epoxy primer before applying skins, which were prepared with EC 3901, as with all other internal Al fittings. Both wings ready for skinning May 2005. Hole locating jigs for the wing/flaperon hinges.
Jigs for flap attachments made using brass tube presssed into 4mm holes; 26mm centres. A similar jig was used for the rivet hole on top of the flap attachment brackets. The front and rear wing pin fittings will be drilled just by measuring stations from the spar.
Gluing wing skins
This huge task was finally completed by the end of May 2005. Several problems arose: none insurmountable. It was difficult to get adequate reflex bend in the wing undersurface and in retrospect I should have worked harder at this. I needed more vacuum than recommended to achieved a good fit and there is a small unbonded gap at one rib, but fortunately at the point of the hinge attachment - so no concern. Also, the trailing edge fold I did by tapping the 2m x 15mm bend over the edge of the workbench. Possible not accurate enough as the right trailing edge debonded slightly. I fixed this by doubling the number of trailing edge rivets (countersunk solid 2,4mm) and trickling superglue in. This worked. Otherwise the wings are great. Took great care to set the washout at exactly 1.5 degrees.
The pump I borrowed had inadequate suction for all my leaks so, with the skins on and the glue rapidly curing -I rushed inside for our Panasonic vacuum cleaner with built in rheostat and bleed hole. This worked a treat and the bonding was consistent and without excess scalloping when i check the next morning - vacuum cleaner still purring happily away.
Finished all flying surfaces Aug 05 next ......... Diary 2