Cricri aerobatic aircraft and other complex projects Page
Front Half of Fuselage.
Assembled from Jan—May 2006. All components fabricated using photocopies to cut ali -from the plans as before. The transverse member for frame 3 came out all right in my bender, but the rudder rails I ended up making with two pieces of 0.5 sheet bonded in the centre.
Principles employed for surface preparation and priming
— all surfaces prepared initially with MEK, then with ajax and green scourer with water, air dried or oven dried for some small parts: and wiped MEK before coating with EC3901, a pink watery 3M product with excellent specs. This was for all parts up until the internal fuselage components when I finished the 500mls of EC 3901. I then used Altex epoxy primer or aluminium etch primer (Altex) - the later for bonded surfaces because of better test strip strength . Once components are assembled the plan is to spray internal parts of the fuselage with Altex epoxy primer . The external surfaces will be dealt wih separately.
Use of 3m’s EC 2216 Gray Epoxy.
Recommended by Graham Smith of AirNZ, this versatile aviation approved epoxy bonding agent has a two hour working life and excellent bond strength. After preparation, drilling and deburring all bonded joints between aluminium were carried out using vascelinised clecos. When dry, the holes were redrilled and deburred as necessary, prior to setting the rivets. As outlined in the manual, this gave a superior joint with minimal distortion of the metal. For measuring, the epoxy was heated to 40 degrees in kitchen oven, then poured into 12ml syringes for accurate dispensing in the 2:3 ratio. Mostly less than 10mls mixed, after preheating syringes to 30 degrees in kitchen oven—better mixing and spreading.
Adjustments to Wingtips and flaperons
10 hours in April 06 spend adjusting flap fittings. After many attempts to obtain a consistent 9mm vertical gap between flaperons and trailing wing edge I eventually made a jig from three pieces of plywood with dimensions from the plans, securing wing and flaperon in position but unattached. It was then a simple task to drill attachment holes at hingepoints. The wing fittings were slotted in mill so I could adjust a few mm until the alignment holes were perfectly positioned.
Front Half fuselage
Assembled in the belly and lateral jigs, and components were fitted, adjusted, drilled, prepared and painted with Altex epoxy primer or aluminium primer (better adhesion, aweful yellow green colour). Almost all components bonded, clecoed and riveted later.
One useful trick from Chris Willis was to use clear polycarbonate to transfer hole locations to parts, eg nose skin to longerons and frames. The right angle drill loaned from Nev Hay was required for many of the internal fittings, particularly the seat mount rails.
Front half fuselage was finally completed on the evening of May 12th, and I have planned to proceed with joining the two halves and removing the plastic wrap before next weeks Northpoint mens shed night and SAA meeting—so it looks better! Just awaiting 100 degree C/S rivets so I can complete the fuselage border.
Order of task tentatively - begin noseleg and undercarriage, engine mounting structures, rudder tray, and seat tray before starting on control links and canopy setup
Know Issues of dissatisfaction
Horizontal tail bearings are standard—not stiff. May have to replace these with stiff ones if I can get them. Email communications suggest the stand GLD06 ones are satisfactory.
Wingtips filled with ‘gorilla’ expanding foam to give rigidity. Slight weight penalty. This could be scraped out if my cricri is heavy, and settle for spongy wingtips.