By Peter Whittaker, EAA 1350577
From the January 2021 issue of EAA’s Canadian newsletter, Bits and Pieces.
The 750 Cruzer project resumed in September after COVID-19 restrictions eased enough to allow a small group to work well spaced in the hangar. Work has progressed while wearing masks and has not been too uncomfortable. The major job through September was to get ready for installation of the wings which took place in early October.
Two wing stands were built to facilitate initial placement of the wings while each forward main spar was drilled for their respective bolts. Once the forward spar bolts were in place, the wing tips were adjusted fore and aft until the measurement from each wingtip to the same point at the centre of the fuselage top skin in front of the rudder fin was within the 50 millimetre tolerance. We were able to get the distances to within 5 millimetres and thus satisfy ourselves that the wings were perpendicular to the fuselage centre line. At the same time, a tight string between the wingtips and running along the main spar rivet line had to be centred along the rivet line. At this position the rear spar wing mount bolt holes were drilled and the wings separated to allow for deburring of the holes and filing of the mounting tabs to allow smooth installation.
The installed wings were supported by the two wing stands in preparation for adjustment of wing dihedral. Dihedral was set by using the tight string between the wing tips and an iterative process of raising and lowering each wingtip in small increments, supported by moving the wing stands inboard or outboard. The objective was to get a measurement of 85 millimetres plus or minus 5 millimetres from the top of the first inboard rib up to the string. This proved to be a fiddly business and we ended up at 80 millimetres on both sides and blocked the wing stands at this point.
With the wings positioned, the next step was to cut the struts to length with the top and bottom strut brackets temporarily bolted on. The parts come with a tight fit and filing of the bracket mating surfaces was required to get a smooth but snug fit. A strut was first drilled and bolted to the bottom bracket which was then slid into place over the landing gear mount. The strut was then swung into place against the top bracket which was temporarily bolted to the wing mount and the length marked. With the final length cut, the top bracket was drilled and bolted to the strut and the full assembly was swung into place and bolted to the top and bottom mounts.
This work took us into mid-October and then installation of the flaps and ailerons began. These components had already been assembled, inspected, and closed by previous Chapter 245 builders a few years earlier so we were able to focus just on installation. Flaps and ailerons are separated control surfaces and are then bolted together with an offset to give built in washout. They become one single flaperon controlled by the centre stick and flap position motor.
Each flap and aileron has a steel counterbalance weight that is supplied by Zenith with ample excess weight. The balance weights must be trimmed to achieve neutral position balance for each control surface. After balancing, the flaps and ailerons are bolted together and checked again for balance. The weights are then drilled and riveted into place. Target weights were used from the same model 750 Cruzer built at RAA Chapter 85 in Delta, British Columbia, and was a project I was closely involved with while in Vancouver. The approximate excess weight was removed using the Craftex Mill/Drill in the machine shop. Between one quarter and one third of the starting mass was removed (all were in the 914 to 924 gram range to begin with) to achieve a final balance.
One final job to complete the starboard wing installation was to locate the missing wing root top skin to match the one on the port wing. The remaining pieces were eventually located on the windowsill in the workshop and the piece had mistakenly been cut up as scrap metal. Word went out to Chapter 245 members for anyone with spare 6061-T6 (either 0.020 inch or 0.025 inch) and Don Walker jumped in to the rescue — this saved either buying new sheet metal or ordering the part from Zenith for nearly $90 U.S.! Thanks very much Don. The port wing piece was used as a template both for the part outline and for the rivet holes. The part was cut, drilled, deburred, primed on the mating surfaces and to our great relief it fit perfectly.
While work was progressing on the wings, struts, and flaperons, the empennage was reattached to the rear fuselage and final fitting checked. The remaining task involved riveting the rudder hinge assembly to the inside and sides of the tail fin. Irving and Edgar undertook this job with the weather getting colder in November. Apart from riveting the balance weights to the flaperons, the flying surfaces are now installed and work can focus on navigation lights, wiring, connecting brake lines, and running a fuel line up to the firewall, installing the adjustable seat pans, the seat frames, the central console, and many more small jobs. There is lots to do and with a tarp over the cockpit and a heater work can continue through the winter.
(A word of appreciation is due here… Peter not only works hard to keep the Cruzer project, moving forward, he also takes a few extra minutes to produce these excellent updates on the project so our entire Chapter can know what’s happening. Thank you, Peter, for your hard work! Mark Briggs, Editor, Chapter 245 newsletter.)