DATUM POINTS.

On the SPACEWALKER, the upper longeron - top side- is the reference point, not the centerline of the longeron itself. On the KARATOO, the centerline of the centre longeron is the datum point.

The critical dimensions are the spar cutouts in relation to the station AA, the undercarriage attach points and the  tailplane attachments. These must be absolutely correct (tolerance +/- 1/32").

WELDING PROCEDURES.

To avoid burning of the ends of tubing when welding connecting pieces, either cut tubing longer than required at these locations (and trim after welding is completed) or use a heat sink inserted into the tube during welding, e.g. a bolt into the tube. Just make sure the bolt is removed after welding has been completed.

If using MIG welding, ENSURE that the MIG wire is preheated before welding. MIG can be used for all welding, but ensure that the welds are full depth, and that the welds are strong. Post heat treatment of welds is required if using MIG and optional if using TIG (recommended for main load bearing joints). It is very easy to do a substandard brittle weld using MIG.

To test the serviceability of your welds, make up several test pieces (whichever form of welding is used). Cut several across the weld with an angle grinder. Can you discern the tubing edge in the weld, or does the weld go full thickness. The requirement is for full thickness welds. Make up a T section with a leg of at least 8". Secure the horizontal part of the T and apply a side load to the vertical piece. The requirement is that you can't break the vertical leg out of the horizontal piece of the T at the weld. You should be able to bend the vertical piece only. If it breaks out of the weld, the welds aren't strong enough.

JIG BOARDS.

 Make up a jig board as per the side fuselage frame plans. The jig can be constructed from plywood or chipboard. The jig can be constructed on a flat table. Thin stainless steel plates are installed under the joints where welding is to be carried out.

SPACEWALKER:

 (1)     Set up side frame jig as per plans.

 (2)     All tubing to be tacked only at this stage. All joints must have a maximum of 1/16" gap when fitting. It is preferable to have a slight gap on joints. Tight joints at every location can produce distortion in the fuselage when the joints get heated during welding.

 (3)     Set upper longeron in place.  Take note of splice joint aft of stn DD. Tubing (B34) forward of DD is ¾ x .035 tubing. Aft of DD (C12) it is 5/8 x .035 tubing. C12 must extend into slice a minimum of 3 ". Tack slice together.

 (4)     Set lower longeron tubing into place. B35/B36/B37 is one piece. Heat and bend according to the jig requirements. Install C13 into splice ensuring a 3" insertion into B35. Tack slice together.

 (5)     Cut and fit B33 to forward fuselage frame at stn AA. Tack into place.

 (6)     Install B27 ( main spar aft  vertical tube). Tack into place. This forms the major datum and checking frame.

 (7)     Install B25 (aft spar support vertical tube).  

 (8)     Install B28 (main spar forward vertical tube).

 (9)     Install remainder of cross tubes B32 to D8. Always start with the longest tubes working towards the smallest tubes. This way, any tube that is incorrectly cut to size may be re-profiled  to use in another position.

 (10)  Install remainder of spar support tubes B29/B30. DO NOT install cockpit rails at this stage.

 (11)  A1 (vertical fin support stern post) is installed when the side frames are welded together with the upper and lower horizontal ladder frames..

 (12)  Remove side ladder from jig assembly.

 (13)  Repeat steps to make second side ladder.

Using a level base board 16 feet x 4 feet, make a base jig build board. Mark out centre line of fuselage and fuselage cardinal points. Fit Jig hold down points. The upper longerons form the datum reference for construction the fuselage.

 (14)  Secure each side frame into the base jig at stn AA, BB, and CC. Fit internal jig boards that match fuselage cross sections at these points. Tack fit B22/B12, B19/B18.

 (15)  Using clamps to secure side frames in position, heat frames at stn CC and bend to suit stn FF cross section jig board. Clamp at FF. Tack fit D7/D12.

 (16)  Heat side frames at FF and bend to join together at the stern post.

(17)  Tack- weld the stern post A1 in position. ENSURE THAT ALL FRAMES AND THE STERN POST ARE IN ALIGNMENT BEFORE PROCEEDING.

 (18)  Proceed to fit remainder of cross tubes tacking only at this stage.

 (19)  Once all tubing has been installed, remove fuselage assembly from base jig and mount the fuselage on a rotating frame.

 (20)  Proceed to weld all joints using either TIG, MIG or oxy - acetylene gas. Do not fully weld any one joint but keep doing small sections of each joint and proceed to cover all joints. This is to minimize heat distortion of the welds. Normalise all welds after completion of welding, again, only heat a small section at a time before moving onto another weld.

 (21)  Install tabs and support bushings as required. Use a master tab board to facilitate correct placement of all tabs and fittings.

 (22)  Fit cockpit side rails, fuselage grip, undercarriage support brackets, seat frames and turtle deck support hoop. The undercarriage attach brackets need to be properly set up to prevent any problems with the undercarriage alignment. A long rod through both brackets will facilitate this alignment.

 (23)  Clean up all welds and carry out corrosion protection of the finished assembly. For enclosed cross tubes, drill a small hole in the bottom of the tube, and inject a quantity of CPC material. CPC is "corrosion preventative compound" and can be a liquid or a spray. Likewise, for the main longerons. Rotate the fuselage assembly on the turning frame to ensure full internal coverage of the tubing, then allow the excess to drain out. Seal all holes. Once internally preserved in this fashion, and with proper external coating, corrosion protection should be ensured for at least 10 years.

 (24)  External protection of the framework is carried out by de-greasing all tubing. Check all surfaces that will come into contact with the covering fabric are smooth. Any blemishes will readily show through the fabric line in the completed aircraft, degrading the overall finish.

 (25)  Prime all steel tubing with a two pack etch primer. Use a small touch-up gun for best effect.   

 (26)  DO A FINAL ALINGMENT CHECK OF THE FUSELAGE STRUCTURE. IF SATISFACTORY, REMOVE FROM TURNING FRAME.

TAIL SURFACES.

Jigs are required for these assemblies. Construction is the same as for the fuselage assembly. Alignment of the control surface hinges is critical to prevent binding of the controls in operation. A long rod through the hinge tubes will ensure alignment. Ensure the spacer plates are fitted behind the hinge tube to give clearance for the moving parts of the hinge structure.

The main structural tubes need to be flattened to meet the end tubes. This can be done by clamping the end 6 inches of the tube between two flat pieces of steel. The tube is then heated to cherry red with an oxy torch and the clamps tightened at one end to achieve the required dimension.   

WING TRUSS FRAMES.

The main spar and aft spar of the wing are held in position by truss frames. These are also constructed in a jig which is built according to the spar dimensions.

UNDERCARRIAGE ASSEMBLIES.

The axle needs the axle nut thread cut into it before welding up the leg assembly. This needs to be done on a lathe, as it can be difficult to find the correct size thread cutting die. Drill the axle for the securing nut slit pin. Jigs are required for making up the support and leg frames.