Installed and tack welded all the fuselage cross members today, in each case the lower member was inserted first and then the fuselage jigged to make sure the centre-line of the cross member was in exact alignment with the centre-line on the building board. The lower member was then very lightly tacked and the top member inserted and using a plumb line the fuselage was re-jigged to make sure the centres of the two cross members were vertically aligned and over the building board centre-line. Then the top member was welded to about 1/3rd of its circumference after which the bottom member was also part welded. Station 144 was done first as it sets the datum for the horizontal stabiliser, has most flexibility and also as I've been nervous that the tacks at the end of the
longeron might let go and the fuselage sides spring apart. Next the top and bottom firewall cross members were inserted in the same way and a diagonal brace tacked in place to ensure they stay square
. The remaining cross members were then installed in order from front to back. The rear spar carry through was fabricated and installed but not welded as this allows the wing incidence to be set. The welding is quite tricky as the current needed for the 0.028" wall tubing (20 amps) will not create a weld pool in the
pre-existing clusters. The technique that seemed to work was to lay a bead along the end of the thin tubing using 20 amps then turn the current up to between 25 and 35 amps depending on the cluster to form the fillet weld. An advantage of
TIG welding is that I can construct the fuselage with the lower
longerons between stations 0 and 48 screwed down to the building board and part weld all the joints without setting fire to anything. This means that I'm very confident that the fuselage is perfectly symmetrical now and should mean that there is very little chance of anything going out of square when I do the final welding.
Installed and tack welded all the fuselage cross members today, in each case the lower member was inserted first and then the fuselage jigged to make sure the centre-line of the cross member was in exact alignment with the centre-line on the building board. The lower member was then very lightly tacked and the top member inserted and using a plumb line the fuselage was re-jigged to make sure the centres of the two cross members were vertically aligned and over the building board centre-line. Then the top member was welded to about 1/3rd of its circumference after which the bottom member was also part welded. Station 144 was done first as it sets the datum for the horizontal stabiliser, has most flexibility and also as I've been nervous that the tacks at the end of the longeron might let go and the fuselage sides spring apart. Next the top and bottom firewall cross members were inserted in the same way and a diagonal brace tacked in place to ensure they stay square
. The remaining cross members were then installed in order from front to back. The rear spar carry through was fabricated and installed but not welded as this allows the wing incidence to be set. The welding is quite tricky as the current needed for the 0.028" wall tubing (20 amps) will not create a weld pool in the pre-existing clusters. The technique that seemed to work was to lay a bead along the end of the thin tubing using 20 amps then turn the current up to between 25 and 35 amps depending on the cluster to form the fillet weld. An advantage of TIG welding is that I can construct the fuselage with the lower longerons between stations 0 and 48 screwed down to the building board and part weld all the joints without setting fire to anything. This means that I'm very confident that the fuselage is perfectly symmetrical now and should mean that there is very little chance of anything going out of square when I do the final welding.
