Tuesday 9 February 2016

Cowl Modification - Part 1

This blog cover the modification to the cowl skin to align with the canopy frame. 

Overview
When fitting the canopy and top cowl as part of the preparation for the shroud a alignment issue was noted. It was decided to modify the cowl profile to match the canopy as this appeared to be the most direct route. 

I can see no error in how the work was undertaken to create this issue but I did email the factory for advice. Franco at Flying Legend advised that a new frame design was to be available in a few weeks but I elected to modify the cowl to avoid the lost time. 

A pair of metal horseshoe's that has begin incorporated into the new design will be fitted onto the canopy on their arrival from the factory.

Misalignment noted at both ends

The factory cowl sheet aligned perfectly with all holes in the fuselage allowing it to be used as a drilling jig. 

Manufacture
The mounting lugs on the front bow were removed and a duplicate manufactured but with longer leg on one side.

The existing sheet was laid on a new sheet of 2024-T3 sheet on a under sheet of foam insulation.  The foam allows the sheet to be drilled and clecoed with the foam providing bite and fixing the sheet. The side that attached to the fuselage side was extended by 25 mm and then all the factory holes duplicated except the side holes. 


Duplicating cover existing cover
The blue tape is to prevent drilling unwanted holes
Removed existing tabs 


Port side tabs installed

The new sheet was refitted to the aircraft and then a set of new tab's 75 x 20 x 0.020'' folded for re-installation. The canopy was shut and with a tab placed under the cowl a spring clamp secured the tab to the frame. Next the canopy was closed, fit checked and if OK, the holes marked, drilled and then clecoed back into the frame, this operation was repeated 14 times over a few hours until a new profile was created.

The openings for the inspection panel were cut out for installation of the doublers then all edges were dressed using files to final profile.




The new cover was treated with Henkel Alodine 1200S Brush On alodine in accordance with the directions supplied and set aside to air dry.

When dry the panel was clecoed into position and all the lower edges were now matched drilled and the panel removed and the edge trimmed and dressed. 

When complete the panel was fully clecoed into position.

A pair of factory supplied doublers were now cleoced into position with no issues.

Ready for final riveting
The fold through the lower rivet line at 5+ degree [approx] was added 
to create a tighter fit when riveted



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