Overview
It was decided to use the Skybolt fasteners based on there success with the RV aircraft with a RV4 kit used as it was felt to be the best option but in the end were were about 12 fasteners short.
Installation
The installation on the firewall was covered in a previous blog on the cowls with the method to locate the holes proving to be a problematic on the Tucano because of the inability to use the mounting brackets supplied.
Note: Using a light to locate a hole then wriggling the step drill to line it up holes is not a good engineering approach.
It was decided to build the whole assembly off the initial cleco holes with these holes enlarged to a 1/2'' using a step drill. To keep the cowl in align as the clecos were removed, lengths of 1/2'' fuel tube were dressed to fit and placed in each hole as drilled.
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| Drilling jig and location pins |
The fastener receptacles mounting holes were drilled using an aluminium jig and 1/2'' fuel tube located in the pre-drilled holes. With the mounting holes drilled the center hole was enlarged to 9/16'' and both mounting holes countersunk with a 120 degree tool. This was undertaken at the rear first so that all the Skybolt fasteners could be fitted.
Note: Would use a hole larger than 9/16"" if doing it again
All were fixed using 3.2 mm [1/8''] countersunk pop rivets not the solid rivets supplied.
With lower cowl now fixed between the firewall and front jig the top cowl could now be addressed. The top side of the cowl had the 32 x 20 mm aluminium angle installed in the previous blog linked above so with the top cowl trimmed to fit, it was mounted onto the firewall and fixed using the fasteners. [see photo below].
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| The cut has been marked in this photo see below |
Before installation a length of blue painters tape was added at the mating edge on the lower cowl for contrast.
The next task was to determine how much to remove at the front. With the cowl in place the distance from the top of the jig plate to the cowl was determined and this was transferred to the side with the rear marked from the lower cowl rear.
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With the edge rough trimmed the same technique used previously to locate the final edge was applied with the edge trimmed and sanded as required.
After trimming the edge to profile with a small amount left for final adjustment the cowl was fitted using the rear fasteners and clecos pitched as required over the length of the top cowl.
Note: At all points the cowls must be fitted to the front jig
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| Cowl ready for fastener installation |
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| Drilling pop rivet holes - fuel tube is used to locate jig |
The technique that was used on the rear was applied to the side rails. Will all the holes now a 1/2'' the top cowl was removed and the mounting holes for the Skybolt fasteners and the receptacles mounted as described above.
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| Finished job - all 41 off...! |
Off the rails
It can go wrong and did so in the starboard side with the hole running to the base of the angle with a new rail manufactured and fitted as well as filling all the holes.
How? - Simple in all the work the angle across the cowl went from 0.5 to 1.0 degrees and this raised that side and a quick check would have revealed this - just to gung ho.
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| Sandbag a must have |
Comment
The method as described works and removes all the variability of the Skybolt method and is quicker.
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| Assembled Cowl - no visible support |
The spinner will be covered in the next blog but was much easier that I expected.
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