Canopy Bubble - Part 1

This blog is to cover the work in the installation of the Australian Tucano.
Reference: UK installation

Marking Out
With the frame positioned in the locked position the canopy was installed in its correct location onto the frame. Two [2] cut-outs were made on the starboard side to allow the canopy to fit snugly onto that side.

Note: The canopy lined up well with the frame so this proved a simple task.

To prevent tearing away to much of the canopy's protective cover a tape line was added around the canopy and then the cover rolled up to the tape, then using more masking tape secured it to the canopy. This process was repeated on the inside with the best technique to roll the cover with the fingers until a roll formed which is pushed / pulled up to the same line as the outer cover.

Note: This was done on the aircraft as the builder was one [1] up not by design 

Ready to mark out

The next decision was were to cut the canopy because of the recess in the frame has a taper, this creates a number of options but it was decided to use the external edge which later proved to be fortuitous. 

A cut line was marked using painters tape tracing chosen external edge.

Marked out ready to cut

Cutting
A Dremel motor tool and snake attachment were used in combination with a thin cutting disk running at about 17000 rpm, this is the same method used by the Brazilian dealer to cut their canopy.

Cutting finished

Finishing off
The canopy and frame were removed and placed on to work stands for the necessary finishing. It was decided to block sand the edges using 80 / 120 / 320 grit aluminium open cut paper. 

With the canopy slid back and placed on timber to allow access and starting at the front the first three sides to the back. The hinge side was ignored to allow final adjustment after the opposite side was prepared, this proved to be a poor decision.

Sanding the edges

The canopy was now placed back onto the frame and it was noted that when sitting centrally there was about a 5 mm over lap from the edge. It was realized that with the canopy sitting on the outside of the frame and choosing the external edge as a cutting line that it was oversize when place into the frame's recess.

This operation was repeated many times and proved quite difficult as there was only one person on the task - see comments.

Marking out the front and rear edges for trimming

It was decided to first correct the front and rear relative to the frame recess and this was done using the sanding paper and required a number of difficult refits begin one up.

With the front and rear edges about 1 mm from the outer edge of the recess it was time to trim both of the sides.

Why God chooses to look after drunks and fools this builder builder can only guess but for no reason I decided to look at the other side revealing a hairline crack.

A stop crack hole was required urgently and the battery drill was quickly fitted with a 2.5 mm drill and a stop hole drilled just in front of the crack. Next this hole was chased with a hot soldering iron with a 3 mm OD tip. 

Success or failure will be determined on the return to the hangar next week.

A home builder greatest fear

Analysis

Offset created by rolling 
canopy starboard

After a period of quite thought it was decided to use the excess on both sides to remove as much as the crack as possible. This placed the canopy a little off the marked centre but at times like this, one has to be pragmatic as a bullet had just been dodged.

Had the work continued with no reference to the hinge side this would have become a total disaster with the next move.

With the canopy re-positioned the excess material was marked out with tape and duly cut and dressed.

Final Fitting

The chamfer on the edge of the frame recess prevents the canopy from nesting correctly. With the outside edge used as a cutting reference that had just saved the canopy this builder had by now lost all taste for working on the canopy and it was decided to just chamfer the edge.

A fine sanding drum fitted into the Dremel and a combination off 30 / 45 degree chamfer's were applied to all four edges of the canopy. 

This was achieved starting with the 30 degree chamfer running against the direction of rotation to start the chamfer and to providing the best control. 

Next cutting was done with the against direction of rotation using light pressure and multiple cuts at 30 degrees in the direction of rotation and finally at 45 degrees. 

With the chamfer established it was all finished with 320 grit to polish the chamfer and finally the edges was radiused by running the paper along the edge with the hand. The bevelled  edge was finally blocked with 320 grit to remove any minor scallops

Finishing the edges.

Texta used to mark radius
Chamfer shows as the clouded line at edge

The line was marked using a felt tip pen to highlight the recess radius then the excess cut with the Dremel motor tool , finally the edge was profiled and chamfered using the drum sander. 

Comment
It could have been worse - maybe.

If doing it again,

• You need two people as the excessive handling required by one person raises the risk of damage significantly.
• Using a Dremel the Thin Cutting disks proved to do the best job at about 17000 rpm
• As soon as the cutting is finished sand every edge to the 120 grit stage before commencing any work or buy a panic button.
• The cutting profile would have to move in from the edge to allow for the canopy to grow in the slot when cut.
• Bevelling the edge did create a neat fit but remember on the Tucano the factory intends the exposed face of the canopy to be on display. With this aircraft a shroud to create the unique Shorts T1 look has to be constructed.
• After every task check all edges of the canopy carefully for any signs of a cracking.
• Have a drill ready to stop drill if required.
• Have a small bottle of Acetone and small paint brush ready to glue any crack together  and to fuse the hole smooth.

Shorts Canopy