Joining carbon fibre tubes

Hi

I'm new to the forum so forgive me if this is too easy a question.

I need to make a sighting triangle for an aerobatic aircraft.

This is a triangular frame which attaches to the leading edge of the wing so I can look down the wing during flight and use the triangle to judge the attitude of the aircraft by comparing the sides of the triangle with the horizon.

The base of the triangle needs to be about 750 mm long and the sides make up an isosoles right angle triangle. There is an existing tube attached to the leading edge into which the triangle needs to insert. The diameter of the hole is 11mm

The triangle needs to be very light and very rigid so that it will not bend under 10G forces.

My initial thoughts were carbon fibre with the base strut reinforced with and inner tube of aluminium which protrudes out of the carbon tube to insert into the wing.

The rest of the trianlge could I think be plain carbon fibre tubing.

My question is how do I attach the three tubes to each other to give the strongest joins at the angles?

Can you buy angled metal inserts or if not which material do I use as a glue?