This is a simple sight-tube protractor to aid in setting up the aerobatic box for F3A contests or practice. The F3A box is defined as having the center pole 150 to 200 meters from the pilot with end poles 60 degrees either side. This protractor has three tubes to sight the three poles across the 120 degree box.
The two large holes near the center tube are threaded to accept a 1/4-20 camera mount, so a tripod can be used.
The other four holes are provided so two 8-32 or similar bolts may be added to square the protractor when sitting on the rail of a runway safety fence. The idea is to reference the center pole with your fence, which is assumed to be parallel with your runway. Once the center pole is determined, set up a camera tripod at the pilot's position behind the fence, aim the center tube at the center pole and then sight the end poles.
The center of the protractor is the middle of the small circular cuttout. The protractor will work sighting the center pole from either side of the middle tube.

Tronxy

Tronxy XY-3/Pro

Doesn't Matter

Doesn't Matter

.175

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