Blue Box – Page 3 – Blue Box Driver

Doesn’t quite fit

#6-40 screw used in the wind drift calculator.

With trainers approaching 80 years old, it’s no wonder many substitutions have been made over the years. Here’s one we have seen several times. Original Blue Box trainers frequently used #6-40 screws; the most common #6 machine screw today is a #6-32. When a #6 machine screw just doesn’t fit right – it may be the wrong thread.

A similar problem occurs with small set screws; Blue Boxes often use Bristol or spline. When standard Allen wrenches don’t fit, get out a magnifying glass and see if a Bristol is in order.

Connector tags

Air Speed “AS” stamped metal tag in remote instrument box.

The remote instrument box includes three primary Telegon instruments, each with identical 5-pin AN connectors. To avoid confusion, Link labeled them with small stamped metal tags. “AS” air speed, “VS” vertical speed, and “ALT” altimeter. Those little labels withstood the test of time.

Stressed Out

Original #8581 bracket (right). Lateral crack near bottom goes all the way across bracket.

Sometimes parts are worn out or broken beyond repair. The original part #8581 (right) is a lever and bracket assembly that supports a pivot point for linkages going back to the tachometer regulator. Like several brackets in the fuselage, it is cast from pot metal. This bracket had many cracks and was broken in several places due to fatigue. We made the substitute (left) from aluminum. Ours doesn’t look as cool but is functional.

Spin the gyro

We recently refurbished the turn and bank indicator regulator bellows for our Blue Boxes. The regulated vacuum output is supplied to a gyro inside the turn section of the turn and bank indicator.

Refurbished turn & bank indicator bellows.

For more details, read the ‘turn and bank indicator regulator bellows’ section under ‘Restoration hints’ in the right column [scroll to bottom for cell phone] , or check out our video.

Refurbishing the turn & bank indicator regulator bellows on a Blue Box Link trainer.

Update December 1, 2020. The bellows refurbishing did the trick. The turn and bank indicator is now working. Yea!

Keep magnetized screw drivers away !

Altimeter transmitter gearbox coupling magnet.

Our altimeter transmitter was stuck. We opened it up, cleaned the gears and oiled the bearings with synthetic clock oil. The Telegon transmitter motor is magnetically coupled to the gear box. Each side has a tiny Y-shaped magnet; the driving and receiving magnet are spaced about 050” apart as they spin. It’s hard to see in the picture; but the North side of the magnet is marked with a faded red stain. Details are shown in the “Altimeter transmitter” section of “Restoration hints”.