Turn & Bank Indicator Plumbed to Venturi

 A Turn & Bank Indicator (below the clock) isn't really needed in something like the Fly Baby.  I've accidentally flown into fog and into a cloud.  Both times the Turn & Bank was used to make a controlled turn out of the murk and back to my VFR world.  Therefore, I'm keeping it.  The problem is it's vacuum powered and there is no vacuum source on a C-85 Continental to spin the gyro in it.

 We've used a venturi mounted on the bottom of the plane behind the flange on the cowl.  This is very disturbed air and not a reliable place to operate a venturi.  To help this we've always used a larger venturi than needed to produce the vacuum at 2" of mercury (Hg).  The larger venturi, when properly mounted, will produce more vacuum than the poor Turn & Bank can handle.

 To control the vacuum we used an AN-5829 Vacuum Restrictor. This is just an orifice with a tapered pin so you can adjust it to reduce the vacuum to the desired 2" Hg.  The venturi is connected to the center port, the Turn and Bank to the top port and, a vacuum gauge to the lower port.

 By turning the needle valve in or out you can adjust the vacuum.  It has a lock nut to keep it adjusted once you have it set.  At that point the gauge is no longer needed.  I have other uses planned for the blank space in the panel, so I didn't want to make permanent room for it.  I've made an aluminum bracket (.070" 2024-T3) which allows me to have it installed until I'm happy with the vacuum adjustment, then remove it.  It just bolts to the lower cabane strut fitting.  When it's removed I'll cap the line and secure the end so I can remount the gauge once a year for the annual inspection.  The line fits nicely between the stringers and the fuselage.

 I used Nylon tubing with brass fittings.  When doing that you need the correct, Nylon, crimp ring and, a Tube Support inserted in the tubing.  The support keeps the line from collapsing when squeezed by the compression ring.  Don't use the brass ring it can cut the Nylon tubing.

When the Tube Support is installed you can just see the end of it past the nut.  If you can't see it it may have fallen out while assembling the fitting.  I squeeze the very end of the tubing slightly to help hold it in during assembly.