The stall warning sensor is a fun little project embedded within the leading edge build. The sensor attaches to the inboard left nose rib, and the stall warning vane protrudes through the slot that was cut earlier in this section of the build. The two main parts are the small mounting and keeper plates, which are easy to final drill and debur according to the plans. The inboard face of the mounting plate is also countersunk for the two primary assembly screws (#30) and the warning vane pivot screw (#19). The assembly uses three different types of washers, which is a good test of the parts inventory and storage process.

Final drilling, deburring, countersinking, cleaning, and priming goes quickly to prepare the parts for assembly. A common question is what torque to use on a MS24693S10 machine screw, which is a 4-40 cadmium plated steel machine screw? The thread diameter of the screw is 0.112 inches, or just under 2/16”. I couldn't find torque specs for an “AN2” bolt, which would be the equivalent of the #4 screw, but I did find minimum tensile strengths for the MS24693S10 machine screw (60,000 psi) and the AN3 bolt (125,000 psi) on the Military Fasteners web site (military-fasteners.com). I made the assumption that if the MS24693S10 screw has roughly half of the AN3 bolt tensile strength, then the torque for the screw should also be roughly half of the bolt. That works out to 10-12 inch-pounds, or 14 in-lbs with a self-locking MS21042 nut. The stall warning assembly uses MS21044N04 self-locking nuts, so I decided to stay with the 10-12 in-lb max value plus drag. Drag on this small screw and nut was negligible. I torqued the nuts to about 8 in-lbs, which is where I got nervous and decided to stop, That left about 3 threads showing and the nuts seem plenty tight.

I made a small change to the pivot for the stall warning vane. There are supposed to be 2 washers on each side of the vane, but that was way too tight for the vane to move freely. I removed one of the outboard washers and tightened the nut to the point where the vane moved freely without binding. There was no need to look up torque values for the MS2469C14 screw since max torque would bind the vane in place and the stall warning sensor would never work. The plans say “Do not over-torque the nut on the screw about which the VA-196 Stall Warning Vane pivots. Insure that the stall warning vane rotates freely.”

The final step was to install the stall warning system to the left splice rib. The 832 x 1/2 screws are driven by a 1/4" hex wrench. Depending on how tight the nut plates are, it may be possible to start the screws by hand, but the hex wrench is definitely required to finish the job. I found it easiest to start the pivot screw first, and leave it loose while installing the upper screw and adjusting the sensor. I ended up rotating the mounting plate all the way to the stop to allow the vane to extend through the slot in the leading edge with just a very minimal travel to depress the button on the sensor. The fit to drive the screws is very tight. I tried reaching through the access panel to see how that might work after the leading edge is mounted to the wing, and I don't have access that way. I think it's fair to say the sensor is a permanent fixture as is, unless I find someone with the correct sized arms to work on it later if needed.

I also noticed a difference between the plans and the parts I received with the kit. The W400, which is essentially a ground wire, that is supplied in the same bag as the WH-00012 wire harness is a black wire and not white as stated in the plans. I looked through the various wire harness bags to ensure I had the right part for the ground wire, and didn't find any appropriate white wires.

Initial Prep (Debur, Trim, Drill, and Cut)
7/30/22 – 0.8h
[Hole and Edge Deburring Tools, #30 Drill, #19 Drill, Small Round and Flat Files]

Final Prep (Dimple, Countersink, and Shape)
7/30/22 – 0.5h
[#30 Countersink Cutter, #19 Countersink Cutter]

Prime
7/31/22 – 0.3h
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Dupli-Color Self Etching Primer (Green – Rattle Can)]

Assemble
8/1/22 – 0.9h
8/20/22 – 0.5h
Description
[Phillips Head Screw Driver, Torque Wrench (In-Lbs), 1/4” Hex Wrench]