Rough and Ready Aerospace: Step 5.4 Leading edge ribs

I couldn't see any reason not to go ahead and fabricate the aileron bracketry. These are constructed as sub assemblies that attach to the rear spars. They are an interesting collection of thick (1/8") sheet aluminium and angle. There are a variety of rivet types and lengths utilized so the plans must be studied carefully.

Once the brackets were riveted on the wing frame, the frame was moved off of the workbench and onto the wing stand.

Then, I moved on to assembling the left wing frame.

With the wing frames on the stands it was time to level and measure the frames. Barely visible in the picture below, the plumb bob is set for measuring wing twist. If the measurement is the same at both ends there is no twist.

The next step after completing the wing frames is to assemble the nose ribs. This portion of the wing is assembled separately from the wing frames using a cradle to hold the skin closed while the ribs are put in place. Here is the cradle under construction.

I'm building the left wing nose assembly first and I quickly realized that the stall warning device, if it will be used, should be assembled and installed before the nose ribs are riveted. I am going to use the device, even though I am also planning an angle of attack meter as well. Some say having both is redundant. And I agree. That's exactly why I'm installing both. Because it is redundant and I like the idea of having a backup to this essential information. Both instruments actually measure the same thing in different ways.

But what is the Van's stall warning device really measuring? It measures the angle of the air impinging on the leading edge of the wing via a small paddle stuck out in to the air stream. When the air moving over the wing blows on the top of the paddle the stall warning is off. But when the angle of the wing (and paddle) is sufficiently high, the wind can get underneath the paddle and turn the switch the other way, thus turning on the stall warning.

How does the Angle Of Attack meter work? The AOA measures a pressure difference between two probes (Pito tubes) set at different angles relative to the air stream impinging on the wing. The difference in air pressure between the two probes is proportional to the angle of the wing, and since a wing will stall at a known angle (or a angle that can be measured), the point at which the wing will stall is determined and the stall warning issued.

So the Van's stall warner is akin to an idiot light in an automobile whereas the AOA meter is more like a temperature gauge since it gives a continuous measure. Feeling drowsy? Ok, back to to build:

Stall warner assembly. Access cover and doubler plate drilled and dimpled.

A slot is cut for the stall warner paddle in the leading edge skin.

The leading edge section is assembled and then clecoed to the wing prior to match drilling. Notice big orange mallet? Sometimes micro-adjustments are necessary. The fuel tank attachment flange is slid into place along the outside perimeter of the W408 end rib and under the wing skin making a very tight fit.

After match drilling the left nose rib skin is dimpled on the DRDT-2 machine.

Meanwhile, Carol comes down to help remove the plastic from the rivet rows on the right leading edge skin. Roxy looks on. I think she was listening to the radio.

Well it was just a matter of time before I joined the drill-your-finger club. I bet that not many get through an airplane build without a membership.

I used the pneumatic squeezer for all of the holes it could reach. The DRDT-2 is a nice machine, but it is not as fast as a squeezer.

With the skin dimpled the left leading edge section is ready to be riveted. All of the rivets on the leading edge piece can be set by one's self, but I found it easier to have help from Carol while setting the two or three on nose. Working alone can sometimes be an advantage since no communication is necessary. But when the required reach is excessive, it's good to have help.