My Wooden Airplane
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9/12/2011 - 9/15/2011

Install Torque Tube

Here is the torque tube installed in the fuselage. There are a couple of things to point out here. First, the horn sticking up in the middle (actually, it's sticking "down", because the plane is upside-down at this point) is about an inch longer than the plans specify. This caused it to actually protrude below the bottom of the fuselage when installed on the specified 10 mm mounting blocks. In order to compensate for this, I used 3 mm mounting blocks. This necessitated carving out some of the floor and seat supports in order to get it to fit. Even though the horn is now (just) inside the confines of the fuselage, I suspect that when it is covered, the fabric will sag slightly between the stringers, and will still contact the horn. Since I have to have an inspection plate here anyway, I think I will make one out of plywood and attach it across the stringers so that the fabric won't sag and touch the horn.

Of course, none of this fiddling would have been necessary had I just followed the plans, right? Well, that brings up the other issue. When sitting in my seat, I was playing with a mock "stick" and noticed that I could only get about 15 degrees of movement in each direction before hitting my knees or stomach or running out of arm length. The plans have a 3-inch throw on the control arm, 3 inches on the elevator bellcrank, and 3 inches on the elevator itself. This implies a 1:1 ratio between stick movement and elevator deflection (i.e 10 degrees of stick movement equals 10 degrees of elevator travel). But my elevator is supposed to have a minimum of 25 degrees of travel. If my stick can only move 15 degrees in any direction, I won't have enough elevator travel. The solution was to monkey with the bellcrank ratio. If I use a 4-inch throw on the control horn and connect it 2 inches from the pivot point of the bellcrank, I will now have a 2:1 ratio between the stick and the bellcrank (i.e. moving the stick 10 degrees causes the bellcrank to rotate 20 degrees). This will allow me to have full elevator travel, even though I only have "half" stick travel.

I'm trying to figure out why I only have 15 degrees of stick travel, though. Tony Bingelis says 5 inches of stick movement in any direction is "normal", which is exactly what my stick does. My stick is 18 inches tall (from the floor and pivot point), and trigonometry confirms 5 inches over 18 inches = 15.52 degrees. (The plans actually show the stick as being 15.25 inches above the floor and pivot point, which would only give me about 18 degrees over that 5-inch range.) In order to get my minimum 25 degrees of travel, the stick would need to be only 11 inches tall. And looking at other planes (Van's RV-6), that's about how tall the stick is, which works because the pilot is practically sitting on the floor. In my plane, the pilot is sitting about 6 inches above the floor, which explains why my stick has to be longer, I guess.

Total Time: 7.5 hrs.