I've had a hard time getting back in the groove with doing updates. I must be getting lazy. Here is a little information on rigging a B-17.
I started the project by making sure I knew what the airplane had been doing the last time it flew. With Doc, Pat, and Steve in the hangar I was able to quiz them about any odd trim issues that might have existed so I wouldn't be surprised by anything I found.
Since there weren't any problems of note I was able to begin the process by checking the tensions of all flight control primary cables and the associated trim cables. Here is a shot of the tensiometer attached to a right aileron control cable:
I found all of the aileron, elevator, and rudder primary cables within the Boeng specifications. The trim cables were another matter, the elevator and rudder cables needed some adjustment. In fact, as I was checking the angular limits of the elevator trim system I managed to get the cables to jump off the drum in the throttle pedestal.
I spent a little while getting the birdsnest untangled and then ran the cables up to the nominal tension. Everything works great when the cables are tight.
I probably should have brought the tension up first, but I wanted to see what the angles of travel were, in order to correct any issues while adjusting the cables.
The next step was to examine the "throws" of each flight control. The manufacturer designs in an angular limit for the up-and-down or left-to-right movement of each control surface and trim tab that must be checked and adjusted as needed. Here are a few photos of the protractor being used to check the throws on the left elevator; all the surfaces are measured in this fashion:
First we start with the neutral position:
Next, Ellen pulls the yoke back to the full nose-up stop and I check the dimension:
Finally, she goes full nose-down with the yoke and I get the degrees of travel again:
These same steps must be done with all the main surfaces and all four trim tabs. In our case, everything was within the Boeing specification as far as the angular travel was concerned. I did have a little issue with the rudder trim cables that had to be corrected. It was fairly simple to correct by disconnecting the right cable:
And here I am rerouting and connecting the same cable. I left a little skin back in there.......That big box next to my head is the autopilot servo unit for the tail.
There is also a measurement that must be taken of trim tab freeplay. The elevator and rudder tabs are nice and snug, but the aileron tab had a little too much play. I wrote it up two weekends ago, and James Kelly went to the warehouse and found us a nice, fresh trim actuator. Here's Elly removing the tab from the aileron so we can get at the actuator:
This is the mounting hole in the aileron:
And this is the unserviceable trim jackscrew after we got it out of there:
Next weekend we'll go forward with installing the new actuator and fully examining and lubricating the control system components.
Scott