372 hours on the hobbs - trimming stiffeners for Left Elevator

After having spent quite a bit of time researching build methods employed for the left elevator and trim tab, I finally got back to actually working on the build. We have had two snow storms in the last 2 weeks that have dumped relatively large amounts of snow for this time of year, and so the shop is quite cold in the evening - despite my efforts to heat it up with my little radiator heater that I bought from HD.

Here is an excerpt from the plans for the RIGHT Elevator that I almost missed. Lots of fun trying to figure all this out when they make notes for the left elevator parts on the right elevator plans and vice versa. The stiffener part numbers are slightly different for the left elevator, in that you are supposed to trim stiffeners E720 J, K, and L from stiffeners D, E, and F. For some reason that still escapes me, they have added some notes to trim the J, K, and L stiffeners a very specific amount. At first I could not understand what they meant, since the notes simply said to trim the aft end of the stiffener based on the dimension given for each one. One example said that that the D stiffener is to be trimmed X= 1 7/8. I had no idea what X was until I reffered to the stiffener detail on the right elevator plans as shown below:

So X is measured from the second to the last hole to the end of the stiffener. The mystery is that this trim measurement did not apply to the D, E, and F stiffeners used on the Right elevator, and I do not know why. All you did was cut them from the angle at the designated marks, and debur the edges, which shortens them up a bit from the original cut. It is clear that they want you to trim the stiffeners for the left elevator just a bit more than that. I am only guessing, but perhaps it has something to do with the flex on the left elevator that may be caused by the added force of the trim tab, and they want you to shorten up the stiffeners to avoid additional cracking that might occur. Again, that is just a guess.

Now for the next one. If you use the dremel cutoff wheel as I do for cutting most of my parts, you will inevitably end up with a mistake that requires a new part at some point. The wheel got away from me and wrapped itself around the stiffener just enough to put a nice gouge right to the rivet hole. This part is toast and will now go into the scrap heap. That makes 4 that I have messed up and either had to repair or replace.

Now that I understand what "X" is, I tranfered the measurements to each of the D, E, and F stiffeners, and included a mark that shows the position of the last hole which has to be match drilled from the hole in the skin.

After screwing up one of the H stiffeners and freezing my tail off after rough cutting one of the two pieces of angle for the longer J, K, and L stiffeners, I decided to call it a night. I will have to add another piece of angle with for the H stiffeners to my order from Van's, and will have to wait for it to arrive before I can finish the prep for all the stiffeners. Just to clarify, until I saw that note that described what "X" was supposed to represent on the plans for the right elevator, I thought that I was supposed to measure the distance specified in the note from the end of the stiffener moving forward.

For those of you that are fellow builders, do not make that mistake. X is measured from the second to the last hole moving aft, exactly as shown in the stiffener detail in the plans for the right elevator. If you do it the incorrect way (from the end moving forward), you will end up removing too much material from the end of the stiffener. Other builders did not seem to have a problem with this, but it sure messed with my head for a while. Lesson learned is to make sure you read ABSOLUTELY EVERYTHING ON THE PLANS as well as in the instruction book. All too often there are notes and instructions on the plan views that are not mentioned at all in the steps in the book.

Sorry if this offends some of you out there, but my personal experience with engineers that try to write instructions for putting together the things that they design is that most are not very good at it. They tend to omit things that they think are obvious based on their own level of knowledge, and this causes problems for the rest of us non-engineer types. Years of reading less than clear instructions for putting together model airplane parts are the basis for my experience in this area.