Alright, here we go with the next steps. As I said in my last post, I've already got most of the wing built but I need to catch up on the paperwork!!!
So far we have the bottom main and rear spars, the trailing edge (TE), the bottom sheeting, and ribs W2 and W3 in place. Now it's time to start setting the rest of the ribs. Although it sounds like a lot of work, the rest of the ribs don't really take that much time. If you are building along it should take less than an evening to get the rest of the ribs in place. The biggest key here is to practice how to set the rib. We are going to use the shear webbing (since they are precut to size) and a ruler to place the ribs. If you were lucky and the notches in your TE match your plans (see the note in my last post) it will be a piece of cake for you to set all the ribs, but for the rest of us we need to set the ribs using the notches in the TE as a guide. Ok, let's get going on these.
The next rib out from W3 is going to be W4, so make sure that you have the correct rib to go in place here. Once the W4 rib is set then all the ribs from there out to the end of the wing will be all W5. As I place these ribs I'm going to do it 2 different ways in order to show both ways of setting ribs. For W4 and the first W5 rib I'm going to measure the distance for each rib. First measure the distance from W3 to W4 at the notch on the TE (picture #2), make sure your measurement is accurate. Remember what I said going into this thread â€śMeasure twice, cut onceâ€ť. Yeah, yeah, yeah, I can hear you now, â€śWe're not cutting, we're glueing!!â€ť You know what I mean!!!!
Picture #3 shows transferring the measurement to the rear spar, you'll do the same thing on the main spar too. Test fit the rib in place where it will sit on the spars. You might ask why we are test fitting it since it won't be glued to sheeting like it was for W2 and W3. Simple. You will need to check the fit on the how it sits on the ribs.
Remember, each bad fitting joint will weaken the wing. But if you take time to ensure all joints fit tightly you'll be rewarded with a very strong wing. I'll let you in on a little secret â€” The difference between and average builder and an expert builder is simply attention to detail. Not rushing through your build and paying attention to things like these joints goes a long way to making an expert builder.
Back to the build. If the rib doesn't fit tight against the board AND the top of the spars, then take a few minutes to adjust the way it fits. Once you are happy you're ready to glue the W4 rib in place. Unlike the W2 and W3 ribs, we are going to put glue only at the notches for the spars and the back end of the rib where it will attach to the TE. Set the rib in place and double check your measurements to ensure the rib is in the correct place. Use 2 sets of the 90Â° brackets I discussed earlier to make sure the rib is perpendicular to the building board. It would also be a good idea to double check with a square to ensure the rib is correct (picture #7). Also, before your glue sets we are going to double check with the SW2 shear web. It should fit snugly between W3 and W4. If it does fit snug then you are good, if not adjust the position of the rib.
Why did I measure the ribs in the first place when it would have been easier to just use the shear webbing to place the ribs? Remember, my main goal for this thread is as a teaching tool for others out there thinking about building a plane. Buy showing different procedures I can hopefully help others out there see ways of doing things in there builds. Although I am building an LT-40, a lot of these procedures will be used as you build other types of planes.
I want to stop here for a moment and point something out in particular to this build. When we built the main spar we used a spar doubler on the inner portion of the spar in order give it added strength. The end of that spar doubler will be at the inside edge of rib W5 (see pictures 9,10, and 11). What should be done here is to cut the spar doubler to length to fit. Once you have your measurements for placing the rib use a straight edge razor blade and very very carefully cut through the spar doubler (be careful to not cut into the spar below it) and remove the extra spar doubler. The rib needs to be fitted tightly against the spar doubler, as this gives extra strength to the wing. Once you have it properly trimmed you can now glue in the first W5 rib using the same procedures for placing and double checking your rib that you did for the W4 rib.
We now have ribs W2, W3, W4, and the first W5 rib in place. This is shown in picture #12.
1. Ribs W2 and W3 in place, ready to start placing the remaining ribs
2. Measuring the distance between ribs by checking the distance between notches on the trailing edge
3. Transferring the measurement to the rear and main spars
4. Double checking the distance between ribs at the leading edge of the ribs.
5.Ribs W4 and W5 in place.
6. Between ribs W3 and W4 before shear webbing
7. Using the shear webs to double check the distance between ribs.
8. Checking to ensure the ribs are perpendicular to the spars
9. Showing position where spar doubler should end
10. Another view of spar doubler end
11. One more view. Important that spar double butting up tight with rib W5 for strength
12. View of ribs W2-first W5 in place.
Until next time