I've been finishing up the whole top-side of the fuselage over many months including Ch 18 and return to Ch 13 for the Nose Top, to get things reasonably well complete before moving to Ch 21. One should realize that I've already completed Ch 19, and I've built the Winglets but will not mount them and make the rudders until I get to hangar (for ease of transport) unless hangar availability becomes an issue ... Right now, it still seems like I have LOTS of work to do, even though this is the last Major structural element I think I need for the Cozy. As you probably already know, I'm working out of the garage, and until now that's meant "my side" of a 2 car garage. In this chapter I must occupy the rest of the garage, much to the disappointment of my wife. I've delayed it as long as I think is practical, and so, here we go...
Mounting the Spar:
I delayed mounting the Spar until now so I could work on the Cozy in 1/2 of our garage. Obviously with strake installation I must occupy the WHOLE garage and work starts by going back to Ch's 14 and 18 and follow the plans for permanently installing the spar and finishing the connections to firewall. This took a couple of weeks, is documented in pages for those chapters, and subsequent strake work is documented here starting late July 2016.
I delayed mounting the Spar until now so I could work on the Cozy in 1/2 of our garage. Obviously with strake installation I must occupy the WHOLE garage and work starts by going back to Ch's 14 and 18 and follow the plans for permanently installing the spar and finishing the connections to firewall. This took a couple of weeks, is documented in pages for those chapters, and subsequent strake work is documented here starting late July 2016.
Preparations:
Lots of reading and re-reading the plans and how others have approached Strake construction. After turning over several approaches in my mind, I believe I'll use an approach that's perhaps closer to the plans than some have used, but still suited to my available resources with the overall structural intent being paramount. One of the things I'm still trying to figure out is when I'll have to turn the fuselage over. Clearly, by the time I need to apply the UNI skin to the bottom I'll need to be upside down, but I definitely want to minimize how many times I have to do this inversion. When it's time to turn it over, I'll be looking for some friends, as my last son will have left for college :-(
Lots of reading and re-reading the plans and how others have approached Strake construction. After turning over several approaches in my mind, I believe I'll use an approach that's perhaps closer to the plans than some have used, but still suited to my available resources with the overall structural intent being paramount. One of the things I'm still trying to figure out is when I'll have to turn the fuselage over. Clearly, by the time I need to apply the UNI skin to the bottom I'll need to be upside down, but I definitely want to minimize how many times I have to do this inversion. When it's time to turn it over, I'll be looking for some friends, as my last son will have left for college :-(
Step 1 - Fabrication of Ribs and Bulkheads:
I started with the normal process of bonding two of the 3/8" H45 PVC foam sheets together on the long edge and 1 BID both sides and peel ply. I'm working with EZPoxy for strakes since most parts will be in contact with the fuel tanks. This was my first large layup with it. I'd done a practice small layups to make sure I understood the mixing proportions (very similar to the MGS that I've been using), viscosity (thicker than MGS) and the cure time with the slow Hardener (maybe slightly faster, but hardly noticeable). I had no trouble with these layups even though EZPoxy/ 87 slow doesn't wet quite as well as MGS. It also has a very strong odor and I wear a full filter mask from the time I open the can to after clean up and make sure the garage door is open for at least the first hour of cure with a fan on. After an hour, I've found the smell dissipates and typically don't need a mask. The other thing to realize is that the hardener is golden brown so the layups are tan colored, vs green with MGS. This is nice as a reminder of where I'm using EZ Poxy for fuel resistance. I then used the layout arrangement published on the Cozy Girls Strakes site, www.cozygirrrl.com/menupage.htm (if you go to this side, click "Chapters" to the left, then select Ch 21 Strakes/your own kit, to find their layout) but modified it slightly to enable me to fit in the 2 long BLE's needed for the extended strakes (the BLE's in the plans and on the layout drawing are not long enough). Triple check your markings before you cut. I found a couple of small mistakes the 2nd time, and this is when I realized I needed to shift the TLE's a little to fit in another long BLE for extended strakes. No problem with the extra lines, I just put little "x's" near the edges where I might be tempted to run the saw as reminder that they were NOT to be cut. When I get some time, I'll draw up the layout I used and put it here. I cut them with help from Garrett (shown) using the Blade Runner (see tips page) which worked fine (1st rough cut to smaller sections of the big sheet, then fine cut on the marking lines). I then used a router to carve out the half circles in the tops and bottoms of B33 and DB pieces. Finally, I put the B33's together and drilled the 1/4" vent line hole per plans. Note that I left the TLE's and BLE's long so I could trim them to fit. I also decided to wait in final shaping of the OD pieces until everything gets set on the spar to best match with the profile of wing and R57. |
|
Marking Water Line 17.4 and Body Lines 33 and 57:
Before going further, I need a good WL 17.4 WL and BL 33 and 57. For this I want to use the 17.4 that I used for the wing alignment (marked on the back of the spar). However, when I did comprehensive measurements of longerons, spar and canard I found that my spar and the marked 17.4 WL were about 0.5 degrees off in roll angle from the longerons up near the IP where I had been referencing. After a lot of fretting and measuring and talking with other builders, I knew I needed to use the wings as the reference, since they are the critical aerodynamic surfaces. I would then allow the longerons to be off slightly in roll angle relative to the wings. Likewise important was maintaining wing pitch angles (angle of attack) relative to the longeron pitch angle for the wing and canard and they both measured to within +/- 0.1 degree with the digital level. Good! To confirm everything, I re-mounted the wings on the spar and the canard up forward and checked alignment. I know that the wings twist the spar slightly more now, vs when I have the strakes built, so I will measure this deflection as well. To have room for mounting the wings, I need to push the fuselage part way out of the garage (see picture), and level everything with the 17.4 WL that corresponds to the previous wing alignment. Naturally the day I have helpers available, it's raining (see photo with tent as we wait). OK, rain stopped in the afternoon so Garrett and Reece helped me get both wings bolted on to the spar. Adjustments and measurements using laser level and reference points on the corners of the wings (see Ch 19 wing leveling and plans for displacements from 17.4 WL) went on for a couple of hours as I looked at and thought about what I was reading. Then I figured out what made sense for my Cozy: a) My 17.4 waterline marking on spar from Ch 19 is appropriate and will remain the key reference. I supported the fuselage to get this line level along with zero longeron fore/aft angle (tires have no influence now). With this done, the wing inboard leading edges are right on (within 0.1 inch elevation) 17.4 WL. b) then I took measurements from this plane using the laser at the outboard corners of the wing and the inboard TE, since the plans specify what these offsets should be in Ch 19 (and I used these figures in my water based leveling last year. These measurements looked good, with only a slight dihedral (mentioned in Ch 19 to get good wing root match with the spar). Wing pitch and roll are within 0.1 degrees of plans spec. In my Cozy this flying configuration results in a longeron roll angle of 0.5 degree's down on the right side. I can live with this. With alignment confirmed, I then made spar-end patterns of foam that matched the wing profiles on each side and 5 min epoxied them to the end of the spar to assist with later shape blending the end of the strake to the wing, since I will be storing the wings again later today. With the fuselage still propped for level 17.4 WL, the canard pitch was re-checked using the F template from the plans and showed 0.4 degrees pitch up with respect to the longerons, which are leveled fore/aft with the 17.4 WL. Discussion on the builder's site suggests that this will be good (negative pitch is not good on the canard - as it increases risk of main wing stall prior to canard) Finally, with the main gear off the ground I measured the roll angle of both wheels and the angle between horizontal of the bottom of each tire for later analysis. That latter angle was 0.8 degrees. This may be something I have to deal with later when I have the Cozy in a level hangar by making a slight adjustment to the landing gear. It's not something I can accurately resolve at this stage in my garage. After all this the wings were removed and stored and the fuselage moved back in the garage and propped back up similarly so I could begin strake construction. Postscript from after flying the plane for a year: this slight misalignment of the spar did not have a big influence on the flight characteristics of N78CZ. I tried to align the canard with the wing after finishing the strakes and this may have helped a little but it's not perfect. The result is she still flies very straight with no bad roll tendency. I just adjusted the roll zero ever so slightly to correspond to stable level flight and never notice roll problems. |
|