I have recovered from my misstep from last weekend and made a small but critical step forward this weekend by getting the Stab and Fin glued onto the Fuselage. I have included a few shots of the dry fit up step before my epoxy fiasco from last weekend. I started by scribing the contour of the stab onto both the sides of the fin using a fine point marker. After trimming back to the scribe line with a Dermel sanding drum, I glued in a scrap of balsa to the bottom rib of the fin. This will provide a good wood to wood bonding surface between the fin and stab (the piece is countered slightly to match the crown of the stab). In hindsight, I wish I had thought to drill holes in the the fin and stab ribs to save a little weight. The last shot shows everything aligned and squared, ready for glue. I also verified that the stab is sitting with proper +1 deg incidence angle using my new handy-dandy incidence meter.
If you look close, you will notice that the extension to the tail of the fuse sheeting on the left side is broken off. This happened during dry fit-up, but I decided to wait until everything was glued up before fixing it.
I convinced myself that my problem from last week was not a bad mix of hardener into the epoxy, but rather that the temperature in my basement workshop was just too cool. My small space heater only gets the temperature up to about 55-57 deg. F in the winter. Comfortable enough to work in, but 15 deg. below the recommended minimum cure temperature for the epoxy I am using. So this weekend, I moved upstairs and set up on the dining room table (with plenty of newspaper). All went well, and the epoxy kicked over just as expected.
The postman showed up with a few goodies this week too!
Well I spent quite a bit of time in my shop this weekend. I made great progress getting the stab and fin fitted to the fuse and aligned. I got everything true and square and ready to go. I even picked up a Robart incidence gauge and used it ensure that the stab had the proper +1 deg. incidence angle. I mixed up the epoxy and got everything glued up and fitted into place. Now I start to worry because after 90 minutes (using 30 minute epoxy), the epoxy left over in my mixing cup is still soft and tacky and shows no sign of kicking. I hit the cup with a little heat and the epoxy immediately turns runny, so I convince myself that I did not add enough hardener.
I know that 30 minutes epoxy takes about 8 hours to fully set up, and that there is some forgiveness to the mix, but I decided that I’d rather be safe than sorry, so I pulled everything apart. Of course, this leaves me with a big sticky mess to clean up. I got most of it cleaned off by heating it up and scraping it off using single edge razor blades. While doing this, I managed to cut my finger and did not notice that it was bleeding until I saw blood stains on the balsa!
I think I have everything cleaned up with only some minor cosmetic damage. I am off to North Carolina again this week, so I won’t be able to try again until next weekend.
Well I finally got a chance to get back into my shop and make a bit more progress on the P-47. Next step is to get the sheeting on the fuse top. I had previously formed the pre-cut lower sheeting around some aluminum ducting to set in the curve.
Last weekend, I had an hour to sneak into my shop, and I thought that would be enough time to get the lower sheeting glued up. Fortunately, I decided to use Titebond aliphatic resin instead of CA. I got the sheeting partway glued down but was really struggling to keep it from buckling. I was totally dissatisfied with how it looked, so I pulled it off, wiped off the glue with a damp rag and decided to leave this for when I wouldn’t feel rushed.
I had a bit more time today, so I took another go at it, again using Titebond. This time, everything went smoothly and I got both lower sheeting pieces glued down.
After the glue set up, I went back and started to trim back the sheeting near the stabilizer saddles. Once again I started to feel like I was rushing things, so I decided to call it a night and leave this fussy step for the morning.
Construction of the fuse top continues with the installation of the stringers and the razorback spine. All very straightforward with no real surprises.
Next step, sheeting the lower section of the upper fuselage. I have spliced on extenders to the end of the tail section on both sides of the precut skins. I then soaked down the outer surface with Windex and gently bent the skins around a length of aluminum duct (anything of a suitable diameter and length will do), using rubber bands to hold everything in place. I was tempted to glue them in place today, but decided to give up and save some fun for next time.
Just to drive myself crazy, I have been keeping a log of the hours spent working on this project. Since the start of the project on October 1st 2011, I have spent 53 hours (I never claimed to be fast!).
Progress continues on the P-47 fuselage top. I spent more time than I care to admit cleaning up and fussing with the formers. It’s hard to see in the photo, but some of the plywood was a bit rough and it was quite a challenge to separate the parts without damage. Although I am working on the fuse top, I took the time to punch out all of the bottom formers and fine tune the fit between the top and bottom formers now. After all the clean-up, the top formers glued up quickly.
I decided to hold off on hinging the elevator/rudder and move on to fuselage construction today. I went back-and-forth a few times, but finally settled on building the razor-back version. So far, I have managed to sort through and separate the parts for the fuse top. Construction in earnest will begin in the morning.
After three short months I have finally finished the tail feathers – well mostly finished anyway. I still need to add the hinges and round the leading edges of the elevator halves and the rudder. To give a more scale-like look, I decided to cut the elevator and rudder tips with curve instead of the straight cut called for in the plans. Below you can see where I marked the elevator for the curved cut near the tip. To generate the curve, I enlarged a section of a three-view drawing on a photocopier (by trial and error) until it matched the size of the stab-elevator assembly. This was transferred onto thin card stock to make a template.
If you look closely, you will see two lines drawn onto the elevator tip. The curve of the “scale” line (bottom line) extends slightly past the solid balsa tip. I modified the curve slightly (the top line) to blend directly into the existing gap – close enough to scale for my purposes. The curves were carefully cut with a jewelers saw. The left tip came out perfect, but unfortunately, the right tip ended up a bit rough. To fix this, I carved the trailing edge of the elevator back slightly and laminated on a piece of scrap 1/16th sheet balsa. Once sanded and blended in, the curve matched up with the elevator perfectly.
The same techniques were used to complete the curve on the fin-rudder assembly.
Well it has been over a month since I last posted and unfortunately, I am still working on the tail feathers. Between work travel and holiday travel, I really have only had a few hours here and there to putter around in my workshop since then. No real surprise, as I knew this was going to be a long slow process!
My major accomplishment on the stabilizer has been to complete carving and shaping the tips. This went much easier than I feared. Below you can see the blocks carved into rough shape using a razor plane (the masking tape helps ensure that I don’t accidentally damage the existing sheeting) and the result of final sanding.
My next step will be to cut the elevator free from the stab. Instead of the straight cut shown on the plans, I will cut them using a scale curve near the tip. I decided to hold off on this for tonight as freehand curve cuts have always been my woodworking “Achilles Heel”. You can see that I have added some lightweight balsa filler to touch up a few low spots, although a bit more final fussing will be needed before final finishing.
On the fin, the right skin has been glued down along with both left and right skins on the rudder. Note the reinforcing blocks added to the rudder to help secure the hinge points. The fin has been lifted from the board (not shown) and the left side prepped for its skin – but that’s as far as I got.
I am back traveling again this week, but I will have some time off after that. Hopefully I will finally be able to get some quality time in my shop!
Unfortunately, I have not been able to make much new progress. I have been traveling for work way too much lately, and we had surprise October snow storm dumping a foot and half of snow over northern Connecticut and knocking power out to much of the state (hard to build when there are no lights).
I was able to put in a few hours today and got the sheeting onto the bottom of the stab, rough shaped the leading edge of the elevator halves, and started construction on the fin.
I used my new Great Planes balsa building board for the fin construction. It is definitely an improvement over my old ceiling tile as items pinned hold much more firmly.
I’m back on the road again for the next two weeks, so I won’t be able to make any new progress for a while.
Not much new progress this week (too many other obligations). Just got the sheeting onto the top of the stab.
I decided to install these with aliphatic resin (yellow wood glue) instead of CA. I prefer this as it is slow drying, giving you time to ‘fuss’ with the pieces and because it produces a very light-weight but very strong bond. Initially, I was having some difficulty curving the leading edge, so I separated the parts and wiped the glue clean with a damp cloth. I then sprayed the outer surface of the leading edge with Windex (the ammonia in the Windex helps loosen the fibers and softens the wood more than just water) and wrapped the leading edge around a piece of 3/4 inch PVC pipe. All it takes is a few minutes to set in the curve. While the wood was still slightly damp, I was able to glue it in place, easily shaping the leading edge to the curve, using small t-pins to hold it in place until the glue dried.
You can see a bottle of CA in the background. This was used to glue a small piece of scrap balsa near the leading edge to help support the joint between the left and right sheeting. You can also see baggies filled with lead shot used as weight to help hold the stab flat while the glue dries.
Hopefully I will have time for a bit more progress next week.