Hog Bipe – Wing Construction Complete

I have been picking away at the wing construction on the Hog Bipe on and off. Sheeting the wing tips went smoothly and I am happy with the end result.

20140707_192906187_iOS

The lower wing is built in two pieces and glued together to obtain the proper dihedral. One little trick I used was to cut a block of scrap wood with the dihedral angle for the inner wing rib. This allowed me to position and clamp the rib in place before gluing to the spar. The first photo below shows the block against the kit supplied dihedral angle gage. The second photo shows it in use.

20140707_195125669_iOS20140707_210628356_iOS

The rest of the lower wing construction was uneventful and came out straight and true with the right dihedral.

20140713_170412729_iOS20140727_223511719_iOS

I bought my kit off e-bay, so I am not really sure when it was made, but I was fortunate enough to have one that included the parts for the optional dual aileron servo setup in place of the single servo in the original kit. The dual servo setup is much stiffer and is less likely to have flutter problems. My only deviation from a stock build so far has been to add a couple of paper tubes for the aileron wires and to use 2 inch wide fiberglass tape t reinforce the lower wing joint instead of the 1 tape supplied with the kit.

20140809_201941630_iOS20140809_205529988_iOS20140809_205516137_iOS

The plans call for using medium or thick CA to saturate the tape weave. I chose to use epoxy instead. This was my first experience using fiberglass cloth and epoxy, and I considered it a small scale trial run for glassing a balsa plane. I sprayed a light coat of 3M-77 adhesive on the glass and laid it down between two strips of masking tape. I chose BSI Finish Cure epoxy. This is similar to laminating resin and was available at the my LHS. To ensure that the epoxy would flow smoothly and to get a good cure, I pre-heated the bottles for 10 seconds in the microwave before mixing. I applied the epoxy with and acid brush and spread it smooth with an old gift card. I rough sanded with 80 grit and applied a second coat after an overnight cure, sanding out with 80 and 150 grit after full cure.

Overall, I am happy with the result. Structurally, I am sure this will be plenty strong. Cosmetically, I am satisfied for this application. It sanded out quite smooth, and would be a good surface for painting (if I was going that direction). I did end up with a few dry spots where the epoxy did not wet through the fiberglass fully, but I know what to look for now and should be able to avoid that in the future.

The last major step was to shape the ailerons to the tip. This also went smoothly with no real surprises or major problems. One minor problem was that one of the supplied aileron blanks did not have a well shaped rounded leading edge – a few minutes with a long sanding bar took care of that.

20140817_220958035_iOS20140817_221024121_iOS

Next up is to start in on the fuselage, but I will need to order my motor so that I can properly drill the firewall first.

New Project – FT Viggen

It’s been a while since I last posted. Summer has been busy but I have found time to get out flying when I can. Like last summer, I got sidetracked with a scratch-build foamy EDF. This time I, went with an established design and put together an FT Viggen. I didn’t bother with documenting the build process at all since there is a great build video on the Flite Test site, and I just followed it along step by step.My only deviation from the FT build was to add a 1×2 mm carbon fiber wing spar. I re-used the fan and all of the electronics from my original (failed) Fan Trainer project, and I must say that I am pretty happy with end results.

I really enjoyed the build process. I transferred the downloaded plans onto the Dollar Tree foam boards by taping the plans down to the board, then pushing a pin through the plans at each corner, or intersection point. I then used a pencil and a straight edge to lightly “connect the dots”. Working with hot glue and foam may not be quite a s rewarding as a full on balsa build, but it fast, cheap, and surprisingly strong. Overall, I can’t argue with the results.

20140707_163827681_iOS

I maidened it a few weeks back, and I must say that I was quite impressed with how stable she was. The guys at Flite Test did a great job with the design! Just a gentle underhand toss with the throttle at about 75% and she flew away and got right on step. She is very sensitive to aileron input and I kept looking for rudder while (i.e.; I’d move the rudder stick, but of course, since there is no moveable rudder so nothing would happen – duh). I may try to add a rudder (or just build another with one).

I did run into one problem and learned a good lesson about battery charging. In particular, that I learned that I need to be mindful of the power supply power/current capacity when charging.

I am using a 4s 3700 mAh batteries (slightly larger than the recommendation of 3300 mAh, but what I had available already). The last time I used these batteries was in my original Hanger 9 Alpha Trainer a few years back. Since then, I bought a new battery charger that allow supports much higher charging rates. While field charging the batteries using my Duracell Powerpack, the charger died about half way through the cycle. At first I was quite certain that my charger had crapped out (I have a Hyperion 1420i charger and they have a reputation for early failure). Fortunately, when I got home, I discovered that the 12V cigarette lighter pulg-to-banana plug adapter that I was using had a blown its 10 amp fuse (I didn’t even know it had a fuse!).

A little math shows the problem:

  1. Battery Voltage (3.7 per cell empty, but  4+ volts per cell charged):  4 x 4v = 16v
  2. Out power to battery:  16 x 7.4 = 118.4 watts
  3. Input current required at 12v (assuming 100% charger efficiency):  118.4 / 12 = 9.9 amp

Knowing that the charger is not 100% efficient, it is pretty easy to see why the 10 am fuse blew. Overall, a cheap lesson. But, given the reputation of the Hyperion 1420i (now discontinued), I may want to think about picking up a new charger before next year’s flying season.