Scratchbuilt JN-4D (Jenny)

I have just recently finished a scratchbuild of a Curtis Jenny based on a set of plans by 81zapper.

I've always been a fan of Curtis's WWI training aircraft, the JN-4D Jenny. It has been said that surplus Jennies and J-1's were essentially the start of civil aviation. My first stick built model was of a Jenny, but I'd put so much work into it I could never bring myself to fly it. So, when I saw an article on a foamboard Jenny I knew I had to build one that I would actually fly. Being such a fan of this historic biplane I wanted to add a little more scale authenticity to my build than Zapper's plans showed.

Initailly I was hoping to make this a swappable, but I forgot to check measurements on the plans before cutting and a powerpod is just a smidge too long. Sadly, I didn't think to take any in progress shots. The basic construction is the same as Zapper's near as I can tell with a few exceptions. Where his build had three bulkheads and an open A-style fold body I used B-style fold to gain a little more room for electronics. His plans showed the sides with the full profile of the fuselage cut into them. I elected to cut these down for slightly more scale height. I then pieced in a forward and center top panel to reduce any possible torquing of the frame.

Since most WWI aircraft were designed for overly heavy powerplants they often hand snubbed noses which, when building in scale, makes it rather difficult to get enough weight forward and counteract tail weight. Because of this I elected to move my servos from the tail to a servo tray just forward of the Cockpits. Semi-circular formers were then glued in as pushrod guides and to shape the posterboard which would make up the top skin of the fuselage. The first two sets of formers were doubled just aft of the motor mount to allow for a removable hatch to be cut in. The firewall was set back about 3/4" to help hide the motor within the cowl.

Wing struts are round chopsticks cut to 5 1/2" and pierced through the outer foam layer both top and bottom. Aileron servos were recessed into the underside of the wing, but the chord thickness wasn't enough to mount them completely within the wing like on the FT Spitfire.

The biggest thing Zapper's Jenny didn't have that I wanted on mine was a set of landing gear. I broke too many props belly landing my FT Flyer withough gear, I didn't want this plane to suffer the same fate. The landing struts are, again, sections of chopsticks with 1/16" ply gussets on the lower end inside and out, assembled with hot glue. The axle is coat hanger, strapped on above the gussets with rubber bands. This adds some amount of spring to the gear allows the axle to free-float and absorbs landing stresses without transmitting them to the plane. (For a good expamle of why sprung gear is important, look up the crash of the Phoenix in 1964)

My Jenny is, near as I can tell, ready to maiden. Hopefully she'll be in the air in the next few days and if I'm lucky and good she'll come back down in one piece. Flying wires and windscreens may come.

EDIT: 10/25/14

Finally maidened today! Yesterday's attempt did not go so well. I overcontrolled and panicked resulting in the following:

After a quick stint with the glue gun last night she was patched up and ready to try again. Strong winds were forecast for this afternoon, so I got up early(ish) and headed down to the park. I opted for a hand launch this time, put it to a 2/3 throttle and let her go just as the wind was kicking up. She flew beautifully. The wind started gusting to 15-20 so I brought her in for a landing, the elastics in the gear weren't strong enough so the gear struts dug in and ripped off. It was a short flight, maybe all of five minutes, but she handles well on low rates and has more than enough power. I'm very pleased the CG was correct and throws acceptable.

For those interested, here are the specs.

Overall weight without battery: 615 grams

Wingspan: 35 inches

Length overall: 35 inches

Wing area: ~315 square inches

Motor: HobbyKing Donkey ST3007-1100kv

ESC: Hobby King 30A ESC

Servos: HXT 500s

Prop: 8x6 Slowfly

Battery: Turnigy 2200 3 cell