A1-D “Juliet II” Prototype

This model is all about learning and experimenting with new things. It is a small electric-powered aerobatic plane, with extensive use of composites materials.

An unexpected project:

Since I started with this hobby, I spent a lot of time researching, window shopping at meeting and expositions. Sometimes simply planning what would the next plane look like, or how it would have had to perform. The A1-D model instead, was completely unforeseen. I wanted to know if I would have been able to make parts for another project with new materials, and I wanted to try these materials first hand. After a few tests, I had the idea of collecting all the possible upgrades to the Juliet and merge them into a fresh design, all while using the new materials and techniques.

A new Juliet, the A1-D

The Juliet II prototype is more than just an evolution. Some ideas that I put into the design were in fact coming from the A1-C experience, but I started to draw from a blank sheet. As a matter of facts, the only parts which are really in common between the two planes are the ribs of the wing.

Although the external dimensions are still similar, the A1-D fuselage is almost twice as wide. This allows for easy access to the battery and all the components, even for my big clumsy hands. Having started the drawings with the electric propulsion in mind, almost half of the fuselage opens up with huge hatch/canopy. It still weights almost the same but with a better weights distribuition, while being several times more rigid.

new, bigger surfaces

Given that a lighter wing loading helps making a better flying model, I considered my options. Reducing the weight sensibly wasn’t a realistic achievement. Besides, the pure weight reduction was not the purpose of this plane. I already knew I was going to over dimension a lot of structural parts just to test how to make them properly, so even with better perfong materials used, my estimate was between the same weight of the A1-C2 and something a little above that figure. The only other way to reduce the wing loading was then to increase the surface. That is why I found a new wing structure, increasing the wingspan by a few centimeters, but the main gain in surface is given by the dramatic increase in the ailerons size. This is something I could actually still retrofit on the A1-C one day, depending on how well it will work on the Juliet II.

Trying new solutions till the end, the New tail

With the upgrades on the wing, I had to modify the tail surfaces as well, not only their dimensions, but also the position is now revised to improve the behaviour in the aerobatic flight. the stabilizer got even smaller than the A1-C’s, but the total surface is actually bigger due to huge elevators.

The rudder is another difference between the two projects. the traditional setup in the first Juliet gives space to a new, bigger and fully movable surface in the A1-D. This is not unheard on 3D planes, but is certainly new for us, and something to test carefully in the first flights. As a contingency, a normal two-pieces rudder can be retrofitted in case of need.

Powering the little beast

Testing an Hacker motor in place of the final Turnigy one

One of the reasons why I kept the dimensions close to those of the Juliet, was to allow an engine transplant in case I had crashed the A1-C before completing the new plane. The 400w on the cyclon motor are not extreme for a 1100gr airframe, but still enough to do decent aerobatics. With the plane almost complete and the Juliet still happily surviving, i went shopping for a new motor. Initially I wanted to use an Hacker motor I had, but later switched it to a Turnigy unit (more of it Here).

The Future Developements

With the interest that this prototype created and a few more things to try out for future projects, I started to think about a new version of the model, thought to be made using normal plywood and balsa. It looked like a small task, a simple matter of adjusting the thickness of the parts to the one required by the less fancy materials. But as usual I managed to complicate my life, this time by adding all the modifications inspired by the flights of the first prototype . But this is another story already, you can read all about it on the Juliet2 page.