Scienceguyorg Ramblings: Sky Demon e20 Build Report

Wednesday, December 7, 2016

Sky Demon e20 Build Report

My interest in the e20 electric free flight event came about mainly because I am looking for free flight models that will fly from smaller flying sites. With electronic DT (dethermalizer) it is possible to accurately set the time that the DT will actuate. I have flown my e36 free flights from pretty small fields by setting the DT time to be short. It was my thought also that a model that only weighs around 30 grams will survive some pretty hard landings without damage.

BMJR Sky Demon

Before selecting an airplane I purchased the electric components from Bob Selman at BSD Micro, I knew of Bob from his tiny micro RC components and our mutual friend Floy Richards who passed away several years ago. I purchased a 2.5 gram unit that controls the motor run length and the DT time, the actuator for DT is a tiny servo that moves in one direction. I built a small pivot arm that one end goes under the servo rod that moves and the other end connects to DT line. With my purchase I also selected the programming box, a Parkzone motor, a propeller, and one battery. From flying tiny RTF RC planes I have many chargers.

BSD Micro Motot/DT Unit

BSD Micro Programmer

For my first e20 airplane I decided I would build a balsa kit airplane and selected the Sky Demon from BMJR. This plane looks like it could be a tiny RC plane because it has a full width fuselage; my thought was if I got tired of flying it as an e20 I could install tiny RC gear in the plane. I installed the motor/DT unit on the outside of the plane with a couple of screws so it could be easily removed.

Motor, Propeller and Battery

EZE Dope

Building the Sky Demon was easy although some of the pieces were rather small and I had to use a tweezers to place them. I covered with Esaki tissue but tried a new to me product EZE Dope to seal the tissue, it doesn’t give off the odor that clear dope I normally use. It did pull the wingtips up when it tightened up giving them washout that I thought might be a good thing. The plane has a left turn under power and glide so I think one wingtip has too much washout.

Sky Demon in Flight

Sky Demon DT in Progress

Last weekend the wind was rather low although it was only 32 degrees F but I decided that was warm enough for test flights. The motor run was set to only 4 seconds and the DT was rather short but long enough to observe the glide. After launch the plane wanted to climb rather steep and to the left, so I launched banked to the right. The firewall of the motor was taped on so I could adjust it later, since then I gave it more downthrust and some right thrust.

Wing and Stab

Stringers in Rear Rather Small

Many flights were made; I am guessing probably around 15 although all were rather short. The plane appeared to fly in a stable manner although the transition from power to glide was not perfect. This will give me something to work on when I fly it again. The DT worked perfectly in those flights although sometimes it was only a couple of feet above the ground on DT.