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.

DT Stab

I am providing the link to NFFS provisional rules for e20. Basically the airplane is limited to 20” wingspan, direct drive brushed motor and 30 grams minimum weight. My airplane weight slightly over 31 grams which I thought was good for a first build.      page 10 E20 Provisional Rules
Bill Kuhl

Related Links  - Sky Demon kit on BMJR website   2.5 gram Motor/DT unit  Programming Box  About Floyd Richards  EZE Dope Video

20 Second Video of Timer / DT

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