Christchurch and District Model Flying Club
 

An electric bubble dancer

By clive spencer

I was pondering the idea of electrifying the BD after the club’s last Friday night thermal meeting. It seemed a shame to not use the model all through the winter, & with the new height limiting regs becoming a real success, the idea became more appealing. I was tempted to modify the existing fuz but on trying to get a battery into the space under the wing, I soon realised that this was not going to happen. The other problem was fitting a motor into the existing nose cone, which would have entailed cutting off the nose & making a new removable one, an idea which did not appeal. I then dropped the whole plan & concentrated on a refurbishment programme, read repair, for the winter. This state of affairs lasted until, whilst walking my dog on Hengistbury head, I came across an abandoned carbon fishing rod bottom half, well it looked abandoned to me? It also looked like a BD tail boom. Thus armed, a new plan was hatched, which included a new electric fuzz to be used with the existing wings.

 After cutting the boom to length & cleaning it up I made a few measurements & found that it was about 6 mm larger in diameter than the original & more importantly, was 2 ozs heavier. This does not have any real affect on a 3.2m thermal soarer but it does on the CG. I also had to do some calculations using the various weights of the motor, prop, esc, receiver & battery to try to effect a balance as near to possible to the existing CG. The result was that the servos & receiver would have to go under the wing seat & the battery just behind the motor with the esc under the battery. This resulted in a deeper, squarer fuz at the front than the original. I won’t bore you with the details of how I made this one as it follows the same method outlined in the March 2009 edition of Sloping Off. I also had to make new a stabilizer fin & rudder.

 Because the boom was a larger diameter than the original, I could not purchase a stabilizer mount, I used an Avia boom & mount on the original BD at the exorbitant price of £26. This was a big worry as, no mount no model. The only thing I could do was make my own but how? The answer came here, http://www.charlesriverrc.org/articles/bubbledancer/PDFs/bd_vmount.pdf.

The same site of the original BD plans. I had to modify the originals slightly to fit the oversize tail boom. The two jigs where copied from the plan & the radius changed to suit the diameter of the fishing rod. I also incorporated a brass tube for the pivot point, as I did not like the existing design, which I thought a little weak. I also used straight 2.5 Oz glass cloth, as I had no carbon fibre to hand.

 I now have a new BD Electric fuz for the price of two HS 81 servos. The motor & ESC were removed from my existing Reichard Sprinter model. The battery is a 4000 aHr three cell Li-Po. Because I’m a bit of a tight wad I covered the stab & fin with blue transparent Profilm which I had left over from another model, I decision that I now regret as the blue does not go with the wing colouring, but hey ho, I may change it when the mood takes me. The fuzz is painted with car plan red acrylic as the original BD; I had that left over as well.

The first flights took place at Howard’s flying site with Trevor providing the grunt & Mike on the camera. I did not quite know what to expect having transferred the settings from the glider version to the new model, with the exception of the spoiler, which I put on a slider control on the tranny. As it happened, the launch was uneventful with quite a powerful climb out. The model behaved exactly like the glider version being very responsive & easy to fly. All was well until I decided to try the spoilers out? Luckily, I was at the requisite three mistakes high. Have you ever seen a three-metre glider do a perfect bunt? You have guessed it, I had inadvertently reversed the stabiliser compensation for the spoiler. So instead of up elevator & got down. That is an embarrassing beginner’s mistake, which could have cost me a year’s work, & two models. It is a sharp lesson to double check the control movements before flying & not take anything for granted.

back to Contents

[Home] [Chairman's Chatter] [Editorial] [Terry Sullivan] [Goodbye!] [Fly Diary] [Wessex League] [Bubble dancer E] [DLG] [Auction night] [C&F 2010] [Sketching] [Mustang]