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Tuesday, September 25, 2007

Mini-Phoenix Rebuild

Looks like all the regular bloggers have either all gone away for the long weekend or have been too busy in their workshops to write.

I've been very busy finishing off a rebuild of my Mini-Phoenix. So, to keep some variety on the blog I'll write a short story of the history of this little electric model.

Bought from the local hobby shop with a Speed 400 motor, added a Skyborne 35A controller and cheapie 2 cell Lipo, installed the radio, set up some flap/aileron mix and it was flying. Not the greatest flyer with it's silly inboard ailerons but good enough to get in some relaxing late afternoon stick time. But why are we modellers are never happy with a reasonably flying model - wouldn't a little more power just be great? A quick upgrade to a 3 cell Lipo gave a much better climb rate ... but what was that ... could it be a smoke trail? Managed to land very quickly and found the battery pack bloated to about twice it's normal size, one cell burst, a bad chemical smell and everything near the battery very hot! Lucky escape and I went home to clean up and analyze. That little motor could never draw enough to cook that battery, the controller was more than enough for the setup, so what was wrong? Electric gurus on the chat group pointed to the controller not being set for the extra cell, causing the Lipo to go way below it's allowable voltage.

Problem solved but the Natal Nats were two weeks away and it was time to move up a notch and have a bash at a brushless motor setup! Picked up an old Walkera heli inrunner that fitted without any modifications to the mount, had a 10A controller lying around and invested in some good FlightPower 2 cell Lipos. Added a mean little Cam 8x6 prop and blew all the indoor plants away in the lounge bench testing the rig.

Above left: At the Nationals - round 1 and ready to go. Note the determination and confidence on that face. Above right: Great climbout for first and final flight. Climbed to a spec in a few seconds and then ... nothing. No control and straight down she came, filtering throught the pine trees before planting into the hard Natal soil.

Problem was obviously (in hindsight) the little 10A controller. It blew itself to pieces with tiny components and solder splattered all over the inside of the fuselage. Structural damage was not too bad but I was never happy with the design and decided to redesign and rebuild - of course it would have to be balsa open structure and the purple finish!

It has taken a few months but now nearing completion as the following photographs show:

Wing underside now covered - found some lovely deep yellow SolarFilm and mixed it with a bright purple - sure to brighten up the sky on a dull day. Sexy F3J wing and tailplane shape evident.

Decided to go almost full house on the wing moving surfaces. And why not with the small and reasonably priced servos available now? One servo driving both flaps from the centre and a servo for each outboard aileron.

Thoroughly enjoyed building the wing joiner system. Three piece wing has bolt down flat centre section with slight dihedral on plug in tips. Pine dihedral joiners and aileron servo mounted ready for connecting rod and then top wing covering.

T-tail stabiliser with control horn to be concealed in rudder post - still going to be a bit of fiddling to get that lot to work in such a small space. Oh, and adding a moving rudder as well (small servos and all that ...)

Still a bit of work to be done on that fuselage but all burn marks will have to stay. Wing mounting area cut down and refilled to fit new wing section and extra layer of cloth added ouside behind the wing where fractured from the crash.

So far so good. Will post more when finished and ready to fly ...

1 comment:

Anonymous said...

Dear Derek,
I like what you have done so far, I am busy with my first electric so have lots to learn,rather nerveous about the firewoks potential though, there is still something rewarding about
balsa bashing though.