Updating an Old Classic
A
superb, stable and easy to fly big foamie model in desperate need of a "freshen up" ......
but if it ain't broke then why bother to fix it you may ask?
Well, this line of Robbe kits date back to the early 1990`s when power options were limited to four Speed 400, 6 volt brushed motors, encouraged to rotate by an 8 cell Nicad / Nimh battery pack. Performance was sedate, but quite respectable with this set up.
Nowadays, all our planes are powered by Lipo battery packs, so I replaced the Nimh`s with a 3s Lipo pack initially, but as you can imagine those wee 6 volt motors couldn't handle the current and self destructed in no time at all. Aha I thought, if I stick in a 2s Lipo pack, the motors should cope OK with that ....... and indeed they did ........ but power in general and for hand launches in particular had now become pretty marginal. If you think back to the Nimh packs the motors at that time were running off 9.6 volts, and now with a 2s Lipo the voltage had dropped to 7.4. Hence the lack of umph!
So my options were to revert back to the old battery technology or go "brushless" and standardise with 3s Lipos, which is pretty much what all my fleet fly on. Seemed like a no brainer to me! The model was looking a bit scruffy anyway, so whilst I have to make modifications I might as well give it a fresh colour scheme too.
The first job was to remove the old motors and fit these new units. The old Sp 400`s could only generate about 250 watts in total and these brushless units should produce 200 watts each, so hand launches will be a tad more comfortable. Additional wiring and modifications to the cowls were required to house the individual ESC`s. Much head scratching and the odd glass of wine helped overcome the difficulties.
component parts completed
During removal of all the old covering film, it was evident that the foam surface was in poor condition, but being a lazy bugger, I only did the minimum of "filling" before covering the wings and fuz with brown paper & white glue. Not a very pretty job really, but I was losing interest so started applying the emulsion paint anyway. Brush marks were a real problem (not one I've encountered before) which was almost entirely cured by mixing a water-based paint conditioner in with the emulsion. It slightly prolongs the drying time, but the paint self levels better with this stuff in it! It's still nae an affa bonnie job, but once in the air I doubt you will notice.
The last job was to add a few panel lines, windows, and the Wideroe logo ...... all were cut out of Solartrim. The whole model was given a single coat of acrylic varnish.
That's the good bit, but the bad news ........ in order to get the CG back to it's original location the 3s Lipo needed to move forward 1.5 inches. Not a problem as there's plenty of space up front, but when I weighed the completed model, it had gained 11 ozs! Well, I was so shocked I nearly spilled my glass of wine. The new motors & ESCs combined were only a couple of ounces more than old Sp 400`s, so all the additional weight must have come from the brown paper and paint job. Nothing much I can do about it now though.
Will it fly? Most probably, but I'm just hoping it won't have totally ruined it`s excellent flying properties ....... time will tell.
Derek Robertson
The Dash had an amazing sound with 4 brushless motors running,
hopefully the conversion will keep the same tone.
Photos Derek Robertson, Mike Pirie & friends
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