The free plan, published in RCM&E in June 2003, uses an O.S.15FP
i.c. motor, but I looked at this with the idea of an alternative
to the Lazy Bee - and also because I had finally re-kitted my
Twinstar beyond economic repair. Being a skint balsa basher and
not having developed the ability to shed an arm and leg for mouldy,
sorry moulded, kits and then regrow said limbs before the weekend,
I committed myself to looking at conversion from i.c to electric.
The finished model came out at just over two pounds AUW with an
8 cell 1100mah battery on board. Here's how......
A quick chat with Jim Ruffell one Saturday brought forth the idea of 1/32" sheet for the formers. Make a former from the first piece then cross grain the second, making a kind of plywood. Lightness being the key to E-lectric, there's more holes than Gruyere in the formers. I had to be careful cutting F3, so that I left enough wood for the undercarriage. I didn't want to cut in around the undercart when covering, so I made up the wire to my specs, saving 7g in the process, and split it at the apex. I soldered a small piece of brass tube to one cut end and after covering fed the wire through the holes I had drilled previously in line with the position shown on the plan. I soldered the other cut end in the tube and sewed the lot to the former, epoxying the whole lot as the magazine write-up instructs.
As the Mamselle is a vintage looking model, there isn't a lot of front end to her. This made battery location and selection interesting for me as a confirmed, but novice B.B. (balsa basher). In the end a sloping tray from low in F2 to high in F3 (above undercarriage) worked. I can get 7 or 8 x 1100mah or 7 x 2100mah packs in with reasonable ease, though the 8 x 1100mah seems perfectly adequate.
Mounting the Permax 480 motor, fitted with the MPJ 3.33:1 gearbox was easyish. I had just bought another mag featuring an electric vintage model and decided to borrow the main part of the motor mounting system. It is basically a piece of ply with a cut-out slightly smaller than the motor diameter. Cable ties pass through holes along the edges of the cut-out to wrap and hold the motor. In principle it worked, but I must remember that liteply won't take the strain if the plane noses over on landing.
The MPJ inline gearbox
(part no.8051) also has tapped holes in a flange at the front
edge. This allows me to attach the recycled Asda pot noodle pot
which was now my cowl after some clever cutting (although in retrospect,
that was unnecessary).
So, if you've skipped on looking for the flying bit, here it is.....
The first flight on Saturday 2nd August was a last minute thing as no-one was about and I wanted at least one good pre-flight photo. A call to Trevor, who said to be quick as he was going out for midday.
I arrived at Trevor's just before 11.00hrs and we got the piccies done, which may be on the club's gallery by now (Not until I've finished the Newsletter! - Ed). Fawcetts field was blowing south to south east quite lightly and, picking our spot on the raised section of field we (Trevor), started range and flying surface checks of the model.
Range checks were o.k. but a warp (wash out in fact) had developed in the port wing - I'm sure it wasn't there before! - too much to take out without proper equipment. Trevor decided to fly anyway, suggesting that turns to the left would be far easier than to the right. I had fitted a 10x7 APCe propeller, and the Mamselle leapt (it seemed to me), rapidly skyward after 2-21/2 mtrs.
After trimming out, and several circuits later, Trevor let me play. First flight was eight or so minutes, mostly on half power, but some time with power off while into wind. Power off and on a good day with a bit of a thermal I think she'll do well. That Saturday into wind she kept her air well with what looked like a reasonably shallow glide.
I found the Mamselle to be the "prop-able" model I should have had 18 months ago before the Twinstar (not that I regret the Twinstar). A sized-up free flight model should have the same stable characteristics as its smaller counterpart. The Mam' seemed that way.
Power on halfway kept the plane in the air happily and, apart from struggling with right turns, it seemed happy doing those basic manoeuvres. Full power seemed to pull the model ever more skywards, though not quite to the point of ballooning.
Having said that, the landing was not all I had hoped. I don't hold anyone but myself to blame as since the Mamselle has nosed over on landing three times now, I think the shown CofG is slightly too far forwards. The broken motor mounting plate has been replaced with 3mm birch ply and longer diagonal braces added. I also put a cross brace in between the diagonals and joined to the underside of the motor plate. Thanks for that idea Trevor.
Second and third flights took place at Kings park on Friday August 8th, as witnessed by Bryan Richards, whose comments were very pleasing to the ear. I had put an equal amount of washout into the starboard wing before this outing but still hadn't moved that CofG. I did find though that if I flared well at about 3ft then the nose pulled up enough to lessen the nosing. Both flights were on the one pack of 8x1100mah, 3mins each. After the first flight I had propped down to a 10x5 and it doesn't seem to have hugely affected things, maybe slightly slower climb after RoG. Didn't I mention that, she'll rise off ground quite happily on 21/4" foam wheels, I'm pleased to say.
I still had to get some more elevator authority, and finish off the front end with cowl and spinner. The cowl fitted and a bright red spinner (why are they never the colour you need?), I suppose a nice shiny spun alloy job would have looked better, but...
I didn't mention covering, did I. I covered the main part of the open structure in transparent Solarfilm and for decoration used that red metallic Solarfilm and trim from the fan trainer. Why...? Well, I was too late to put the part-built model in the Construction & Finish comp before the Summer break and hoped to sneak in at the last minute in September, with the generally open build and clear film making it easy to check out the structure and finish at the same time. The clear film also proved beneficial at the recent scout fete as the Mamselle was possibly the only film-covered model that didn't look too bothered sitting in the sun.
A Footnote:
The Mamselle has flown without incident, almost a dozen times
now, in a range of winds, each flight easier than the last. Changes
have been made to increase the elevator by adding 1/32" sheet
to the top and bottom of the original elevator, which seems to
have had a positive effect on pitch control. Also changed is the
c of g, which resulted in more ballooning when power is applied.
The thrustline has been altered to give right thrust and downthrust,
the the aim of controlling the pitch up under power and improving
the right turn response. In respect of the latter, I think I will
have to attach a longer arm to the servo to increase the rudder
movement. The main reason for moving the c of g though was to
stop the nose over on landing but bending the undercarriage forward
has lessened this, along with improved flaring just prior to touchdown.
What I haven't covered yet is the radio gear. Small and light is ideal, but as I've already saved a pound in weight, what the heck, you could get away with standard servos, any suitable speed controller and a standard 4 or 5 channel receiver. In fact, I used a 5 channel Hitec receiver, a pair of Supertec naro max servos (mounted on one fixed rail and one moveable rail to facilitate servo changes) and a 40 amp Ripmax Xtra speed controller - which is probably twice the current that I need.
I know the Mamselle is no Cougar and it may be lacking in some respects against the Lazy Bee, but I am so pleased with this model that I may have to build another with a few alterations, including a larger rudder, set further forwards to allow more elevator movement, and maybe eventually an aileron wing.
Some people would have you believe that there is something
wrong with you if you enjoy building from plans. I think they
are miffed because balsa bashers are taking bread from their table,
or crisps from their lunch box....