building the Sig Kit
The editor handed me the Sig box and looked for a reaction: “This’ll slow you down,” he said. Regular readers may have noticed that I’ve been pretty busy since joining the RCM&E team at the start of the year. Hardly a month goes by without a product review of some sort from yours truly. Of course, it’s not particularly difficult since the choice of models passing through the office here is, as you’d expect, pretty extensive and whilst most are posted out to our review team, one or two stay behind for us editors to play with.
Most boxes don’t hang around for long but after a while I realised that one in particular was starting to collect dust. It was a traditional kit, the Sig Smith Mini Plane - a kit for which a home couldn’t seem to be found.
I’ve built from traditional kits and plans in the past yet the last year or so has seen my skill-set very much stuck in the ARTF lane. This bothers me from time to time; in much the same way as I often feel sloth-like when I haven’t gone out and exercised on my push-bike, I sometimes feel guilty that my building skills have become dormant. Screwing together an endless line of ARTFs doesn’t really satisfy and after a while the ‘Chinese takeaway’ metaphor seems appropriate.
Anyway, since the kit was in the office, every so often I found myself lifting its dusty lid for a peek. Kits are kits after all and it’s always nice to see what’s inside. The weeks passed and I kept lifting the lid, unfolding the plan and studying the design. I’d never built, owned or flown a biplane but I started to take a liking to the Mini Plane. It was clearly straightforward in terms of construction, although there was no hiding the fact that two wings are two wings and I was unsure if I could commit to the amount of time the project clearly required. Sad as it may seem I’d actually forgotten how long it really takes to finish a model like this, primarily because my modelling reference points had receded into the distant past. Finally, fed-up with my indecision, Graham placed the kit in my in-tray!
SMITH MINI PLANE
Introduced by Sig in the mid ‘70s and still in production, the Mini Plane struggles to hide its vintage. It is, quite simply, a superb example of a ‘70s US R/C kit. It has some charm though, and brought back memories of watching father build his Sig Piper Cub, some thirty years ago! At the time, I recall, I used to assemble my Airfix kits alongside his huge building board.
So, what’s in the box? Well, there’s a lot of wood! In fact, at first I though they must have mistakenly squeezed in two kits of material, such was the amount of strip, ply and balsa in evidence. Two large plan sheets, some wire and hardware, along with cowl and spat pieces made up the rest. But oh the wood! The wood! There seemed to be enough to build a half scale version, let alone this diminutive 44” example.
It’s also interesting to note that, throughout the build, I kept popping into my local model shop for bits, then back for more, and then some more! Actually, I lost count of the number of times. The proprietor said I reminded him of the good old pre-ARTF days, when customers were always popping in for supplies and leaving with more than they’d intended to buy. Very much the good old days as far as he was concerned!
What exactly is a Mini Plane, then? In short, we’re talking 1950s US home-built types here. With a wingspan of just 17’, you can see that the plane lives up to its name. Frank Smith designed the Mini’ to be a cheap, easy-to-build and easy-to-fly everyman’s transport. His prototype first flew in 1958 and home builders seem to fit the aircraft with a 120hp engine which gives it a top speed of around 100 - 120mph. It’s pretty aerobatic, although I’ve read one account that mentions bathtub flight tendencies if the engine happens to cut.
Interestingly, this particular kit has been a steady seller since it was introduced and even now you’ll find a small yet determined group of builders hard at it discussing all things Mini Plane on the internet forums.
In some ways the shape is a little unfashionable. After all, aerobatic models these days seem to feature lots of straight lines, and snappy names like Ultimate, Extra or Edge. Yet, before these, and before the letters A, R, T and F had been strung together, it was aircraft such as this that R/C modellers aspired to build and fly.
The instruction manual is very good, typical of its period, which isn’t a surprise, yet I have to say that it can still kick sand in the face of some ‘manuals’ I’ve recently encountered. It works well through the construction stages, perhaps less so in the finishing steps but I rarely referred to it once the woodwork was complete.
The project seemed to pass through three stages - build, cover and the final engineering.
It’s a misconception that the building segment is the longest stage, or at least it is for this model. It took me just a month of evenings and rainy weekends to build the basic airframe.
By today’s ARTF standards the structure is over-engineered, but that’s not a fault and translates into a model that will last a very long time. The wings are just so incredibly strong, in fact they feel as if they’d fly through tree branches without a scratch; the fuselage likewise.
Construction is entirely traditional in every respect, indeed the fuselage is a simple square, two-sided flat-frame job with stringers, cross members and sheeting at the nose. The wings are simple main-spar, ribs, sheeting and cap-strip affairs, whilst the tail feathers are just flat frames.
Although the kit suggests using balsa pushrods to actuate the tail feathers, I much prefer snakes in sport models so I built these into the fuselage early on whilst adding supports along their length to prevent slop.
Like the full-size, the model has ailerons on the lower wing, although I decided to mount a mini servo alongside each, so negating the traditional centre servo in an attempt to free up some fuselage space and improve control response. As such, I sheeted over the centre servo location and mounted servo bearers in each wing half for the Hitec (metal gear) 81s.
The great thing about real building is that the model can be engineered to suit particular requirements and it also means that mistakes can be corrected or hidden! For some strange reason I sheeted the upper front fuselage section with 1/16 and not 1/8 as directed. I had to run smaller stringers along the fuselage to blend in better and in this respect had to use strip wood, as thinner balsa stringers wouldn’t have been strong enough - hopefully it doesn’t show!
It’s funny how some of the stages that I’d assumed would be dreadful turned out to be pretty easy. The pre-bent undercarriage (u/c) wire just needed binding and soldering, so that was pretty straight forward. Likewise the cabane supports where the fuselage mounting arrangement was concerned, although cladding the struts themselves was a different matter, as you’ll see.
There are some very attractive Mini Plane schemes out there, although I stuck with the version adopted for Glen Sig’s own aeroplane and, unsurprisingly, the version that Sig Manufacturing have chosen to base their kit on. I used Pro-film and wished I’d used it years ago - wonderful stuff. Why was I the last to find out?
The red sunburst effect was added using Pro-trim, first by cutting paper templates by eye, then using these to cut the film. Anyway, it seemed to have got slightly easier by the time I’d finished. Incidentally, the excellent decals you see on the model are included in the box and, as I’m sure you’ll agree, they add a very nice touch.
My pilot was a 1/5 scale chap from the J. Perkins range. He may look big but the Mini Plane is a very small aircraft in reality, so he’s actually a nice scale fit. A few instruments in the cockpit and a nice shiny spinner finish the model off but there’s plenty of scope to go to town and add other detail if you’re so inclined. I’d intended my model to sit squarely in the sport-scale category so the result you see is just about ‘there’ for me, although I may add a few small details this winter.
Since this one’s a biplane it goes without saying that there’s some struttery to complete, this being an area where one of the construction steps seems unsatisfactory. In essence it’s the method of cladding the struts that seems too workman-like. Now then, Sig recommend cladding each strut in balsa which should be shaped to profile. This, of course, means cutting a groove in a thin strip of wood, sticking it over a strut wire and then using filler to hide the gaps. I clad the cabane struts in this way but since I wasn’t happy with the finished appearance I chose a different approach for the interplanes. Here, quite simply, I glued a hardwood strip behind each piano wire strut, then wrapped Solartrim around both, leaving a strong yet attractive strut.
The spat mounting arrangement is another area where, again, Sig leave the builder to get on with it. The instructions refer to an after-market fixing method, one that I personally believe should have been included in the kit. Having said that, and whilst I normally prefer the appearance of spats, I have to say that in my opinion, the Mini Plane looks better without them, more muscular, somehow. Interestingly, most full-size variants don’t seem to have them either, if my internet picture searches are anything to go by.
The cowl is a two-piece affair that was far easier to make than a first glance might suggest. I used the recommended method of running thinners down the join to weld the halves together, cut the holes, then sprayed the whole with grey primer followed by paint and fuel proofer.
Back in the ‘70s Sig’s prototype was flown with an Enya .45 two-stroke and although a four-stroke would sound nice, I used an SC .46 that I had sitting idle. Bolted to this, a Just Engines Pitts style muffler proved less obtrusive than the usual torpedo type. As for the fuel tank bay, this is very large, in fact it’s big enough for a 10 - 14oz tank which means that long flight times should be a reality.
My fuselage houses Hitec mini servos for rudder and elevator (metal gear version on the elevator) and with all the gear installed she balanced right where she should, on the lower wing leading edge.
With all said and done the model took three months to complete, at the end of which I was both very satisfied, and in some ways glad it was all over and glad to be moving on to new projects. Strangely, like a proud father, I kept stealing back to my workshop just to stand and stare at her. I know it sounds silly but I couldn’t quite believe I’d built the thing. Of course, there were some sections I wished I’d done better but more than anything, she was all my own work.
I’m not immune to first flight nerves but I wasn’t particularly bothered about the Mini Plane’s maiden outing. I’d checked the model over thoroughly, she balanced where she should, the control throws were as stated on the plan and the motor run-ups and range testing were carried out without incident.
So it was that she tore along the strip and with a little right rudder to keep her straight, lifted off following a modest input of elevator. Some aircraft just feel ‘right’ as soon as they leave the ground and the Mini Plane was one of them. This model was the first bipe I’d flown but I couldn’t really say that the biplane traits I’d heard of gave me anything to worry about, in fact she felt very much like a low-wing sports aerobat.
The starting roll rate was a little tame but nothing that a rate adjustment wouldn’t cure and power from the .46 meant that the vertical climb performance was very impressive indeed.
I gained some height from which to check the slow speed handling and on completion of the test, found this to be the biggest surprise. Despite the acceptable figure produced by my wing loading calculation, I’d gained the impression that the model was a little heavy and anticipated I’d need to exercise care at low speed. In reality, I couldn’t have been more wrong. She simply refused to stall, despite my best efforts to provoke a reaction.
The only trait that needed adjustment was the model’s desire to climb. Did I need more engine down-thrust? An adjustment to the wing incidence? Perhaps! Mind you, I did cure the tendency with trim so the problem wasn’t, and hasn’t, been sufficient to spoil flight enjoyment.
Aerobatics are fun, in fact biplane spins and flick-rolls are somehow more animated (must be the extra wing) and the Mini Plane doesn’t disappoint. She looks particularly graceful gyrating around her own length at the top of a climb, whilst inverted flight requires just a little forward pressure on elevator. The Mini Plane looks superb on a fly-by and I don’t mind telling you I could do these all day. Regular aerobatics really do come to life when a model looks as realistic as this.
When it comes to landing the draggy biplane trait is apparent in that she loses quite a bit of height when the power is at idle. I like this and found that she settles herself nicely into a controlled descent, a little throttle adjustment being all that’s needed to see her home. She’s easy to land really, and that’s all there is to it.
THREE MONTHS ON...
Three months from box to flying field. By my standards those were three pretty intense months of building and covering, and whilst there were moments of frustration, most of it was sheer pleasure. I just love her to bits though and more than anything she’s re-affirmed my own confidence in my building abilities. For the first time in many years, I feel quite genuinely proud of something I’ve built.
The kit costs £130, give or take, and when you consider that items such as wheels, a fuel tank, covering materials and a host of other little bits must be purchased separately (my covering materials alone came to £25) then cheap isn’t a word you’d use to describe the route to Mini Plane happiness.
Having said this, and as the Mini Plane has served to remind me, you can’t put a price on building enjoyment and the satisfaction of piloting a model you’ve made yourself. It’s of little surprise that Sig still produce this kit, the model has a heck of lot going for it. The Mini Plane is compact so it can stay in one piece from week to week, it’ll fit in a car boot, it’s full of character, looks highly attractive, is very strong and has great sport / aerobatic flying characteristics.
Name: Smith Mini Plane
Model type: Semi-scale aerobat
Manufactured by: Sig Manufacturing Co. USA
UK distributor: Pegasus Models
Fuselage length: 42˝
All-up weight: 5½ lbs
Wing area: 672 sq. in
Wing loading: 19 - 20oz / sq. ft
Control functions: Aileron, elevator, throttle, rudder
|Sig Smith Mini Plane|
By Terry Godfrey
by Terry Godfrey
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