Back in 1997…

recalls George Stringwell

…when brushless motors were strictly for the wealthy and lipo batteries were just a gleam in the manufacturer's eye, I felt the need for a compact lectric sport aerobatic model to fly at the quite small field that my then club (CHEFS in Cheshire) used. At the time I had just started selling plans of a couple of E400 soaring models I had designed (Sundancer 60 and 74) and so decided to design a model which would be a suitable addition to the plans range. I had the idea of creating a series of small, lightweight, designs which could be flown with inexpensive 6 x AA nicad battery packs and so the first Square Dancer evolved. Actually, it wasn't really the first as the name was selected since the outline of the model, although not it's structure, bore a family resemblance to a 1.5cc powered control-line aerobatic model I had designed back in the early 60's. The model was to be powered by a 6 volt Speed 400 motor driving a 125mm x 110 mm white Gunther plastic airscrew (despite it's "toy" appearance I already knew this was THE prop. for a light fast-flying 400 model) from the aforementioned 6 x 600AA pack.

With a target weight of 14 ounces, the battery pack was clearly going to be a large percentage of the airframe weight, so I elected to split the wing leading edge so it could be accommodated in the ideal position. The smallest servos I had at the time were relatively hefty 14 gram ones, so two only were used, one on aileron and one on the elevator function of the "V" tail. In the event, covered in Esaki tissue over 5 micron mylar, it was half an ounce over target, not too bad. The structure evolved as strictly functional, built in one piece with the fuselage sides slid over the spars after one wing panel was built, followed by building the second wing panel and then inserting fuselage formers to produce an "instant airframe" - just the way we used to build control-line stunt and combat models in fact. The performance amazed me; certainly it didn't have the umpf for sustained vertical, or anything like it, but it was a delight to fly and was capable of all aileron/elevator aerobatics. It needed to be flown smoothly in an "energy conservation" style, rather like an aerobatic slope soarer but, given this, was capable of some extraordinary things for such a low powered model.

I drew up the plan master and it immediately proved popular, but sadly the prototype only lasted a few months as I managed to "run aground" at full chat during a low inverted pass - we've all been there! So happy was I with it that I immediately set to and built not one, but two replacement models. The first was a "V" tail identical to the original, the other had a slight reduction in nose and tail moment and a conventional tail and fin. The biggest change however was the use of two wing mounted micro servos for ailerons which, with the programming features of my Futaba FF8, allowed experimentation with aileron/elevator mixing and flap/aileron mixing. This enhanced control, coupled with a weight reduction to under 14 ounces, extended the aerobatic capability to include such specialities as square inside and outside loops, square horizontal eights and even, with a dive to build up some speed, a top hat. Both these models were terrific performers and I flew them for several years, often having three or four eight-minute flights with each on both Saturday and Sunday each weekend. In the meantime lots of other versions appeared inside and outside the club. One of our "visiting" members, Vic Nightingale, introduced it to his home club in the south and the result is seen in the "stack" of mass-produced airframes in the photo.

Eventually both these models suffered wear and tear and just really wore out, each with well over one hundred flights on the clock.

Not wanting to be without a Square Dancer, I built a fourth model, another "V" tailed one, this time with a QRP Hyper 400 timed motor and an option to use a 7 cell 500AR battery pack when I felt the "need for speed" and this lasted me until it was sold prior to our retirement move to central/south-west France.

Fast forward to 2010…..

….Having finally sorted our little farm house out (LOTS of work) I had the time to do a little building again, which was a good job as some of the models I had brought with me were getting somewhat worn, and most of the others were not suitable for flying in the small field attached to our orchard, although OK at the club site fifteen minutes drive away. There is something nice about being able to decide to fly at a minute's notice and simply pick up a model and stroll up the garden; I had vintage and soaring models, and even a scale 400 size Sopwith Triplane to fly "at home", but decided what I needed was another Square Dancer - so I built two, my fifth and sixth, right. Number 5 is a conventional tailed model, with a QRP 400, BUT, the big difference, using a 1300 MaH 20C 2S lipo pack, which brought the finished weight down to 13 ounces. The other one sports a Towerpro brushless motor and an option of running it on an 8-inch prop and a 2S 1300 pack for 80 watts or a 6-inch prop with a 3S 1000 pack for 130 watts. Both models featured a little judicial carbon fibre reinforcement of the wing roots in view of the expected higher performance. I have not been disappointed with the performance, the 400 model is better with the lipo pack than its ancestors were with either 6 or 7 cell nicads, the brushless one is very nice indeed on the 2S and a bit scary with the 3S which endows it with a decent vertical performance, albeit the motor gets a rather warm if I am heavy handed with the throttle.

As with the original prototype both models are finished in Esaki jap tissue and dope over mylar, which gives a "surfboard" like quality to the wings, I know of no other covering which gives such good torsional rigidity for such light weight. Besides, the finish LOOKS like a model aeroplane rather than a plastic artefact! Give it a try, both materials are from Mike Woodhouse at www.freeflightsupplies.co.uk

Wayne Campbell's home-made vacuum box

 Wayne demonstrates his vacuum box

The sheet is PETG (Polyethylene Terephthalate Glycol) which comes under several proprietary brand names such as Vipet, and in various thicknesses. I use .75 mm but heavier gauges up to about 2mm are available but then are too difficult to pull. I bought a 2.4 metre x 1.2 metre sheet for A$65, should last me for years!

The heater elements are from used household electric cooker ovens, wired up to seperate switches so I can use both or one element.
There is a earth safety circuit built in. The box for this is made from bits of the cooker and pine board, it's not on for long and doesn't heat up much.

The vacuum box was made large, 600 x 400 so I could do the canopy, but it can be masked off with paper and smaller sheet frames used for small items such as wing servo covers, I use stick-on foam strip cut to size to seal the sheet frame. Any box will do as long as air capacity is low as then the vacuum has less air to pull out when working. I use a household vacuum cleaner with all the filters removed which provides , more than enough suck.

The top is peg board. Make the structure strong with internal bracing as there is a lot of air weight coming on to the top and bottom.
It creaks and groans as it pulls in. The sheet frame can be also any reasonably strong frame, I have used old picture frames and stapled the PETG to it.

With all this there is quite a bit of wriggle room as the PETG is quite tolerant of heat range, etc,. so don't get too precious about requirements.
Some tricks such as use a heat air gun to heat the edges as the sheets tends to heat more in the centre. PETG can be reheated and shaped several times. If wrinkles form at the edge of the plug place a small block away from that area or corner to take up the slack PETG.
Make your plugs about 20mm higher at the base so the Petg sheet pulls past the edge to be used.

The plug can be anything that won't collapse, from hard foam to balsa, pine, cement, plaster etc. The plug must be really smooth as every little blemish will show up, this is the longest part of the job. Use talcum powder as a release agent over the plug, if oil or grease is used it can seal and cause bubbles. Sometimes I pull a sheet over the plug, trim it, leave it on then pull over it for a really smooth finish. Be prepared for failures as estimating the temp for the sheet is important, but if not too bad the sheet can be reheated and tried again.

I have seen glider nose cones made without vacuum simply by pulling the heated sheet over the vertically held plug - see video here.

The FPV is a long time coming but as prices are starting to drop it
looks like I can start soon.
I want to build a fairly complex/complete system with tracking antennas,
gps navigatio, on screen display etc
My total cost at present is around US$1,500 but coming down each month,
under US$1,000 and I'm in !
Will keep you informed.

John Wheater's Jabberwok

Here we see John's progress to date on his re-designed Jiant Jabberwock which he is working up as a plan and an aticle to be published in a future issue of Quiet & Electric Flight. John is designing this plane 'on the hoof', which he admits is proving to be a slow process, getting it wrong then doing it again!" One wing down, one to go," he says, adding, " It's amazing how big these things are at only 66" span. The holes in the ribs BTW are for the servo wires, not lightening!"