SLOPING OFF...
...the Newsletter of Christchurch and District Model Flying Club for...December 2024
FROM JETEX TO EDF…IN 66 YEARS,
By Mike Roach. Photos by MR and Geoff Harris
Some Club members will recall that my adventure with EDF came to a frustrating and embarrassing end when my brain and thumbs simply refused to catch up with the little Arrows Hawk I bought myself as a birthday present. After three increasingly awful crashes (one at County – even worse!), I excavated the hardware out of the wreckage and put it all on a shelf, well out of sight.
A couple of months later I was talking to Frank and others about EDF and the various Keil Kraft and Veron models we had built as kids. My favourite was the Avro 707. We had a big garden in the 1950s and it made perfect sense to treat it as a glider with a long piece of elastic thread to launch it gently along the flight path. A browse on the Outerzone website (Outerzone.co.uk/Keil Kraft*) found the plan I remembered so fondly: the model has a span of 13.5” and the 50mm fan from the Hawk would easily fit in a twice-size version, and with much more wing area it would surely fly slowly enough for my old head to follow – wouldn’t it? The plan even has the parts that we used to cut out with a broken razor blade (actually, that’s a lie, I had a proper knife and never cut a finger off). Then I got a video from Ivan Pettigrew of the 707C at Farnborough, back in 1955 or 56, and the die was cast.
I made the longerons from two layers of 3mm square strip, wetted and pre-curved over a foam form to take out any stresses.
The wing root is pretty well to scale and holds the half-fuselage in place. The large hole is to allow air to the fan. The CG marking is from the plan and just about perfect.
I built the fuselage and wing root pretty well according to the plan, adding in extra formers and putting the fan and efflux where Frank suggested. Making the efflux from Corn Flakes packet cardboard was simple and light – I recommend it. The parts from the printed list were modified by reducing the former diameter by 2mm to allow for the planking, but my childhood hero, Albert E Hatfull, had done an excellent job of designing this and the other KK scale series. All the hardware from the Hawk, the fan, SC and my RX were plumbed in and a balsa battery plate added – far too far forward, it turned out! Most of the 2.5mm soft balsa planking - three whole sheets of 3 x 36 soft! - was satisfyingly glued in place, leaving enough access for the wing servo wires to be fed in to the RX.
The wing did need a complete structural redesign along traditional lines. I added a CF tube as the main spar and a smaller rod for the incidence peg, but I could not face all the packing and jigging needed to get the symmetrical section ribs to line up. The simplest solution was to cut them in half along the chord and build the lower half first, adding the locations for the spar and peg, glueing the lower D box, aileron spar, cap strips and servo plates in place as I went. With the half wing off the board the upper ribs and then the rest of the balsa was easy enough to add.
I glassed the fuselage lower half using a water-based varnish then glued the wings in place – testing the radio connections before it was too late. Covering was with “Bright Red” film from George at 4-Max, the generic bubble canopy came from Steve at Vortex Vacforms and the markings from Calliegraphics. The difference adding scale markings makes to a model is always incredibly satisfying, as well as taking the eye off the obvious slight wrinkles. I could not find a red paint to match the very bright red, even the scanner at Homebase failed. This explains the darker red nosecone and cockpit.
Finally ready to fly, would the fan be powerful enough, would the model fly as well as my 13-year-old version did? The Arrows Hawk weighs about 1lb, my 707 weighs 8oz more…time to find out!
A brisk hand launch at half throttle to test lateral stability and she settled gracefully onto the grass. Another try with more throttle and up trim and yes! She flies! A gentle circuit, still climbing, ease off the elevator trim and gradually a fast jet came to life (but not so fast I lost track of it). 4 minutes flight on a 3s 2200 and the glide in to land seemed to go on and on and made me a very happy old fella.
In conclusion, the CG is an inch or so too far forward; my design fault that can’t be changed in this model. A 3s 1300 puts it in the right place for a loss of flight time. The noise the fan makes is really disappointing and I put it down to resonance in the light balsa frame – after months of telling pusher prop fliers to keep the noise down, this seems far worse!
The Keil Kraft Jetex series has one more tailless delta, the Douglas Skyray, but the Javelin (for two 50s?) is in the same mould. Slightly less easy to convert but very attractive shapes are the Hunter, Swift, Attacker, Panther and many more. The Veron range is smaller, but includes some larger plans, originally for IC ducted fan. All plans are available on Outerzone, just search by manufacturer. The Avro 707 has no fewer than four shape options and numerous colour schemes. A 64mm fan and 4s would give far more performance than I feel happy with. I had great fun making this model and sorting out the very few problems in its design. Have a go!
The real thing: a series of one-third scale prototypes were built to assess the low-speed characteristics of the delta wing for the Avro Vulcan. The 707 came in four shapes and a number of colour schemes which can be explored on Mr Google. There was a well-publicised Farnborough fly-past with two white Vulcans and four 707s in red, white and blue.
707B, short nose, VX784. The first to fly, with the air intake behind the cockpit. Natural metal. It crashed during testing.
707B, long nose, VX790. A similar aircraft, but with a much more attractive longer nose that became the standard for the series. Natural metal and then blue.
707A, straight wing, WD280. The Keil Kraft model with the now standard wing root intakes. A mere four colour options: yellow, pink, orange and bright red.
707A, kinked wing, WD280. The “kinked” Vulcan wing tested on the A series aircraft. White.
707C. The only 2-seater version, WZ744 (must have been pretty cramped) Natural metal with a black anti-dazzle patch.
*Thousands of other plans are available!
