Jetex.org: Smoke Trails for March 2006




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Smoke Trails 2 (March 2006)
by Roger Simmonds

Reprinted from SAM 35 Speaks, March 2006

As readers will remember, we have discussed the IMA (International Model Aircraft Ltd.) rocket-propelled Target Drone on a number of occasions, most comprehensively in the ((Jet)X Files, November 2004. This included an excerpt from Andy Blackwell’s and my interview with Bert Judge, in which he also referred to two other IMA unmanned airborne vehicles for the Department of Miscellaneous Weapons Development (DMWD): an earlier twin finned glider (also for gunnery practice), and a larger, more sophisticated rocket-powered one for smoke laying (right).


Other columns:
2006
No 1	No 2	No 3	No 4	No 5	No 6	No 7

2007
No 8 No 9 No 10 No 11 No 12 No 13


2002-2004
The (Jet)X Files

2005
The Smoky Addiction

These ingenious ancestors of today’s UAV’s were the brainchilds (or should that be ‘brainchildren’?) of Joe Mansour, Sydney Hansell and others within IMA in liaison with Neville Shute Norway (a commander in the DMWD at that time) and Alec Menhinick. Whilst the target drones were produced in their many thousands, and examples can still be found, for example at the Tangmere Aviation Museum, fewer than thirty of the highly ‘hush-hush’ twin-boomed ‘Swallow’, which was designed to lay a smoke screen over the Normandy landings, were ever built, and none has survived. It has thus remained comparatively obscure, and the illustration (right – from the J W R Taylor’s 1957 Aircraft Annual) is the only one I’ve seen. With a span of 19', the Swallow was, like the Target Drone, launched from a catapult ramp, but was powered by no fewer than four rockets in the central pod. These were presumably similar to those that (singly) powered the Target Drone, i.e., a Bakelite body encasing a cordite propellant, with a thrust of about three pounds. According to Xavier Toff’s Encyclopaedia of twin-boom designs, 1939-1945, the Swallow prototype “had elliptical fins and two booms, while the developed version used square fins and additional beams to support the main booms”. The flight pattern was controlled by a complicated arrangement of levers, cams and clockwork cogs.

Bert attended one of the first flights at Farnborough in 1943, where, launched from its catapult track, it made a good level flight, and he recalls the roar from the catapult rockets and the quartet that powered the Swallow was “quite awesome”. He was also present at trials on the Beaulieu River. These were less successful: the Swallow crashed into the water after only a short flight, due to the link rod from the mechanical mouse in the tail becoming disconnected by the fierce acceleration of the launch ramp. Once this problem was identified and corrected, however, it flew well, but it was then too late for it to see action on D-Day and the project was cancelled in July 1944. In our interview of Bert in 2003, he says that these collaborations with the DMWD and Neville Shute (with whom Joe Mansour got on well) were the beginning of Joe Mansour’s interest in rocket-propelled models that would eventually lead to Jetex.

IMA Swallow – drawing

- Aircraft Annual, 1957

IMA Swallow – Xavier Toff’s drawing

- Forked Ghosts, Christophe Meunier, 2004

Potty Productions’s IMA Swallow model

- Fred Steer (retouched JMC)

The above ‘potted’ history has been compiled from John Anderson’s recent interview of Bert Judge for the Neville Shute Norway Foundation, our own discussions with Bert, and last, but no means least, with the help of Fred Steer of Potty Productions [sic] who has, wonder of wonders, recently produced a Swallow kit for Jetex 50 power (right).

Fred, whose website is full of good vintage stuff, writes: “The model has been designed to approx 1/10 scale, giving a wingspan of 22.5''. Built from balsa, [the wing is sheet over ribs] with vac-formed nose parts, tail gyrocover, brass catapult spools and aluminium boom and fin braces, it weighs only 2 oz including a loaded vintage Jetex 50 unit. Only the smoke nozzle (just visible under the nose) has been left off the flying model, as this would be liable to damage, although the size, shape etc. are detailed on the GA drawing for those who wish to build a static model. The glide is amazing and the performance under power is Something Else”. The kit includes a four-page history, and, at £12.00, it appears very reasonable. Though Fred designed his unique Swallow for a Jetex 50, it might go well with a Rapier L-2. Or one of the new L-3s.

Talking of Rapiers, there has been a worrying hiatus in production as Dr Zigmund expands and retools. This is quite depressing, and several well-known rocket fliers are down to their remnants. Fortunately, production has now resumed: it will be interesting to see if general availability and quality control will improve.

Steve Bage has been encouraging the good folk on the Small Flying Arts Forum (SFA) to make model jets. The response has been very good, and, despite the uncertainties about Rapiers, most are rocket powered, though there are a couple of catapult and rubber powered models. All but a few are ‘traditional builds’. Whilst this is most encouraging, it is a little disappointing that so few are ‘classic’ Jetex designs. Steve himself contributed a Bachem Natter (Richard Crossley’s design enlarged for L2), a BV 215 and an O/D Okha, the kamikaze design of 1945 (right).

Having finished these (Steve reports the tailless BV 215 flies like a duration job, the Natter can cavort about the sky in a spectacular fashion from a catapult launch, and the Okha needed some sorting out but now flies well and will be a plan and article in RC Model Flier). Steve is considering a Keil Kraft DH 110 (available from Replikit) and the unusual and complex 1950s Comet Panther.

Mike Stuart contributed an O/D Fiat G-91 to the SFA project, but also likes vintage designs, and has nearly finished his Skyleada YF-100 (right). He writes: “It has been test-glided in the garden, prior to painting and adding the canopy. Like the Mystère IV, it is nose heavy, and as the last thing I wanted was to add tail weight, I cut the tailplane loose and introduced a whole ¹/16" more incidence. The glide is now much better. It is built full-size to the plan, and at the moment weighs 20 g without a motor. With such a lot of wing area, I hope it will [like the Mystère] fly with a standard L-2.”

Steve Bage’s Okha

- Steve Bage

Mike Stuart’s Skyleada YF-100

- Mike Stuart

The next model is especially interesting: Laurence Mark’s re-creation (right), for Rapier L-2, of D P Golding’s classic Boulton Paul P.111A (Aeromodeller, May 1954) (see below). At 24", this was intended for a Jetex 200 or Jetmaster and augmenter tube. Laurence has reduced it to 12.5" and retained the partially sheeted wings, but modified the original monocoque fuselage to ‘formers and stringers’ with some filling in, and the motor is mounted in a trough. It weighs 32 g. The original reflexed airfoil is not reproduced either; instead, Laurence made a semi-symmetrical wing and turned up the (scale) elevons several degrees.

Laurence Marks’ re-creation of D P Golding’s Boulton Paul P.111A for Rapier L-2 (2005)

- Laurence Marks

Laurence has written to me: “I would be interested if anyone has built the Aeromodeller original, as mine has a really weird flying style. The 1954 article states that ‘stall recovery is extremely good’, but this simply turns into a mush on mine, even under power. The elevons don’t seem to do much, and I think that’s why I can’t trim it ? the original has lots of reflex. I have now removed the entire trailing edge and added full span elevons. Hopefully that should make it more trimmable”.

Laurence calls his delightful model ‘scrappy’, saying he will make a ‘proper’ model for Old Warden using less wood once he has sorted it out. I wish my models were as scrappy! As to its problems; it sounds like the CG is too far forward, and perhaps he needs to split the flaps and elevons, which allows differential reflex and thus washout to be easily adjusted. This little wrinkle worked a treat on my F.D.2, which is a very stable and predictable flier.

Laurence Marks’ plan of his re-creation of Golding’s P.111A (2005)

- Laurence Marks

Peter Smart’s F.D.1

- Mike Stuart

Laurence could also have a look at Pete Smart’s F.D.1 (left), which was also unforgiving until Pete found the right L-2LT. However, as Steve Bage points out, the full size P.111, nicknamed the ‘Yellow Peril,’ was also very unforgiving!

Mr Golding does say in his article that small ailerons can be fitted as a trimming aid ‘if desired’, and to avoid a ‘nose up float’. His construction methods, too, are worth discussing in some detail, especially for anyone contemplating reproducing a Jetex ‘Tailored’ model. Mr Golding eschews his earlier ‘hollow log’ approach, and writes: “commence by carving a solid block fuselage, preferably from obechi. This is the only ‘awkward stage of construction, but is essential for true scale appearance. The block is carved ¹/32" undersize overall, smoothed and given a coat of dope. Four sheets of fairly soft ¹/32" balsa are required, soaked in hot water for 10 minutes. After shaking off the surplus, lay one edge on the block centre line and bind tightly with ¼" rubber. Where wrinkles occur cut and allow to overlap, but-joining when dry. The corresponding quarter is made in the same way, and, when dry, butt-joined to the first piece, replacing the complete half-shell on the former and binding in place. Steam in front of the kettle for a couple of minutes and allow to dry. The bottom half repeats the process, and two ¹/32" × ¼" strips are cemented along the edges to facilitate joining. Rubber marks, etc., will sand away quite easily.”

D P Golding’s Boulton Paul P.111A

- Aeromodeller, May 1954

D P Golding’s P.111A – detail of fuselage construction

- Aeromodeller, May 1954

The article then describes fitting of the fuselage formers around the augmenter tube, and the motor mount. It all sounds eminently practicable, at least for simple shapes like the P.111 (or F.D.2!) and much preferable to carving from solid and hollowing out. I just wonder if ¹/16" wouldn’t be easier to work with. Perhaps Laurence can be persuaded to try a monocoque on his Mk 2!

I had been casting about for a suitable vintage subject for some time, and all but decided on Howard Boys’ Vampire, when an Australian reader, Alwyn Smith, sent me the interesting design below. This first appeared in Hobbies Illustrated, (1949) and was, so the header to the article says, “Designed by M J Robinson in association with Bill Evans (Jet motor now available in Australia)”. Alwyn says of Mr Evans, “Bill had a company in Adelaide called Model Aircraft Industries, which had a hobby shop in Adelaide. He made kits of his designs, and the plans often appeared in various Australian magazines, like Hobbies Illustrated and his own publication, Australian Model Hobbies, which came out as nine issues between 1949 and 1953. He had a [bad!] habit of copying other people’s models and designs, and then publishing them under his own name. It would not surprise if this one is a slight redraw of the Wilmot Mansour design.”

D P Golding’s Boulton Paul P.111A

- Aeromodeller, May 1954

Curiously, the plan has no scale, neither are details of the motor given; but Alwyn reckons the span is about 24", which would suggest either a Jetex 100 or 200. So it is actually not the Wilmot Mansour design (below right); to start with, it’s distinctly better looking and the motor is enclosed in the fully sheeted fuselage. A questionable aspect of the design – revealing the designer’s inexperience of Jetex – is that the scale intakes are dummy and ventilation is provided by tiny air scoops. This would have done little for the motor’s efficiency.

The accompanying article for this model of what it calls “Britain’s outstanding jet fighter plane” begins promisingly enough: “The availability of these model jet motors makes it possible for the aeromodeller to construct many interesting types of model, which previously had to be spoilt by the adding of rubber motors or some other form of power which was quite different to the original aircraft, and so spoilt its authenticity. The Vampire is very close to true scale and is one of the most attractive models to take to the air”. However, as is typical with these sorts of publications, the building and flying instructions are sketchy, and the instructions for finishing merely state, “The Australian Vampires are finished in all-silver with blue and white roundels and black markings”.

Perhaps this model, and, indeed, Hobbies Illustrated generally, were aimed at experts. But even they could not have been, at that time, expert in Jetex. The trimming instructions, having recommended a balance point at the traditional ‘one-third of the chord back from the leading edge’, continue, “Now is the time to keep your fingers crossed. [!] Seek out a field of tall soft grass and proceed to test-glide … correct any tendency to nose up or down with adjustments to the elevator. The flight pattern of a jet model is different to a propeller driven aircraft, as there is no torque, and any maladjustment quickly becomes obvious. Slight upthrust (jet pointing downwards) seems to give best results. Light the jet, wait for maximum thrust and launch nose down into the wind”. It seems to me that these pointers are just not good enough for someone attempting his first Jetex model, and Bill Winter’s recommendations on flying his Swish (see Smoky Addiction 7) are much more useful and honest. Bill Evan’s article ends, “We would be pleased to hear of your experiences with the Vampire”. I wonder if he ever did receive any feedback from his Australian colleagues. One possible comment that springs to mind is, “where in the name of a dead dingo can I find a field of tall soft grass?”

M J Robinson ’s Vampire

- Hobbies Illustrated, 1949

This ambitious antipodean offering is preferable to the (slightly later) Wilmot Mansour kit (below) and more practicable than Cockle’s 1948 Aeromodeller design. It could, given a few modifications, for example reduction to about 14-16" wing-span, removal of most of the fuselage’s internal structure, the addition of a trough and a bit more wing incidence and dihedral, be a viable, and nicely vintage, model for Rapier L-2.

Jetex Vampire

Wilmot Mansour’s Vampire

- Model Aircraft, May 1951


	Acknowledgements - Article: Roger Simmonds - Illustrations: Roger Simmonds, Mike Bage, MAAC archives via Bill Henderson, Laurence Marks, Alwyn Smith, Fred Steer, Mike Stuart

Queries? Corrections? Additions? .