Jetex.org: The (Jet)X Files for August 2004




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The (Jet)X Files 20 (August 2004)
by Roger Simmonds

Reprinted from SAM 35 Speaks, August 2004

Afterburning

Peter Tolhurst, evidently as enamoured of the CO2 propelled ‘Speedjet’ as Tony Brookes had been, writes; “Your article last month (June) galvanised me into action. I have just finished drawing up a 7.5’’ version for Rapier L1 (with catapult launch), albeit with a profile fuselage. I know … you don’t like profile models, but this isn’t a scale model of a ‘real’ aircraft”. I look forward to seeing how Peter’s ‘hybrid’ trims out and performs at our SAM Gala.


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2003
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2004
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Jul	Aug	Sep	Oct	Nov	Dec

Apropos of catapult models, illustrations of three period profile models recently arrived from Sten Perrson. These attest to the popularity of jets in Scandinavia, and that Isacson was not the only endogenous kit producer at this time. To pre-empt Funf, the designer’s name does suggest a not inappropriate pun (true design?)!

What is most intriguing is that though these nicely prefabricated kits were for catapult launch, Jetex power was also presented as an option. The rather fanciful illustration [below right] might possibly be a 50C. This rather contradicts the received wisdom that catapult gliders and Jetex models need setting-up in different ways.

Semo Jetex/catapult profile Lansen parts

Stan Pearson comments: “I never thought Jetex and catapult power were compatible. The slower Jetex models needed several degrees of incidence, akin to a rubber job, whilst the catapult variety trim out (if you are lucky!) closer to zero-zero”.

Stan has more to say about his early catapult jets (see last month): “The MiG 15 replaced one that went OOS in Richmond Park; at 1/48^th scale with a span of only 8-9 inches OOS comes up much more rapidly than you might think. The Meteor replaced a profile model, and was cut from very soft 3/8" sheet … there was no attempt to hollow out the fuselage or the engines, so it was in fact a ‘flying solid’ … and very well it flew too, thermalling away over a block of flats. It was given up for lost, and then spotted nestling in a rose bush in a neighbour’s garden. The success of these was no doubt due to the lightness of the wood and the fortuitous decalage built in, and later models were nowhere as successful. Some of the more exotic jets were scaled from ‘Jet Aircraft of the World’ by William Green and Roy Cross, and were of questionable accuracy”.

I loved Green’s books as a boy (knowing his Fighters of WW II practically by heart) and have a precious first edition of Jet Aircraft of the World. It is a fascinating compilation of pre-1955 jets (see the Hawker P.1081 3-view in April’s article); but Stan is right about the smaller drawings; that of the Leduc 021, for example, is particularly misleading.

Semo Jetex/catapult profile kits

Semo Jetex/catapult profile Draken parts

- Sten Perrson

Fortunately, most modern publications are better in this respect; Tony Buttler’s British Secret Projects: Jet Fighters since 1950 (Midland Publishing, 2000) has many unique 3-views and illustrations, including the Sapphire powered (though subsonic) Hawker P.1091 (right) and the mildly supersonic P.1083 (below right). Both these Hunter derivatives can easily be adapted (see last month's discussion of the P.1083) from period Hunter plans.

The P.1091 is very shapely, and the delta wing will give stable and probably spectacular flying characteristics. Another ‘must have’ book is British Experimental Turbojet Aircraft by Barry Jones (Crowood Press). Its many large 3-views of prototypes, from the Gloster Whittle to the TSR 2 and Hawker P.1127, are in full colour and provide an excellent source of templates for homemade decals.

Whilst on the subject of transmuting old plans, Andy Blackwell has just finished a KeilKraft Attacker, and thinks it would not be too difficult to convert this to the Scimitar-winged H.P.88. This research vehicle for the Victor bomber will make a very attractive model, especially if finished in the prototype’s dark blue. He also thought a Fairey Delta F.D.2 could be modified to a BAC 221. The Concorde-like wing planform should make for interesting flying characteristics. There are many other possibilities, of course, and plastic modellers have long been expert at this sort of thing. There are several derivatives of the Javelin, for example, or an F-104 could be modified to the shoulder-winged Lockheed X-27 CL-1200 Lancer, with beneficial effects on its flying characteristics – but please, please, don’t even contemplate turning a P.1A or P.1B Lighting into the horrible ‘boiler plate’ S.B.5, complete with fixed undercarriage!

Hawker P.1091

Hawker P.1083

- British Secret Projects: Jet Fighters since 1950


	By happy coincidence, given the discussion of Skyleada models in June’s column, Mike Stuart has built what we concluded was one of the less capable designs in the series. He writes; “I was very pleased to get hold of a pair of old Sklyeada jet kits via eBay, one of which was the Mystère IV. This is a model I had not seen before, and I rather liked the design, so a replica was started from a copy of the plan using my own wood, as it would be a shame to cut into a kit which is 50 years old. Though the wingspan is 15" I am hoping that if I build light I will get away with a standard Rapier L2. “I agree with your comments about modifying designs being OK as long as you maintain the spirit of the thing. I find it very hard to leave ‘well alone’. Modifications to the Mystère include: cockpit area and first two bays filled in; balsa fairing to the canopy to avoid a tricky join to the spine; thickened spine, and lots of gussets at the wing roots. I enlarged the tailplane by 6% as it just looked too small compared to the wing, and added diagonals to stiffen it torsionally and reduce the risk of warping. I left the trough unchanged and put the Rapier where the Jetex 50 would be, but added balsa sheet over the motor to maintain the fuselage contours for a further bay. “Airframe weight is 22g without motor. Test glides showed it was very nose heavy, but rather than add tail weight [Mike seems as averse to this stratagem as the rest of us] I decided there was not enough tailplane incidence. “I was very glad I used a water-based glue, as I was able to loosen it eventually with a paint brush dipped in water and add a couple of degrees. It now glides reasonably flat with a loaded motor. The canopy and pilot will add a bit more noseweight; no way will I move the CG backwards!” Mike has made a splendid job of a unique kit (see below). He has even controlled the urge (which I would find all but irresistible) to add extra fuselage stringers, so that his modifications don’t affect the somewhat basic appearance of this fifties design. There is a grand range of colour schemes available: Chris Starleaf’s ‘Easy built’ MiG 15 on Mike’s own website shows how a good finish and details like wing fences and panel lines can enhance even the crudest design. I look forward to seeing Mike’s Mystère fly, but I shall be surprised if it doesn’t need at least a 220mN L2 HP. If it does fly well, I shall be tempted to try the YF-100 Super Sabre, a similar, and at first sight as unpromising, model by the same designer. Who this was remains a mystery. Lindsey Smith suggests R H Warring, a modeller not otherwise celebrated for his scale models. Does any reader know better?		Skyleada Mystère IV kit - Mike Stuart
	We had a good time at Old Warden in July, and the weather was kind, though we missed the presence of Pete Smart and Richard Crossley. Chris Strachan’s OD Lansen [right] flew very well indeed with a single Rapier L2, affirming his views (see May’s column) on the efficiency of ducted motors. Andy Blackwell trimmed his Jetex 50 powered KeilKraft Hunter [below right] with single pellets. This might have affected the thrust, as it wallowed about a bit in a nose-up attitude. However, it seemed quite stable, and after modification to the thrustline, or perhaps with a 50B and a full complement of ‘Red spot’ pellets, it might go very well. Andy’s model is au naturel clear dope, as was his father’s before him, and the tissue and trough remained remarkably clean and unsullied by motor exhaust. In contrast, the rear fuselage of my meticulously finished Skyleada Hunter (which, by the way, trimmed out very nicely with a 110mN L2) was scorched after only a few flights, quite spoiling its delicate pale green finish. Rapiers burn a lot hotter and dirtier than Jetex; it makes sense to deepen the trough on Jetex designs, if not for aesthetic reasons, then to protect the airframe.		Chris Strachan's Lansen - Chris Strachan Andy Blackwell's Jetex 50 KeilKraftHunter - Andy Blackwell
	Andy also gave his Jetmaster Swift [right] a few chucks: the glide appeared straight and true. I did suggest, however, that he should dope a layer of tissue on the wing tabs, as the wings fell off at every arrival. Here are a couple of shots of the Swift; the one on the right shows it posing with a Douglas Skyrocket for L2 (another Richard Crossley design) to give you an idea of the impressive size of Bert Judge’s favourite Jetex model. Vintage Free Flight		Blackwell's Swift and Crossley's Skyrocket - Andy Blackwell
	Another of the highlights of July’s Old Warden meeting, apart from seeing the Bristol Box kite trundle around in the late evening air, giving every indication of needing rocket-assist, was Leigh Richardson’s diminutive Zephyr. This Tim Hervey design for Jetex 200 was of course the primogenitor of all Jetex duration models, and was published in the iconic June 1948 Aeromodeller with the overly ambitious Meteor. Leigh writes: “This version of the Zephyr was built in 1988 for Jetex 50, but was overpowered, and did 100 foot loops above my head. Fuselage construction is ¹/16" square balsa, wing ribs are ¹/32", and the tail surfaces are laminated. At 20" span, all up weight is 17g. It is slightly underpowered by an L1, so an L2 will be fitted in due course”. I suggested an L2 LT would be about right.		Tim Hervey's Zephyr - Leigh Richardson


	John Bowring has built a ‘full size’ Veron Air-o-jet, and as the original was for Jetex 100, decided to use a Rapier L4, with a not, alas, an altogether happy outcome. John writes: “After test gliding on Saturday evening, I took it to Old Warden on Sunday. This has broken my rose tinted glasses. Out of ten L4s (two boxes) the first three were used to test fly; the next three at least lasted the length of the flight, without much attempt to climb, the seventh was better, having tinkered with the thrust line, and on the eighth flight it climbed away for about twelve seconds, then went into reverse. This didn’t last long, as the end pug had blown out of the motor and the exhaust blew a hole in the nose block. Flight number nine followed a similar pattern, only this time it set fire to the pod. I have one motor left, any suggestions?” I told John that L4 fliers used to ‘superglue’ both ends (of the motor). John replied, “I Araldited the ends of my tenth motor. The Air-o-jet climbed to 30-35 feet, and then came down almost as quick, but it was the best flight so far, and I will quit while ahead. The L4 doesn’t seem to have the thrust of the old Jetex 100, so now for something completely different”. This is a pity, as John has made a fine replica of Phil Smith’s early 1949 design. We have all had faulty motors (remember Rapiers are a product of a ‘cottage industry’) and it is good practice to inspect each motor for splits, asymmetric nozzles and the like. I have only had one blow-out; this was a standard L2, and the bang came as quite a shock, as I was holding the Bell XS-1 at the time! The L4 had a reputation for ‘blowing a gasket’ and needing careful handling; it is indubitably not as powerful as the Jetex 100, though it’s quite a bit lighter, which is some compensation. Generally, Rapiers are very reliable and easy to use – easier than Jetex – once one is aware of their idiosyncrasies and the pitfalls associated with variable thrust ratings, but, as with any other novel motor, there is quite a steep learning curve, so start out with an L2 or L1, and adjust the size of your favoured model to suit. Peter Redhead, you will remember, ((Jet)X Files, Feb. 2004) had to modify his KeilKraft Star-Jet quite a lot for the L4; perhaps John’s red and yellow Airspan covered model is a trifle overweight and needs a similar approach to optimise its performance.		John Bowring's Veron Air-o-jet - John Bowring
	André Bird has had many wonderful flights with the L4, and is expert at getting the best from his unusual models. He has sent me details of a gadget that facilitates adjustment to the motor thrustline. The wire (W) is affixed to the fuselage (F) and motor tube (MT) and kept under tension to abut the Rapier against packing (P). André says his models fly well with thin card wedged in to adjust the motor angle, but a nice refinement is to add bolt (B), which makes small increments of thrust angle both easy to ‘dial up’ and repeatable.
	I hope Leigh’s delightful Zephyr will encourage others to try some of the more unusual free flight designs out there. As an encouragement, here is the gull-winged Mosca pour Jetex 50 (Le Modèle Réduit d'Avion, October 1953) that I pinched from a number of classic designs available on the Jetex.org website. It has a quoted weight of 19g, and with its 16" span and 12" length it looks just right for an L2. The designer, one Monsieur R. Parlatoré, comments, “Mosca has a slightly supersonic look about it [?] … the motor is mounted in the upper part of the fuselage, which positioning has absolutely no detrimental effect on Mosca's flying capabilities, and my fingers appreciate staying in the cool”. Please let me know if you would like a better copy of the plan to build from. Jigtime		Mosca - Le Modèle Réduit d'Avion, October 1953
	No, not a dance, but a series of prefabricated all-sheet kits for the fledging flier created by Carl Goldberg in the 1950s. These featured tabs and slots as neat aids to building, and the coloured balsa parts came with all markings pre-printed. Most designs were for rubber power; for example the Piper Vagabond and Curtis P-40, and the semi-scale Arrowjet, whose balsa was covered in thin aluminium. Of especial interest to us, however, are the jet models, which included a 9.25" span catapult MiG 15, and the slightly larger ‘Superform’ models. The latter are featured in the advertisements [right] (from Model Airplane News, Dec. 1954), which were sent to me by Chris Strachan. Like the Swedish Semo products, they were advertised for “Jetex and catapult”, but what is more interesting is that they were contemporaneous with, and similar in construction to, Jetex ‘Tailored’ models. I wonder if Carl Goldberg was influenced by Joe Mansour’s creations? The balsa shells are mounted on formers, but, in contrast to the Wilmot Mansour models, they were ¹/16" thick and “die-cut for exact fit”. They were also, like the all-sheet wings, pre-coloured and decorated. Paul Bradley’s superb website (www.parmodels.com) reviews the history of the Jigtime series in some detail, and many of the plans can be downloaded. Paul’s reproductions of the Superform models have planked octagonal fuselages, not moulded monocoques [see the F-86 and MiG 15 below], but this is a reasonable compromise in the circumstances – and their all-sheet construction makes a pleasant change from the usual ‘Flying Scale’ designs. Rick Carnick in the US has an F-86 built from Paul’s plans that he says flies very well with a standard L2.		Carl Goldberg's Jigtime models - Model Airplane News, Dec. 1954
	The next (Jet)X Files will review a fascinating historical series of articles, ‘Jet Propulsion and the Model’ written by G W W Harris, G A Henwood, R H Eaton-Williams and others that appeared in the source between 1945 and 1949.		Paul Bradley’s replica Jigtime F-86 and MiG 15 - Paul Bradley


	Acknowledgements - Article: Roger Simmonds - Illustrations: Roger Simmonds, Sten Perrson, Mike Stuart, Chris Strachan, Andy Blackwell, Leigh Richardson, John Bowring, André Bird, Edward Jones, Paul Bradley

Queries? Corrections? Additions? .