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JETS `N` THINGS

Second to my usual day job of racing tethered hydro's I have had a long time interest in small reaction powered surface vehicles (boats and cars) powered by Jetex, Rapier, and low powered rocket motors (Estes and the like).

This fascination started at an early age when I was still at school and had joined the model making class at the evening classes there. The instructor was a big fan of Jetex powered models, mostly aircraft but he did build some boat and car models and it must have been that that started me on my interesting the subject. I remember in these early days before the jolly old HSE was around we used to run small tethered speed model aircraft, and in my case cars in the class room, you would not believe the amount of smoke a Jetex 50 produces in 15 seconds, but it was great fun. Well it was until the day when the motor came loose on one model and shot round the room like a demented squib this cleared the room in double quick time it also put pay to indoor jet, and car operations.

Time moved on and yours truly discovered that the Jetex Company produced several sizes of jet unit much larger than the little 50b size motor that at up to this time had powered all forms of boat and car model. These were the 150 PAA-LOADER, and SCORPION and it was that these motors that I stuck with for the rest of my adolescent (and adult) jet modelling escapades.

Over the years I suppose I have built dozens of models both published ones from the pages of Model Maker, and MECCANO magazine, and also the heady tomes such as The EAGLE Book of Balsa Models, Model Boats, and Model Cars.

Also many (too many?) of my own designs which I am still building to the present day that are still powered by many of my original motors. Itís quite amazing that even though Jetex have been out of production for many years tins of fuel and igniter wick in perfectly good working order can still be found at swap meets and toy fairs (never eBay too bloody expensive) to keep my toys running.

At one point not all that long ago when I thought it might be impossible to run the original Jetex motors due to, I thought at the time, the lack of suitable fuel I turned to the low powered miniature rocket motors produced by the ESTES Company in the USA these were much more powerful beasties that were capable of outputs of 3Kg of thrust, where the Jetex motors were only capable of thrust levels measured in grams, 180 at most, the big draw back with the rockets though was the very short thrust duration this being only 2-3 seconds. Enter the rocket car era.

The last 20 years or so of my working life I worked at a university located in Dartford, Kent. The great thing about this place was that it had extensive grounds, a very large sports ground great for model flying (two of my colleagues found this out very quickly), and a series of five tennis courts lined up side to side. Perfect for R/C cars, small tether cars, and in my case straight line rocket powered cars. In the summer months the courts were used for boring things like playing tennis (sad), but in the autumn and winter months the nets and other bits and pieces were stropped out leaving a very large and importantly flat area about 100 yds long.

The first of a series of rocket cars christened The Rapid Rickshaw was quite a crude effort using a 1-1/14 inch dia cardboard tube and model aero wheels, and when finished resembled the Blue Flame land speed car.

First runs were very encouraging using small B and C size motors speeds of around 50-60 mph being realised. Mods were made, ball raced knife edge wheels and parachute braking system (things were getting serious). I was also running on a straight line course using running line made from A2 class tethered hydro line. The car was attached to this by a guide system, the course length being about 120 yds diagonal distance. This time, fitted with a much larger D size motor, a staging system was used and when the car was run in this version I recorded my first 100 mph run timed by speed gun. The car was run several times after this recording speeds from about 98 to about 110 mph, however all things donít run smoothly all the time and on itís last run the motor decided it was going to be a weapon of mass destruction blowing the car into confetti.

Enter Techno Games.

I had watched two series of Techno Games on the tele, and was immediately drawn to the rocket car competition and thinking "I could do that", and so it came to pass yours truly built what was to be a very successful, if only to be a disappointing entry.

Filming was at Shepperton Studios the rocket car comp being filmed over one day. There were many entries so it was decided to run a four lane track so as to get through high numbers. I had made a purpose built car, (getting completely out of my tree) with the main body made from carbon/Kevlar composite, plasma welded stainless steel running gear, and light weight billet turned ball bearing wheels weighing under 120 grams complete with motor, a work of art even if I do say so myself. So imagine how I felt when we were all told that the minimum weight had been raised to 150 grams. After some hunting around I managed to get hold of some solder strip from one of the sparks on site, and with aid of some 5 minute epoxy soon had Rapid Rickshaw Mk4 up to spec.

The competition went quite well, very well in fact and I soon found my self in the final, but this was where disaster struck. All the launches up until this point were faultless, except this one. As the count down reached zero (all very dramatic in tale terms) all the motors in the other cars fired o.k. not mine though it decided just like the motor in the first car I built to be a small explosive device and completely blew the rear of the car to shreds. All I can say is that the kids in the audience thought I was great, I think I got more applause than the winner.

Not long after this one of the other competitors in the competition, Pete Barrett of the H.A.R.T model rocket club, informed me of the clubs rocket car league and invited me to run at their track. Imagine my surprise and amusement when I found that the track was yet at another school site and on disused tennis courts deja vu or what. Some good times were had there and it was at this place that I recorded my fastest ever speed, a fraction over 200 mph. The car was purpose built to go fast, made from carbon and glass fibre it weighed 180 grams and was powered by an Aerotech motor with a thrust of some 8 kilograms, a power to weight ratio of 45 to 1, no wonder it went quick.

All things come to an end and the school decided it wanted its tennis courts back to build something or other on so bye, bye rocket league. I still have all the cars and it would be nice to think that it would be possible to run again some where, who knows.

The not too serious cars. Built using the bodies from two model rockets they proved to be very successful, Purple Thing recorded a fastest speed of 1.6 sec for 35 metres.

 

The very serious cars. These two cars the fastest cars that I produced using the old Techno Games rules. The un named yellow car was the one that achieved 200 mph. The other one Rapid Rickshaw 5 achieved 1.35 sec for 35 metres.

 

The definitely not serious cars. Bottle Job was built for the funny car class at techno games but never run due to there being too many in the class at the time, fastest speed 1.8 sec for 35 metres. Ow Zapp was built using real miniature cricket bat bought in a local sports shop. It eventually turned out a bit on the heavy side but still managed a run of 2.3 sec for 35 metres.

That all took place some eight to ten year ago and I soon went back to my roots to start to build small jet powered hydroplanes powered by original Jetex motors. I was lucky to find very large amount of fuel and igniter fuse for these at a local swap meeting for not much money (very important). I also used the newly introduced Rapier Jet motors that had come onto the market in three different thrust ranges.

The cars were all great fun to build and run, but my roots were always in the model boat world and to this end the design and building of small jet powered hydro's has always given me great pleasure.

As I said at the beginning I started building these little craft when I was still at school (not quite pre-history but almost) and to try to describe all that were built would not only be stunningly boring, but would need a fair sized book, so instead of this I have decided to describe the ones built over the last few years by way of photoís and brief description.

So here goes

Jetex and Rapier jet powered hydroplanes

The Hydro Jet

This is the second one of these models that I built; the first one was powered by a reproduction JETEX 350 motor that was fuelled with Scorpion pellets, the problem was that I completely under estimated the power of this motor and on its first outing it was totally destroyed as it slammed into pond side at some stunning speed.

This is the second version, powered by a JETEX SCORPION motor; it is a lot lighter, and with another 1oz of thrust goes a long way in a short time. Speed about 25mph. As I understand it, this was the largest of the published designs.

Green Mamber

This is my own design and is 17" long and 5" wide and is a reverse 3 point hydroplane and power by a SCORPION motor. Constructed of 3/32", and 1/16 "balsa wood, it only weighs 4oz. I have only run it once and it frightened me stiff, 120 yds in 8 seconds.

Adamcraft Jet Ho

This one was built as per drawing, but instead of the JETEX 200 (that I didnít have at the time) I elected to use a PAA Ė LOADER with excellent results 100 YDS on two pellets. Not sure of the speed but it looked lovely only just touching the water surface.

Another of my own designs, a single step hydroplane powered by a PAA-LOADER again. The rear wings are functional and are flat bottom section, set about 2 degree incidence. At speed the rear of the hull is lifted clear of the water with only the guide fin and the tip of the step in contact with the water surface. I havenít run it with a full charge yet but 200+ feet on one fuel charge is a good start.

Swordfish

Built from the drawing in the EAGLE Book of Balsa Models this version is the fifth one, all the others being powered by the good old JETEX 50c this is the second one using Rapier motors in this case the L3 version.

Using the Rapiers the speed is much higher, but things can get tricky, with blowovers being common in windy weather but on the whole a really stable performer. Unfortunately, this picture was taken just after a particularly long run where it ran into the side of the lake at full tilt.

Detour

1961 Model Maker Magazine

This is one of the most unusual and smallest (only 6 Ĺ long) models that I have built but still a very good performer. Power in this version is Rapier L2 90 Mn motor. I have just got hold of some 100Mn, and 140Mn motors so it will be interesting to see what the performance will be in the future.

Water Fly

Definitely the ugliest, but most definitely the fastest of my own designs

This outrigger 3 point hydroplane was recorded by a friend using a speed gun at just over 45 mph. Itís been modified and repaired many times in the past but with these mods in mind a new version will soon be built. Power for this version is Rapier L4 but for the new version L3 will have to be used as I understand that L4 are no longer available.

Water Skipper

The latest of the fleet, this diminutive L2 powered model, was built to operate on a piece of water much smaller than the one I usually run on. It has a flat underside with no step so the speed is quite a bit slower than usual but is still fun to run.

Not all the models are successful as the two models in this series of photos prove. The reverse 3 point hydroplane was the first in a series of these types of craft. I managed to get a lot of things wrong with this particular one, balance point, planeing angles, too much power, and that was just for a start. On one memorable outing I had just launched it and as it travelled about 20ft in zot seconds flat it lifted its nose and shot some 30 or 40ft in the air, then levelled out turned upside down and flew for the rest of the motor run.

The other little model appeared in an old copy Hobbies Magazine and was originally designed for Mk1 JETEX 50. How it was meant to run is any ones guess, with a loaded motor it weighed over 1 Ĺ oz and had 10 degrees of angle on the front planes. I powered my own version with L3 power and lengthened the hull with the extensions seen in the picture.

The last three pictures are included to illustrate my comments about the difference in motor power curve difference that I commented on in www.jetex.org website. The model in question is the Swordfish and was originally powered with a JETEX 50c, JET-X 50 (dead loss). With the 50c, the performance was very good with a distance run of about 80 to 100 yds.

I then discovered the Rapier range of motors first fitting an early L2, ok but not up to J50 performance, but not bad. I then found the L3 and L4 motors and thatís when everything changed. I made a motor tube from light alloy and fitted at first the L3 motor, this produced almost instant acceleration and a 110 yd run, then I got greedy fitted an L4 and fired it up, the speed to what I had been used to was nothing short of ballistic, and fatal as the picture shows. It hit the end of the lake with an audible thud and a reduction in hull length, I was hooked on the Rapier motors for the smaller models (you still canít beat a PAA-LOADER) from that moment on.

I still donít think there is a replacement for the PAA- LOADER and SCORPION motors. I have got a finite amount of fuel for both so unless Dr Z comes up with something bigger, I think the bigger boat models may not be a viable proposition.

So there it is, these are the type of easily constructed little models that still bring the fun side of model making, and running to me. They are not super high tech in their construction, made simply from balsa and thin ply wood, but the kick that I personally get when one of these little gems gets going is priceless.

If any one is interested in this type of model please get in contact with me, Jhafree2@aol.com and have a chat about the models.

Jim Free

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