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TOPIC: John's Jetex Journey

John's Jetex Journey 2 months 1 week ago #719

  • rogersimmonds
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Hi Guys,
John Holman has sent me details and pictures of his latest models, which are for genuine Jetex propulsion.
John writes:
"I was born in 1949 and grew up building and flying and had a great time with FF and C/L throughout the 50s and early 60s. Inevitably, I stopped for a while, then got heavily into radio, but got a bit bored! Since retirement have got back into building and flying again, joining SAM35 earlier this year and returning to my first love: small scale rubber, electric, Gasparin CO2 -- all free flight of course! And now, thanks to jetex.org, Jetex!

Many years ago, when I was about 12 or 13 years old, I enjoyed some success with a 50C powered Keil Kraft 'Flying Scale' MiG 15. It flew quite well, although I painted it with silver dope and it was probably a bit too heavy, so it didn't perform beyond a few seconds, but I well remember the thrill of hearing the hiss and seeing the white plume trailing behind the model as it skimmed the grass. Happy days! It is a wonder more kids don't get involved in this sort of thing these days, but I guess that is another story!

Where was I? Oh yes, being inspired to give Jetex another go, I bought some reproduction kits and managed to secure some Jetex stuff - motors and pellets through SAM contacts and from eBay (an inconsistent source in availability, quality and price). I was assured the 50+ year old motors, pellets and fuse would still work! My first model was a 'Brankit' Hawker Hunter, a reproduction of the Keil Kraft 'Flying Scale' Hawker Hunter.



A short length of fuse from the oldest looking tin burst into fizz immediately with a match flame and I dried out some Sebel pellets. I also had some Powermax Jet-x stuff from John Emmet I have no past experience of the Powermax stuff, although I remember them appearing years ago, when I ran a small model shop. I bought them from an interest point of view. My memory of flying Jetex is still pretty good with a few exceptions, so with a bit of extra advice from Roger, who told me about the new-to-me 'Car Plan' aluminium tape (to line the troughs) and assured me the old asbestos sheet I found in a Jetex box was still usable, I was all set!
All my models are made for flying, not display, and I treated the Hunter as a test bed. Tissue covered (I found it quite a challenge to cover - it must be me I expect!) it weighed only 19.9 grams with a motor clip, but needed 6.1 grams added to holes in the nose block to get it to balance and get a nice glide. The total weight with an unloaded Jetex 50C is 36.5 grams. I do not know how these weights compare with others - I am a bit of a heavy builder, something I guess stems from building large RC stuff where scales and balances were not part of the work shop and is something I am trying to correct!
Fortunately where I live I have one or two fields on my doorstep, so to speak, well suited to Jetex and free flight in general and a local farmer has given me the okay outside the shooting season in case I frighten the pheasants! I was thrilled when at the third attempt the Hunter climbed away for a short but reasonable flight.

I used one Sebel pellet and one Powermax, the fuse poked into the hole, so no gauze fitted. The Powermax pellet burned very rapidly so this combination of fuel gave a shorter run than I remember. The first two flights I had a problem with it stalling badly under power, and this third flight was achieved with a good amount of nose weight! without the last bit of nose weight added to achieve the flight mentioned, the Hunter still climbed away in a series of stalls. But it was still a thrill to see the Hunter climbing away, brief as it was. I asked Roger about the flight pattern. He commented,

"So pleased to hear of your success with the KK Hunter - and with genuine Jetex too. Well done! The flight pattern you describe - stalling under power - is typical of the KK Hunter, which has an over-large tailplane and excess 'decalage'. The Skyleada version is thought to be superior and more scale-like to boot. Modern thinking is to modify troughs so that they incorporate 'down thrust' as the exhaust deflects off the trough".

I had built it according to the KK plan supplied with kit. The 50C is mounted at an angle, relative to the wing, front end up, so the thrust line is pointing down. I have figured this has the effect of pushing the nose up under power.

So I remounted the motor with the thrust pointing slightly upwards into the trough. This cured the tendency to stall and the model now flies with less nose weight. In early March I got a great flight out of it, two right hand circles followed by a straight climb out and glide. I thought it looked terrific against the blue sky. For this flight I used a 50B with an ICI pellet, giving longer duration. It flies flew better than my MiG 15 of all those years ago ever did!

As the weather now became quite windy and further flying not possible, I was able to finish my Panther, MiG 15 and Skyray. All these were bought from the 'Vintage Model Company' who have taken over from Mike Brannan. See:

www.vintagemodelcompany.com/jetex-powered-models.html







the MiG weighs 34 grams and the Panther 32 grams with an unloaded 50C. I have built them to fly, and hopefully they will. Like my other models, they are presentable but not show pieces, although I do admire pristine scale models built to standards I cannot attain. They are finished in unpainted tissue with stringers a plenty, but when they are skywards you can't see the stringers!



The Skyray is a bit strange. The 'Easy Built' plan supplied in the kit looks a copy of the Keil design but it spans 14.5" as opposed to the quoted 13.5" of the KK one, and mounting the motor where shown on the plan produces a very tail heavy model.



So I moved it forwards 60mm and I still think it might need nose weight. Time will tell if this was a good idea!

Well, that's my story so far. I hope it might inspire others to give Jetex another go. I have not tried Rapiers, though I have been given some old ones in green boxes. I recently obtained the 'Eagle Book of Spacecraft Models', which I had when I was a boy, and from it built the 'flying saucer' and 'man in space', I remember they both flew well, and so at some point in my busy building program, I intend to build them again.

You can see I am quite enthusiastic about the prospects of future Jetex flying. I only hope the weather at Old Warden is better this year than it has been, where, says Roger, I can join the other 'Old Reactionaries'!"

I think you'll agree this is an inspiring story. And it's (hopefully) just the first chapter .:cheer:

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Last Edit: by rogersimmonds.
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