Jetex Blog

An online resource covering the technical and historical aspects of small sustained thrust micro rocket motors for use in model airplanes and other craft.

Jetex and Rapier performance

Howard Metcalfe has recently been flying on Salisbury Plain, see:

http://www.jetex.org/forum/model-jet-planes-flying/274-flying-at-salisbury-plain.html

This was (for us Brits) a hotter-than-average day: 27o Celsius.  Howard reports that his Rapier L-2 motors were giving more thrust than he expected:

"I was frustrated by poor flights caused (in my opinion) by the high temperatures.  I‘ll try and explain. In the winter, the only way I could get a reasonable performance from the motors when flying on a snow covered field was to warm them up by keeping them next to my skin in my trouser pocket.  In my experience cold definitely reduces thrust. 

So I should not have been surprised by the much higher thrusts I was now getting in the  heat.  The Valiant and Comet performed high speed loops . . . and, in the case of the Comet, this was with an L-2LT!  I eventually worked out what was going on and selected lower power motors and got some good flights with my profile Skyray, and, with old green L-1s, with my 1.6x oversized Bill Dean Spook.  This climbed to a considerable height in a series of steps.  [Oh wow! - Roger].  I used the same L-1s in my Depron BAe Hawk (designed for original L-1s).  These gave long high flights, demonstrating once again that the power was well up -  to around at least 80-90mN.

 Is it only me or has anyone else experienced this phenomenon?  It can’t be just the batch of motors from the last year or so as the L1’s were from way back." 

Howard presents a plausible hypothesis, and if, on a hot day, my models start looping or cavorting about the sky unpredictably on a flying day's afternoon, when previously, in the cooler morning, they'd been flying steadily,  I will suspect the motors are indeed getting more potent.  If a day's flying continues into the evening I shall be very interest if the flight patterns of my models calm down! 

To test, or prove, Howard's theory properly will entail the use of cooler bags, hand warmers and either my test rig or a very reliable model like the Jetex Wren or Keil Kraft MiG 15.  Given the known variability of Rapiers, though, each cold/warm/hot data point will need to be at least in triplicate.  A lot of work, a lot of motors.  Personally, I'd rather be flying, and, as a day warms up, choose models from my "likes a lot of thrust" box.  For example my power-hungry T-38 Talons.

Talons blog

Now Howard has alerted us to this phenomenon I look forward to other rocketeers' observations and feedback. 

It is thought that Jetex motors, in general, give smoother flights.  Last year I had some really excellent sorties with my profile F-80 KK Comet powered with a ribbed Jetex 50 and ICI pellets.  I also had ome quite spectacular, if short lived, flights with a Wren powered by a Jetex 50C and Sebel pellets.  So I decided to test the thrust these motors were actually giving.

 

First, an original ribbed 50:

J50 ribbed ICI Pellet

Next a Jetex 50B, which proved rather more potent:

J50 B ICI Pellet

And then a 50C:

J50C Sebel

This gave a lot more thrust.  Worryingly, the duplicates were not that similar, perhaps because the pellets came from a different tin.  Hmmm .... this suggests yet another batch of experiments ... how have the pellets been stored, had they been dried well before use (perhaps in an oven); what was the diameter of the motors' orifices?  Etc etc.    But the 'bottom line' to be taken from the above graphs is:  it is perfectly possible to fly genuine Jetex today with stuff bought from eBay!

The formal  experiments with Jetex motors and pellets will not be done.  At least, not by me -- I'm quite content to take 'pot luck' when flying my small jets, and accept we will never, ever, pin down all the variables.  A good flight and, better yet, the occasional outstanding flight, more than makes up for the frustrations.  Even Howard was, at the end of his day at Salisbury Plain, happy!

Howard models

 Above:  Howard's Spook, Hawk, Skyray and Valiant at his recent trip to Salisbury Plain.  They look good to me!

 

 

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FROG 'Penguin' Plastic Scale Model Kits1936 - 1950" by Peter van Lune

Another slightly 'off topic' topic, but one that will, I hope, interest Jetex enthusiasts:

PVL Penguin

 

Model flyers naturally have a great interest in the old FROG flying models, and Mike Stuart's wonderful website: http://www.houseoffrog.co.uk contains a plethora of plans to enable the replication of many classic FROG models. FROG nostalgia has been well served too, by "FROG Model Aircraft" by Richard Lines and Leif Hellstrӧm which was published in 1989. This marvelous book covers well the history of the founding of FROG by Charles and John Wilmot and Joe Mansour and the development of their innovative products like the prewar Interceptor, the Junior and Senior range of model aircraft after the war (including the World's first all-metal modelaircraft) and the well-respected FROG plastic kits that are still with us.

The book also includes fine compendia of all FROG models, including listings of all the 'Penguins', the non flying (thus the name) scale models moulded from cellulose acetate. The development of these, the archetype of all 1/72 plastic kits. is, however, only briefly described and there has been no book dedicated to the history of these fascinating kits, which even well respected histories of plastic models ignore or misrepresent. And there has been no written history of the little known 'Wimco' Hollows produced by Jetex in the 1960s. Until now.

 Peter, in his just-published book,  covers the genesis of both Penguinsand the troublesome hollows (the progenitors of today's 'vac forms')  in some detail. There is much else  of interest modellers: as well as the many photos and  adverts  ( yes, they are mostly of plastic models, but which who didn't build a few static models in his youth?)  there is, splendidly,  the Jetex connection, as Charles Wilmot and Joe Mansour founded Jetex after they were forced out of IMA soon after the war. 

CWilmot PVL

Above: a previously unknown (1948?) photo of Charles Wilmot with a prototype Jetex model. 

Jetex, as Peter recounts, were soon joined by Bert Judge, who helped produce the early FROG Diesel engines, and the innovation continue.  The somewhat strained relationship between FROG and Jetex is covered (FROG didn't  produce any models for Jetex power, a great shame, the FROG 'Mamba' would have gone splendidly with a Jetex 50).

In short, Peter tackles every aspect of Penguin kits and from their creation to their demise comprehensively, with many personal touches about the idiosyncratic characters involved in the saga and the sad and gradual fading of both Jetex and FROG, and reasons for this are not ignored. There are many unique photos, all except the historical ones in colour, and the text is never less than readable, and the colourful layout is very attractive.  I found Peter's account of his odessy from youthful builder to collector then historian fascinating, and the chapter on model restoration (cellulose acetate is not very stable!) of especial interest.

This  magnificent book -  well more an encyclopedia -  is available from Peter's website: http://frogpenguin.com/ for just 30 Euros.  It  is thoroughly recommended. One thought: a similar book about Jetex is sorely needed. To make it as good as this one, though,  is quite a  challenge!

 

 

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Dan Dare Exhibition, Herne Bay 29 April - 1 July 2017

Howard Smith has  just  told me about an exhibition he is organising that I think will be of great Intest to many Jetex flyers.  Here is the poster : 

Dan Dare Ex 1

 

And here are the details:

 

Dan Dare Ex 2

This promises to be a most exciting event!  For those who doubt there is a 'Dan Dare-Jetex connection, this will remind you:

 

DD Spaceship montage 11 15

If any forum member gets there before I do (I don't travel too well at the moment) plese tell all of us about it.

 

Onwards and upwards,

Roger 

Added 05/07/17: I've just had this from Howard:

Here’s a photo of the Spaceship – not that great a shot. I have the main plans alongside if and not displayed I also have the Launcher plans and building instructions.

Currently into first week and much has happened with people coming forward with items never seen and stories of relatives who were involved.

If any of your Jetex colleagues come to the show, get them to contact me beforehand and I’ll meet them and bring the other plans along:

Jetex Blog

 

This looks to be a great event - if any Jetexinista visits please tell us! 

 

Roger 

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Jetex and Rapier Flying in 2015 - a new beginning.

 

Those who have read my latest postings on the forum will realise that I am now, with a refurbished set of heart valves working as about as well as a mint condition (though antique) Jetex 50 or, perhaps, a new Rapier L-2X,  ready to give Jetex.org the attention it deserves.

 

Folk that I meet on the flying field are appreciative of the website.  This nice - it is there for the free flight rocket flyer - and it is my hope to add to the site and make it an even better resource for those, young and old, who want to fill the sky with smoke trails, and not the thrumming of the latest ARTF drone.

 

I have not been altogether idle during my enforced months of convalescence, and I have put together several new designs, including this 'semi-profile' T-38 Talon:

Talon 1

 

T38 1 

 

T38 2 

T38 5

Above:    My latest models were designed, if that is the right word, by modifying  3-views retrieved from the Internet.  After some manipulation of the flying surfaces, templates were then refined and decorated using 'Paintshop pro'.  

The printed templates were then transferred to (generally) 1/16" light balsa.

 I made two versions of the T-38 in the livery of the USAF aerobatic team (the 'Thunderbirds'): number '1'  to check everything went together OK, (note the square fuselage) and no '3', where the fuselage is 'fleshed out' and a lot more rounded.  

Both await their  'rocket pods' (for Rapier L-2) and  trimming. 

 

Well-known rocket-flyer and 'prime pilot' Andy Blackwell has recently 'beta tested' this design for me:

AB T-38 

Above: Andy was quicker finishing his T-38 Thunderbird (no 2') than I was with numbers 1 or 3!  Here he is after its first very successful and spectacular flight.

 

Next, something for the Francophiles (you know who you are!): 

Mirage 2

 

Mirage 3 

Above: Following the success of my semi-profile F-106 Delta Dart, I couldn't resist trying a  Mirage III.  If it flies as well as the Delta Dart I will be well pleased.  This is 'printed paper over balsa', which allows for a more rounded fuselage.

 

Back to the US: 

CorsairII 1

CorsairII 2 

Above: The Corsair II has all the proportions of a very stable model - large flying surfaces and plenty of fuselage side area.

 

And now for something completely different: 

Cutlass 3

 

Cutlass 1

Above: The Cutlass was let down in real life by its poor engines.  In miniature it presents a challenge, but I'm hoping that my version, powered by a Rapier L-2X, will show what the original could have done for the US Navy.

The Corsair II and Cutlass are printed 'Dark T-shirt' heat activated transfers over balsa.  This allows for a colourful model - note the balsa doesn't show through, but fuselsges are best left with square edges. 

 

Designing and building all (balsa) sheet models was therapeutic, but by this time I was fed up with staring at the computer screen, and hankered after something' stick and tissue' that needed a little more building: 

Hawker Hunter 2 

 

Hunter 1

Above: My original Skyleada Hawker Hunter was wrecked by a Rapier 'blow out' in 2008.  Here it is brought back from the dead and ready for covering.  Note the attention paid to the jet pipe, which looked a little 'naff' on my first one.

 

Here it is again, canopy fitted and ready for airbrushing - not my favourite procedure:

Hunter 2015 blog

Above:  It is covered in white 'Starspan': green Modelspan would have been better, as I hope to finish it in the 'eu de nil' ('duck egg green') of WB188, the first prototype.

 My building skills don't approach those of ubermodellers Mike Stuart, Peter Smart, Richard Crossley et al, but it's the best I can do.

I also cannot build light:  at the moment the Hunter a little over 26g without paint, motor mount or nose weight.  So think '32-34g' ready to fly.  It will probably need all of the 160 mN of thrust an L-2 X can provide.  We shall see.

 

 

Howard Metcalfe, too, has been taking a break from profile models:

HM Cougar 2 

Above: Howard's Cougar.  This is Andy Ray's design.  I do hope it will be finished before the end of the 2015 Flying Season.

 

If any reader is interested in any of the new profile models, I can supply templates that you can print out and attach to balsa, for example:  

Cutlass blog 

 

Or a set of finished balsa parts.  These, though, will cost you £17.50 including postage.

 

So there you have it: I'm all set for the 2015 season.  I would love to hear from you about your own models, especially 'work in progress'.  Please email me with a picture or two and some words.

 

I also hope to meet you on the flying field  - my next meeting is Middle Wallop in mid June.

 

 

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Jetex and Rapier Flying in 2015 - a new beginning.

 

Those who have read my latest postings on the forum will realise that I am now, with a refurbished set of heart valves working as well as a mint condition Jetex 50 or a new Rapier L-2X, am about ready to give Jetex.org the attention it deserves.

Folk that I meet on the flying field are appreciative of the website.  This nice - it is there for the free flight rocket flyer - and it is my hope to add to it and make it an even better resource for those, young and old, who want to fill the sky with smoke trails and not the thrumming of the latest ARTF drone.

I have not been altogether idle during my enforced months of convalescence, and have put together several new designs:

T38 4

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Apologies for lack of communication

Jetex Jim has been very much out of it for the last two months. Apologies for the lack of communication and any unfulfilled orders.

He's been having his gaskets renewed and although they are fine the rest of his 1947 Jetex aero-body will need a lot of time to recover. Roger.

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