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.

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I have now tested some of the latest L-2 and L-1 motors collected from Dr Zigmund by our very own 'Nighthawk'. 

Dr Z's  nominal thrust ratings are:

70Mn for L1
130Mn for L2
150Mn for L2X
200+Mn for L2HP
 
We have, as yet, no examples of the 2014 'L-2 HP' or L-3 motors.  
 
In actual tests, and these were in duplicate or triplicate to be sure I wasn't measuring a 'one off' rogue motor, this is what I found for the motors we do have in stock:
 
L12014 thrust
 
 
Above: note the 2013 L-1 motor tested with the others.  Thrust is a bit down from when I tested these in 2013, but still very usable.
 
 
L2 2014 thrust
 
 
 
L2 X2014 thrust
 
 
 
The first thing thing to be said is that these thrusts bear little relation to dr Z's 'nominal'  ratings, and I really don't know how Dr Z arrives at his figures.  But mine are what I found, and I have the videos of the thrust rig to prove it!
 
 
 
However, the good news is that the output of the 2014 L-1 motors is healthy, a bit higher than those from 2013, but great for  profile scale models of 8-10" span.
 
The 'standard' L-2 motors are disappointing, the thrust is low, and though the run time is gratifying, the motor cases did come close to 'burning through':
 
L2 2014
 
 
They are of too low a thrust for the old 'Flying Scale' models and though suitable for profile models, I did find them difficult to light.  They needed extensive 'boring out' with a 1mm reamer and the addition of 'fairy dust' (ground up match heads) to get going.  I would advise these are used with caution.  In the right (light!) model the long burn time could give a splendid flight and a long walk!
 
I hope that when Dr Z visits in July he can bring some standard L-2's of a more useful specification.
 
 
The good news is that the 2014 'L-2X' motors are quite close to what I found for the 2013 examples:
 
L2X Blog
 
Above:  L-2 X motors tested in 2013.  This graph is included for comparison.  Ace flyers like Mike Suart found them very useful, and my larger F-100 Super Sabre liked these motors a lot!
 
 

 

Note the  shorter, though still acceptable, burn time of the 2014 motors.  The 2013 L-2X  motors worked well in built up models, and  larger profile ans semi profile models (like my F-100) and I hope these 2014 motors will be the same.

 

The less than good news is that stocks of these 2014 L-2 X's are limited - so order now.  

 

For those who want to fly Rapiers this year, and are starting out - my advice would be to buy some L-1's (of which I have good stocks ) and put it them in a (colourful) profile model (see the Jetex.org store!).

 

I hope  talk to Dr Z in July  so we can get some good L-2 motors of 120-130 mN, but until then we do have to, as in years gone by, work with what we've got!

 

As an 'addendum' to the above, here are some photos taken during the actual tests, just to prove I'm not making any of  this up!L2 test

 

Above: a standard L-2 in the middle its run.  Note the reading hovers on '11 grams'.  The weight of the motor at this point can be calculated to be about 3-4 grams.  The exhaust is barely visible.

 

L2 2014 thrust end

 

Above: a standard L-2 at  the end of its run.  Note the reading, seen through the smoke, is now '0 grams'.

 

By subtracting the weight of the motor at each time point (the motor looses about 5-7 grams during the power run ) it ca readily be calculated that the thrust of these standard L-2 motors is, at best, below 100 mN.  Note the charred motor case.

 

L-2X thrust

 

Above: an L-2 at mid run.  Note the reading hovers on '27 grams'  If the motor at this point weighs about 4 or do  grams it means the (static) thrust is over 200 mn.  

This is a useful amount of grunt, but not the 150 mN' specified.  Note the rather impressive glowing exhaust which contrasts with the more feeble exhaust of the 'standard' L-2.  The L-2 X was a lot louder, too!

 

I must emphasise that these simple static thrusts  are useful in the comparing of motors, and the thrust in a model in high speed flight will be different.

 

 

 

 

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Tis Spring, and in the spring, an old aeromodeller’s fancy turns to thoughts of trimming all those models built during the dark damp days of winter.  Readers will remember my current penchant for profile models, and I have just returned from the local recreation ground with a spring in my step and a bag of no less than five newly trimmed scale jets: 

 Profiles March 2014 3

Above:  new profile models for 2014.  All glided well from a strong hand launch, needing only a little nose weight and little adjustment of adjustable rudders (Mig-19 and Alpha Jet) or elevons (F-106).  They now just need motor mounts and a calm day!

 

For lots of good reasons profile scale models (‘PSMs’) make a lot of sense for us jet jockeys.  There are a lot of excellent designs, new and old, available at the click of a mouse; they are easy to make, fly well and if you lose one due to a dubious motor it’s no big deal.  They are great, too for experimenting with unusual planforms. 

RS 0709 707 

Above:  Roger Smith at Old Warden, September 2013.  The sadly undecorated profile Avro 707 was a lot of fun and flew splendidly with a (side mounted) Rapier L-2HP.

 

But I did have a problem with profile models in the old days,  though, believing the term ‘profile scale’ was an oxymoron.  To me they were crude and unsophisticated, even if (to repeat) they were quick to build, light, easy to adapt to a range of thrusts, and, if damaged by errant motors, were easy to repair or replace.  I couldn’t, somehow,  accept them as legitimate.

Part of the problem was that in my early rocketeering days I saw, and was attacked by, some very lacklustre models launched by quite prestigious modellers.  I was very unimpressed by their pale wooden bodies and great lumps of Blu-Tac stuck on their noses (the models, not the modellers). 

 

 

Fortunately, I was converted by the wonderfully decorated models of Howard Metcalfe: 

Howards profiles 

Above:  a selection of Howard's profile models from a few years ago.

 

HB 508

Above: Howard’s more recent Supermarine 508.  Note the meticulously painted (sprayed, I believe), finish and the thrust tab.  The butterfly tail is quite unusual.

HM Skyray 

Above:  Another of Howard's more recent models.  This is what Bill Dean's Skyray should look like!  Howard prepared the templates using CAD.  These were then printed on tissue which was then affixed to sheet balsa before assembly. 

 

Others, too, showed me what PSMs could look like: 

WS Javelin 02 10 

Above: Walter Snowdon’s fine Jetex Javelin.  Such beautiful paintwork takes more skill and patience than I can easily muster! 

So it was that I started the ‘Campaign for real PSM’s’ whose members eschew bare wood, will crush, dismember or surreptitiously eliminate any examples of, say,  Bill Dean’s Skyray or Hunter that lack national markings and fin flashes.  

The old Veron and Keil Kraft ‘ARTF’ profile kits like the Sea Hawk came pre-decorated, and looked good on the flying field without too much effort from the builder.  Though they are easy to recreate using computer graphics programs, they appear only to appeal to old guys like me who remember them from the first time round!  This is a pity as they still make an excellent introduction to rocket flying.

 

George Foster, like many older modellers,  prefers to design his own models.  But, I am pleased to say,  he obviously aggrees with the principles of CRPSM:

GF Provost naked 

 

GF Provost 1

Above: George’s Depron Jet Provost before and after decoration with felt tip pens.

 

But for me, there was a  ‘problem’: finishing the bare wood (or Depron) requires skills with paint (or  felt-tip pens) that I don’t find easy.  I lack the patience and artistic acumen to do this well.  

So I prefer the ‘printed paper on balsa (or Depron)  methods which have  been all but perfected by Rob Smith: 

F-100 Pair April 2013 

Above: it’s easy (and quick) when you know how.  Rob’s two Super Sabres.  Take your pick!

 

This method can be taken as far as you want to go, if one is happy with a square fuselage the templates can be transferred directly to balsa or Depron sheet: 

MiG-19 sq 

 

Alpha Jet sq 1

Above: two examples of my profile models ‘just off the press’  with square '3D' fuselages.  Here, printed templates are transferred directly to sheet balsa. 

 

Alternatively, you can complicate matters by going for a rounded fuselage: 

MiG-19 rd

 

Alpha Jet rounded 1 

Above: also ‘just off the press’ - two models with rounded fuselages.  Here, templates are transferred to the balsa surfaces after construction.  Not easy! 

 

Is rounding the fuselage  worth the effort?  Probably not, even though it saves a little weight.  The  square ones seem to fly equally well, and in the air, who is to notice?  And all the extra complication rather goes against the received wisdom that profile models should be ‘quick and easy’.

 

John Rigby is another member of CRPSM, and uses (I think) printed tissue on his true profile models:

JD MiG-21

Above: John’s very nice MiG 21.  Hadrian Tucker has ponted out that tissue on balsa is not particularly light, and printing directly on balsa would be better.  Yes, but how? 

 

 Chris Richards, too, believes in properly decorated profile models:

Mig29 L2

Above: Chris’s MiG 29 triumphed at the 2014 Peterboro' Flying Aces.  Built from sheet balsa, templates could be transferred to balsa sheet before building.  But this is more than a simple profile model:  perhaps ‘semi profile model’ is an apt description?  

 

Meanwhile, I carry on with my own obsession.  Here is the latest:

Tiger 1

 

If anybody would like to join the CRPSM, please contact me.  Members could receive a T-shirt and a badge, and a full set of felt tip pens to use on any bare bodied models (I know, I know) they find on the flying field! 

 

Oh yes: if anyone can suggest an easy ways to transfer printed copies of computer generated templates of models to balsa, or knows of a reasonably priced flat bed printer that can handle 1/16" sheet balsa, please let me know.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Every organisation, well the ones I’m familiar with, like the Society of Antique Modellers, the British Model Flyers Association and the Village Tidily Winks Team,  share a grave (and I use the word ‘grave’ with its morbid resonance advisedly) common concern: “Who will carry on after we are gone?”

A trip to model flying events, especially  free flight, shows that the vast majority of flyers are either in, or are approaching, what are, one chap said, their ‘twilight years’.  Hmmm. 

There is the occasional youngster on the field with granddad, but of 15-20 year olds (the group amongst whom modelling was so popular in the 1950s-1960s), there is little sign. 

So are we the last free flight sport modellers, and, more pertinent to Jetex.org, the last ‘Jetex’ modellers?

Perhaps young modellers (under the age of 45) fly the splendidly cheap R/C RTF models – park flyers – and the like?  But if they are, I don’t see them.  Perhaps they are busy on their simulators, and will one day graduate from this solipsistic obsession to the real world.  We can but hope.  And that, having crashed their first real model, they don’t look for the ‘reboot’ key!

In the spirit of, “It is better to light one candle than bemoan the dark” the BMFA promotes a number of cheap and cheerful models suitable for the fledging flyer. 

One of these, the Aerojet delta, might go well with a Rapier … this got me thinking: in the main, the simple Jetex kits suitable for the beginner, like the Veron Sea Hawk or Keil Kraft Shooting Star, are over fifty years old and (apparentlu) attractive only to those who remember them from their youth.  The Jetex.org ‘part kits’ are, I think, very nice, but sell only to those happy to part with a small proportion of their pension:

Jetex org Sea Hawk

 Above: the Jetex.org Sea Hawk.  It is a faithful replica of Phil Smith's original Veron 91950?) kit for Jetex 50.  Only bought today, alas, by modellers of a 'certain age'!  

 

So to try attract youngsters I thought I might try something more colourful; a MiG-19 for example:

 

MiG19 1

 

Above:  The prototype MiG-19, inspired by the Japanese Tiger kit of 1958-1960. It is more modern than the Sea Hawk, but will it still be seen as desparately old fashioned?  

 

I then thought, what else is out there likely to attract the young Jet Jockey?  Jason Wentworth, similarly concerned to evangelise modelling in general and rocket flying in particular, sent me examples of a little chucky popular in the US that he thought might just be suitable for an L-1: 

DD Chucky blog

 Above: readily available in the US, Jason thought these near-unbreakable chuckies might go well with an L-1. Perhaps, though they are a trifle small.  Could be a lot of fun, though.

 

Perhaps, I thought, there are some more suitable 'quick and easy' models  out there?  A quick survey of the giganormous Hobby King site  came up with a few suitable  candidates:

Alpha Jet HB

 Above:  Hobby King's all Depron Alpha Jet.  At only a few ponds I expect they sell well.  But will the young jet jockey graduate from this to something a little more challenging?  

 

Sukhoi 2

 Above: Hobby King's SU-11.  An exciting model, and at just a few pounds (though don't forget the tax and the (quite steep) postage) it costs less than the kits available on Jetex.org. 

 

OK, and according to my friend André Bird the Hobby King jets  can be rocket powered, given a bit of serious ‘fettling’ (his Raptor needed two Rapiers mounted atop!):

AB F22

 Above: Andre showed off his adaptations of the Hoby King F-22 Raptor and F-18 at the 2014 Peterboro Flying Aces.  He says they do fly (though he declined to do so in the wind we had) but are more than a little tricky to trim. 

 

And this is the point worth emphasising.  I can produce an Alpha Jet nearly as tasty looking as that offered by Hobby king:

Alpha Jet 1

 Above: My prototype (and unfinished) Alpha Jet.  Being all-balsa  the flying surfaces are very stiff, and trimming with a Rapier L-2 should be straightforward.

 

It does, of course, need more 'building' than Hobby King's models, but it will (I hope) fly in a fast and in a smoky way with a Rapier motor ‘off the shelf’. This justifies the asking price, but will the punters see it that way?

To conclude: has  anyone else out there attached Rapiers to Hobby king’s products?  And finally, how can the joys of Jetex and the rewards of Rapiers be evangelised to the next generation?  Any thoughts?   

 

 

 

 

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We've just added some more models into the Jetex Store ? if you go to the Store you can scroll to the bottom of the page and then navigate to the second and third pages which also now display models :)

You can now choose between L1 and L2 power for your new model. Simply click next to the power of your choice.

Other profile and semi-profile models are in the pipeline, including a MiG-19 and
F-102 based on the vintage Japanese Tiger models, and an original Alpha Jet.

migs

 

Please contact Jetex.org for the latest availability of Rapier motors.

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Our intrepid contact with Dr Zigmund (‘Nighthawk’) will soon be collecting Rapiers for the 2014 flying season.  He asks what types we would like him to collect, so I told him, “A repeat of the 2013 types please”.

These motors were favourably received by rocketeers, as the L-2X motors were perfect for models like the Aerographics Bell XS-1, Bluebottle Bell X1E, Mike Stuart’s Thunderstreak, and the larger profile models like Bill Dean's Hawker Hunter or my own F-100.

The L-2HP is potent enough for the older larger Flying Scale models and the Aerographics Sukhoi SU-11 or Steve Bage’s MiG 21,and the latest L-1s are just perfect for smaller profile models.

 

Rapier Shinden 3

 

 

Above:  Rob Smith's unusual Jet Shinden flies splendidly with a Rapier L-1.

 

 

My thrust-time graphs I produced for the 2013 motors are shown below:

L2X Blog

 

 

Above: L-2X

L2-HP 2013

Above: L-2 HP - pretty potent!

 

L1 2013

Above:  The latest L-1s - a really great motor!

 

So (a) think about what jets you should be building this year, secure in the knowledge that, at least on this side of the pond, you will have something to power them with (b) ask yourself what motors you would like this year. 

And you could always  phone up SAMS Models in the UK and encourage  George to restock with his Rapier kits!

 

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