Mounting Rapiers in Models Part 2.
Intro: My previous blog on this subject was about the use of asbestos in a Rapier mount to see if this would prevent a model being damaged in the event of a Rapier case burn through. Experiments showed (you will remember) a mount with two thicknesses of asbestos proved ineffective.
The need for a robust motor mount was made even clearer when I tested a batch of Rapier what turned out to be L-2 LT motors:
Above: the thrust is adequate for a light model; however, there is a thrust spike towards the end of the (very nice 20 sec plus) burn time. The cases of two motors burned through at this point, with enough heat and flame to damage a model.
I wouldn't put one of these motors in a model, and certainly wouldn't provide them to even a brave modeller!
Following previous blog, I was contacted by Rob Mcconaghy, who suggested a ceramic or metal mount would resist the heat of Rapier propellant.
In the first instance, Bob offered to make some metal tubes of various aluminium alloys and one of stainless steel that I could test with Rapier L-1 and L-2 motors.
Rob was as good as his word, and a few days ago some beautiful tubes arrived by post:
Above: these alloy tubes are sized for L-1 and weigh only 0.6g. Those for L-2 were larger: those made of alloy weighing 0.9-1.2g, the stainless steel one weighed in at 2g.
And very beautifully machined they are too It almost seemed a pity to test them!
I first tested the stainless steel tube with a standard L-2. This had a small 1 mm hole drilled through the case to ensure a 'blow-out':
Above: We have ignition! The tube glowed red-orange but did not burn through and the model would have been protected.
I repeated the experiment with one of the suspect L-2 LT motors. The tube remained intact:
Above: The stainless steel (303SS) tube withstood L-2 blowouts. The L-2 on the left was predrilled to ensure a 'blow out'. Nasty. The L-2 LT on the right is scorched but intact.
So far so good!
Rob had high hopes for the lighter alloy tubes. He hoped their good conductivity would prevent them being melted.
This is the actual experiment with a prepared L-2:
Above: The Rapier ignited easily, gave a good thrust (about 160 mN) then a 'blow torch' flame on the right appeared.
And here's the alloy tube post-run:
Above: The Rapier 'blow-out' has burned a neat hole through the alloy. The model would not have been protected.
This was disappointing. I then tried an alloy tube with L-1. These motors are smaller. But do they burn as hot as an L-2? After two runs with prepared L-1s, this was the result:
Above: L-1 alloy tube with a Rapier L-1 on the left. The alloy (6061-T6 Al) has been melted through. This implies the Rapier burns hotter than 550 degrees Celsius.
Conclusion: no scientific experiment is a 'failure' if it gives a clear result. In this case it is: alloy is not effective; stainless steel is the way to go. A layer of ceramic tape around a stainless steel tube will be needed to protect a model from the high temperatures. I think we can live with the extra 2g weight.
My thanks must go to Rob for making and posting these tubes.
As an aside, turning to the actual models:
I have been protecting my profile models with self adhesive metal tape behind the motor:
Above: The Corsair II ready for its maiden flight. Note the metal foil and the down-thrust tab (made from the thin metal off a coffee can top).
Caution: (red alert!) The self-adhesive metal tape currently sold by, for example Halfords (in the UK) is too thin. This stuff is far better:
Above: this works fine for me. Available on eBay.
I look forward trying out ceramic mounting tubes, and trying a stainless steel Rapier mounting tube in a model.
Watch this space!
Recent Jetex Articles for the Society of Antique Modellers
In a previous life, I published more than a hundred Jetex and Rapier-related articles in SAM (35) Speaks, the prestigious monthly journal of the Society of Antique Modellers in the UK (chapter 35).
Copies of these were available month by month on the Jetex.org website, and PDF copies were sent out by email to jet modellers all over the world.
I would also add that a data disc of all my 'Jetex' articles, from 2002 was put together, and is still available for a small fee.
Earlier this year I resumed writing articles about the UK 'small jet scene' and these have been published by the estimable Colin Hutchinson, the new editor of SAM (35) Speaks. The response to these has been quite favourable, so I am offering PDF's of my new scribblings to any interested modeller.
Here is the first page of the Spring 2015 article:
And here is a taster of last summer's offering:
There are two more, autumn and winter, articles in the pipeline.
My articles are of course UK centered, but I'm hoping to include more 'international' news via a wider distribution of these which will result in feedback from the many jet modellers overseas.
If you would like copies, please contact me with your email address. In time, I will compile a subscription list, and the latest 'Jetex and Rapier' can be sent out to all those on the list automatically.
Any comments about the articles, and contributions to future articles, are very welcome.
Rapier L-2 type Motors in the USA
The lack of Rapiers has been a great source of frustration to US modellers, but it has been a great spur to the development of 'Micro EDF', but not everybody has been happy with the status quo, and Chris Sorenson of Maker Research Labs is determined to do something about this, partly because he believes the excitement of rocket planes will be a great way to get youngsters enthused about science and technology. I have been liaising with Chris for over a year and he and his colleagues have developed a Rapier L-2 analogue that looks most promising. I received examples of their prototype X-1 and X-2 motors for testing earlier this year. As Chris has gone public with his endeavours:
now is a good time to publish my results. I also tested one of the 2017 L-2 LT motors for comparison.
The thrust time profile of the L-2 LT ‑ a very useful 125 mN for 18 seconds ‑ is in-line with the many fine flights we have seen with these motors and shows just why they are so popular. The X-1 motors, of very similar size and weight to L-2s, fired up without problems, and their performance of roughly 140 mN for 12 sec is promising. A little more duration would be nice, and experiments with the jet orifice diameter and a combustion inhibitor could pay dividends.
Below are the 'empty' brown X motors with a used Rapier L-2 motors for comparison
Added 6 May 2017:
Have a look at Chris's latest video:
The thrust of the latest motors appears 'spot on' ... we just need a little more duration!
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 :
And here are the details:
This promises to be a most exciting event! For those who doubt there is a 'Dan Dare-Jetex connection, this will remind you:
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,
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:
This looks to be a great event - if any Jetexinista visits please tell us!
Rapier Motors 2017
I really should update info on the availability of Rapiers more often as there still seems to be the 'fake news' out there that you can't get them!
Well, we still have stocks of L-2 and L-1 motors of good performance. The current L-2LT motors are particularly nice:
This, in old money, is about 1/2oz for nearly 20 seconds - which is equivelent thrust to a Jetex 50 for a gratifying 6-7 sec longer. They work splendidly in my Veron Quickies and Keil Kraft shadow profile models, f'rinstance the Shooting Star:
Note the Rapier in a Jetex mounting clip -this allows comparisons of the L-2LT and original Jetex 50 to be made easily. Interesting!
Hurry whilst stocks last! Dr Z hopes to be in the UK in July with fresh supplies - contact me for updates.