2021 has seen the most widespread marketing of miniature, sustained thrust, solid fuel reaction motors since the days of Jet-X. And about time too, that was in 1986. For this we have to thank Piotr Tendera who has taken on significant expense and effort to get the CE mark for his Tendera motors. And while it might be argued that this has resulted, due to the mandated use of the wider green fuze, motors with a lower overall Specific Index. But, for myself the widespread availability of the CE marked motors is a price worth paying. Already we are seeing signs of interest from people who are outside the usual demographic of the vintage modeller. I expect to see some novel and interesting Tendera powered creations appear over the next months.
Additionally, I think, we are likely to see the most interesting developments using the larger of the motors in Piotr’s range. The L3 and L4 both offer some new possibilities and on these fronts I’ve been making (rather slow) progress.
Radio Control is of course one possibility. Indeed, one of my correspondents from here in Germany (Frank Schwellethin) has been flying R/C with the more usual short duration motors from the Estes range and he will now, I think, have a go with the Tendera type.
Frank sent me several videos of his R/C rocket gliders in flight and inspired I was moved to complete a Klima Me163 and fit it with an Tendera L4. (This is intended for a D3 model rocket motor.) I haven’t had the chance to fly it yet as I’ve been awaiting the delivery of a miniature receiver, a Lemon Stability + from the USA. This, as its name suggests, is not just a receiver but it also includes additional hardware to build in a modicum of pitch and roll stability.
Electronic stability is the second possibility and it has long been an interest of mine. Since I started hardware that weighed over 50 Kg can now effectively be replaced with modern electronics weighing just a few grams. Luckily for me, the principals, and the maths, remain the same.
Now R/C receivers such as the Lemon and the Spektrum SAFE range include the ability to re-establish hands-off level flight at almost no additional cost. And configurations such as quadcopter, that have no inherent stability, and even helicopters without the stabilising fly-bars are feasible. But what about fixed wing free flight and specifically scale, reaction powered flight?
Seeing a recent copy of the Aeromodeller I feared that once again I'd prevaricated too long. The byline, ‘Low wing FF stabiliser’ caught my eye. The article, by Steve Glass, sounded something like what I had in mind. In fact Steve is using an add on stabiliser, the A3S3, designed to work, downstream as it were, from a conventional RC system. Steve has added some circuitry to simulate the pulse stream from an R/C receiver and, it must be said, this is pretty much purely a wings levelling system. What I have in mind is something more specific for reaction power. Additionally, the A3S3 has a setup facility that must be installed on a PC or mobile phone. Not, I fancy, something that will find favour with everyone.
For me what is required is something that can be set up on the flying field. The user can set the glide angle manually and adjust the rate of ascent. The controller consists of a solid-state gyro accelerometer board, a micro controller, battery and two miniature servos.
One would go to the field with the model with controller installed, switch on and first sort out the power off glide with a used motor installed. When this is satisfactory, select (guess) an angle for power-on ascent. This could be done by holding the model at the desired pitch angle. This is saved in the controller with a button press.
The model is then loaded for powered flight and hand launched with the motor building up thrust.
The controller detects an X axis acceleration from the thrust which it can integrate to approximate airspeed. The appropriate pitch up is wound in on the elevator/elevons. (The board would need to be capable of managing elevator and ailerons or elevons). Perhaps a potentiometer is used to preset the power on flying speed. The controller would start to wind in pitch once this airspeed is achieved.
We should now see the model climbing to best altitude. The controller detects the end of the thrust phase and changes the pitch trim to that for best glide. We might also have a gentle turn trimmed in!
Sounds simple and maybe all this is justified as a means to achieve that perfect scale, no dihedral, rear mounted motor Lockheed U2.
But what class of model would this be? It’s not R/C, it’s not C/L and its not quite F/F either. I leave that philosophical question as an exercise for the reader.
Looking forward to doing some flying in 2022.
Hello from Terry and Tendera developments
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Latest Motors from Dr Zigmund
Dr Zigmund, developer and manufacturer of our 'one shot' Rapier motors, delivered a fresh batch of three types of L-2's (L-2 LT, L-2-X and L-2 HP) when he visited Old Warden's model meeting in July.
I have now tested these with the following results
These are quite pleasing: the L-2X motors appear a bit more powerful than the 'HPs' but both are usable. The L-2 LTs have less 'oomph' than last year's, but, again, they are perfectly acceptable.
The L-1 motors are quite powerful:
We have good stocks of all these motors, so please contact me for details of how to get them.
New L-1 and L-2 Motors from Poland
Regular 'Jetex' flyers and readers of the various motor-related threads on the forum will know that motors are in a bit of a short supply at the moment. We have no Rapier L-1's and stocks of about 300 Rapier L-2's.
I have sorted out these last motors for distribution and measured their performance:
Fortunately, when these are all gone, we have an alternative, a brand new, and hopefully secure, supply of motors for our beloved rocket planes. These are the new TSP 'Tender' motors. Below are examples of the L-1 and L-2:
These are very close to the sizes of the Rapier L-1 and L-2 motors. Note these are 'used' motors and that the casings have done their job well!
Below are the TSP L-2's with the Rapier L-2's:
Note they are similar in size to Rapiers, if a bit thicker. No problem, though!
The performance of the Tender L-'s are great:
And the thrust is consistent:
The Tender L-2 motors too, measure well:
And the thrust on the test rig with different sizes of nozzles is predictable:
Boring out the two types of L-2 and L-2L to 1.7 mm gives particularly good results:
Piotr, who is responsible for the development and manufacture of these motors, tells me he will now concentrate on the 'L-2L' type. These can be used with confidence in any of the profile Jetex.org kits, or the many Jetex kits from the Vintage Model company:
More about these motors can be found on two forum threads, see
Piotr is happy to discuss the supply of these motors to flyers in the UK. His email address is:
I shall be getting a supply of the Tender L-1 motors from him, and and I look forward to trying out Piotr's motors on the flying field. The motors are beautifully produced and can be put in that precious scale model with confidence!
Above: a TSP Tender L-2L motor on the test rig. The reading equates to a steady thrust of 150mN, just perfect for those vintage models!
All of the above is very much 'work in progress' so do look at the forum for news of further developments, like an L-3 and a TSP L-2 HP!
Jetex and Rapier related ‘blogs’
Welcome to the first of what I hope will be regular 'Jetex and Rapier related 'blogs'. As this is my first foray into the 'blogosphere' it will take me time to find my niche, so please bear with me.
These will of course be full of interesting observations about the modern 'small model jet plane flying' scene which will motivate a loyal cadre of enthusiasts to keep up with the latest news about motor availability, upcoming meetings and how to take part in what I hope will be a growing part of the free flight aeromodelling scene. Note the 'free flight' bit. I have nothing to say about those marvellous and sophisticated RC jets that we see showing off at meetings. However, free flight EDF is pertinent to our hobby and is one way of keeping our models flying. We shall see!
What with the winter weather – my own flying field is more suited to hydroplanes than aeroplanes at the moment – I have been designing some new models for the new flying season. These are simple 'semi-profile' models like the Cougar above suitable for the latest batch of Rapier L-1 and L-2 motors.
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