A recent and very welcome addition to the small team of fliers of rocket powered free flight models is Martin Lambert. Martin is a superstar of reaction powered model flight as he is the designer and manufacturer of a range of miniature gas turbines, the Kolibri range. These units are engineering which masterpieces generate up to 5 kg of thrust and, of course  are intended for large radio control models.  Last year I paid a visit to Martin’s workshop which is rather north of me here in Munich and a little south of Frankfurt.

https://lambert-modellturbinen-onlineshop.de/

Kolibri (humming bird)

When I visited him Martin demonstrated one of these turbines in his test area. He has a grown up version of the thrust test rig that I use for testing the Tendera motors and a very well appointed workshop and test chamber.

Martin also has a collection of model aircraft piston engines some of which have been modified by him for radio control. I recall, I think, a Frog diesel which has had an R/C throttle added to it.

Martin also showed me a video of another one of his brainchildren, this was a hybrid rocket motor using nitrous oxide, which is available as a propellant for whipped cream, and I think celluloid as the fuel component of this hybrid motor. 

However, in recent times Martin has been talking to us and sharing his experiences with Tendera powered free flight models. He’s produced a Jetex Wren modified for Tendera L1 power and a beautifully executed Graupner Temco Pinto which is also modified for Tendera power. 

I’ve included several of Martin’s excellent photographs by way of illustration. 

 

Martin is a master craftsman and modelling custom canopies is but one of his skills.  

The model featured is a Graupner Temco Pinto 420mm span, 400 mm long.

All up weight 28gm with an L2 motor 38gm. 

Covered with Japan Gampi paper 9gm/square meter. Then coated with nitrate dope and finally airbrushed with Revell Aqua Color acrylic.

 

 

See the Pinto fly

 

 

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.

Best wishes

Terry Kidd

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: 

These are all very useful in the right model, so and please contact me (This email address is being protected from spambots. You need JavaScript enabled to view it.) if you would like some.

 

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:

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

More about these motors can be found on two forum threads, see

http://www.jetex.org/index.php/jetex-forum?view=topic&catid=8&id=317

and

http://www.jetex.org/index.php/jetex-forum?view=topic&catid=8&id=319

Piotr is happy to discuss the supply of these motors to flyers in the UK.  His email address is:

This email address is being protected from spambots. You need JavaScript enabled to view it.

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!

 

This blog is different from the usual in that this is Terry Kidd writing. Roger has kindly (and bravely) trusted me with the keys to Jetex.org . So I’m hoping to get this written and uploaded without scratching the paint work! I anticipate a little hesitation as I get accustomed to the controls, please be patient if things are not as polished as with Roger.
 
As some of you may recall I was, before Roger’s time, the Jetex correspondent for SAM 35. At the time my interest in Jetex was re-ignited (sorry) by the then availability of Jet-X. While Jet-X fuel left much to be desired the unique thrill of reaction powered flight was certainly there.
 
Well, a lot of water has gone under the bridge since then and in the interim we’ve had the end of Jet-X, the launch and demise of Rapier and now the introduction of Tendera. I took up a 6 month employment contract in Bavaria in Germany and after 16 years I’m still here. I’ve met Dr Zigmund on a couple of occasions -- the last of these last year when he produced the final Rapier batch. And I’ve had the pleasure to meet Piotr Tendera, who manufactures the Tendera motors and we have had some interesting conversations.
 
But now the big news is that the Piotr’s range of sustained thrust solid fuel motors (as I’m inclined to define the Jetex type) has achieved CE approval. With this CE marking there is now the possibility of model shop over-the-counter sales of these unique motors. Of course, many of the readers will have already had the opportunity to try the initial Tendera products that we’ve seen in the last 18months and that Roger has sold at Old Warden and other UK events.
 
The new CE marked Tendera range will comprise the following variants:
 
 
Type Thrust mN Duration Seconds
L1 100 11
L2 170 17
L2HP 250 15
L3 500 17
L4 1000 19

 

 
 
 
 
 
Distribution in Western Europe Scandinavia and the Benelux countries will be handled by the Klima Raketenmodellbau, Klima have for a number of years been manufacturing a range of short duration solid motors for ballistic rockets. They are not too far from me here in Bavaria in Emersacker and I've visited them a couple of times. For the UK The Vintage Model Company, who of course do a large range of classic kits, will handle distribution.
 
Now I know from comments placed on my You Tube channel that a substitute for classic Jetex has long been sought in the USA. And some progress has been made here too. Piotr has some contacts over there with one of the free flight/vintage product distributors and he is investigating what additional permits might be needed to import the Tendera product to the USA.
 
So this is all quite an achievement. I know Piotr has put a lot of effort and investment into this and I’m sure we all wish him well.
 
With world-wide distribution of these motors we now have the possibility to see some real innovation in reaction powered, aerodynamically lifted free flying model aircraft. The Jetex of the Wilmot Mansour era was famous for innovation and novelty with, for example their Tailored kits and such as their pendulum stability systems. In the 70 years or so since W&M were around some huge technological changes have taken place. And now, perhaps, can we see some new technologies applied to the structure and stability of reaction powered models? More on this next time!

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.