through the good offices of Terry Kidd, I have been liaising with Piotr of TSP Modelar, who make a range of powerful rocket motors for 'ballistic' type model rockets.
The good news is that they have started to manufacture 'Rapier-type' motors (low thrust, long burn) that are now available in the UK.
I have been able to obtain some samples for testing, and Piotr has agreed I can share the results so far. First up is the Tender L-1:
Above: the new 'Tender' L-1 motors with a Rapier L-1 motors for comparison. Note the TSP motor is 5 mm shorter, but otherwise will fit the motor mounts in our existing models, which is good news!
Motors ignited quite easily after boring out, with fuse or electric igniter. The first motor was noticeably quieter than the others and is perhaps an outlier; the other two give a steady thrust of about 80 mN (say 8 grams) for ten seconds.
The actual run time is not easy to measure as there is an initial output of 130 mN for 1-2 seconds or so before the thrust settles down. Overall, this performance is very acceptable, though a little more run time would be very welcome.
I'm much looking forward to flight tests of these L-1 motors in a Wren and a profile Lansen.
Next up for testing will be Piotr's Tender L-4 and Tender L-2, and I will be reporting these results in due course.
These TSP motors can be bought with confidence and are especially welcome as we have no Rapier L-1 motors at all!
For more details of these motors and how to get them, Piotr's email address is:
What a fascinating thread this is. I read with great interest the info that Guanadine Nitrate can be used in car airbags. It would be interesting to see how the contain and trigger GN airbag inflators. I wonder how big of a pellet must be used to fill an airbag?
I have now tested samples of Piotr's 'Tender L-2' and'Tender L-2 L' motors. The L-2 L motors are more equivalent to a Rapier L-2 LT.
The size of the TSP is similar to the Rapier L-2:
from the nozzle end:
Below are the raw statistics:
and for the TSP Tender L-2 L
As can be seen, they are quite similar to the Rapier L-2, though a bit thicker, and their 12.1 mm diameter matches a readily available commercial motor tube. The L-2 L has more propellant (note it weighs 1.3 grams (or so)) more than the L-2.
The motors ignited in a similar way to Rapiers and responded well to a little 'boring out' with a bit of appropriate size. The 'L-2 L' motors show a useful increase in burn time when the nozzles are bored out.
the graphs are interesting:
As can be seen, 'boring out' is very worthwhile, giving a steadier thrust as well as increased duration. The extra propellant of the L-2 L helps here too.
Boring out the nozzles to 1.7 mm gave very pleasing results:
The L-2 L 1.7 mm nozzle looks especially nice for our light scale models.
Note: the 'run time' duration quoted in the table is for usable thrust, which starts at about 2 seconds or so. Judging when this begins is a matter of judgement. We tend to launch our models only when the thrust is steady.
Above: a motor on the test rig. There was an initial thrust surge just after ignition, peaking at many mN, but the thrust settled down after 2-3 sec or so.
Above: the initial thrust surge - just like a Rapier - settles down after some seconds.
Piotr says he will concentrate on the TSP L-2 L rather than the TSP L-2 with its shorter duration.
Bottom line: I'm still mulling over these results, but I'm pretty happy with these motors. Next up for testing is the TSP L-1 version 2, so watch this space.