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TOPIC: New Motors from TSP Modelar

New Motors from TSP Modelar 2 years 3 months ago #1568

  • rogersimmonds
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I had an interesting communication from John Emmet, who is looking to make an igniter for TSP motors and old (and sometimes hard to start) Rapiers:



Above: John's well regarded and still-available. Jetex igniter.

John writes
"1. It looks like the electric igniter problems that people are having are down to low thermal energy rather than low temperature. Unfortunately, there are conflicting requirements here, as you need good thermal conductivity down the probe in order to get the heat into the fuel. Unfortunately high electrically conductivity is needed for the batteries sake, and that comes with poor thermal conductivity. Copper has a thermal conductivity 20 times that of (say) Kanthal heater wire, that is why the old coaxial igniters had a copper core, but with 3 volt batteries you need at least 5 x that resistance.

2. The good news comes from the below longitudinal sections of a TSP L-1 and a Rapier;
Here you can see that both have a 1.4mm diameter nozzle, which gives us twice the area of any suitable Jetex probe. Also any TSP/Rapier probe only needs about 7mm depth reach, as apposed to 1mm diameter with a 20mm reach needed for a Jetex 50C.



3. A most professional touch in the nozzle of the TSP is the narrow layer of (probably) black powder as an ignition booster. You can see its effect in the start up sparks, as well as the thrust peak.

I do wonder if an electric igniter is really essential if the fuses turn out to have no problems associated with them? Of course any open flame close to tissue/dope is bound to be dodgy, so I will be going ahead anyway."

I replied:

" many thanks for this, it's good stuff. You have a good point about temperature vs. thermal conductivity : A 30 SWG Nichrome element gives a healthy orange/yellow glow in a Cord Zap with two quality AA batteries, but (in my experience) hopeless at igniting the Rapier propellant. 28 SWG is a good compromise. 26 SWG is better but (a) you need more batteries, (b) the Rapier nozzle is so narrow it's difficult to get the heating element down the 'ole.The Vintage Model Company) have a 2 mm plus nozzle diameter so 26 or even 24 SWG Nichrome would work with these.
That TSP motors have a black powder as an ignition booster. This reflects Piotr's experience with motors for 'ballistic' model rockets. I'm not sure they are such a good idea for our sorts of models though. Troughs will need to give your Hawker Hunter adequate protection. When I first ignited a TSP CE motor the initial squib-like exhaust made me jump! Scary!"

Inspired by john, and blow the expense, I then cut a CE TSP motor in half:



Note the fuse fits the nozzle 'only just'.



Note the different colour (pink) of the CE propellant from the earlier motors black). Note also the black powder ignition booster.

John then asked, "Is an electric igniter really essential if the fuses turn out to have no problems associated with them? Of course any open flame close to tissue/dope is bound to be dodgy, so I will be going ahead anyway."

I answered,

"I didn't find poking the CE green fuse in the nozzle and getting a good contact that easy, So yes, we do need one"! :)

I look forward to what John, a very clever engineer, comes up with. B)
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New Motors from TSP Modelar 2 years 3 months ago #1569

  • Terry Kidd
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Today I've had chance to try some more otherwise standard L2s with the nozzles opened to 2.4mm I also 'modified' the cases by wrapping each motor in a single layer of 50mm wide masking tape.



As you'll see the thrusts are pretty similar and none of the cases burned through. Average thrust, 152mN, 135mN and 139mN. Peeling the masking tape off all the tubes are a bit brown at the nozzle end but no sign of a burn through. It was a pretty chilly day, about 3 C so maybe that helped perserve the tube..

So, it does seem as though a drop in replacement to a Jetex 50 is pretty close. (duration of thrust aside perhaps.)
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New Motors from TSP Modelar 2 years 3 months ago #1571

  • JJ
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I have just bought some L2 motors from VMC, to fit in a Skyjet 50. This hasn't flown yet - waiting for good weather! - it didn't with a Jet-X motor. It does occur to me that there were also Skyjet 100 and 200 models for the larger Jetex motors; I am rather tempted by the Skyjet 200, as there os a plan for this in Outerzone. Are the Tender L3 and L4 the same as the Jetex 100 and 200?

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New Motors from TSP Modelar 2 years 3 months ago #1572

  • Terry Kidd
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Hi JJ,
nice to hear from you.
I think the average thrust of a Jetex 100 should be 1 ounce (278mN) with a 200 coming up with 2 ounces (556mN).

So, going off the measurments I made of the new CE motors last month I got these average thrusts:
L2 200mN
L2HP 350mN
L3 535mN
So, in fact the L3 at an average of 539mN is not too far off the Jetex 200 then.
The Jetex 100, oddly is more problematic. This falls between the L2 and the L2HP.

Of course, one might try widening the nozzle on an L2HP but really, it might be best just to scale up the plan. :)

cheers Terry
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New Motors from TSP Modelar 2 years 3 months ago #1573

  • rogersimmonds
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Hi JJ,

be aware the KK Skyjet doesn't like being overpowered, at least until fully trimmed out. So I would recommend 'boring out' the nozzle for those crucial first flights.

I also have stocks of 'pre CE L-2 motors of lower thrust if you are interested. These are in packs of ten 17.50 GBP plus £4.50 p&p. :)

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New Motors from TSP Modelar 2 years 3 months ago #1576

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Yes please - how can I order and pay for them?

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