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Author Topic: Thimble Drome Sportsman 15  (Read 551 times)
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Steve Thornton
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« on: January 23, 2014, 04:49:05 PM »

I received this Thimble Drome Sportsman 15 engine for my 11th birthday.....many decades ago, and put it on a Ringmaster.  It did fine for 2 laps, and then it started running backwards.  I'd like to put it into a trainer for my grandsons to fly if anyone knows of a fix for this?
Thank you,

Sometimes I believe I can and sometimes I believe I cannot, but whichever I believe, I am almost always correct.
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« Reply #1 on: January 23, 2014, 05:25:06 PM »

Do you have it mounted on another Ringmaster ? Is the motor broken in? What size prop are you running on it? The glow plug tight? Give the whole thing a good look. Hope to see here that you and the boys all had fun flying with this old reliable engine.
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aka staubkorb


« Reply #2 on: January 24, 2014, 07:24:21 AM »

If you mean that you can no longer get it to start, spinning in the right direction, it was a common "problem" with the Cox engines (and others).  I quickly learned to flick the prop "backwards".

Never had an engine that was running suddenly start to spin backwards, but I have heard of it happening.  Could be an over-rich condition that "burped" and then continued to run backwards.  Check the needle spring/detent - might be too weak, allowing the setting to back out (going rich) with vibration.  Prop slippage - a "burp" (backfire) will usually loosen the prop, especially the wood ones, just enough to create havok but still tight enough to flip start the thing.  Two laps later, the prop slips - poo!

Flyace46's tips are gold.

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« Reply #3 on: January 26, 2014, 11:54:20 PM »

If you do an ebay search on 'Cox Sportsman .15' [or 'Cox Olympic .15'] you should turn up one or two examples of the spring starter unit-exactly like the original Babe Bee/Golden bee/QZ 049 one-only bigger-which was fitted to both these .15 engines as standard equipment. Stops backward starts if you use it correctly.....
   FWIW most reed valves will start and run backwards with equal alacrity as forwards-and this reverse running is exacerbated by smaller props-exactly what you tend to get in C/L...

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