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Author Topic: FAC catajet question  (Read 401 times)
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Mikek
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« on: January 10, 2018, 10:05:59 PM »

Haven’t competed in Catajet yet. I know you get to record six launches.

Is there a rule of thumb about how many launches you can reasonably get out of the rubber before changing it? How often does everyone change theirs?

Thanks!

Mike
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MKelly
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« Reply #1 on: January 10, 2018, 10:23:29 PM »

I use mine 'till it visibly tears or breaks.  However, I can't claim to be a top-tier competitor...

Cheers,

Mike
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rpendzick
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« Reply #2 on: January 13, 2018, 09:19:58 AM »

FAC jetcat is best 3 of 6 flights - no max. So if you fly 5 minutes on your first flight, you could stop there.
have fun -Rick
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Bredehoft
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« Reply #3 on: January 13, 2018, 11:24:46 AM »

a two-part answer:

FIRST, the flying and scoring.  Here are the rules from the FAC Rulebook

VIII-4.0 JET CATAPULT SCALE For glider models of any man carrying jet or rocket propelled aircraft.
A. Profile fuselages are permitted.
B. Canopies and windows may be represented with tissue, paper or paint; clear material is not required
C. Wing span: Not applicable.
D. Launch technique: Stretched rubber catapult.
  1. Catapult dowel may be of any diameter.
  2. Dowel may not exceed six inches in length.
  3. Rubber not to exceed 1/2” total cross section. Example: Two strands of 1/4” or four strands of 1/8”.
  4. Finished rubber loops may not exceed nine inches.
E. Scale points:
  1. Coloring and markings 0 - 8 points
  2. Details 0 - 8 points
  3. Workmanship 0 - 4 points
F. Bonus points: Cumulative; added just once to the total flight points.
  POINTS CRITERIA
    5 Flying wing or Canard
    1 Each scale engine, pod or tank in profile not contained within the contours of the airframe.
G. Official flight: No minimum, no maximum
H. Flight scoring: Total, best 3 of 6 flights
I. Total score: Scale points + bonus points + Flight Points = Total Score

NOTE - NO Minimum and NO Maximum flight time.  Also, best 3 of 6 attempts.

SECOND:  the Rubber.  As someone stated, use it until it breaks.  Chances are you are not going to be exceeding the elasticity of a 9" loop of rubber.  This is because rubber can be stretched AT LEAST seven times its length and probably more.  So, 9x7 = 56"  That is just under 5 feet.  Given that you are not over-stressing the rubber, the catapult will last you a long time, maybe all season (maybe not).

I hope that helps,

--george
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Mikek
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« Reply #4 on: January 14, 2018, 09:43:01 PM »

Thanks all!
Was curious what other people do. Makes sense that the rubber wouldn’t wear out as fast as when you wind it up.
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lincoln
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« Reply #5 on: January 16, 2018, 02:47:06 AM »

Can't you just wind some of the loop around the launch handle??
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danberry
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« Reply #6 on: January 16, 2018, 11:35:02 AM »

Can't you just wind some of the loop around the launch handle??

Yes but you are not supposed to start with more than a 9inch loop.
No body has long enough arms to fully stretch a 9" loop of Tan SS rubber. Pirelli rubber is a different animal.
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lincoln
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« Reply #7 on: January 16, 2018, 08:00:51 PM »

Actually, I've met someone who probably CAN fully stretch a 9 inch loop. Fortunately for most of us, he's in the RC world, though I'll admit it's a bit intimidating when a 7 foot guy shows up at a DLG contest.

I seem to recall that if you keep rubber hot enough for long enough, or just let it age, it isn't quite a stretchy. Might be worth trying.
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Bredehoft
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« Reply #8 on: January 17, 2018, 07:53:19 AM »

I seem to recall that if you keep rubber hot enough for long enough, or just let it age, it isn't quite a stretchy. Might be worth trying.

I look forward to flying against you  Wink

--george
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