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Author Topic: P30 rubber sizes  (Read 3973 times)
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applehoney
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« Reply #25 on: February 04, 2019, 03:47:43 PM »

A  Gizmo nose assembly or, alternatively, a spring stop on the shaft obviates 2 pegs ..and no braiding required
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randoloid
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« Reply #26 on: March 04, 2019, 08:10:18 AM »

Can someone please let me know the weight a P30 rubber motor should be
l would very much appreciate it thanks

10 gram limit
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applehoney
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« Reply #27 on: March 04, 2019, 09:31:56 AM »

10g lubricated.   9.5g is safe
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skyrocket
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« Reply #28 on: March 05, 2019, 01:24:34 PM »

I have been using 12 x 1/16" for the past couple of years and like it very much...9.5 grams before lube...with a orange Chinese prop...short motor but a great punch for altitude coupled with a high aspect ratio under-cambered wing...this set up does have its problems with D/T but if you pop the wing, okay....sad to hear of John Barker passing. His Hep Cat is a hoot to fly and very dependable. He always gave sage advise on this web site.
Dave
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cglynn
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« Reply #29 on: April 05, 2019, 02:28:13 PM »

Maybe Bill was just trying to make up the right size motor from some May 99 TAN II rubber that could not be stripped to make a single loop Smiley

I talked to Bill about that at a contest.  That is exactly what happened (though I think it may have been 3/02 rubber).  The thought is in indoor that rubber cross section size does not matter, but weight per length does matter.   When Bill tied his scrap rubber strands into a motor for an F1N, he was only paying attention to loop length and weight.  Reason being a given weight and length of motor will store the same amount of energy as a different motor of the same length and weight.  Testing showed that it doesn't really matter how you achieve that weight and length.

Now, slight caveat.  For indoor, the motors are very rarely over 3g, and usually much less than that.  So a single loop makes sense.  For outdoor flying, multiple loops are required due to the mass of the motor.  When flying motors of significant weight and strand count, greater number of strands is preferred.  I have been told that this allows for one of the strands to possibly break, but because it is surrounded by many other strands, it will not blow the whole motor. 

Those with more outdoor experience, feel free to add.
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Tmat
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« Reply #30 on: April 05, 2019, 02:56:23 PM »

The thought is in indoor that rubber cross section size does not matter, but weight per length does matter.   When Bill tied his scrap rubber strands into a motor for an F1N, he was only paying attention to loop length and weight.  Reason being a given weight and length of motor will store the same amount of energy as a different motor of the same length and weight.  Testing showed that it doesn't really matter how you achieve that weight and length.
It seems to me that if we assume that the rubber density is close to uniform across a batch, or segment of a batch, then I'd argue that weight per length IS the measure of the cross section. And I imagine that if it's tricky to accurately measure small motor cross section (it's not metal and is squishy 'cause it's rubber!) then weight per inch is a more sensible way to determine it.
Then 3 strands that weigh the same per inch as 2 strands should be the same equivalent cross sectional area and thus give similar energy.

Tmat
-but what do I know?? :-)
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F1B guy...
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VictorY
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« Reply #31 on: May 04, 2019, 01:46:48 AM »

What is the typical motor run for a P-30? I thought I had my torque meter calibrated in the ball park but am getting 50+ seconds of run time on a 6 strand x 1/8" motor wound to "3" on my meter.
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flydean1
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« Reply #32 on: May 04, 2019, 10:27:16 AM »

TSAR--That sounds about right.  The 6-strand motors are for powering up through the ground clutter.  Where does the 6 strand motor break on your meter?
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VictorY
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« Reply #33 on: May 04, 2019, 10:40:19 AM »

Thanks. I tested a dry motor that wasn't exactly brand new to destruction and the meter went to "6". I'm going to do more testing when I get my new box of rubber. No need to continue with the couple of motors I have left from a batch that is a couple of years old. My main motivation for getting a motor up near max winds was to check my half tube/stooge setup to make sure that it actually works. I think it's almost time for my first contest. Smiley
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flydean1
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« Reply #34 on: May 04, 2019, 10:17:15 PM »

Test a lubed short length motor to destruction.  If it goes to 6 for example, use 5-1/2 for contests.  You also need to see what is safe with your model.  Make up a motor of, say, 5 or 6 loops.  Using the meter, "sneak" up on a torque of 6.  If the model handles it, you're golden.  BTW, a much thicker motor will "torque up" on very few winds so the motor run, even at a high torque will be mercifully short.  Also the extra weight will resist long flights.
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VictorY
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« Reply #35 on: May 05, 2019, 01:03:53 AM »

New rubber, lubed, half length for testing, made it up to 10 on my meter before letting go at the peg end. I should be able to wind to 6 and be quite safe. I think the limiting factor on this plane is going to be the amount of down/right thrust that I can dial in before the drive cup on the GG starts to hit the fuse.

And I finally got a chance to get the Pirate high enough to see it glide. Looks like I won't need much trimming other than the thrust angle and slight decalage changes, both made with set screws. Smiley
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flydean1
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« Reply #36 on: May 05, 2019, 07:01:10 PM »

So far so good.  However, you might wish to wind to 8 or 9 at a contest.  You have no idea what is safe for your model.  All the more reason to make up a thicker motor for torque testing.  Your fuselage is really small at the rear.  Probably need to come up with some sort of extension aft of a motor that is well short of the length hook to peg.  I've seen some made with hard balsa or spruce 3/8 in square with a cross tube on the aft end to engage the rear peg and a hook on the front.  The CG will probably be off but you are only interested in how well the airframe will handle the high torque.

My Gollywock flies on a 12 strand motor.  I made up one with 18 strands which allowed me to test at 30 on my meter which is the limit on the 12 strand.  It got to 30 on well under half the turns the 12 strand.  Also weighed more so glide was limited to fit my small test field.  Going to contests I could wind to just under the limit (28) knowing the model could handle the torque.  The fact that I let go of the Crocket Hook on my  5th flight didn't help. Cry
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