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Outdoor Free Flight Forum => P-30 Class Sport and Competition => Topic started by: BigR on March 16, 2015, 06:57:04 PM



Title: P30 rubber sizes
Post by: BigR on March 16, 2015, 06:57:04 PM
Hi All,

I have been flying my Hotbox on 6 strands of 1/8 rubber. Yesterday at the Taibi contest in Perris I "won" some 1/16 rubber. I was thinking of using this in the Hotbox.

I weighed it and it comes out to about 2 feet per gram, about what was expected. That means a 10 gram motor would be 20 feet long. A ten strand (5 loop ) motor would be 24 inches long. This would be about halfway between a four strand and a six strand 1/8 rubber motor. Has anybody tried this? I'm using a Gizmo Geezer front end.

John in Kalifornia


Title: Re: P30 rubber sizes
Post by: Dave Andreski on March 16, 2015, 07:33:44 PM
BigR,
Why not use 12 strands of the 1/16" Rubber?
Dave


Title: Re: P30 rubber sizes
Post by: danberry on March 16, 2015, 08:03:01 PM
12 strands will pretty much be the same as what you have been using with 6 strands 1/8"
The longer motor run technique won't be wonderful unless you are at minimum weight to start with.


Title: Re: P30 rubber sizes
Post by: betocastrucci on March 16, 2015, 08:56:34 PM
We have 3 rubber options 1/16", 3/32" and 1/8". From long to short motors, in basis of 1/32":

loops x width
2 x 1/8 = 8
4 x 1/16 = 8
3 x 3/32 = 9
5 x 1/16 = 10
6 x 1/16 = 12
4 x 3/32 = 12
3 x 1/8 = 12

I like 3 x 3/32 for mine Saturns P30, but they are under weight, have to put some lead under the wing to get > 40 g. Motor runs  1:15 to 1:20.


Title: Re: P30 rubber sizes
Post by: Tapio Linkosalo on March 17, 2015, 03:09:43 AM
Most of all I fly my models with 6 strands of 1/8", but I have also tried 5 (or 10 strands of 1/16"). The attached altitude log would seem to suggest that 5 strands is better, it does not get as high but the 60 second motor run vs. 40 seconds for 6 strands gives some benefit. However, the log shows some variation in the only 5 strand flight, so the air may have been a bit more buoyant. However in thermal conditions I prefer a faster climb to higher altitude, so most of all I fly with 6 strand motors. Without VIT I think the 5 strands would be of more benefit, as the 6 strand motor requires the VIT to get the initial burst straight and fast, to get max altitude.


Title: Re: P30 rubber sizes
Post by: BigR on March 17, 2015, 04:19:27 AM
That is a very interesting chart.  I'll have to dig out my Zlog recorder and do some testing.  It's fun to experiment but difficult to eliminate the variables. The air is constantly changing.

My plane weighs 55 grams so may need the extra torque of the  6 strand 1/68 motor.

Preliminary testing to destruction of a sample 10 strand 1/16 inch motor show max torque of 10 percent less than a six strand 1/8 motor. However the calculated total number of turns went up close to 50 percent, based on a higher turns per inch and a longer motor. I think the Gizmo Geezer would go into free wheeling mode long before the turns were used up, however. The latter part of the motor run would be just a cruise with little or no altitude gain.

John in Kalifornia   



Title: Re: P30 rubber sizes
Post by: BigR on April 08, 2015, 08:44:11 PM
Hi All,

Went to Perris today and got some tests in. The Hotbox does better with the six strand 1/8 motor. The motor run with the 1/16 10-strand rubber was longer but the plane didn't reach as high an altitude. Only did a couple of flights but there was a definite trend there. Time with the six strand motor 1:45; with the 10 strand motor 1:36. Now if the plane was built to 50 grams minimum weight it may be a different story.

It's nice when the flight performance matches theory.

BTW, the Hotbox (I have two examples) likes to fly right/right. There needs to be a pronounced right turn in the climb. Without the right thrust, it just flops around and never establishes a pattern.

John in Kalifornia




Title: Re: P30 rubber sizes
Post by: calgoddard on April 13, 2015, 07:41:13 PM
John:

The San Diego Orbiteers flying club is having a John Oldenkamp memorial P-30 contest on April 26, 2015.  The contest will be held at the club's Otay Mesa flying site.  The contest is limited to the HOT BOX P-30 that John Oldenkamp designed.

There will be $100 in prizes distributed.

See www.sandiegoorbiteers.com for further information.

Come on down and join us with your HOT BOX.

BTW, from everything I have seen, the HOT BOX flies best with three loops of 1/8 inch rubber, as you have seen with your test flights at Perris.  This is pretty typical for a P-30 that uses the 9 1/2 inch GizmoGeezer prop assembly.

Personally I prefer a fast, high climb with my P-30s, and the resultant chance for thermal hunting, as opposed to a slow climb and less altitude.


Title: Re: P30 rubber sizes
Post by: BigR on April 13, 2015, 09:36:15 PM
Hi all,

Actually, I'm CD'ing a P30 event as part of the monthly Scamps Club Contest Wednesday, day after tomorrow. I'll bring my 2 Hotboxes in case nobody else shows up with a plane.

Now, should I use 6 strands of 1/8 or 12 of 1/16th? Maybe one of each to see if there is any difference.

John


Title: Re: P30 rubber sizes
Post by: Flyguy on April 13, 2015, 11:05:59 PM
Now, should I use 6 strands of 1/8 or 12 of 1/16th? Maybe one of each to see if there is any difference.

John

Please post your results! I've been interested in exactly that question as well, I made up both 6 and 12 strand 1/8 and 1/16 motors to look at it in my next flying session, but it's just been too windy. According to some charts, you should be able to get some more winds with the 1/16.


Title: Re: P30 rubber sizes
Post by: calgoddard on April 14, 2015, 01:12:23 PM
I have a 5 lb box of 1/8 inch TSS rubber and a 5 lb box of 1/16 inch TSS rubber of equivalent quality. I end up making my P-30 motors using the 1/8 inch rubber for two reasons.  First, the 1/16 rubber often gets tangled up when trying to make up a 9.8 gram motor. I have tried various rubber motor jigs, including an adjustable one with free wheeling spools, and they are a real pain to use.  Second, when a P-30 motor is made from 1/16 inch rubber I have found that it is slightly shorter than a P-30 motor made from 1/8 inch rubber. This can prevent free wheeling of the prop if you are using a simple dog on the front end of the prop shaft that engages the standard ramp on an injection molded prop.

I have heard, however, that you can wind in more turns if a motor is made from 1/16 inch rubber instead of 1/8 inch rubber.    


Title: Re: P30 rubber sizes
Post by: Tmat on April 14, 2015, 01:21:40 PM
Carl,
I don't know where you have heard that you can wind more turns with 1/16" rubber than 1/8" (all else being equal) but from my tests with F1B motors, the max turns is based on the stretch ratio of the rubber (varies from batch to batch) and the cross section of the rubber. Same stretch ratio, same cross section, same number of turns regardless of the number of strands. And the motor would come out the same length too. If your 1/16" motors are different length than the 1/8", then either the batch is different, or the width is not really 1/16" (which is often).

Tmat


Title: Re: P30 rubber sizes
Post by: billdennis747 on April 14, 2015, 02:30:18 PM
Carl,
I don't know where you have heard that you can wind more turns with 1/16" rubber than 1/8" (all else being equal) but from my tests with F1B motors, the max turns is based on the stretch ratio of the rubber (varies from batch to batch) and the cross section of the rubber. Same stretch ratio, same cross section, same number of turns regardless of the number of strands. And the motor would come out the same length too. If your 1/16" motors are different length than the 1/8", then either the batch is different, or the width is not really 1/16" (which is often).

Tmat
I know nothing about this but when I asked a top F1B flyer why he used 1/16, he said 'would you use one strand of 1/4 square, four strands of 1/4 flat, 8 strands of 1/8 etc


Title: Re: P30 rubber sizes
Post by: Tmat on April 14, 2015, 03:02:55 PM
The only reason I, as an F1B flyer would use 1/16" is to achieve a finer length variation so that I can make up motors close to the exact length I need. That's it. I've measured no difference in energy using 1/16", 3/32" or 1/8". Perhaps at 1/4" you might see some effect, but I'd be skeptical.

Tmat


Title: Re: P30 rubber sizes
Post by: calgoddard on April 14, 2015, 03:26:22 PM
Tmat,  your explanation (Reply #11) makes perfect sense.  I should have realized this. What was I thinking?

I have two friends that are expert outdoor rubber fliers.  They regularly fly Old Time Rubber models with motors made up of 1/4 inch rubber and win contests regularly.  They don't bother with 1/8 inch rubber motors for these models.

Your explanation is also backed up with my experience with indoor duration models as well.  For an LPP, for example, you might fly a 2.2 gram motor of one loop of nominally 0.100 inch rubber, but you would never bother to make up a 2.2 gram motor of two loops of 0.050" inch rubber from the same batch. If you could truly get more turns in by having the same weight of rubber from the same batch, with half the cross-section, experts would be doing it, and I have never seen any indoor expert do this, e.g. Cezar Banks, Kang Lee, Steve Brown. Of course with indoor duration models, the experts vary their motor size using motor length and weight, as opposed to motor width and weight.



Title: Re: P30 rubber sizes
Post by: Tmat on April 14, 2015, 03:46:54 PM
That's right Carl.
To muddy things up Bill Gowen has set records with 3 strand motors indoors ..... ;-)

Tony


Title: Re: P30 rubber sizes
Post by: calgoddard on April 14, 2015, 04:05:26 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 :)


Title: Re: P30 rubber sizes
Post by: Hepcat on April 15, 2015, 08:59:55 AM
It  may interest people who have not done much stripping that it is not as simple as you may imagine.  Some pieces do come off at just the width you want and some will be some thousandths different and of course the residue at the end of the stock material could be anything.  Indoor flyers do not throw the wrong ones away, they keep them all separately in little envelopes marked with their widths. Later you may find that you do not have the exact width of strip you want  but that two smaller strips will fill the bill.  I have quite often used multi strand motors indoors.

I must emphasize that although I have referred to strip width above that is only because a lot of flyers still talk that way.  Most competition flyers talk instead of the specific weight of the rubber, in g/" or g/m for example which is more sensible.

John
 


Title: Re: P30 rubber sizes
Post by: Tapio Linkosalo on April 16, 2015, 03:42:34 AM

I recall reading that the reason for Bill to use three stranded motor was just that - he had strip that made the right size motor on three strands.

So the major reason to use motors with other strand number than two is to utilise strip that would otherwise be obscure.

There is, however, one potential reason to a number of strands, that is even and larger than two: thinner motor makes smaller knots. On classes where the motor weight is limited (F1D, F1M) the knot is "dead weight", portion of motor that does not give power for flight. In a 4 strand motor you have a knot much smaller than on 2 strand motor, therefore you have a (slightly) better motor! 


Title: Re: P30 rubber sizes
Post by: Colin miller on November 18, 2017, 03:04:18 PM
Can someone please let me know the weight a P30 rubber motor should be
l would very much appreciate it thanks


Title: Re: P30 rubber sizes
Post by: DerekMc on November 18, 2017, 03:15:36 PM
Can someone please let me know the weight a P30 rubber motor should be
l would very much appreciate it thanks

10 grams with rubber lube.  I make the motors with 9.6-7 grams of rubber and the lube takes it up to 10.


Title: Re: P30 rubber sizes
Post by: Colin miller on November 18, 2017, 04:17:30 PM
Hi Derek, thanks for the quick reply, that helps a lot.


Title: Re: P30 rubber sizes
Post by: goodeye on February 04, 2019, 02:06:01 PM
Don't beat me up but inquiring minds (me) want to know.. I notice that several P-30 model designs have 2 locations for the motor peg, long and short. My question is : why?


Title: Re: P30 rubber sizes
Post by: Colin miller on February 04, 2019, 02:09:32 PM
I would think it’s something to do with power burst
in a long and a shorter motor, but not sure.


Title: Re: P30 rubber sizes
Post by: billdennis747 on February 04, 2019, 02:47:27 PM
I think there are broadly two approaches to P30 - 'fast' climb with 1/8 motors or slower with longer 3/32" motors, but pre-tensioning would obviate the need for two peg positions.


Title: Re: P30 rubber sizes
Post by: applehoney 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


Title: Re: P30 rubber sizes
Post by: randoloid 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


Title: Re: P30 rubber sizes
Post by: applehoney on March 04, 2019, 09:31:56 AM
10g lubricated.   9.5g is safe


Title: Re: P30 rubber sizes
Post by: skyrocket 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


Title: Re: P30 rubber sizes
Post by: cglynn 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 :)

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.


Title: Re: P30 rubber sizes
Post by: Tmat 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?? :-)


Title: Re: P30 rubber sizes
Post by: VictorY 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.


Title: Re: P30 rubber sizes
Post by: flydean1 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?


Title: Re: P30 rubber sizes
Post by: VictorY 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. :)


Title: Re: P30 rubber sizes
Post by: flydean1 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.


Title: Re: P30 rubber sizes
Post by: VictorY 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. :)


Title: Re: P30 rubber sizes
Post by: flydean1 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. :'(