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Author Topic: P30 rubber sizes  (Read 1307 times)
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BigR
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« 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
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Dave Andreski
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« Reply #1 on: March 16, 2015, 07:33:44 PM »

BigR,
Why not use 12 strands of the 1/16" Rubber?
Dave
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danberry
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« Reply #2 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.
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betocastrucci
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« Reply #3 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.
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Tapio Linkosalo
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« Reply #4 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.
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Re: P30 rubber sizes
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BigR
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« Reply #5 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   

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BigR
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« Reply #6 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


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calgoddard
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« Reply #7 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.
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BigR
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« Reply #8 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
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Flyguy
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« Reply #9 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.
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calgoddard
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« Reply #10 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.    
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Tmat
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« Reply #11 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
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billdennis747
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« Reply #12 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
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Tmat
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« Reply #13 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
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calgoddard
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« Reply #14 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.

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Tmat
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« Reply #15 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
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« Reply #16 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 Smiley
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Hepcat
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« Reply #17 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
 
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Tapio Linkosalo
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« Reply #18 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! 
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Colin miller
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« Reply #19 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
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DerekMc
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« Reply #20 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.
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« Reply #21 on: November 18, 2017, 04:17:30 PM »

Hi Derek, thanks for the quick reply, that helps a lot.
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