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Author Topic: Torque Range and Turns Range, Min and Rough Maximum, ounce inches  (Read 303 times)
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PantherM100
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« on: April 09, 2021, 03:50:20 PM »

Hi Guys:
A quick question:  What would be the minimum and maximum
Torque range of the rubber motor (roughly) in ounce inches, on a P30 aircraft. 
 What would be the range of number of turns on a P30 class aircraft (roughly).
Thanks in advance!
Jon B. Shereshaw
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calgoddard
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« Reply #1 on: April 09, 2021, 07:24:35 PM »

Jon -
,
The torque range depends on the weight of the P-30, the configuration of the model, the trim, and the cross-section of the rubber motor.

Certainly a minimal launch torque is needed to get the model to climb to a reasonable altitude, i.e. one that has a chance of achieving a 120 second flight. The maximum launch torque would of course be the torque the rubber motor could take without breaking.  This depends on the batch of rubber and the cross-section of the rubber motor.

I will take a stab at giving you some launch torque ranges from memory.  I don't have my paper flight logs accessible to me at my current location.

If you go with the long slow climb strategy, using a 4 x 1/8 or 6 x 3/32 - -  9.8-gram rubber motor the launch torque can range between 3.5 and 6 inch-ounces.  The "thin" rubber motor will probably break above 6-inch ounces. You need a model that is very close to the 40-gram minimum and calm conditions to pursue this strategy.

If you go with the rocket climb strategy, using a 6 x 1/8 or 12 x 1/16 - - 9.8 gram rubber motor, the launch torque can range between 6 and 10 inch-ounces of torque. Some fliers may be able to wind a "thick" rubber motor of this type to higher torque without breaking.  When you launch at very high torque you will need a suitable trim of the model to avoid looping or worse, veering hard into the ground. In order to achieve a nice steep corkscrew climb, the model needs a relatively aft CG, low decalage, just the perfect amount of down thrust and right thrust, wash-in in the right inner wing panel, minimal, if any, right rudder, etc.

Don DeLoach's chart says that 85% of breaking torque for a 19-inch long 6 x 1/8-inch rubber motor is achieved at around 1,000 turns. That length of rubber motor is pretty typical for a 6 x 1/8-inch  - - 9.8 gram rubber motor made from 2009 or later Tan Super Sport (TSS) rubber.

Derek and Tapio can probably provide better answers.

 
« Last Edit: April 09, 2021, 09:03:17 PM by calgoddard » Logged
calgoddard
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« Reply #2 on: April 09, 2021, 08:01:52 PM »

Jon -

See my previous reply.

I just wound a 4 x 3/16 - - 9.9 gram rubber motor to breaking.  It was January 2014 TSS rubber. This is the same cross-section as a 6 x 1/8 rubber motor.

The rubber motor was well-lubricated.  The weight was before lubing so it might not have been a legal motor.  It is better to go with 9.8 grams.

I stretched 6-8 times before winding, and wound with the walk-in method.  The motor broke at 11 inch-ounces of torque.  

You asked for a range of winding turns on a P-30 rubber motor.  Again this depends on the weight of the P-30, the configuration of the model, the trim, and the cross-section of the rubber motor.  For the thin rubber motor, you might be able to get in 2,000+ turns.  For the thick rubber motor, anything above 1,000 turns is getting near breaking. The minimum number of turns for the thin and thick motors are not really relevant.  You need a minimum launch torque to get a reasonable climb.

You may have heard this before, but you will get better, more consistent flights by winding to a specific launch torque.  I only use the estimated maximum number of turns to govern my walk-in winding.  I typically stretch out 6 - 8 times the relaxed rubber motor length, then put in half the estimated maximum turns, and then continue winding as I gradually step in.  I monitor the torque meter to decide when to stop winding.  My winding technique is pretty typical.

« Last Edit: April 09, 2021, 08:16:24 PM by calgoddard » Logged
Red Buzzard
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« Reply #3 on: April 10, 2021, 12:21:58 PM »

Cal,

Good on you! A man after my own heart. My personal practice almost to a "T". My only variant in general is the "stretch" at the beginning. I have to shorten that up as the strand count goes up. I too use turns to govern my rate of coming-in.

Jon,

The best advice anyone can give you is to just break a bunch of motors! At ten grams each you can break several at little expense while learning the art in the comfort of your own garage. Just be careful with what is behind your stooge as the little balls of rubber really do fly and bounce around. Keep pets out of the way as well as your lightweight shop tools. A clean, uncluttered local environment makes it easier to find flying Crocket hooks. Eye protection is not out of order. It's a blast!

Always better to practice at home where you don't have to burn up contest time digging around in the model to change a motor. Of, you'll break them at a contest, too, but less frequently if you have a good idea of what you're doing.

Bill
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Tapio Linkosalo
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« Reply #4 on: April 10, 2021, 01:06:22 PM »

I stretched 6-8 times before winding, and wound with the walk-in method.  The motor broke at 11 inch-ounces of torque.  

I'll second this. I prefer 6 strands of 3mm (1/8") rubber, giving 50 to 55 seconds of motor run on the Chinese / Volare orange prop. I typically wind to 600 g*cm (or slightly less) torque, but have wound to 700. My winder has a bit too large ratio (1:9), making the final turns hard to crank in, so I plan to modify the winder to something like 1:7. That 11 in-oz translated to 770 g*cm.

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TimWescott
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« Reply #5 on: April 10, 2021, 01:24:07 PM »

... using a 4 x 1/8 or 6 x 3/32 ...

Really dumb terminology question -- does that mean four loops of 1/8 in rubber, or four strands (i.e., two individual loops, or one loop doubled).  Put another way -- if I draped a 4 x 1/8 motor across my hand, spread out the strands and counted what I saw, would I count four, or eight?
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DerekMc
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« Reply #6 on: April 10, 2021, 03:16:30 PM »

... using a 4 x 1/8 or 6 x 3/32 ...

Really dumb terminology question -- does that mean four loops of 1/8 in rubber, or four strands (i.e., two individual loops, or one loop doubled).  Put another way -- if I draped a 4 x 1/8 motor across my hand, spread out the strands and counted what I saw, would I count four, or eight?

Strands.  You would count four.  6 x3/32 would be 6 strands in 3 loops.
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Derek
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« Reply #7 on: April 10, 2021, 08:02:45 PM »

No need to use a full 10 gram motor to determine breaking torque.
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cvasecuk
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« Reply #8 on: April 11, 2021, 05:11:10 AM »

There is a big difference between 4 strands of 1/8" and 6 strands. Why do so few people use 5 as I do. Easily done with one loop of 1/8" and one loop of 3/16" (or 10 strands of 1/16" if you have it!) This gives about 1350 turns easily.
Ron
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Tapio Linkosalo
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« Reply #9 on: April 11, 2021, 06:17:36 AM »


I tested 5 strand motors on 2011 (10 years ago already!). It gave a longer motor run, and although the max altitude was higher, shóuld have given a bit longer duration. But at that time I flew with Ikara prop that gave only 40 secs of motor run with 6 strands, my current prop (orange Chinese / Volare) gives 55 secs on 6 strands, so on 5 I'd guess the motor run would be like 70 secs. I wonder if that is a bit too long already - in any case I prefer the more positive initial start from the shorter motor. But maybe it would be time to test 5 strands again, with the new prop. Just have to wait until summer, this time of year the air is too unstable to have comparable conditions on consecutive flights....
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