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Posted: December 29th, 2014, 8:14 pm
If you want some much more useful knots for joining rope, the fisherman's knot, zeppelin bend, and carrick bend are what I would recommend because of their strength, low profile, and ease to untie. For tying things of rectangular cross-section and/or of different size, you will need the sheet bend. For the rubber, though, your best friend will be the water knot. It is constructed as an overhand follow-through, but the second time you actually follow it in the reverse direction that it was tied (from the working end to the standing end) instead of the typical direction (from the standing end to the working end). The water knot is different from the double overhand knot due to this difference in direction, which results in a much lower profile because the standing ends of each side are on opposite sides of the knot. I often do get lazy and use use square knots, my father uses the double overhand, and we both use a figure eight follow-through.
One should note that what jander14indoor describes is not the double overhand knot. He describes the process of tying two double overhand knots of opposite handedness. This is in some way similar to fisherman's knot, but this is neither the double overhand knot nor the fisherman's knot.
Re: Winding (previously in Design thread)
Posted: January 11th, 2015, 11:27 am
Here's a link to a video of an international level competitor winding his rubber motor off of the airplane. His rubber motor is attached to a torque meter. He is taking quite a bit of time to wind as in AMA competitions there is not the 8 minute Science Olympiad flight window. You will want to wind and load the motor to your airplane quicker than this.
Thanks for this link. Very interesting. We've revisited our winding technique; slow and patient, with the rubber stretched way out, definitely puts more turns on the motor. But here is a question. I see the him spend a fair amount of time stretching the rubber in and out, and massaging it during the wind. This is done to reduce the amount of rubber trapped inside of knots, and increase turns and energy storage, would be my guess. Is that right?
Also, after backing off to the desired launch torque, he immediately removes the rubber from the winder and torque meter and mounts it on the plane. This is what we have always done as well. But just recently we observed that if you back off to a given torque, and then massage the rubber a bit, pulling it back and forth a little, the torque meter reading increases a little. Actually, more than a little, considering how sensitive planes can be to the magnitude of the launch torque. So I am wondering, does it make any difference, other than the launch torque value that you record in your flight log? Also, it seems odd to me that doing this would cause the torque to increase rather than decrease. I think I'll do some experimentation, to see if you back off to torque "X", then manipulate the rubber, does the torque reading always increase by the same amount?
In the meantime, I'm wondering if you or Jeff or other experienced fliers out there have any thoughts about this. Thanks.
Posted: January 11th, 2015, 6:36 pm
Congratulations on your thorough testing of winding technique. Sounds like you're getting some great data. I'm assuming that you saw Jeff Anderson's correction of my comment about winding quickly to deal with the 8-minute window. Jeff reminded us that the 8-minute window starts with the beginning of the first flight. Which (not official of course) I believe means the release point of your first launch. This would mean that you should have a time to wind your first flight methodically.
The flyer pictured in this video was the 2000 F1D world champion and is one of only two people that have beaten the one-hour mark for a single flight of an indoor rubber powered model. So, he really knows his stuff. I believe that what he is doing by massaging the rubber band while winding is evening-out the knots. This process reduces localized stress buildup in the motor so that more turns can be cranked-in and also should make the unwinding of the motor smoother.
Another popular technique for packing-in more turns is to stretch to full length and wind in 25% of the anticipated maximum turns and then walk in while winding in another 25%, then restretch the motor back to full stretch and wind in 12.5% and walk in while winding another 12.5%, then restretch the motor to full stretch again and repeat this last cycle once again. Different flyers use variations of this technique and other very successful flyers don't use this technique.
Although I agree with Jeff Anderson that the most common strategy for maximum duration for low ceiling flying (low means low enough that you have to backoff turns) is to wind to close to maximum turns/torque and then backoff to launch torque. However, remember that most serious indoor rubber competitors are using TanII and if you are using TanSS it is good to remember that this rubber behaves different than TanII. Some recent comments I have seen about TanSS from high-level competitors is that the mid-range suffers a little (maybe lessening the cruise and letdown) if it is wound very hard before backing off. The students I coach have been testing this lately and we are getting very good results winding to about 85% of maximum torque. The data that my students have is inconclusive, but this is an interesting idea that you might want to test and it is much easier on the rubber to wind to 85% than to try to wind to 95%. We are currently using motors that are about .057g/in and 17.25" long and the students are winding to about 1.0 in oz max and then backing off to desired launch torque, although all of this may change as additional propeller variations are tested.
Of course, when flying at a high ceiling site, and no backoff is needed, the above strategy of winding to 85% and backing off does not apply and every turn you can pack-in is probably desirable.
Good luck and keep testing.
Posted: January 12th, 2015, 7:31 am
. . .if you are using TanSS it is good to remember that this rubber behaves different than TanII. Some recent comments I have seen about TanSS from high-level competitors is that the mid-range suffers a little (maybe lessening the cruise and letdown) if it is wound very hard before backing off. The students I coach have been testing this lately and we are getting very good results winding to about 85% of maximum torque. The data that my students have is inconclusive, but this is an interesting idea that you might want to test and it is much easier on the rubber to wind to 85% than to try to wind to 95%. We are currently using motors that are about .057g/in and 17.25" long and the students are winding to about 1.0 in oz max and then backing off to desired launch torque, although all of this may change as additional propeller variations are tested.
Thanks for your detailed response. Actually, my students have not been winding beyond about 1 in-oz, as they are relatively inexperienced at winding, and I advised them not to wind too aggressively. But your observations above suggest that they don't need to push the rubber any harder.
Just as an interesting historical note, I had another look at the winding video. I hadn't paid any attention to the person doing the winding, and now I can see that it is John Kagan. About 10 years ago, I spent a day flying in hanger #1 at Lakehurst. It just happened to be July 4th, 2005, and so I was privileged to witness John's epic flight!
Posted: January 17th, 2015, 4:57 pm
What are some of the best rubber thicknesses you guys have found? And with how many winds?
Posted: January 17th, 2015, 5:37 pm
I'll rely on the more experienced indoor freeflight plane builders to correct/verify:
That really depends on the ceiling height and condition. What I've found is that the lower the ceiling height, the thinner the motor you want to use. The thicker a motor, the quicker it will climb. For regions, I ended up using 0.081 inch in thickness because the effective ceiling height was only 16 feet, and there were girders and wires that would kill times if the plane hit them. If the heights are around 20-30, I use 0.087 inches. anything 30+, I use 0.094.
I use about 80-100 turns. But to be honest, my data is still pretty limited based off of only 27 flights.
Posted: January 17th, 2015, 6:45 pm
nxtscholar's information is good and he or she should be congratulated for compiling a good set of data and analyzing. Other factors that will affect the rubber thickness and corresponding rubber motor loop length that gives best duration include: propeller pitch, propeller blade area, airplane trim (a forward center of gravity may result in increased decalage angle and more drag requiring a different optimum propeller and rubber), airplane design (some designs generate more drag than others).
The students I am coaching have found that a more propeller area requires a slightly thicker rubber motor (on the design they are using this means about .094" rubber) and a lower blade area propeller is working best with a thinner rubber motor (.087" or .090"). My students are not varying motor thickness to adjust for different ceiling heights, they are varying the number of backoff turns and corresponding launch torque.
Also, for low ceilings, a good variable to experiment with is minimizing the left wing washin to reduce the climb rate (remembering that reducing washin also alters decalage angle and might require an increase in wing incidence) . The first circle of a well trimmed low ceiling airplane may exhibit a banking characteristic (maybe 5 or 10 degrees) and may only climb a few feet, or less in this first circle. This banking characteristic will usually reduce in the second circle, or soon thereafter, but the climb rate should remain just a few feet each circle. If you are looking for pretty significant improvements in performance, a flaring propeller (Google search "Chris Goins Double Trouble" for the concept) would also be a good thing to try.
Good luck, keep testing and keep logging data,
Posted: January 19th, 2015, 6:33 pm
Quick question, why do people unwind their rubber to adjust for ceiling height? Why not just wind it less in the first place?
I've also had a lot of inconsistency with winding rubber, they all seem to snap at totally different points. My 0.87 with armor-all has been snapping anywhere between 1700 and 2200 turns, am I doing something wrong?
Posted: January 19th, 2015, 7:04 pm
Soinc.org has a great guide on Wright Stuff that I suggest you look at; helped me out a lot. But here is the answer:
"If you have a well-trimmed airplane and fly it in a
low-ceiling site, such as a school gym, with maximum
turns in the motor, it will rapidly climb into
the beams and wires and baskets and all sorts of
other trouble. To avoid that happening, the flyer
takes advantage of a characteristic of rubber by
unwinding some of those hard-won turns before
launching. The available torque from a rubber
motor decreases rapidly as the first few turns are
taken off. With reduced torque, the propeller rpm
is also reduced, the airplane flies a little slower
and doesn’t climb as fast. It is much better to
wind the motor to its maximum (1300 turns) and
then unwind to 1200 turns than it is to wind to
1200 turns and launch. The initial torque of the
motor wound to 1200 is much greater than that
of the motor reduced to 1200 turns after being at
With regards to snapping your motor, more details please? There are a lot of factors involved beyond just the number of turns you have.
1.For example, what iteration number were you on? A rubber motor that's been winded hard the first few flights will be more liable to break later on. I bring this up only because you may have mixed old motors with new ones? Idk. It's possible based on only the given information.
2. But something about your question tells me that's not the case. It could also be along the lines of how far you stretch the motor. Some teams stretch the motor up to 3-4 times its length unstretched while winding to fit in more turns. Eventually, you'd need to walk toward the winder (or vice versa) to slowly lessen how much you stretch the motor. Assuming you do this process, you could be stretching and unstretching at different rates.
3. The amount of lubricant you add is inconsistent?
Posted: January 20th, 2015, 8:19 am
A couple of years ago, we got rubber that had some very tiny nicks on the cut edge. You could not see it unless you looked closely while stretching and relaxing a section of the band. The nicked band would fail upwards of 20% sooner.