Wright Stuff B

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hogger
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Re: Wright Stuff B

Post by hogger » February 27th, 2017, 7:27 am

bernard wrote:
hogger wrote:How do you make a rubber with a weight in the precision of .001 gram? Maybe I am missing something or some special technique, but we are talking about a sliver of rubber at that weight. When I do mine, I make the first one by trial and error and estimating where to tie the knot to get closest and just under 1.5 grams. Then all subsequent ones, I just cut it about an inch longer than the first one to have enough handles to tie the knot. Then I try to tie the knot so it yields precisely the same length as my first one. Sometime, I went a little over and sometime I went a little under 1.5 grams, and I can't tell this until I make the final trim of the excess rubber. I tend to be a little more conservative so I don't lose that piece of rubber being 1.51 grams, so many come out to about 1.46-1.48 grams. My scale does not even have +-.001 gram precision. I keep the 1.48-149 for the competition and the ones at 1.46-1.47 and the ones over 1.5 for practice.
Bring both 1.46-1.47 g and 1.48-1.49 g motors to competition. You don't know what the Event Supervisor's scale may read, perhaps it will read a 1.48 g motor on your scale as 1.51 g on theirs.

For tying motors, I tie a knot, pull it tight, and snip off most of the excess. Then I weigh again and if needed, I roll the knot and keep snipping. Finally, I add a drop of glue between the two strands at the knot.
If that is the case, we should bring 1.51 and 1.52 too. :)

jander14indoor
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Re: Wright Stuff B

Post by jander14indoor » February 27th, 2017, 1:13 pm

No, no. If you use the right knot there is no "Guessing" where to tie it.
- I weigh my motors and o-rings before I tie them. To as close to 1.5 gms as I dare vs the judges scales. As others have said, have a selection of motors in the range of 1.45 to 1.50 gm. Oh, side note, the static in rubber motors messes up some electronic scales, causing them to be inconsistent. You might want to weigh the same motor multiple times to see if your scale is susceptible to this problem. Its one reason I use only a mechanical balance at competitions.
- Lube the motor, at least the area where you'll tie the knot. Temporary lube is OK here, water works.
- I then make the ends even and tie an overhand knot, fairly near the end but no precise location.
- Then, grab both ends of the rubber on the inside of the loop near the knot and pull apart slowly. The knot will slip outward, making the tails shorter. Take that as close as you dare, I typically leave tails around 1/16 of an inch. Too short and this knot (which will become the outer knot) will sometimes slip. But that is surprisingly short.
- If the tails are too uneven, I keep pulling and pull the knot apart to start over.
- Now, here comes the magic.
-- Tie a second overhand knot inside the first, but in the opposite direction. I'm right handed and tie an overhand knot by spinning it clockwise around my left index finger. So to tie it the opposite direction I just stop and think and spin it counter clockwise around my left index finger.
-- Now, grab both ends of the rubber again on the inside of the loop and pull apart. This second know will slip outwards again, UNTIL it hits the first knot. It stops there and WON'T move. Ever. MANY years of flying, many years of coaching others, I've never had this double knot slip in use, no glue needed.

Oh, don't forget the O-rings before you tie the second knot! It is possible to pick this knot apart, but frankly I find it easier to just start over.

Jeff Anderson
Livonia, MI

hogger
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Re: Wright Stuff B

Post by hogger » February 27th, 2017, 4:25 pm

That technique is very cool.

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Re: Wright Stuff B

Post by calgoddard » February 28th, 2017, 6:42 am

I have used the technique for tying rubber motors described by Jeff Anderson a couple of posts ago for many years. It works great. This technique allows you to make up rubber motors that are close to a target weight reliably, and with precision, assuming your scales are accurate.

I learned this technique from Bill Gowen, who has held multiple indoor flying records.

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Re: Wright Stuff B

Post by JasperKota » March 2nd, 2017, 2:36 pm

I used to use only one o-ring, so this problem did not occur before, but I switched to two after my partner snapped the rear hook off while trying to get the wound rubber onto the plane >.>

One time while using two o-rings, the knot ended up being about an inch forward from the rear hook, which resulted in a bad time because the knot kept getting stuck on the motor stick. Since then we've been careful about having the knot as close to the oring as possible, but I think there's still a few winds between the knot and the o-ring. I am using the knotting technique described by Jeff and calgoddard. Is there a knot that's shorter and close to or just as strong that I could use, so it does not get caught on the motor stick?

EDIT (just came back from final testing before regionals): Doesn't seem to be affecting much, as long as the knot is right next to the o-ring. Using never-used-before seems to make my plane skyrocket (as in just climb higher), and using old rubber doesn't climb as much but the difference is merely three or four seconds.
2020 Events: Fossils, Gravity Vehicle, Wright Stuff, Ping Pong Parachute
2019 Events: Fossils, Mousetrap Vehicle, Wright Stuff
2018 Events: Helicopters, Mousetrap Vehicle, Parasitology, WIDI
2017 Events: Ecology, Invasives, Wright Stuff
2016 Events: Crave the Wave, Dynamic Planet, Invasives

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Re: Wright Stuff B

Post by jander14indoor » March 2nd, 2017, 5:10 pm

I've always just made sure the knot is near the back o-ring. I can generally get it close enough to not lose any turns.

Jeff Anderson
Livonia, MI

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Re: Wright Stuff B

Post by JasperKota » March 3rd, 2017, 5:20 pm

I've been repeatedly posting on this forum recently, partly because of right before competition panic, but how do event supervisors weigh your plane? Will you have to take it apart and have them weigh the stabilizer, motor stick, wing separately? I ask because my assembled plane will fall over if just placed on a scale, making it read to be lighter than 7.5. I've been weighing by putting a stick of books underneath the left wing tip so the plane is not tilted, and it shows that it meets the requirement. Weighed separately it's also over 7.5, but I would like to avoid doing that at the check-in so I won't have to do too many trim flights adjusting the angle of incidence.
2020 Events: Fossils, Gravity Vehicle, Wright Stuff, Ping Pong Parachute
2019 Events: Fossils, Mousetrap Vehicle, Wright Stuff
2018 Events: Helicopters, Mousetrap Vehicle, Parasitology, WIDI
2017 Events: Ecology, Invasives, Wright Stuff
2016 Events: Crave the Wave, Dynamic Planet, Invasives

hogger
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Re: Wright Stuff B

Post by hogger » March 4th, 2017, 3:10 am

I do not claim to know for sure about your ES but most likely he or she will not take it apart to weigh. Mine had a clip that grab onto the plane and hang it down pulling on a scale. The whole plane stay intact the way you give it to him. I expect all ES to have a way to weigh it without changing any configuration so that you need to re-trim.

The easy way to deal with underweight plane is to have a little putty with you, and you put a little speck of the putty right at the center of gravity, one speck at a time until it is at the minimum weight.
Last edited by hogger on March 5th, 2017, 3:29 am, edited 1 time in total.

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Re: Wright Stuff B

Post by bjt4888 » March 4th, 2017, 9:41 am

Jasperkota,

Having coached this event for a number of years, I always prepare my students to perform the competition sequence by going through all steps a number of times like a dress rehearsal. Every step is done the same way and in the same order every time. Ex. Model box on the table, models assembled and incidence double and triple checked by both team members, five prepared and broken in motors weighed in, airplane weighed (flip upside down and rest wing on scale, bring a medium sized paper cup in case the ES doesn't have a raised platform on the scale to allow this upside down weighing, place the cup on the scale, tare the scale and then weigh the airplane, never never let an ES handle your airplane, practice respectfully telling the ES that the event matierals direct that only the students should handle airplanes and you can place it on the scale and hold it up to measuring devices that are securely sitting on a table ( not being held by another person), etc., etc.

We even bring our own collapsible table. Last year, our Regional organizer provided a table with wheels on it (?!); not good for mounting a torque meter and stretching rubber.

Brian T

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Re: Wright Stuff B

Post by JasperKota » March 4th, 2017, 1:56 pm

Thanks for the responses, I will be preparing for states and will definitely do practice runs. Turns out I had no reason to worry, the event supervisors did not know what they were doing, will post more about it in the "Poorly Run Events" forum. 1 minute 20 seconds was the winning time for my region, however the ceiling was triangular, quite low (I estimate a little less than 20 feet, as they did not tell us the room parameters ahead of time :evil: ), and also filled with hanging lights, ropes, and gymnastic rings. As far as I know, no planes broke, but crashes were very, very common.
2020 Events: Fossils, Gravity Vehicle, Wright Stuff, Ping Pong Parachute
2019 Events: Fossils, Mousetrap Vehicle, Wright Stuff
2018 Events: Helicopters, Mousetrap Vehicle, Parasitology, WIDI
2017 Events: Ecology, Invasives, Wright Stuff
2016 Events: Crave the Wave, Dynamic Planet, Invasives

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