Flight B/C

[randomdogonapc]

Nevermind. I was accidentally following the instructions for making the prop in the plans that were included in the post after the one with the Ikara.

[danxmemes]

Something I forgot to post about earlier, but my rubber keeps breaking, and not in the times you would expect it to. When winding, it is usually fine, but sometimes when the rubber is on the plane, the rubber breaks, and sometimes midflight, the rubber breaks. I have a competition next Saturday, and I can't have the rubber breaking during the flight. How can I solve this issue?

[pumptato-cat]

Are you lubing the rubber?
If so, how are you tying knots? I had a similar issue, and it was because I wasn't lubricating before tying the knot. The rubber would rub against itself and cause little nicks to form, leading to early failure.

[jander14indoor]

Also, once lubed, how are you caring for your motor? Do you sit it down on a surface? Drop it on the floor? All opportunities to pick up grit that will damage your motor next time it is wound causing unexpected weak spots and unpredictable failures.
Basic rubber handling. Before first use, wash with soap and water. Rinse well and dry. Store in some sort of clean container. Baggies, envelopes, etc. When you are ready to use, lube with appropriate lubricant. Once lubed, make sure you don't drop your motor or set it down on unknown surfaces. Between flights, put it back in a clean container.

Oh, and of course avoid heat, sunlight, ozone, petroleum chemicals. All things which damage the actual rubber bonds, shortening life drastically.


Jeff Anderson
Livonia, MI

[coachchuckaahs]

Jeff made a very important point in his excellent reply. "Appropriate lube". This is often overlooked as a source of issue because we assume appropriate is common knowledge.

As state es last year, I saw one team that flew pretty well in testing that morning. However, after getting on the clock, all of their rubber failed! They even re tied some broken loops and they failed.

Ends up their lube was WD-40! This, over tens of minutes, destroyed their rubber.

Be sure your lube is not petroleum based. Armor all, rc shock absorber oil, etc work well.

Coach Chuck

[danxmemes]

Thank you for the help! I have a slight feeling that the lubricant might be the problem, so I will change that out. Even though it says silicon lubricant, the rubber is breaking a lot more with this lubricant than the other one I used before. Again, thanks!

[Astronomyguy]

Updates from before:

- I have started lubing my rubber (Got my 0.54 g/in to 1800 winds today), but my plane while flying its maximum flight only uses about half of the winds. The longest flight I've recorded winds left for was 1:14, and that had 750 remaining out of 1575. I had a 1:27 yesterday with 1725 but I had to get to class so I did not have time to count the remaining winds. I know that I need denser rubber to maximize my planes, and the right thickness arrived yesterday.

1. I know that denser rubber provides more power and more torque. Should I increase the prop pitch to compensate for the faster ascent?

More importantly, the AC in our school gym is very annoying and is controlled by the county. I will try emailing the superintendent about the issue and hopefully, we can have it off in the morning. I had a 1:27 flight yesterday (The best I've had so far) Was a flight that had a great climb, but its turn shifted and it nearly crashed. The height was perfect; it barely skimmed the rafters. I should have launched it in the middle of the gym but I was trying to account for the circle shift to the front right, so I launched it slightly back and left from the center. However, the plane veered exactly the wrong way, and after dodging many obstacles on the ceiling, randomly dived right before hitting a basketball hoop. The circle shifts seem very random, and the AC probably contributes to this. Today, it hit the basketball hoop and the propeller broke off, causing the rubber band to snap in, where it probably broke the TE wing post, tearing the wing off the plane. I will have to redo the wing of the plane and glue the propeller on more securely. The A team was also in the gym flying their planes, which were also visibly affected by the AC. One of them broke a winglet, and the other was stuck in a basketball hoop.

2. Is there any way I can trim the plane so that it will be more resilient to circle shifting? Should I make the circle smaller? The plane doesn't seem to be affected by the AC (except maybe during descent), only the path it takes.



Flight log: https://docs.google.com/spreadsheets/d/ ... sp=sharing
(the CG is probably grossly inaccurate. I will need to remeasure it)

[coachchuckaahs]

Astronomy:

You need to match the prop to the rubber. If you are leaving many winds, you go to thicker rubber (for more power later in the flight) or lower pitch. Both will use more winds. However, there will be an optimum combination. Typically a Pitch-to-Diameter ratio of 1.6 to as high as 2.

Therefore, if you go to thicker rubber, but then INCREASE your pitch, you are negating the thicker rubber.

Instead, you will wind to near-breaking, and then unwind to a lower launch torque than you had before. This will decrease the energy available at high torque (initial climb) but increase the available power (and energy) during letdown. Manage letdown rubber use with rubber width (and prop pitch), and then manage climb with launch torque. Never wind UP to launch torque. Always wind up to max torque, and then unwind to launch torque.

AC issues are a problem for indoor flying. If you know you will have to fight AC issues at the event, then you may want to increase your stability. The plane will still get knocked around, but will recover faster and with less loss of altitude. This is not ideal, as the drag will be higher, but you cannot afford to lose altitude due to the AC. Improve stability by moving the CG forward a few mm, and then increase decalage enough to restore optimal letdown. You may even have (in your log) different setups of CG/decalage for different air conditions.

Note that every AC unit stirs the air differently. Some blow directly down, some across. None are ideal. Your plane will be disturbed by the air motion. How quickly it recovers once out of the moving air is what you can adjust.

A more stable plane MAY be less prone to steer in bad air as well. But this is specific to the site. A smaller circle may allow you to avoid the air currents (see the Austin facility, lots of air at the edges, dead calm in the middle), but may make it less stable in roll if it does get hit with air.

Coach Chuck

[coachchuckaahs]

A reminder to all contestants: YOU are responsible to know your box size! The rules restrict the external dimensions of the box. There are MANY commercial boxes, and some that appear "about right" will not pass!

We are STILL SEEING a large number of non-conforming boxes at invitationals, even this late in the season. At some events ES's are reporting 50-60% of the boxes are too large! Your plane must fit in the appropriate box in flight configuration. This means nothing can fold, nothing can be dis-assembled, nothing can flex to make it fit.

If you build your own box (or even with commercial boxes), leave enough room for imperfections, bowing, etc. A poorly built box may have panels that are cut the right size, but are assembled askew and will not pass inspection.

The box is part of the construction parameters, and a non-conforming box is a tiering factor.

Please, measure your box, both the dimensions and the squareness. Measure at multiple points along each dimension!

Coach Chuck

[danxmemes]

I'm back after flying today, and I see some very interesting issues that I have no clue about how to fix.

I have fixed the stalling, and for the most part, the plane flies like how it should fly, except it does not get nearly the times I used to get with the rubber. Before, I was able to get high 2 minutes with the Div B plane, but now its barely two minutes. Number of winds on motor remain the same, about 1250, and launching torque, ceiling height, and winds remaining remain the same, at about 300. Why does the flights run out of rubber much quicker and come down much quicker than before? And how can I fix this?

Second thing, just kind of weird, is the way my lubricant is applied. This is the lubricant that I use: https://www.homedepot.com/p/Blaster-11- ... 529794-_-N

The interesting part is that whenever I directly spray it onto the rubber, all is fine, and I have tested this across over 10 rubbers. However, when I spray the lubricant into a bag and then do the same winding process, the rubber is significantly weaker and has a bunch of tears in it after only 2 winds. Just a weird thing that I wanted to share, but am I being superstitious or is there something else going on?

Main issue is still about the plane getting more time, any guidance is greatly appreciated. Thanks in advance!