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Author Topic: .015" rubber  (Read 1635 times)
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cglynn
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« on: November 26, 2014, 01:12:06 AM »

Greetings all.  I've just started playing around with some ministick type models and was wondering if anyone would be willing to strip a few feet of rubber to .015 for me.  The smallest I've got is .030 and it is just too much--Though my wife did get a kick out of watching the newly built model rocket to the ceiling in about a second.  As entertaining as that was, I would like to see what the little plane can do in a more controlled fashion.

I will gladly cover cost of rubber, shipping, and time for anyone that can lend me a hand.  Just send me a PM and we can work out the details.

Thanks much. 
Chris
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ykleetx
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« Reply #1 on: November 26, 2014, 01:38:25 AM »

Chris,

You could use a single strand of .030" instead of a .015" loop. 

It is actually very hard to strip .015" rubber consistently.

-Kang
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Maxout
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« Reply #2 on: November 26, 2014, 06:31:38 AM »

Chris, email me and we'll work something out.
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cglynn
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« Reply #3 on: November 26, 2014, 08:42:49 AM »

Thanks Josh and Kang.  I think I will try the single .030 strand for now.  That's a relatively simple fix with materials I have on hand, and so obvious, I am wondering how I didn't think of it.  I will blame the time of night and the Christmas Ale.

Thanks again guys.
 Have a good Thanksgiving

Chris
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frash
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« Reply #4 on: November 26, 2014, 09:02:58 AM »

Yes, stripping 0.015-in rubber will be hard. I used 0.018-0.019-in and that was too thick. I got back my 2012 Mini-Stick in many pieces last week. It had spent over 2.5 years in the ceiling of the Johnson City, TN Mini-Dome (since late May of 2012 at USIC/AMA Indoor FF Nats).

Fred Rash
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flydean1
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« Reply #5 on: November 26, 2014, 09:53:03 AM »

OK, for us gassers and other flyers of obscenely heavy airplanes, how do you use a single strans of rubber?  How do you engage the prop and motor stick hooks?
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kullas
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« Reply #6 on: November 26, 2014, 10:03:04 AM »

I would just tie a loop in each end
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Maxout
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« Reply #7 on: November 26, 2014, 10:36:50 AM »

I think it's important to point out that .015" rubber is quite thin for ministick. I've stripped thinner than that for very small models, but in the case of ministick, .025 is a more common size, and is the size I use in all ceiling heights, using the prop to dictate climb profile.

If you're needing .015, your prop pitch is much too low. My experience indicates that 13-14" is the best pitch range for low ceilings. Higher ceilings seem to require about 12" pitch from what I've seen, though some use slightly lower settings. Any lower and you run into excessively long motors and loss of prop efficiency.
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cglynn
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« Reply #8 on: November 28, 2014, 01:23:03 PM »

Hmmm....that is interesting Josh.  This model isn't actually a ministick.  It has about an 8" wingspan, and currently a 6 x 9 prop.  I actually built it because I wanted to test a balsa stripper that I built, and figured there was no use wasting balsa the balsa.  I haven't weighed it, but it I am sure for its size it is over weight.  The balsa used for the spars (wing and stab) was cut from some (gasp) 8lb 1/32 sheet that I had laying around, and I threw the whole thing together in about 15 mins using (gasp again) CA glue.  So I know this model isn't anywhere near a serious duration model.  It is really just for fun flying in the school gym.  Though with your comments on ministick props, I may play around with the prop a bit.  I have a (bad?) habit of useing a short piece of 1/16" sq wood for a prop hub, and then a tissue tube glued to that to mount the spars.  A little cement on the tube holds the spars in place.  A little acetone can then be used to change the pitch. 

From my initial tests, which were conducted in my living room, the model flew well on single strand of .030" rubber.  I tied a short loop in each end, wound in 600 turns and the model was at cruise.  It flew for about 30 seconds with that combination.  The loop I used is really short, say 6" or so.  Honestly, I didn't measure it because I just wanted to see how the model flew under some power.  As I get more time to play with the critter in a larger space.

I am actually glad Kang suggested I use a single strand.  I would honestly feel a bit bad if someone took the time to strip some rubber for this at best, "sport" indoor model. 

Still, it is always fun and challenging to see what kind of performance can be squeezed from a given airframe, and that is exactly what I will do with this thing, as in doing so I can further my trimming skills.

I am out of town right now, but will get some pictures and specs of the "critter" when I get home.

Thanks
Chris
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ykleetx
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« Reply #9 on: November 28, 2014, 02:46:19 PM »

OK, for us gassers and other flyers of obscenely heavy airplanes, how do you use a single strans of rubber?  How do you engage the prop and motor stick hooks?

Tie an o-ring to each end of the rubber strand.  A square knot should hold it.  .030" is thin enough that the knot will be small and hold well.
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cglynn
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« Reply #10 on: November 29, 2014, 11:57:36 PM »

Just got back from Holiday fun with the inlaws.  I actually get along really well with my inlaws, and they own a really nice winery, so it was actually a good time.  I had a moment after the kids fell asleep to get a picture of my little sport flyer and weigh it.  Turns out, my neanderthalic building techniques weren't as bad as I thought.  The final weight, less rubber, is 380 mg.  Not too bad for considering the model has a 7.75" wingspan, 6" span stab, and was built without testing or weighing a single piece of wood.  The prop is a 5.25 x 9, but it was formed on a tapered pub glass.  Fred Rash's spreadsheet on bucket props shows that on this particular prop form, the tips are pitched lower than 9.  It was near the tip however that I measured to set the pitch angle for a 9" prop, so I am assuming the inner portion of the prop, where most of the prop area is, runs at a pitch higher than 9.  

I did a few more flights in my basement using a 5" long single strand of .030 rubber.  I didn't bother weighing it becuase it has really long loops on each end, so it would be hard to get an actual useful weight of the motor.  With 600 turns in this motor, the model cruises nicely.  The motor is rather short, so it uses turns quickly.  Still, I was able to get about 3 circuits of the room before it started to descend.  I cranked in 900 turns and the model is starting to climb.  The circle opens up a bit as well, but its hard to tell what the real behavior under torque will be because the model ends up hitting one of my basement walls.  By time I relaunch, the torque has lessened due to the model sliding down the wall, so who knows.  I will be flying in a school gym on Dec 7th and will further test this mode.  

So far, I am very happy with the model.  Considering the complete lack of planning or thought that went into its construction, I am pleased with the result.  It is nice to see that I can build something light, even though it is a smaller model.  This is encouraging considering my events for the year are going to be F1L, LPP, and F1D.

Chris
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Maxout
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« Reply #11 on: November 30, 2014, 08:28:40 AM »

That's a nice airplane. Well done. Sounds like you might want to use a little side thrust to keep the turn from opening up. Another trick we use is to offset the wing a little. One further bit is that bottom rudders do have some funny prop wash properties as well as the odd consequences when you add stab tilt by twisting the boom. This is not, of course, to say that bottom rudders are a bad thing (I'm starting to use them again).

I still think the prop pitch looks a little low, but for a first attempt, it's great. Keep us posted on your progress, and contact me privately when you are ready to build an F1D.
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