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Old Apr 03, 2009, 02:55 PM
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FairlyFaded's Avatar
Palo alto CA
Joined Oct 2004
716 Posts
Question
Useful information on band and prop power system sizing?

Hello, Michael Norcia here.

While I generally stay in the DLG side of our curios hobby, I have been drawn as of late towards rubber band powered aircraft.

Do any of you know of any pages with good information, and better yet data on rubber band sizing as well as prop sizing? (when I search for rubber band data etc I only seem to get lists of kits.) The art of using the correct prop and bands is more complex than I had originally guessed, as well as much more important for good flight characteristics.

I am trying to build a few ~12" long gliders of varying designs (one classic flying stick like model and one resembling the "string less wonder") to be flown in calm conditions or indoors. My goal is to have between 30-1 minute flights with simple, fairly light weight depron and balsa frames. I dont want ballistic performance, but enough power to cruise and allow for observation of the flight characteristics, if that helps.

Thanks in advance!

Michael
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Old Apr 03, 2009, 07:35 PM
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Gluehand's Avatar
The windy west coast of Sweden
Joined Sep 2008
2,776 Posts
As there is a huge amount of experience lurking out here (hopefully filling all the blanks, eventually), please take these "rules of thumb" as "go-from-here-advices".

As I understand the models are going to be of around 12" span....

Prop size:
Think "1/3 span"

Rubber size:
Use 1/8" strand, start with one loop about 1 1/2 times the fuselage length.
(a winder should be used)

Prop shaft thrust line:
About 2 down / 2 right would be a good guess for a start.

If lightly built and a decent decalage and C/G setup, this would give fairly long flight times....to be further developed...

...for 1/2 a penny's worth...
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Last edited by Gluehand; Apr 03, 2009 at 08:01 PM.
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Old Apr 09, 2009, 12:15 PM
Free Flight rubber flyer
South Carolina
Joined Mar 2005
466 Posts
If you want serious indoor performance on a 12" wingspan, look at a 6" prop. I know that sounds big, but it's not. That will give you an efficient prop diameter without being hard to trim. You'll probably be using a loop of 3/32. Might get away with 1/16 if you build light.
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Old Apr 09, 2009, 01:44 PM
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carbondale il
Joined Jan 2007
2,557 Posts
Yea, I had a plane with a 12 1/2" span and a 7" plastic propeller with a loop of 1/8" rubber which flew well enough to land in the top of a tree a minute, ten seconds into the flight.

Kev
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