Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
March 28, 2017, 03:44:52 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: [1]   Go Down
Print
Author Topic: Choosing correct rubber  (Read 342 times)
0 Members and 1 Guest are viewing this topic.
BR549
Copper Member
**

Kudos: 0
Offline Offline

United States United States

Posts: 6

Topic starter


Ignore
« on: March 19, 2017, 06:56:05 PM »

I see that the more advanced fliers advocate selecting rubber primarily on weight. Width has to be a variable in the equation though, doesn't it?

I'm a noob, but it seems to me that the wider the rubber the more torque it has the and larger prop it can swing.

Am I off base?
Logged
p40qmilj
Platinum Member
******

Kudos: 24
Offline Offline

Canada Canada

Posts: 1,402


love that P40Q



Ignore
« Reply #1 on: March 20, 2017, 05:31:22 AM »

 Grin  not really.  i size rubber by what powers the plane and gives reasonable duration.  for my flying scale models in 24 inch class (40 to 50 GM) 2 x 3/16 strip works ok for 20 models i like 2 x 1//8 and smaller use 1 x 3/16 while sticj and no cals use 1 x 1/8.

jim Grin
Logged
mkirda
Gold Member
*****

Kudos: 10
Offline Offline

United States United States

Posts: 560

WWW

Ignore
« Reply #2 on: March 20, 2017, 10:08:17 AM »

So here is the deal.

Rubber varies in thickness. It also varies in density. Different batches also very in energy return.

To account for all of these things, it is considered common practice among F1D fliers to talk about either loop length (given that it is a constant weight of 400mgs under the current rules) or density per length.
i.e. 6" loop or 40mgs/inch (second one is just made up). Width matters in that this is what we can strip the rubber to. Thickness and density are variable. So cutting to 0.047" width for example might not give use the same loop length, even with the same batch of rubber. It can vary by more than 1/4" in either direction in real life.

Regards.
Mike Kirda

Logged

BR549
Copper Member
**

Kudos: 0
Offline Offline

United States United States

Posts: 6

Topic starter


Ignore
« Reply #3 on: March 20, 2017, 10:47:40 AM »

Thanks for the answers.

I was probably reading the F1D forum and applying something there to all indoor models. At their scale you have to think differently.
Logged
mkirda
Gold Member
*****

Kudos: 10
Offline Offline

United States United States

Posts: 560

WWW

Ignore
« Reply #4 on: March 20, 2017, 11:01:27 AM »

Thanks for the answers.

I was probably reading the F1D forum and applying something there to all indoor models. At their scale you have to think differently.

Well, the same thing applies even to SO Wright Stuff (which are significantly heavier than F1D) or LPP.
LPP might be 2.8 gram loop 23" long. Very clear and consistent measurement that is easily comparable.
Saying 19" loop of 0.055" doesn't give you the right information (total weight) that is needed to make up an identical loop.

Again, this is for indoor competition flying. For sport flying or general help, saying 19" loop of 0.055" will convey something pretty meaningful and get someone in the right ballpark.
But saying 1.5 gram 19" loop of March 2016 Tan SS would be much more precise.

As an exercise, try cutting precise lengths of rubber, then weighing them on a milligram scale. You'd be surprised on the amount of difference in weight. I've see upwards of 10% on occasion.
This is when I finally understood why density per length is the right way to go.

Regards.
Mike Kirda
Logged

ram
Silver Member
****

Kudos: 3
Offline Offline

United States United States

Posts: 213



Ignore
« Reply #5 on: March 20, 2017, 12:56:23 PM »

Here is another way of looking at it which may or may not make sense to you:

Let’s say that you want to fly a similar motor to one that was used to set a site record.  That motor is listed at 17” long x .050 wide x 1.13grams.  The only way to match that motor in cross-section is to make a motor 17” long x 1.13grams and ignore the width.  The record motor may have been .050 wide  X .040 thick, but the odds of your particular rubber being the exact thickness is remote, plus you don’t know how thick that motor was in the first place and it is very difficult, if not impossible, to measure the width consistently and accurately.  This is especially true between different people taking measurements.

The easiest way to get started is to know your rubber by weighing it and calculating the grams per inch. Then it becomes a simple matter of stripping your rubber to that particular length.  In the example above that site record motor weighs .033 grams per inch (34” / 1.13grams).  If your rubber weighs .080 grams per inch (1/8” unstripped as an example), use that information to setup your stripper, then strip samples until you get .033 grams per inch and then strip your final motor to length.  This is no different than stripping samples until you get a particular width, except that your result is accurate!

Rey
Logged
BR549
Copper Member
**

Kudos: 0
Offline Offline

United States United States

Posts: 6

Topic starter


Ignore
« Reply #6 on: March 20, 2017, 07:10:48 PM »

Thanks to everyone for the input. I'm sure it will be helpful to more than just me.

I followed many peoples advice (completely against my character) and made a Harlan rubber stripper one of my first purchases. It has already paid big dividends in my flight times. I'm just trying to gather more info so I utilize it intelligently.

Bob
Logged
Pages: [1]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!