I think that I am more or less in accordance with Bill Gowan on this. I was
fortunate to be advised to use weight per unit length in my early days in
Indoor flying and it was so obviously sensible that I adopted it straight
away. Talking to people who used a rubber stripper it became apparent that
one could not cut a strip to a width that was accurate to better than
several thousandths of an inch and it was equally apparent that a width
difference of several thousandths made a big difference in performance. Now
although strip width is very important from a performance point of view it
is a difficult thing to measure with normal measuring instruments and the
weight per unit length is a simple and sufficiently reliable way of
predicting the way the rubber will work in a motor.
I should mention, in case any newcomers to Indoor read this, that flyers
strip their rubber as closely as possible to the weight/unit length (or
width) that they require but almost always some pieces will be wider or
narrower than intended. Each piece is measured and put into a little
envelope with the actual weight/unit length (or width) recorded on the
outside. When flying these 'near similar' pieces can be used to make motors
that enable the flight performance to be finely tuned.
My procedure when stripping rubber is as follows:
I run several A4 sheets through my printer as attachment below. I cut each
sheet to make four small envelopes, each printed with the following on the
outside: g/inch, g/m, width(approx.) and turns/inch.
I cut a piece of rubber for stripping 40" long. This is usually long enough
to cut several motors but short enough to wrap conveniently into the
envelopes. I set the stripper to the width I want and cut a strip. I then
weigh the strip. Divide the weight by 40 and write on the envelope the
g/inch. Divide by 1.016 and mark g/m to compare with people who use funny
units! Like Kang I multiply the g/inch by 1.5 to give a strip width which
is good enough for people who ask. For convenience I put on the expected
turns/inch that a two strand motor will take.
A final point that most flyers don't seem to think about; those thin offcuts
often left at the end of cutting a strip can make very effective multi
strand motors.
John Barker - England
From: Indoor_Construction_at_yahoogroups.com
[mailto:Indoor_Construction_at_yahoogroups.com] On Behalf Of William Gowen
Sent: 17 September 2013 20:33
To: Indoor_Construction_at_yahoogroups.com
Subject: Re: [Indoor_Construction] Re: Rubber cross-section
First let me say that this discussion has gone in a direction I didn't
intend. My original statement was intended to say that telling another
person the width motor that you're using doesn't convey much in the way of
useful information. By the same token asking another person what width motor
they're using is not going to be very helpful to your own efforts to
understand what they are doing. What's important is length and weight and
how you arrive at those parameters can certainly be done many different
ways.
To answer Gary's question I usually cut 2 or 3 one inch pieces from my
unstripped rubber, make a trial cut of one of them with my stripper and
weigh the cut piece. If it's not what I want I make an adjustment to the
stripper and try again. When I get a piece that I consider correct I'll
usually do another trial cut using a 2" piece. If that looks good then I'll
cut a piece a little longer than the motor length I want and use the cut
piece to make a motor. I don't use anything to measure the width of the
strip at any point in the process.
After doing things this way for a couple of years I actually don't know how
wide any of my motors are. If you ask me about motor width and you get kind
of a blank stare from me then that's the reason.
This is the method I use and it's what I'm comfortable with. It's like a lot
of other techniques used in indoor building and flying - there are lots of
ways to accomplish any given task and you just have to decide what makes
sense to you and what gives you the outcome that you are looking for.
On Sep 17, 2013 1:44 PM, <Warthodson_at_aol.com <mailto:Warthodson_at_aol.com> >
wrote:
Bill, Mike or anyone,
But the catch-22 is that first you must accurately measure the width of the
strip, then accurately set your slicer to cut a specific width in order to
end up with a specific weight loop!
For the sake of this discussion, assume there is no max. motor weight
requirement & you wanted a loop weight of 1 gram, what tolerance would you
consider acceptable?
How many test cuts do you usually need when trying to cut a new width strip?
I would say it typically takes me at least 3 short test strips.
Gary H
From: William Gowen wdgowen_at_gmail.com <mailto:wdgowen_at_gmail.com>
So you calculate the density of your 1/8" rubber and then calculate the
strip width based on the density. I rest my case.
On 9/17/2013 10:50 AM, mkirda_at_sbcglobal.net <mailto:mkirda_at_sbcglobal.net>
wrote:
Here is an example for F1L.
Find the loop length that you want. Cut a bit of rubber to be the length
plus 2 inches.
i.e. 14" loop, cut (14+1)*2 = 30 inch length = 15" doubled.
Measure the width of the rubber with micrometer - i.e. 0.128"
Weigh the length of rubber. i.e. 2.54 grams.
You decide you want the rubber to weight 1 gram exactly.
Here is the math:
1/2.54 * (15/14) * 0.128 = .05399
Strip it to 0.054" and you when you tie off a 14" loop it should be
precisely 1 gram.
I set up the spreadsheet to have only 1" additional length, but the math
above is the same.
If anyone has problems with this, I will define variables and post the math
that way.
Regards.
Mike Kirda
- application/x-ygp-stripped attachment: stored
Received on Wed Sep 18 2013 - 05:00:03 CEST