Re: Re: Rubber testing: Chiming In [1 Attachment]

From: William Gowen <wdgowen_at_gmail.com>
Date: Fri, 09 Nov 2012 16:13:12 -0500

Hey Rick
Weren't you the one asking awhile back whether it really mattered what
size rubber motor you used on an indoor model? (I'm still a little
ashamed of my answer)

Seriously, I do a lot of testing but I call it motor testing rather than
rubber testing. I make my best guess as to what's going to be the right
motor for a particular site and then test all the motors I plan to use.
I haven't found it necessary or advisable to wind them hard for the
testing. My usual method is to do a wind to about 60% of max torque,
back off turns to an estimation of the launch torque I'll need, and then
take torque readings for every 200 turns (10 winder turns for me) down
to zero. The summation of the torques at each step gives me a "score"
for a particular motor. A higher score is better in nearly any situation.

A fly in the ointment is that variation in the length and weight of
possibly "right" motors will skew the results toward heavier motors. I
use a correction factor in the final "score" that tries to balance the
effects of a higher wing loading vs. higher available energy.

This may not be exactly what you're talking about but it does tell me
which motors are going to perform better in the air. That's what's
important in my view. Another really important aspect of this kind of
test is that I can avoid wasting contest time flying on a bad motor - or
maybe a better way to put it is a motor that's not as good as a "good"
motor.

On 11/9/2012 3:49 PM, themaxout_at_aol.com wrote:
> [Attachment(s) <#TopText> from themaxout_at_aol.com included below]
>
> To all....imitation is the best form of flattery. Sotme time back I
> put out the attached little dissertation. It seems indoor model power
> systems are the key component for a given model. If one had
> sufficient test dta for a great performer, say Brett's or John's
> models at peak performance,a nd I mean the rubber/prop system "as flown."
> In my former life, the mantra was test like you fly. My thinking is
> you need the whole flight profile for a give rubber/prop
> configuration. The torque, prop dia, etc.
> If this does not come through, email me directly and I will send it
> directly to you.
> This begs for somebody willing to get out the stopwatch and the meters
> and make up the test fixture.
> /Rick Pangell
> Editor of "The Max-Out" Newsletter of
> The Magnificent Mountain Men FF Club of Colorado
> In a message dated 11/9/2012 1:18:28 P.M. Mountain Standard Time,
> j.bartek_at_sbcglobal.net writes:
>
> Mike
> Looking at your initial post, I see that you'll be using 5 X
> extension on 0.053 inch rubber for the start of your "wind to
> failure" test. Not sure how long a loop would last stretched that
> far. I haven't used that much stretch for Bostonians and such
> with wider rubber. Do you measure force to stretch the loop with
> a fish scale or similar? Perhaps adding weights to a suspended
> loop, like a high school physics Hooke's Law experiment would give
> you that.
>
> A starting point would perhaps use a 6 inch loop of 0.053 inch
> rubber stretched between 2 No. 10 wood screws 18 inches (3X) apart
> in a board. The larger wood screws might be smooth enough to keep
> the strain from concentrating there.
>
> I've got a box of FAI tan in 3/32 inch (0.094") and should
> generate some preliminary data before we talk "exact" though.
>
> Joe
>
> --- In Indoor_Construction_at_yahoogroups.com, "mkirda_at_..."
> <mkirda_at_...> wrote:
> >
> > Be happy to if you could write up exactly what you want me to try.
> >
> > --- In Indoor_Construction_at_yahoogroups.com,
> >
> > Maybe
> > > > Mike Kirda could take some loops of his rubber and stretch
> them over
> > > > some nails in a board, with and without lube, to give a
> "days to break"
> > > > number.
> >
>
>
>
>
> ------------------------------------
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Received on Fri Nov 09 2012 - 13:13:18 CET