Re: Thermodynamics of rubber bands

From: nick <nickaikman_at_hotmail.com>
Date: Wed, 23 Jun 2010 14:52:27 -0000

'Above 40C (something over 100F) the rubber tends to get soft and break abruptly.'

Aha - Belgrade temperature!!!

--- In Indoor_Construction_at_yahoogroups.com, Tapio Linkosalo <tapio.linkosalo@...> wrote:
>
> tim.haywardbrown_at_... wrote:
> >
> >
> > > Temperature affects the elasticity of a rubber band in an unusual way.
> > > Heating causes the rubber band to contract, and cooling causes
> > > expansion.
> >
> > Don't F1B flyers use heating jackets to keep their (wound) motors warm
> > on cold flying days? Does that make the rubber contract? And what does
> > that do to the torque?
>
> Not any more; use of external heating of the motors was banned some
> years ago. It did work pretty well in the winter flying, when rubber
> tends to loose up to 30% of the power. It did not affect the number of
> turns much (as current flying with cold rubber does not), but maintaned
> the motor torque on "warm day" level.
>
> BTW, cooling of the motors is still commonplace on hot days: take a rag,
> wet it with water, and wrap around the motor tube while the motor is in.
> Above 40C (something over 100F) the rubber tends to get soft and break
> abruptly.
>
> You can easily observe the thermodynamics of the rubber when breaking
> F1B motors in by stretching. The warming of the rubber when stretched
> may not be that easily observed, but when you keep the motor under load
> for 4 minutes, it cools back down to room temperature, and when you then
> release it, is is clearly colder than ambient temperature.
>
>
>
> -Tapio-
>
Received on Wed Jun 23 2010 - 07:52:50 CEST