Re: Re: Thermodynamics of rubber bands

From: Tapio Linkosalo <tapio.linkosalo_at_iki.fi>
Date: Wed, 23 Jun 2010 14:06:03 +0300

tim.haywardbrown_at_rocketmail.com 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 - 04:06:15 CEST