RE: Measuring rubber - before or after break-in?

From: John Barker <john.barker783_at_ntlworld.com>
Date: Tue, 12 May 2015 22:39:40 +0100

Tapio,

What I try to do is: cut the rubber, measure the weight/unit length, write that figure on an envelope and put the rubber inside. When making a flight I write the weight/ unit length figure on the flight data sheet, when the flight is finished I put the rubber back in the envelope. It sounds so simple but I confess I do not always remember to do it.

John.

 

From: Indoor_Construction_at_yahoogroups.com [mailto:Indoor_Construction_at_yahoogroups.com]
Sent: 12 May 2015 16:18
To: Indoor_Construction_at_yahoogroups.com
Subject: [Indoor_Construction] Measuring rubber - before or after break-in?

 

  


I was making some new F1M motors for a contest in a few weeks. I had
made and flown some half-motors, and as these were good, cut some more
rubber with the same settings. However, when I measured the motors, the
half-motors were 2.15mm wide strip, and the new rubber from the stripper
was 2.25. Had my precious setting changed? Then I realised, that
obviously the half motors were broken in in use, so they were longer and
thinner because of that! In F1B I have found that the break-in causes a
permanent increase in motor length of about 3%, and the reduction in
strip width matches that figure.

So my question is: when you measure the data, especially when cutting
strip to some specific g/m, is that measure before or after motor
break-in? And if it is before, do you then use that figure ever since,
and not measure the motor dimension once the motor has been used?

(My half motors were 160mm long loops, and the new motors that I made
were 310mm. But after pulling them tight between my hands for a few
minutes, they are now 320mm. Broken in!)

-Tapio-
Received on Tue May 12 2015 - 14:39:43 CEST