[RocketsNW] Parachute protection options

[Steve Cutonilli]

Yeah, I suppose dual skirt pistons will work, but the via for the Kevlar
lanyard is supposed to exit the piston face and it's unnecessary bulk to
deal with if you have to reach even further to the skirt mouth for the
attachment loop.

The piston lanyard I use on 38/54mm is 1/4-inch tubular Kevlar - it can
get torched hundred's of times w/o concern for fatigue / failure.  The
ends are looped (thus the bulk concerns above).  Loops aren't sewn, but
rather wrapped at their junction with Kevlar thread which further
contributes to compact packing.  Think of a hangman's noose - where the
coil thread wrap is then soaked with a thin laminating epoxy - it's
exceedingly strong. 

Yeah, I know - different strokes...

/Steve

-----Original Message-----
From: kmcgoffin at worldaccessnet.com [mailto:kmcgoffin at worldaccessnet.com]

Sent: Friday, November 07, 2008 4:19 PM
To: Steve Cutonilli
Cc: kmcgoffin at worldaccessnet.com; 'Azinger, Fred'; rockets at rocketsnw.com
Subject: RE: [RocketsNW] Parachute protection options

Is there any law that says you can't put the piston skirt on both sides?
+McG+


> Naa - keep the skirt non-inverted that way the piston ID takes the BP
> hit thus leaving the airframe contact surface clean for more reliable
> function.  /Steve
>
> -----Original Message-----
> From: rockets-bounces at rocketsnw.com
> [mailto:rockets-bounces at rocketsnw.com] On Behalf Of
> kmcgoffin at worldaccessnet.com
> Sent: Tuesday, November 04, 2008 9:09 PM
> To: Azinger, Fred
> Cc: rockets at rocketsnw.com
> Subject: Re: [RocketsNW] Parachute protection options
>
> Yup.  And with aluminum parts, don't forget the superlube.
> +McG+
>
>
>> Don't forget to "invert" the piston -- skirt forward.
>> Think of an automobile piston on the power stroke....skirt away from
> the
>> charge...
>> Yes -- when coefficients of expansions are matched, pistons work
well.
>>
>>
>> -----Original Message-----
>> From: rockets-bounces at rocketsnw.com
>> [mailto:rockets-bounces at rocketsnw.com] On Behalf Of
Mfreptiles at aol.com
>> Sent: Monday, November 03, 2008 8:35 PM
>> To: rockets at rocketsnw.com
>> Subject: Re: [RocketsNW] Parachute protection options
>>
>> I think Steve is on to something in certain situations.
>>
>> Taking Steve's advice, I've built a piston for my 38mm all aluminum
>> rocket.
>> The piston is machined aluminum and slides really smoothly within
the
>> aluminum airframe and won't bind because the piston skirt is several
>> calibers long
>> and the piston and airframe is the same material.  My  previous
> problem
>> was
>> the bulk of the recovery gear wrapped with nomex.   Even then, my
> kevlar
>> harness
>> was exposed to the ejection gasses and would  degrade after a few
>> flights.
>> With the piston, there is less bulk to pack,  and the harness above
> the
>> piston
>> stays like new.  The kevlar harness  section below the piston will
>> degrade,
>> but since it is shorter, less $ to  replace.
>>
>> Now if you asked me if I believe in phenolic pistons in cardboard, or
>> plastic airframes........forget it! :)
>>
>> Mike F.
>>
>>
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